CA1219497A - Fault detection apparatus for parenteral infusion system - Google Patents
Fault detection apparatus for parenteral infusion systemInfo
- Publication number
- CA1219497A CA1219497A CA000451623A CA451623A CA1219497A CA 1219497 A CA1219497 A CA 1219497A CA 000451623 A CA000451623 A CA 000451623A CA 451623 A CA451623 A CA 451623A CA 1219497 A CA1219497 A CA 1219497A
- Authority
- CA
- Canada
- Prior art keywords
- signal
- pressure signal
- fluid
- patient
- fault detection
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M5/00—Devices for bringing media into the body in a subcutaneous, intra-vascular or intramuscular way; Accessories therefor, e.g. filling or cleaning devices, arm-rests
- A61M5/14—Infusion devices, e.g. infusing by gravity; Blood infusion; Accessories therefor
- A61M5/168—Means for controlling media flow to the body or for metering media to the body, e.g. drip meters, counters ; Monitoring media flow to the body
- A61M5/16831—Monitoring, detecting, signalling or eliminating infusion flow anomalies
- A61M5/16854—Monitoring, detecting, signalling or eliminating infusion flow anomalies by monitoring line pressure
- A61M5/16859—Evaluation of pressure response, e.g. to an applied pulse
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M5/00—Devices for bringing media into the body in a subcutaneous, intra-vascular or intramuscular way; Accessories therefor, e.g. filling or cleaning devices, arm-rests
- A61M5/36—Devices for bringing media into the body in a subcutaneous, intra-vascular or intramuscular way; Accessories therefor, e.g. filling or cleaning devices, arm-rests with means for eliminating or preventing injection or infusion of air into body
- A61M5/365—Air detectors
Abstract
ABSTRACT OF THE DISCLOSURE
Apparatus and related method for use in a parenteral administration system, for detecting fault conditions such as an infiltration, an open fluid line or an air bubble in the fluid line. The apparatus is particularly adapted for use with a parenteral adminis-tration system of the type that includes a pulsing infusion device for incrementally infusing fluid through a fluid tube to a patient's venous or arterial system.
The apparatus qualitatively evaluates the pressure in the fluid tube to detect characteristic patterns indicative of each such fault condition and actuates an alarm whenever one is detected.
Apparatus and related method for use in a parenteral administration system, for detecting fault conditions such as an infiltration, an open fluid line or an air bubble in the fluid line. The apparatus is particularly adapted for use with a parenteral adminis-tration system of the type that includes a pulsing infusion device for incrementally infusing fluid through a fluid tube to a patient's venous or arterial system.
The apparatus qualitatively evaluates the pressure in the fluid tube to detect characteristic patterns indicative of each such fault condition and actuates an alarm whenever one is detected.
Description
FAVLT DETECTION APPARATUS
~OR PARENTERAL INFUSI SYSTEM
BAC GROUND OF THE INVENTION_ This invention relates generally to systems for 5 administering parenteral fluids to a patient, and, more particularly, to systems of this type having an infusion apparatus for infusing the fluid into the patient s vascular system.
Systems of this particular type have enjoyed 10 widespread usage in hospitals for administering paren-teral fluids at precise rates. The systems are useful for both venous and arterial infusions and typically include an infusion pump and an associated controlling device for pumping the parenteral fluid through a ~luid 15 tube and needle to the patient s vein or artery.
One drawback to conventional infusion pump systems of this type is that the needle can sometimes become dislodged from the patient s vein or artery. This will normally cause an increase in back pressure, but the 20 pump will nevertheless continue to pump fluid at substan-tially the same fixed rate. The fluid therefore can infiltrate into the patient s body tissue and cause severe damage. Similarly, the needle can sometimes become dislodged from the patient entirely, yet the pump 25 will continue to pump the fluid at the same fixed rate.
One known prior technique for detecting fluid infiltrations is to monitor the patient s skin tempera-ture in the vicinity of the needle. Since the parenteral fluid is ordinarily cooler than the patient s body tempera~ure, and since the fluid is not carried away as rapidly when an infiltration occurs, an infiltration will ordinarily create a temperature drop in the vicinity of the needle. Thus, whenever a drop in skin temperature is detected, it is deduced that an infiltration is occur-ring. This technique is not believed to have provencompletely satisfactorily in all circumstances, such as, for example, when the parenteral fluid has a temperature substantially the same as that of the patient s blood.
Other known prior techniques for detecting an infiltration of a parenteral fluid into a patient s body tissue involve intervention by hospital personnel. In one~such technique, an attendant visually inspects the region around the needle, to detect any swelling that might indicate an infiltration. In another technique, useful only when the fluid is being administered from a bottle under the force of gravity, the attendant periodically lowers the bottle to an elevation below the needle such that fluid flows outwardly from the patient.
If when this is done the patient s blood does not appear in the fluid tube, it can be deduced that the needle is not in fluid communication with a vein or artery.
Neither of these techniques has proven to be entirely satisfactory, one reason being that they both require the presence of trained hospital personnel and cannot be performed automatically.
Still another prior technique for detecting infiltrations and other fault conditions is used in a parenteral administration system that regulates flow rate using a pinch valve located in the fluid tube, between a drop chamber and the patient In particular, the pinch valve is controllably adjusted in order to maintain the frequency of fluid drops into the drop chamber at a selected value. If the limits of the pinch valve are exceeded in attempting to maintain 5 the selected drop frequency, it is deduced that a fault condition is present. Operator intervention is still required, however, in order to determine the particular type of fault condition, e.g., an infiltra tion, that is present.
A complete dislodging of the needle from the patient, such that the fluid is directed onto his skin, bedding, etc., is ordinarily detected only through a visual inspection by a hospital attendant. Such active participation by hospital personnel is not believed to be 15 an entirely satisfactory solution to this problem.
It should be appreciated from the foregoing that there still is a need for an effective method and apparatus for automatically detecting faults such as infiltrations or an open line in a parenteral adminis-20 tration system of the type having an infusion device rThe present invention fulfills this need.
SUMMARY _ F THE_INVENTION
The present invention is embodied in a fault detection apparatus, and related method~ for use with a 25 parenteral administration system of the type having an infusion device for infusing a parenteral fluid through a fluid tube and needle to a patient s vascular system.
The apparatus includes pressure transducer means for monitoring the pressure of the fluid in the fluid tube 30 and producing a corresponding pressure signal. In accordance with the invention~ the apparatus further includes automatic fault detection means for quali-tatively evaluating the pressure signal to determine when '7 .
the fluid tube is not in proper fluid communication with the patient s vascular system, and for producing a corresponding alarm signal. This frees hospital per-sonnel to perform other tasks without the need for 5 repeatedly monitoring the status of the parenteral administration system.
One embodiment of the fault detection means is adapted for use with a parenteral administration system that includes a pulsing-type infusion device for adminis-10 tering the parenteral fluid to a patient s venous sys-tem. The fault detection means produces the alarm signal whenever it detects an infiltration of the fluid into body tissue separate from the venous system. In this embodiment, the fault detection means analyzes the 15 pressure signal following each infusion pulse to detect impedance changes distal to the needle. Specifically, the fault detection means detects an infiltration by determining if the pressure signal ever fails to return to its steady state level within a predetermined time 20 duration following each infusion pulse. In particular, the fault detection means high-pass filters the pressure signal and compares the filtered pressure signal with a prescribed threshold. The alarm signal is produced whenever the filtered pressure signal exceeds the thresh-25 old for longer than a prescribed time period followingeach infusion pulse.
Another embodiment of the fault detection means detects infiltrations whenever the infusion device is infusing fluid at a relatively high rate, e.g., 40 ml per 30 hour. In this embodiment, the fault detection means includes pressure change means for determining if the pressure signal ever increases by more than a particular amount during a predetermined time duration. This pressure change means preferably includes means for 35 sampling the pressure signal at spaced intervals of time, along with means for comparing the current pressure signal sample with with previous pressure signal sample, to determine if the pressure signal has increased by more than the prescribed amount during the interval between 5 samples. The pressure change means is preferably enabled only after pressure derivative means has determined that the instantaneous rate of change of the pressure signal exceeds a prescribed levelO
Two other embodiments of the fault detection 10 means of the invention are adapted for use when the parenteral administration system administers the paren-teral fluid ~o a patient s arterial system. In one such embodiment, the fault detection means low-pass filters the pressure signal to remove the effects of 15 the patient s heartbeats and compares the filtered pressure signal with a predetermined threshold. An alarm signal is produced whenever the signal drops below the threshold. In another such embodiment, the fault detection means high-pass filters the pressure signal 20 to pass only the siqnal components attributable to the patient's heartbeats. An alarm signal is pro-duced whenever a dropout in the heartbeat pulses is detected.
Yet another embodiment of the fault detection 25 means detects an open line or air bubble in the fluid tube connection between the pulsing-type infusion device and the patientO When such a condition occurs, the configuration is underdamped and the pressure signal has a ringing characteristic following each infusion pulse.
30 The fault detection means detects this ringing by analyz-ing the pressure signal following each infusion pulse, to measure impedance changes distal to the needle. Speci-fically, the fault detection means determinesr after each infusion pulse, if the ac pressure signal (i.eO, high-35 pass filtered pressure signal) drops below a prescribed ~2~ 7 negative pressure threshold~ This threshold is prefer-ably a prescribed negative fraction of the peak positive ac pressure signal occurring immediately after each infusion pulse.
In the preferred embodiment of the apparatus, the fault detection means includes several of the embodi-ment ~ scribed above~__f_r detecting venous and arterial infiltrations and open lines. Appropriate switching circuitry enables operation of either the venous or the 10 arterial infiltration circuit, depending on the use to which the system is being made. The alarm is actuated when any of the various circuits detects a fault.
Other aspects and advantages of the present invention should become apparent from the following 15 description of the preferred embodiments, taken in conjunction with the accompanying drawings, which illus-trate, by way of example, the principles of the inven-tion.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a parenteral administration system having circuitry for detecting venous infiltrations, arterial infiltrations and open fluid lines;
FIG. 2 is a simplified schematic diagram of a 25 low infusion rate venous infiltration detector included in the system of FIG. l;
FIG. 3(a)-(f) illustrate a series of waveforms that can be present in the venous infiltration detector of FIG. 2;
FIG. ~ is a simplified schematic diagram of a high infusion rate venous infiltration detector included in the system of FIG. 1;
FIG. 5 is a simplified schematic diagram of one embodiment of an arterial infiltration detector suitable for use in the system of FIG. l;
FIG. 6 is a simplified schematic diagram of an alternative ar~erial infiltration detector suitable for 5 use in the system of FIG. 1, FIG. 7 is a simplified schematic diagram of an open line detector included in the system of FIG. l;
and FIG. 8(a)-(c) illustrate several waveforms that 10 can be present in the open line detector of FIG. 7.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, and particularly to FIG. 1, there is shown fault detection circuitry 10 for use in a system for administering a parenteral fluid 15 to the vascular system of a patient 11. The system includes a conventional infusion pump 13 and associated pump controlling device 15 for pumping the parenteral fluid through a fluid tube 17 and needle 19 to the patient. The pump is preferably of the peristaltic 20 type, which pumps the fluid in a cyclic fashion.
The pump controlling device 15 outputs a motor step signal for coupling on line 21 to the infusion pump 13. The signal is a sequence of pulses, each of which increments the pump by one step, to infuse a predeter-25 mined volume of parenteral fluid to the patient 11.
The parenteral administration system furtherincludes a pressure transducer 23 and an associated a~
amplifier 25 for monitoring the fluid pressure in the fluid tube 17 and producing a corresponding pressure signal for output on line 27.
In accordance with the invention, the fault 5 detection circuitry 10 evaluates the pressure signal on line 27 to detect certain characteristic patterns indica-tive of an improper fluid communication between the fluid tube 17 and the patient s vascular system. An alarm 29 is actuated if the circuitry detects such a condi-10 tion. Such fault conditions include infiltrations of thefluid into body tissue other than the patienL s vascular system, as well as a complete dislodging of the needle 19 from the patient 11 or a leak or air bubble in the fluid tube. In this way, a proper administration of the 15 parenteral fluid can be ensured without the need for frequent monitoring or testing by hospital personnel.
More particularly, the fault detection cir-cuitry 10 includes a low infusion rate venous infiltra-tion detector 31 for detecting infiltrations when the 20 infusion pump 13 is pumping parenteral fluid into the patient s venous system at a relatively low rate, and a high infusion rate venous infiltration detector 33 for detecting infiltrations when the pump is pu~ping fluid into the venous system at a relatively high rate. The 25 fault detection circuitry further includes an arterial infiltration detector 35 for detecting infiltrations when the pump is pumping fluid into the patient s ar-terial system, and an open line detector 37 for detecting when there is a leak of some kind or an air bubble in the 30 fluid connection between the pump and the patient 11.
The system further includes a mode switch 39 for indicating whether the system is intended to adminis~
ter parenteral fluid to the patient s venous system or arterial system. The system also includes an infusion 35 rate detector circuit 41, operable whenever the switch '7 g indica~es that the system is pumping fluid into the patient s venous system to indicate whether the fluid is being pumped at a relatively high rate or a relatively low rate. The switch 39 and detector circuit 41 are used 5 to enable operation of the appropriate venous infiltra-tion detector circuit 31 or 33 or arterial infiltration detector circuit 35, depending on the system's operating mode.
More particularly, the mode switch 39 is a 10 single-pole, double-throw switch having its middle terminal connected directly to ground and its two re-maining terminals connected through separate resistors 43 to a positive voltage. The binary signals present on these two terminals are therefore opposite in phase to 15 each other. One such signal is defined to be an arterial enable signal and the other is defined to be a venous enable signal.
The arterial enable signal is coupled on line 45 directly to the arterial infiltration detector circuit 20 35, and the venous enable signal is coupled on line 47 to the infusion rate detector 41. The infusion rate detector circuit relays the venous enable signal to either the low infusion rate venous infiltration detector 31 or the high infusion rate venous infiltration detector 25 33, depending on the infusion rate being effected by the infusion pump 13.
The infusion rate detector circuit 41 includes a frequency discriminator 49 for monitoring the motor step signal present on line 21 and producing an output 30 signal having a voltage level generally proportional to the motor step signal's frequency. This output signal is coupled on line 51 to the positive input terminal of a comparator 53, which compares it with a selected refer-ence level coupled to its negative input terminal. The 35 reference level is supplied on line 55 from the wiper of r~
a potentiometer 57, whose remaining two terminals are connected between ground and a positive supply voltage.
If the discriminator output signal exceeds the threshold, indicating that the infusion pump 13 is pumping at a 5 relatively high rate (e.g., above about 40 ml per hour), the comparator outputs a positive voltage level. On the other hand, if the discriminator output signal does not exceed the threshold, indicating that the pump is pumping at a relatively low rate, the comparator outputs a low 10 voltage level signal.
The signal output by the comparator 53 is coupled on line 59 to a first AND gate 61 for ANDing with the venous enable signal supplied on line 47 from the mode switch 39. This produces a high infusion rate 15 venous enable signal for coupling on line 63 to the high infusion rate venous infiltration detector 33. The detector 33 is thereby enabled to detect infiltrations whenever a venous infusion is selected by the mode switch and the infusion rate exceeds the prescribed threshold.
The signal output by the comparator 53 of the infusion rate detector 41 is also coupled on line 59 to a NOT gate 65, for inversion and coupling in turn on line 67 to a second AND gate 69, where it is ANDed with the same venous enable signal present on line 47. The 25 resulting low infusion rate venous enable signal is coupled on line 71 to the low infusion rate venous infiltration detector 31. This detector 31 is thereby enabled whenever a venous infusion is selected by the mode switch 39 and the infusion rate does not exceed the 30 prescribed threshold.
Referring now to FIG. 2, there is shown a simplified schematic diagram of the low infusion rate venous infiltration detector 31. This circuit monitors the pressure signal supplied on line 27 from the ampli-35 fier 25, to detect a characteristic pattern indicative of '7 an occlusion or infiltration of fluid into the patient sbody tissue separate from his venous system. When the circuit detects such a condition, it outputs an alarm signal for coupling on line 73 to the alarm 29. Basic-5 ally, the circuit determines that an occlusion or aninfiltration has occurred whenever the pressure signal fails to return to its nominal value within a prescribed time duration following each of the successive pumping pulses of the infusion pump 13.
The low infusion rate venous infiltration detector 31 includes a 0.1 Hz high-pass filter 75 for filtering the pressure signal supplied on line 27, to produce a filtered pressure signal for output on line 77. The pressure signal, which is depicted in FIG. 3(c), 15 normally includes a series of positive pressure pulses, each with an exponentially-decaying tail, as a result of the successive motor steps of the infusion pump 13.
A comparator 79 compares the filtered pressure signal with a selected positive voltage threshold sup~
20 plied on line 81 from the wiper of a potentiometer 83.
The other two terminals of the potentiometer are con nected between ground and a positive potential. If the filtered pressure signal has a voltage level exceeding the threshold, the comparator outputs a positive signal 25 on line 85 as shown in FIG. 3(d). The threshold is preferably selected to be about 30 percent of the pulse s peak value. Typically, the threshold is about four to six cm H2O.
The detector 31 further includes a monostable 30 multivibrator or one-shot 87 and a flip-flop 89 for sampling the signal output by the comparator 79 about 0.2 seconds after each pulse of the motor step signal (FIG.
3(a)). In particular, the motor step signal is supplied on line 21 to the one-shot, which produces a correspond-35 ing sequence of pulses (FIG. 3(b)), each having a dura-'7 tion of about 0.2 seconds. This one shot signal is coupled on line 91 to the clock input terminal of the flip-flop, which samples the pressure derivative signal at the trailing edge of each pulse. I~ the 5 comparator output signal is still a positive value at this time, the flip-flop outputs a positive signal as The signal output by the flip-flop 89 is coupled on line 93 to one input terminal of an AND
10 gate 9~, which ANDs the signal with the low infusion rate venous enable signal supplied on line 71. It will be recalled that this enable signal indicates that the parenteral administration system is intended to be administering fluid to the patient s venous system at a 15 relatively low rate. If both inputs to the AND gate are a positive value, it is deduced that an infiltration is occurring and the A~D gate outputs a trigger signal for coupling on line 95 to a latch 96, which, in turn, produces an alarm signal for coupling on line 73 to the 20 alarm 29 (FIG. 1).
During normal situations, when the needle 19 is properly inserted into the patient s vein, the pressure signal (FIG. 3(c)) returns to its nominal value rela-tively quickly after each pulse of the motor step signal 25 (FIG. 3(a)). As a result, the pressure signal does not exceed the threshold and the comparator output signal (FIG. 3(d)) is at a low level at the successive sample times. The detector circuit 31 therefore does not produce an alarm signal.
On the other hand, during abnormal situations, when the needle 19 is not in proper communication with the patient s venous system and an infiltration is occurring, the pressure signal (FIG. 3(e)) has a rela-tively long decay time. This apparently occurs because 35 of an inability o~ the body tissue to dissipate rapidly each infusion of parenteral fluid. Because of the long decay time, the comparator output signal (FIG.
3(f~) is still at a high level at the time it is sampled by the flip-flop 89. An alarm signal is therefore produced on line 73.
Referring now to FIG. 4, there is shown a simplified schematic diagram of the high infusion rate venous infiltration detector 33 of FIG. 1. Basically, this circuit monitors the pressure signal supplied on line 27 to determine if the pressure in the fluid tube 17 10 ever increases by more than a selected amount during a predetermined time period. It makes this determination only after the instantaneous rate of change of pressure first exceeds a prescribed level, e.g., 30 cm H2O per second. A positive pressure slope less than this lower 15 threshold can occur during normal situations. A positive pressure slope greater than about 250 cm H2O per second can indicate a downstream occlusion, but is treated by the detector circuit as though it were an infiltration.
When the instantaneous rate of change of the pressure 20 signal first exceeds the 30 cm H2O per second thresh-old, the detector circuit samples the pressure signal immediately and again approximately four seconds later.
If the second sample exceeds the first by more than a prescribed amount, e.g., 75 cm H2O it is deduced 25 that an infiltration is occurring. An alarm signal is then output on line 97 for coupling to the alarm 29 (FIG. 1)~
The detector circuit 33 of FIG. 4 is suitable for use in detecting infiltrations when the parenteral 30 administration system is administering fluids at rates above about 40 ml per hour. The low infusion rate venous infiltration detector 31 of FIG. 2 could also function properly at such infusion rates, but would ordinarily require the momentary disabling of the infusion pump 13 35 each time it seeks to detect an infiltration. This is because the successive pulses of the infusion pump would then be occurring less than 0.2 seconds apart, which is the nominal sample delay time required by the circuit.
The high infusion rate venous infiltration detector 33 includes a differentiator 99 for producing a 5 pressure derivative signal, along with a comparator 103 for comparing the pressure derivative signal with a threshold corresponding to 30 cm H20 per second. The pressure signal is input to the differentiator on line 27, and the pressure derivative signal is output by the 10 differentiator on line 105 for coupling to the compara-tor s positive input terminal. The comparator s negative input terminal is coupled on line 111 to the wiper of a potentiometer 1130 The remaining two terminals of the potentiometer are connected to ground and a positive 15 supply voltage, so the voltage present at the wiper of the potentiometer represents a selected positive voltage threshold. The comparator produces a positive-valued trigger signal whenever the pressure derivative signal exceeds the threshold.
The detector circuit 33 of FIG. 4 further includes first and second sample and hold circuits 121 and 123 and a four second monostable multivibrator or one-shot 125. The trigger signal produced by the com-parator 103 is coupled on line 117 to both the first sample and hold circuit and the one-shot. Whenever the trigger signal goes into a high state~ indicating that the instantaneous pressure derivative signal has just exceeded the rate of change threshold, the first sample and hold circuit samples the pressure signal supplied on line 27 and the one-shot simultaneously initiates a four second output pulse that is in a low state. The one-shot output signal is coupled on line 129 to the second sample and hold circuit, whereupon four seconds later it like-wise samples the pressure signal.
The signal output by the first sample and hold ~2~
circuit 121 is coupled on line 131 to a summer 133, for summing with a selected positive voltage level supplied on line 135 from a potentiometer 137. This voltage level represents the minimum amount by which the pressure signal must increase during a four second period for an infiltration to be detected. A comparator 139 compares the summer output signal with the signal output by the second sample and hold circuit 123. In particular, the summer output signal is coupled on line 141 to the comparator's negative input terminal, and the second sample and hold circuit output signal is coupled on line 143 to the comparator s positive input terminal. I the sample and hold signal exceeds the summer signal, it is deduced that the pressure in the fluid tube 17 has increased by more than the prescribed amount (75 cm H2O) during the preceeding four second period and that an infiltration has therefore occurred.
The signal output by the comparator 139 is coupled on line 145 to an AND gate 147, for ANDing with the high infusion rate venous enable siqnal supplied on line 63 from the infusion rate detector circuit 41 (FIG.
1). If both AND gate input signals are high, the AND gate produces a high signal for coupling on line 153 to the data input terminal of a flip-flop 155. A clock pulse signal for clocking the flip-flop occurs shortly after the end of the four second period, at which time the comparator and AND gate output signals have stabil-ized. This clock pulse signal, which is coupled to the flip-flop s clock terminal on line 149, is produced by a clock pulse one-shot 151 in response to the one-shot pulse supplied on line 129 from the four second one-shot 125. The flip-flop in turn produces the alarm signal for output on line 97.
Referring now to FIG. S, there is shown a simplified schematic diagram of one embodiment of the arterial infiltration detector 35 of FIG. 1. Basically, the circuit compares the rnean pressure signal, which should correspond to the patient s mean arterial pres-sure, to a prescribed positive threshold, preferably 5 about 60 cm of watery and outputs an alarm signal on line 157 whenever the signal drops below the threshold.
More particularly, the arterial infiltration detector 35 of FIG. 5 includes a 0.1 Hz low-pass filter 159 and a comparator 161. The filter filters the pres-10 sure signal supplied on line 27 to produce a mean ar-terial pressure signal for coupling on line 163 to the comparator s negative input terminal. The prescribed positive threshold is coupled to the comparator s posi-tive input terminal on line 165 from the wiper of a 15 potentiometer 167. During normal operation, when the needle 19 is properly inserted in the patient s artery, the mean arterial pressure signal will exceed the thresh-old selected by the potentiometer and the comparator will output a signal having a negative level. Conversely, 20 when the needle is not properly inserted in the patient s artery and an infiltration is occurring, the mean ar-terial pressure signal will not exceed the threshold and the comparator will output a signal having a positive level. A bandwidth of about 0.1 Hz is preferred for the 25 low-pass filter, to substantially remove the effects of the patient s heartbeats.
The signal output by the comparator 161 is coupled on line 169 to an AND gate 171, for ANDing with the arterial enable signal supplied on line 45. If both 30 signals are at a positive levely then the AND gate likewise outputs a positive level signal. This AND gate output signal is coupled on line 173 to a latch 175y which produces the alarsn signal for output on line 157.
With reference now to FIG. 6, there is shown a simplified schematic diagram of an alternative embodiment of the arterial infiltration detector 35 of FIG. 1. In this embodiment, infiltrations into the patient s body tissue separate from his arterial system are detected by 5 monitoring the pressure signal to detect dropouts in the pressure variations caused by the patient's heartbeat.
More particularly, the arterial infiltration detector 35 of FIG. 6 includes a 0.1 Hz high-pass filter 177, a level detector with hysteresis 179, a frequency 10 discriminator 181 and a comparator 183. The high-pass filter filters the pressure signal supplied on line 27 to remove its dc level and pass only the successive pulses representative of the patient s heartbeats. The heart-beat pulses are present in the pressure signal whenever the fluid tube 17 and the needle 19 (FIG. 1) are coupled directly to the patient's arterial system. The high-pass filtered signal is coupled on line 185 to the level detector, which converts the signal to a corresponding pulse sequence signal. The level detector detects only 20 pulses having a magnitude of at least about 15 cm H2O.
The pulse sequence produced by the level detector is coupled on line 185 to the frequency discriminator, which produces an output signal having a level proportional to the frequency of its input signal.
Thus, if the needle 19 is properly inserted into the patient s arterial system, the heartbeats will be represented in the pressure signal and the frequency discriminator 181 will output a relatively high voltage level signal. On the other hand, if the needle is not properly inserted into the patient s arterial system, the heartbeats will not be represented in the pressure signal and the frequency discriminator will output a relatively low level signal.
The discriminator output signal is coupled on 35 line 187 to the negative input terminal of the comparator ~L~
183, which compares it with a selected positive reference level supplied to its positive input terminal on line 189 from a potentiometer 191. Thus, if the frequency dis-criminator output signal ever drops below the reference level, the comparator outputs a positive voltage level.
The reference level preferably corresponds to a pulse frequency of about 15 beats per minute.
The signal output by the comparator 183 is coupled on line 193 to an AND gate 195, where it is ANDed with the arterial enable signal supplied on line 45.
If both signals are at a positive level; it is deduced that an arterial infiltration has occurred and the AND
gate outputs a corresponding signal for coupling on line 197 to a latch 199. The latch, in turn, outputs the alarm signal for coupling on line 157 to the alarm 29 (FIG. 1).
A simplified schematic diagram of the open line detector circuit 37 is depicted in FIG. 7. This circuit monitors the pressure signal supplied on line 27 to detect a fluid leakage, i.e., an open line or an air bubble in the fluid tube 17 between the infusion pump 13 and the patient 11. If the circuit detects such a condition, it outputs an alarm signal for coupling on line 201 to the alarm 2~.
During normal operation, when the needle 19 is properly inserted into the patient s vein or artery, the pressure signal (FIG. 8(b)) reflects an overdamped or critically damped condition. The signal includes a positive pressure pulse immediately following each pulse of the motor step signal (FIG. 8(a)), with each pulse having an exp~nentially-decaying tail as the patient s vein or artery carries away the small volume of fluid being infused. Conversely, when an open line condition is present, the pressure signal (FIG. 8(c)) reflects an underdamped condition. Each pulse of the motor step ~L~ 7 signal results in an initial increase in fluid pressure, followed immediately thereafter by a momentary decrease in pressure to a level less than the level before the pulse occurred.
Basically, the open line detector 37 detects the occurrence of an open line condition by detecting an underdamped characteristic in the pressure signal, i.e., an overshoot or ringing in the pressure signal following each pulse of the motor step signal. More particularly, 10 the open line detector includes a 3 Hz high-pass filter 203 and a positive peak detector and hold circuit 205.
The high-pass filter filters the pressure signal supplied on line 27, to remove its dc level but pass the fre~
quencies associated with the successive steps of the 15 infusion ~ump 13. The filtered signal is coupled on line 209 to the peak detector and hold circuit, which outputs a level equal to the signal s positive peak. The peak detector circuit, which is reset by each pulse in the motor step signal supplied on line 21, can include for 20 example, a series-connected diode followed by a capacitor to ground.
The signal output by the positive peak detector and hold circuit 205 is coupled on line 211 to an ampli-fier 213 for amplification by a prescribed fractional 25 amount, e.g., negative two-thirds. This amplified signal serves as a threshold to which the high-pass filtered pressure signal is compared in a comparator 215.
If the filtered signal is ever more negative than the threshold, it is deduced that there is substantial 30 ringing occurring in the pressure signal and that an open line condition is therefore present.
More particularly, the signal output by the amplifier 213 is coupled on line 217 to the comparator s positive input terminal and the high-pass filtered 35 pressure signal is coupled on line 209 to the compara-tor s negative input terminal. The resulting comparator output signal is coupled on line 219 to a latch 221, which produces the alarm signal for coupling on line 201 to the alarm 29.
The alarm 29 is responsive to any of the four alarm signals coupled to it on lines 73, 97, 157 and 201 from the fault detection circuitry 10. It includes a four-input OR gate that OR s together the four signals and actuates a visual or audible indicator whenever any 10 of the signals is high. It further includes a switch for use in selectively clearing the latches or flip-flops at the output stage of each detector in the fault detection circuitry.
It should be appreciated from the foregoing 15 description that the present invention provides an improved apparatus and related method for detecting fault conditions such as an infiltration or an open line in a parenteral administration system. The apparatus is particularly adapted for use with a system of the type 20 that includes a pulsing infusion pump for incrementally pumping a parenteral fluid through a fluid tube and needle to a patient s vascular system. The apparatus monitors the pressure in the fluid tube to detect charac-teristic patterns indicative of infiltrations of the 25 fluid into the patient s body tissue separate from either his venous system or arterial system, as well as an open line or air bubble in the fluid coupling between the infusion pump and the patient.
It should also be appreciated that the fault 30 detection circuitry 10 and the infusion rate detector 41 described above can be implemented in both hard-ware and software.
Althou~h the present invention has been des-cribed in detail with reference to the presently pre-35 ferred embodiments, it should be understood by those of 34~7 21~
ordinary skill in the art that various alternatives,modifications and equivalents can be constructed without departing from the invention. Accordingly, the invention is limited only by the following claims.
~OR PARENTERAL INFUSI SYSTEM
BAC GROUND OF THE INVENTION_ This invention relates generally to systems for 5 administering parenteral fluids to a patient, and, more particularly, to systems of this type having an infusion apparatus for infusing the fluid into the patient s vascular system.
Systems of this particular type have enjoyed 10 widespread usage in hospitals for administering paren-teral fluids at precise rates. The systems are useful for both venous and arterial infusions and typically include an infusion pump and an associated controlling device for pumping the parenteral fluid through a ~luid 15 tube and needle to the patient s vein or artery.
One drawback to conventional infusion pump systems of this type is that the needle can sometimes become dislodged from the patient s vein or artery. This will normally cause an increase in back pressure, but the 20 pump will nevertheless continue to pump fluid at substan-tially the same fixed rate. The fluid therefore can infiltrate into the patient s body tissue and cause severe damage. Similarly, the needle can sometimes become dislodged from the patient entirely, yet the pump 25 will continue to pump the fluid at the same fixed rate.
One known prior technique for detecting fluid infiltrations is to monitor the patient s skin tempera-ture in the vicinity of the needle. Since the parenteral fluid is ordinarily cooler than the patient s body tempera~ure, and since the fluid is not carried away as rapidly when an infiltration occurs, an infiltration will ordinarily create a temperature drop in the vicinity of the needle. Thus, whenever a drop in skin temperature is detected, it is deduced that an infiltration is occur-ring. This technique is not believed to have provencompletely satisfactorily in all circumstances, such as, for example, when the parenteral fluid has a temperature substantially the same as that of the patient s blood.
Other known prior techniques for detecting an infiltration of a parenteral fluid into a patient s body tissue involve intervention by hospital personnel. In one~such technique, an attendant visually inspects the region around the needle, to detect any swelling that might indicate an infiltration. In another technique, useful only when the fluid is being administered from a bottle under the force of gravity, the attendant periodically lowers the bottle to an elevation below the needle such that fluid flows outwardly from the patient.
If when this is done the patient s blood does not appear in the fluid tube, it can be deduced that the needle is not in fluid communication with a vein or artery.
Neither of these techniques has proven to be entirely satisfactory, one reason being that they both require the presence of trained hospital personnel and cannot be performed automatically.
Still another prior technique for detecting infiltrations and other fault conditions is used in a parenteral administration system that regulates flow rate using a pinch valve located in the fluid tube, between a drop chamber and the patient In particular, the pinch valve is controllably adjusted in order to maintain the frequency of fluid drops into the drop chamber at a selected value. If the limits of the pinch valve are exceeded in attempting to maintain 5 the selected drop frequency, it is deduced that a fault condition is present. Operator intervention is still required, however, in order to determine the particular type of fault condition, e.g., an infiltra tion, that is present.
A complete dislodging of the needle from the patient, such that the fluid is directed onto his skin, bedding, etc., is ordinarily detected only through a visual inspection by a hospital attendant. Such active participation by hospital personnel is not believed to be 15 an entirely satisfactory solution to this problem.
It should be appreciated from the foregoing that there still is a need for an effective method and apparatus for automatically detecting faults such as infiltrations or an open line in a parenteral adminis-20 tration system of the type having an infusion device rThe present invention fulfills this need.
SUMMARY _ F THE_INVENTION
The present invention is embodied in a fault detection apparatus, and related method~ for use with a 25 parenteral administration system of the type having an infusion device for infusing a parenteral fluid through a fluid tube and needle to a patient s vascular system.
The apparatus includes pressure transducer means for monitoring the pressure of the fluid in the fluid tube 30 and producing a corresponding pressure signal. In accordance with the invention~ the apparatus further includes automatic fault detection means for quali-tatively evaluating the pressure signal to determine when '7 .
the fluid tube is not in proper fluid communication with the patient s vascular system, and for producing a corresponding alarm signal. This frees hospital per-sonnel to perform other tasks without the need for 5 repeatedly monitoring the status of the parenteral administration system.
One embodiment of the fault detection means is adapted for use with a parenteral administration system that includes a pulsing-type infusion device for adminis-10 tering the parenteral fluid to a patient s venous sys-tem. The fault detection means produces the alarm signal whenever it detects an infiltration of the fluid into body tissue separate from the venous system. In this embodiment, the fault detection means analyzes the 15 pressure signal following each infusion pulse to detect impedance changes distal to the needle. Specifically, the fault detection means detects an infiltration by determining if the pressure signal ever fails to return to its steady state level within a predetermined time 20 duration following each infusion pulse. In particular, the fault detection means high-pass filters the pressure signal and compares the filtered pressure signal with a prescribed threshold. The alarm signal is produced whenever the filtered pressure signal exceeds the thresh-25 old for longer than a prescribed time period followingeach infusion pulse.
Another embodiment of the fault detection means detects infiltrations whenever the infusion device is infusing fluid at a relatively high rate, e.g., 40 ml per 30 hour. In this embodiment, the fault detection means includes pressure change means for determining if the pressure signal ever increases by more than a particular amount during a predetermined time duration. This pressure change means preferably includes means for 35 sampling the pressure signal at spaced intervals of time, along with means for comparing the current pressure signal sample with with previous pressure signal sample, to determine if the pressure signal has increased by more than the prescribed amount during the interval between 5 samples. The pressure change means is preferably enabled only after pressure derivative means has determined that the instantaneous rate of change of the pressure signal exceeds a prescribed levelO
Two other embodiments of the fault detection 10 means of the invention are adapted for use when the parenteral administration system administers the paren-teral fluid ~o a patient s arterial system. In one such embodiment, the fault detection means low-pass filters the pressure signal to remove the effects of 15 the patient s heartbeats and compares the filtered pressure signal with a predetermined threshold. An alarm signal is produced whenever the signal drops below the threshold. In another such embodiment, the fault detection means high-pass filters the pressure signal 20 to pass only the siqnal components attributable to the patient's heartbeats. An alarm signal is pro-duced whenever a dropout in the heartbeat pulses is detected.
Yet another embodiment of the fault detection 25 means detects an open line or air bubble in the fluid tube connection between the pulsing-type infusion device and the patientO When such a condition occurs, the configuration is underdamped and the pressure signal has a ringing characteristic following each infusion pulse.
30 The fault detection means detects this ringing by analyz-ing the pressure signal following each infusion pulse, to measure impedance changes distal to the needle. Speci-fically, the fault detection means determinesr after each infusion pulse, if the ac pressure signal (i.eO, high-35 pass filtered pressure signal) drops below a prescribed ~2~ 7 negative pressure threshold~ This threshold is prefer-ably a prescribed negative fraction of the peak positive ac pressure signal occurring immediately after each infusion pulse.
In the preferred embodiment of the apparatus, the fault detection means includes several of the embodi-ment ~ scribed above~__f_r detecting venous and arterial infiltrations and open lines. Appropriate switching circuitry enables operation of either the venous or the 10 arterial infiltration circuit, depending on the use to which the system is being made. The alarm is actuated when any of the various circuits detects a fault.
Other aspects and advantages of the present invention should become apparent from the following 15 description of the preferred embodiments, taken in conjunction with the accompanying drawings, which illus-trate, by way of example, the principles of the inven-tion.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a parenteral administration system having circuitry for detecting venous infiltrations, arterial infiltrations and open fluid lines;
FIG. 2 is a simplified schematic diagram of a 25 low infusion rate venous infiltration detector included in the system of FIG. l;
FIG. 3(a)-(f) illustrate a series of waveforms that can be present in the venous infiltration detector of FIG. 2;
FIG. ~ is a simplified schematic diagram of a high infusion rate venous infiltration detector included in the system of FIG. 1;
FIG. 5 is a simplified schematic diagram of one embodiment of an arterial infiltration detector suitable for use in the system of FIG. l;
FIG. 6 is a simplified schematic diagram of an alternative ar~erial infiltration detector suitable for 5 use in the system of FIG. 1, FIG. 7 is a simplified schematic diagram of an open line detector included in the system of FIG. l;
and FIG. 8(a)-(c) illustrate several waveforms that 10 can be present in the open line detector of FIG. 7.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, and particularly to FIG. 1, there is shown fault detection circuitry 10 for use in a system for administering a parenteral fluid 15 to the vascular system of a patient 11. The system includes a conventional infusion pump 13 and associated pump controlling device 15 for pumping the parenteral fluid through a fluid tube 17 and needle 19 to the patient. The pump is preferably of the peristaltic 20 type, which pumps the fluid in a cyclic fashion.
The pump controlling device 15 outputs a motor step signal for coupling on line 21 to the infusion pump 13. The signal is a sequence of pulses, each of which increments the pump by one step, to infuse a predeter-25 mined volume of parenteral fluid to the patient 11.
The parenteral administration system furtherincludes a pressure transducer 23 and an associated a~
amplifier 25 for monitoring the fluid pressure in the fluid tube 17 and producing a corresponding pressure signal for output on line 27.
In accordance with the invention, the fault 5 detection circuitry 10 evaluates the pressure signal on line 27 to detect certain characteristic patterns indica-tive of an improper fluid communication between the fluid tube 17 and the patient s vascular system. An alarm 29 is actuated if the circuitry detects such a condi-10 tion. Such fault conditions include infiltrations of thefluid into body tissue other than the patienL s vascular system, as well as a complete dislodging of the needle 19 from the patient 11 or a leak or air bubble in the fluid tube. In this way, a proper administration of the 15 parenteral fluid can be ensured without the need for frequent monitoring or testing by hospital personnel.
More particularly, the fault detection cir-cuitry 10 includes a low infusion rate venous infiltra-tion detector 31 for detecting infiltrations when the 20 infusion pump 13 is pumping parenteral fluid into the patient s venous system at a relatively low rate, and a high infusion rate venous infiltration detector 33 for detecting infiltrations when the pump is pu~ping fluid into the venous system at a relatively high rate. The 25 fault detection circuitry further includes an arterial infiltration detector 35 for detecting infiltrations when the pump is pumping fluid into the patient s ar-terial system, and an open line detector 37 for detecting when there is a leak of some kind or an air bubble in the 30 fluid connection between the pump and the patient 11.
The system further includes a mode switch 39 for indicating whether the system is intended to adminis~
ter parenteral fluid to the patient s venous system or arterial system. The system also includes an infusion 35 rate detector circuit 41, operable whenever the switch '7 g indica~es that the system is pumping fluid into the patient s venous system to indicate whether the fluid is being pumped at a relatively high rate or a relatively low rate. The switch 39 and detector circuit 41 are used 5 to enable operation of the appropriate venous infiltra-tion detector circuit 31 or 33 or arterial infiltration detector circuit 35, depending on the system's operating mode.
More particularly, the mode switch 39 is a 10 single-pole, double-throw switch having its middle terminal connected directly to ground and its two re-maining terminals connected through separate resistors 43 to a positive voltage. The binary signals present on these two terminals are therefore opposite in phase to 15 each other. One such signal is defined to be an arterial enable signal and the other is defined to be a venous enable signal.
The arterial enable signal is coupled on line 45 directly to the arterial infiltration detector circuit 20 35, and the venous enable signal is coupled on line 47 to the infusion rate detector 41. The infusion rate detector circuit relays the venous enable signal to either the low infusion rate venous infiltration detector 31 or the high infusion rate venous infiltration detector 25 33, depending on the infusion rate being effected by the infusion pump 13.
The infusion rate detector circuit 41 includes a frequency discriminator 49 for monitoring the motor step signal present on line 21 and producing an output 30 signal having a voltage level generally proportional to the motor step signal's frequency. This output signal is coupled on line 51 to the positive input terminal of a comparator 53, which compares it with a selected refer-ence level coupled to its negative input terminal. The 35 reference level is supplied on line 55 from the wiper of r~
a potentiometer 57, whose remaining two terminals are connected between ground and a positive supply voltage.
If the discriminator output signal exceeds the threshold, indicating that the infusion pump 13 is pumping at a 5 relatively high rate (e.g., above about 40 ml per hour), the comparator outputs a positive voltage level. On the other hand, if the discriminator output signal does not exceed the threshold, indicating that the pump is pumping at a relatively low rate, the comparator outputs a low 10 voltage level signal.
The signal output by the comparator 53 is coupled on line 59 to a first AND gate 61 for ANDing with the venous enable signal supplied on line 47 from the mode switch 39. This produces a high infusion rate 15 venous enable signal for coupling on line 63 to the high infusion rate venous infiltration detector 33. The detector 33 is thereby enabled to detect infiltrations whenever a venous infusion is selected by the mode switch and the infusion rate exceeds the prescribed threshold.
The signal output by the comparator 53 of the infusion rate detector 41 is also coupled on line 59 to a NOT gate 65, for inversion and coupling in turn on line 67 to a second AND gate 69, where it is ANDed with the same venous enable signal present on line 47. The 25 resulting low infusion rate venous enable signal is coupled on line 71 to the low infusion rate venous infiltration detector 31. This detector 31 is thereby enabled whenever a venous infusion is selected by the mode switch 39 and the infusion rate does not exceed the 30 prescribed threshold.
Referring now to FIG. 2, there is shown a simplified schematic diagram of the low infusion rate venous infiltration detector 31. This circuit monitors the pressure signal supplied on line 27 from the ampli-35 fier 25, to detect a characteristic pattern indicative of '7 an occlusion or infiltration of fluid into the patient sbody tissue separate from his venous system. When the circuit detects such a condition, it outputs an alarm signal for coupling on line 73 to the alarm 29. Basic-5 ally, the circuit determines that an occlusion or aninfiltration has occurred whenever the pressure signal fails to return to its nominal value within a prescribed time duration following each of the successive pumping pulses of the infusion pump 13.
The low infusion rate venous infiltration detector 31 includes a 0.1 Hz high-pass filter 75 for filtering the pressure signal supplied on line 27, to produce a filtered pressure signal for output on line 77. The pressure signal, which is depicted in FIG. 3(c), 15 normally includes a series of positive pressure pulses, each with an exponentially-decaying tail, as a result of the successive motor steps of the infusion pump 13.
A comparator 79 compares the filtered pressure signal with a selected positive voltage threshold sup~
20 plied on line 81 from the wiper of a potentiometer 83.
The other two terminals of the potentiometer are con nected between ground and a positive potential. If the filtered pressure signal has a voltage level exceeding the threshold, the comparator outputs a positive signal 25 on line 85 as shown in FIG. 3(d). The threshold is preferably selected to be about 30 percent of the pulse s peak value. Typically, the threshold is about four to six cm H2O.
The detector 31 further includes a monostable 30 multivibrator or one-shot 87 and a flip-flop 89 for sampling the signal output by the comparator 79 about 0.2 seconds after each pulse of the motor step signal (FIG.
3(a)). In particular, the motor step signal is supplied on line 21 to the one-shot, which produces a correspond-35 ing sequence of pulses (FIG. 3(b)), each having a dura-'7 tion of about 0.2 seconds. This one shot signal is coupled on line 91 to the clock input terminal of the flip-flop, which samples the pressure derivative signal at the trailing edge of each pulse. I~ the 5 comparator output signal is still a positive value at this time, the flip-flop outputs a positive signal as The signal output by the flip-flop 89 is coupled on line 93 to one input terminal of an AND
10 gate 9~, which ANDs the signal with the low infusion rate venous enable signal supplied on line 71. It will be recalled that this enable signal indicates that the parenteral administration system is intended to be administering fluid to the patient s venous system at a 15 relatively low rate. If both inputs to the AND gate are a positive value, it is deduced that an infiltration is occurring and the A~D gate outputs a trigger signal for coupling on line 95 to a latch 96, which, in turn, produces an alarm signal for coupling on line 73 to the 20 alarm 29 (FIG. 1).
During normal situations, when the needle 19 is properly inserted into the patient s vein, the pressure signal (FIG. 3(c)) returns to its nominal value rela-tively quickly after each pulse of the motor step signal 25 (FIG. 3(a)). As a result, the pressure signal does not exceed the threshold and the comparator output signal (FIG. 3(d)) is at a low level at the successive sample times. The detector circuit 31 therefore does not produce an alarm signal.
On the other hand, during abnormal situations, when the needle 19 is not in proper communication with the patient s venous system and an infiltration is occurring, the pressure signal (FIG. 3(e)) has a rela-tively long decay time. This apparently occurs because 35 of an inability o~ the body tissue to dissipate rapidly each infusion of parenteral fluid. Because of the long decay time, the comparator output signal (FIG.
3(f~) is still at a high level at the time it is sampled by the flip-flop 89. An alarm signal is therefore produced on line 73.
Referring now to FIG. 4, there is shown a simplified schematic diagram of the high infusion rate venous infiltration detector 33 of FIG. 1. Basically, this circuit monitors the pressure signal supplied on line 27 to determine if the pressure in the fluid tube 17 10 ever increases by more than a selected amount during a predetermined time period. It makes this determination only after the instantaneous rate of change of pressure first exceeds a prescribed level, e.g., 30 cm H2O per second. A positive pressure slope less than this lower 15 threshold can occur during normal situations. A positive pressure slope greater than about 250 cm H2O per second can indicate a downstream occlusion, but is treated by the detector circuit as though it were an infiltration.
When the instantaneous rate of change of the pressure 20 signal first exceeds the 30 cm H2O per second thresh-old, the detector circuit samples the pressure signal immediately and again approximately four seconds later.
If the second sample exceeds the first by more than a prescribed amount, e.g., 75 cm H2O it is deduced 25 that an infiltration is occurring. An alarm signal is then output on line 97 for coupling to the alarm 29 (FIG. 1)~
The detector circuit 33 of FIG. 4 is suitable for use in detecting infiltrations when the parenteral 30 administration system is administering fluids at rates above about 40 ml per hour. The low infusion rate venous infiltration detector 31 of FIG. 2 could also function properly at such infusion rates, but would ordinarily require the momentary disabling of the infusion pump 13 35 each time it seeks to detect an infiltration. This is because the successive pulses of the infusion pump would then be occurring less than 0.2 seconds apart, which is the nominal sample delay time required by the circuit.
The high infusion rate venous infiltration detector 33 includes a differentiator 99 for producing a 5 pressure derivative signal, along with a comparator 103 for comparing the pressure derivative signal with a threshold corresponding to 30 cm H20 per second. The pressure signal is input to the differentiator on line 27, and the pressure derivative signal is output by the 10 differentiator on line 105 for coupling to the compara-tor s positive input terminal. The comparator s negative input terminal is coupled on line 111 to the wiper of a potentiometer 1130 The remaining two terminals of the potentiometer are connected to ground and a positive 15 supply voltage, so the voltage present at the wiper of the potentiometer represents a selected positive voltage threshold. The comparator produces a positive-valued trigger signal whenever the pressure derivative signal exceeds the threshold.
The detector circuit 33 of FIG. 4 further includes first and second sample and hold circuits 121 and 123 and a four second monostable multivibrator or one-shot 125. The trigger signal produced by the com-parator 103 is coupled on line 117 to both the first sample and hold circuit and the one-shot. Whenever the trigger signal goes into a high state~ indicating that the instantaneous pressure derivative signal has just exceeded the rate of change threshold, the first sample and hold circuit samples the pressure signal supplied on line 27 and the one-shot simultaneously initiates a four second output pulse that is in a low state. The one-shot output signal is coupled on line 129 to the second sample and hold circuit, whereupon four seconds later it like-wise samples the pressure signal.
The signal output by the first sample and hold ~2~
circuit 121 is coupled on line 131 to a summer 133, for summing with a selected positive voltage level supplied on line 135 from a potentiometer 137. This voltage level represents the minimum amount by which the pressure signal must increase during a four second period for an infiltration to be detected. A comparator 139 compares the summer output signal with the signal output by the second sample and hold circuit 123. In particular, the summer output signal is coupled on line 141 to the comparator's negative input terminal, and the second sample and hold circuit output signal is coupled on line 143 to the comparator s positive input terminal. I the sample and hold signal exceeds the summer signal, it is deduced that the pressure in the fluid tube 17 has increased by more than the prescribed amount (75 cm H2O) during the preceeding four second period and that an infiltration has therefore occurred.
The signal output by the comparator 139 is coupled on line 145 to an AND gate 147, for ANDing with the high infusion rate venous enable siqnal supplied on line 63 from the infusion rate detector circuit 41 (FIG.
1). If both AND gate input signals are high, the AND gate produces a high signal for coupling on line 153 to the data input terminal of a flip-flop 155. A clock pulse signal for clocking the flip-flop occurs shortly after the end of the four second period, at which time the comparator and AND gate output signals have stabil-ized. This clock pulse signal, which is coupled to the flip-flop s clock terminal on line 149, is produced by a clock pulse one-shot 151 in response to the one-shot pulse supplied on line 129 from the four second one-shot 125. The flip-flop in turn produces the alarm signal for output on line 97.
Referring now to FIG. S, there is shown a simplified schematic diagram of one embodiment of the arterial infiltration detector 35 of FIG. 1. Basically, the circuit compares the rnean pressure signal, which should correspond to the patient s mean arterial pres-sure, to a prescribed positive threshold, preferably 5 about 60 cm of watery and outputs an alarm signal on line 157 whenever the signal drops below the threshold.
More particularly, the arterial infiltration detector 35 of FIG. 5 includes a 0.1 Hz low-pass filter 159 and a comparator 161. The filter filters the pres-10 sure signal supplied on line 27 to produce a mean ar-terial pressure signal for coupling on line 163 to the comparator s negative input terminal. The prescribed positive threshold is coupled to the comparator s posi-tive input terminal on line 165 from the wiper of a 15 potentiometer 167. During normal operation, when the needle 19 is properly inserted in the patient s artery, the mean arterial pressure signal will exceed the thresh-old selected by the potentiometer and the comparator will output a signal having a negative level. Conversely, 20 when the needle is not properly inserted in the patient s artery and an infiltration is occurring, the mean ar-terial pressure signal will not exceed the threshold and the comparator will output a signal having a positive level. A bandwidth of about 0.1 Hz is preferred for the 25 low-pass filter, to substantially remove the effects of the patient s heartbeats.
The signal output by the comparator 161 is coupled on line 169 to an AND gate 171, for ANDing with the arterial enable signal supplied on line 45. If both 30 signals are at a positive levely then the AND gate likewise outputs a positive level signal. This AND gate output signal is coupled on line 173 to a latch 175y which produces the alarsn signal for output on line 157.
With reference now to FIG. 6, there is shown a simplified schematic diagram of an alternative embodiment of the arterial infiltration detector 35 of FIG. 1. In this embodiment, infiltrations into the patient s body tissue separate from his arterial system are detected by 5 monitoring the pressure signal to detect dropouts in the pressure variations caused by the patient's heartbeat.
More particularly, the arterial infiltration detector 35 of FIG. 6 includes a 0.1 Hz high-pass filter 177, a level detector with hysteresis 179, a frequency 10 discriminator 181 and a comparator 183. The high-pass filter filters the pressure signal supplied on line 27 to remove its dc level and pass only the successive pulses representative of the patient s heartbeats. The heart-beat pulses are present in the pressure signal whenever the fluid tube 17 and the needle 19 (FIG. 1) are coupled directly to the patient's arterial system. The high-pass filtered signal is coupled on line 185 to the level detector, which converts the signal to a corresponding pulse sequence signal. The level detector detects only 20 pulses having a magnitude of at least about 15 cm H2O.
The pulse sequence produced by the level detector is coupled on line 185 to the frequency discriminator, which produces an output signal having a level proportional to the frequency of its input signal.
Thus, if the needle 19 is properly inserted into the patient s arterial system, the heartbeats will be represented in the pressure signal and the frequency discriminator 181 will output a relatively high voltage level signal. On the other hand, if the needle is not properly inserted into the patient s arterial system, the heartbeats will not be represented in the pressure signal and the frequency discriminator will output a relatively low level signal.
The discriminator output signal is coupled on 35 line 187 to the negative input terminal of the comparator ~L~
183, which compares it with a selected positive reference level supplied to its positive input terminal on line 189 from a potentiometer 191. Thus, if the frequency dis-criminator output signal ever drops below the reference level, the comparator outputs a positive voltage level.
The reference level preferably corresponds to a pulse frequency of about 15 beats per minute.
The signal output by the comparator 183 is coupled on line 193 to an AND gate 195, where it is ANDed with the arterial enable signal supplied on line 45.
If both signals are at a positive level; it is deduced that an arterial infiltration has occurred and the AND
gate outputs a corresponding signal for coupling on line 197 to a latch 199. The latch, in turn, outputs the alarm signal for coupling on line 157 to the alarm 29 (FIG. 1).
A simplified schematic diagram of the open line detector circuit 37 is depicted in FIG. 7. This circuit monitors the pressure signal supplied on line 27 to detect a fluid leakage, i.e., an open line or an air bubble in the fluid tube 17 between the infusion pump 13 and the patient 11. If the circuit detects such a condition, it outputs an alarm signal for coupling on line 201 to the alarm 2~.
During normal operation, when the needle 19 is properly inserted into the patient s vein or artery, the pressure signal (FIG. 8(b)) reflects an overdamped or critically damped condition. The signal includes a positive pressure pulse immediately following each pulse of the motor step signal (FIG. 8(a)), with each pulse having an exp~nentially-decaying tail as the patient s vein or artery carries away the small volume of fluid being infused. Conversely, when an open line condition is present, the pressure signal (FIG. 8(c)) reflects an underdamped condition. Each pulse of the motor step ~L~ 7 signal results in an initial increase in fluid pressure, followed immediately thereafter by a momentary decrease in pressure to a level less than the level before the pulse occurred.
Basically, the open line detector 37 detects the occurrence of an open line condition by detecting an underdamped characteristic in the pressure signal, i.e., an overshoot or ringing in the pressure signal following each pulse of the motor step signal. More particularly, 10 the open line detector includes a 3 Hz high-pass filter 203 and a positive peak detector and hold circuit 205.
The high-pass filter filters the pressure signal supplied on line 27, to remove its dc level but pass the fre~
quencies associated with the successive steps of the 15 infusion ~ump 13. The filtered signal is coupled on line 209 to the peak detector and hold circuit, which outputs a level equal to the signal s positive peak. The peak detector circuit, which is reset by each pulse in the motor step signal supplied on line 21, can include for 20 example, a series-connected diode followed by a capacitor to ground.
The signal output by the positive peak detector and hold circuit 205 is coupled on line 211 to an ampli-fier 213 for amplification by a prescribed fractional 25 amount, e.g., negative two-thirds. This amplified signal serves as a threshold to which the high-pass filtered pressure signal is compared in a comparator 215.
If the filtered signal is ever more negative than the threshold, it is deduced that there is substantial 30 ringing occurring in the pressure signal and that an open line condition is therefore present.
More particularly, the signal output by the amplifier 213 is coupled on line 217 to the comparator s positive input terminal and the high-pass filtered 35 pressure signal is coupled on line 209 to the compara-tor s negative input terminal. The resulting comparator output signal is coupled on line 219 to a latch 221, which produces the alarm signal for coupling on line 201 to the alarm 29.
The alarm 29 is responsive to any of the four alarm signals coupled to it on lines 73, 97, 157 and 201 from the fault detection circuitry 10. It includes a four-input OR gate that OR s together the four signals and actuates a visual or audible indicator whenever any 10 of the signals is high. It further includes a switch for use in selectively clearing the latches or flip-flops at the output stage of each detector in the fault detection circuitry.
It should be appreciated from the foregoing 15 description that the present invention provides an improved apparatus and related method for detecting fault conditions such as an infiltration or an open line in a parenteral administration system. The apparatus is particularly adapted for use with a system of the type 20 that includes a pulsing infusion pump for incrementally pumping a parenteral fluid through a fluid tube and needle to a patient s vascular system. The apparatus monitors the pressure in the fluid tube to detect charac-teristic patterns indicative of infiltrations of the 25 fluid into the patient s body tissue separate from either his venous system or arterial system, as well as an open line or air bubble in the fluid coupling between the infusion pump and the patient.
It should also be appreciated that the fault 30 detection circuitry 10 and the infusion rate detector 41 described above can be implemented in both hard-ware and software.
Althou~h the present invention has been des-cribed in detail with reference to the presently pre-35 ferred embodiments, it should be understood by those of 34~7 21~
ordinary skill in the art that various alternatives,modifications and equivalents can be constructed without departing from the invention. Accordingly, the invention is limited only by the following claims.
Claims (16)
1. Fault detection apparatus for use with a parenteral administration system having an infusion device for infusing parenteral fluid through a fluid tube to the vascular system of a patient, comprising:
pressure transducer means for monitoring the pressure of the fluid in the fluid tube and producing a corresponding pressure signal; and fault detection means for evaluating the pressure signal over a period of time to detect characteristic patterns in the waveform of the pressure signal evaluated which are indicative of improper fluid communication between the fluid tube and the vascular system of the patient and for producing a corresponding alarm signal whenever the fault detection means detects such a characteristic pattern.
pressure transducer means for monitoring the pressure of the fluid in the fluid tube and producing a corresponding pressure signal; and fault detection means for evaluating the pressure signal over a period of time to detect characteristic patterns in the waveform of the pressure signal evaluated which are indicative of improper fluid communication between the fluid tube and the vascular system of the patient and for producing a corresponding alarm signal whenever the fault detection means detects such a characteristic pattern.
2. Fault detection apparatus as defined in claim 1, wherein the infusion device infuses the parenteral fluid to the patient in a pulsing fashion and the fault detection means include:
means for detecting an infiltration of the parenteral fluid into body tissue separate from the vascular system by determining if the pressure signal does not return to a steady state level within a predetermined time period following an infusion pulse and for producing an alarm signal whenever such an occurrence is detected.
means for detecting an infiltration of the parenteral fluid into body tissue separate from the vascular system by determining if the pressure signal does not return to a steady state level within a predetermined time period following an infusion pulse and for producing an alarm signal whenever such an occurrence is detected.
3. Fault detection apparatus as defined in claim 2, wherein the fault detection means includes:
means for high-pass filtering the pressure signal to produce a filtered pressure signal; and means for comparing the filtered pressure signal with a predetermined threshold signal and for detecting when the filtered pressure signal exceeds the threshold signal for a predetermined time period following an infusion pulse and for producing an alarm whenever such an occurrence is detected.
means for high-pass filtering the pressure signal to produce a filtered pressure signal; and means for comparing the filtered pressure signal with a predetermined threshold signal and for detecting when the filtered pressure signal exceeds the threshold signal for a predetermined time period following an infusion pulse and for producing an alarm whenever such an occurrence is detected.
4. Fault detection apparatus as defined in claim 1, wherein the fault detection means includes means for detecting if the pressure signal ever increases by more than a predetermined amount during a predetermined time period and for producing an alarm signal whenever such occurrence is detected .
5. Fault detection apparatus as defined in claim 4, wherein the fault detection means further includes:
means for determining the derivative of the pressure signal with respect to time; and means to compare the derivative of the pressure signal with a predetermined threshold signal, and producing an alarm signal whenever the derivative signal exceeds the threshold signal.
means for determining the derivative of the pressure signal with respect to time; and means to compare the derivative of the pressure signal with a predetermined threshold signal, and producing an alarm signal whenever the derivative signal exceeds the threshold signal.
6. Fault detection apparatus as defined in claim 1, wherein the parenteral administration system is arranged to administer parenteral fluid to the arterial system of the patient and the fault detection means includes means for low-pass filtering the pressure signal to produce a filtered pressure signal; and means for comparing the filtered pressure signal with a predetermined threshold signal and producing the alarm signal whenever the filtered signal drops below the threshold signal.
7. Fault detection apparatus as defined in claim 1, wherein the fault detection means includes:
means for high-pass filtering the pressure signal to produce a variable pressure signal; and means for evaluating the variable pressure signal to detect a dropout in variable signal components attributable to the patient's heartbeats and for producing the alarm signal whenever such an occurrence is detected.
means for high-pass filtering the pressure signal to produce a variable pressure signal; and means for evaluating the variable pressure signal to detect a dropout in variable signal components attributable to the patient's heartbeats and for producing the alarm signal whenever such an occurrence is detected.
8. Fault detection apparatus as defined in claim 7, wherein the infusion device infuses the parenteral fluid to the vascular system of the patient in a pulsing fashion, the fault detection means including:
means for detecting a disconnection between the fluid tube and the patient or an air bubble in the fluid tube by detecting an underdamped characteristic in the pressure signal following an infusion pulse and for producing an alarm whenever such an underdamped characteristic is detected.
means for detecting a disconnection between the fluid tube and the patient or an air bubble in the fluid tube by detecting an underdamped characteristic in the pressure signal following an infusion pulse and for producing an alarm whenever such an underdamped characteristic is detected.
9. A method of detecting faults in the operation of a parenteral administration system, wherein an infusion device infuses a parenteral fluid through a tube to the vascular system of a patient, said method comprising:
monitoring the pressure of the fluid in the tube and producing a corresponding pressure signal;
evaluating the pressure signal over a period of time to detect characteristic patterns in the waveform of the pressure signal evaluated which are indicative of improper fluid communication between the fluid tube and the vascular system of the patient; and producing an alarm signal whenever such characteristic patterns are detected.
monitoring the pressure of the fluid in the tube and producing a corresponding pressure signal;
evaluating the pressure signal over a period of time to detect characteristic patterns in the waveform of the pressure signal evaluated which are indicative of improper fluid communication between the fluid tube and the vascular system of the patient; and producing an alarm signal whenever such characteristic patterns are detected.
10. A method of detecting faults as defined in claim 9, wherein the parenteral fluid is infused in a pulsing fashion and wherein the step of evaluating includes:
evaluating the pressure signal over a period of time to detect if the signal fails to return to a steady state level within a predetermined time period following an infusion pulse; and producing an alarm signal whenever such an occurrence is detected.
evaluating the pressure signal over a period of time to detect if the signal fails to return to a steady state level within a predetermined time period following an infusion pulse; and producing an alarm signal whenever such an occurrence is detected.
11. A method of detecting faults as defined in claim 10, wherein the step of evaluating includes steps of:
high-pass filtering the pressure signal to produce a filtered pressure signal;
comparing the filtered pressure signal with a prescribed threshold signal;
detecting when the filtered pressure signal exceeds the threshold signal for a prescribed time period following each infusion pulse: and producing an alarm signal whenever such an occurrence is detected.
high-pass filtering the pressure signal to produce a filtered pressure signal;
comparing the filtered pressure signal with a prescribed threshold signal;
detecting when the filtered pressure signal exceeds the threshold signal for a prescribed time period following each infusion pulse: and producing an alarm signal whenever such an occurrence is detected.
12. A method of detecting faults as defined by claim 9, wherein the evaluating includes the steps of evaluating the pressure signal over a period of time to detect if the pressure signal increases by more than a predetermined amount during a predeter-mined time period; and producing an alarm signal whenever such an occurrence is detected.
13. A method for detecting fluid infiltrations as defined in claim 9, wherein the step of evaluating includes steps of:
determining the derivative of the pressure signal with respect to time, comparing the derivative of the pressure signal with a predetermined threshold signal; and producing an alarm signal whenever the derivative signal exceeds the threshold signal.
determining the derivative of the pressure signal with respect to time, comparing the derivative of the pressure signal with a predetermined threshold signal; and producing an alarm signal whenever the derivative signal exceeds the threshold signal.
14. A method of detecting faults as defined in claim 9 for infusing parenteral fluid to the arterial system of a patient, wherein the step of evaluating includes the steps of:
low-pass filtering the pressure signal to remove variable signal components attributable to the patient's heartbeats;
comparing the filtered pressure signal with a predetermined threshold signal; and producing the alarm signal whenever the filtered pressure signal drops below the threshold signal.
low-pass filtering the pressure signal to remove variable signal components attributable to the patient's heartbeats;
comparing the filtered pressure signal with a predetermined threshold signal; and producing the alarm signal whenever the filtered pressure signal drops below the threshold signal.
15. A method of detecting faults as defined in claim 9, wherein the step of evaluating includes:
high-pass filtering the pressure signal to produce a variable pressure signal;
evaluating the variable pressure signal to detect when a drop out occurs in variable signal components attributable to the patient's heartbeats;
and producing an alarm signal whenever such an occurrence is detected.
high-pass filtering the pressure signal to produce a variable pressure signal;
evaluating the variable pressure signal to detect when a drop out occurs in variable signal components attributable to the patient's heartbeats;
and producing an alarm signal whenever such an occurrence is detected.
16. A method of detecting faults as defined in claim 9, for infusing parenteral fluid to the vascular system of a patient in a pulsing fashion, wherein the step of evaluating includes:
detecting an underdamped characteristic in the pressure signal following each infusion pulse, such an underdamped characteristic indicating an open fluid line or an air bubble in the fluid line; and producing an alarm signal whenever such an underdamped characteristic is detected.
detecting an underdamped characteristic in the pressure signal following each infusion pulse, such an underdamped characteristic indicating an open fluid line or an air bubble in the fluid line; and producing an alarm signal whenever such an underdamped characteristic is detected.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US483,903 | 1983-04-11 | ||
| US06/483,903 US4534756A (en) | 1983-04-11 | 1983-04-11 | Fault detection apparatus and method for parenteral infusion system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1219497A true CA1219497A (en) | 1987-03-24 |
Family
ID=23921968
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000451623A Expired CA1219497A (en) | 1983-04-11 | 1984-04-10 | Fault detection apparatus for parenteral infusion system |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US4534756A (en) |
| EP (1) | EP0121931B1 (en) |
| JP (1) | JPS6034454A (en) |
| CA (1) | CA1219497A (en) |
| DE (3) | DE3485377D1 (en) |
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-
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- 1984-04-10 EP EP84103975A patent/EP0121931B1/en not_active Expired - Lifetime
- 1984-04-10 DE DE8484103975T patent/DE3482620D1/en not_active Expired - Lifetime
- 1984-04-10 DE DE8989105436T patent/DE3486071T2/en not_active Expired - Lifetime
- 1984-04-10 CA CA000451623A patent/CA1219497A/en not_active Expired
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Also Published As
| Publication number | Publication date |
|---|---|
| DE3486071T2 (en) | 1993-05-27 |
| US4534756A (en) | 1985-08-13 |
| JPS6034454A (en) | 1985-02-22 |
| EP0121931B1 (en) | 1990-07-04 |
| JPH0429397B2 (en) | 1992-05-18 |
| EP0121931A2 (en) | 1984-10-17 |
| DE3485377D1 (en) | 1992-01-30 |
| DE3486071D1 (en) | 1993-03-25 |
| DE3482620D1 (en) | 1990-08-09 |
| EP0121931A3 (en) | 1985-09-11 |
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