WO2013045119A1

WO2013045119A1 - Device for the determination of peripheral regional anaesthesia using contactless photoplethysmography

Info

Publication number: WO2013045119A1
Application number: PCT/EP2012/055147
Authority: WO
Inventors: Aleksejs Miščuks; Renārs Erts; Uldis RUBĪNS; Jānis SPĪGULIS; Māris Mihelsons
Original assignee: Latvijas Universitate
Priority date: 2011-09-30
Filing date: 2012-03-22
Publication date: 2013-04-04
Also published as: LV14444B; LV14444A

Abstract

The invention relates to anaesthesia and, in particular – to the determination of efficiency of human anaesthesia and for registration the same, using contactless photoplethysmography (PPG) equipment. The device for contactless determination in real time of the effect of regional anaesthesia comprises a light source adapted for irradiation of the skin surface being anaesthetized with white light, a three-color RGB light-sensitive sensor-matrix adapted for image converting into digital format, assigning each image pixel the determined RGB value range, a device's memory, adapted for the storage of said value range, an analysis unit adapted for calculation of photopletizmographyc signal (PPG) amplitude from the green G colour channel video signal at each cardiac cycle, and for PPG average median values calculation from it in the specified time interval, an analysis block adapted for recording the effect of anaesthesia according to PPG amplitude changes, an output device designed for displaying time chart or numerical values of PPG amplitude, a control unit, which is connected with the light source, the light-sensitive sensor-matrix and the analysis unit, and adapted to control their operation.

Description

DEVICE FOR THE DETERMINATION OF PERIPHERAL REGIONAL ANAESTHESIA USING CONTACTLESS PHOTOPLETHYSMOGRAPHY

Technical field

The invention is intended for use in anaesthesia, namely, for the determination of efficiency of human anaesthesia after the peripheral nerve plexus block in regional anaesthesia (RA).

Background Art

One of the main objectives of anaesthesia is to ensure a patient relief from pain. Classically motor, sensory and sympathetic blocks are considered as positive effects of RA. Looking back on the overall experience in the determination of RA, it appears that the effect of anaesthesia can be detected by various methods. However only clinical methods are widely used. The determination of the level of regional anaesthesia basically includes testing of sensory functions and determination of physiological responses. Testing of sensory functions is only possible if the patient is conscious and cooperative enough. For the present there is no direct, the ideal method known for the determination of presence of RA or its degree for an unconscious patient.

Sensing threshold and the effect of RA (i.e. - loss of sensitivity) is traditionally determined by the minimal needle stabs in determining loss of sensation or, determining by loss of sensation of coldness, after the contacting with cold, for example, an ice cube (according to neuroscience standards). These clinical "sensory" RA methods are undeniably simple, but subjective and based on the doctor/patient contact. Unfortunately, the contacts tend to be more difficult due to objective reasons. First, the variable level of the patient's consciousness should be noted, which depends on numerous factors - stress, the presence and severity of injuries, unusual circumstances, mental characteristics of age, underlying conditions, drug background, level of premedication and sedation level and so on. So very often physically it is simply impossible to get adequate response from the patient about his sensory feel and even more - the answer obtained in this way may be not only vague and uncertain, but false positive. This in turn can lead to the situation where the prepared and positioned before the surgery patient is not actually anaesthetized, but a switch to another type of anaesthesia in this situation is not implementable. The situation is dangerous not only from an ethical point of view, but also from a purely medical, for unexpected severe pain associable with surgical skin incision may lead, for example, to threatening coronary pain or hypertensive crises, in particularly on unfavorable to the above background.

The current technologies do not allow direct measurement of pain, but a lot of factors enable to judge about the level of pain indirectly. Starting of motor block is the secondary evidence about starting of anaesthesia, but without adequate correlation with the sensory block. In other words, the motor block can not to be, but anaesthesia occurs, and vice versa. Secondly, here again the contacts with the patient is necessary, so that he can make conscious active movements. By contrast, more difficult to establish, but independent of the patient starting of sympathetic block is, for example, physiological and hormonal changes in the body, in response to stress, surgery, anaesthesia. One part of them can be determined in laboratory (a level of adrenal hormone Cortisol in plasma, of IL6, CRP- in the second phase of inflammation). Here limitations should be noted - time and cost limits, which makes identifying changes in the laboratory directly for routine anaesthesia to be impractical. The second part involves the direct measurement reflecting the neurophysiological changes of brain associated with stress and pain. The third part is associated with physiological changes in response to RA administration. After the administration of RA, by the occurrence of adequate anaesthesia, sensory, motor and sympathetic blocks are expected, according to compromised innervation zone. If the sensory block cannot directly be measured, the sympathetic effects can be attempt to assess, and then after it implicitly judge about the expected sensory effects. The sympathetic effect is associated with prominent peripheral vasodilation, peripheral blood flow increase and, as a result, increase of peripheral skin temperature. Routine monitoring of temperature is very effective, but limited to very small skin surface, i.e., the temperature is determined only in the place of a temperature sensor attachment. As one of the most modern methods enabling to assess a larger area, a thermal camera should be noted, allowing perform a graphical visualization of the dynamics of indirect RA starting process.

Serious attention was given to RA quantification in the world, especially if only clinical methods are widely used in the daily practice of anaesthesiology, which are mostly focused on the determination of sensor block in RA. The clinical methods are non-quantitative and based on the doctor-patient contact. Due to the fact that the patient's mental condition is variable and depends on numerous factors such as age, level of sedation, general somatic condition, there other quantitative methods are absolutely necessary.

There are several non-invasive methods and devices for RA detection invented and patented in recent years.

There is known a device and method for monitoring of success of spinal anaesthesia

(WO 2010075997), which provides at least one electronic temperature sensor placement on the skin surface within at least single dermatome. The device gives an optical and/or acoustic signal for the situation, when the temperature measurement results changes of 2-3 °C, indicating a positive result of anaesthesia.

There is known a method of evaluation of adequacy of block in conduction anesthesia

(patent: RU2357660), where the patient pulse index is used, which is measured once per minute, starting with the 5th minute, simultaneously on the operable and healthy limbs. The average coefficient of the blocked and healthy limb is evaluated, and in case if the difference between the coefficients is more than three times, the anaesthesia is considered to be successful.

There are known publications where methods of use of a thermal camera are described, by use of which the temperature difference between the anesthetized and non-anesthetized areas is examined for patients to which surgery on upper limbs is provided (Tejs Jansen et al, 2010).

Very popular is the combination of an ultrasound visualization device with pulse oximetry for the performance of RA and approval of peripheral block (WO 2010076808).

Other methods for the determination of anaesthesia are based on different principles, for example, an electrodermal activity. Skin conductivity changes were established after the sympathetic block starting, that is associated with successful RA (T.Ledovski et al, Anaesthesia, 2007, 62, p.989-993).

There are designed also other devices, such as PAINVISION PS-210 (osachi Ltd, 2003) for the quantitative monitoring of perception, where observation parameters of common standard anaesthesiology (ECG, LA, etc.) and adjustable electric stimulus are used.

There are also known mechanical devices, the so-called palpometers, for use of which contact with patient is needed (Nature Medicine, Volume I, N 11, Nov.1995, p. 1139-1140). Another known method, where special needles with weights are used, proposed for sensory ability control of diabetic patients. This method is comparable with the determination of level of anaesthesia by peripheral block (AW Chan, J Neurol Neurosurg Psychiatry, 1992; 55 (1): p. 56-59).

Comparing RA preventive methods also general anaesthetic (GA) stress detection methods can be considered, which in theory could not be used. Practical surgical stress can be observed only in case of failed RA, not timely diagnosed. As a basis for the method the change of the wave's downstream part of the pulse of patient's photoplethysmography as the response to increased heart rate and elevated blood pressure because of reacting to stress, is used (CN101785660 A).

Photoplethysmography (PPG) is a non-invasive optical method for measuring the blood volume pulsations. Method is based on the ability of optical radiation to penetrate tissue for several millimeters in depth. Radiation is absorbed in the soft tissues and blood. Due to the functioning of the heart and breathing, as well as a result of vasomotion, blood volume periodically changes, and the radiation intensity in the subcutaneous tissue is modulated due to these processes. Blood volume changes can be measured by using a method of PPG contact based on one or more radiation sources and a photodiode, which detects the radiation passed through skin (tissue) or reflected. PPG method is used for the detection of blood pulse and blood oxygen levels in commercial medical monitoring systems. Contact PPG method has the following drawback: the pulse of blood volume can be measured only in a small skin (tissue) area that is in direct contact with the sensor. When distancing the source of radiation and the sensor from the skin surface, the method becomes a non-contact PPG. For recording of radiation the sensor of video camera with lens can be used. The image of skin surface is focused on the sensor, and the PPG signal is recorded in each skin point. So a two-dimensional distribution of PPG signal from the skin surface is obtained. This technique is known as photoplethysmography imaging (PPGI). By the method of PPGI the PPG amplitude, phase, and others hemodynamic parameters can be made. Method can be used for skin tissue blood flow (perfusion) monitoring, which is important in medical examinations.

A sympathetic effect induced by RA causes increase of peripheral blood flow, resulting in increase of PPG signal amplitude in skin until it reaches a certain threshold. The starting point of PPG amplitude increase may be considered as successful effect of the RA. The researcher T.Wung from Aachen (Germany) in 2003 has designed a PPGI pilot device for monitoring of skin perfusion [T. Wu. PPGI: New Developments in Noninvasive and Contactless Diagnosis of Dermal Perfusion Using Near InfraRed Light. . GCPD e.V., 1 (1): p. 17-24, 2003]. The device consists of an infrared LED source and video camera. The radiation caused by LED after penetration into the skin in depth of several mm, was received by a video camera having a filter penetrating infrared radiation put in front of it. The video camera was connected to a computer, and was operated using a controller, which ensured the operation of video camera in real-time, as well as a display of video material on the screen of monitor. At the same time it was possible to change the size of the image area of interest and coordinates, i.e. the location of the PPG virtual sensor on the skin surface, as well as the frame rate. At the end of the measurement, a computer program made a variety of image processing calculations, such as motion compensation, median filtering and image segmentation.

Researchers from the Louisville (USA) in 2006 developed a new method for arterial pulse acquisition from thermal video signal [S.Y. Chekmenev, A.A. Farag and E.A. Essock. Multiresolution Approach for Non-Contact Measurements of Arterial Pulse using Thermal Imaging. Proc. 2006 Conf. on Computer Vision and Pattern Recognition, p.129, 2006]. Skin surface temperature distribution can be determined using the thermal image. Due to blood pressure pulsation the thermal image of the skin periodically pulsates in places where the arteries are located. If enough exactly paces on arteries are selected, where the pulse is strong enough, the signal of good quality can be obtained. Automatic selection of such areas of interest can be a serious problem, therefore it is performed manually. The study monitored the human face and neck. First the area was selected, where the thermal signal is of sufficiently large amplitude. It may be a region of temple or neck. Then a special algorithm separates the areas of interest in images of different resolution and performs a deeper analysis.

Other researchers succeed in recording PPG signal using ambient light and a conventional video camera with standard resolution (SD) [W. Verkruysse, L.O. Svaasand, J.S. Nelson. Remote plethysmographic imaging using ambient light. Opt. Express, 16 (26): p. 21434-21445, 2008]. The researchers found that exactly the green light component in visible light contains a significant part of the PPG signal associated with blood haemoglobin absorption peak in this spectral range. Filming was performed of few minutes, with a frame frequency of 15 or 30 frames per second, and with pixels image resolution 320x240 or 640x480. Each frame was divided into 50x40 pixel areas. PPG amplitude imaging in green RGB spectrum of healthy face skin was performed. Measurements were made for pathological skin with "wine stain" syndrome before and after laser treatment. When Fourier analysis of PPG signal was performed, the researchers found that there a phase shift exists between PPG signals of healthy and pathological skin.

Disclosure of the Invention

The objective of the invention is to create a new non-invasive and contactless device, by means of which it is possible to quantify the success and failure of RA and exclude the subjectivity in determination of RA.

According to the present invention the skin surface being anaesthetized is illuminated by visible or near infrared spectral range of radiation, which being reflected from the skin surface is registered with the light-sensitive sensor-matrix. Due to heart functioning blood volume under the skin periodically changes; as a result the radiation in the subcutaneous tissue is modulated. By identifying digital values of the intensities recorded in each image pixel in predefined skin area, the average (median) value of intensity in each frame is calculated. Then the PPG signal is distributed, corresponding to the changes of intensity in cardiac frequency range, the signal amplitude for each cardiac cycle is calculated, and the changes of the signal amplitude is calculated. Every minute the average (median) value of PPG amplitude and the value of standard deviation in minute interval is calculated. As moment of statistically significant occurrence of anaesthesia is considered the time, at which the amplitude of the PPG in the standard deviation interval STD2 exceeds the amplitude at the moment of the measurement inception in the standard deviation interval STDl (Fig. 2). When statistically significant effect of anaesthesia starts, measuring can be interrupted, and without unnecessary waiting surgery manipulations can be started.

The invention creates non-invasive and contactless possibility for using the peripheral circulatory changes in the upper limb after Plexus brachialis regional block, being detected by the contactless PPG signal obtained from the reflected light during video recording in order to detect success or failure of RA. Short Description of Drawings

Fig. 1 shows the principal scheme of the contactless regional anaesthesia monitoring;

Fig. 2 shows the chart of the recorded PPG signal amplitude and the moment, when its increase was determined, meaning that the regional anaesthetic effect is starting;

Fig. 3 shows the block diagram of the contactless regional anaesthesia monitoring device.

The device for the contactless regional anaesthesia monitoring containing:

- the radiation source 1 , such as operating lamp or LED searchlight, by which the anesthetized skin surface is irradiated (according to different embodiments of the invention the radiation source can be is a white light, a green light, or a near-infrared spectrum radiation source);

- the digital (preferably, monochrome) light-sensitive sensor-matrix 3 (for example, video camera) being provided with a lens, adapted to convert image in digital form by conferring to each pixel certain digital value and store it in the memory unit 4,

- the analysis unit 5 adapted for calculation from video signal the PPG amplitude for each cardiac cycle, and calculation the average (median) value of the signal in predefined time interval;

- the analysis block 6, adapted for recording the effect of anaesthesia from changes of PPG signal amplitude;

- the output device 7, for example, graphic display or numeric indicator, displaying time chart or numerical values of PPG amplitude;

- the control unit 8, which is connected with the light source 1, the light-sensitive sensor- matrix 3 and the analysis unit 5, and is adapted to control their operation.

The device operates as follows: the control unit 8 sends a signal to the radiation source 1 , which irradiates the anesthetized skin surface. Upon receipt a command from the unit 8 the digital light-sensitive sensor 3 makes an image of the irradiated anesthetized skin surface and converts it into digital format, assigning to each pixel certain digital value being stored in the memory unit 4. Upon receipt a command from the block 8 the analysis unit 5 from the video signal calculates PPG amplitude and its average (median) value, and the value of standard deviation in pre-defined time periods (e.g. 1 minute interval). The analysis block 6 registers changes of the signal in the standard deviation interval between these time periods. The anaesthetic effect is defined in case, if the standard deviation of signal does not overlap. PPG amplitude time chart or numerical value is displayed in the output device 7. Measurements were made in the same room (operating room certified according to the ISO2000 standard with controlled air temperature of 23.2 ± 0.8 °C). The measurement reference point is two minutes before the start of the manipulation (after temperature stabilization). The measuring duration took place up to 30 minutes.

Being adequate (successful) anaesthesia is considered, when there was no need to add additional assuagement or fully transfer to another type of anaesthesia, as well as according to traditional clinical criteria: the motor block, the sensory block, the patient's subjective sense of coldness (contact with ice), discomfort or sense of pain after the beginning of surgery manipulations. Being inadequate (failed or semi-successful) anaesthesia is thought, when for the provision of adequate analgesia additional assuagement or fully transfer to another type of anaesthesia was necessary, because of a disproportional increased (the determining) the patient's subjective discomfort.

By the proposed method and the equipment setting in process of the regional anesthesia is easily determined and viewed from a user perspective - uncomplicated. The detection process is objective, independent of the patient's mental and physical condition. There are no restrictions associated with the patients or surgeons subjective opinion. There are no restrictions associated with the time limit or the high costs of the apparatus, while respecting its prevalence and ease of access (practically in almost any workplace, namely the operating room). There is no limit, which is associated with a long and expensive training of staff of the PC and video use.

Claims

1. A device for contactless determination of the effect of regional anaesthesia comprising a white light source (1) adapted for irradiation of the skin surface being anaesthetized, a three-color RGB light-sensitive sensor-matrix (3) adapted for video acquisition, a memory unit (4), adapted for the storage of video images, an analysis unit (5) adapted for calculation of photoplethysmography signal (PPG) amplitude from the green G channel of video in every cardiac cycle, and for calculation of PPG median values in the specified time intervals, an analysis block (6) adapted for determining the effect of anaesthesia according to PPG amplitude changes, an output device (7) designed for displaying time chart or numerical values of PPG amplitude, a control unit (8), which is connected with the light source (1), the light-sensitive sensor-matrix (3) and the analysis unit (5), and adapted to control their operation.

2. The device according to claim 1, wherein the output device (7) is a monitor.

3. The device according to claim 1 or 2, wherein the light source (1) is a green light source and the light-sensitive sensor- matrix (3) is a monochrome light-sensitive sensor-matrix.

4. The device according to claim 1 or 2, wherein the light source (1) is a near-infrared spectrum radiation source and the light-sensitive sensor- matrix (3) is a monochrome light-sensitive sensor-matrix.