WO2011057283A1

WO2011057283A1 - Expandable cannula for infusion of fluids

Info

Publication number: WO2011057283A1
Application number: PCT/US2010/056060
Authority: WO
Inventors: Amy Lee Hammack; Stanley R. Conston; Ronald K. Yamamoto
Original assignee: Iscience Interventional Corporation
Priority date: 2009-11-09
Filing date: 2010-11-09
Publication date: 2011-05-12

Abstract

An apparatus is provided comprising a cannula having a proximal end accommodating a fluid connector, a distal end, and a lumen for fluid flow between the proximal connector and the distal end; wherein the distal end comprises a segment having a convertible configuration, the configuration convertible from a low profile for entry into the posterior chamber of an eye to an expanded profile for use within the eye providing an increase in flow rate of fluids through the cannula relative to the flow rate of fluids through the cannula with the segment in the low profile.

Description

EXPANDABLE CANNULA FOR INFUSION OF FLUIDS

RELATED APPLICATION

Priority is claimed pursuant to 35 USC 119(e)(1) of U.S. provisional patent application Serial No. 61/259,503, filed November 9, 2009, which is incorporated by reference herein for all purposes in its entirety.

BACKGROUND OF INVENTION

A retinal detachment is a sight-threatening condition of the eye that may occur due to trauma or to disease processes. A rhegmatogenous retinal detachment is associated with a break in the retina that allows vitreous fluid to enter the sub-retinal space to cause the retina to separate from the retinal pigment epithelium. There are also forms of retinal detachment that are caused without a retinal break, due to the accumulation of sub-retinal fluid. For all cases of retinal detachment, rapid treatment is crucial to regain vision before the detached retina is permanently compromised.

Retinal detachments are treated by several methods. Key to success is relieving vitreous tractional forces on the retina, re-apposition of the retina to the underlying pigment epithelium, closure of any retinal breaks and removal of sub-retinal fluid.

The retina is typically re-apposed by the use of endotamponade agents. A variety of fluids or gases are introduced into the posterior chamber to exert forces to flatten the retina. Different agents are used depending on the location and size of the retinal detachments. The agents may be gases to exert a buoyancy force, heavier than water fluids to exert downward force, or a silicone fluid to provide a combination of a buoyancy force and surface tension to seal a retinal break.

Silicone fluids, often called silicone oil, are used in a variety of viscosities ranging from 1000 cs to 12,500 cs. These fluids are much more viscous than water and may present some difficulty to infuse into the posterior chamber. Modern vitreoretinal surgery utilizes small incisions or sclerotomy ports to access the posterior segment for surgery to minimize trauma. High viscosity fluids are more difficult to infuse through small tubing as characterized by the Poiseuille equation for flow through a cylindrical pipe. Volumetric Flow Rate = Q = Δ ΡΓ⁴ /ηΙ_ ; ΔΡ = pressure drop across pipe

; r = radius of pipe

; η = viscosity of fluid

; L = length of pipe

Due to the difficulties in handling high viscosity silicone oil, often a powered viscous fluid injector is used to apply pneumatic pressure to a silicone oil syringe to facilitate infusion into the eye.

The invention relates to a design of a cannula with expansive properties to transfer silicone oil or other high viscosity fluid, designed with novel characteristics to maximize the flow rate while allowing insertion through a small incision or sclerotomy port into the posterior chamber of an eye

SUMMARY

An apparatus is provided comprising a cannula having a proximal end accommodating a fluid connector, a distal end, and a lumen for fluid flow between the proximal connector and the distal end; wherein the distal end comprises a segment having a convertible configuration, the configuration convertible from a low profile for entry into the posterior chamber of an eye to an expanded profile for use within the eye providing an increase in flow rate of fluids through the cannula relative to the flow rate of fluids through the cannula with the segment in the low profile. In some embodiments the configuration may be convertible from the low profile to the expanded profile by infusion of fluid from the proximal end. In some embodiments the configuration may be convertible from the low profile to the expanded profile by mechanical activation. The activation may be provided by removal of a mechanical restraining element retaining the distal end in the low profile, whereby the distal end converts to the expanded profile.

In one embodiment the convertible segment of the distal end comprises a plurality of longitudinal slits in the low profile convertible to splayed elements in the expanded profile.

In another embodiment the convertible segment of the distal end comprises an expandable helical ribbon. In another embodiment the convertible segment of the distal end comprises folded pleats in the low profile convertible to expanded pleats in the expanded profile.

For adaptation for insertion into the posterior chamber of an eye the outer diameter in the low profile of the cannula according to the invention is usefully no larger than about 0.036 inches (0.91 mm) (20 gauge). The outer diameter in the low profile of the cannula is typically no larger than about 0.026 inches (0.66 mm) (23 gauge). An outer diameter in the low profile of the cannula no larger than about 0.021 inches (0.53 mm) (25 gauge) is useful.

The length of the cannula is usefully in a range from about 0.079 to 1.18 inches (2 to 30 mm).

BRIEF DESCRIPTION OF THE FIGURES:

1. Figure 1 - Cannula placed into posterior chamber of an eye 2. Figure 2 - Cannula with splayed element distal end prior to deployment

3. Figure 3 - Cannula with splayed element distal end deployed into expanded configuration

4. Figure 4 - Cannula with helical ribbon distal end prior to deployment

5. Figure 5 - Cannula with helical ribbon distal end deployed into expanded configuration

6. Figure 6 - Cannula with folded or pleated distal end prior to deployment

7. Figure 7 - Cannula with folded or pleated distal end deployed into expanded configuration

DESCRIPTION OF PREFERRED EMBODIMENTS: The present invention is directed at a cannula for transfer of fluids, especially viscous fluids, to and from the posterior chamber of an eye 10. The cannula 11 is adapted for placement through the sclera into the posterior chamber at the pars plana region, either directly through a small incision or through a sclerotomy port. See FIG. 1. The proximal end may accommodate a connector such as a Luer connector for attachment of the cannula is positioned within the posterior chamber.

Once inserted into an eye, the distal end of the cannula may be deployed into an expanded configuration with an increased effective radius of the flow path as compared to the proximal portion of the cannula, to decrease flow resistance and/or increase flow rate. The deployment may be accomplished by an active mechanical expansion or by a shape change caused by the flow of fluid through the cannula. In the case of deployment by active mechanism not maintained by the flow of fluid through the cannula, the cannula also has the advantage an increased flow rate and decreased flow resistance to fluids for aspiration of fluids from the eye.

The present invention may utilize several configurations to provide an expanded fluid flow pathway. One embodiment comprises a cannula 11 with a distal tip 12 comprising longitudinal slits 13 at the distal end to form a conical, splayed distal end under fluid flow, such as shown in FIGs. 2 and 3. The slits allow the distal end to flex and form outwardly splayed elements 14 under fluid pressure during infusion from the proximal end. The resultant conical shape provides for an effectively larger radius of the flow path to increase flow rate. From the Poiseuille equation, an increase in radius of 20% results in a doubling of flow rate. This is especially beneficial when attempting to infuse viscous fluids through a small cannula. According to the invention the viscosity and surface tension of an infused fluid was surprisingly found to limit the flow of the liquid through the slits such that a steady stream of infusion fluid was provided with minimal generation of separate droplets that may contribute to poor visualization of the retina through the fluid in the posterior chamber. The thickness of the individual splayed elements 14 may be varied along the length to tailor the resultant deployed shape. The splayed elements may be set into the splayed configuration and retained together in a low profile configuration during insertion by a mechanical clip (not shown). Upon insertion into the eye, the clip may be removed and the cannula deployed into the expanded configuration. Alternatively, the splayed elements may be configured into a low profile configuration for insertion and the internal pressure during fluid infusion used to deploy the distal tip into the splayed configuration. In another embodiment, the splay tip may be pre-configured in an open position and then manually compressed for insertion into the eye. The gap 16 between the splayed elements may also be varied along the length to tailor the geometry of the deployed configuration. For example, the gap may be progressively increased along the length toward the distal tip to allow greater deflection and flow of fluid through the gap as the fluid flows through the cannula lumen.

The number and placement of the longitudinal slits may be varied, typically from one (1) to four (4) slits arranged evenly around the circumference of the distal shaft. The length of the longitudinal slits in the direction of the shaft axis may be varied. Slits of different lengths may be incorporated, for example in a four slit configuration, two of the slits may be longer than the other two, with the same length slits arranged 180° apart from each other. In another embodiment, the slits may progress from short to long around the circumference, for example in a "stair step" pattern.

Another embodiment of the invention would comprise a helical ribbon to form the distal end of the cannula. The ribbon 17A may be preset into an expanded configuration, such as shown in FIG. 5, and constrained mechanically during insertion into an eye, and released to deploy in-situ. Alternatively, the ribbon 17B may be formed in the low profile configuration approximating a tube, such as shown in FIG. 4, and allowing the internal fluid pressure during infusion to deploy the distal end into the expanded configuration. The wall thickness of the ribbon may be varied to tailor the expanded configuration.

Another embodiment of the invention may comprise an expanded distal end 18A with a lumen radius larger than the proximal portion but folded or pleated to allow a low profile configuration 18B prior to deployment in-situ. See FIGs. 6 and 7.

The distal end of the cannula may also be surface treated to tailor the interfacial surface tension between the fluid and the cannula material. For example the material may be treated with a silane to increase hydrophobicity and decrease surface tension during infusion of a hydrophobic fluid such as silicone oil. The gaps of the expanded distal end may be treated with a hydrophilic coating to increase the interfacial surface tension to limit transport of the fluid through the gaps. The cannula distal shaft may be sized to fit appropriately in standard sclerostomy ports which are commonly sized at 20, 23 and 25 gauge. The shaft is sized to maximize the flow path diameter and the design preferably incorporates thin walled tubing, for example polyimide tubing with a wall thickness in the range of 0.0005 to 0.001 inches (12.7 to 25.4 microns). For 20 gauge ports, the shaft is preferably in the range of 0.034 to 0.036 inches (0.86 to 0.91 mm) in outer diameter; for 23 gauge ports, the shaft is preferably in the range of 0.023 to 0.026 inches (0.58 to 0.66 mm) in outer diameter; and for 25 gauge ports the shaft is preferably in the range of 0.018 to 0.021 inches (0.46 to 0.53 mm) in outer diameter.

The length of the shaft is preferably in the range of 0.079 to 1.18 inches (2 to 30 mm) encompassing the minimum length to penetrate through the pars plana and into the vitreous cavity up to the maximum length to approach in close approximation to the posterior pole of the eye.

EXAMPLES:

Example 1

Devices according to the invention were fabricated and tested. The 23 gauge devices were comprised of a 0.39 inch (10 mm) length of polyimide tubing with a 0.001 inch (25 micron) wall thickness and 0.020 inches (500 microns) inner diameter, as the main shaft. The main shaft proximal end was inserted into a Luer fitting to a depth of 0.078 inches (2 mm) resulting in a shaft length of 0.31 inches (8 mm). UV cure cyanoacrylate adhesive was used to bond the main shaft to the Luer. Three different tip configurations were made. The distal end of the polyimide main shafts were longitudinally slit in four places, 90° apart, to lengths of 0.079 inches (2 mm), 0.157 inches (4 mm), and 0.236 inches (6 mm) creating a splay tip.

The assembled devices were attached to a 1 ml syringe filled with 5000 cP silicone fluid and vertically mounted into a fixture with the device tip positioned downward 5 mm above a reservoir filled with 5000 cP silicone fluid. A weight was applied to the syringe plunger to generate a force equivalent to 70 PSI and then released. The silicone fluid contained within the syringe was expelled out of the tip of the device and into the reservoir. The expansion of splayed tip was observed as the pressurized silicone fluid was forced through the device. The flow rate was measured as the amount of time required to expel 1 ml of silicone oil and is shown in Table 1. Table 1: Flow rates versus slit length, 23 Gauge

Example 2

A device according to the invention was fabricated and tested. The 25 gauge device was comprised of a 0.31 inch (8 mm) long polyimide tube with a 0.018 inch (457 microns) inner diameter with a 0.001 inch (25 micron) wall, and was assembled as described in Example 1. A helical cut 0.16 inches (4 mm) long was made into the distal end of the main shaft.

The device was attached to a 1 ml syringe with silicone fluid and placed in the fixture as described in Example 1. The 70 PSI force equivalent weight was applied. Expansion of the helical tip was observed as the pressurized silicone fluid was expelled from the device tip. The fluid flow rate through the device was measured at 1.4 ml/min.

Example 3

A device according to the invention was fabricated and tested. The device was assembled using thin wall 25 gauge polyimide tubing main shaft as described in Example 2 and a polycarbonate Luer fitting. The main shaft length was 6 mm. The main shaft was bonded to the Luer using UV cure acrylic adhesive. The distal end of the assembly was cut into 4 equal longitudinal slits at 0.138 inches (3.5 mm) length and the device was then autoclaved. A second device was fabricated without the slits to compare flow rate results.

The devices were attached to a 20 ml vitrectomy system syringe filled with 1 ml of 5000 cP silicone fluid. The vitrectomy system was set up for infusion mode, the infusion pressure was set to 70 PSI and the silicone fluid flow rates were measured for both designs and are shown in Table 2. Table 2 Comparison of Flow Rates, 25 Gauge

Claims

Claims:

1. An apparatus comprising a cannula having: a proximal end accommodating a fluid connector, a distal end, and a lumen for fluid flow between the proximal connector and the distal end, wherein the distal end comprises a segment having a convertible configuration, said configuration convertible from a low profile for entry into the posterior chamber of an eye to an expanded profile for use within the eye providing a decrease in flow resistance of fluids through said cannula relative to the flow resistance of fluids through said cannula with said segment in said low profile.

2. The apparatus according to Claim 1 wherein said configuration is convertible from the low profile to the expanded profile by infusion of fluid from said proximal end.

3. The apparatus according to Claim 1 wherein said configuration is convertible from the low profile to the expanded profile by mechanical activation.

4. The apparatus according to Claim 3 where in said activation is provided by removal of a mechanical restraining element retaining said distal end in said low profile, whereby said distal end converts to the expanded profile.

5. The apparatus according to any one of Claims 1 to 4 wherein the distal end comprises a plurality of longitudinal slits in the low profile convertible to splayed elements in the expanded profile.

6. The apparatus according to any one of Claims 1 to 4 wherein the distal end comprises an expandable helical ribbon.

7. The apparatus according to any one of Claims 1 to 4 wherein the distal end comprises folded pleats in the low profile convertible to expanded pleats in the expanded profile.

8. The apparatus according to Claim 1 wherein the outer diameter in the low profile of the cannula is no larger than about 0.036 inches (0.91 mm) (20 gauge).

9. The apparatus according to Claim 8 wherein the outer diameter in the low profile of the cannula is no larger than about 0.026 inches (0.66 mm) (23 gauge).

10. The apparatus according to Claim 9 wherein the outer diameter in the low profile of the cannula is no larger than about 0.021 inches (0.53 mm) (25 gauge).

11. The apparatus according to Claim 1 wherein the length of the cannula is in a range from about 0.079 to 1.18 inches (2 to 30 mm).