WO2000012003A1

WO2000012003A1 - Air coupled pressure tip cannula for by-pass surgery

Info

Publication number: WO2000012003A1
Application number: PCT/US1999/019398
Authority: WO
Inventors: James E. Cole
Original assignee: Becton, Dickinson And Company
Priority date: 1998-08-26
Filing date: 1999-08-25
Publication date: 2000-03-09
Also published as: AU5691099A

Abstract

A cannula that is usable to remove blood from the heart during bypass surgery on a patient where the cannula has a flexible bladder located at or adjacent the location within the heart where the blood is being removed. The flexible bladder forms a closed chamber that communicates through a closed system to a pressure transducer external of the patient such that the pressure within the flexible bladder can be continuously monitored. By monitoring the pressure within the bladder, the user can insure that the pressure within the chamber of the heart does not become negative and thus harmful to the patient. The flexible bladder is partially filled with air and is sufficiently flexible and pliant so as to not be affected by the touching of the inner wall of the heart chamber.

Description

AIR COUPLED PRESSURE TIP CANNULA FOR BY-PASS SURGERY

Background

This invention relates to a special cannula that is usable during heart by-pass surgery and where the cannula is capable of being employed to remove blood directly from the heart while at the same time, provide a device to continuously monitor the pressure within the heart during that blood removal.

In carrying out various procedures that require a heart bypass operation, blood is removed directly from the patient's heart and to do so, a cannula is introduced into the left side of the heart i.e. from the left ventricle or atrium where the blood is pumped away and then reintroduced into the heart through the right side of the heart. The blood is pumped from the heart by means of a special pump, one of which is the Jarvik heart pump and which pulls the blood from the left heart and replaces the blood back into the right heart. A cannula is therefore placed with its distal end into the particular chamber of the patient's heart and which sucks the blood from that chamber. The cannula is generally a very large device to be capable of relatively large flows of blood and, as an example, can be ofthe size of 24 or 28 French. Since the cannula is directly introduced into the heart to withdraw the blood, it is obviously of extreme importance that the pressure in the heart chamber not become negative, that is, where the heart chamber could collapse from the over-removal of the blood. The danger is that the blood will be removed at such a high rate of flow that the heart itself will be sucked dry. Accordingly, in heart bypass procedures, a pressure transducer is used to maintain an internal constant monitor of the pressure of the blood within the heart chamber as it is being removed. As such, therefore, the pressure transducer can even, if desired, have control of the pump and slow down the pump in the event the pressure within the heart chamber is reduced to a predetermined pressure, approaching a negative value, and which assures that the negative pressure is not reached within the heart.

In current devices, a liquid filled coiumn is used and which is introduced into the heart adjacent the location of the distal end of the cannula that is removing the blood. There are, however, several drawbacks to the use of a liquid filled column in determining the pressure of the blood in the heart chamber. As one difficulty, the tip of the liquid filled catheter or tube containing the liquid can become occluded if it presses against the inner heart wall and therefore will not read the correct pressure in the heart. In addition, the transducer that is attached to the catheter or tube and which is external of the patient, must be positioned at the heart level at all times.

Since the pressures being measured are so low in the heart, the error that will be caused by not having the transducer at the exact level can be critical, that is, a difference of one inch in position of the transducer below the level of the heart will indicate 2 mmHg. higher than the actual pressure and such a difference is considerable when taking into account that the pressures measured in the heart may approach 0 mmHg. and, as stated, it its critical that the pressure remain positive.

One type of pressure sensing instrument that has been proposed for the monitoring of a patient blood pressure has been the use of a flaccid balloon that extends outwardly from the distal end of a cannula. The balloon is thus introduced into the patient to position that flaccid balloon in the patient at a position within the patient where the blood pressure is desired to be monitored. As a feature of that system, the flaccid balloon, located at the end of the cannula, communicates with a pressure transducer located external of the patient by means of small passageways that are filled with air, thus forming an air column from the balloon to the pressure transducer. Therefore, that air column communicates the pressure within the flaccid balloon to a pressure transducer located exterior of the patient. By the air column, rather than a liquid column, the pressure in the patient's blood vessel is communicated from the interior of the balloon, along the minute lumen and thus to the external transducer where the blood pressure is communicated to the user. In such uses, however, the balloon has been extended distally of a dedicated cannula or tube and the uses involved blood pressure at relative high positive values.

Summary of the Invention

The present invention comprises the use a continuous pressure monitor where an air filled column approach is used in combination with the cannula that is directly placed within the left heart to withdraw blood from the heart. The cannula has a main channel that draws the blood from the particular heart chamber through its distal end and which transmits that blood to the proximal end where it is drawn by the heart pump and re-circulated back to the right side of the heart. At the distal end there is provided a resilient, pliant bladder that forms a closed chamber surrounding the distal end and which is positioned within the particular chamber from which the blood is being withdrawn. The closed chamber within the bladder is thus partially filled with a predetermined volume of gas, preferably air, and that closed chamber is air coupled to a pressure transducer that is located external of the patient. The air coupling may be through a lumen formed within the cannula itself and which, in turn, communicates with a minute tubing external of the patient for connection to the pressure transducer. The cannula provides a continuous monitoring of the pressure within the heart chamber to insure that such pressure does not become negative. The predetermined volume of air in the system is precise to insure that a reading can be take at 0 mm Hg and therefor the bladder forming the closed chamber is not totally inflated. The bladder itself is made of an extremely compliant material so that the touching of the inner wall of the heart will not affect the reading of the pressure within the heart by sending a false signal to the pressure transducer.

In the cannula, therefore, the partially inflated bladder, in use, is located at or near the distal end of the cannula so that it indicates the pressure of the blood within the chamber of the heart from which the blood is being pumped so that it can read the critical and needed pressures.

The above and other advantages and features of the present invention will be apparent in the following detailed description of the preferred embodiment when read in conjunction with the appended drawings wherein the same reference numerals denote the same or similar parts throughout the several views.

Brief Description of the Drawings

FIG. 1 is a sectional view, partly schematic, of a cannula constructed in accordance with the present invention ;

FIG. 2 is an end view of the cannula of FIG. 1; and

FIG. 2 is an enlarged elevational view of a flexible bladder usable with the cannula of FIG. 1.

Detailed Description of the Invention

Referring now to FIG. 1 , there is shown a sectional view of a cannula 10 constructed in accordance with the present invention. As can be seen, the cannula

10 comprises a length of flexible tubing 12 having a central bore 14 that extends from the distal end 16 through to the proximal end 18. As used herein, the distal end 16 shall refer to the end of the cannula 10 that is intended to be inserted into the heart of the patient to remove blood therefrom and the proximal end 18 shall refer to the end of the cannula 10 that remains external of the patient and which is adapted to be connected to the pump (not shown) that draws the blood through the cannula 10 from the heart.

Typically, cannula 10 is comprised of a plastic material of a nature that is of sufficiently flexible so as to be relatively maneuverable as it is positioned by the user in the desired location withdrawing blood from the heart, such as the left ventricle or atrium. Although various size cannulas can be used, it is preferred in the use of the cannula for bypass surgery that the cannula be in the range of a 24 French to about

34 French so that the central bore 14 is sufficiently large to remove the flow of blood from the heart needed to divert flow otherwise passing through the heart during a bypass operation.

At the distal end 16 of the cannula 10 there is formed a cannula tip 20 that, as explained, is actually placed in the particular chamber of the patient's heart to withdraw the blood. In normal bypass surgery, that chamber would be the left ventricle or the atrium and the blood returned through the right heart chamber. As shown, the cannula tip 20 includes a plurality of slots 22 (see also FIG. 2) that allow the suctioning of the blood from the heart chamber and, a further opening 24 may be formed in the cannula tip 20 so that the blood enters the cannula tip 20 and proceeds through the central bore 14 to the proximal end 18 where some connection is provided to direct the blood to the heart pump for re-circulation back to the heart.

At or adjacent to the distal end 16, there is positioned a flexible bladder 26 and, as shown, that flexible bladder 26 surrounds the outer periphery of the cannula 10 forming a closed chamber 28 between the flexible bladder 26 and the outer surface of the cannula 10. The flexible bladder 26 is better shown in the enlarged elevational view of FIG. 3, taken along with FIG. 1 , and the flexible bladder 26 is preferably formed of a material that is biocompatable with the blood system, such as polyvinyl chloride, silicone rubber or urethane. The flexible bladder is preferable of a thickness of between about .004 to .010 inches in thickness with a nominal thickness of about .005 inches. As can be seen in FIG. 3, the center portion 30 of flexible bladder 26 is formed in an outwardly bowed configuration and the ends 32 and 34 may be of a predetermined internal circular diameter so as to be sealed to the outer peripheral surface of the cannula 10. The means of securing the flexible bladder 26 to the peripheral surface of the cannula 10 may be by an adhesive or other means such as ultrasonic bonding and which completely seals the ends 32 and 34 of the flexible bladder 26 to the cannula 10 to assure that the closed chamber 28 is not subject to leaking.

A lumen 36 is preferable formed in the wall of the flexible tubing 12 and communicates with the interior of the closed chamber 28. Lumen 36 can be formed during the extrusion process and run the entire length of the flexible tubing 12. At its distal end 38, lumen 36 communicates with the interior of the closed chamber 28 and at its proximal end 40, the lumen 36 connects to, and communicates with, a tubing 42 that extends to and terminates in a fitting such as a female Luer fitting 44 as shown. It will be understood that the female Luer fitting 44 is one of many fitting that can be used and, in the present embodiment, the female Luer fitting 44 connects to a pressure transducer 46, shown schematically, so that the pressure within the closed chamber 28 can be continuously monitored and which is, of course, indicative of the pressure within the chamber of the heart from which the blood is being withdrawn. Accordingly, that pressure can be monitored to make sure the pressure does not go negative and disrupt the system and, as a feature, the pressure transducer 46 can be used to control the speed of the pump that is withdrawing the blood from the heart. A three way stopcock 48 is also provided between the female Luer fitting 44 and the input to the pressure transducer 46 and preferable is mounted on or just adjacent to the pressure transducer 46. IN the position as shown in Figure 1, the three way stopcock 48 allows communication between the air contained within the closed chamber 28 and the pressure transducer 46. As is conventional, the three way stopcock can be moved to its other position, not shown, by a counterclockwise rotation of ninety degrees, so that the closed chamber 28 is vented through the three way stopcock 48 to the atmosphere via a side port and communication with the pressure transducer 46 is blocked. The three way stopcock is a standard device and its purpose later explained.

The pressure transducer can be a commercially available transducer and one of which may be the Model DTX-TNF, or the Model RTX, both of which are commercially available from Becton and Dickinson Company. Other commercial transducers are usable with the present system providing their specifications meet the criteria that the zero shift due to temperature changes be at or better then 0.1 mmHg/degree O, that is , they have a zero shift for temperature changes of one degree Centigrade of 0.1 mmHg. The strict temperature zero shift is necessary to maintain the accuracy of the overall system at the pressures experienced within the heart.

It is important, in using the present invention with a bypass surgical procedure, to provide a sensitive pressure signal where the pressure is about 0 mmHg. since that is the pressure where the system is approaching the negative value in the heart. As such, therefore, the amount of air that is sealed within the air column that includes the lumen 36 and the closed chamber 28 must be partially inflated with a predetermined volume of air but not totally inflated. Since the flexible bladder 26 is of a very resilient, flexible material, the pressure can be accurately monitored at or near 0 mmHg. even when the flexible bladder 26 presses against the inner wall of the heart chamber.

That volume of air contained within the system during its use is determined easily during the attachment of the cannula 10 to the transducer 46 having the three way stopcock 48 attached to the pressure transducer 46. During that attachment, the stopcock 48 is positioned such that the line to the pressure transducer 46 is blocked and the line from the cannula 10 is vented to the atmosphere through the side port. At this point, the cannula 10 can be fluidly connected to the pressure transducer 46 without a build up of pressure in the system since the cannula 10 is being vented. Once the cannula 10 is connected to the pressure transducer 46, the flexible bladder 26 on the cannula 10 is flattened on one side, thereby forcing air out of the overall system via the side port of the three way stopcock 48. While the flexible bladder 26 is thus flattened on one side, the three way stopcock 48 is moved to its other position such that the cannula 10 communicates with the pressure transducer 46 and the side port is closed, thereby creating a closed system between the cannula 10 and the pressure transducer 46 having a predetermined volume of air entrapped within the system to allow the flexible bladder 26 to be relatively pliant and not be affected by contact with the inner walls of the heart.

As such, if the flexible bladder 26 were to be positioned directly against the inner wall of the heart, it is still of sufficient flexibility as to not be affected by that contact but still provide a reliable signal via the air column to the pressure transducer 46. In the preferred embodiment, the overall fully inflated volume of the flexible bladder is about .22 cc. and the bladder is deflated about .03 cc. Therefore the volume is reduced from the fully inflated condition to the usable condition of about 15 percent. It has been found that the reduction in volume can be in the range of about 10 to 20 percent reduction and the flexible bladder has sufficient flexibility so as to function properly even when in contact with one of the inner walls of he heart. Accordingly while the preferred reduction in volume is about 15 percent, the flexible bladder 26 can be operable within the aforementioned range.

While the above presents a working embodiment of the invention, there are others which will be obvious to those skilled in the art. The invention is not limited to the embodiments specifically described but is to be inteφreted only in conjunction with the scope of the appended claim and their functional equivalents.

Claims

CLAIMSclaim:

1. A cannula for introduction into a patient's heart for removing blood therefrom, said cannula having a proximal end that remains outside the patient and a distal end that is inserted into the heart for removing the blood, said cannula having a bore therethrough for movement of the blood during the withdrawal thereof from the heart, a closed chamber formed on the distal end of said cannula and adjacent the distal end thereof, said closed chamber comprising a flexible bladder that expands and contracts in accordance with the pressure of the blood surrounding said chamber, a lumen communicating the pressure in said closed chamber to a point external of said patient, a pressure transducer communicating with said lumen and adapted to monitor the pressure within said lumen and said closed chamber and provide an signal indicative of that pressure, said closed chamber containing a predetermined volume of a gas such that said closed chamber can both expand and contract as said pressure of the blood increases and decreases within the heart.

2. A cannula for introduction into a patient's heart as defined in Claim 1 wherein said closed chamber contains air.

3. A cannula for introduction into a patient's heart as defined in Claim 1 wherein said flexible bladder is formed in the shape of an annulus surrounding said cannula at said distal end of said cannula.

4. A cannula for introduction into a patient's heart as defined in Claim 3 wherein said flexible bladder is comprised of a biocompatable material and has a thickness of between about .004 and .010 inches.

5. A cannula for introduction into a patient's heart for removing blood therefrom, said cannula having a proximal end that remains outside the patient and a distal end that is inserted into the heart for removing the blood, said cannula having a bore therethrough for movement of the blood during the withdrawal thereof from the heart, a sealed flexible bladder forming a closed chamber adjacent the distal end thereof, said sealed, flexible bladder containing a predetermined volume of air to enable said flexible bladder to expand and contract in accordance with the pressure of the blood surrounding said flexible bladder, and a pressure transducer adapted to continuously monitor the pressure within said flexible bladder while within the patient's heart.

6. A cannula for introduction into a patient's heart as defined in Claim 5 wherein said pressure transducer has a maximum allowed zero shift due to changes in temperature.

7. A cannula for introduction into a patient's heart as defined in Claim 6 wherein said zero shift of said pressure transducer is no more that about 0.1 mmHg./degree Centigrade.

8. A cannula for introduction into a patient's heart as defined in Claim 5 wherein said flexible bladder has a thickness of between about .004 and .010 inches.

9. A cannula for introduction into a patient's heart as defined in Claim 5 wherein said flexible bladder has a fully inflated volume and said volume of said flexible bladder during use is reduced from said fully inflated volume by between about 10 to 20 percent.

10. A cannula for introduction into a patient's heart as defined-in Claim 9 wherein said volume in said flexible bladder is about 85 percent of its fully inflated volume.