Blood chamber

Abstract

A blood chamber for an arterial line of an extracorporeal blood system. The chamber is a flow through device for blood with an air cushion over the blood and access structure for sampling and treating the blood. A pressure tap in the chamber communicates the air cushion with a pressure transducer to facilitate measurement of blood pressure within the chamber. Undesirable obstruction of the pressure tap by blood foam is reduced by introducing blood into the chamber through a submerged inlet. The blood chamber may be situated upstream from a blood pump in a single needle extracorporeal dialysis system so as to avoid pump starvation.

Description

BACKGROUND

1. Field of the Invention

The present invention relates to method and apparatus for providing access to and controlling the flow of blood in an extracorporeal blood handling system.

2. The Prior Art

In extracorporeal blood handling systems, blood access has historically taken place in the venous line, the venous line being defined as the extracorporeal blood line which returns blood from a treatment device to the patient. Blood access, whether for pressure measurement, sampling or treatment, is more difficult in the arterial line due to the greater pressures and pressure fluctuations therein. The arterial line is defined as the extracorporeal blood line carrying blood away from the body to a treatment device.

However, blood pressure measurement in an arterial blood line, for example, in certain methods of hemodialysis, is important because pressure measurements have been found necessary to control extracorporeal systems of the single needle type.

Pressure measurement of blood usually entails some form of pressure transferring medium such as a gas (air, for example) or a flexible diaphragm. Direct blood contact by a pressure transducer may be used but often introduces sepsis and is susceptible of fouling. A flexible diaphragm prevents direct blood contact between the blood and the pressure transducer; however, similar problems are encountered when using the flexible diaphragm. An example of a diaphragm type sensor is found in U.S. Pat. No. 3,713,341. Air, as a pressure transmitting medium, permits placement of the pressure transducer at a convenient distance from the blood chamber and easily accommodates asepsis. However, air over the surface of the blood often tends to increase the incidence of foam formation which conventionally has been carried into the pressure transmitting air line where it interferes with the pressure sensing system. This is particularly true where the blood is subjected to negative pressures.

Other prior art devices such as disclosed in U.S. Pat. Nos. 3,690,312 and 3,157,201 employ manifolds wherein a plurality of access ports are provided to the blood. These devices are limited in that they are not directly interposed in an extracorporeal bloodstream but merely provide access thereto. Blood stagnation and clotting in such devices would, conceivably, become extreme during long term usage.

In single needle dialysis, pump starvation has been found to be a serious problem. Pump starvation is defined as the condition that exists when the availability of blood upstream from the pump is less than the delivery capacity of the pump. Historically, pump starvation in single needle dialysis systems results when the supply of blood from the patient to an operating pump is not adequate. The action of the pump causes a negative pressure upstream which tends to collapse the extracorporeal blood lines and even more importantly frequently collapses the patient's blood vessel against the indwelling needle or catheter. When the blood vessel collapses against the needle orifice, blood cannot be aspirated from the patient.

It is significant that a collapsed blood vessel frequently cannot be normalized to permit free flow of blood until the pressure within the blood vessel and the extracorporeal blood line is equalized. Since essentially all blood pumps are unidirectional, the blood pressure usually cannot be normalized with at least partial disassembly of the extracorporeal blood handling system.

The foregoing problems can be alleviated by providing in the arterial line of the extracorporeal system a blood chamber which permits blood flow through with minimum frothing and at the same time provides a reservoir of blood to avoid pump starvation.

BRIEF SUMMARY AND OBJECTS OF THE INVENTION

The present invention provides a unique apparatus and method for transmitting blood pressure to a measuring device and providing access to the blood in an extracorporeal blood handling system. The apparatus includes a chamber with a gas cushion above the blood. Access to the blood chamber is provided for coupling a pressure transducer to the gas cushion and for sampling, treating, amending, or other such procedures. Foaming of the blood as it passes through the chamber is significantly reduced by introducing the blood into the chamber through a submerged inlet. Blood stagnation and clotting are also significantly reduced by suitably orienting the inlet and outlet ports to provide for limited subsurface turbulence and low residence times for the blood in its passage through the chamber. In one preferred embodiment, pump starvation is avoided by locating the chamber upstream from the pump.

It is, therefore, a primary object of this invention to provide improvements in extracorporeal blood handling systems.

It is another object of this invention to provide improvements in measuring the blood pressure in the arterial line of an extracorporeal blood handling system.

It is a further object of this invention to reduce foaming of blood in a blood chamber having a gas cushion above the blood.

It is an even further object of this invention to provide a plurality of access ports in a blood chamber, giving access to the blood contained therein.

Another desirable object of the present invention is to alleviate pump starvation.

It is one still further object of this invention to provide an improved method for monitoring blood in an extracorporeal blood system.

These and other objects and features of the present invention will become more fully apparent from the following description and appended claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a perspective view of one preferred embodiment of the blood chamber of this invention.

FIG. 2 is a schematic diagram of an extracorporeal hemodialysis blood system with the blood chamber embodiment of FIG. 1 interposed therein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention is best understood by reference to the drawing wherein like parts are designated with like numerals throughout.

The Apparatus

The blood chamber of the present invention serves a multiplicity of purposes, including, for example, blood pressure measurement, a reservoir to avoid pump starvation, blood sampling, blood treatment, and fluids addition to the bloodstream. The foregoing purposes are readily achieved with the blood chamber embodiment of FIG. 1. In addition, the present invention greatly reduces frothing and clotting of the blood in the chamber.

Referring to FIG. 1, a blood chamber 10 is molded as a right cylinder and has a cap 12 sealed thereto. Preferably, chamber 10 is molded from any commercially available medical grade plastic which is sterilizable and blood compatible. Visual observation of blood level 26 and the presence of foam, if any, are also desirable features and, accordingly, chamber 10 is preferably constructed of a transparent plastic.

Sufficient rigidity of chamber 10 to resist flexure permits more accurate pressure readings of the contents of chamber 10. Cap 12 may be opaque but should also resist flexure and has a plurality of nipples 14, 16 and 18 for providing access to the interior of the chamber. Clearly, any suitable number of nipples could be used within the scope of this invention.

A hanger tab 20 with an aperture 22 serves as a hook point for suspending blood chamber 10 from a suitable I.V. stand or the like (not shown). Suspension of chamber 10 by tab 20 also serves to retain chamber 10 in a vertically oriented position.

Nipples 14, 16 and 18 may, for example, serve to receive tubing 15, 17 and 19, respectively, shown in broken lines. Tubing 15, 17 and 19 provide access to the blood, for example, for heparin and saline infusion and pressure monitoring. Numerous combinations are possible and, accordingly, only the foregoing representative example is given.

A blood sample port 34, which is sealed with a rubber cap 36, permits blood samples to be drawn with conventional techniques. The rubber constituting cap 36 is preferably latex or like material which self-seals after penetration. An injection into the blood with a syringe and a hollow needle may also be made by penetrating cap 36 in the manner previously described.

Chamber 10 has, for example, in this preferred embodiment, a total volume of about 30 cc and is adapted to receive a quantity of blood 24 which is less than 30 cc. Accordingly, blood only partially fills chamber 10 and establishes a blood level 26 with an air cushion 28 above.

Blood passes through chamber 10 from an inlet 30 to an outlet 32. Inlet 30 and outlet 32 are interposed serially in an arterial blood line 48 of an extracorporeal blood handling system (FIG. 2). It should be particularly noted that inlet 30 is below blood level 26. This arrangement precludes the high pressure blood entering the chamber 10 at inlet 30 from squirting into the surface 26 thus creating excessive quantities of foam. The foam thus produced tends to intrude into, and even occlude, nipples 14, 16 and 18. Instead, the inlet 30 is submerged and the relatively high pressure blood flow is used to create limited subsurface turbulence in blood 24 to inhibit clot formation and, on occasion, provide mixing when fluids are amended to the blood through adapters 16 and 18 or sample port 34. Outlet 32 is, of course, submerged to prevent air from being carried away from chamber 10. While the illustrated embodiment locates the inlet and outlet normal to the bottom wall of the chamber 10, any suitable orientation of the inlet and outlet which locates the interior orifice below the normal blood level is suitable.

Referring now to FIG. 2, a single needle extracorporeal hemodialysis system is shown schematically and has the blood chamber of FIG. 1 interposed therein, preferably upstream from the pump. With blood chamber 10 located in the arterial line 48 on the low pressure or upstream side of pump 38, a reservoir of blood is continuously available to the pump 38 so as to prevent pump starvation. Of course, if desired, the chamber 10 could be located downstream from the pump 38 to monitor high pressure, if desired.

Arrows on the schematic indicate direction of blood flow and a controller 42 in cooperation with pump 38 controls direction of blood flow through the extracorporeal system and through a blood access cannula 40. Blood is alternately withdrawn from and returned to the patient (not shown) through cannula 40 by controller 42. Controller 42 may be the commercially available unit from Vital Assists, Inc., of Salt Lake City, Utah, and sold under their trademark UNIPUNCTURE.

The blood passes from the patient to the blood chamber 10, thence to pump 38 and thereafter into a dialyzer 44. A conventional venous bubble trap 46 may be interposed in venous line 47. Controller 42 routes the blood back to the patient. Although the single needle hemodialysis system is illustrated herein to demonstrate the placement and function of the blood chamber of the present invention, any extracorporeal blood handling system could beneficially use the blood chamber disclosed herein.

The Method

The presently preferred blood chamber embodiment of this invention has been advantageously used in single needle hemodialysis systems such as is disclosed in U.S. Pat. No. 3,756,234.

According to the presently preferred method embodiment of this invention, the chamber 10 is connected into the arterial line 48 preferably upstream from the pump 38 (FIG. 2). One of the adapters 14, 16 or 18 is selected to communicate directly with a pressure sensing device. The remaining adapters may be capped or, alternatively, connected directly to a source of medicament, blood or other desirable fluid.

The sample port 34 has a cap 36 which prevents inadvertent outflow of blood 24 from the chamber 10. At the same time, the cap 36 is penetrable by a hypodermic needle or the like to facilitate sampling of the blood 24.

In the operation of the system of FIG. 2, the venous line 47 is clamped and the blood pump 38 draws blood from the needle 40 into the chamber 10 through the inlet 30 by creating a negative pressure in the chamber 10. Because the inlet 30 is submerged, turbulence and thorough mixing of blood in the chamber 10 is possible so as to inhibit clot formation and at the same time the inrushing blood is prevented from carrying significant amounts of air into the blood which would otherwise create bubbles and accumulate excessive froth. With the reduction of froth, communication between the air cushion 28 and pressure sensor 49 is maintained clear and free of solidified blood froth.

As the blood is drawn into the chamber 10, a reservoir of blood accumulates to provide an adequate supply for the pump 38. Continued operation of the pump even against a negative pressure in the chamber 10 has been found to significantly reduce blood vessel collapse at the patient. When a single needle system is employed, the low pressure sensor will trigger the controller 42 at a predetermined level so as to close off the line 48 and allow the blood 24 to pass through the dialyzer 44 and through the venous branch 47 to the needle 40. Accordingly, the blood carried by the system of FIG. 2 is forced to move in the direction of the arrows shown in the Figure. The volume of blood in the chamber 10 is alternately reduced and increased responsive to the change in blood availability and the clamping state of the controller 42.

In view of the foregoing, the present invention provides an improved method for monitoring extracorporeal pressure, for alleviating pump starvation, and for providing access to blood in an arterial bloodstream of an extracorporeal blood handling system while minimizing foam and clot formation.

The invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive and the scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

1. A method for monitoring blood in an arterial line of an extracorporeal blood handling system comprising venous and arterial blood lines, a blood pump and a dialyzer, the improvement comprising:

providing a cylindrical blood chamber, the cylindrical configuration minimizing blood stagnation in the chamber;

interposing the chamber in an arterial blood line of an extracorporeal blood handling system upstream of the pump, the chamber having means for maintaining a vertical orientation of the chamber;

passing blood through a variable volume pool of blood in the chamber from a submerged inlet to a submerged outlet while simultaneously minimizing blood foaming by introducing blood into the chamber through the submerged inlet;

inhibiting clot formation in the blood and also enhancing mixing fluids selectively amended to the blood by creating limited subsurface turbulence in the blood, the turbulence being created by introducing the blood into the cylindrical chamber below the blood surface;

maintaining a constant quantity gas cushion above the pool of blood in the chamber; and

communicating pressure developed in the gas cushion by the blood to a

2. A method as defined in claim 1 further comprising sampling blood within

3. A method as defined in claim 1 further comprising delivering fluids into

4. A blood pressure and blood treatment access device for an arterial line of a single needle extracorporeal blood handling system which comprises arterial and venous blood lines, a blood pump, a dialyzer down stream from the pump and a controller for determining the direction of blood flow in the single needle, further, comprising:

an enclosed cylindrical chamber operable to receive a variable quantity of blood and to maintain a constant quantity gas cushion above said blood;

means for maintaining a vertical orientation of the cylindrical chamber;

a blood inlet and a blood outlet through a wall of the chamber, each located below a minimum blood level, said inlet and outlet being located upstream from the blood pump of the single needle system to provide a reservoir of blood from which the blood pump can draw even when pressure is periodically reduced in the chamber to thereby avoid pump starvation; and

a plurality of access means into the chamber, at least one of which is operable to communicate pressure through the gas cushion to a pressure sensing device, at least one other access means which is in direct communication with the interior of the chamber for sampling blood and introducing fluids into the blood within the chamber.