GB2210797A

GB2210797A - Blood oxygenator apparatus

Info

Publication number: GB2210797A
Application number: GB8823710A
Authority: GB
Inventors: Adib Domingos Jatene; Jose Francisco Biscegli
Original assignee: MACCHI ENG BIOMEDICA
Current assignee: MACCHI ENG BIOMEDICA
Priority date: 1987-10-13
Filing date: 1988-10-10
Publication date: 1989-06-21
Anticipated expiration: 2008-10-10
Also published as: IT1224486B; UY22854A1; GB2210797B; FR2621489A1; AR240021A1; IN172091B; PT88727A; IT8867916A0; PT88727B; FR2621489B1; BR8705585A; GB8823710D0; MX168207B; DE3834952C2; DE3834952A1; ES2011147A6

Description

22107 9 7 BLOOD OXYGENATOR APPARATUS The present invention relates to a

blood oxygenator apparatus particularly designed for use in cardiopulmonary surgery with extracorporeal blood circulation.

The second half of the 20th Century has witnessed an,accelerated development in surgical techniques. In the last 30 years, no surgical technique has developed faster than open-heart cardiopulmonary surgery, that is surgery in which the normal beating of the heart is interrupted and its cavities are cut open in order to allow the examination of the interior of the organ and the proper correction of its functions.

Open heart cardiopulmonary surgery as described above requires the use of extracorporeal blood circulation systems. An extracorporeal blood circulation system is a system which effects the blood circulation function ordinarily accomplished by the circulatory system and also the breathing function, including the gaseous exchange and blood oxygenation ordinarily performed by the respiratory system. This extracorporeal blood circulation system desirably has a performance as similar as possible to the physiological performance of the human body.

Because it is essential in cardiopulmonary surgery to-interrupt the normal heart function, the artificial blood circulation system must be able, when used in an adult patient, to collect from 4 to 5 liters of blood per minute, 2 deliver this volume of blood to a gaseous exchange surface having a certain minimum area, and to pump this blood back into the circulatory system of the patient.

Additionally, depending on the length of the surgical procedure, which usually lasts several hours, the artificial blood circulation system must be capable of performing its programmed functions reliably over several hours without substantially altering the physiological properties of the blood or of the patient's organs, i.e. without impairing the integrity of the extremely fragile blood cells or causing any harm to the easily affected proteins present in the plasma in order not to cause "denaturation',.

Basically, the known extracorporeal blood circulation systems comprise a pumping apparatus such a's a peristaltic pump, to pump and maintain the circulation of the blood, and an oxygenator to oxygenate the blood. Peristaltic pumps are well known and their operation-does not normally affect significantly the physiological properties of the blood. However, the blood oxygenator apparatus does have a very significant part to play in the preservation of the physiological properties of the blood, since it is inside the oxygenator that the blood cells undergo a direct contact with the gaseous exchange surface, which contact can be hazardous to the integrity of the cells.

The presently known blood oxygenators are of three types: film oxygenators, bubble oxygenators, and-membrane oxygenators. Each of these oxygenates the blood in a different way. The one which is closest in performance to the physiological oxygenation process and which therefore offers the least risk of causing harm to the blood cells, is the membrane blood oxygenator. In this type of oxygenator, the blood is forced to flow through a core formed by a hollow fiber membrane having capillary dimensions and supplied with a f low of oxygen therethrough, the blood being oxygenated by a direct transfer of this oxygen to the blood cells.

In addition to oxygenating the blood, the blood oxygenators are also ordinarily used to control the temperature of the patient. Normally, during a lengthy surgical procedure the temperature of the patient's body is lowered in order to reduce its metabolic functions to a minimum, and after the surgery is completed the temperature is raised back to its normal level. This control of the patient's temperature is accomplished by means of a heat exchanger incorporated in the blood oxygenator apparatus, through which the blood passes in a heat exchange relation with a cooling or heating fluid, according to what is necessary.

Thus, a conventional membrane blood oxygenator comprises three main parts: a blood reservoir to receive and accumulate the blood collected from the patient, a heat exchanger to control the temperature of the blood, and an oxygenation chamber in which the venous blood is oxygenated (arterialized) before it is pumped back to the patient.

The first membrane blood oxygenator apparatus commercially available comprised a blood reservoir in the form of an opaque, collapsible bag with a separate combined heat exchanger and oxygenation chamber unit. The blood accumulated in the collapsible bag passed through the peristaltic pump to the combined heat exchanger and oxygenation chamber unit, and then back to the patient in a closed circulation system. This arrangement, however, has a number of disadvantages. Firstly, it needs a large number of blood lines connecting and directing all the venous blood from the patient to the collapsible bag, from the bag to the pump, from the pump to the combined heat exchanger and oxygenation chamber unit, and from this unit back to the patient. This large number of connections makes it difficult to replace the blood oxygenator in an emergency.

4 A second disadvantage is that the opaque, collapsible bag reservoir, does not provide the medical staff performing the surgery with any indication either of the volume of venous blood within the bag (except when it is completely empty) or of its condition since the blood cannot be seen.

A first solution proposed to overcome these disadvantages was to replace the opaque bag by a bag made from a transparent material, so that the amount and condition of the blood in the reservoir could be observed.

A second solution previously proposed to overcome these disadvantages was to place the transparent collapsible bag in a rigid frame integrally formed with the combined heat exchange and oxygenation chamber unit, thus reducing the number of connections and facilitating the emergency replacement of the blood oxygenator apparatus, while still maintaining a closed blood circulation system.

In a later improvement, the collapsible bag was replaced by a rigid reservoir for the venous blood, made from a transparent plastic material, and the heat exchanger was placed within the reservoir. With this improvement, the closed blood circulation system was replaced by an open circulation system in which the blood was not maintained under pressure all the time, the open system having proved better for preserving the physiological properties of the blood.

This open circulation system, comprising a blood oxygenator apparatus integrally formed in a single piece and having the heat exchanger within the blood reservoir, however, also has some disadvantages, particularly in connection with the performance of the heat exchanger. In particular, the positioning of the heat exchanger inside the blood reservoir means that it is upstream of the peristaltic pump. Thus, the blood passing through the heat exchanger is not subjected to any pressure other than atmospheric.

As a result, the exchange of heat is effected mainly while the blood is passing along the heat exchange surface as the blood descends under gravity to the bottom of the blood reservoir, or it depends on the volume of blood contacting the heat exchanger inside the blood reservoir. In both cases the efficiency of the heat exchange is seriously hindered because it is not exchanging heat along all of its exchange surface.

We have now devised a blood oxygenator apparatus which mitigates or overcomes the above discussed disadvantages of the prior art oxygenators.

According to the present invention, the blood oxygenator apparatus comprises blood pumping means and blood oxygenator means, said blood oxygenator means comprising a rigid blood reservoir, a heat exchanger and an oxygenation chamber integrally formed in one piece, said oxygenation chamber being interposed between said blood reservoir and the heat exchanger, whereby the blood collected in the reservoir first passes through said peristaltic pump prior to its passage through the heat exchanger and the oxygenation chamber.

In order that the invention may be more fully understood, an embodiment thereof will now be described by way of example only, with reference to the accompanying drawings, in which:

FIGURE 1 is a front elevation view of the embodiment of blood oxygenator apparatus; and FIGURE 2 is a schematic illustration of the lines connecting an extracorporeal blood circulation system using a blood oxygenator apparatus according to the present invention to a patient.

With reference now more particularly to the drawings, a blood oxygenator apparatus according to the present invention for use in an extracorporeal blood circulation system comprises, basically, a blood reservoir 1,-an oxygenation chamber 2 and a heat exchanger 3 integrally formed in only one piece.

6 The blood reservoir 1 is formed from a rigid and transparent plastic material having physical-chemical properties that allow it to be heat sterilized, having its upper extremity closed by a lid 4 with a plurality of connec-tions for receiving blood lines.

These connections comprise a main venous blood entrance 5 to receive the venous blood collected from the patient, auxiliary connections 6 to receive the venous blood collected by aspirators 30 and fed in lines 31, a connection 7 to receive the venous blood from a cardiotomy reservoir (not shown), a connection 8 to allow the recirculation of the blood from the blood oxygenator apparatus, a connection 9 to prime the blood oxygenator apparatus, and a connection 10 through which gas can exit.

Additionally, the blood reservoir 1 is provided with an exit connection 11 opposed to the upper extremity to allow the blood accumulated therein to flow freely, as well as a connection 12 to allow the taking of blood samples, and a connection 13 to receive a thermometer to measure the temperature of the blood. The lid 4, in addition to the above cited connections, may also be provided with one or more'connections thereon to allow drugs to be injected into the blood accumulated in the reservoir.

The blood reservoir 1 can also be used as a cardiotomy reservoir, as long as its volume is great enough to provide a balance of the dynamic flow. When this balance cannot be obtained, then the cardiotomy reservoir must be used to receive the blood from the aspirators, and the respective connections 6 for the aspiration lines must be kept closed.

A bubble breaker sponge 14 is positioned inside the blood reservoir 1, adjacent to its upper extremity, and a filter 15 to retain eventual coagula transported in the venous blood is placed immediately beneath said sponge, wh-ereby all the venous blood collected from the patient is forced to pass through said sponge 14 and filter 15 when it enters the blood reservoir 1 in a first treatment step.

The venous blood, free from impurities, bubbles and coagula, accumulates in the interior of the blood reservoir 1, which has a bottom surface 16 slightly inclined in order to direct the venous blood towards the blood exit connedtion 11.

Immediately beneath the blood reservoir 1, but without any communication therewith, is the oxygenation chamber 2. The oxygenation chamber of the blood oxygenator apparatus comprises a core made from a hollow porous airpermeable, filament having capillary dimensions, and the venous blood flows along this core during the oxygenation process.

A gas entrance 17 is provided in the upper extremity of the oxygenation chamber 2, close to the blood reservoir 1, the chamber being also provided with a connection 18 to allow the collection of the blood arterialized by the oxygenation process, and with a connection 19 to receive a thermometer therein to measure the temperature of the blood, both these connections being located close to the gas entrance 17. The exit for the gas used in the oxygenation,process 20 is located within the chamber 2, which is additionally provided with a connection 21 to allow the recirculation of the blood to the reservoir, when so desired.

The entrance of the venous blood to the oxygenation chamber is directly from the exit of the heat exchanger 3, positioned adjacent to the lower extremity of said oxygenation chamber, and the blood after being treated in the oxygenation chamber exits the chamber 2 through the exit connection 22.adjacent the upper extremity thereof.

The heat exchanger 3 comprises a plurality of vertically positioned tubes having a relatively small length, with a heat exchanging fluid, typically water, ci-rculating therethrough. The flilid is fed to the heat exchanger 3 through an entrance connection 23 and is removed therefrom through an exit connection 24, both these 8 connections being in the lower extremity lid 25 of the heat exchanger 3. The entrance connection 26 for the venous blood to be treated in the heat exchanger is also located in the lid 25.

As can be better seen from Figure 2, the venous blood from the blood reservoir 1 is directed to the blood pumping apparatus, in the present case a peristaltic pump 27, and from the pump to the heat exchanger entrance connection 26. The exit from the heat exchanger opens directly into the interior of the oxygenation chamber 2, from which the blood arterialized by the oxygenation process is removed through the exit connection 22 at its upper extremity and redirected to the patient.

From the above description it should be noted that the oxygenation process of the venous blood is effected in counter-current, that is the venous blood flows upwards inside the oxygenation chamber while the gas used in the process is pumped downwards towards the exit connection 20 located in the bottom extremity of the chamber.

The constructional features of the apparatus of the present invention provide improved efficiency when compared to the blood oxygenators of the prior art, because the heat exchange function does not depend on the volume or the amount of venous blood in the reservoir, and because the blood is pressurized before it passes through the heat exchanger so that heat exchange is forced.

Another advantage provided by the blood oxygenator apparatus of the present invention is the smaller volume of blood sequestered from the patient to prime the extracorporeal blood circulation system (approximately 450 ml). This is a significant advantage because the smaller the amount of blood sequestered from the patient prior to the surgical procedure, the better the patient's condition to withstand the surgery.

Additionally, the direct connection from the exit 9 of the heat exchanger to the entrance of the oxygenation chamber enables the flow of blood inside the heat exchanger to be radially oriented in relation to the elements conducting the heat exchange fluid, which improves the perfor mance of the exchange.

Having described the invention with reference to a preferred embodiment, it is to be understood that the embodiment may be modified in various ways without departing from the invention.

Claims

CLAIMS:

1. A blood oxygenator apparatus for use in an extracorporeal blood circulation system, the apparatus comprising a blood pumping means and a blood oxygenator, the blood- oxygenator comprising a rigid reservoir for the blood, an oxygenation chamber and a heat exchanger integrally formed in one piece, characterized in that the inlet for blood into the oxygenation chamber is connected to the outlet for exit of blood from the heat exchanger, whereby all the blood collected in said blood reservoir passes through the pumping means before it enters the heat exchanger.

2. Apparatus according to claim 1, wherein the oxygenation chamber inlet is connected directly to the heat exchanger outlet.

3. Apparatus according to claim 1 or 2, wherein the oxygenation chamber comprises a core made from a hollow porous air-permeable filament.

1

4. A blood oxygenator apparatus substantially as herein described with reference to Figure 1 or Figure 2 of the accompanying drawings.

LZ.-.don WC1R 4TP rur-t:e:-::pes =.ky be obtamed C=. The Pa%en. w Publuted 1988 W- The PW-fnt offce. St&.' Re.:5C 66 71. ofCe.

Sales Branch, S, Mary Cray. OrPM9t= Kent BRS 3RD prtnted by Muluplex tecluuques ltd, St M ary CraY. Kent. COM 187.