WO2011048054A1

WO2011048054A1 - Evacuation device for fluid exiting an oxygenator of an extracorporeal circulation apparatus

Info

Publication number: WO2011048054A1
Application number: PCT/EP2010/065645
Authority: WO
Inventors: Giovanni Guglielmo Landoni; Francesco De Simone; Luigi Cassara'
Original assignee: Fondazione Centro San Raffaele Del Monte Tabor
Priority date: 2009-10-19
Filing date: 2010-10-18
Publication date: 2011-04-28
Also published as: ITMI20091793A1

Abstract

An evacuation device for fluid exiting an extracorporeal circulation apparatus for the purpose of preventing release and inhalation of fluids such as volatile anaesthetics by personnel present in the operating theatre. The device comprises a conduit (2) provided with first means (3, 11) for connection to a main discharge port (4) of an oxygenator (10) and with second means (5) for connection to a wall suction port (9) of an operating theatre, said conduit (2) presenting at least one suction aperture (7, 31, 15) enabling air to enter its interior from the surrounding atmosphere, such that this air can mix with the fluid originating from the oxygenator (10) before reaching the suction port (9).

Description

EVACUATION DEVICE FOR FLUID EXITING AN OXYGENATOR OF AN

EXTRACORPOREAL CIRCULATION APPARATUS

The present invention relates to an evacuation device for fluids exiting an extracorporeal circulation apparatus.

In certain types of operations in which direct access to a patient's heart or large vessels is required, apparatus must be used for extracorporeal circulation. In this respect, the need to operate on the heart often means arresting or supporting the cardiac or pulmonary functions and replacing or aiding them with an assembly of devices which are implemented by a cardiopulmonary bypass (CPB).

A cardiopulmonary bypass is involved, consisting of short-circuiting both the heart and the lungs by replacing their functions. Apparatus for CPB hence comprise a pump which replaces the function of the heart, and an oxygenator which replaces that of the lungs.

A bypass circuit also requires further means such as: venous and arterial cannulas for conveying the blood from and to the extracorporeal circuit, a reservoir for venous reserve, a heat exchanger for heat exchange, aspirators, and filters to retain gaseous or corpuscular particles.

The cannulas used in extracorporeal circulation are tubes of polymer material. Their function is to connect the patient to the extracorporeal circulation tubes.

The cannula for draining the blood from the patient is generally positioned within the right atrium or within the hollow veins (depending on surgical requirements), whereas the cannula which returns the treated blood to the patient is positioned within the aorta or within the femoral artery (again in this case the location depends on surgical requirements).

The cannulas are designed such as to cause the blood to circulate with minimum turbulence.

CPB apparatus also comprise a reservoir in which the blood drained from the patient is deposited.

This device, generally positioned with a level difference from the heart right atrium of thirty or more centimetres, acts as a venous reserve; in this respect, precisely because of the level difference it almost completely "empties" the vein reserves into the reservoir.

The reservoir interior also receives the free blood originating from the field of operation and that drained from some heart sections due to an "anomalous" return (for example the blood originating from the bronchial circulation terminating in the left ventricule).

Various types of pumps are used in the extracorporeal circulation circuit, namely a master pump which replaces the heart function, pumps for administering cardioplegia (a solution enabling the heart to be arrested), and pumps used as aspirators.

The main pump can be of different types, but is generally of roller or centrifugal type.

Depending on subjective parameters, the pump has to ensure an adequate flow rate to the patient, even flows exceeding six litres per minute.

Two basic types of oxygenators can be used in CPB, namely bubbling type (no longer used) and membrane type (generally with hollow fibres). The different oxygenator types require different pump positioning within the circuit.

In all cases the oxygenator is fed with air mixed with pure oxygen.

In membrane oxygenators (currently in use), the gas compartment and blood compartment are separated by a microporous membrane. The oxygenator enables the gases to pass (from and to the blood) by completely emulating the function of the natural lung. In this respect, gaseous exchange also follows Flick's law in this case. In bubbling oxygenators (no longer used), although following the same exchange rule, they are structured differently in that there is no separation between gas and blood.

The membrane must evidently be supplied with an air and gas quantity in excess of that which can normally be absorbed by the blood. This excess is freely discharged into the atmosphere through a main discharge port of the oxygenator together with the carbon dioxide released from the blood. The oxygenator also comprises secondary (or emergency) discharge ports which are useful should the main port be obstructed for any reason.

EEC apparatus also comprise heat exchangers the function of which is to regulate the blood temperature and consequently the patient's temperature.

The heat exchanger is usually integrated into the oxygenator.

Aspirators are also present, used to recover the free blood within the thorax cavity due to surgical injuries and to recover the blood from the left ventricule originating from the bronchial circulation as already described. The recovered blood is fed into the venous reserve after being filtered through another container integrated into a reservoir known as a cardiotome.

During the extracorporeal circulation stage, anaesthesia by anaesthetic gases such as desflurane and sevoflurane is known to be beneficial to the patient and can be performed via the oxygenator.

In this respect, volatile anaesthetics have protective properties against organ ischemic damage. The use of these properties during anaesthesia can provide a further treatment or prevention instrument (or both) against ischemic damage during the perioperative period. In this respect four recent papers (one randomized controlled trials, one metaregression, one case match study and one meta-analysis of randomized trials) have suggested that halogenated anaesthetics reduce perioperative mortality after cardiac surgery.

Multicentric randomized trials have previously shown that the use of volatile anaesthetics can reduce postoperative release of Tropin I, the need for support by inotropic drugs, and the number of patients needing prolonged hospitalization after a coronary bypass operation. Administration of volatile anaesthetic agents during the cardiopulmonary bypass operation also increases these beneficial effects.

In particular, Bignami E et al., (J Cardiothorac Vase Anesth. 2009) has shown that the mortality reduction in cardiac surgery by the use of halogenated gases is proportional to the administration time and is a maximum in patients who also receive halogenates during extracorporeal circulation. De Hert et al. (Anesthesiology, 2004) have already shown that the release of myocardial necrosis markers is reduced by the use of halogenated anaesthetics and is a minimum when these halogenates are also administered during extracorporeal circulation.

The anaesthetic gases are essentially vaporized into the air and oxygen flow fed to the oxygenator.

As already described, the main discharge port of the oxygenator releases into the surrounding atmosphere any fluid not used for heat exchange with the blood (including C0₂). The result is that anaesthetics such as desflurane and sevoflurane present at the oxygenator discharge port are released (if used) into the operating theatre and can be inhaled by personnel present therein, with consequent drawbacks for the health of the personnel.

An object of the present invention is therefore to provide an evacuation device for the fluid exiting an oxygenator of an extracorporeal circulation apparatus which collects and disposes of any volatile anaesthetics present in the exit stream of the oxygenator, hence preventing its dispersal into the operating theatre environment.

This and further objects are attained by an evacuation device in accordance with the technical teachings of the accompanying claims.

Further characteristics and advantages of the invention will be apparent from the description of a preferred but non-exclusive embodiment of the device of the invention, illustrated by way of non-limiting example in the accompanying drawings, in which:

Figure 1 is a schematic view of an CPB apparatus connected to a patient; Figure 2 is a schematic view of the evacuation device of the present invention associated with an oxygenator of Figure 1 ; Figures 3, 4 and 6 are a schematic view of alternative embodiments of the invention of Figure 2 and

Figure 5 shows schematically another different embodiment of the device of Figure 3.

With reference to said figures, these show an evacuation device for fluid exiting an oxygenator 10 of an extracorporeal circulation apparatus.

The extracorporeal circulation apparatus is substantially of known type and is illustrated schematically in Figure 1 . It comprises cannulas 50 for connecting the machine to the patient, a venous container 51 , a cardiotome filter container 52, a main pump 53, a hollow fibre hemoconcentrator 54 (if positioned), an arterial filter 55, aspiration pumps 56 and an oxygenator 10 with which the device 1 of the present invention is associated. The operation of the EEC apparatus is known and will therefore not be repeated. Moreover the indicated configuration of the EEC machine is provided purely by way of example, and the device 1 can be applied to an oxygenator associated with EEC apparatus which are also very different from that described.

According to the invention, the oxygenator presents a feed line or conduit 44 which provides it with air mixed with oxygen withdrawn from a cylinder 45 or from one or more wall supplies. The line 44 comprises a pressure regulator 46 and an anaesthetic vaporizer 47 (for administering halogens to the flow) supported by a suitable bracket 47A. In concluding the oxygenator description it should be noted that it presents a first entry line 48 for the blood to be oxygenated and a second exit line 49 for the oxygenated blood. Conduits 13 for feeding heat exchange fluids are also present. The oxygenator also comprises a fluid discharge port 4. In the present text the term fluid means the mixture of air, carbon dioxide and possible volatile anaesthetic which is expelled from the oxygenator during its operation.

The evacuation device presents a conduit 2 provided with first means 3 for connection to a main discharge port 4 of the oxygenator and second means 5 for connection to a wall suction port 9 of an operating theatre. The conduit 2 is preferably formed of a first portion 2A made of flexible material, connected to a suitably shaped second portion 2B, itself connected to a third portion 2C provided with means for its connection to the suction port 9 of the operating theatre.

The second portion 2B presents a first convergent section 6. In proximity to a sized lesser cross-section 6A of the first convergent section 6, a suction aperture 7 is provided, communicating with the external environment.

Advantageously the suction aperture 7 is also defined at the lesser cross- section of a convergent element 8, the greater cross-section of which freely faces outwards; the cross-section of the suction aperture 7 is sized such as to regulate the flow (flow rate) of its entering air.

When in use, the conduit 2 is connected to a suction port 9 having a very high suction rate, equal to 25 litres per minute.

The suction port 9 puts the conduit under vacuum so that it collects (arrow F) that expelled by the main discharge port 4 of the oxygenator 10. As is known, the discharge rate of the oxygenator is about 2 litres per minute, for a suction rate through the port 9 of about 25 litres per minute. The aperture 7 provided in the conduit prevents the oxygenator 10 from being put under vacuum by too high a suction rate. In this respect, the aperture 7 enables air to be drawn from the atmosphere (arrows G) into the conduit, and mixed with that originating from the oxygenator, to be then drawn in (arrow H) by the suction port 9.

Advantageously, the cross-sections 6A and/or 7 are sized such as to regulate the air flow rate entering through them. The first convergent section 6 and the convergent element 8 improve the device performance by preventing or minimizing turbulence formation.

Valve regulator means can evidently be provided to regulate the flow rate of the air which flows through the first part of the conduit 2A or which is drawn in by the aperture 7. These valve means can be associated either with the convergent conduits or directly with the cross-section 6A or with the aperture 7.

Advantageously the aforedescribed embodiment can be associated, for safety reasons, with a shell 1 1 disposed about the oxygenator 10. In this respect, the oxygenator 10 comprises secondary discharge ports 19 which work when the main discharge port 4 is obstructed or if the fluid rate expelled thereby is less than that which needs to be effectively eliminated by the main discharge port 4.

In that case, a part of the fluid which should be discharged by the main discharge port leaves from the secondary discharge ports 19.

The interior of the shell 1 1 disposed about the oxygenator is put under vacuum by a further conduit 20 which connects it via suitable means 5' to a further suction port 9'. Any air expelled by the oxygenator secondary discharge ports 19 (arrow M) is mixed with that of the external environment which penetrates (arrow L) between the shell 1 1 and the oxygenator 10 from a aperture 15 provided between the oxygenator wall and the shell wall.

Advantageously an anaesthetic sensor 18 is provided below the oxygenator 10 inside the shell, to indicate if anaesthetic fluid is present in that position.

In an alternative embodiment, shown in Figure 6, the conduit 2 associated with the main oxygenator discharge port is not present. This latter discharges directly into the interior of the shell 1 1 which collects all the discharge air. The aperture 15 has a similar purpose to that of the aperture 7 of the preceding embodiment. Essentially, the interior of the shell 1 1 is associated with the main discharge ports 4 and secondary discharge ports 19, the conduit 2 being defined by the shell 1 1 itself and by the further conduit 20.

In both embodiments, the aforedescribed shell 1 1 is preferably formed from two half-shells 1 1 A, 1 1 B, each comprising a substantially cylindrical wall (but geometrically modifiable according to the form of the oxygenator which it is to contain) and a base portion. The coupled half-shells form a cylindrical lateral wall closed by a baseplate 1 1 C. It is preferably made in three pieces 1 1 A, 1 1 B and 1 1 C connectable together (for example by snap-fitting) such as to surround the oxygenator 10 and form its base. Within the shell there are also provided passages 190 for the conduit 4 and for a double tube 13 for liquid for heat exchange with the oxygenator and for other tubes through which the blood flows.

An alternative embodiment of the invention of Figure 2 is shown in Figure 3. In particular, the first conduit portion 2A and the third portion 2C are not substantially different from that already described. In contrast, the portion 2B' presents a substantially different configuration from that previously provided.

The suction aperture 7 faces an inlet section 30 of an end conduit 2D which connects to the suction port 9 (via the third conduit portion 2C). The inlet section 30 has a greater diameter than the suction aperture 7. Hence an annular aperture 31 is formed communicating with the main oxygenator exit via the first portion 2A. In particular, this exit 4 communicates with a preferably hermetic casing 32 disposed about the end conduit 2D and about the element 33 which defines the suction aperture 7. The element 33 defining the suction aperture can be slightly spaced from the inlet 30, or be positioned at the inlet itself, or be partly inserted into the end conduit 2D.

Advantageously the element 33 has a section 33A converging towards the aperture 7.

In this embodiment, valve means 34, 35 can also be provided associated respectively with the suction aperture 7 and/or with the first conduit portion 2A enabling the fluid flow rate respectively through the suction aperture 7 or through the annular aperture 31 to be regulated. Preferably only the valve means 34 is provided in the described embodiment.

Preferably the end conduit 2D presents, in the fluid indraw direction (arrow H), a divergent section 37 followed by a convergent section 36 of lesser length than the divergent section. A portion 38 of constant cross-section can be present between the divergent section 37 and the convergent section 36.

The operation of this embodiment is slightly different from the preceding. In fact in this case the valve means 34 is regulated such as to draw in from the oxygenator discharge port 4 an air quantity slightly greater than that effectively expelled. This enables the interior of the oxygenator to be placed under slight vacuum, hence causing the secondary discharge ports 19 to operate by drawing air from the external environment (arrows N). In this manner all traces of anaesthetic are drawn in by the port 9, and the shell 1 1 is not required.

In the schematic view of Figure 5, the valve 34 is regulated based on the reading of sensor 18, placed near the secondary discharge ports 19 of the oxygenator. If the sensor 18 detects discharge of anaesthetic from the ports 19, the valve 34 is gradually closed, thus increasing the airflow withdrawal from the main discharge port 4 of the oxygenator.

The regulation of the valve 34 can also be effected automatically based on the reading of the sensor 18. The regulation of the valve means 34 based on the reading of the sensor can be effected in the other embodiments of the present invention herein described.

An alternative embodiment of the invention is shown in Figure 4.

Again as in the preceding case, the first portion 2A of the conduit and the third portion 2C are totally similar to those illustrated in the preceding embodiments.

In particular the portion 2B" can simply replace the configuration of the section 2B described in the first embodiment.

Here the configuration is similar to that described in the embodiment of Figure 3. In this respect, an annular aperture 31 ' is present but in communication with the outside via a valve 34, whereas the element 33' is connected to the main oxygenator discharge port and is partly inserted into the end conduit 3D'. In contrast to the configuration of Figure 3, both the element 33' and the end conduit 3D' have a constant cross-section. The operation of the embodiment just described can be identical to that of the embodiment of Figure 3, or, if the valve means is absent and if sized cross-sections of the element 33' and of the end conduit 3D' are present, it can be very similar to that of the first embodiment, to be used either in combination or not in combination with the shell 1 1 .

Advantageously, in each of the aforedescribed embodiments, there can be provided, associated with the main discharge port 4 of the oxygenator 10 and preferably on the same portion of the conduit 2A, a branch 40 which conveys part of the air expelled by the oxygenator to a gas analyzer 41 . Upstream of the gas analyzer a cock 42 is provided enabling that flow to be selected which originates either from the branch 40 or from a further branch 43 provided on the conduit 44 by which fluid (air, oxygen, carbon dioxide and anaesthetic) is fed to the oxygenator 10.

In this manner by acting on the cock 42, the quantity of anaesthetic present in the feed flow to the oxygenator and the quantity of anaesthetic present in the exit flow can be analyzed, hence obtaining by difference the true quantity of anaesthetic administered to the patient.

The anaesthetic sensor 18, positioned below the oxygenator, is also connected to the gas analyzer 41 via the cock 42 to evaluate any gas dispersions within the shell 1 1 or freely into the air if the device does not comprise the shell, as in the embodiments 3 and 4.

Essentially the aforedescribed systems for regulating the aspiration (via the valves 34, via convergent conduits and/or sized cross-sections) enable the value of the gases (halogenates - carbon dioxide), monitored at the exit of one of the secondary discharge ports of the oxygenator, to be maintained equal to 0% with regard to halogenates and equal to 0 mmHg with regard to carbon dioxide, in addition to maintaining the gauge pressure at the exit of the oxygenator gas compartment equal to 0 mmHg (hence at atmospheric pressure of 760 mmHg).

To obtain these results it should be noted that the aspiration depends on the following factors: gas flow at the oxygenator inlet 44, cross-sectional area of the main oxygenator gas discharge port 4, total cross-sectional area of the oxygenator secondary gas discharge ports 19, cross-sectional area of the tube 2A connecting the oxygenator exit to the venturi entry, length of this tube, cross-sectional area of the tube 2C connecting the venturi system to the outside and length of this tube, suction flow of the centralized port 9 used for gas disposal.

It is therefore important to maintain a correct suction flow balance between the tube 2A connecting the venturi to the main gas discharge port of the oxygenator 4 (discharge gas flow 4 from the oxygenator together with the air flow drawn in from the outside through the oxygenator secondary gas discharge ports 19 - if present) and the convergent section 8 connecting the venturi to the outside.

This balance is either fixed or adjustable depending on whether valve regulator means 34 (or 35) for the flow entering the venturi are or are not present.

In the case of fixed balancing, this is achieved, as already stated, by correctly sizing the various passage cross-sections 7, 6A, 31 of the different embodiments. If valve regulator means are present, in addition to the "rough" regulation achieved by the sized passage cross-sections, very precise regulation of the ratio between the external air suction G and the fluid F originating from the oxygenator discharge port is also achievable.

This is possible via said valve regulator means and in particular those provided for regulating the air flow G originating from the outside.

The suction regulator (for example the valve 34 of Figure 3 or 4), for equal suction flow through the centralized gas disposal port 9 as it gradually closes, favours greater suction by the tube 2A connecting the main discharge port 4 of the oxygenator 10 to the section 2B.

If suction flow by the main discharge port 4 of the oxygenator 10 exceeds that leaving the oxygenator, the secondary discharge ports 19 of the oxygenator 10 are activated, which by drawing external air N into the gas compartment of the oxygenator 10 prevent depressurization of the oxygenating chamber.

In contrast when the flow regulator 34 is reopened the opposite effect occurs, enabling a greater external air quantity G to be drawn in, so reducing the vacuum in the tube 2A connecting the oxygenator discharge port 4 to the section 2B.

This regulation is achieved on the basis of sensing any gas dispersions by a probe 18 positioned at the exit of the secondary discharge ports 19 of the oxygenator 10.

The advantage achieved by regulating the suction flow compared with a fixed regulation is to be able to adapt it to any type of oxygenator and to any type of circuit connecting the main discharge path 4 of the oxygenator 10 to the suction system for gas disposal independently of the gas flow 44 entering the oxygenator and of the suction flow of the centralized gas disposal port 9.

This system enables the operation to be carried out with maximum safety, without the risk of depressurizing the oxygenating chamber because of too high a suction flow while at the same time correctly eliminating the discharge gases through the centralized port 9.

Various embodiments of the present invention have been illustrated, however others can be conceived utilizing the same inventive concept. For example in the whole description reference was made to the connection of the evacuation device to the main port of the oxygenator. Obviously the evacuation device of the present invention can be connected to every port that discharges fluids from the oxygenator.

In the previous described embodiment reference was made to a shell coupled with the oxygenator. The shell can be realized in one single piece specifically designed to be coupled with a specific type of oxygenator. As described it can also be realized preferably in two (or more) parts in order to allow it to be coupled with different types of oxigenators.

In a further embodiment the shell is a structural part of the oxygenator and can't be separated from it. The term structural part in this description should be intended that the shell is specifically designed and projected for that kind of oxygenator and fixed to the oxygenator both at the moment of sell and when the oxygenator is in operation. The shell can be separated from the oxygenator only in case of maintenance.

In another embodiment the oxygenator presents a bottom wall (base) that is in common, and preferably integrally formed with the base of the shell. In this case there is no need to provide passages in the shell for the blood conduit as the base of the shell is the same of the oxygenator.

Claims

1 . An evacuation device for fluid exiting an extracorporeal circulation apparatus, comprising a conduit (2) provided with first means (3, 1 1 ) for connection to a main discharge port (4) of the oxygenator and with second means (5) for connection to a wall suction port (9) of an operating theatre, said conduit (2) presenting at least one suction aperture (7, 31 ', 15) enabling air to enter its interior from the surrounding atmosphere, such that this air can mix with the fluid originating from the oxygenator before reaching the suction port.

2. A device as claimed in the preceding claim, wherein said suction aperture (7) presents a sized cross-section which regulates the air flow entering it.

3. A device as claimed in one or more of the preceding claims, wherein said suction aperture (7) is defined by the lesser cross-section of a convergent element (8), the greater cross-section of which faces outwards.

4. A device as claimed in one or more of the preceding claims, wherein directly upstream of said suction aperture (7), in that conduit portion exiting the oxygenator, a first convergent section (6) is provided presenting a sized lesser cross-section (6A).

5. A device as claimed in one or more of the preceding claims, wherein a shell element (1 1 ) is provided housing at least that portion of said oxygenator positioned in proximity to at least one secondary discharge port (19) thereof, the interior of said shell element being put under vacuum by a further conduit (20) connected to a further suction port (9'), said shell element comprising at least one aperture (15) acting as a suction aperture for the entry of air withdrawn from the atmosphere into the shell interior.

6. A device as claimed in the preceding claim, wherein said inlet aperture (15) is provided between at least one lateral wall of said shell and said oxygenator.

7. A device as claimed in one or more of the preceding claims, wherein said shell (1 1 ) presents a substantially cylindrical lateral wall (1 1 A, 1 1 B) closed at its lower end by a baseplate (1 1 C) and/or wherein said shell is formed in at least three pieces which can be coupled together to at least partly surround the oxygenator, and/or wherein said shell presents passages for the tube conduits (13) for the liquid for heat exchange with the oxygenator and passages for the tubes (22) for blood passage from and to the oxygenator, and/or wherein the inlet aperture (15) is provided between upper walls of the oxygenator (10) and the upper edge of the walls of the shell (1 1 ).

8. A device as claimed in one or more of the preceding claims, wherein said suction aperture (7, 31 , 31 ') is associated with means (34) for regulating the air quantity flowing through it and/or wherein a valve means (35) is provided upstream of the suction aperture in the conduit leaving the oxygenator, to regulate the flow of fluid originating from the oxygenator.

9. A device as claimed in one or more of the preceding claims, wherein said suction aperture (7) faces the inlet section (30) of an end conduit (2D) for connection to the suction port, said inlet section having a greater diameter than the suction aperture, such as to create an annular aperture (31 ) communicating with the main exit of the oxygenator.

10. A device as claimed in one or more of the preceding claims, wherein the end conduit (2D) presents, in the fluid indraw direction, a divergent section (37) followed by a convergent section (36) of lesser length than the divergent section, and/or wherein a portion (38) of constant cross-section is present between the divergent section and the convergent section, and/or wherein a casing (32) is provided surrounding the suction aperture (7) and the inlet section (30) of the end conduit, the casing interior communicating with the main discharge port (4) of the oxygenator.

1 1 . A device as claimed in one or more of the preceding claims, wherein said suction aperture (7) is defined by an annular aperture (31 ') formed between an element (33') connected to the main discharge port (4) of the oxygenator and the end conduit (3D¹) connected to the suction port (9), and/or wherein said suction aperture (7) is defined by the interstice (15) present between the wall of said shell (1 1 ) and the wall of said oxygenator.

12. A device as claimed in one or more of the preceding claims, wherein associated with the main oxygenator discharge port (4) there is a branch (40) opening into a gas analyzer (41 ), and/or wherein, in proximity to the oxygenator secondary gas discharge port (19), means (18) are present for sensing any anaesthetic dispersions into the surrounding environment.

13. An extracorporeal circulation apparatus comprising at least one venous container (51 ), a main pump (53), an oxygenator (10) and an arterial filter (55), characterised in that a fluid evacuation device (1 ) in accordance with one or more of the preceding claims is associated with said oxygenator (10).

14. An apparatus as claimed in the preceding claim, wherein a vaporizer (47) is provided to vaporize a volatile anaesthetic into the air flow entering the oxygenator.

15. An apparatus as claimed in the preceding claim, wherein associated with the oxygenator gas inlet (44) there is a branch (43) opening into a gas analyzer (41 ).

16. An apparatus as claimed in one or more of the preceding claims, wherein the following are present: a gas supply (45), and/or a gas (air/oxygen) pressure and mixing regulator, and/or a vaporizer support bracket (47A), and/or an anaesthetic vaporizer (47), and/or a branch (43) for measuring the concentration of the indrawn anaesthetic, and/or a branch (40) for measuring the exiting anaesthetic, and/or a sensor (18) for sensing any halogenated leakages into the atmosphere.

17. An apparatus as claimed in one or more of the preceding claims, wherein the shell is a structural part of the oxygenator.

18. An apparatus as claimed in one or more of the preceding claims wherein the oxygenator presents a bottom wall in common with the shell.