In heart operations with cardiopulmonary bypass <BR> <BR> <BR> (CPB), the patient's blood is drained from Vena Cava Superior (VS), Vena Cava Inferior (VCI) or the atrium by means of one or more venous catheters to a reser- voir/filter system suitable therefor, before the blood is taken back to the patient's own arteries by means of a peristaltic pump via an oxygenator. The driving force in the drainage derives partly from the gravitation of the liquid column connecting the patient with the reservoir, partly the possible overpressure in the vessels. It has therefore been common practice to place the reservoir in a low position and to use tubes of a fairly big cross section to obtain a satisfactory drainage. These measures do not, however, make it possible in practice to improve the drainage, for which reason methods for assisting the drainage have been developed, such that smaller tubes may be used from catheters to reservoir and such that smaller catheters may be used to increase the safety against increased pressure in the central vessels and thus reduce the risk of oedema. One of the possibilities proposed is to

assist the drainage by producing a slight vacuum in the reservoir, which is to be compared to an increase of the height difference between patient and reservoir. In practice, a vacuum of from 0-100 mm Hg may be produced which corresponds to an increase in the height differ- ence of approx. 130 cm.

Regulators are known for producing a vacuum in a reservoir of the type used in heart surgical treatment.

This regulator produces a vacuum corresponding to a predetermined set value, which under normal circum- stances will increase the drainage. The regulator does not, however, provide an optimal safety against compli- cations under special conditions which may occur during an operation.

The object of the invention is to establish a pressure regulator which is easier to control during an operation and which thus increases the safety of the patient, in particular in case of complicated oper- ations. This object is met by the pressure regulator according to the invention, which pressure regulator is characterized by the subject matter of the characteriz- ing clause of claim 1.

During a surgical procedure with a hard-shell reservoir the blood level in the reservoir will raise and fall as a consequence of varying arterial blood flow and varying return flow. The reservoir with vacuum assisted drainage is completely closed towards the ambient air. To avoid an increasing vacuum with de- creasing blood level, as will be the case with already known pressure regulating equipment, it is imperative that the pressure regulator is able to reduce an underpressure which exceeds the predetermined value. By introducing a 2-way control of the vacuum, the risk of collapse of the vein, in which the catheter is inserted, is reduced, and also the risk of damage of

the blood cells or formation of micro bubbles in the blood is minimized. These drawbacks may admittedly be avoided by manual intervention such as disruption of the vacuum in the reservoir, but such manual intervention requires extraordinary attention from the operator and is subjected to the occurrence of human errors, as such intervention is often necessary in connection with other events requiring special atten- tion.

The pressure regulator according to the invention is a separate unit which by means of a tube or in another manner is connected with the reservoir and which comprises a component group consisting of a pressure registering means positioned in the connection to the reservoir and valve means positioned in the connection to the vacuum source and valve means in connection with the ambient air. In designing the pressure regulator as an independent, complete unit, which by means of a single tube is connected with the reservoir, the arrangement procedure prior to the operation is simplified, and the control thereof is simplified in relation to the control of frequently used operation equipment which comprises tubes for the individual functions and which are occluded by means of forceps or the like.

According to the invention the pressure regulator may be designed as an electronic regulator as stated in claim 3. The preferred embodiment is, however, mechan- ical and comprises the measures stated in claim 4. The use of a balanced slide valve of the type which is commonly used in hydraulic installations ensures a wide regulation range and a high sensitivity on account of the outbalanced pressure forces in the varying pressure levels. The design moreover contributes to making the

regulation insensitive to fluctuations in the pressure of the vacuum source.

The regulation of the set value takes place as stated in claim 5 by means of a control handle which is adapted to displace the counter-stop of a spring outbalancing the pressure difference on the two sides of the membrane. The regulation may in practice take place by means of a thread such that the control handle may be turned several revolutions between the two distal positions.

According to the invention the slide valve is a cylindrical slide valve.

According to the invention the pressure regulator further comprises safety valves as stated in claim 7.

These safety valves are preset on values which would otherwise represent a life-threatening condition for the patient, should they be transgressed. These valves will in most cases represent a supplement to other possibilities which surgeons establish or will not bar themselves from using, but contribute, by their pres- ence, to simplifying the setup of the equipment prior to a surgical operation.

The invention will be described in detail in the following with reference to the drawing, in which Fig. 1 shows a strongly schematic arrangement for a heart surgical operation and with a diagram of the pressure regulator according to the invention inserted in chart form, Fig. 2 is a sectional view through an embodiment of the pressure regulator according to the invention, and Fig. 3 is a diagrammatical view of an electronic embodiment of a pressure regulator according to the invention.

In the operational arrangement shown in Fig. 1, a patient is indicated by 1, said patient undergoing a heart operation, in which the heart function is taken over via a circuit outside the patient. By means of a catheter inserted in Vena Cava Superior at some place in the venous system of the patient, the blood is drained to a reservoir 2 by means of a tube connection 3. In the reservoir 2, the blood is filtered by means of a tube connection 3. In the reservoir the blood is normally filtered in an exterior filter 4. In the reservoir 2, a blood level 5 adjusts, and from the reservoir blood is via a pump 6 introduced through an oxygenator 7 provided with means for controlling the temperature of the blood back to the arterial circuit of the patient through a tube 8. A driving force in the drainage of blood through the tube 3 derives from a height difference h between the patient 1 and the reservoir 2. By using comparatively thin and resilient tubes, this height difference is, however, not suffi- cient for ensuring a stable and sufficient blood flow.

It is therefore common practice by means of a vacuum in the reservoir 2 to establish a supplement to the effect of the height difference. In such a vacuum unassisted drainage, care is taken that the reservoir is closely sealed in respect of the surroundings, i. e. the connec- tions to the surroundings are kept capped.

The vacuum used in such operations is normally kept at a level of 0-100 mm Hg to avoid damage to the blood cells, release of dissolved gases forming micro bubbles, which are most damaging to the patient, and to avoid a collapse of the vein in the area in which the tube is inserted. The vacuum is established on basis of the installation which is normally available in oper- ation rooms, i. e. by means of a controllable pressure reducing valve. For reduction of the pressure in the

general installation, accurately functioning pressure reducing valves are available. These valves do not, however, eliminate the risk that the vacuum, on account of falling blood level in the reservoir 2, may be increased beyond the level preset. The invention provides a pressure regulator which eliminates this risk, the regulator establishing a 2-way regulation maintaining the predetermined vacuum irrespective of fluctuations in the liquid level. This function is in practice an essential help for the operator which is to maintain the external and internal blood circuit of the patient stable during a surgical operation.

Fig. 1 shows a diagram of a pressure regulator according to the invention. The pressure regulator is built into a housing 9 and comprises a connection branch 10 in connection with the reservoir 2. The connection branch 10 is connected with a vacuum switch- off setting the regulator in function. From the switch- off 11 a main duct 12 leads to the various components of the regulator. A branching leads to a manometer displaying the preset vacuum. A second branch leads to safety valves 14 and 15 adapted to ensure that the vacuum does not transgress a predetermined limit value and that a superpressure does not occur in the reser- voir 2. The function of the reduction valve is per- formed by a slide valve 16 controlled by a membrane 17 which on one hand is influenced by the preset vacuum via the tube and on the other hand by the ambient pressure. The vacuum is adjusted by means of a spindle 19 actuating a spring 20 biassing the force from the membrane 17. The spindle 19 is turned by means of a control handle 21. The valve slide 16 is provided with a recess defined by guiding edges which bar openings to a circuit 22 connected with a vacuum source and to a connection 23 to the ambient air.

Fig. 2 is a sectional view of a practical embodi- ment of the pressure regulator according to the inven- tion. In Fig. 2, references identical with those in Fig. 1 have been used as far as possible. The necessary connection ducts are substantially bored or milled in two plane component blocks 24 and 25, between which a membrane serving as a packing has been clamped. The design makes it simple to make a periodical check of the functions of the regulator and to exchange the mem- brane, which at the same time serves as a sealing in the safety valves 14,15 and between the component blocks.

The diagram according to Fig. 3 is a schematic veiw of the regulator according to the invention. The connection 28 to the reservoir 2 is provided with a branching for a pressure transducer 29 emitting a signal to a signal regulator 30 via an amplifier 30.

The signal regulator emits a control current to two magnet valves 32 and 33 which are connected with the ambient air and a vacuum source, respectively. The electronic design depends on a current supply, but is basically equivalent to the design according to Figs 1 and 2. On account of the electronic design the pressure regulation may according to Fig. 3 be further developed with electronic monitoring or be adapted to receive additional control signals from external control systems which may for example be a part of the monitor- ing of the patient's condition.