APPARATUS FOR IMPROVING THE DISTRIBUTION OF GAS

Abstract: When treating patients (2) with severely injured or sick lungs, there is often the problem of providing a life sustaining treatment without risking further damages to the lungs through the treatment itself. The apparatus according to the present invention is intended to be used for improving the distribution of gas in the lungs of a patient (2). The apparatus comprises means (24, 26A-B, 28) adapted to direct a controllable pressure to one or several selected positions on the patient's (2) thorax. In one embodiment of the apparatus, the means comprises a vest (24) which includes compartments which can be filled with a fluid under pressure from a pressure source (28) via tubes (26A-B).

Description: Description Apparatus for improving the distribution of gas The present invention relates to an apparatus for improving the distribution of gas in the lungs of a patient during respiratory treatment. Respiratory treatment is vital for many patients and has saved many lives over the years. The equipment, i. e. ventilators and respirators has been developed to be able to supply a number of different respiration modes with a high accuracy in supplied pressure and volume of breathing gas. When treating patients with severely ill (through sickness or injury) lungs, there is often the problem of providing a life sustaining treatment without risking damages on the lungs through the treatment itself. For many of these patients physicians are reluctant in providing higher pressures than 35 cmH2θ, as this was a limit proposed at a concensus conference in 1994. This pressure limit is intended for trans ural pressure, but is sometimes misinterpreted as the peak inspiratory pressure. The tidal volume for patients with severely sick or injured lungs is often very small, actually it may for an adult be as low as the tidal volume of a baby (hence the expression Baby lung syndrome) . Due to the condition of the lung, the pressure within different compartments of the lung may vary considerably and some compartments or clusters of alveoli may be collapsed. 2 A collapsed alveolus can be compared to a balloon. It requires a high pressure to even make it begin to inflate (open up) , but once its been opened up, a lower pressure is sufficient for further inflation. If the required pressure is supplied from a ventilator, other parts of the lung may be exposed to pressures that might cause overdistention (disrupting the important exchange of gas between the lungs and the circulatory system) or even barotrau a. When supplying breathing gas to the patient under a pressure which will not damage the lung, the gas will most likely be distributed to healthy parts of the lungs. This may cause the sick or injured parts of the lungs to deteriorate further. The gas exchange between the lungs and the circulatory system is better at the lower part of the lungs, close to the diaphragm. This is due to a better blood perfusion m these parts of the lungs. But since these parts are the most remote from the ventilator (or trachea) it takes more time for the gases m these lower parts to be transported out of the lungs and replaced with fresh gas. It would be beneficial to the patient, if the lower parts of the lungs could receive sufficient ventilation. It is therefore important to obtain an even distribution of supplied breathing gas m the lungs. Most patients are placed m a supine position during treatment. Visual monitoring of the patients condition by the staff, as well as access for other equipment, such as infusion apparatus, ECG apparatus, EEG apparatus, etc. is much better when the patient is in the supine position. Experiments have shown, that as many as 70o of patients with acute lung injury have improved gas exchange if they are placed m a prone position. The reason for this is believed 3 to be an improved distribution of gas from the upper part of the lungs to the lower parts of the lungs, due to decrease m chest wall compliance. As already stated, placing patients m a prone position is very impractical and may even impede other treatment. An object of the invention is to provide an apparatus which can be used for obtaining a more even distribution of gas in the lungs. The object is achieved through the invention m that the apparatus is constructed as stated m the characterising portion to claim 1. The object of the invention is also achieved m that the apparatus is constructed as stated m the characterising portion to claim 12. Advantageous improvements of the apparatus according to the invention are apparent from the depending claims. Basically, the apparatus according to the invention needs only be adapted to provide a pressure, or force on one or several specific positions on the patient's chest. Preferably on the upper part of the chest, on each side of the sternum (breastbone) . Naturally, the patient should be m a position which provides access to the chest. In its simplest considerable construction, the apparatus may even consist of a weight, shaped to be securely placed on the patient's chest. This would, however, require more staff for handling the apparatus. The more preferred embodiments, described below, does not need the same supervision from the staff. By providing a sufficient pressure of the chest wall by means of the apparatus, the transmural pressure gradient m the 4 lungs can be decreased, indicating that higher peak mspiratory pressures can be used. Thus, not only will the distribution of gas be improved, but higher peak pressures can also be supplied from a ventilator or respirator without increasing the risk of damaging the lungs. It should be noted that the apparatus according to the invention is different from known CPR-apparatus, which include some kind of means for providing heart massage by applying force on or near the sternum, above the heart. CPR is used when the heart has stopped and thus presents a completely different situation. The CPR systems are therefore not suitable for improving the distribution of gas m the lungs . In US 4,676,232 a system for promoting blood circulation is described. This system basically comprises a device which encloses the patients chest and abdomen. The device prevents the chest and abdomen from expanding during respiration, thereby forcing the lungs to expand "inwardly", m particular against the heart. By correlating respiration phases with heart beats, the pressure on the heart will increase, resulting m an increase m stroke volume of the heart. In similarity with systems of providing respiration by enclosures around chest and abdomen, the known system is not suitable for improving the distribution of gas m the lungs. For the apparatus according to the invention, it is most beneficial to supply the pressure m synchronicity with inspiration phases, during which the pressure applied on the chest could be varied according to predetermined patterns. Any such pattern could be set by a physician before onset of inspiration, or be controlled by the physician during inspiration. Automation is also possible, if the gas pressure within the lung is measured at several locations within the 5 lungs. Or by obtamg measurements reflecting the transmural pressure . During expiration, the pressure is preferably removed to allow normal exhalation from the patient. But it should be noted, that for some disease groups, it might be beneficial if pressure is delivered during expiration as well, e. g. as a continuous positive pressure. It is not necessary to apply the pressure during each respiratory cycle. The preferred embodiments of the apparatus according to the invention could have numerous shapes, all suitable for applying the pressure m a controlled and safe manner. In one embodiment of the invention, an arm is arranged over the bed, holding one or several mechanical actuators which can be brought into contact with the chest for supplying the pressure. The actuators could be bellows-shaped and pneumatically controlled, or telescopic and hydraulically controlled, or even a combination. The force could also be exerted by means of springs, pistons, gears or any other mechanical means. A very simple, but effective alternative, is to use a weight as actuator. The pressure is applied either by lowering the arm towards the chest, or by lowering the weight (by strings or similar means) . The actuator could be an integrated part of the arm, whereby both parts move in order to supply the pressure. The arm is therefore preferably made to be freely positionable m a number of positions for facilitating the positioning of the actuators on the chest. 6 In another embodiment a support in the shape of an arc above the patient is used instead of the arm. The actuator could basically be any of the actuators mentioned above. In a third embodiment a inflexible cover is placed across the chest. The cover comprises compartments which are utilised for generating the pressure on the chest. Basically, the cover could be a cloth, which is draped across the chest. The compartments above the positions to be pressurised could be filled with solid elements, for instance rubber. A system for tightening the cloth pulls the cloth tighter across the chest when the pressure is to be applied, whereby the elements will be pressed against the proper places on the chest. In the alternative, a pneumatic or hyraulic fluid system could be used for causing the elements to press against the chest with the controllable pressure. In another embodiment, the cover is made as a vest, which is worn by the patient. The vest includes compartments which can be pressurised by fluids, preferably a gas. The vest could also consist of a back plate, placed under the patient, and a front piece, which is securely stringed to the back plate at the sides of the patient. Different combinations of the disclosed alternatives is also possible, where applicable. Care should be taken not to expose the chest to too much strain or monotonous load. In particular, bed soars should be avoided by selecting proper application of the pressure. One way of doing this is to somewhat vary the position between eah pressure cycle. 7 In the following, embodiments of the invention will be described m more detail, with reference to the figures, whereby, FIG. 1 shows a first embodiment of the apparatus according to the invention, FIG. 2 shows a detail of the apparatus according to the first embodiment, FIG. 3 shows a second embodiment of the apparatus according to the invention, FIG. 4 shows a detail of the apparatus according to the second embodiment, FIG. 5 shows a third embodiment of the apparatus according to the invention, and FIG. 6 shows a detail of the apparatus according to the third embodiment. In FIG. 1 a patient 2 is shown lying on a hospital bed 4. The patient 2 is connected to a ventilator 6 via a tubing system 8 for receiving respiratory treatment. In order to improve the gas distribution within the lungs, and thereby improving the gas exchange between the lungs and the circulatory system, an apparatus for providing a controllable pressure on selected positions on the patient' s chest. The apparatus comprises a support 10A m the shape of an arm, which is firmly fixed to the bed and stretches up over the patient's 2 head and chest. A bellows system 12, which is described m greater detail m connection with FIG. 2 below, can be placed on selected positions on the chest. Preferably on the upper part of the chest, and with a small inclination from the breastbone. Pressurised gas is supplied from a gas source 14 via a tube 16 to the bellows system 12 at onset of an inspiration phase. This is controlled by using the control signal from the ventilator 6 itself. The supplied pressure could vary during the inspiration in any selected manner, depending on the condition of the patient 2 etc. The supplied pressure will cause the breathing gas supplied from the ventilator 6 to become more evenly distributed in the lungs, in particular towards the lower parts of the lung. The bellows system 12 comprise (FIG. 2) in this embodiment six bellows 12A, 12B, 12C, 12D, 12E, 12F, all connect to the arm 10 and the tube 16. By controlling a valve 18A, 18B, 18C, 18D, 18E, 18F which separates each bellow 12A, 12B, 12C, 12D, 12E, 12F from the tube 16, any selectable number of bellows could be filled with gas for supplying the pressure. By varying the positions in this manner, bed soars could effectively be avoided, even if pressure is supplied each inspiration phase. In FIGs. 3 and 4 a second embodiment of the apparatus is shown. In this case, the apparatus comprises a support 10B in the shape of an arc above the patient 2. The arc 10B is firmly attached to the bed 4, as can be seen more clearly in FIG. 4. From the arc 10B, two piston shaped actuators 22A, 22B are situated. The actuators 22A, 22B can be moved along the arc 10B in order to be positioned suitably at selected positions on the chest of the patient 2. The actuators 22A, 22B are so positioned, that they activate their exertion of pressure on the chest in response to chest movements indicating the onset of an inspiration. The actuators 22A, 22B are equipped with pressure sensors (not shown) . In FIGs. 5 and 6 a third embodiment of the apparatus is shown. In this embodiment the apparatus is made as a vest 24, which is placed on the patient 2. The vest includes in this case two compartments 30A, 30B which can selectively be 9 filled with pressurised fluid, preferably gas, via gas tubes 26A, 26B from a gas source 28. The vest 24 could be tightened on the patient 2 via a string 32. The vest 24 is made m an inelastic, strong material to ensure that the pressure is directed to the chest. The vest 24 could alternatively be made to comprise two parts, a back piece, which is placed under the patient (and which may even constitute an integral part of the bed) , and a front piece, which is placed on the chest and attached to the back piece on both sides, e. g. with strings. The vest could also comprise several compartments, each fillable with a pressurised fluid. The compartments could include a solid plate directed towards the patient's 2 chest, whereby the plate is forced against the chest when the compartment is filled. The shown embodiments could be combined where appropriate. For instance, the bellows system 12 shown m the first embodiment could be used m the arc 10B shown m the second embodiment. The pressure can be obtained by utilising gravity on a weight, pneumatic means, hydraulic means, mechanical means or any other conceivable pressure generating means. Although the patient has be shown to be m a supine position in all embodiments, other positions are possible, as long as the chest is accessible for the apparatus.

Claims: 1 0 Cl aims 1. Apparatus for improving the distribution of gas m the lungs of a patient (2) during respiratory treatment, characterised by means (10A, 12A-F, 14, 16, 18A-F; 10B, 22A-B; 24, 26A-B, 28, 30A-B) adapted to direct a controllable pressure to one or several selected position (s) on the patient's (2) thorax. 2. Apparatus according to claim 1, characterised m that the means is adapted to vary the controllable pressure according to a predetermined pattern over one or several respiration cycles . 3. Apparatus according to claim 1 or 2, characterised m that the means is adapted to direct the pressure to the selected positions in synchronicity with inspiration phases. 4. Apparatus according to any of claims 1 - 3, characterised m that the means (10A, 12A-F, 14, 16, 18A-F; 10B, 22A-B) comprises a support (10A; 10B) , adapted to be mounted above the patient (2) and at least one mechanical actuator (12A-F; 22A, 22B) connected to the support (10A; 10B) and adapted to be brought m contact with the selected position for directing the pressure. 5. Apparatus according to claim 4, characterised m that the support is shaped as an arc (10B), spanning above the patient (2) from side to side. 6. Apparatus according to claim 4, characterised ι n that the support is shaped as an arm (10A), preferably attached to a head side of a bed (4) and stretching over the patient's (2) head and chest. 11 7. Apparatus according to any of the claims 4 - 6, characterised in that the mechanical actuator consists of a weight, stringed to the support. 8. Apparatus according to any of the claims 4 - 6, characterised in that the mechanical actuator (12A-12F; 22A, 22B) consists of an expandable element connected to the support . 9. Apparatus according to any of claims 1 - 3, characterised in that the means (24, 26A-B, 28, 30A-B) comprises an inflexible cover adapted to be secured across the thorax and including compartments (30A, 30B) which can selectively be pressurised for directing the pressure to the selective portions. 10. Apparatus according to claim 9, characterised in that the cover is shaped as a vest (24) . 11. Apparatus according to claim 9 or 10, characterised in that the compartments (30A, 30B) are connectable via valves to a source of pressurised fluid (28), whereby the pressure exercised by each compartment (30A, 30B) is controllable by supplying a controlled amount of fluid to each compartment (30A, 30B) . 12. Apparatus for improving the distribution of gas in the lungs of a patient (2) during respiratory treatment, characterised by first means (12A-F; 22A-B; 24) adapted to be placed on one or several selected position (s) on the patient (2)'s thorax, second means (14; 10B; 28) adapted to generate a controllable force and third means (16, 18A-F; 10B; 26A-B, 30A-B) adapted to direct at least part of the controllable force to the first means (12A-F; 22A-B; 24) .

Inventors: GATTINONI LUCIANO, GATTINONI, LUCIANO
Applicants: SIEMENS ELEMA AB, SIEMENS-ELEMA AB
Application year: 1999
Main classification: A61H31
IPC codes: A61H23, A61H31