WO2013064183A1

WO2013064183A1 - Apparatus for ventilating a patient

Info

Publication number: WO2013064183A1
Application number: PCT/EP2011/069278
Authority: WO
Inventors: Christoph Manegold; Jürgen KORTHAUER
Original assignee: Ac Aircontrols Gmbh
Priority date: 2011-11-03
Filing date: 2011-11-03
Publication date: 2013-05-10
Also published as: DE112011105813T5

Abstract

Oxygen and pressurized air are fed to the adjustable mixing valve device (5), which allows for setting the desired oxygen content in the supply duct (6). The volume flow in the supply duct (6) is controlled using an adjustable valve device (8). The binary gatekeeper valve (10a) is controlled for intermittent supply of pressurized gas to the main inlet (12) of the venturi (11). In order to achieve decelerating flow profiles, a proportional valve (10b) is used. From the outlet (14) of the venturi (11), the inspiration gas is fed to the patient port (16). An injection duct (19) bypassing the venturi (11) is provided for intermittent injection of oxygen from the cylinder (1) to the patient port (16). The injection valve (20) allows controlled injection of oxygen during an initial phase of the inspiration phase. Through the recirculation duct (22) exhaled gas is fed to the side inlet (13) of the venturi (11) for recirculating. An absober unit (23) reduces the concentration of carbon-dioxide in the recirculated exhalation gas.

Description

APPARATUS FOR VENTILATING A PATIENT

Technical Background The present invention relates to an apparatus for ventilating a patient, in particular to a ventilation apparatus comprising a source of pressurized gas, a venturi with a main inlet, a side inlet and an outlet, a supply duct for supplying the pressurized gas to the main inlet of the venturi and a ventilation duct for establishing a connection between the outlet and a patient port.

Ventilation of patients is important in many medicinal settings, e.g. in connection with anesthesia during surgery, in intensive care and emergency care. For the various fields of application, many different types of ventilators have been developed over time, in particular, among others, ventilation apparatus of the type initially mentioned. In emergency ventilation, usually ambient air is drawn in as a second gas component via the side inlet of the venturi, through which the pressurized gas is led functioning as a propellant gas. If pure oxygen is used as the propellant gas, which usually is the case, an average oxygen concentration arises from the partial flows of the pure oxygen as the first gas component and the ambient air as the second gas component at the gas outlet of the venturi. Since pure oxygen as a propellant gas is the first gas component, it is utilized optimally, and the volume of the oxygen cylinder typically used as the source of pressurized gas can be kept as small as possible. However, the oxygen concentration in the gas mixture can be changed to a limited extent only. At small volume flows of oxygen the venturi cannot produce a sufficient suction flow for fluid dynamic reasons, and high volume flow can only be generated by increased inflow of oxygen from the oxygen cylinder. Therefore, a certain minimum flow of oxygen is required not only defining a lower limit of oxygen concentration but also implicating a higher consumption of oxygen than desired in certain situations. In particular, when a patient is to be ventilated over a longer period of time, consumption of oxygen can become a limiting factor. US 6,830,048 discloses a ventilator with a plurality of differently sized Venturis in order to allow a desired concentration of the first gas component, which is provided as the pressurized gas, to be achieved at different volume flows of the resulting gas mixture. However, the principle limitation remains, that the consumption of pressurized (first component) gas cannot be reduced below a certain minimum level in relation to the required total volume flow. In use, low consumption of pressurized gas is particularly important for transport ventilation, when a ventilated patient needs to undergo transport for a longer period of time, because both space and payload are limited in vehicles, helicopters and airplanes typically used for patient transport. It thus highly desirable to avoid the need for carrying extra pressurized gas cylinders.

Further, not only consumption of pressurized gas is to be kept as low as possible in the field of long-distance patient transport, but keeping energy consumption of the ventilator as low as possible is also an issue. State of the art vehicles, helicopters and airplanes typically used for patient transport are usually equipped with a variety of other electrically powered devices such as patient monitors, air condition, refrigerating devices etc. This makes it desirable to design onboard equipment, such as ventilators, with energy-saving technology.

The practical use of conventional state of the art ventilators designed for transport ventilation is typically limited to time spans of approximately four or five hours. This makes it difficult or even impossible to transport patients over longer distances in regions where lack of appropriate infrastructure slows down transport or requires larger detours. Such problems may particularly arise in developing countries, in disaster areas or in war zones. But even if an appropriate infrastructure is available, long distance transport of a patient may be necessary e.g. for reaching a specialized treatment facility in a sparsely populated country or in order to bring a patient to a hospital located closer to his family or the like. Intercontinental flights in particular are a challenge for transport ventilation or even impossible under reasonable effort using conventional ventilation technology.

Similar problems may arise for stationary use of ventilators where consumption of pressurized gas and energy can be an issue e.g. due to application at a secluded location, extraordinary circumstances such as a post catastrophic situation, use in a provisional military hospital facility or the like. Generally, regular supply of pressurized gas requires a functioning infrastructure, yet the probability for severe patient conditions requiring ventilations may be higher in situations, where the infrastructure is impaired

Summary of the Invention

It is therefore an object of the present invention to allow for ventilating a patient keeping the consumption of pressurized gas - in particular oxygen consumption, where applicable - as low as possible. It is further desirable, to keep energy consumption low for ventilating a patient.

Though the present invention can be used in connection with various applications of patient ventilation, its main focus is use in emergency ventilation and transport ventilation, in particular over long distances and/or in situations, when supply of energy and/or pressurized gas is limited.

According to one aspect of the present invention, an apparatus of the type initially mentioned comprises a recirculation duct for recirculating exhaled gas from the patient port (such as an endotracheal tube or respiratory mask) to the side inlet of the venturi.

In other words, according to the present invention recycles exhaled air in that the venturi draws air from the recirculation duct rather than, or in addition to, from ambient air. This results in a reduction of necessary oxygen supply as the oxygen concentration in exhaled air is still considerable.

According to an advantageous embodiment of the present invention, the source of pressurized gas is a first source of pressurized gas, and the apparatus further comprises a second source of pressurized gas. Preferably, the oxygen concentration of gas from the first source is lower than the oxygen concentration of gas from said second source. In particular the first source may advantageously be source for pressurized air and the second source a source for pressurized oxygen.

According to a particularly advantageous embodiment, the supply duct comprises a mixing valve device for adjusting a ratio between gas from the first source and gas from the second source to enter said supply duct. Thus, a propellant gas with a lower, prefarably adjustable, oxygen content than known from the prior art can be used. As a side note, and according to another aspect, this concept of providing a ventilator of the type initially mentioned, wherein the supply duct comprises a mixing valve device for adjusting a ratio between gas from a first source of gas and gas from a second source of gas with an oxygen content higher than the gas from the first source to enter said supply duct, per se can be highly advantageous.

Preferably, the mixing valve device comprises a mixing valve and an actuator, e.g. a step motor, for adjusting the mixing valve. It is thus possible to adjust the gas composition, in particular the oxygen concentration, of the propellant gas and, in consequence, of the ventilation gas at the outlet within fully discretionary limits. Various mixing valve types known per se from the prior art can be adavantageously employed for the mixing valve device.

In a particularly preferred embodiment of the present invention, an injection duct is provided for supplying pressurized gas from the second source to the patient port bypassing the venturi, wherein the injection duct comprises a controlled injection valve for allowing intermittent injection of the pressurized gas, usually oxygen, from the second source. Preferably, the apparatus further comprises means for determining a defined phase of an inspiration cycle of the patient and a controller for controlling the injection valve to allow injection of the pressurized gas from the second source only during the defined phase. It is thus possible to avoid enriching inspiration gas filling dead volume (such as ventilator tube, respiratory mask, mouth, trachea and bronchi) with oxygen but rather enrich mainly the inspiration gas actually reaching the alveoli with oxygen. In most cases, said defined phase will be the initial phase of the inspiration phase. In this manner, the amount of oxygen fed from the second source can be greatly reduced. According to another advantageous embodiment of the present invention, the apparatus comprises means for temporarily increasing the flow of pressurized gas to the patient port for performing a recruitment maneuver. Recruitment techniques in connection with ventilation devices based on which the skilled person can implement a suitable recruitment procedure are referred to and described in WO 2005/102432 Al , i.e. recruitment techniques as such can be implemented essentially as known from the prior art.

Ventilatory recruitment maneuvers serve the purpose of "re-opening" so-called "collapsed" lung areas, i.e. making alveoli available for oxygen exchange that have become inactive (e.g. as a reaction to high oxygen supply). Recruitment maneuvers include a controlled increment in airway pressure until the opening airway pressure is reached, i.e. the airway pressure at which the closed (or "collapsed") areas of the lung start opening. Afterwards, mechanical ventilation reassumes baseline ventilation with a level of positive end-expiratory pressure (PEEP) higher than the lung's closing pressure (i.e. airway pressure at which opened areas start closing again).

Preferably, in the embodiment suitable for performing a recruitment maneuver, a bypass duct for temporarily supplying the pressurized gas to the patient bypassing the venturi is provided as well as means for controlling the supply through the bypass duct for performing the recruitment maneuver. Therein, it is not necessary (yet possible) to design the bypass duct in a manner allowing the entire gas volume required for the recruitment maneuver to be fed through the bypass duct. Instead, it is usually preferable to feed a major fraction of the gas volume required for the recruitment maneuver through the supply duct including the venturi and only a remaining fraction of the required gas through the bypass duct.

In a particularly preferred embodiment with two sources of pressurized gas and an injection duct as described above, which is suitable for performing a recruitment maneuver (as described above as well) a joint duct is shared by the bypass duct and the injection duct thus simplifying construction of the apparatus.

In a particularly preferred embodiment of the apparatus according to the present invention, the supply duct comprises adjustable valve means for adjusting volume flow though the supply duct. Various valve types known per se from the prior art can be adavantageously employed for the adjustable valve means. However, it is particularly advantageous to provide valve means comprising a valve bank with a plurality of binary valves, preferably latch valves. It is a major advantage of latch valves that they require power only for switching but keep their respective present state without consuming power.

According to another preferred embodiment, the supply duct comprises a gatekeeper valve for intermittent supply of said pressurized gas to the main inlet of the venturi. Depending on the specific desired application conditions, the gatekeeper valve may advantageously be implemented employing proportional valve means, binary valve means or a combination of both.

According to another particularly advantageous embodiment, the venturi is adjustable, wherein preferably an actuator, such as a step motor, is provided for adjusting the venturi. Various means for adjusting a venturi a known in the prior art, from which the skilled person will readily choose a variant suitable for the particular application intended.

According to another particularly advantageous embodiment, the apparatus is adapted to selectively provide the flow of pressurized gas to the patient employing a time variant flow profile, i.e. a flow profile with a non-constant flow during the inspiration phase. Preferably the flow profile is selectable from a decelerating flow profile or a non-decelerating flow profile. Generally, the apparatus can advantageously be adapted to offer a plurality of selectable flow profiles.

In a particularly preferred embodiment, the recirculation duct comprises means for reducing in the exhaled gas the concentration of a gaseous component thereof, preferably means for withdrawing carbon-dioxide, e.g. absorber means, a wash bottle or the like. In a preferred embodiment, the recirculation duct comprises a passive feed valve for feeding ambient air to the recirculation duct, as required. Optionally, a controlled valve can be provided.

Preferably, the recirculation duct comprises an excess pressure relief valve. In an advantageous embodiment, the apparatus further comprises an adjustable PEEP (positive end expiratory pressure) valve for adjusting a maximum positive end-expiratory pressure.

According to a particularly preferred embodiment, the apparatus is installed in a powered patient transport means, such as a vehicle, airplane or helicopter.

According to another aspect, the present invention generally provides for a method of ventilating a patient, wherein exhaled gas is recirculated for ventilation and gas with a concentration of oxygen which is higher than the concentration of oxygen in ambient air is injected into the ventilation gas during a defined phase of an inspiration cycle of the patient.

Preferably, carbon-dioxide is withdrawn from said exhaled gas.

In a particularly advantageous application, the method is carried out during transportation of said patient.

In a particularly advantageous application, the method is carried out over a period longer than four, six or even eight hours, thus allowing, e.g., patient ventilation even in intercontinental flights.

Generally, any of the embodiments described or options mentioned herein may be particularly advantageous depending on the actual conditions of application. Further, features of one embodiment may be combined with features of another embodiment as well as features known per se from the prior art as far as technically possible and unless indicated otherwise.

In the following, the invention is described in more detail. The accompanying drawings, which are schematic in nature, serve for a better understanding of the features of the current invention. Corresponding elements are provided with corresponding reference numerals.

Brief Description of the Drawings In the enclosed drawings,

Fig. 1 is a flow sheet of an example of a first preferred embodiment of the present invention, and

Fig. 2 is a flow sheet of an example of a second preferred embodiment of the present invention.

Detailed Description of Advantageous Embodiments

In Fig. 1, an oxygen cylinder 1 is provided as a first source of pressurized gas and a pressurized air cylinder 2 is provided as a second source of pressurized gas. Via respective pressure regulators 3, 4 the oxygen and pressurized air are fed to the mixing valve device 5, which is adjustable to allow for setting the desired oxygen content in the supply duct 6 within the range of, for example, 21% to 100 %. An oxygen sensor 7 is provided for measuring the concentration of oxygen in the supply duct 6. The volume flow in the supply duct 6 is controlled using an adjustable valve device 8. In the depicted example, a valve bank comprising five binary valves 9a, 9b, 9c, 9d, 9e, 9f with a throughput of two, four, eight, 16, 32 and 18 liters per minute, respectively, serves as adjustable valve device 8. In this example, binary valves 9a, 9b, 9c, 9d, 9e, 9f are provided as latch valves requiring no supply of energy for keeping the current state "open" or "close", respectively, but requiring a supply of energy for switching only. The binary gatekeeper valve 10a is controlled for intermittent supply of pressurized gas from the supply duct 6 to the main inlet 12 of the venturi 11. The supply can thus be interrupted for exhalation and resumed for inspiration. Preferably, for saving energy, the gatekeeper valve 10 is also of the latch valve type.

For additionally adjusting the flow through the venturi, a proportional valve 10b is used. A control duct 32 comprising a (proportional) piezo valve 33 is employed for adjusting the proportional valve 10b. In the example depicted in Fig. 1, the oxygen cylinder 1 serves as source of pressure for the control duct 32. Downstream from the piezo valve 33 the control duct 32 is branched in a first branch 32a for adjusting the proportional valve 10b and a second branch 32b for controlling the PEEP valve 21 described herein-below. The first branch 32a comprises a combination of an adjustable throttle 34 and a leak throttle 35 blowing off to the ambient air. The leak flow through the leak throttle 35 can be kept very low within a range of only few milliliters per minute.

In addition or as an alternative to controlling the flow through the main inlet 12 in the manner described above, adjustment of the venturi 11 can be achieved, for example, employing an adjustable inlet orifice at the main inlet 12 and/or side inlet 13, respectively, and/or employing a moveable displacer in the venturi and/or a plurality of binary switchable side inlets provided instead of single side inlet 13. For adjusting a venturi 11 which itself is adjustable in such a manner, an electrical step motor may be used as an actuator.

From the outlet 14, the inspiration gas is fed to the patient port 16 through the flexible tubing 15a. A self-controlled over-pressure release valve 17 avoids sytem over-pressure to exceed a predetermined threshold, e.g. 100 mbar.

The patient port 16 can be implemented employing a respiratory mask, an endotracheal tube or the like. Close to the patient port 16 or integrated therein is a sensor unit 18 for providing pressure and flow measurements.

An injection duct 19 bypassing the venturi 11 is provided for intermittent injection of oxygen from the cylinder 1 to the patient port 16. The injection valve 20 is configured to allow controlled injection of oxygen during a defined phase, typically an initial phase of the inspiration phase. The injection valve 20 can be time-controlled or volume-controlled or both, i.e. open during a defined time span or until a given integral throuput has been reached in the present inspiration phase. Preferably, for the purpose of saving energy, the injection valve 20 is also of the latch valve type and can be powered (like the gatekeeper valve 10a) by pressure of the air cylinder 2 (as shown for the gatekeeper valve 10) or of the oxygen cylinder 1.

Preferably, the oxygen is led all the way to the patient port separately from the gas coming from the outlet 14 of the venturi 11. However, it may be possible (and even advantageous in some cases, e.g. in order to enable use of conventional tubing) to implement a joint duct uniting the gas flows from the outlet 14 and the injection duct 19. Particularly advantageous is a hose-in-hose arrangement with an oxygen injection hose 15b belonging to the injection duct being arranged within a supply hose 15c. The exhalation hose 15d may be integrated in a joint tubing 15a as well or provided separately.

A controlled valve functions as PEEP valve 21. Preferably, the PEEP (positive end expiratory pressure) is adjustable to a high PEEP for recruitment maneuvers and to a lower PEEP for regular operation. As indicated above, the PEEP valve 21 can be controlled employing the second branch 32b of the control duct 32. Thus, the piezo valve 33 functions as a control valve for both the venturi 11 and the PEEP valve 21. This is possible since controlling the venturi 11 is required only during inspiration and controlling the PEEP valve 21 is required only during expiration. Through the recirculation duct 22 exhaled gas from the patient port 16 is fed to the side inlet 13 of the venturi 11 for recirculating. An absober unit 23 reduces the concentration of carbon-dioxide in the recirculated exhalation gas. The absorber unit 23 comprises a disposable absorber cartridge 24 filled with a suitable dry or wet C0₂-absorbing medium as known per se from the prior art. Check valves 26 and 27 with a counter-pressure of, in the depicted example, 2 mbar and 4 mbar, respectively, may be provided in the recirculation duct 22 for ensuring the desired direction of flow and avoiding over-pressure or under-pressure, respectively. A passive feed valve 28 (e.g. set to a feed pressure of -2 mbar) is provided for feeding ambient air to the recirculation duct 22 in order to compensate volume losses due to withdrawl of carbon-dioxide and in order to react to volume-flow changes of propellant gas in the venturi 11. An adjustable throttle 25 can be used to control the recirculated volume flow through the side inlet 13 of the venturi 11. A step motor 36 can be used as an actuator for controlling the adjustable throttle 25.

An optional bypass duct 29a, 29b may be provided in order to temporarily supply additional gas volume to the patient port for performing a recruitment maneuver.

In one embodiment, the bypass duct 29a and the injection duct 19 may share, in part, a joint duct 30, thus enabling the injection valve 20 to be used in controlling a recruitment maneuver. A three-way valve 31a is used in this embodiment to connect the joint duct 30 either with the oxygen cylinder 1 (for oxygen injection) or with the pressurized air cylinder 2. If the three- way valve 31a is configured to allow intermittent interruption of both the flow from the oxygen cylinder 1 and the pressurized air cylinder 2, it may double as injection valve thus making a separate injection valve 20 dispensable.

In an alternative embodiment, the bypass duct 29b may branch of from the supply duct 6 downstream of the mixing valve device 5 and upstream of the adjustable valve device 8. A controllable three-way valve device 31b is configured to allow intermittent feeding of the bypass duct 29b leaving at the same time the supply duct 6 open. In order to limit the pressure to which the patient's lungs are subjected when the bypass duct 29b is open, suitable pressure limiting means 37 may either be intergrated in the three-way valve device 31b or otherwise be provided in bypass duct 29b, e.g. comprised by additional proportional valve means.

As in Fig. 1, in Fig. 2 there is also provided an oxygen cylinder 1 as a first source of pressurized gas and a pressurized air cylinder 2 as a second source of pressurized gas. Via respective pressure regulators 3, 4 the oxygen and pressurized air are fed to the mixing valve device 5, which is adjustable to allow for setting the desired oxygen content in the supply duct 6 within the range of, for example, 21% to 100 %. An oxygen sensor 7 is provided for measuring the concentration of oxygen in the supply duct 6.

The volume flow in the supply duct 6 is controlled using an adjustable valve device 8. In the depicted example, a valve bank comprising five binary valves 9a, 9b, 9c, 9d, 9e, 9f with a throughput of two, four, eight, 16, 32 and 18 liters per minute, respectively, serves as adjustable valve device 8. In this example, binary valves 9a, 9b, 9c, 9d, 9e, 9f are provided as latch valves requiring no supply of energy for keeping the current state "open" or "close", respectively, but requiring a supply of energy for switching only. The binary gatekeeper valve 10a is controlled for intermittent supply of pressurized gas from the supply duct 6 to the main inlet 12 of the venturi 11. The supply can thus be interrupted for exhalation and resumed for inspiration. Preferably, for saving energy, the gatekeeper valve 10a is also of the latch valve type. By operation of the binary gatekeeper valve 10a, a square flow profile of the supply of pressurized gas to the patient can be achieved.

For additionally adjusting the flow through the venturi, in particular in order to achieve decelerating flow profiles of the supply of pressurized gas to the patient, a proportional valve 10b is used. By selectively using either binary valve 10a or proportional valve 10b, two principle modes of operation can be selected, i.e. a first mode with a substantially time invariant flow in the inspiration phase (square flow profile controllable by binary valve 10a) and second mode with a flow that varies over the inspiration phase (in particular a decelerating flow profile). In operation, as an example, said first mode may advantageously be used for emergency ventilation and said second mode for transport ventilation.

A control duct 32 comprising a (proportional) piezo valve 33 is employed for adjusting the proportional valve 10b. The piezo valve 33 thus acts as a control valve of the active state. In the example depicted in Fig. 2, the oxygen cylinder 1 serves as source of pressure for the control duct 32. The control duct 32 is branched at the first selector valve 38 in a first branch 32a for adjusting the proportional valve 10b and a second branch 32b for controlling the PEEP valve 21 described herein-below. The second selector valve 39 allows to selectively vent the first branch 32a or the second branch 32b.

The control duct 32 further comprises a combination of an adjustable throttle 34 and a leak throttle 35 blowing off to the ambient air. The leak flow through the leak throttle 35 can be kept very low within a range of only few milliliters per minute.

In addition or as an alternative to controlling the flow through the main inlet 12 in the manner described above, adjustment of the venturi 11 can be achieved, for example, employing an adjustable inlet orifice at the main inlet 12 and/or side inlet 13, respectively, and/or employing a moveable displacer in the venturi and/or a plurality of binary switchable side inlets provided instead of single side inlet 13. For adjusting a venturi 11 which itself is adjustable in such a manner, an electrical step motor may be used as an actuator. From the outlet 14, the inspiration gas is fed to the patient port 16 through the flexible tubing 15a. A self-controlled over-pressure release valve 17 avoids sytem over-pressure to exceed a predetermined threshold, e.g. 100 mbar.

An injection duct 19 bypassing the venturi 11 is provided for intermittent injection of oxygen from the cylinder 1 to the patient port 16. The injection valve 20 is configured to allow controlled injection of oxygen during a defined phase, typically an initial phase of the inspiration phase. The injection valve 20 can be time-controlled or volume-controlled or both, i.e. open during a defined time span or until a given integral throuput has been reached in the present inspiration phase. Preferably, for the purpose of saving energy, the injection valve 20 is also of the latch valve type and can be powered (like the gatekeeper valve 10a) by pressure of the air cylinder 2 (as shown for the gatekeeper valve 10) or of the oxygen cylinder 1. Preferably, the oxygen is led all the way to the patient port separately from the gas coming from the outlet 14 of the venturi 11. However, it may be possible (and even advantageous in some cases, e.g. in order to enable use of conventional tubing) to implement a joint duct uniting the gas flows from the outlet 14 and the injection duct 19. Particularly advantageous is a hose-in-hose arrangement with an oxygen injection hose 15b belonging to the injection duct being arranged within a supply hose 15c. The exhalation hose 15d may be integrated in a joint tubing 15a as well or provided separately.

A controlled valve functions as PEEP valve 21. Preferably, the PEEP (positive end expiratory pressure) is adjustable to a high PEEP for recruitment maneuvers and to a lower PEEP for regular operation. As indicated above, the PEEP valve 21 can be controlled employing the second branch 32b of the control duct 32. Thus, the piezo valve 33 functions as a control valve for both the venturi 11 and the PEEP valve 21. This is possible since controlling the venturi 11 is required only during inspiration and controlling the PEEP valve 21 is required only during expiration.

Through the recirculation duct 22 exhaled gas from the patient port 16 is fed to the side inlet 13 of the venturi 11 for recirculating. An absober unit 23 reduces the concentration of carbon-dioxide in the recirculated exhalation gas. The absorber unit 23 comprises a disposable absorber cartridge 24 filled with a suitable dry or wet C0₂-absorbing medium as known per se from the prior art. Check valves 26 and 27 with a counter-pressure of, in the depicted example, 2 mbar and 4 mbar, respectively, may be provided in the recirculation duct 22 for ensuring the desired direction of flow and avoiding over-pressure or under-pressure, respectively. A passive feed valve 28 (e.g. set to a feed pressure of -2 mbar) is provided for feeding ambient air to the recirculation duct 22 in order to compensate volume losses due to withdrawl of carbon-dioxide and in order to react to volume- flow changes of propellant gas in the venturi 11. An adjustable throttle 25 can be used to control the recirculated volume flow through the side inlet 13 of the venturi 11. A step motor 36 can be used as an actuator for controlling the adjustable throttle 25.

The entire system as illustrated in Fig. 1 or Fig. 2 can advantageously be integrated in an ambulance car, a patient transport plane, a rescue helicopter or a lifesaving cruiser.

As indicated above, other advantageous configurations can also be implemented within the scope of the present invention. For example, a joint valve unit incorporating the functions of both the mixing valve device 5 and the adjustable valve device 8 can be provided. If such a joint valve unit is configured with two adjustable inlet valves (connected with the oxygen cylinder 1 and the pressurized air cylinder 2, respectively) and two adjustable outlet valves (connected with the inlet 12 of the venturi 11 and the bypass duct 29b, respectively), such a joint valve unit could in addition incorporate the function of the three-way valve 31b In Fig. 1.

Claims

Apparatus for ventilating a patient, comprising

- a source of pressurized gas,

a venturi, which comprises a main inlet, a side inlet and an outlet,

- a supply duct for supplying said pressurized gas to said main inlet of said venturi a ventilation duct for establishing a connection between said outlet and a patient port,

characterized in that

said apparatus further comprises a recirculation duct for recirculating exhaled gas from said patient port to said side inlet.

Apparatus according to claim 1 , wherein said source of pressurized gas is a first source of pressurized gas, and said apparatus further comprises a second source of pressurized gas.

Apparatus according to claim 2, wherein the oxygen concentration of gas from said first source is lower than the oxygen concentration of gas from said second source.

Apparatus according to claim 2 or claim 3, wherein said supply duct comprises a mixing valve device for adjusting a ratio between gas from said first source and gas from said second source to enter said supply duct.

Apparatus according to claim 4, wherein said mixing valve device comprises a mixing valve and an actuator for adjusting said mixing valve.

Apparatus according to any of claims 2-5, further comprising an injection duct for supplying pressurized gas from said second source to said patient port bypassing said venturi, wherein said injection duct comprises a controlled injection valve for allowing intermittent injection of said pressurized gas from said second source.

7. Apparatus according to claim 6, further comprising means for determining a defined phase of an inspiration cycle of said patient and a controller for controlling said injection valve to allow injection of said pressurized gas from said second source only during said defined phase.

8. Apparatus according to any of the preceding claims, further comprising means for temporarily increasing the flow of pressurized gas to said patient port for performing a recruitment maneuver.

9. Apparatus according to claim 8, further comprising a bypass duct for temporarily supplying said pressurized gas to said patient bypassing said venturi and

means for controlling said supply through said bypass duct for performing said recruitment maneuver.

10. Apparatus according to claim 6 or claim 7, further comprising a bypass duct for temporarily supplying said pressurized gas from said first source to said patient bypassing said venturi and

means for controlling said gas supply through said bypass duct for performing a recruitment maneuver.

wherein a joint duct is shared by said bypass duct and said injection duct.

11. Apparatus according to any of the preceding claims, wherein said supply duct comprises adjustable valve means for adjusting volume flow though said supply duct.

12. Apparatus according to claim 11, wherein said adjustable valve means comprise a valve bank with a plurality of binary valves.

13. Apparatus according to claim 12, wherein said binary valves are latch valves.

14. Apparatus according to any of the preceding claims, wherein said supply duct comprises a gatekeeper valve for intermittent supply of said pressurized gas to said main inlet of said venturi.

15. Apparatus according to any of the preceding claims, wherein said venturi is adjustable.

16. Apparatus according to claim 15, further comprising an actuator for adjusting said venturi.

17. Apparatus according to any of the preceding claims, wherein said apparatus is adapted to provide said flow of pressurized gas to said patient employing a time-varying flow profile.

18. Apparatus according to claim 17, wherein said apparatus is adapted to selectively provide said flow of pressurized gas to said patient employing a decelerating flow profile or a non-decelerating flow profile.

19. Apparatus according to any of the preceding claims, wherein said recirculation duct comprises means for reducing in said exhaled gas the concentration of a gaseous component of said exhaled gas.

20. Apparatus according to claim 19, wherein said means for reducing are means for withdrawing carbon-dioxide.

21. Apparatus according to any of the preceding claims, wherein said recirculation duct comprises a passive feed valve for feeding ambient air to said recirculation duct.

22. Apparatus according to any of the preceding claims, wherein said recirculation duct comprises an excess pressure relief valve.

23. Apparatus according to any of the preceding claims, which further comprises an adjustable PEEP valve for adjusting a maximum positive end-expiratory pressure.

24. Apparatus according to any of the preceding claims which is installed in a self- propelled patient transport means.

25. Method for ventilating a patient, wherein exhaled gas is recirculated for ventilation and gas with a concentration of oxygen which is higher than the concentration of oxygen in ambient air is injected into the ventilation gas during a defined phase of an inspiration cycle of said patient.

26. Method according to claim 25, wherein carbon-dioxide is withdrawn from said exhaled gas.

27. Method according to claim 25 or 26, wherein said method is carried out during transportation of said patient.

28. Method according to any of claims 25-27, wherein said method is carried out over a period longer than four hours.