Abstract:
A device for reducing dead space in a ventilator system has a first tube connectable to the dead space in the ventilator system for producing a flow path for the transport of gas from dead space in the ventilator system, a suction device connected to the first tube for generating an adjustable negative pressure in the first tube, a second tube connectable to dead space in the ventilator system, for producing a flow path for the transport of gas to dead space in the ventilator system, a pump connected to the second tube for generating an adjustable positive pressure in the second tube, and a control unit which regulates the suction device and the pump. The suction device and the pump are formed by a first chamber and a second chamber, respectively, in an enclosure, separated by a gas-tight, moving partition. The control unit regulates the moving partition to regulate the suction device and the pump for achieving simpler and more reliable operation.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a device for reducing dead space in a ventilator system, as well as to a ventilator system employing such a device. 
     2. Description of the Prior Art 
     In the mechanical ventilation of a patient with a ventilator system (in intensive care, anesthesia etc.), an abnormal amount of dead space develops for the patient. The term “dead space” refers to the volume in which there is no gas exchange. As a result, expired gas in the dead space is returned to the patient at the next inspiration. The ventilator system&#39;s dead space mainly consists of the connection between a Y-piece and the patient (e.g. a tracheal tube and humidifier/heat exchanger and a measurement tube for measuring gas contents, flow, pressure etc.) Dead space can be relatively large, depending on the design of the ventilator system. 
     Since, as a rule, the last gas expired in every breath contains the highest concentration of carbon dioxide, the larger dead space causes greater re-breathing of carbon dioxide. 
     U.S. Pat. No. 5,400,778 describes a ventilator system containing a device for reducing the re-breathing of carbon dioxide. In one embodiment, gas is suctioned out of a tracheal tube while gas is delivered at the same time by the ventilator system through an inspiratory line. Additional gas can be supplied through additional connected lines, making it necessary to compensate the regulation of flows for the different volumes supplied to and evacuated from dead space. 
     Although the known device/ventilator system functions well, there is still a desire to achieve a device producing the same or equivalent effects with a simpler construction, especially with regard to control over-evacuated and delivered gas. Achieving a device that can be easily moved between different ventilator system, regardless of the design and application, would also be desirable. Another desire is to achieve a device that ensures simple maintenance of device functionality in the event of a power failure etc. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a device that fulfills one or more of the aforementioned desires. 
     The above object is achieved in accordance with the principles of the present invention in a device for reducing dead space in a ventilation system having a first tube connectable to dead space in the ventilator system for producing a flow path for transport of gas from the dead space, a suction unit connected to the first tube for generating an adjustable negative pressure in the first tube, a second tube connectable to the dead space for producing a flow path for transport of gas to said dead space, a pump connected to the second tube for generating an adjustable positive pressure in the second tube, the suction unit and the pump being formed respectively by a first chamber and a second chamber in an enclosure with the first and second chambers being separated by a gas-tight, movable partition, and a control unit for regulating the suction unit and the pump by moving the partition. 
     A suction unit connected to a pump is achieved in an embodiment wherein enclosure is provided with two chambers separated by a moving partition. The interconnected suction unit and pump unit make it possible to achieve simultaneous evacuation and delivery of a selected volume of gas in a simple and effective fashion. The chambers are connected to dead space via the tubes, and the entire device is compact and easy to transport and move between different kinds of ventilator systems. 
     The first chamber can be devised with an evacuation unit in order to empty the suction means when the movable partition moves back and forth. In the corresponding manner, the second chamber can be devised with a gas connection for delivering fresh gas. Here, the gas connector can be connectable to the ventilator system. This provides the advantage that no separate gas supply is necessary. 
     When equipped with a signal input for receiving signals, the device is able to receive signals from the ventilator system. Especially signals indicating where the ventilator is in the breathing cycle. The device is for activation primarily during the end phase of expiration (or during a pause following expiration) in order to reduce dead space in the ventilator system. 
     Information about the breathing cycle can alternatively be obtained from a flow meter arranged in the ventilator system&#39;s expiratory components. 
     Increased accuracy in maintaining a volume of evacuated gas of the same magnitude as the volume of gas delivered is achieved by connecting a first manometer to the first tube or first chamber and a second manometer to the second tube or second chamber. For additional accuracy, pressure in dead space can be determined, either by means of a signal from the ventilator system or by a separate, third manometer connectable to the ventilator system&#39;s dead space. When the prevailing pressure (and pressure gradient) is(are) known, the device can be controlled to ensure that the volumes evacuated and delivered are virtually identical. 
     The device can be completely integrated into a ventilator system. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a first embodiment of the inventive device connected to a ventilator system. 
     FIG. 2 shows a second embodiment of the inventive device connected to a ventilator system. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a general view of a device  2  according to the invention and a ventilator system  4 . Here the dividing line designates a possible division between the device  2  and the ventilator system  4 . This will be explained in detail below. 
     The ventilator system  4  can be connected to a patient  6  in order to facilitate, support or control the patient&#39;s  6  breathing. In principle, the ventilator system  4  here can consist of any breathing apparatus  8  that can be connected to an air-breathing creature (human or animal). A ventilator, respirator or an anesthetic machine in particular. The breathing apparatus  8  is equipped with a tubing system for connection to the patient  6 . In this instance, the tubing system comprises an inspiratory tube  10 , a patient connector  12  and an expiratory tube  14 . 
     The dead space of the ventilator system  4  consists almost entirely of the patient connector  12 . However, this is not the only volume which presents a re-breathing risk to the patient  6 . To this must be added some or all of the patient&#39;s  6  dead space. The amount of added dead space of the patient  6  depends on the type of patient connector  12  used. As a rule, tracheal tubes and tracheotomy tubes cause some of the dead space of the patient  6  to disappear, whereas face masks and nasal connectors do not, as a rule, affect the dead space of the patient  6 . The latter usually have a smaller dead space than the former, so the device according to the invention is most advantageous with patient connectors  12  such as tracheal tubes and tracheotomy tubes. 
     Other components can be connected to or be part of the patient connector  12 . Humidifiers and heat exchangers (usually referred to as HME&#39;s) and measurement channels for flow measurement and/or gas analysis are examples of such components. As a rule, these components increase dead space. 
     The device  2  according to the first embodiment has an enclosure  16  with an interior subdivided into a first chamber  18  and a second chamber  20  by a movable partition  22 . 
     The first chamber  18  is connectable to the patient connector  12  by a first tube  24 , and the second chamber  20  is connectable to the patient connector  12  by a second tube  26 . More exactly, the chambers  18 ,  20  are connectable to dead space. 
     The partition  22  is connected to a shaft  28  driven and regulated by a control unit  30  so it can be moved in a controlled manner. Any known power transmission unit, i.e. pneumatic, electromagnetic etc., is capable of actuating the shaft  28 . 
     These components would actually suffice in the simplest version of the device  2 . In an initial stage, the partition  22  could be arranged so the volume of the first chamber  18  is zero. The second chamber  20  could simultaneously be filled with fresh gas to a specific positive pressure in relation to an anticipated average pressure in dead space at the time of evacuation/replenishment. (In principle, this would correspond to the patient&#39;s  4  positive end expiratory pressure, i.e. PEEP.) In this position, the second chamber  20  would have a virtually maximal volume, e.g. two liters. The partition  22  could be moved a distance, for every evacuation/filling performed, corresponding to the volume to be evacuated from or added to dead space. With e.g. 20 milliliters as the volume to be withdrawn and replenished respectively, 100 evacuations/fillings could be performed (100 movement steps by the partition  22 ). It would then be necessary to detach the device  2  in order to return the partition  22  to its starting position (simultaneously emptying evacuated gas and supplying fresh gas.) A different number of evacuations/replenishments would naturally be needed with other volumes. 
     The timing of the point at which gas is withdrawn/replenished can be obtained from a signal input  32  for the control unit  30 . Information on the breathing cycles is sent from the breathing apparatus  8  to the control unit  30  via a signal line  44 . 
     However, the simplest version of the above would make it necessary for the device  2  to be devised with a relatively large volume. In addition, it would have to be periodically disconnected from the ventilator system  4 . Disconnecting the embodiment of the device  2  shown in FIG. 1 from the ventilator system  4  in order to remove evacuated gas and replenish with fresh gas would not be necessary. The device  2  according to FIG. 1 can therefore operate on a somewhat varied principle in which gas replacement takes place after each evacuation/replenishment. 
     The device  2  is accordingly devised with an evacuation unit  34  for the first chamber  18  and a gas connector  36  for the second chamber  20 . Evacuated gas can be discharged into atmosphere or connected to the expiratory tube  14  (preferably close to the breathing apparatus  8 , shown with a dotted line in FIG. 1) or some special device for collecting gas. The gas connector  36  is connected to the inspiratory tube  10  via a valve  38  and a gas reservoir  40 . The gas reservoir  40  is not inherently necessary. In many instances, especially when the ventilator system is devised for adult patients, the inspiratory tube  10  holds a sufficiently large volume of gas to fill the second chamber  20 . The risk of expired gas being sucked into the inspiratory tube  10 , thereby contributing to re-breathing of carbon dioxide, can be avoided by, e.g. adding a bias flow of gas through the inspiratory tube  10  and expiratory tube  14 . 
     When evacuation/replenishment are to occur, the partition  22  is moved forward (upward in FIG.  1 ), causing negative pressure to develop in the first chamber  18  and positive pressure to develop in the second chamber  20 . The pressure gradient between the respective chambers  18 ,  20  and dead space (the patient connector  12 ) gives rise to a flow of expired gas to the first chamber  18  and a flow of fresh gas to dead space. 
     After evacuation/replenishment have been concluded, the partition is returned to its starting position (advantageously in the end position against the first chamber  18 , i.e. at the bottom of FIG.  1 ). Evacuated gas is now forced out into atmosphere (or to a separate vacuum evacuation unit or to the expiratory tube  14 , which is suitable when the gas contains an anesthetic or other gases that should not be discharged directly) via the evacuation unit  34 . At the same time, the second chamber  20  is filled with fresh gas via the gas connector  36 . This can take place at a suitable point in the breathing cycle, e.g. during the introductory phase of an expiration (i.e. after the inspiratory phase following the evacuation/replenishment.) 
     The exact times for evacuation and replenishment respectively can vary in the patient connector  12  and even be arranged in the patient  4  below the patient connector  12 . Even if the figure schematically depicts evacuation closer to the patient  4  than replenishment, the reverse circumstance can be employed, i.e. replenishment of fresh gas closer to the patient  4  (or deeper inside the patient  4 ) than evacuation. 
     Even though evacuation/replenishment in each breathing cycle would be advantageous with movement of the partition  22  (e.g. from one end position to the other end position, like a piston stroke), a number of other options is conceivable if the volume to be withdrawn/replenished must be greater than the volume achievable with a partition movement. Thus, this implies that the entire device can be made very compact and operate continuously with a number of “piston strokes” for each breathing cycle. With a volume of 10 ml in every “piston stroke” and evacuation of 20 ml in each breathing cycle, for example, two “piston strokes” would be required etc. The advantage of a compact (small and light) device  2  is that it can be placed very close to the patient  4 , enabling the use of much shorter tubes  24 ,  26 . 
     It is evident that the size of the device  2  can vary considerably. The simple version previously described could conceivably hold up to 5 liters of fresh gas or more, whereas the compact version could hold a volume of fresh gas of 10 milliliters or less. Especially in respect to the smaller volumes, other ways of moving the partition are obviously available. For example, the partition could be a shuttle, activated by electromagnetic means, able to move between end positions. A roller membrane moved between two positions could work as well as a piston and possibly even display less friction resistance. In other words, all known pumping principles can be applied to this invention. 
     The valve  38  is intended for switching the gas outlet on the breathing apparatus  8  to enable the gas reservoir  40  (or second chamber  20 ) to fill with gas on a periodic basis, preferably during expiration phases. The valve  38  can be devised to divert only part of the total flow when diverting gas from the inspiratory tube  10  during the inspiratory phase. Or it can change the entire gas flow for brief periods of time. In some modern breathing machines  8 , the latter methods may present certain regulatory problems and the generation of needless alarms. This can be avoided by returning withdrawn gas to the expiratory line  14  from the evacuation unit  34 . This would then result in a closed system for the device  2  in relation to the breathing apparatus  8 . If the breathing apparatus  8  contains a separate second gas outlet, this outlet could be used. 
     The gas reservoir  40 , preferably formed by a bellows or some other variable-volume container, mainly makes it possible for the second chamber  20  to be filled to the same gas pressure (adjustable) in each replenishment. This gas pressure obviously does not need to be identical to the pressure of the gas diverted from the inspiratory line  10 . Compression or decompression can take place in the gas reservoir  40  before or in conjunction with the filling of the second chamber  20 . 
     For complete transferability between different ventilator systems  4 , the valve  38  should be part of the device  2  and devised as an adapter that can be connected onto the inspiratory line  10 . Here, it does not matter if the valve  38  is devised with a variable connection diameter or if the device  2  is equipped with multiple valves  38 , each of which devised for connection to a specific tube diameter (for the inspiratory line  10 .) 
     A first valve  42 A is arranged at the first tube  24 , a second valve  42 B is arranged at the evacuation unit  34 , a third valve  42 C is arranged at the second tube  26  and a fourth valve  42 D is arranged at the gas connector  36  to ensure that gases flow in the right direction. The valves  42 A,  42 B,  42 C,  42 D can be check valves. 
     A first manometer  46  is arranged to measure pressure in the first tube  24 , and a second manometer  48  is arranged to measure pressure in the second tube  26  in order to increase accuracy in ensuring agreement of the volumes withdrawn and replenished. In principle, one of the manometers  46 ,  48  may suffice, but two would convey additional reliability and accuracy. It should be noted that the manometers  46 ,  48  are by no means essential components. Sufficient accuracy can be achieved without them. 
     During periods in breathing cycles in which the device  2  is inactive (is evacuating/replenishing), flow is null in the tubes  24 ,  26 . Placement of the manometers  46 ,  48  in the tubes  24 ,  26  (instead of in the chambers  18 ,  20 ) makes it possible to even measure pressure in dead space (the patient connector  12 ). Measured pressure could therefore be used as an indication of the course of the breathing cycle, i.e. be used for determining when evacuation/replenishment should take place. 
     A second embodiment of the device  2 A is shown in FIG.  2 . Components and parts that can be identical have been retained with the same designations as in FIG.  1 . 
     The statements above in connection with FIG. 1 apply to the components that are identical therewith in FIG.  2 . In principle, the differences between the embodiments are as follows. 
     The device  2 A illustrates a separate gas source  50  for adding fresh gas to the second chamber  20 . The separate gas source  50  can consist of a gas cylinder, a compressor, a pump, a wall gas connection or ambient air. This conveys special advantages in cases in which a gas composition other than the one supplied by the breathing apparatus  8  must be initially supplied to the patient  6 . This other gas composition can be everything from another concentration composition of the gases (e.g. a higher concentration of oxygen) delivered by the breathing apparatus  8  to completely different compositions (medical gases, medication etc.) 
     A flow meter  52  is devised for placement in the expiratory line  14 , e.g. by means of a tube adapter. The flow meter  52  supplies information on the breathing cycles. The measurement signal is sent to the control unit  30  via a first measurement line  54 . 
     A third manometer  56  is arranged to measure the pressure in dead space. The measurement signal is sent to the control unit  30  via a second measurement line  58 . 
     There are further versions of means for controlling the device  2 ,  2 A in addition to those set forth above. 
     For example, the evacuation unit  34  can be connected to a vacuum source in order to achieve a constant negative pressure reinforcing the negative pressure generated in the first chamber  18  when the partition  22  moves. This can be used when large amounts of gas must be withdrawn or if the volume of replenished gas is harder to regulate because of the pressure of fresh gas at the gas connector  36 . 
     Alternatively, the evacuation unit  34  can be used to admit gas into the first chamber  18  at the same time as it sucks gas out of dead space. This can be used when small volumes are desired (instead of regulating stroke length, moving the partition  22  etc.) or if replenished gas is harder to regulate because of the pressure of fresh gas at the gas connector  36 . 
     Conversely, the gas connector  36  can be used in the corresponding fashion. In these functional versions, it would be advantageous (sometimes necessary) for one or more of the valves  42 A,  42 B,  42 C,  42 D to e adjustable valves rather than check valves. Adjustable valves may also be used if certain time delays are desired in evacuation/replenishment. For example, evacuation can be initiated a few milliseconds before replenishment and vice versa. 
     The two described embodiments (including described alternate versions) are fully combinable with respect to components and functions. 
     Another advantage of the device  2 ,  2 A is that the risk of an adverse impact on the lung is reduced (compensation is automatically made for evacuated gas, thereby avoiding hazardous negative pressure). 
     Humidification of the fresh gas has not been addressed above. In principle, gas evacuation could cause the extraction of moisture from the patient. Humidifying fresh gas in a known way before replenishment or after fresh gas is pumped into the patient connector  12  can compensate for this. In the device  2 A in FIG. 2, the gas supplied separately from a gas source  50  can be humidified gas. 
     The tubes  24 ,  26 , and their connection to the patient connector  12  can be devised in a number of ways. For example, the tubes  24 ,  26  may be catheters inserted into the patient connector  12  at the transition to the inspiratory line  10  and the expiratory line  14 . One of the tubes  24 ,  26  (the catheter) can then be introduced more deeply (into) the patient  4  than the other. If the first tube  24  is introduced more deeply into the patient, it can also transport mucous and secretion from the patient  4  (and accordingly make separate mucous removal unnecessary.) Alternatively, the patent connector  12  can be devised with channels for the different functions, and tubes  24 ,  26  can be connected to these channels. 
     A combination of the two (a catheter and a channel) is also possible. 
     It should be noted that e.g. tracheal tubes with multiple lumina are well-known in the ventilator field. 
     Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.