GB2446495A - Respiratory humidify with threshold point controller system. - Google Patents

Abstract

A respiratory humidifier (1) comprises an input (3), into which input gas (2) to be moistened can be fed. Vapour (21) is mixed with the input gas (2) in a mixing chamber (4). Moistened output gas (5) flows out of an outlet (6). In the cases in which the temperature of the input gas (2) is so great that the temperature of the output gas (5) lies above a setpoint value, the internal setpoint value is adjusted. The output gas (5) can then cool down to the setpoint value on the path through an inhalation tube (7).

Description

Device and method for making available moistened respiratory gas The

invention relates to a device for making available moistened respiratory gas with a gas inlet, via which the input gas to be moistened can be fed, and with a gas outlet for the moistened output gas, as well as with a vapour or moisture supply, into which a liquid to be evaporated can be fed and which is provided with an evaporation device, eg an evaporator, which is controlled by a control device which adjusts the output temperature and the output moisture content of the output gas.

The invention further relates to a method for making available a moistened respiratory gas.

Such a device and such a method are known from DE 19808 590 Al. The known device is in particular a respiratory humidifier. The known respiratory humidifier has a respiratory gas line with a gas inlet, into which the input gas to be moistened can be fed, and a gas outlet from which the moistened respiratory gas is removed. The device also has an evaporation device, into which a liquid to be evaporated can be fed. The fed-in liquid is conveyed by means of a metering pump to an evaporator which evaporates the liquid to be evaporated and which feeds the generated vapour to the respiratory gas flowing in the respiratory gas line. The evaporation device is connected to a control device, which adjusts the output temperature and the output moisture content of the respiratory gas flowing out of the gas outlet. The output temperature and output moisture content can be regulated independently of one another. The evaporation device can for example comprise a metering pump, which conveys a quantity of liquid proportional to the volume flow of the respiratory gas through the respiratory gas line to an evaporation unit. The output temperature of the output gas can then be adjusted independently of the supplied quantity of liquid, in that the temperature of the evaporation unit is regulated in such a way that the vapour generated by the evaporator reaches a specific temperature and a mixture of respiratory gas and vapour arises which has the desired output temperature.

It should be noted, however, that the temperature of the vapour cannot lie below the boiling point of the liquid. In addition, there are hygiene regulations which require a vapour temperature above the boiling point of the liquid. This can lead to an excessively high output temperature arising at the gas outlet of the device, if the input temperature assumes excessively high values. This can occur, for example, when the respiratory gas is fed to the gas inlet of the respiratory humidifier with the aid of a fan or another pump device.

The present invention is as claimed in the claims.

The invention provides a device and a method for making available moistened respiratory gas, which enables a supply of heated respiratory gas.

In the device and the method of the present invention, the output temperature to be expected for a predetermined setpoint moisture content is determined by the control device. In the cases in which the temperature to be expected lies above a predetermined setpoint value for the output temperature, the output temperature is adjusted to a temperature above the setpoint temperature. Since the respiratory gas has to cover the path through the inhalation tube from the gas outlet of the device up to, for example, a so-called "V-piece" connected to the gas outlet, the raised output temperature at the gas outlet is harmless. This is because the output gas cools down on the path from the gas outlet to the V-piece to an extent such that the setpoint temperature is again reached at the V-piece.

The output temperature to be expected is preferably determined on the basis of a measured value of the input temperature. Although, in principle, it is possible to use empirical values for the input temperature, the measurement of the input temperature represents an additional safety feature, since the input temperature can vary depending on the ambient temperature.

Furthermore, the temperature to be expected is preferably determined as a function of the vapour temperature, which has been adjusted by the control device or detected with the aid of a temperature sensor. The latter offers the advantage that the temperature fluctuations of the vapour can be taken into account.

The determination of a temperature to be expected, furthermore, may be based on a minimum permissible vapour temperature. In cases in which the actual vapour temperature lies below a minimum permissible vapour temperature, therefore, the minimum permissible vapour temperature is used for the determination of the temperature to be expected.

Values for the temperature to be expected that are not permissible on the basis of hygiene regulations are thus avoided.

In order to ensure that the temperature of the output gas reaches the setpoint value by the desired point, eg the so-called Y-piece, the temperature of the output gas can be detected at the proximal end of the inhalation tube with the aid of a temperature sensor.

If the temperature of the output gas at the proximal end of the inhalation tube exceeds the predetermined setpoint value, the internal setpoint value, to which the output temperature of the output gas is regulated, can be lowered in steps until the temperature of the output gas at the proximal end of the inhalation tube essentially corresponds to the predetermined setpoint value of the output gas.

In addition, it is possible to reduce the heat input into the output gas by reducing, in steps, the quantity of water introduced into the output gas until the temperature of the output gas at the proximal end of the inhalation tube essentially corresponds to the setpoint value of the output gas.

Further features and advantages of the invention emerge from the following description, in which examples of embodiments of the invention are explained in detail with the aid of the appended drawings of which: Figure 1 is a schematic diagram of a respiratory humidifier, in which the output moisture content and the output temperature are regulated either jointly or separately; and Figure 2 is a flow chart of a method for controlling the respiratory humidifier of Figure 1.

Figure 1 shows a humidifier 1, with which inflowing respiratory gas 2 can be moistened.

lnf lowing respiratory gas 2 passes via a gas inlet 3 to a mixing chamber 4. Respiratory gas flowing out from mixing chamber 4 passes via a gas outlet 6 into an inhalation tube 7.

Outf lowing respiratory gas 5 thus passes via a distal end 8 of inhalation tube 7 to a proximal end 9 of inhalation tube 7, which is connected with its proximal end to a Y-piece not represented in Figure 1. Treated respiratory gas 10 finally passes from proximal end 9 of inhalation tube 7 via the Y-piece into the patient's respiratory tract.

Connected to mixing chamber 4 is a vapour line 11, which leads to an evaporator 1 2.

Arranged upstream of evaporator 12 is a metering pump 1 3, which delivers liquid from a liquid reservoir 1 4 to evaporator 1 2. The liquid is typically water or anaesthetic. Metering pump 13 and evaporator 12 are connected to a control device 1 5. Control device 15 adjusts the quantity of liquid fed to inflowing respiratory gas 2 and the temperature of the vapour, in such a way that outflowing respiratory gas 5 has a predetermined moisture content and a predetermined output temperature. Since inhalation tube 7 is usually heated, the moisture content and the temperature of the outf lowing respiratory gas can be retained on the path through inhalation tube 7, so that the moisture content and the temperature of respiration gas 10 at proximal end 9 of inhalation tube 7 are the same as the moisture content and the temperature of outflowirig respiratory gas 5.

In order to monitor the temperature of the vapour generated by evaporator 12, a vapour temperature sensor 16 is provided which is disposed in vapour line 11 and is connected to control device 1 5. A further input temperature sensor 17, which is disposed in the region of gas inlet 3, is provided in order to detect the temperature of inflowing respiratory gas 2.

An output temperature sensor 18 disposed in the region of gas outlet 6 is used to determine the temperature of outfiowing respiratory gas 5. Finally, the temperature of respiration gas 10 can be detected with a temperature sensor 19 which is located in the region of proximal end 9 of inhalation tube 7.

Finally, a flow sensor or flow meter 20 is also provided, which detects the volume flow of the inf lowing respiratory gas. Flow sensor 20 can also be disposed in the region of gas outlet 6 or at another suitable point, in order to determine the volume flow of the respiratory gas.

Humidifier 1 can be operated with various control regimes. A first possibility is to control the moisture content and the temperature of outfiowing respiratory gas 5 separately. In this case, metering pump 1 3 is adjusted by control device 15 in such a way that a quantity of water proportional to the volume flow of the respiratory gas is delivered to evaporator 12. The heat output of evaporator 1 2 is further controlled in such a way that the supplied quantity of water is evaporated and such that vapour is thereby generated with a vapour temperature which, during mixing with inflowing respiratory gas 2, leads to outflowing respiratory gas 5 with a predetermined temperature and moisture content.

In another control regime, the quantity of water fed per unit of time to the evaporator is changed according to the deviation of the temperature of outf lowing respiratory gas 5 from a setpoint value. This control concept requires that vapour 21 emerging from evaporator 1 2 has a vapour temperature that remains constant. This in turn requires that the temperature of evaporator 12 has a small error and that vapour 21 emerging from evaporator 12 assumes the temperature of evaporator 12. Both conditions are as a rule met in practice. With this control concept, changes in the temperature of outflowing respiratory gas 5 can be corrected by a change in the quantity of water fed by per unit of time to evaporator 1 2.

Both control concepts do however have their limits when the temperature of inflowing respiratory gas 2 assumes values which are so great that the setpoint value for the temperature of overflowing respiratory gas 5 can no longer be adhered to. This is because the temperature of water vapour 21 cannot at all events fall below the boiling point of water. In addition, hygiene regulations also have to be complied with in practice, which require for example that the temperature of water vapour 21 does not fall below 130 C.

Although, in principle, there is also the possibility of reducing the quantity of water fed per unit of time to evaporator 1 2 and thus of reducing the quantity of heat fed to inflowing respiratory gas 2, this leads to a reduction in the moisture content in outflowing respiratory gas 5, so that the lungs of the patient undergoing artificial respiration can become desiccated.

In order to avoid this risk, the various control concepts are modified according to figure 2.

In figure 2, the main process steps of a modified control process are represented, which can optionally be one of the two control methods.

The modification of the control method represented in figure 2 starts with a read-in step 22, in which various parameters are read in, insofar as they have not already been read in in previous process steps not represented in figure 2. In detail, predetermined setpoint value T8.0 is read in for the temperature of outflowing respiratory gas 5. Further parameters to be read in are mass mi of the quantity of liquid fed to evaporator 12, mass mgd of inflowing dry respiratory gas 2 and mass rn9 of the quantity of liquid contained in vapour form in inflowing respiratory gas 2. These measured quantities are detected, if need be, by suitable measurement sensors. Moreover, temperature T1of inflowing respiratory gas 2 is read in from input temperature sensor 17. Furthermore, a heating temperature Th is also determined, which in principle is equal to the heating temperature that is required in order that outf lowing respiratory gas 5 assumes setpoint value which however is at least equal to the boiling-point temperature of the liquid or the minimum temperature prescribed for reasons of hygiene.

A mixed temperature T8 to be expected for outf lowing respiratory gas 5 can be _m, clThm,-cdT1mX, c,7', m, c?+md*cd+mZ, ci calculated on the basis of these parameters: wherein c is the specific heat of vapour 21 of the liquid and Cd is the specific heat of dry inflowing respiratory gas 2.

The calculation of mixed temperature to be expected is based on the fact that the enthalpy of outfiowing respiratory gas 5, on account of the mixing process, is equal to the sum of the enthalpy of inflowing respiratory gas 2 and the enthalpy of supplied vapour 21.

Following calculation step 23, a branch step 24 takes place, in which it is ascertained whether output temperature T8-8 to be expected is greater than setpoint value Ta-sot for respiratory gas 5 that is to flow out.

If temperature T-to be expected is less than or equal to the predetermined setpoint value, the internal setpoint value is set to predetermined setpoint value T&sot in an allocation step 25, after which the control process can be continued.

If, on the other hand, T8.& to be expected is greater than predetermined setpoint value the internal setpoint value is set equal to temperature value T8-8 to be expected in allocation step 26.

If this is the case, temperature Tecc to be expected of outflowing respiratory gas 5 is used as the internal setpoint value for the control of the temperature of outflowing respiratory gas 5. Respiratory gas 5 flowing Out from gas outlet 6 then has a temperature which lies above predetermined setpoint value If, on the other hand, output temperature to be expected is not greater than setpoint value Ta-1, the temperature of outflowing respiratory gas 5 detected by output temperature sensor 18 is regulated to determined setpoint value Ta-set.

Consequently, the temperature of outfiowing respiratory gas 5 may lie above setpoint value Ta-set if temperature 1 of inflowing respiratory gas 2 assumes excessively high values. On the path through inhalation tube 7, however, outflowing respiratory gas 5 will dissipate heat if the heating of inhalation tube 7 is duly regulated. There is therefore the possibility of the temperature of outfiowing respiratory gas 5 falling to setpoint value Ta-set Upon reaching proximal end 9 of inhalation tube 7.

Moreover, in order to monitor the temperature of respiration gas 10 at proximal end 9 of inhalation tube 7, a respiratory gas temperature T of respiration gas 10 is determined by temperature sensor 1 9. In a branch step 27 arranged downstream of allocation step 26, an inquiry is made as to whether detected respiratory gas temperature T is greater than a setpoint value Tv-set of the respiratory gas temperature. If this is not the case, the control process is continued. Otherwise, in a reduction step 28, either the quantity of the liquid fed to evaporator 12 is reduced or the temperature of vapour 21 is lowered and finally the control process is continued.

It should be noted that the process steps represented in figure 2 can be repeated at periodic intervals.

Independently of the configuration of the control method that is used to control the moisture content and temperature of the output gas, it is advantageous if input temperature T1 of respiratory gas 2 flowing in at gas inlet 3 is known. Moreover, the volume flow should be determined, from which the mass flow can readily be determined when the pressure is known. In addition, the mass flow can also be determined directly with the aid of hot-wire gas mass meters or hot-film gas mass meters. In addition, the mass flow of inflowing respiratory gas 2 can be delivered by a respiratory apparatus. The mass flow of the liquid fed into evaporator 1 2 results either on the basis of the delivery capacity of metering pump 13 or can be deduced from characteristic curves which link the temperature of vapour 21 to the temperature of outfiowing respiratory gas 5 on the assumption of a specific input temperature 1.

Furthermore, it should be noted that, instead of metering pump 13 and evaporator 1 2, use can also be made of an evaporation device with a capillary pump with an integrated evaporator and a downstream heating device. In this case, the evaporation takes place in the capillary pump. The evaporated quantity of liquid depends here on the evaporation capacity of the capillary pump. The temperature of the vapour can then be brought, if need be, to a predetermined value by the downstream heating device.

The device described here and the method described here offer a number of advantages.

The triggering of an unnecessary alarm is avoided by the device and the method, since humidifier 1 also continues to operate when the temperature of outfiowing respiratory gas lies above the adjusted setpoint temperature. On the other hand, humidifier 1 can also be operated at high ambient temperatures and humidities. In particular, it is possible to feed inflowing respiratory gas 2 with the aid of a blower. Even if, for physical reasons, moisture can only be fed to a limited extent, excessively dry respiratory gas is avoided with the device, since sufficient moisture is still supplied as long as the temperature of respiration gas 10 at proximal end 9 does not exceed permitted threshold values.

According to a variant of the invention, vapour supply 11, 12, 1 3 is designed as a moisture supply, into which the quantity of liquid to be evaporated can be fed and which is provided with an evaporation device, which is controlled by a control device 15 which adjusts the output temperature and the output moisture content of respiratory gas 5, whereby control device 15 determines a temperature of output gas 5 to be expected with a given setpoint moisture content and whereby control device 15 adjusts the output temperature to a temperature above the setpoint temperature in cases in which the temperature to be expected lies above a setpoint value. Control device 1 5 is connected in particular to an input temperature sensor 17, with which the input temperature of inflowing respiratory gas 2 can be detected. In addition, the respiratory gas flow is optionally detected.

Finally, it should be pointed out that features and properties which have been described in connection with a specific example of embodiment can also be combined with the other exemplary embodiment, except when this is excluded for reasons of compatibility.

Finally, it should also be pointed out that the singular includes the plural in the claims and in the description, except when anything to the contrary emerges from the context. Both the singular and the plural are intended especially when the indefinite article is used. -11 -

Claims (20)

1. A device for making available moistened respiratory gas having a gas inlet, via which input gas to be moistened can be fed, and a gas outlet for the moistened output gas, as well as a moisture or vapour supply, into which a liquid to be evaporated can be fed and which is provided with an evaporation device, which is controlled by a control device which is arranged to adjust the output temperature and the output moisture content of the output gas and in which the control device is arranged to determine a temperature of the output gas to be expected with a given setpoint moisture content and that the control device and to adjust the output temperature to a temperature above the setpoint temperature in cases in which the temperature to be expected lies above a setpoint value.

2. The device according to claim 1, in which the control device is connected to an input temperature sensor with which the input temperature of the inf lowing respiratory gas can be determined.

3. The device according to claim 1 or 2, in which the control device is arranged to adjust the temperature of the vapour generated by the evaporation device.

4. The device according to any one of claims 1 to 3, in which the control device is arranged to determine the temperature to be expected by taking into account the minimum permissible vapour temperature.

5. The device according to any one of claims 1 to 4, in which the control device is arranged to regulate the output temperature to the temperature to be expected in cases in which the temperature to be expected lies above the setpoint value.

6. The device according to any one of claims 1 to 5, in which the control device is connected to a temperature sensor, with which the respiratory gas temperature of -12-respiration gas, which flows out from the proximal end of an inhalation tube connected to the gas outlet, can be determined.

7. The device according to claim 6, in which the control device is arranged to reduce the temperature of the vapour generated by the evaporation device when the respiratory gas temperature detected at the end of the inhalation tube exceeds a predetermined threshold value.

8. The device according to claim 6 or 7, in which the control device is arranged to reduce the quantity of liquid fed to the evaporation device when the respiratory gas temperature detected at the end of the inhalation tube exceeds a predetermined threshold value.

9. The device according to claim 7 or 8, in which the control device is arranged to control the evaporation device in steps.

10. A method for making available moistened respiratory gas, with the following process steps: a) feeding-in of input gas to be moistened into a gas inlet of a humidifier; b) feeding-in of liquid into a vapour supply of the humidifier and evaporation of the liquid with the aid of an evaporation device; c) mixing of the input gas with vapour to form a moistened output gas; d) conveying of the moistened respiratory gas out of a gas outlet of the humidifier; e) adjusting the output temperature and the output moisture content of the output gas with the aid of a control device connected to the evaporation device; f) determining an output temperature to be expected by the control device for a predetermined setpoint moisture content of the output gas; and g) adjusting the output temperature of the output gas by the control device to a temperature above the setpoint value in cases in which the output temperature to be expected exceeds a setpoint value.

-13 -

11. The method according to claim 10, in which the input temperature of the input gas is detected by the control device.

1 2. The method according to claim 10 or 11, in which the temperature of the vapour generated by the evaporation device is adjusted by the control device.

13. The method according to any one of claims 10 to 12, in which the temperature to be expected of the output gas is calculated by taking account of a minimum permissible temperature of the vapour generated by the evaporation device.

14. The method according to any one of claims 10 to 13, in which the temperature of the output gas is regulated to the temperature to be expected.

15. The method according to any one of claims 10 to 14, in which the respiratory gas temperature in the region of a proximal end of a line connected to the gas outlet is detected with the aid of a temperature sensor.

16. The method according to claim 15, in which the temperature of the vapour generated by the evaporation device is reduced when the respiratory gas temperature lies above a predetermined threshold value.

17. The method according to claim 15 or 16, in which the quantity of liquid evaporated in the evaporation device is reduced when the respiratory gas temperature lies above a predetermined threshold value.

18. The method according to claim 16 or 17, in which the reduction processes take place in steps.

19. A device for making available moistened respiratory gas substantially as hereinbefore defined with reference to, and/or as shown in, the accompanying drawings.

20. A method for making available moistened respiratory gas substantially as hereinbefore defined with reference to, and/or as shown in, the accompanying drawings. * ** * S S * ** S... * . S... * S * ..* * *S5 *..S * S* * . * e..

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20. A method for making avalable moistened respiratory gas substantialy as hei*before defined with reference to. and/or as shown in. the accompanying drawings.

Amendments to the claims have been filed as follows: 1. A device for making available moistened respiratory gas having a gas inlet, via which input gas to be moistened can be fed, and a gas outlet for moistened output gas, as well as a moisture or vapour supply, into which a liquid to be evaporated can be fed and which is provided with an evaporation device, which is controlled by a control device which is arranged to adjust the temperature and the moisture content of the output gas and in which the control device is also arranged to determine an expected temperature of the output gas with a given setpoint moisture content and to adjust the temperature of the output gas to a temperature above a predetermined setpoint temperature when the expected temperature of the output gas is above the predetermined setpoint temperature. * **

2. The device according to claim 1, in which the control device is connected to an input temperature sensor with which the input temperature of the input gas can be :. determined. *

3. The device according to claim 1 or 2, in which the control device is arranged to *: adjust the temperature of the vapour generated by the evaporation device. S..

4. The device according to any one of claims 1 to 3, in which the control device is arranged to determine the expected temperature of the output gas by taking into account the minimum permissible vapour temperature.

5. The device according to any one of claims 1 to 4, in which the control device is arranged to regulate the temperature of the output gas to the expected temperature when the expected temperature of the output gas is above the predetermined setpoint temperature.

6. The device according to any one of claims 1 to 5, in which the control device is connected to a temperature sensor, with which the proximal temperature of the output gas, at the proximal end of an inhalation tube connected to the gas outlet, can be determined.

7. The device according to claim 6, in which the control device is arranged to reduce the temperature of the vapour generated by the evaporation device when the proximal gas temperature of the output gas at the end of the inhalation tube exceeds a predetermined threshold value.

8. The device according to claim 6 or 7, in which the control device is arranged to reduce the quantity of liquid fed to the evaporation device when proximal temperature of * *. the output gas at the end of the inhalation tube exceeds a predetermined threshold value. * * * * ** S...

9. The device according to claim 7 or 8, in which the control device is arranged to control the evaporation device in steps. *

10. A method for making available moistened respiratory gas, with the following process : steps: a) feeding an input gas to be moistened into a gas inlet of a humidifier; b) feeding a liquid into the humidifier and evaporating of the liquid with the aid of an evaporation device to produce a vapour; C) mixing the input gas with the vapour to form a moistened output gas; d) conveying of the output gas out of a gas outlet of the humidifier; e) adjusting the output temperature and the output moisture content of the output gas with the aid of a control device connected to the evaporation device; f) determining an expected temperature of the output gas for a predetermined setpoint moisture content of the output gas; and g) adjusting the temperature of the output gas by the control device to a temperature above a predetermined setpoint temperature when the expected temperature of the output gas exceeds the predetermined setpoint temperature.

11. The method according to claim 10, in which the temperature of the input gas is determined by the control device.

12. The method according to claim 10 or 11, in which the temperature of the vapour generated by the evaporation device is adjusted by the control device.

13. The method according to any one of claims 10 to 1 2, in which the expected temperature of the output gas is determined by taking account of a minimum permissible temperature of the vapour generated by the evaporation device.

14. The method according to any one of claims 10 to 13, in which the temperature of * *. the output gas is regulated to the expected temperature of the output gas. * S S * .* S...

15. The method according to any one of claims 10 to 14, in which the proximal :*. temperature of the output gas in the region of a proximal end of a line connected to the gas * outlet is detected with the aid of a temperature sensor. S..

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* .. 16. The method according to claim 1 5, in which the temperature of the vapour generated by the evaporation device is reduced when the proximal temperature of the output gas lies above the predetermined threshold value.

17. The method according to claim 15 or 16, in which the quantity of liquid evaporated in the evaporation device is reduced when the proximal temperature of the output gas lies above a predetermined threshold value.

18. The method according to claim 16 or 17, in which the reduction of temperature of the vapour take place in steps.

19. A device for making available moistened respiratory gas substantially as hereinbefore defined with reference to, and/or as shown in, the accompanying drawings.