WO1991004067A1

WO1991004067A1 - A method of and apparatus for monitoring gas

Info

Publication number: WO1991004067A1
Application number: PCT/GB1990/001465
Authority: WO
Inventors: William Odita Tarnow-Mordi
Original assignee: The University Court Of The University Of Dundee
Priority date: 1989-09-23
Filing date: 1990-09-21
Publication date: 1991-04-04
Also published as: AU6409490A

Abstract

Apparatus for monitoring gas from a ventilator is described in which a sensor is provided in a sensing chamber (103) which is in gaseous communication with a gas supply conduit (102) which supplies gas from the ventilator to a patient. The gaseous communication (11) between the chamber (103) and the conduit (102) enables gas from the conduit (102) to enter the sensing chamber (103) and subsequently to re-enter the conduit (102). Typically, a baffle (15) is provided to divert a portion of the gas in conduit (102) into the chamber (103) and a heater coil (107) may also be provided to ensure that the temperature of the gas in the vicinity of the sensor is above the dewpoint of the gas.

Description

_[ Method of and Apparatus for Monitoring Gas"

This invention relates to a monitoring apparatus, and in particular to a monitoring apparatus for artificial ventilation.

Artificial ventilation of patients must be carefully monitored to ensure that the air being inspired by the patient is at the correct setting: the flow rate, the ratio of gases in the mixture and the temperature and humidity of the inspired air must all be regulated. In particular, regulation of the humidity of gas reaching the lungs is important.

For example, in adults inadequate humidification of inspired gas results in increased viscidity of secretions, decreased ciliary activity and mucus flow and reduced static compliance. In babies, the consequences of inadequate humidification may be severe, resulting in a ten-fold increase in the risk of endotracheal obstruction.

Conversely, excessive humidification of inspired gas may cause fever and fluid overload by eliminating normal respiratory heat and water losses. Newborn or premature babies are particularly at risk.

Apparatus has been proposed for monitoring the relative humidity of the gas entering the infant, but its measurements depend on tapping a small amount (3-4%) of gas from the gas supply and feeding this through an electronic hygrometer and its associated thermistor. Consequently the sample size is small and the readings may be inaccurate.

According to the present invention there is provided apparatus for monitoring gas from a ventilator, comprising a gas supply conduit and a sensor for sensing one or more parameters of the gas, the sensor being in communication with the conduit so that in use a portion of the gas flowing in the conduit is diverted from the conduit to the sensor and thence re-joins the conduit.

Further according to the present invention there is provided a method of monitoring gas from a ventilator, comprising diverting a portion of the gas flowing from the ventilator, sensing one or more parameters of the portion and allowing the portion of gas to re-join the flowing gas.

The gas supply conduit may be a line which supplies a mixture of air and oxygen to a patient receiving respiratory support from the ventilator. The sensor may be disposed in a sensing chamber.

The conduit may be adjacent the sensing chamber and in communication with the chamber through a branch of the conduit. Most preferably the conduit and the sensing chamber share a mutual wall which is cut away to provide a 'window' through which the gas from the conduit has access into and out of the sensing chamber. Preferably the flow rate of the gas ensures that this occurs in a turbulent fashion to ensure a good mix and give accurate sampling. A baffle or other obstruction may be provided in the conduit to cause positive diversion of a portion of the gas to the sensor.

Preferably, the sensor comprises a probe. The probe may be attached to apparatus which measures physical parameters such as relative humidity and temperature. Such apparatus may be an electronic hygrometer and a thermistor.

Preferably, the gas at the sensor is at a temperature that exceeds its dewpoint. This avoids condensation which may lead to inaccurate measurement. Most preferably the temperature is from 37 to 40 degrees C.

A heating coil may be provided to ensure the temperature of the gas is higher than its dewpoint. The heating coil is preferably wrapped around the sensing chamber, and may also be wrapped around the ^' conduit in the vicinity of the sensing chamber.

Embodiments of the invention will now be described with reference to the drawings in which:-

Fig. la is a side view of a first embodiment of monitoring apparatus of the present invention; Fig. lb is a cross-sectional view along A-A of Fig. la; Fig. 2a is a side view of a second embodiment of monitoring apparatus of the present invention; Fig. 2b is a cross-sectional view along B-B of 1 Fig. 2a;

2 Fig. 3 is an end view of the monitoring apparatus

3 of Fig. 2a;

4 Figs. 4a, 4b and 4c are an end view, a

5 cross-sectional view and a plan view, respectively

6 of the sensing chamber of Fig. 2a;

7 Figs. 5a, 5b and 5c are an end view, a

8 cross-sectional view and a plan view, respectively

9 of the air line of Fig. 2a; and,

10 Figs. 6a and 6b is a sectional side view and an

11 end view, respectively of the electrical connector

12 of Fig. 2a. 13

14 Figs, la and lb show a first embodiment of a monitoring

15 apparatus 1 for inflowing gas for an incubator. The 6 apparatus comprises a gas supply conduit in the form of

17 a gas line 2 which conveys a mixture of air and oxygen,

18 and a sensor in the form of a probe 4 which is located

19 at one end 5 of a sensing chamber 3. The sensing

20 chamber 3 is blocked off at its other end 6. The

21 sensing chamber 3 is wrapped in an insulated heating

22 coil 7 which heats the gas to 37°C and is attached to

23 the gas line 2 through tubes 8 which branch off the gas

24 line 2 and allow passage of gas in and out of the

25 chamber 3. The heating coil 7 is electrically

26 connected by a socket 9 to an external power source

27 (not shown) . 28

29 A second embodiment of monitoring apparatus is shown in

30 Fig. 2a and corresponding parts are labelled as in the 3: first embodiment plus 100, i.e. 1 = 101. In the

3. apparatus 101 a gas line 102 and a sensing chamber 103

33 share a mutual wall 10 which has a section missing to

34 form a window 11 (see Fig. 2b). The gas line 102 and

35 the chamber 103 are both wrapped in an insulated coil 107 and a socket 109 (see also Fig 3)is provided to heat both the gas line 102 and the chamber 103 to the same temperature. The gas line 102 is shown in more detail in Figs 5a to 5c and is a tube which has an internal diameter which is narrower than the internal diameter of the chamber 103. As shown in Figs 2b, 5a and 5b and in phantom in Fig 2a, a baffle 15 is located in the line 102 and diverts air from the line 102 into the sensing chamber 103 through the window 11. The chamber 103 is blocked at one end 106 and its other end 105 is used to admit a probe (not shown). Figs. 4a to 4c show the sensing chamber 103 in more detail and Fig. 4b shows that the sensing chamber 103 is internally threaded at 12 and the probe has a corresponding thread to enable the probe to be screwed into the sensing chamber 103.

The probe is connected to an electronic hygrometer and its associated thermistor (not shown). The thermistor and the humidity sensor are combined and may be, for example, a VAISALA (Trade Mark) humidity and temperature probe. As shown in Fig. 3 an insulating jacket 13 is wrapped around the socket 109 and Figs. 6 and 6a show how the socket 109 is fitted into its jacket 13.

Because the chamber 103 and the gas line 102 are side by side, gas flowing along the line is subjected to high turbulence as it moves in and out of the chamber. A high percentage of the gas flow is therefore available for sensory measurement. In the first embodiment there is no significant difference between gas in the chamber or the flow line because of the short length of the tube 8. The diameter of this tube 8 compared to the diameter of the gas line 2 is approximately 2:5 in Fig. la.

Because both embodiments provide a closed loop between the gas line 102 and the sensing chamber 103, loss of pressure in the gas line, which may adversely affect the baby, is prevented.

Modifications and improvements may be incorporated without departing from the scope of the invention.

Claims

1. Apparatus for monitoring gas from a ventilator comprising a gas supply conduit (2;102) and a sensor (4) for sensing one or more parameters of the gas, the sensor (4) being in communication with the conduit (2;102) so that in use a portion of the gas flowing in the conduit (2;102) is diverted from the conduit (2;102) to the sensor (4) and thence re-joins the conduit (2;102).

2. Apparatus according to Claim 1, wherein the gas supply conduit (2;102) is a line which supplies a gas mixture of air and oxygen to a patient receiving respiratory support from the ventilator.

3. Apparatus according to Claim 1 or Claim 2, wherein the apparatus further comprises a sensing chamber (3;103) and gas communication means (8:11)between the sensing chamber (3;103)) and the gas supply conduit (2), and wherein the sensor (4) is disposed in the sensing chamber (3;103).

4. Apparatus according to Claim 3, wherein there is a common wall (10) between the gas supply conduit (102) and the sensing chamber (103) and the gas communication means comprises an aperture (11) in the common wall (10).

5. Apparatus according to any of the preceding Claims, wherein the apparatus further comprises a baffle (15) located in the gas supply conduit (102) and which diverts a portion of the gas in the conduit (102) to the sensor.

6. Apparatus according to any of the preceding claims, and further comprising a heating coil (7;107) adjacent to the sensor.

7. A method of monitoring gas from a ventilator comprising diverting a portion of gas flowing from the ventilator, sensing one or more parameters of the portion of the gas and allowing the portion of the gas to re-join the flowing gas.

8. A method according to Claim 7, the method further comprising providing a sensing chamber (103) in gas communication with the flowing gas and sensing the one or more parameters in the sensing chamber (103).

9. A method according to Claim 7 or Claim 8 wherein the flow rate of the flowing gas is such that the gas flow is turbulent.

10. A method according to any of Claims 7 to 9, and further comprising heating the gas in the vicinity of the sensor to above the dewpoint of the gas.