WO2016203211A1

WO2016203211A1 - Medical gas flow safety system

Info

Publication number: WO2016203211A1
Application number: PCT/GB2016/051753
Authority: WO
Inventors: Peter Jeffrey Young
Original assignee: Venner Medical Technologies Sa
Priority date: 2015-06-13
Filing date: 2016-06-13
Publication date: 2016-12-22
Also published as: GB201510384D0

Abstract

The present invention relates to a medical gas flow safety system. A gas flow or pressure generator (1) provides a medical gas flow (2) to the at least one gas outlets of a nasal cannula (5). The system comprises a means for preventing or reducing a gas flow (3) to the at least one gas outlets of a nasal cannula (5) upon application of a face mask (6). The application of the face mask (6) being applied to a section (4) of a gas delivery tube which delivers the medical gas from the gas flow or pressure generator (1) to the at least one outlet of a nasal cannula (5).

Description

Medical Gas Flow Safety System

The invention relates to a medical gas flow safety system. The invention more specifically relates to a medical gas flow safety system adapted to prevent pressure exceeding a predetermined safe level at the outlet of a medical gas delivery system.

Formation of an airway by tracheal intubation is critical prior to performing surgical procedures. Endotracheal tubes are used to provide such airways and are often inserted with the assistance of a laryngoscope. This process involves insertion of the laryngoscope and subsequent guiding of a flexible endotracheal tube into the trachea. The laryngoscope is then removed and ventilation of the lungs provided through the endotracheal tube.

During normal pre-operative intubation, pre-oxygenation is performed using a nasal cannula and/or a face mask. A patient will then receive anaesthesia and neuromuscular blockade. An anaesthetist has a finite window, known as the apnoeic time or apnoeic window in which to intubate the patient. During this time, the patient cannot breathe on their own and are reliant upon oxygen already circulating in the bloodstream or residual oxygen remaining within the alveoli. Therefore, intubation of a patient must be performed swiftly in order to prevent hypoxaemia which occurs due to oxygen desaturation of the blood.

If there are difficulties during the intubation and the time spent attempting intubation exceeds a safe apnoeic window, then intubation may have to be abandoned and oxygenation using a nasal cannula and/or a face mask recommenced. Successive cycles of attempted intubation followed by re-oxygenation only serve to exacerbate the difficulties of successfully intubating the patient.

The regulation of pressure in the nasal cannula and/or facemask providing pre- oxygenation or re-oxygenation is important to ensure rapid oxygenation of the blood.

The Transnasal Humidified Rapid-Insufflation Ventilation Exchange (THRIVE) method described by Patel and Nouraei in the journal of the Association of Anaesthetists of Great Britain and Ireland, Anaesthesia (Anaesthesia, 2015 vol. 70(3) pp. 323-9), has been shown to increase apnoea times in patients with difficult airways and allowed for continuous oxygenation (apnoeic oxygenation) during tracheal intubation. The technique uses high flow oxygen delivered by nasal cannula at 60-80 1 min^"1 which remained in situ during laryngoscopy. THRIVE enables safe apnoea times of up to 1 hour without ventilation.

In light of these advantages, this and other methods using high flow delivery devices have become useful for delivery of oxygen enriched medical gases to critically ill patients and more recently to improve oxygenation of patients prior to and during induction of or emergence from anaesthesia. It is desirable in some circumstances for a face mask to be used over the top of the nasal cannula. The face mask is commonly shaped and/or has a cushioned interface to allow a seal over facial variations and medical tubes and the like. If a face mask is applied over an oxygen delivery nasal cannula however, with the high flow delivery occurring at the same time through the nasal cannula, pressures at the face and in the patient's upper airway increase to unsafe levels and can cause pressure injury or barotrauma to the upper airway, ears or lungs and may cause gas to pass to the patient's oesophagus and stomach, all of which are undesirable. Even with pressure controlling elements within anaesthetic apparatus attached to the face mask, the high flow rates from the high flow delivery systems are sufficient to risk stomach insufflation.

A second problem is that when a face mask is applied the clinician may wish to provide breaths of positive pressure ventilation to the patient and ensure that recognisable waveforms of carbon dioxide are produced on a capnograph within the face mask breathing system or circuit. A nasal cannula with gas flow being delivered through an outlet at the face or nostrils will interfere with normal face mask ventilation and impede a clinician's ability to ensure the airway is open and interfere with the capnograph trace due to dilution of the expired gases.

Another problem relates to the concurrent use of inhalation anaesthetic agents administered by face mask. In this situation with nasal cannula in place and high flow gas concurrently flowing, the anaesthetic agent may be diluted and risk lightening of anaesthesia or awareness.

The invention described herein seeks to overcome at least the above-mentioned problems.

According to a first aspect of the invention, there is provided a medical gas flow safety system comprising means for preventing or reducing a gas flow to at least one gas outlet of a nasal cannula upon application of a face mask. Preventing or reducing the gas flow to the at least one outlet of a nasal cannula upon application of a face mask is advantageous because it prevents a pressure increase in a patient's trachea that can lead to unsafe pressure levels which may cause pressure injury or barotrauma to the upper airway, ears or lungs and may cause gas to pass to the patient's oesophagus and stomach.

Preferably, the gas flow is a high gas flow. This system is particularly useful for high flow medical gas delivery systems.

Preferably, the means for preventing or reducing a gas flow to at least one gas outlet of a nasal cannula is a pressure sensitive relief valve that vents the gas flow to at least one gas outlet of a nasal cannula to the atmosphere upon application of the face mask. This is advantageous as it relives pressure already in the system upon application of a face mask. Relieving the pressure already in the system reduces the risk of reaching unsafe pressure levels within the patient's trachea and oesophagus.

Preferably, the medical gas flow safety system comprises means for switching off the gas flow upon application of the face mask. This is advantageous as it prevents a further increase in pressure by further flowing gas to the at least one gas outlet of a nasal cannula upon application of a face mask

According to a second aspect of the invention, there is provided a kit for a medical gas flow safety system comprising a gas flow source, a nasal cannula, gas flow tubing and a means for switching off or reducing a gas flow to at least one gas outlet of a nasal cannula gas upon application of a face mask. According to a third aspect of the invention, there is provided a method of preventing gastric insufflation comprising activating a means for preventing or reducing a gas flow to at least one gas outlet of a nasal cannula upon application of a face mask. According to a fourth aspect of the invention, there is provided a method of using a medical gas flow safety system comprising attaching a nasal cannula with at least one gas outlet to a patient, applying high flow medical gas delivery to the patient via the nasal cannula, attaching a face mask delivering medical gas to the patient, activating a means for preventing or reducing a gas flow to the at least one gas outlet of a nasal cannula upon application of the face mask.

The invention will now be illustrated by way of example with reference to the following drawings, of which: Figure 1 shows a schematic diagram of the medical gas flow safety system; and Figure 2 shows a bar chart of the results of Experiment 1.

Figure 1 shows a gas flow or pressure generator (1), a medical gas flow (2), a means for preventing or reducing a gas flow (3), a section of delivery tube, a section of which comes into contact with the face mask when applied (4), gas outlets of a nasal cannula (5), and a face mask (6) being applied and about to come into contact with the delivery tube. The medical gas flow safety system allows the delivery of medical gas to a nostril or both nostrils through the outlet(s) of a nasal cannula (5) or into the airway through a cannula (for example nasal, oral, pharyngeal or laryngeal spaces). The outlet will be referred to as a nasal cannula (5) in this description. The medical gas flow safety system specifically ensures that the pressure does not exceed a predetermined safe level at the outlet of the nasal cannula (5) or reduces or stops gas flow at the outlet if a face mask (6) is applied to a patient.

A preferred embodiment of the medical gas flow safety system is intended for high flow gas delivery systems such as those described by the THRIVE method described above which is humidified. However, in one embodiment of the medical gas flow safety system, the medical gas is not humidified and in a further embodiment has liquid added to the gas flow to keep the patient's nasal passages moist and comfortable. High flow can be defined as flows (2) above 4 litres per minute and as much as 160 litres per minute but an embodiment of the medical gas flow safety system could be used at any flow rate. Current desirable flow rates are normally from 10 to 90 litres per minute.

In some embodiments, it is desirable in some circumstances for a face mask (6) to be used over the top of the nasal cannula (5) (at section (4) in Figure 1). The face mask commonly is shaped and or has a cushioned interface to allow a seal over facial variations and medical tubes and the like.

If a face mask is applied over an oxygen delivery nasal cannula however, with the high flow delivery occurring at the same time through the nasal cannula, pressures at the face and in the patients upper airway increase to unsafe levels. It is therefore desirable that the gas flow (2) through the nasal cannula is reduced or stopped when a face mask is applied to allow normal face mask ventilation then gas flow (2) recommenced when the face mask is removed.

Gas flow can be reduced or stopped by many mechanisms including but not limited to the following:

1. In one embodiment, the medical gas flow safety system switches off or reduces the outlet gas flow (2) by venting the gas flow to the atmosphere in the circuit on the gas delivery side of the invention (that is before section (4)) when a face mask is applied. This may be achieved using a pressure relief valve positioned before section 4, for example in the delivery tubing or at the gas flow or pressure generator (1) or means for preventing or reducing a gas flow (3)

2. In another embodiment, the gas flow source (1) is switched off when a face mask (6) is applied.

The switching mechanism which switches off or reduces the gas flow or pressure can be achieved by many mechanisms including but not limited to:

1. An electronic pressure switch on the delivery tube of the medical gas flow safety system at a section (4) which comes into contact with the face mask when applied. The electronic pressure switch being adapted to activate due to the mechanical pressure placed upon it by the seal formed by the edges of the face mask pushing against the delivery tube.

2. A collapsible delivery tube segment at a section (4) which comes into contact with the face mask when applied which is physically compressed by the face mask when applied to the face over the collapsible segment thereby impeding flow and increasing pressure in the proximal side (at (1), (2) or (3)) of the medical gas flow safety system and gas venting through a pressure sensitive release valve or another mechanism to vent gas or reduce or stop gas flow.

3. A gas pressure detector under the mask (for example near the outlet(s) of the nasal cannula (5)) measuring pressure and electronically feeding back to the medical gas flow safety system to stop or reduce flow or pressure through the medical gas flow safety system.

4. The pressure at all points within the medical gas flow safety systems gas delivery pathway will be relatively constant for a given gas flow or pressure generation. If pressure at the outlet of the nasal cannula increases for example if a face mask is applied and the outlet pressure (at the position the outlets of the nasal cannula (5)) increases to a predetermined or an unsafe level, then the increase in pressure at any point of gas flow (2) in the medical gas flow safety systems gas delivery pathway can be detected and trigger a reduction or stopping of the gas flow or pressure.

One embodiment of the medical gas flow safety system will detect gas flow pressure within the nasal cannulae or more proximally in the system (for example at (3)) to detect a fall in gas flow pressure indicating that the facemask has been removed and flow can recommence.

One embodiment of the invention will restart flow at intervals of time and check pressure generation to see if obstruction to flow, for example by application of a facemask, is still occurring (whereby flow is stopped) or if the face mask has been removed (whereby flow is delivered). This embodiment of the medical gas flow safety system will conveniently prevent over pressure to the airway from the medical gas flow safety system.

A preferred embodiment of the invention is adapted to resemble a common format of the outlet(s) of a nasal cannula (5), namely nasal prongs, whereby the tubing prior to section 4 splits into two hollow gas (2) carrying tubes, one hooking over the right ear and one hooking over the left ear and rejoining and terminating at the outlet(s) of the nasal cannula (5). In an embodiment of the invention with collapsible segments at section 4 in this embodiment there will be two collapsible segments at section 4.

Current systems commonly have heated humidification and large bore tubing (commonly inner >lcm diameter). This makes the delivery of high flow gas more comfortable for the patient and is more gentle on the upper airway mucosa. This is however commonly more expensive to make and inconvenient and time consuming to change whole systems between patients and a separate humidification heater is required to be installed and powered. One embodiment of the medical gas flow safety system has a fluid injection system at any point in the system for example at or close to (1), (2), (3) or (4) which provides moisture in vapour, droplet or other liquid for to the nasal space through the outlet(s) of the nasal cannula (5)

In one embodiment the fluid injection system is a pressured syringe or venturi system.

In another embodiment the fluid injection system is a chamber within the system releasing droplets of fluid such as a nebuliser or modified nebuliser with sufficiently low resistance to allow high flows of gas for example between 4 and 160 1/min or between 10 and 90 litres per minute. Traditionally nebulisers are used to provide fine droplets that are propelled into the airway of a patient, however the invention only requires larger droplets of fluid to be propelled into the nasal space with the high flowing gases to enable the medical gas flow safety system to be used reasonably comfortably for 5 minutes to 1 hour.

Experiment 1

As described above, THRIVE enables safe apnoea times of up to 1 hour without ventilation. However there is theoretical risk of gastric insufflation, particularly if a tight fitting face mask is used concurrently with THRIVE. Whilst not part of usual practice with THRIVE, situations occur where a face mask may become necessary. A mannequin study was performed of pressures in and flow through the oesophagus with THRIVE, with and without a tight fitting face mask applied (anaesthetic machine adjustable pressure limiting valve (APLV) set to 0, 5 and 60 cmH20). A resuscitation mannequin was adapted by addition of a Wright's respirometer, pressure gauge and APLV to the oesophagus. The APLV was calibrated to open at 20 cmHO, simulating the lower oesophageal sphincter. Local R&D approval and ethical waiver were granted.

Results shown in figure 1. With THRIVE in normal use oesophageal pressures remain low and no flow occurs. With the APLV fully open, similarly low pressures and no flow occur with a face mask applied. However if the APLV is closed (fully or partially), high pressures generated overcome the model's lower oesophageal sphincter, allowing significant gas flows through the oesophagus. This high fidelity model shows risk of gastric insufflation to be low with THRIVE in normal use. However use with a face mask will cause significant gastric insufflation.

A medical gas flow safety system according to one embodiment of the invention was adapted for safe use of a face mask with THRIVE. The medical gas flow safety system (THRIVE-safe nasal cannula) consists of wide bore nasal cannula, collapsible tubing connected to a pressure relief valve. Use of a face mask automatically occludes flow through cannula, venting occurs through the pressure relief valve. With mask removal, flow resumes as the collapsible tubing reopens. Use of the THRIVE safety nasal cannula prevented the risk of gastric insufflation when a face maskwas used in conjunction with THRIVE. The results were statistically significant (ANOVA P<0.05) (see Figure 2) Therefore, the new THRIVE- safety cannula prevents the risk of gastric insufflation, enabling safe use of a mask with THRIVE, opening possibilities to combine the beneficial aspects THRIVE with other techniques, e.g. noninvasive ventilation preoxygenation or inhalational agent use.

Claims

1. A medical gas flow safety system comprising means for preventing or reducing a gas flow to at least one gas outlet of a nasal cannula upon application of a face mask.

2. A medical gas flow safety system, wherein the gas flow is a high gas flow.

3. A medical gas flow safety system according to claims 1 or 2, wherein the medical gas flow safety system further comprises a gas flow or pressure generator at a proximal end and a nasal cannula at a distal end, and gas flow tubing in fluid communication with the gas flow or pressure generator and the nasal cannula.

4. A medical gas flow safety system according to claims 1 to 3, wherein means for preventing or reducing a gas flow to at least one gas outlet of a nasal cannula is a pressure sensitive relief valve that vents the gas flow to at least one gas outlet of a nasal cannula to the atmosphere upon application of the face mask.

5. A medical gas flow safety system according to claims 1 to 3, wherein the medical gas flow safety system comprises means for switching off the gas flow upon application of the face mask.

6. A medical gas flow safety system according to any one of the preceding claims, wherein the medical gas flow safety system comprises a switching mechanism adapted to activate the means for preventing or reducing a gas flow to at least one gas outlet of a nasal cannula upon application of a face mask.

7. A medical gas flow safety system according to claim 6, wherein the switching mechanism comprises gas flow tubing adapted to collapse and prevents gas flow upon application of the face mask.

8. A medical gas flow safety system according to claim 7, wherein increased pressure in the gas delivery tubing after the gas delivery tubing has been collapsed upon application of the face mask opens the pressure sensitive release valve.

9. A medical gas flow safety system according to claim 6, wherein the switching mechanism comprises an electronic pressure switch adapted to activate upon application of the face mask.

10. A medical gas flow safety system according to claim 6, wherein the switching mechanism comprises a gas pressure detector located in a gas delivery tubing or nasal cannula within in the region covered by the face mask.

11. A medical gas flow safety system according to claim 6, wherein the switching mechanism comprises a gas pressure detector.

12. A medical gas flow safety system according to claim 11, wherein the gas pressure detector detects gas flow at the outlet of the nasal cannula.

13. A medical gas flow safety system according to claim 11, wherein the gas pressure detector detects gas flow through the gas flow tubing.

14. A medical gas flow safety system according to claims 11 to 13, wherein the gas pressure detector is adapted to recommence gas flow when it detects the face mask has been removed.

15. A medical gas flow system according to claims 3 to 14, wherein the gas flow or pressure generator is adapted to recommence gas flow at predetermined time intervals such that pressure can be checked to determine if the face mask has been removed.

16. A medical gas flow safety system according to claim 15, wherein the medical gas flow safety system comprises a fluid injector.

17. A medical gas flow safety system according to claim 16, wherein the fluid injector humidifies the gas flow.

18. A medical gas flow safety system according to claims 16 or 17, wherein the medical gas flow safety system comprises a pressured syringe or venturi system

19. A medical gas flow safety system according to claims 16 or 17, wherein the fluid injector is a nebuliser.

20. A medical gas flow safety system according to claim 19, wherein the nebuliser is adapted to allow for high gas flow of from 4 1/min to 160 1/min.

20. A medical gas flow safety system according to claim 19, wherein the nebuliser is adapted to allow for high gas flow of from 10 1/min to 90 1/min

21. A kit for a medical gas flow safety system comprising a gas flow or pressure generator, a nasal cannula, gas flow tubing and a means for switching off or reducing a gas flow to at least one gas outlet of a nasal cannula gas upon application of a face mask.

22. A method of preventing gastric insufflation comprising activating a means for preventing or reducing a gas flow to at least one gas outlet of a nasal cannula upon application of a face mask.

23. A method of using a medical gas flow safety system comprising attaching a nasal cannula with at least one gas outlet to a patient, applying high flow medical gas delivery to the patient via the nasal cannula, attaching a face mask delivering medical gas to the patient, activating a means for preventing or reducing a gas flow to the at least one gas outlet of a nasal cannula upon application of the face mask.