Printer Friendly

The patient inflating valve in anaesthesia and resuscitation breathing systems.

SUMMARY

Patient inflating valves combined with self-inflating bags are known to all anaesthetists as resuscitation devices and are familiar as components of draw-over anaesthesia systems. Their variants are also commonplace in transfer and home ventilators. However, the many variations in structure and function have led to difficulties in their optimal use, definition and classification. After reviewing the relevant literature, we defined a patient inflating valve as a one-way valve that closes an exit port to enable lung inflation, also permitting exhalation and spontaneous breathing, the actions being automatic. We present a new classification based on the mechanism of valve opening/closure; namely elastic recoil of a flexible flap/diaphragm, sliding spindle opened by a spring/ magnet or a hollow balloon collapsed by external pressure. The evolution of these valves has been driven by the difficulties documented in critical incidents, which we have used along with information from modern International Organization for Standardization standards to identify 13 ideal properties, the top six of which are non-jamming, automatic, no bypass effect, no rebreathing or air entry at patient end, low resistance, robust and easy to service. The Ambu and the Laerdal valves have remained popular due to their simplicity and reliability. Two new alternatives, the Fenton and Diamedica valves, offer the benefits of location away from the patient while retaining a small functional dead space. They also offer the potential for greater use of hybrid continuous flow/draw-over systems that can operate close to atmospheric pressure. The reliable application of positive end- expiratory pressure/continuous positive airway pressure remains a challenge.

Key Words: patients inflating valve, one-way breathing system, anaesthesia, resuscitation

**********

Intermittent positive pressure ventilation (IPPV) of an apnoeic patient is an essential part of respiratory support in anaesthesia and resuscitation. Most commonly, a reservoir bag is kept inflated by a continuous flow of pressurised gas. In continuous flow systems, a variable pressure spill valve, also called an adjustable pressure limiting valve (APL), is used to control the bag volume and facilitate inflation of the lungs. Alternatively, in draw-over systems, the carrier gas may be ambient air, with or without supplemental oxygen, drawn into a bag or bellows and then pushed through a one-way patient inflating valve in order to ventilate the lungs.

More sophisticated anaesthetic machines require time-consuming checklists and computer software to control gas flow. This has arisen as these machines must adhere to medical systems software regulations as well as anaesthetic standards. However, they may create a potential hazard if the equipment malfunctions, resulting in gas supply failure (1). A resuscitator with a self-inflating bag and patient inflating valve has therefore become a mandatory back-up to maintain oxygenation and ventilation of the lungs if necessary.

The inflating valve replaces the need for continuous gas flow to inflate the lungs during IPPV by automatically occluding the exit port of the breathing system; gas is directed to the patient during the inspiratory phase of a positive pressure breath and then vented to atmosphere during the expiratory phase. During spontaneous ventilation, the inflating function does not operate, although most valves still ensure a one-way flow of gas from the system to the patient.

The required exit-occlusion effect during IPPV uses the same positive pressure that inflates the lungs so the user has only to squeeze a bag or bellows and ventilation occurs without any adjustment required or additional power source. Therefore, there is no need for a separate APL valve.

As small portable devices, resuscitators are ideal for lung ventilation during resuscitation or field use by anyone who can squeeze a bag and maintain a clear airway. Room air will be drawn in automatically if the gas supply fails.

However, there are usually no pre-use checklists or explanations provided on how the valves operate. Though the devices may be familiar and used with confidence, their modes of operation differ and are often not understood. They may be routinely dismantled, perhaps reassembled wrongly or used in various anaesthesia breathing systems without sufficient knowledge of their differing characteristics, thereby creating a hazard.

In facilities that use draw-over anaesthesia equipment because compressed gas is not available, such valves are also used for lung inflation during anaesthesia when combined with one-way valves to prevent air entry at the patient end and re-breathing.

In recent times, hybrid breathing systems for anaesthesia (combining draw-over and continuous flow in one unit) have appeared that necessitate a re-evaluation of the draw-over system and the operation of the patient inflating valve. Such systems offer potential improvements over currently accepted standards.

This article will attempt to define and put into context the range of patient inflating one-way valves, looking at the evolution, the problems and hazards of the device, to facilitate a better understanding of their place in modern equipment used during anaesthesia or resuscitation.

METHODS

Relevant published articles were searched on the following electronic resources: Med-line, Medline in Process, Embase, Cochrane Central Database of Controlled Trials and Google Scholar. Standard phrases including technical descriptions, synonyms and brand names were used including: breathing and valve, patient inflating valve, one-way valve, non-return valve, Ambu valve, Laerdal valve, universal breathing valve, Oxford inflating bellows, Diamedica, Ruben valve, non-re-breathing valve, draw-over and continuous flow.

The search identified 61 publications of which the authors found 17 containing descriptions of anaesthetic inflating valves between 1960 and April 2012. The search was limited to human literature and all but five articles retrieved were published in English. These five articles had English abstracts; where this indicated relevance the article was fully translated.

In addition, bibliography searching and author searching was conducted in order to augment the citation searching. This revealed a further 28 relevant publications.

Where gaps in the literature were evident, such as publications alluding to further work in progress that was not identified by further detailed searching or simply an absence of user reports, the authors contacted the equipment manufacturer and the corresponding author of the initial publication for information. This is the basis of the personal communications listed within the text.

Due to the nature of publications found through the search strategy, recta-analytical techniques were thought to be inappropriate. Much of the literature focuses on descriptions of new valves by the inventor and then subsequent publication of case reports and hazards by users. We used this information to construct a functional classification system and examine the reported problems, before suggesting the ideal properties of a patient inflating valve.

DEFINITION

Detailed descriptions, diagrams and photographs of anaesthetic, resuscitation and ventilator valves have been published by Davey (2). Here we describe the various definitions that have been used and propose a more comprehensive alternative.

The terminology for different types of breathing valve has been defined (3). Valves fall broadly into two categories: those that ensure gas flows in only one direction or at one time during the respiratory cycle, and in a continuous flow system those with a pressure-limiting function to control the amount of gas in the system. The pressure limit may be fixed or user-adjustable.

A 'patient valve' is additionally defined as a device that directs gas to the patient during inspiration and out to atmosphere during expiration.

Further terminology includes 'inflating valve', which is a device that enables lung inflation during IPPV, defined in a later International Organization for Standardization (ISO) publication specifically for draw-over systems (4). This also includes the term 'anaesthetic patient valve', being one that combines the facility to inflate the lungs and ensure one-way gas flow in a single unit.

For improved clarity, lung inflation and one-way gas flow may be considered as two separate functions that have been achieved by physically separate devices, both past and present. Therefore, the term 'inflating valve' will be used in this review in order to focus on this important function that is specific to a draw-over system.

We define this in more detail as 'a device located within a breathing system that operates without external power source and which when used with positive pressure from a self-inflating bag or bellows (such as the Oxford Inflating Bellows), closes an exit port to enable lung inflation, but also permits exhalation and spontaneous breathing through it when no pressure is applied, the actions being automatic'.

This definition excludes such devices as the Manley Minute Volume Divider, the East Freeman and Flomasta (5) ventilators, which might otherwise be considered patient inflating devices with valves; it also excludes a paediatric non-return valve described by Zuck (6), which does not allow spontaneous breathing, and a similar arrangement for paediatric anaesthesia with a reservoir bag described by Lee (7), which has a one-way 'inhalation valve' but delivers IPPV by occluding a compressible exhaust tube without a valve.

Most intensive care ventilators operate by fully or partially closing an exit port to raise system pressure and ventilate the patient's lungs. However, these require external power and often additional feedback mechanisms, so they are not automatic in the sense of the definition we have used.

The enclosed afferent reservoir systems and enclosed preferential flow systems (8) fulfil several aspects of the definition, in that they have an automatic valve closing and opening function for both spontaneous and controlled ventilation but require adjustment of a separate variable orifice on changing between spontaneous and controlled modes.

Many manual resuscitators and gas or electrically powered home ventilators have inflating valves that fulfil the definition previously given. These are not listed individually in this article as they are not in use for anaesthesia; most are copies or modifications based on original concepts from anaesthetic practice subsequently described.

In the following text, we have included examples of valves used principally for controlled ventilation, where the devices highlight particular design or functional aspects of importance in the evolution of inflating valves. This includes the Drager Oxylog valve, with which many clinicians will be familiar, although it does not fulfil our definition completely (as the 1000 valve had no facility for spontaneous ventilation and the 2000/3000 valves require a continuous flow of gas for spontaneous breathing function). These valves are confined to ventilators and are not used principally for anaesthesia or with manual resuscitators.

CLASSIFICATION

There have been many individual descriptions of specialised valves in breathing systems to enable lung inflation. The methods of operation vary, there is no systematic classification and the valves are often not well understood. To simplify the nomenclature and show how they work, the different structures used within the valve to block the exit port and inflate the lungs may be reduced to three broad categories that involve either a flap, a sliding spindle or a hollow structure (Table 1).

The early Ambu valve (invented by Hesse, who was the founder of Ambu, and Ruben) and its successor the Ambu E1 (though no longer made) may be considered the standard and most familiar valve that combines both lung inflation and one-way gas flow using one silicone flap as shown in Figure 1 (labelled 19-04). A second identical flap downstream serves to prevent room air being drawn in if the patient breathes spontaneously.

Using the same principle, a paediatric version (the Paedivalve) is available as part of a resuscitator that can also be used to provide anaesthesia (12).

The E2 valve is like the E1, but lacks the exit flap so that if the patient breathes spontaneously, room air is drawn in at lower resistance than anaesthetic gas drawn from the system.

The Laerdal valve (Figure 2) uses a different system, namely a duckbill type one-way valve made of silicone that opens during inspiration and also impinges upon a flat silicone ring that moves to close the exit port during IPPV. When the inflating pressure is released, the duckbill closes allowing the ring to fall back opening the exit port. As with the Ambu valve, sustained positive pressure, such as from continuous gas flow, will cause the ring to jam in the inspiratory position maintaining closure of the expiratory orifice while the duckbill remains open.

Ruben's 1984 modification of a continuous flow system with absorber is less well known; an ingenious configuration (Figure 3) (20) in which a hollow mushroom-shaped vessel seals an exit port to allow lung inflation, similar to other valves in category 3 (Table 1). His twin aims were to avoid pressure rising in the system and to remove the need for the APL valve. However, a report by Sik et al in 1988 (23) found that the seal could not prevent re-breathing during spontaneous respiration in paediatric anaesthesia with small tidal volumes. This finding was supported by clinical practice but as the volumes in question were of no significance in adult anaesthesia, clinicians considered the system to function well and valued the ease of use without having to adjust an APL valve when changing the mode of ventilation. The valve assembly was mounted in a way that the mushroom valve could be easily inspected during use and the spill valve was kept vertical to prevent leaflet malfunction (Howard Spenceley and Tony Nightingale, personal communication).

A modification was made by Ambu, but no follow-up testing report can be found.

Potential difficulties with inflating valves during normal use

Some valves made a disturbing noise of a vibrating flap or diaphragm or clicking. The Ruben valve (1955) could get stuck in the inflating position (24). If inflating pressure continued to build up this could cause the valve to become jammed in the closed position and malfunction. Other valves needed the user to adjust them when going from spontaneous to controlled ventilation, e.g. to use the thumb or turn a knob. The magnets in the Mitchell Epstein valve could be reassembled with the wrong polarity.

Early valves used latex rubber for flexible components that deteriorated after a few months' service in a humid breathing system. Some valve bodies were made from metals that are heavy and did not allow a visual check of the components.

The currently available inflating valves have a three port T-configuration, i.e. there is an inlet port, a patient port and an outlet port. For anaesthesia use, the valves prevent re-breathing and air entry during spontaneous respiration. These ports may have ISO 22 mm tapers enabling connection to anaesthesia systems or they may only be compatible with a dedicated self-inflating bag for resuscitation, such as the Ambu Mk III. The older devices predate the ISO connection standard.

With a T-configuration, inflating valves cannot be located in the expiratory limb of a breathing system or on the anaesthetic machine (except as subsequently described). The valve must be located at the patient's airway with a short to and fro gas flow section to minimise dead space. This is disadvantageous, because the valve may be concealed if the head is draped, and the tracheal tube is more easily kinked or dislodged. Active scavenging of waste gas adds to the risk and it is inconvenient due to the bulk of the connections; fitting a bacterial filter adds additional bulk.

Paediatric use is also problematic. One valve available for infants is the Ambu resuscitation Paedivalve, which can also be used for anaesthesia (12). The valve leaflets do not seat as well as in the adult model and when used on patients <5-7 kg the valve resistance means that sustained IPPV is needed in order to keep the patient adequately oxygenated and anaesthetised. A pressure limiting device may be fitted, but airway pressure cannot be measured. The pressure may be too high and accompanied by noisy valve operation. The position of the valve at the airway makes displacement of a small tracheal tube likely and places the exit of the volatile agent close to the operative field.

In the case of the Ambu, Laerdal and Ruben valves, the T-configuration arises because the exit-occluding leaflet must be upstream from the patient so that when the inflating pressure falls to zero at the end of a breath, the leaflet falls back due to its own elastic recoil (or a spring in the case of Ruben's valve) and patient airway pressure on the distal side that allow expiration to atmosphere via the now open exit port. At the same time, the leaflet prevents back-flow of expired gas into the system.

Pre-oxygenation using a duckbill valve has been shown to be less effective, with only 40% oxygen or less being delivered (25).

Positive end expiratory pressure (PEEP) or continuous positive airway pressure (CPAP) is sometimes indicated during anaesthesia or when patients require ventilation in intensive care (26). All currently available patient inflating valves offer little resistance to expiration (when used correctly) and in contrast to continuous flow systems with APL valves, the user cannot increase the resistance of the valve to provide PEEP or CPAP. In response to these requirements with the Ambu Valve, an adjustable PEEP valve is available (27) that may be attached to the 30 mm scavenging adaptor and functions well with both the Ambu and Laerdal valves. Clearly, scavenging must be discontinued while the valve is in use. Independent reports are awaited on how PEEP and CPAP may be delivered with the Diamedica valve; early experience of the Universal Anaesthesia Machine (UAM) balloon valve (28) shows a PEEP of 5 cm[H.sub.2]O can be achieved.

Potential malfunction of inflating valves

The self-assembly character of draw-over systems means that configuration errors may occur more frequently compared to conventional systems. The inflating valve may be mounted with the correct direction of gas flow reversed or other components, such as a bacterial filter, may be incorrectly placed (29).

The Ambu E1 valve could deliver a lower than intended tidal volume if volumes were small and/ or low inflation pressure failed to move the flap forward sufficiently to block the exit port (situation 'T' in Figure 1). The gas bypasses the patient and exits the valve. The same effect has been reported at high flows using the Ambu Paedivalve, which has smaller valve parts (30). Bypassing is an inherent fault in any inflating valve and designs try to minimise the effect. The Ambu Mark III had improved inflation efficiency, but this also increased the risk of the valve getting jammed in the inflation position if there was a continuous forward flow of gas. For this safety reason, the Mark III has a connection that is incompatible with anaesthesia delivery systems.

If the leaflet continues to occlude the exit port, most commonly if the inflating pressure does not fall to zero, the valve leaflets will remain in the inflating position and the patient cannot breathe out, the valve is said to be jammed. A valve with a flat surface, as used in Ambu and Laerdal valves, will be more susceptible to a build-up of pressure on the proximal side, jamming it tightly closed; whereas, in the case of a balloon impinging on an orifice, provided the balloon wall is thin, the all round pressure on such a spherical structure will tend to collapse the surface away from the orifice to release pressure, which can be made lower inside than out.

Jamming causes the system back bar pressure and the inflation pressure to rise to the ISO specified maximum of 55-125 cm water for a gas delivery system. Apnoea is immediate and cardiac arrest will follow within minutes unless the patient is disconnected as an emergency.

The hazardous event of jamming is usually associated with misuse of the valve (e.g. using it with a continuous flow anaesthesia machine or high oxygen flows (31,32)), from dirt causing sticking or if the valve is placed incorrectly or wrongly assembled (33), which gives rise to a flow from the machine towards the patient throughout the respiratory cycle creating unwanted resistance during expiration. A safety valve to release the inflation pressure was described by Lee (34). The hazard usually occurs when IPPV is applied to an apnoeic patient after giving a neuromuscular blocking drug. During spontaneous ventilation (when the inflating function does not operate), it appears there is no problem with the breathing system, provided patient minute volume is greater than the supplied gas flow. It is thus the inflating function of the devices that causes jamming and makes them incompatible with continuous flow machines.

The traditional way that unwary anaesthetists discovered they could not inflate the lungs using the Oxford Inflating Bellows with an Ambu valve was in failing to place the magnet (Figure 4) that disables the adjacent valve by pulling up the steel disk (Figure 4A). When functioning, this valve prevents the airway pressure dropping to zero; the inflating valve jams after about three breaths with the lungs hyperinflated (Figure 4C). If the magnet is missing or forgotten, continued inability to ventilate an intubated patient gives the mistaken impression of airway obstruction or oesophageal tube placement.

Placing the magnet after this occurs does not solve the problem; the circuit must be disconnected. The parked magnet (Figure 4B, valve enabled) is the correct position when using an adjustable, non-inflating Heidbrink valve to prevent re-breathing. It is a confusing requirement and if Ambu (or Laerdal) valves are the only available valves in use, it is common practice when using the Oxford Inflating Bellows to simply remove the steel disk and dispense with the magnet.

Some inflating valves can be disassembled for service and sterilisation. However, errors in reassembly may cause a major hazard, even resulting in unnecessary chest surgery due to an inability to ventilate the patient when the valve is not identified as the fault (24,30,35,36). The valves are relatively expensive for poorly resourced operating theatres and therefore scarce. In practice they are often transferred from one patient to the next without cleaning, giving a contamination risk.

Some models are well-known to get stuck in inflation, even when used correctly, or they made loud 'burping' noises (indicating intermittent or impending jamming) during lung inflation, especially against high airway resistance. In testing nine devices, Carden (37) found 'the most common malfunction was sticking of the inflating valve in the inspiratory position'. The same concerns about inspiratory jamming led an Australian investigating committee to recommend the inclusion of a blow-off valve in all systems with an inflating valve (38).

Sticking due to water condensation or dirt may also occur, particularly of small valve moving parts that are less susceptible to being moved by low pressure changes such as the Ruben spindle. Small parts also are less easy to see and their absence harder to detect (39). However, sticking may occur with any one-way valve or other devices placed in the breathing system (40, 41).

All these difficulties and hazards have contributed to existing models not being used in modern anaesthesia. However, newer developments subsequently outlined have demonstrated a renewed potential for inflating valves in alternative breathing systems.

Properties of an ideal inflating valve

Many unbranded copies of valves using the Laerdal, Ambu and even Ruben method of operation are made by unregulated manufacturers in developing countries. Even though of variable quality, such copies are widely distributed around the world. The complex mode of action merits different models of inflating valve to be assessed by comparison with an 'ideal' valve (Table 2).

The use of inflating valves in different breathing systems

Continuous flow systems

From the early decades of the 20th century, the preference in developed countries was divided between two types of continuous flow system: recycling + absorber + APL and one that used a valve for lung inflation but with no absorber or APL. Both required pressure in the system to fill a bag for lung inflation. The competing systems were also called 're-breathing' and 'non-re-breathing', respectively (19,42). The circle (rebreathing) system ultimately became the standard and the non-re-breathing valve disappeared.

However, the increasing complexity of modern anaesthesia machines has greatly increased their purchase price, putting them out of reach of many poorer countries, as do issues of compressed gas supplies, sensitivity to power fluctuations, over sophistication and servicing failures. Alternative breathing systems, not dependent on this type of support, are still required in many parts of the world.

Draw-over systems

The solution to these issues has been the draw-over system. The system has been reviewed previously in detail (43,44).

The original configuration with a bellows and inflating valve originated as a result of the polio epidemic in Copenhagen in 1952, requiring oxygen supplementation only (42). Macintosh attempted to popularise this configuration as draw-over for anaesthesia in 1955 (45) following his experience giving anaesthesia outside well-equipped centres. However, the system was not used in mainstream practice.

The best known embodiment of the basic draw-over configuration is the Tri-Service apparatus (46) (Figure 5).

Traditional draw-over systems need an inflating valve, but no machine that uses this type of valve has been CE (European Conformity) marked for anaesthesia use (except as below) as they pre-date the requirement for CE marking of medical equipment. Due to the popularity of circle systems used in conjunction with a standard Boyle's type machine, equipment manufacturers considered the expense of CE marking unnecessary for draw-over equipment with a limited European market. Thus, in recent decades a divide has come to exist between operating theatres that have compressed gas supplies and require CE marked equipment, excluding draw-over, and theatres without compressed gas that can provide anaesthesia only using draw-over equipment.

Notwithstanding these limitations, the draw-over system has the advantages that it will function under field conditions and operate at atmospheric pressure, thereby avoiding the risk of pulmonary barotrauma, which may result if a continuous flow machine malfunctions and exposes the lungs to a high gas pressure due to failure of the delivery system safety mechanisms (47,48).

New developments in inflating valves

Solving the previous problems and dangers of inflating valves could enable them to be used in both continuous flow and draw-over systems. This would allow the innovation of a breathing system that exploited the advantages of both systems in one unit.

Although older valves were manufactured with a metal housing and were undoubtedly more robust than their modern equivalents, plastic valves can offer entirely adequate strength with the potential added advantages of being lighter and transparent, allowing the user to visually inspect the valve function.

In manufacture, silicone rubber is now the preferred material for valve leaflets over latex. Silicone has higher tear strength than latex, as well as better resistance to oxidation and fungal growth. Awareness of latex allergies has also influenced purchasers towards silicone components in re-usable equipment, combined with the property of increased temperature resistance that makes silicone components wear less with standard cleaning.

To utilise these potential advantages and also to elevate draw-over into compliance with ISO/CE standards, the UAM uses a silicone rubber balloon (the Fenton balloon) for the inflating function, located in the lumen of the expiratory limb, but separates this action from the one-way valves in the breathing system, placing it away from the patient on the anaesthesia machine, the first such arrangement in a draw-over machine (49).

As with the earlier flexible hollow devices (Table 1, Beves, Ruben), the Fenton balloon uses patient airway pressure to inflate a balloon to occlude gas flow at the exit port but achieves a better seal by the use of an annular ring (Figures 7 and 8). The dome of the balloon impinges on this ring and occludes the exit port more effectively. Jamming is less likely because an abnormal increase in ventilation pressure outside the balloon (i.e. above patient airway pressure inside) causes the side wall of the balloon to deform which peels away the dome from the sealing ring and releases the pressure, unlike with a flap or diaphragm which will close ever more tightly with rising pressure. As an additional safety measure, the interior of the balloon normally reverts to atmospheric pressure during expiration, being connected to the upstream side of a valve where pressure is atmospheric.

The earlier balloons were used only with Boyle's type machines, i.e. they were dependent on a continuous gas flow to operate, whereas the UAM combines a low pressure (limited to 5 cm[H.sub.2]O on the back bar) continuous gas flow with a default to a bellows-operated draw-over system if patient minute volume exceeds the gas flow or if the gas flow stops entirely. In the latter case, the default carrier gas becomes entrained room air. Non-dependence on a compressed gas supply simplifies the system and thereby reduces cost. As the system operates at close to atmospheric pressure (limited to 55 cm[H.sub.2]O between the bellows and the patient), patient safety is also improved by avoidance of high pressures, such as from a pipeline, reaching the lungs. Initial reports confirm the operation and user acceptability of this bellows and valve system in clinical practice (21,28).

There is a recent report of another valve compatible with draw-over anaesthesia, the Diamedica non-re-breathing valve (13). This valve has separate inspiratory and expiratory components connected with a conduit to allow inspiratory pressure to occlude the expiratory limb and allow lung inflation. Early experience with this valve suggests that it functions well in adults and children as small as 10 kg (Peter Armstrong, personal communication).

With both new valves the benefit of separating inspiratory and expiratory components is that this facilitates the use of a simple Y-piece breathing system and gives the combined advantages of moving all one-way valve components to the machine end of the breathing system, potential reduction in equipment dead space and facilitates the use of scavenging and bacterial filters, which are bulky attachments when connected near the patient's airway when using Ambu-type valves. Although purely for use with a ventilator, it is notable that the paediatric system for the Drager Oxylog 3000 has adopted the same configuration (Figure 9).

SUMMARY

Patient inflating valves combined with self-inflating bags are known to all anaesthetists as resuscitation devices and are familiar as components of draw-over anaesthesia systems. Their variants are commonplace in transfer and home ventilators. In spite of their essential requirement, continued use and evolution, they have received little attention in the medical literature. The sheer number of devices available and lack of a classification system has contributed to a poor understanding of the principal ideal features defined in this review.

Issues of valves sticking, allowing gas to bypass the patient, lack of facility for easy transition from spontaneous to controlled ventilation and bulky attachment to the airway have led to many devices falling out of production.

The Ambu and the Laerdal valve have remained popular due to their simplicity and reliability. Two new alternatives, the Fenton and Diamedica valve, offer the benefit of location away from the patient and on the anaesthetic machine while retaining a small functional dead space. These valves have addressed many of the issues of their fore-runners and offer the potential for greater use of hybrid continuous flow or draw-over systems that can operate at close to atmospheric pressure. The reliable application of PEEP and CPAP remains a challenge.

It is incumbent on practising clinicians to be well-informed about the structure and function of devices they may use infrequently, but on which they rely in an emergency situation due to failure of more complicated modern medical technology (50).

ACKNOWLEDGEMENTS

We would like to thank Dr Tony Nightingale and Dr David Wilkinson for their support and comments on an earlier draft of this paper.

CONFLICT OF INTEREST

Paul Fenton is the inventor of the UAM, which uses the Fenton breathing system, and is a consultant to Gradian Health Systems LLC, a US based not-for-profit company that owns the rights.

Caption: Figure 1: The Ambu E1 value: components and function. R = during inspiration with an assisted breath the valve leaflet moves forward, blocks the exit port and directs gas to the patient. S = during expiration, the valve leaflet falls back and the patient's expired gas passes through the exit port. T = Error in use: the inflating pressure is too low so most gas bypasses the patient. Copyright of Corporate Design Team, GIZ, permission granted to reproduce (41).

Caption: Figure 2: The Laerdal IV valve. Dobson M. Anaesthesia at the District Hospital. World Health Organization 2000; p. 18.

Caption: Figure 3: The Ruben circle system. V = volumeter, P = pressure gauge. (c) 1984 Anaesthesiologica Scandinavica Fonden (20)

Caption: Figure 4: Using the magnet with the Oxford Bellows. A. magnet in use, B. magnet parked, C. jammed valve. A=bellos inlet valve, B=non-return valves, C=exit port valve, X=valve leaflet, Y=outlet port. Copyright of Corporate Design Team, GIZ, permission granted to reproduce (41).

Caption: Figure 5: A draw-over system. The Triservice apparatus. Initially described with two vaporisers in series but more commonly used with only one. Modern (non-original) oxygen regulator shown. With permission from by NHS medical illustration dept Glasgow Yorkhill Hospital.

Caption: Figure 6: Separating the inflating function from the one-way valve function, diagrammatic representation of the UAM. A third valve is required beyond the balloon to prevent back flow during spontaneous breathing. During IPPV, pressure in pipe (7) inflates the balloon (6) which impinges against the ring (8) which blocks the exit port and directs gas to the patient.

Caption: Figure 7: Universal anaesthesia machine with Fenton balloon. Annular ring is seen at base of transparent housing.

Caption: Figure 8: Schematic diagram of Diamedica nonre-breathing valve. I=inlet port, O=outlet port, P=patient port, 1=inspiratory one-way valve, 2=expiratory one-way valve, 3=diaphragm, 4= connecting conduit. (c) 2010 The Authors. Anaesthesia

Caption: Figure 9: Drager Oxylog 3000. The modern Oxylog 3000 paediatric valve assembly used for a transfer ventilator has adopted many of the features of the new anaesthetic patient inflating valves; Inspiratory valve leaflet (1) is now large, Y-piece connector (2) to reduce dead space, removal of the expiratory valve away from the patient end (3) and pressure linkage(4) between inspiratory limb and expiratory valve. Note the paired narrow bore tubes (5) are for spirometry monitoring, not valve function. With permission from by NHS medical illustration dept Glasgow Yorkhill Hospital.

REFERENCES

(1.) Association of Anaesthetists of Great Britain and Ireland. Safe Anaesthesia Liaison Group NPSA patient safety update July-Sept 2011. From www.aagbi.org/sites/default/files/SALG-PATIENT-SAFETY-UPDATE-DEC2011.pdf. Accessed December 2012.

(2.) Davey AJ, Diba A (eds). Wards Anaesthetic Equipment, 5th ed. London, UK: Elsevier Limited 2005; p. 231-239, 492-494.

(3.) International Organization for Standardization. Anaesthetic and respiratory equipment--vocabulary. From www.iso.org/ iso/home/search.htm?qt=ISO+4135%3A2001&published=o n&active_tab=standards&sort_by=rel. Accessed December 2012.

(4.) International Organization for Standardization. Inhalational anaesthesia systems--draw-over vaporizers and associated equipment. From www.iso.org/iso/home/search.htm?qt=ISO +TS+18835&published=on&active_tab=standards&sort_ by=rel Accessed December 2012.

(5.) Jones PL, Hillard EK. The flomasta. A new anaesthetic ventilator. Anaesthesia 1977; 32: 619-625.

(6.) Zuck D. A non-return valve for use with intermittent positive pressure respiration during paediatric surgery. Br J Anaesth 1964; 36: 674.

(7.) Lee S. The advantages of a combined T-piece and non-rebreathing valve: a simple device. Br J Anaesth 1964; 36: 521-523.

(8.) Miller DM, Miller JC. Enclosed afferent reservoir breathing systems. Description and clinical evaluation. Br J Anaesth 1988; 60: 469-475.

(9.) Cullen S. Current comments and case reports. Anesthesiology 1956; 17: 618-619.

(10.) The Wood-Library Museum. Fink collection. From http:// woodlibrarymuseum.org/museum/item/23/fink-collection. Accessed December 2012.

(11.) Fink BR. A nonrebreathing valve of new design. Anesthesiology 1954; 15: 471-474.

(12.) Kamm G. Paediatric anaesthesia with the ambu-paedi-valve and bag. Trop Doct 1980; 10: 66-71.

(13.) Payne S, Tully R, Eltringham R. A new valve for draw-over anaesthesia. Anaesthesia 2010; 65: 1080-1084.

(14.) Oxylog Emergency Ventilator Instructions for Use, 4th ed. Lubeck, Germany: Dragerwerk AG 1993; p. 10,15.

(15.) Oxylog 3000 Emergency Ventilator Instructions for Use, 2nd ed. Lubeck, Germany: Drager Medical AG & Co. KGaA 2002; p. 59,69.

(16.) Ruben H. A new nonrebreathing valve. Anesthesiology 1955; 16: 643-645.

(17.) Mitchell JV, Epstein HG. A pressure-operated inflating valve. Anaesthesia 1966; 21: 277-281.

(18.) Searle JB. Inflating valve. Anaesthesia 1958; 13: 345-346.

(19.) Beves PH. A non-rebreathing valve. Anaesthesia 1962; 17: 533-537.

(20.) Ruben H. Anaesthesia system with eliminated spill valve adjustment and without lung rupture risk. Acta Anaesthesiol Scand 1984; 28: 310-314.

(21.) Van Hasselt G, Barr K. The first Universal Anaesthesia Machine, an evaluation. J Anaesth Practice 2011; 4: 128-134.

(22.) Fenton E Maternal mortality and anaesthesia technology in the 21st century. Anaesthesia News 2010; April: 5-8.

(23.) Sik MJ, Eveleigh DJ, Lewis RB. The Ruben circle anaesthesia system. An investigation of reverse flow of patient expired gas during spontaneous breathing. Anaesthesia 1988; 43: 141-145.

(24.) Wisborg K, Jacobsen E. Functional disorders of Ruben and Ambu-E valves after dismantling and cleaning. Anesthesiology 1975; 42: 633-634.

(25.) Nimmagadda U, Salem MR, Joseph N J, Lopez G, Megally M, Lang DJ et al. Efficacy of preoxygenation with tidal volume breathing. Comparison of breathing systems. Anesthesiology 2000; 93: 693-698.

(26.) Gattinoni L, Carlesso E, Brazzi L, Caironi R Positive end-expiratory pressure. Curr Opin Crit Care 2010; 16: 39-44.

(27.) Boidin MP. A portable PEEP valve for 0-20 cm H2O. Acta Anaesthesiol Belg 1982; 33: 69-74.

(28.) de Beer D, Bell G, Walker I. Universal Anaesthesia Machine (UAM): evaluation of a new anaesthesia workstation for use in the developing world. Br J Anaesth 2012; 108: 1247.

(29.) Schmitt C. Possibility of an incorrect connection between certain respiratory filters and the expiratory segment of the Ambu-A non-rebreathing valve. Ann Fr Anesth Reanim 2000; 19: 205-208.

(30.) Lindhal S, Nordstrom L, Olsson AK. Expired minute volume measurements during anaesthesia using non-rebreathing valves. Acta Anaesthesiol Scand 1981; 25: 427-429.

(31.) Tweed WA, Amatya R, Lekhak BD. Fresh gas flow and carbon dioxide rebreathing in a low pressure semi-open anaesthesia system. Can J Anaesth 1993; 40: 1096-1101.

(32.) Birt R. The effects of the addition of oxygen to various inflating devices. Anaesthesia 1965; 20: 323-328.

(33.) Ho AM, Shragge BW, Tittley JG, Fedoryshyn JN, Puksa S. Exhalation obstruction due to Laerdal valve misassembly. Crit Care Med 1996; 24: 362-364.

(34.) Lee S. A universal valve for anaesthetic circuits. Br J Anaesth 1964; 36: 318-321.

(35.) Pauca AL, Jenkins TE. Airway obstruction by breakdown of a non-rebreathing valve: how foolproof is foolproof? Anesth Analg 1981; 60: 529-531.

(36.) Grogono AW, Porterfield J. Ambu valve: danger of wrong assembly. Br J Anaesth 1970; 42: 978.

(37.) Carden E, Bernstein M. Investigation of the nine most commonly used resuscitator bags. JAMA 1970; 212: 589-592.

(38.) Holland R. Special committee investigating deaths under anaesthesia: memorandum on the dangers of non-rebreathing valves. Med J Aust 1970; 2: 46-47.

(39.) Day C J, Nolan JP. A rebreathing non-rebreathing valve. Anaesthesia 1994; 49: 456-457.

(40.) Johnson RA, Vries LA. High airway pressures with sticking one-way valves in a circle system. Anaesthesia 1999; 54: 406.

(41.) King M (ed). Primary Anaesthesia. Oxford, UK: Oxford University Press 1994. p. 72-75.

(42.) Sykes MK. Nonrebreathing valves. Br J Anaesth 1959; 31: 450-455.

(43.) Simpson S. Draw-over anaesthesia review. Update in Anaesthesia 2002; 15:article 6.

(44.) Dobson M. Anaesthesia at the District Hospital. World Health Organization 2000; p. 57-68.

(45.) Macintosh R. A plea for simplicity. Br Med J 1955; 2: 1054-1057.

(46.) Houghton IT. The Triservice anaesthetic apparatus. Anaesthesia 1981; 36: 1094-1108.

(47.) Dean HN, Parsons DE, Raphaely RC. Case report: bilateral tension pneumothorax from mechanical failure of anesthesia machine due to misplaced expiratory valve. Anesth Analg 1971; 50: 195-198.

(48.) Otteni JC, Ancellin J, Cazalaa JB, Feiss P. Anesthesia equipment: fresh gas delivery systems. I. Mechanical systems with rotameters and calibrated vaporizers. Ann Fr Anesth Reanim 1999; 18: 956-975.

(49.) Fenton PM. Inhalation anaesthesia in developing countries: the problems and a proposed solution--2 and 3. Anaesthesia News 2003; 190, 191: 10-11, 8-9.

(50.) Association of Anaesthetists of Great Britain and Ireland. Checking anaesthetic equipment 3 2004; p. 12. From www. aagbi.org/sites/default/files/checking04.pdf. Accessed January 2013.

P. M. FENTON *, G. BELL ([dagger])

Department of Anaesthesia, College of Medicine, Blantyre, Malawi, Africa; and Department of Anaesthesia, Royal Hospital for Sick Children, Yorkhill, Glasgow, Scotland

* MB, BS, DTM&H, FFARCSI, Professor of Anaesthesia, College of Medicine, Malawi, Africa.

([section]) MB, ChB, FRCA, Consultant Paediatric Anaesthetist, Royal Hospital for Sick Children, Glasgow; and Honorary Senior Lecturer, University of Glasgow, Scotland.

Address for correspondence: Professor P. Fenton. Email: uam.paul@ gmail.com

Accepted for publication on January 20, 2013

Table 1

Inflating valves classified by method of operation

Method of exit valve    Valve name             Remarks

Closing (flexible       Lewis and Leigh (9)    Non-automatic
flap or diaphragm) *
Opening (elastic        Fink (10,11)           First use of a duct
recoil of the                                  allowing inspiratory
material) (#)                                  pressure to occlude
                                               the expiratory port

                        Ambu E1, E2            E2: resuscitation
                                               only
                                               Both: bypass effect

                        Ambu Paediatric (12)   Needs IPPV to
                                               maintain adequate
                                               ventilation

                        Ambu single shutter    Resuscitation only

                        Laerdal                Adults and children

                        Diamedica (13)         Valve located on
                                               anaesthesia machine

                        Drager Oxylog 1000     Single flexible
                        valve (14)             diaphragm with
                                               central opening
                                               spindle functioning
                                               as second valve. No
                                               spontaneous
                                               breathing function

                        Drager Oxylog 2000     Double diaphram with
                        & 3000 valves (15)     duct for inspiratory
                                               pressure--exp limb

Closing (rigid          Ruben (1955) (16)      Prone to sticking
sliding spindle) *
Opening (spring or      Cardiff                Not intended for
magnet)#                                       anaesthesia

                        Mitchell-Epstein       Did not allow
                        (17)                   spontaneous
                                               breathing

                        Searle (18)            APL valve with
                                               inflating feature

Closing (flexible       Beves (19)             Modified balloon
hollow mushroom or                             valve after Etheridge
balloon) *
Opening (external       Ruben (1984) (20)      First valve located
pressure collapses                             on anaesthesia
structure)#                                    machine. Balloon did
                                               not seal, allowed
                                               re-breathing with
                                               small tidal volumes
                                               during SR

                        Ambu Mk III            Jams with continuous
                                               flow--made for
                                               resuscitation only

                        UAM (21,22)            Valve located on
                                               anaesthesia machine

* Inspiratory phase of intermittent positive pressure ventilation, (#)
expiratory phase of intermittent positive pressure ventilation  or
spontaneous respiration. IPPV=intermittent positive pressure
ventilation, APL = adjustable pressure-limiting, SR = spontaneous
respiration, UAM = Universal Anaesthesia Machine.

Table 2

Properties of the ideal inflating valve

      Property                      Remarks

1     Non-jamming                   To avoid pulmonary barotrauma,
                                    the device must not get jammed in
                                    the inflating position when a
                                    continuous gas flow is applied. A
                                    collapsible balloon is least
                                    likely to get jammed.

2     Automatic                     Operates for controlled or
                                    spontaneous respiration without
                                    switching or other change needed
                                    by the user.

3     No bypass effect              (Figure 2'T') Effective operation
                                    is flow independent without
                                    adjustment from intermittent
                                    draw-over (i.e. gas flow=0) to
                                    high continuous gas flow

4     No re-breathing or air        ISO permitted maximum is 60 ml
      entry at the patient end      each breath

5     Low resistance in             No specified ISO figure for draw-
      inspiration and expiration    over. Ideally less than 0.5 cm
                                    water at clinically appropriate
                                    flows

6     Robust construction, easy     Without fine tolerances that may
      to service                    move or distort; easy to
                                    disassemble, clean and reassemble
                                    without error.

7     Connects to patient and       Labelled connections and/or
      breathing system without      impossible to misconnect, e.g.
      error                         fixed to anaesthesia machine.

8     Facilitates the use of        No currently available valve does
      PEEP/CPAP                     this adequately in all modes of
                                    ventilation without attachments

9     Minimises dead space          Use of conventional patient
                                    connections

10    Can be located remotely       Ruben (1984), UAM, Diamedica.
      from the patient

11    Moving components visible     As with almost all anaesthetic
      to the user                   equipment, a visual user function
                                    check is a valuable safety
                                    feature

12    Noise of operation is not     Non-intrusive sound of operation
      annoying.                     is a desirable monitoring feature

13    Compatible with scavenging    Allow AGSS connection without
                                    compromise of valve function or
                                    airway.

ISO = International Organization for Standardization, PEEP = positive
end expiratory pressure, CPAP = constant positive airway pressure,
UAM = Universal Anaesthesia Machine, AGSS = anaesthesia gas scavenging
system.
COPYRIGHT 2013 Australian Society of Anaesthetists
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2013 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Author:Fenton, P.M.; Bell, G.
Publication:Anaesthesia and Intensive Care
Article Type:Report
Date:Mar 1, 2013
Words:7231
Previous Article:Carbon dioxide clearance in critical care.
Next Article:Is suppression of apoptosis a new therapeutic target in sepsis?
Topics:

Terms of use | Privacy policy | Copyright © 2018 Farlex, Inc. | Feedback | For webmasters