Universal Anaesthesia Machine (UAM) – functional testing of a new anaesthesia workstation for use in the developing world De Beer DAH, Walker IA, ♦Bell G, *Rapuleng A, *Collins MDepartment of Anaesthesia, *Department of Biomedical Engineering, Great Ormond Street Hospital NHS Trust, London.♦Department of Anaesthesia, Royal Hospital for Sick Children, Glasgow.

Introduction

The provision of safe anaesthesia in many developing countries is compromised by a lack of appropriately designed anaesthesia equipment. The unsuitability of modern complex anaesthesia work stations in areas with potentially challenging environmental conditions (temperatures [5oC-40oC], humidity [15%-95%]) and limited logistical supplies of electricity and anaesthetic gases has led to the development of a new anaesthesia workstation. The Universal Anaesthesia Machine (UAM) is a low cost, full-size anaesthetic machine which combines continuous flow configuration with draw-over reliability to provide inhalation anaesthesia using an oxygen concentrator if there is electricity or, if not, using an external source of oxygen including room air [1].

Electrical supply - Failure of mains electrical supply did not result in any interruption to gas flow provided an alternative source of oxygen was available. The oxygen monitor remained functional throughout.

Means of gas delivery a) Oxygen concentrator - A maximum oxygen concentration of 91.2% was achieved after 250 sec (73.3% at 60 sec, 89.0% at 120 sec, 90.9% at 180 sec, 91.1% at 240 sec). b) Alternative oxygen sources - While in operation the concentrator was used in preference to either pipeline or cylinder supplies. When switched off the hierarchy of use of alternative oxygen sources was pipeline and then cylinder supplies. Gas flow remained unchanged throughout the transition. With complete oxygen failure the inflating bellows could still be inflated using the room air entrainment inlet. Means to prevent hypoxic gas mixtures of oxygen and nitrous oxide a) Oxygen analyser/ apnoea alarm - The oxygen analyser was found to operate within narrow limits (± 1%) at both 21% and 100% oxygen concentration. The apnoea alarm could be muted but it was not possible to disable it. b) Rotameters - The glass rotameters were accurate to within ± 5% of set flow at 100% oxygen across its range (0.1-10l.min-1). Accuracy was reduced at extreme low flow rates. The hypoxic guard terminated flow of nitrous oxide when the analyser recorded an oxygen concentration less than the “LOW alarm” limit (18-50% oxygen). As the oxygen concentration returned above this lower limit nitrous oxide flow was re-introduced at the previous flow meter setting. Draw-over vaporizer (DOV) In experiments using continuous flow draw-over, the DOV almost always produced measured vapour concentrations less than set concentrations at all temperatures tested (20, 25, 30oC) (Figure 2). This difference was more pronounced at higher set vapour concentrations and at higher temperatures. Results for tests using intermittent flow draw-over and those examining changes in vapour concentration over time are still outstanding. Means for manual ventilation of the patient Tests in progress Means for delivering gas to the patient Tests in progress Other tests (see methods) Tests in progress

Does vapour concentration remain constant over time?

Results and Discussion

1. Fenton P. Maternal mortality and anaesthesia technology in the 21st century. Anaesthesia News 2010; 273: 5-10.2. ISO/FDIS 8835-7 2011 (Final draft). Inhalational anaesthesia systems – Part 7: Anaesthetic systems for use in areas with limited logistical supplies of electricity and anaesthetic gases. 3.English WA, Tully R, Muller GD, Eltringham RJJ. The Diamedica Draw-Over-Vaporizer: a comparison of a new vaporiser with the Oxford Miniature Vaporizer. Anaesthesia 2009; 64: 84-92.4. Donovan A, Perndt H. Oxford Miniature Vaporizer output with reserved flows. Anaesthesia 2007; 62: 609-14.

References

Electrical supply - test ability of machine to function and ensure delivery of anaesthetic gases in the event of mains electricity supply failure.

• Means of gas delivery - test compliance and function of integrated oxygen concentrator (ISO 8359/ISO10083) and fittings for alternative oxygen sources including the ‘hierarchy’ of use and automatic use of room air entrainment inlet when alternative oxygen sources are unavailable.

• Means to prevent hypoxic gas mixtures of oxygen and nitrous oxide - test hypoxic guard and accuracy of rotameter calibration including condensation check. Test calibration of integral fuel cell oxygen monitor and function of the apnoea alarm.

Draw-over vaporizer (DOV) - test structural components (including calibration and internal resistance ISO/TS 18835) and functionality against ideal characteristics [2] and other commercially available draw-over vaporizers [3, 4]. In particular, test that the vapour concentration output accurately reflects dial settings, remains constant over time and does not differ across clinically relevant ranges of flow rates (especially low flow rates) and ambient temperatures.

Means for manual ventilation of the patient - test efficiency of inflating bellows.

Means for delivering gas to the patient either by continuous flow breathing system (compliant with ISO 80601-2-13) or draw- over breathing system (compliant with ISO/TS 18835). Evaluation of the effects of CPAP/ PEEP on the system to determine the occurrence of flow reversal and to quantify the reduction in gas flow occurring when using the Ayre’s T-piece (static CPAP test).

Other tests including negative and positive pressure relief valve unit, balloon inflating valve, pressure relief valve and gas scavenging.

Methods

The UAM appears to be a well designed and manufactured anaesthetic machine. Completion of the first part of testing confirms a reliable means of gas delivery, even in the absence of electricity and an effective hypoxic guard. With continuous flow draw-over the DOV tends to under deliver the set vapour concentration.

Conclusions

Objectives

Although the UAM is CE-certified and manufactured in an ISO-qualified factory, it has not been formally evaluated. The aim of this study was to test the UAM against the manufacturer’s specifications and the proposed ISO international standard for anaesthetic systems for use in areas with limited logistical supplies of electricity and anaesthetic gases.

Fig 1. The Universal Anaesthesia Machine

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Fig 2. Graphs representing measured vapour concentration (%) and set vapour concentration during continuous flow at differentflow rates (l.min-1) and different temperatures (20, 25 and 30oC) for the UAM draw-over vaporizer (DOV).

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Declarations: None of the authors or evaluators has any financial interest in this project