Anaes · The anaesthetic machine
The anaesthetic machine
Also known as Anaesthetic machine · Anaesthesia workstation · Gas delivery system · Circle system · Pre-use check · Vaporiser
The anaesthetic machine is the device that delivers a precisely controlled mixture of gases (oxygen, nitrous oxide, medical air) and vapourised anaesthetic agents to the patient, removes the carbon dioxide, and provides the means for controlled ventilation. The framework rests on four exam-critical ideas: the gas supply (the pipeline and the cylinder, the pressure regulation, the flowmeters); the vaporiser (the variable-bypass plenum for the volatiles, the heated pressurised for desflurane); the breathing system (the circle system with the unidirectional valves, the CO2 absorber, and the APL valve); and the pre-use check (the AAGBI checklist: the power, the gas supply, the leak test, the flowmeters, the ventilator). Built on the AAGBI checking-equipment guidelines (2012), the closed-circuit review (Parthasarathy 2013), and the anaesthetic-machine assessment test (Tiviraj 2016).
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Red flags
- A failure of the anaesthetic machine — the disconnection, the gas failure, the vaporiser malfunction, the ventilator failure — is a crisis that can kill the patient in minutes. The pre-use check is the single most important safety measure; never start an anaesthetic without it. The emergency cylinder and the self-inflating bag must be to hand.
Meet the patient
A 45-year-old woman is anaesthetised for a cholecystectomy. Ten minutes after induction the oxygen pipeline pressure alarm sounds, the FiO2 drops, and the ventilator bellows collapses. The pipeline supply has failed. Your first move is not to diagnose the machine — it is to disconnect the patient and ventilate with a self-inflating bag on cylinder oxygen, then open the O2 cylinder and switch to TIVA.[1]
The two questions the machine exists to answer: is the gas I am delivering what I think it is? (the flowmeters, the vaporiser, the agent analyser) and is it reaching the patient safely? (the breathing system, the valves, the scavenging). The pre-use check answers both before the patient arrives — never start an anaesthetic without it.[1]
References7ShowHide
- [1]Hartle A, Anderson E, Bythell V, et al. Checking anaesthetic equipment 2012: association of anaesthetists of Great Britain and Ireland Anaesthesia, 2012.PMID 22563957
- [2]Parthasarathy S The closed circuit and the low flow systems Indian J Anaesth, 2013.PMID 24249885
- [3]Tiviraj S, et al. Development of An Assessment Test for An Anesthetic Machine J Med Assoc Thai, 2016.PMID 27501622
- [4]Das S, Chattopadhyay S, et al. The anaesthesia gas supply system. Indian J Anaesth, 2013.PMID 24249882
- [5]De Cooman S, Schollaert C, et al. Hypoxic guard systems do not prevent rapid hypoxic inspired mixture formation. J Clin Monit Comput, 2015.PMID 25270987
- [6]Pauling M, Ball CM Delivery of anoxic gas mixtures in anaesthesia: case report and review of the struggle towards safer standards of care. Anaesth Intensive Care, 2017.PMID 28675797
- [7]Lauber R, Steiner A, et al. Accuracy, alarm limits and rise times of 12 oxygen analysers. Anaesthesia, 1994.PMID 7864324