The Komesaroff anaesthetic machine for delivering sevoflurane to dogs

Objective To quantify the vapour output of the Komesaroff machine when using sevoflurane and to determine its performance for inducing and maintaining sevoflurane anaesthesia in dogs. Study design Prospective experimental study. Animals Six clinically normal beagles, aged 3-6 years and weighing 20 ± 1.65 kg (mean ± SEM). Methods The first study was performed using five Komesaroff vaporizers to measure the sevoflurane concentration delivered at each tap setting (I to IV) at 5, 10, 15, 20, 25, 30 and 35 minutes. For this study a ventilator was connected to the Komesaroff machine and set to deliver a tidal volume of 250 mL at 10 cycles minute^-1; oxygen flow was 100 mL minute^-1. A three-litre reservoir bag was attached to the Y-piece connector to act as a lung model. In the second study anaesthesia was induced in dogs with sevoflurane delivered by face-mask mask and carried in 2 L minute^-1 100% oxygen and with the vaporizer set at the fully open position. The quality and speed of induction were recorded. After orotracheal intubation, anaesthesia was maintained for 60 minutes with sevoflurane using an oxygen flow of 100 mL minute^-1. The dogs were allowed to breathe spontaneously. The respiratory rate (RR), heart rate (HR), oesophageal temperature, systolic (SAP) mean (MAP) and diastolic (DAP) arterial pressure, end-tidal CO₂ concentration (Fe'_CO2) end-tidal (Fe'_SEVO) and peak-inspired (Fi_SEVO) percentages of sevoflurane, and vaporizer tap setting were recorded every 5 minutes during anaesthesia. Results The delivery of sevoflurane was constant for each vaporizer setting. The mean output of sevoflurane was 0.44 ± 0.01% for setting I, 2.59 ± 0.18% for setting II, 3.28 ± 0.22% for setting III and 3.1 ± 0.5% for setting IV. In the second study, the mean induction time was 7.72 ± 0.60 minutes and the quality of the induction was good in all dogs. The mean vaporizer tap setting for the maintenance of anaesthesia was 3.48 ± 0.12 and the mean values for Fe'_SEVO and Fi_SEVO were 2.42 ± 0.04% and 2.87 ± 0.06%, respectively. The pedal withdrawal reflex persisted throughout anaesthesia. Conclusions It proved impossible to produce surgical anaesthesia with sevoflurane delivered by the Komesaroff machine despite the highest possible sevoflurane concentration being delivered. Clinical relevance Sevoflurane delivered from the Komesaroff machine cannot be relied upon to maintain surgical anaesthesia in spontaneously breathing dogs.