Efficacy of the Komesaroff anaesthetic machine for delivering isoflurane to dogs.

The Komesaroff machine is a low-flow, closed-circle circuit with a low resistance vaporiser, of the Goldman type, in circuit. This trial assessed the mechanical consistency of the delivery of isoflurane by the vaporisers, and used six dogs to compare the in vivo cardiorespiratory effects of the anaesthetic agent delivered by the Komesaroff machine with the effects of a circle system with high flows in the semi-closed mode. The delivery of isoflurane was constant for each vaporiser setting and no potentially dangerous concentrations of isoflurane were observed. The mean (sem) percentages of isoflurane were 0.18 (0.019) at setting I, 1.46 (0.055) at setting II, 3.12 (0.066) at setting III and 3.01 (0.047) at setting IV. There were no significant differences between the two types of circuit in vivo, and the measured haemodynamic variables were satisfactory throughout the experiments.

Anaesthetic potency of isoflurane in cattle: determination of the minimum alveolar concentration.

OBJECTIVE: To determine the minimum alveolar concentration (MAC) of isoflurane in cattle. STUDY DESIGN: Prospective study. ANIMALS: Sixteen healthy adult female Holstein-Friesian cattle weighing 612 ± 17 kg (× ± SEM) and aged 5.7 ± 0.9 years old. METHODS: The unsedated cattle were restrained in right lateral recumbency using a rope harness technique. Anaesthesia was induced with isoflurane (ISO) in oxygen via a face mask connected to a large-animal, semiclosed anaesthetic circle system. Each cow was intubated with a cuffed orotracheal tube (25 mm ID). Inspired and end-tidal ISO were monitored using a calibrated infra red analyser with a methane filter. The MAC of ISO that prevented gross purposeful movement in response to a tail and dewclaw clamp was determined. The time from the start of ISO administration to intubation, the time interval between discontinuance of ISO and the time the animal regained sternal recumbency, were recorded. Time to standing and quality of recovery were also recorded. RESULTS: The time from the start of ISO administration to tracheal intubation was 18.68 ± 2.77 minutes. The MAC of ISO in these cattle was 1.27 ± 0.03% (1.14 ± 0.01% corrected to sea level). Time to sternal recumbency after 90 ± 16 minutes of anaesthesia from intubation was 4.60 ± 0.58 minutes and time to standing was 6.70 ± 1.02 minutes. All cattle were extubated when they regained sternal recumbency. CONCLUSION: The MAC of isoflurane in these cattle was 1.27 ± 0.03% (1.14 ± 0.01% corrected to sea level). ISO provided a smooth induction to, and rapid recovery from, anaesthesia. CLINICAL RELEVANCE: Knowledge of the MAC of ISO in cattle will facilitate its appropriate clinical use.