• S Laing, V Paul, and P J Murison.
• Division of Companion Animals, University of Bristol, Langford House, Langford, Bristol BS40 5DU, UK.
• J Small Anim Pract. 2009 Feb 1;50(2):82-6.

ObjectivesTo assess rate and quality of recovery from anaesthesia where isoflurane was delivered in oxygen or oxygen/nitrous oxide.MethodsDogs anaesthetised with propofol were randomly allocated to receive isoflurane maintenance in either 100 per cent oxygen (group 1) or 66 per cent nitrous oxide (N(2)O)/34 per cent oxygen (group 2). Time from end of anaesthesia to achieving sternal recumbency was recorded. Incidence of adverse behaviours (vocalisation, uncontrolled head movement and restlessness) were assessed. Recovery quality was recorded on a visual analogue scale (VAS) (anchored at 0 with "best possible" recovery and "did not recover" at 100 mm). Age, weight, gender, anaesthetic duration, mean vaporiser setting, VAS scores, recovery times, postoperative temperature and behavioural scores were compared (chi-squared test, Mann-Whitney U test or t-test as appropriate, significance P< or =0.05).ResultsObjective data from 54 dogs were analysed, only VAS data where the observer was unaware of treatment group were used (n=33). Recovery was faster in group 2 dogs (median 10 min [range 4 to 31] compared with 14 minutes [3 to 43] in group 1, P=0.049) with less restlessness (0 [0 to 4] compared with 2 [0 to 4] in group 1, P=0.013) and uncontrolled head movement (0 [0 to 4] compared with 1 [0 to 3] in group 1, P<0.001). However, VAS scores were not statistically different between groups (group 1: mean 39.4 mm [s.d. 24.0)]; group 2: 30.1 mm [25.9]; P=0.303).Clinical SignificanceAddition of N(2)O to isoflurane anaesthesia results in a lower incidence of adverse behaviour (for example restlessness) and marginally faster recovery.

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