Propofol-halothane-nitrous oxide/oxygen anaesthesia for mega-voltage radiotherapy in dogs

Observations were made on 49 dogs aged 3–13 years, of ASA Grades I and 11, during 83 periods of mega-voltage radiotherapy. The dogs weighed 5.847.0 kg and the total duration of anaesthesia ranged from 12–52 min (mean ± sem, 22 ± 8). No premedication was given. Anaesthesia was induced with iv propofol and, following endotracheal intubation, maintained with halothane/nitrous oxide/oxygen and intermittent injections of propofol. The dose of propofol needed to induce jaw relaxation sufficient for intubation was 3.5–10.8 mgkg bwt (5.67 ± 0.15) administered over 7–137 s (36 ± 2). On 91 occasions in 54 periods of anaesthesia, supplementary doses of propofol ranging from 0.2–4.9 mg/kg bwt (1.42 ± 0.14) were needed during positioning for irradiation. The times elapsing from extubation to swallowing, response to voice, spontaneous head lifting and walking were 3, 6, 7 and 13 min, respectively. A 12% incidence of tonic-clonic movements indicated that the method of anaesthesia cannot be regarded as entirely satisfactory for mega-voltage radiotherapy.