Studies on lorazepam as a premedicant for thiopental anaesthesia in the dog

Four mg of lorazepam was given intravenously 5 min prior to thiopental anaesthesia in 5 clinically healthy dogs weighing 14 +/- 2 kg and aged about 10-12 months. Animals required only 7.0 +/- 1.5 ml of 5% thiopental sodium to achieve surgical anaesthesia which lasted about 30.4 +/- 3.3 minutes. There was adequate muscle relaxation and loss of pedal and palpebral reflexes. Five min after administration of lorazepam, there was no appreciable change in various cardiopulmonary dynamics. However, there was moderate arterial hypertension, tachycardia and arterial hypoxemia 15 min after the onset of the thiopental anaesthesia. There was no respiratory depression. The lorazepam-thiopental combination was also attempted in 16 clinical cases varying from repair of fractures of long bones (9), mammary tumour (2), ear haematoma (1), ear cropping (1), tail gangrene (2) and rectal prolapse (1). This combination of anaesthesia proved extremely useful for orthopaedic surgery as the muscle relaxation was adequate and reduction of the fractured ends was comparatively easier.