Urethane as a sole general anaesthetic in cats used for electroretinogram studies

Cats are very sensitive to induction of anaesthesia by urethane. To anaesthetize cats with urethane, 1.0-1.3 g/kg, of freshly prepared urethane is administered intravenously at a rate of 1.92 g/h, while anaesthesia is maintained with 0.5% halothane in a 66%/33% nitrous oxide/carbogen gas mixture. Cats can then be maintained for up to 3 days by intravenous infusion at a rate of 4 ml/h of a 100 ml solution containing 50 IU heparin, 2.4 mg atropine, 4.7 g anhydrous D-glucose, and 240 mg urethane/kg. Using this anaesthetic, excellent electroretinograms can be recorded with no interfering eye movements.