The study of natural sleep after general anaesthesia in the cat.

The sleeping patterns of postanaesthetic state and behaviour in unrestrained cats were studied for two weeks. The percentages of wakefulness, slow wave sleep, drowsiness, and paradoxical sleep were not affected by nitrous oxide anaesthesia. Sleeping patterns were changed for several days after halothane anaesthesia; firstly paradoxical sleep decreased and drowsiness increased, then paradoxical sleep increased and drowsiness decreased. The rebound period was different among the 0.5%, 1.0%, and 1.5% halothane. Complete recovery of paradoxical sleep after 1.5% halothane anaesthesia for 5 hours required nine days in this experiment. This finding shows that the recovery of natural sleep from general anaesthesia takes longer than behavioural recovery.