OXYGEN AND ANAEMIA: THEIR EFFECTS IN MICE, ON INDUCTION TIME AND SURVIVAL TIME WITH HALOTHANE ANAESTHESIA

This paper reports the results of five studies on female miceto investigate the effects of halothane anaesthesia in air and100 per cent oxygen on induction time, survival time and sensitivityto halothane, in bled and unbled mice. Studies on the effectof anaemia on induction time and survival time showed that reductionsof haemoglobin content significantly reduced induction timesin mice anaesthetized with 10 per cent halothane in air and100 per cent oxygen (2 1./min), but did not significandy affectthe survival times in the same groups of mice. The use of 100per cent oxygen instead of air as the anaesthetic vehicle causeda highly significant increase in induction times and survivaltimes in both bled and unbled mice. Toxicity studies to determinethe halothane concentrations required to kill 50 per cent and99 per cent of mice in 30 minutes were used to confirm the resultsof the above survival studies. One study showed that in unbledmice, the mice were significantly more sensitive to halothane/airanaesthesia than to halothane/100 per cent oxygen anaesthesia.Other studies showed that a mean haemoglobin reduction of 31per cent did not significandy affect the mouse sensitivity tohalothane/100 per cent oxygen anaesthesia, but a reduction of45 per cent significantly increased the sensitivity of the bledmice to halothane/100 per cent oxygen. Body weight was shownto have a highly significant effect on induction time and survivaltime with 10 per cent halothane/100 per cent oxygen, but a non-significanteffect with 10 per cent halothane/air.