Halothane Dissolved in Fat as an Intravenous Anaesthetic to Rats

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Abstract
The anesthetic properties of a halothane-in-fat solution given either as a single i.v. dose or as a continuous i.v. infusion were investigated in rats. Halothane 0.3 ml of a 5% solution in a fat emulsion was injected i.v. into 15 awake rats. At the end of the 30 s injection, all rats had collapsed from the upright position and showed no response to a firmly applied tail clamp. Breathing usually became shallow and irregular just after injection. Two rats died. In the surviving rats, movement in response to clamping of the tail reappeared after some 30 s (range 15-90 s). The rats regained the upright position after .apprx. 100 s and appeared fully awake .apprx. 3 min (range 2-5 min) after injection. Surviving rats behaved normally after the experiment, and gained in weight. They were killed 1-29 days later. The lungs, kidneys, heart, brain and liver had a normal macroscopic and microscopic appearance. In a 2nd set of experiments (n = 9), a 10% solution of halothane was continuously infused i.v. (3.75 .mu.l/min). The anesthetic depth, as well as the mean arterial pressure, heart rate, respiratory rate and arterial PCO2 [Co2 partial pressure] and PO2 [O2 partial pressure] were similar to values observed during inhalation of halothane in air at an inspired concentration of 1.1%. By doubling the infusion rate, MAP [mean arterial pressure] was reduced by 23%. It was easy to adjust anesthetic depth by changing the infusion rate; recovery was fast.