The effect of halothane on the baroresponse of adult and baby rabbits.

The effect of anesthesia on the baroresponse of infants is not known. Therefore, the authors studied the baroreceptor activity of adult and 10- to 14-day-old rabbits during halothane anesthesia. The arterial systolic pressure was increased 20 to 30 per cent by injecting 0.03-0.04 mg/kg of phenylephrine into the femoral or external jugular vein while recording the electrocardiogram and femoral arterial blood pressure. The slope of the R-R interval on systolic pressure (baroresponse) was determined. The studies were done in the awake, unmedicated state and at 0.5, 1.0, and 1.5 MAC halothane. Oxygen was the carrier gas. The sensitivity of the response was different in the two groups of animals. When awake, the adults' slope was greater than that of the babies. During anesthesia the slopes decreased in both groups, but the decrease was greater in the babies. At 0.5 MAC halothane, the baroresponse was reduced 80 and 54 per cent in baby and adult rabbits, respectively. Lag time (the time between the onset of the rise in systolic blood pressure and the change in R-R interval) was prolonged in both the babies and the adults. Both showed the same prolongation during anesthesia, although the percentage change in the babies was greater.