Thermoregulatory thresholds for vasoconstriction in pediatric patients anesthetized with halothane or halothane and caudal bupivacaine

Abstract

The thermoregulatory threshold for vasoconstriction has been studied in infants and children given isoflurane, but not in those given halothane anesthesia. More importantly, the effect of vasoconstriction on central temperature in pediatric patients remains unknown. Also unknown is the effect of caudal analgesia on vasoconstriction thresholds. Accordingly, in the first portion of this study, we determined the central thermoregulatory threshold in 23 infants and children given ≃0.6% halothane and caudal anesthesia for abdominal surgery. Patients were prospectively assigned to one of four weight groups: 5-10, 10-20, 20-30, and 30-50 kg. The threshold was considered the central temperature triggering peripheral vasoconstriction, and significant vasoconstriction was defined as a forearm - fingertip skin-surface temperature gradient exceeding 4° C. Thresholds were similar (≃35.7° C) in each study group, suggesting that thermoregulatory responses to halothane anesthesia are similar in infants and children of differing weights. However, they were higher than expected based on the previously reported thresholds in pediatric patients given isoflurane anesthesia. After peripheral vasoconstriction, central temperature continued to decrease in patients weighing more than 30 kg but remained constant or increased slightly in the others. These data suggest that thermoregulatory responses are more effective in infants and small children than in bigger children or adults. In the second part of this study we evaluated the effect of caudal analgesia on the thermoregulatory threshold for vasoconstriction. Children undergoing hypospadias repair were anesthetized with halothane (0.9%) and oxygen. Following induction, they were randomly assigned to caudal analgesia (n = 7) or penile nerve block (n = 6). The threshold was 35.9 ± 0.5° C in the caudal group and 35.7 ± 0.5° C in patients given a penile nerve block, indicating that caudal analgesia per se has little effect on the thermoregulatory threshold for vasoconstriction during halothane anesthesia.