The effects of cesarean section anesthesia on heat loss and heat production in the newborn rabbit.

The newborn of some smaller animals rely upon heat produced by nonshivering thermogenesis in the brown fat to prevent a fall in body temperature after birth. Because of their pharmacological properties, some drugs may affect nonshivering thermogenesis. Therefore, in this study, the ability of newborn rabbits delivered under Innovar-Vet, ketamine hydrochloride, methoxyflurane and epidural anesthesia to maintain the rectal, subcutaneous interscapular and lumbar temperature was investigated at an ambient temperature of 35 degrees C or 22 degrees C and the results compared with control newborns delivered without anesthesia. When the newborns were exposed to 35 degrees C, the anesthetics studied had no effect on the ability of the newborn to maintain the rectal temperature and the subcutaneous temperature over the interscapular fat pad was similar to the lumbar subcutaneous temperature thereby indicating that nonshivering thermogenesis was not activated. However, at an ambient temperature of 22 degrees C Innovar-Vet or methoxyflurane reduced the temperature difference between interscapular and lumbar temperatures to 1.6 degrees C compared to 2.5 degrees C in controls and the difference between core temperature and ambient temperature to 3.5 degrees C greater compared to 7.5 degrees C in controls. Ketamine hydrochloride or lidocaine hydrochloride plus meperidine has less effect because these compounds lack adrenergic blocking properties. These data suggest that newborns delivered under anesthetics or tranquillizers that have adrenergic blocking properties require a warm (35 degrees C) environment to prevent a fall in core temperature.