Thermogenetic response to mild hypothermia in anaesthetized infants and children

Metabolic correlates were related to room, core body and skin temperatures in 66 anaesthetized infants and children. Forty-one who had normal cardiorespiratory function were undergoing minor lower abdominal surgical procedures and were spontaneously breathing O₂/air mixture and halothane (body weight, 3.4–25.3 kg). Twenty-five had congenital heart malformations; 14 were cyanotic (weight, 3.4–24.3 kg) and 11 were acyanotic (weight, 3.7–20 kg). These 25 had balanced anaesthesia with halothane and their lungs were mechanically ventilated. Oxygen consumption (V?o₂), i. e. heat production, and CO₂ elimination (V?co₂) were measured by mass spectrometry. Indirect calorimetry was used for calculation of energy consumption. Temperatures were recorded in the lower third of the oesophagus (core temperature), at the mammillary level along the anterior axillary line (skin temperature), and in room air. Oesophageal temperatures ranged from 34.0°C to 38.1°C and skin temperatures from 32.1°C to 37.4°C (mean ± SD, 34.5°C ± 1.2°C). Heat production (V?o₂) was not related to body, skin or room temperatures. In concordance V?co₂ and energy expenditure were unrelated to the measured temperatures. Thermogenesis is thus eliminated in infants as well as in children, by the anaesthetic techniques used in the current study. This emphasizes the importance of prevention of heat loss in paediatric anaesthesia. Since the reduced skin and body temperatures in this study did not increase oxygen consumption, temperature regulation via an enhanced V?o₂ does not appear as a factor that aggravates hypoxaemia in cyanotic infants and children with congenital heart malformations.