The effect of major operations on heart rate, respiratory rate, physical activity, temperature and respiratory gas exchange in infants.

Perioperative changes in heart rate (HR), respiratory rate (RR), physical activity, body temperature, oxygen consumption (VO2), carbon dioxide production (VCO2) and resting energy expenditure (REE) were studied in fourteen infants (weight 3.1 +/- 0.2 kg) who had a major operation. VO2 and VCO2 were measured by indirect calorimetry preoperatively, and postoperatively for the first 12 hours continuously and at 24 hours, 48 hours and 5 days. HR, RR and physical activity were recorded on a minute to minute basis, and rectal temperature was recorded hourly. REE was calculated. HR, RR, VO2, VCO2 and REE increased postoperatively, peaking at 2-4 hours, and returned to baseline levels by 12-24 hours. In all of these variables, peak levels were significantly higher than Baseline levels (p < 0.001 for all variables). Physical activity and rectal temperature did not vary significantly throughout the study. This study demonstrates that newborn infants exhibit a short-lived postoperative increase in HR, RR, VO2, VCO2 and REE, which is not related to any alteration in physical activity or body temperature.