Ventilatory response to carbon dioxide in term infants after halothane and nitrous oxide anesthesia

The purpose of this study was to determine whether the ventilatory response to CO2 is depressed in term infants after halothane and N2O anesthesia. Ventilatory response to CO2 was determined by using a maskless CO2 response test in which a ventilation ratio is calculated from measurements of transcutaneous PCO2 (PtcCO2). Ventilation ratio represents the fractional increase in ventilation that occurs in response to inspired CO2. Eight infants were studied who were at least 36 wk gestational age and 12 +/- 4 wk postnatal age, did not have apnea in the perioperative period (values are means +/- SD). Ventilation ratio measured with a 4%-inspired-CO2 stimulus increased significantly after anesthesia (3.5 +/- 0.8 vs 3.0 +/- 0.5, P = 0.02). Baseline PtcCO2 was significantly lower after anesthesia than before anesthesia (37 +/- 4 vs 42 +/- 3, P < 0.01) which may reflect the development of a relative metabolic acidosis. (The occurrence of postoperative metabolic acidosis was in fact documented in another group of eight infants.) Ventilatory response to CO2 was not depressed after halothane and nitrous oxide anesthesia in these term and near-term infants.