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 res ponse to CO2 is depressed in term infants after halothane and N2O anes thesia. Ventilatory response to CO2 was determined by using a maskless CO2 response test in which a ventilation ratio is calculated from mea surements of transcutaneous Pco2 (P(tc)CO2). Ventilation ratio represe nts the fractional increase in ventilation that occurs in response to inspired CO2. Eight infants were studied who were at least 36 wk gesta tional age and 12 +/- 4 wk postnatal age, did not have apnea in the pe rioperative period (values are means +/- SD). Ventilation ratio measur ed with a 4%-inspired-CO2 stimulus increased significantly after anest hesia (3.5 +/- 0.8 vs 3.0 +/- 0.5, P = 0.02). Baseline P(tc)co2 was si gnificantly lower after anesthesia than before anesthesia (37 +/- 4 vs 42 +/- 3, P < 0.01) which may reflect the development of a relative m etabolic acidosis. (The occurrence of postoperative metabolic acidosis was in fact documented in another group of eight infants.) Ventilator y response to CO2 was not depressed after halothane and nitrous oxide anesthesia in these term and near-term infants.