DECREASED CARBON-DIOXIDE SENSITIVITY IN INFANTS OF SUBSTANCE-ABUSING MOTHERS

Objective. To determine whether there is a demonstrable abnormality in control of breathing in infants of substance-abusing mothers during t he first few days of life. Methods. We enrolled 12 drug-free control i nfants and 12 infants of substance abusing mothers (ISAMs). These infa nts experienced otherwise uncomplicated term pregnancies and deliverie s. The infants were assigned to a group based on the results of matern al histories and maternal and infant urine toxicology screens. Studies were performed during quiet sleep during the first few days of life. We measured heart rate, oxygen saturations via a pulse oximeter, end-t idal carbon dioxide (ET-CO2) level, respiratory rate, tidal volume, an d airflow. The chemoreceptor response was assessed by measuring minute ventilation and the ET-CO2 level after 5 minutes of breathing either room air or 4% carbon dioxide. Results. The gestational ages by obstet rical dating and examination of the infants were not different, althou gh birth weights and birth lengths were lower in the group of ISAMs. O ther demographic data were not different, and there were no difference s in the infants' median ages at the time of study or in maternal use of tobacco and alcohol. The two groups had comparable baseline (room a ir) ET-CO2 levels, respiratory rates, tidal volumes, and minute ventil ation. When compared with the group of ISAMs, the drug-free group had markedly increased tidal volume and minute ventilation on exposure to 4% carbon dioxide. These increases accounted for the difference in sen sitivity to carbon dioxide, calculated as the change in minute ventila tion per unit change in ET-CO2 (milliliters per kg/min per mm Hg). The sensitivity to carbon dioxide of control infants was 48.66 +/- 7.14 ( mean +/- SE), whereas that of ISAMs was 16.28 +/- 3.14, Conclusions. T hese data suggest that ISAMs are relatively insensitive to challenge b y carbon dioxide during the first few days of life. We speculate that this reflects an impairment of the chemoreceptor response.