Decreased ventilatory response to hypoxia in sedated newborn piglets prenatally exposed to cocaine

Abstract

OBJECTIVE: Infants exposed to cocaine in utero have been reported to have a higher incidence of apnea and altered ventilatory response to carbon dioxide and hypoxia. We investigated whether in utero cocaine exposure results in greater ventilatory depression during hypoxia in piglets. METHODS: Cocaine hydrochloride, 1.0 or 2.0 mg/kg given intramuscularly, or saline solution was administered daily to pair-fed pregnant sows during the last month of gestation. Thirteen cocaine-exposed piglets (mean ± SD: age, 4.4 ± 1.3 days; weight, 2.10 ± 0.10 kg) and 15 saline solution-exposed piglets (age, 4.6 ± 1.1 days; weight, 2.32 ± 0.42 kg) were studied under chloral hydrate sedation. Minute ventilation (v̇ E), arterial blood pressure (BP), heart rate (HR), oxygen consumption (v̇ O 2), and arterial blood gases were measured in room air. During hypoxia (fraction of inspired oxygen = 0.10), the values for v̇ E, BP, and HR were obtained at 1, 5, and 10 minutes, v̇ O 2 was calculated during the last 5 minutes, and arterial blood gas samples taken after 10 minutes. RESULTS: Basal v̇ E did not differ between saline solution- and cocaine-exposed animals. The increase in v̇ E at 1 minute of hypoxia was also similar. However, at 5 and 10 minutes of hypoxia, v̇ E was significantly lower in the cocaine group than in the saline group (6% ± 9% and 4% ± 10% vs 15% ± 13% and 21% ± 14%; p <0.02). Mean baseline BP and the initial increase in BP during hypoxia were not different between groups. However, BP remained increased throughout hypoxia only in the saline solution-exposed animals ( p <0.05). Changes in HR, v̇ O 2, arterial oxygen tension, and base excess during hypoxia were similar between groups. CONCLUSIONS: These results show a decrease in the ventilatory response to hypoxia in newborn piglets prenatally exposed to cocaine. This change is most likely to be centrally mediated because the initial hypoxic hyperventilation was not modified by the intrauterine cocaine exposure. This decrease in ventilation cannot be explained by changes in metabolic rate or in cardiovascular or acid-base status. (J P EDIATR 1996;128:389-95)