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Prenatal Cigarette Smoke Exposure Attenuates Recovery from Hypoxemic Challenge in Preterm Infants

¹ Department of Pediatrics and Institute of Maternal and Child Health, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada

Correspondence and requests for reprints should be addressed to Shabih U. Hasan, M.D., Department of Pediatrics, Health Sciences Center, 3330 Hospital Drive NW, Calgary, AB, T2N 4N1 Canada. E-mail: hasans{at}ucalgary.ca

Rationale: The effects of prenatal cigarette smoke (CS) exposure and hypoxemia on cardiorespiratory control have been investigated in full-term infants. However, few data are available in preterm infants, who form a particularly vulnerable population, with developmentally immature cardiorespiratory control.

Objectives: To investigate the effects of prenatal CS exposure on the duration and recovery of breathing pauses and oxygen saturation levels under baseline and hypoxemic conditions in preterm infants.

Methods: The study was performed on 22 (12 born to smoking and 10 to nonsmoking mothers) spontaneously breathing preterm infants between 28 and 36 weeks' gestation. Cardiorespiratory variables were recorded under baseline normoxemic and hypoxemic conditions.

Measurements and Main Results: Breathing pauses, pause indices, time to recovery, percent pause recovery, oxygen saturation (Sp_O2), periods of wakefulness, and cardiorespiratory rates were compared between the two groups. Spontaneous recovery of breathing pauses (P = 0.03) and Sp_O2 levels (P = 0.017) were attenuated in CS-exposed infants as compared with the control group during the hypoxemic and posthypoxemic periods, respectively. The episodes of wakefulness during the hypoxemic challenge were similar between the two groups. Furthermore, CS-exposed infants showed a greater increase in heart rate (P < 0.001) during the hypoxemic challenge when compared with control infants.

Conclusions: We provide evidence of how prenatal CS exposure and hypoxemic episodes affect the duration and recovery of breathing pauses in preterm infants. These observations could help explain why these infants are at a particularly high risk for sudden infant death syndrome.

Key Words: apnea • hypoxemia • SIDS • smoking • oxygen saturation

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject The effects of prenatal cigarette smoke exposure and hypoxemia on cardiorespiratory control have not been investigated in preterm infants, who are among the most vulnerable group for sudden infant death syndrome (SIDS). What This Study Adds to the Field We provide evidence that prenatal cigarette smoke exposure, which is the principal risk factor for SIDS, leads to adverse effects on spontaneous recovery of breathing pauses and oxygen saturation during hypoxemia in preterm infants.