Presented at the Neonatal Society 2011 Autumn Meeting.
Ali K, Bhat R, Hannam S, Rafferty GF, Wolff K, Greenough A
Division of Asthma, Allergy and Lung Biology, King’s College London, King’s College Hospital, Denmark Hill, London, UK
Background: Infants of smoking mothers have an increased risk of sudden infant death. A possible explanation for the association is that such infants have neurodevelopmental abnormalities of the control of ventilation. We have previously shown that newborns of smoking mothers have a dampened ventilatory response to added dead space (1). The aim of the study is to test the hypothesis that infants of smoking mothers compared to infants of non-smoking mothers would have a poorer ventilatory response to hypercapnia.
Methods: Infants were recruited before maternity unit discharge. Infants were assigned to groups based on the maternal smoking history. Respiratory flow was measured using a pneumotachograph inserted into a face mask placed over the infant’s mouth and nose. Tidal volume was derived by digital integration of the flow signal. The ventilatory response to three levels of inspired carbon dioxide (baseline = 0%, 2% and 4% CO2) was assessed. The study was undertaken in accordance of UK ethical guidelines.
Results: Thirteen infants of smoking mothers and 13 infants of non smoking mothers (median gestational age 39 (36-41) weeks and 39 (37-42) weeks respectively) were studied at a median postnatal age of 30(10-120) hours. The birth weight was significantly higher in the infants of the non-smoking mothers (median 3290 (2068-4740) gms versus 2822 (1924-3672) gms) (p=0.03), but there were no significant differences in the other demographics of the two groups. The two groups had similar baseline respiratory rates, tidal volumes and minute ventilation. On exposure to 4% CO2, infants of smoking mothers had a significantly lower increase in minute ventilation (median 61 (39-125)%) compared to infants of non-smoking mothers (median 85 (32-188)%) (p=0.03). Carbon dioxide sensitivity, calculated as the change in minute ventilation per unit change in ET-CO2 was also significantly lower in infants of smoking mothers (median 15.9 (7-22) versus 21.4 (9-64)ml/kg/min/mmHg) (p=0.01).
Conclusion: The lower response to hypercapnia in the infants of smoking mothers suggests that intrauterine exposure to tobacco smoke may dampen chemoreceptor responsiveness.
Corresponding author: anne.greenough@kcl.ac.uk
References
1. Bhat R, Broughton S, Khetriwal B, Rafferty GF, Hannam S, Milner AD, Greenough A. Arch Dis Child 2005; 90(4): F316-319.