Dampened ventilatory response to added dead space in newborns of smoking mothers.

BACKGROUND Term newborns can compensate fully for an imposed dead space (tube breathing) by increasing their minute ventilation. OBJECTIVE To test the hypothesis that infants of smoking mothers would have an impaired response to tube breathing. DESIGN Prospective study. SETTING Perinatal service. PATIENTS Fourteen infants of smoking and 24 infants of non-smoking mothers (median postnatal age 37 (11-85) hours and 26 (10-120) hours respectively) were studied. INTERVENTIONS Breath by breath minute volume was measured at baseline and when a dead space of 4.4 ml/kg was incorporated into the breathing circuit. MAIN OUTCOME MEASURES The maximum minute ventilation during tube breathing was determined and the time constant of the response calculated. RESULTS The time constant of the infants of smoking mothers was longer than that of the infants of non-smoking mothers (median (range) 37.3 (22.2-70.2) v 26.2 (13.8-51.0) seconds, p = 0.016). Regression analysis showed that maternal smoking status was related to the time constant independently of birth weight, gestational or postnatal age, or sex (p = 0.018). CONCLUSIONS Intrauterine exposure to smoking is associated with a dampened response to tube breathing.