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

Abstract

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.