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Impaired response to tube breathing in infants born to smoking mothers

Presented at the Neonatal Society 2003 Summer Meeting (programme).

Bhat RY, Broughton S, Hannam S, Rafferty GF, Milner AD, Greenough A

Dept of Child Health, Guy's, King's and St Thomas' Medical School, London

Background: Infants of smoking mothers have an increased risk of sudden infant death, a possible mechanism being reduced drive to breathe (1). We have previously demonstrated that newborns are able to compensate fully for an imposed physiological dead space (tube breathing) by increasing their minute ventilation (2).

Objective: To test the hypothesis that infants of smoking mothers would have an impaired response to tube breathing.

Methods: A face mask was placed over the infant's face. Flow was recorded from a pneumotachograph, which was connected to face mask by a wide bore tube. The flow signal was integrated to give volume and the breath to breath minute volume calculated. A three way tap was connected to the pneumotachograph by a second wide bore tube. When the three way tap was in the neutral position, a 2L/min flow of gas passed directly to the face mask. When the three way tap was rotated, the flow was redirected down the side arm of the system and a dead space of 2ml/kg was incorporated into the circuit without having to remove the face mask. The infant breathed through the dead space for two minutes. The breath by breath minute ventilation was plotted against time (seconds) and a polynomial regression line was drawn through the data points. The maximum minute ventilation (MMV) was recorded and the time taken to achieve 63% of the MMV calculated.

Patients: Ten infants of smoking mothers and ten infants of non smoking mothers (median gestational age of 39 (37-42) weeks and 41 (38-42) weeks respectively) and (median postnatal age of 42(22-53) hours and 26(20-44) hours respectively) were studied.

Results: The median MMV achieved by the two groups was similar [442 (262-631) ml/min/kg versus 395(192-518) ml/min/kg, p=0.4]. The infants of smoking mothers, however, took longer to achieve 63% of the MMV [19 (8.3-22.4) seconds versus 11 (5.1-23.7) seconds, p= 0.049].

Conclusion: The impaired response to tube breathing suggests intrauterine exposure to tobacco smoke dampens chemoreceptor response.

1. Ueda Y, Stick SM, Hall G, Sly PD. Control of breathing in infants born to smoking mothers. J Pediatr, 1999; 135: 226-232.
2. Upton CJ, Milner AD, et al. Dynamic response to tube breathing during the first 10 days of life. Paediatr Pulmonol, 1990; 9: 72-9.

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