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 nonsmoking 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. I nfants whose mothers smoke during pregnancy are at increased risk of sudden infant death syndrome compared with infants of non-smoking mothers; the increase in risk has been reported to be twofold to fourfold, but as high as sixfold if associated with other risk factors.1-3 A possible explanation for the association is that the infants have neurodevelopmental abnormalities of the control of ventilation. 4 If that explanation were correct, infants of smoking mothers would be predicted to have a reduced ventilatory response to hypercarbia. [4][5][6] Term newborns can compensate fully for an imposed dead space (tube breathing) by increasing their minute ventilation.7 It has been argued that hypercarbia is the most important stimulus to ventilation during tube breathing.8 9 If then infants of smoking mothers do have neurodevelopmental abnormalities of ventilation, they would be predicted to have an impaired ventilatory response to tube breathing. The aim of this study was to test that hypothesis. We therefore compared the response to tube breathing of infants of smoking and non-smoking mothers, all examined in the first week after birth before discharge from hospital. METHODSInfants of smoking and non-smoking mothers were recruited from the postnatal wards. Smoking status was determined by questioning the mothers and examining their antenatal records. Smoking mothers admitted smoking at least five cigarettes a day throughout pregnancy. Cigarette smoking was recorded to the nearest five cigarettes a day. Urinary cotinine concentrations were not assessed. Infants were recruited if born at term, more than 6 hours old, and had no obstetric or perinatal problems. Informed, written parental consent was obtained, and the study approved by the King's College Hospital Ethics Committee.Infants were studied while awake, but ...

Ventilatory Response to Hypercarbia in Newborns of Smoking and Substance-Misusing Mothers

“…Our results are consistent with our previous findings that infants of mothers who smoked antenatally and were studied before maternity unit discharge had a dampened ventilatory response to added dead space, in which the major stimulus is hypercarbia when compared with control subjects (17). There are strengths and some limitations to our study.…”

“…A similar magnitude of difference had been detected in the ventilatory response to added dead space, tube breathing, in which the main stimulus is hypercarbia (16) between newborns of smoking and nonsmoking mothers (17). See online supplement for additional information.…”

Position and ventilatory response to added dead space in prematurely born infants

“…In a previous study, 6 we demonstrated that the coefficient of repeatability of T c was 11 sec. Recruitment of 25 infants allowed, with at least 90% power at the 5% level, detection of a difference in the T c between positions of at least 11 sec.…”

“…The coefficient of repeatability of T c had been previously shown to be 11 sec. 6 Respiratory muscle strength was then assessed by measurement of the maximum pressure generated during a multiple breath end expiratory airway occlusion (MIOP). During the procedure neck position was carefully controlled to avoid flexion.…”

“…4 Intrauterine exposure to smoking, however, another known risk factor for SIDS, 5 is associated with a dampened response to tube breathing. 6 We, therefore, hypothesized that prematurely born infants would have a dampened response to tube breathing in the prone compared to the supine position. The aim of this study was to test that hypothesis and a secondary aim was to determine if any dampened response to tube breathing in the prone position was associated with lower respiratory muscle strength.…”