Smoking during
pregnancy
Premature infants whose mothers smoked during
pregnancy may be at even higher risk for sudden infant death
syndrome (SIDS) than preemies whose mothers did not smoke, according
to new research out of the University of Calgary. In the first-ever
experimental study to compare the breathing reflexes of preemies of
smokers versus non-smokers, researchers found that babies whose
mothers had smoked showed a number of signs of impaired respiratory
function.
"Smoking during pregnancy is a double-edged sword with respect to
SIDS," said Shabih Hasan, M.D., a staff neonatologist and professor
in the department of pediatrics at the University of Calgary, and
the principal investigator of the new study. "Not only does it raise
a mother's likelihood of having a preterm baby, who is already among
the most vulnerable to SIDS, but it increases the infant's
susceptibility to SIDS even further."
The research will be published in the first issue for September of
the American Thoracic Society's American Journal of Respiratory
and Critical Care Medicine.
Studies have indicated that a combination of hypoxia (low oxygen)
and hypercarbia (excess of carbon dioxide) may be acute precursors
to SIDS. Infants at the greatest risk for SIDS have been shown to
have both attenuated arousal and ventilatory responses to hypoxia
and/or hypercarbia.
"Preterm babies are known to have increased breathing difficulties
in proportion to their prematurity and cigarette smoke is known to
increase apneas in full-term babies," said Dr. Hasan. "But until
now, cigarette smoke exposure and preterm birth have not been
investigated together with respect to their potential effects on
respiratory dysfunction."
To analyze the effects of cigarette smoke exposure on preterm
infants' respiratory health and their risk of SIDS, the researchers
recruited 22 preterm infants who had been spontaneously born between
28 and 32 weeks with no other complicating respiratory factors.
Twelve of the infants had mothers who had smoked five or more
cigarettes every day in pregnancy. The mothers of the other ten
infants did not smoke during pregnancy.
They obtained baseline readings on the infants' breathing patterns
in normal conditions, assessing breathing rate, pauses in breathing,
recovery period and heart rate. Saturation of oxygen in their blood
was also monitored. After baseline readings were recorded, the
infants were challenged with a five-minute period of decreased
oxygen delivered through a nasal cannula. During this period they
were monitored very closely with infant resuscitation equipment near
at hand.
The two groups were remarkably similar in some measures: respiratory
rates and number of breathing pauses were similar among both groups
of infants.
But there were significant differences between the two groups of
preterm babies with respect to heart rate and recovery period. The
cigarette-smoke exposed infants showed increased heart rate during
the hypoxemic period compared with their baseline values, but there
was no difference in heart rates was observed in control infants,
indicating that the oxygen depletion put their bodies under more
stress than the control groups.
Furthermore, while blood oxygen levels decreased similarly in both
groups during the hypoxemic challenge, infants who were exposed to
cigarette smoke did not recover as well, as quickly or as often as
the infants born to non-smoking mothers.
"Our study shows that preterm infants make incomplete and/or delayed
recovery from interruptions in breathing," said Dr. Hasan. "This has
clear implications for their risk of SIDS. But there is even still
another reason for concern even after the risk of SIDS has passed.
Inability or delayed recovery from repeated low oxygen episodes can
also be detrimental to brain development. There is increasing
evidence that infants exposed to prenatal cigarette smoke are at
high risk for developmental and behavioral disorders."
To explain their findings, the researchers point to evidence that
suggests that nicotine interacts with highly selective endogenous
neuronal nicotinic acetylcholine receptors, which may in turn affect
development of areas in the central nervous system essential for
respiratory control. Alternatively, alterations in lung development
and lung mechanics could contribute to poor gas exchange leading to
poorer recovery seen in the group exposed to cigarette smoke.
Regardless of the mechanism, the study has immediate clinical
relevance: "Since preterm infants continue to have significant
cardiorespiratory events after discharge from the hospital, our
study may help identify the infants at risk for attenuated recovery
from hypoxemic episodes while at home," said Dr. Hasan.
"Furthermore, it might help distinguish the infants, who will arouse
in response to hypoxemia. The infants identified to be at risk can
subsequently be further investigated and/or monitored at home."
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Article adapted by Medical News Today from original press
release.
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