SIDS Risk Greater When Women Smoke During Pregnancy

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Title: SIDS Risk Greater When Women Smoke During Pregnancy
URL: http://www.pslgroup.com/dg/22A32A.htm
Doctor's Guide
August 29, 2008

NEW YORK -- August 29, 2008 -- Premature infants whose mothers smoked during pregnancy may be at even higher risk for sudden infant death syndrome (SIDS) compared with preemies whose mothers did not smoke, according to a study published in the September issue of the American Journal of Respiratory and Critical Care Medicine.

In the first-ever experimental study to compare the breathing reflexes of preemies of smokers versus nonsmokers, researchers found that babies whose mothers had smoked showed a number of signs of impaired respiratory function.

"Smoking during pregnancy … 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," said lead investigator Shabih Hasan, MD, Department of Pediatrics, University of Calgary, Calgary, Alberta.

To analyse 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.

Of the infants, 12 had mothers who had smoked 5 or more cigarettes every day in pregnancy. The mothers of the other 10 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 5-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 2 groups were remarkably similar in respiratory rates and number of breathing pauses. However, there were significant differences between the 2 groups 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 no difference in heart rates was observed in control infants, indicating that the oxygen depletion put their bodies under more stress compared with those in the control group.

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 nonsmoking 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."

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.

"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."

SOURCE: American Thoracic Society

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