Ventilatory Responses in Infants Who Have Had Apparent Life Threatening Events (ALTE) or Gastro-Oesophageal Reflux (GOR)

Abstract □ 98

SIDS may be the result of an inappropriate response to an exogenous stressor due to an underlying vulnerability. We have used a mild asphyxial test, mimicking rebreathing to measure the ventilatory and arousal responses of infants who may be at risk of SIDS. Infants with an ALTE or GOR may have manifestations of an underlying vulnerability. GOR has been associated with SIDS via a sustained apnoeic response accompanied by a lethal bradycardia, triggered by a laryngeal reflex.

METHOD: ALTE infants (age 0-10 weeks n=7, 10-64 weeks n=8) and GOR infants (age 0-10 weeks n=1, 10-64 weeks n=6) were recruited following admission to the Pediatric Ward, Dunedin Hospital. Control infants were recruited from the maternity ward and studied at 0-4 weeks (n = 49) and 11-14 weeks (n=46) of age. Each infant slept supine and was exposed to a mild asphyxial test, which mimicked rebreathing. For this a 5%CO₂/13% O₂ gas mixture was slowly introduced into a perspex hood covering the infant's head and shoulders. Ventilatory changes were measured by inductive plethysmography. Inspired CO₂ reached a maximum of 5% and inspired O₂ a minimum of 13.5% over 5-6 minutes when the test stopped and atmospheric air was flushed through the hood. A linear curve plotting Ln ventilation against inspired CO₂ was used as a measure of the ventilatory asphyxial sensitivity (VAS). VAS values in the rebreathe test below 0.1, without arousal and P_ACO₂ levels of 50-60mmHg were coded as a poor response as they represent only a 65% increase in ventilation (compared to 150% increase normally) possibly indicating inappropriate control. Asphyxial tests were attempted twice in each sleep state i.e. quiet sleep (QS) and active sleep (AS). Arousal and sleep state was recorded by behavioural criteria. RESULTS: After matching for age and sleep state, the difference between the mean VAS for ALTE and Control infants, 0.007 (CI -0.037, 0.051) was not significantly different. p=0.746. The difference between the mean VAS for GOR and Control infants at the older age group, 0.112 (CI 0.018, 0.206) was significant at p=0.020. The normal range described in the control group includes abnormal VAS values that may describe a dampening of control in these infants. Six case tests had VAS below or close to 0.1, two of these tests were associated with arousal. CONCLUSION: Infants with GOR have a higher ventilatory response to rebreathing than controls. This could be a reflection of hyperactivity also presented as sleep disturbance/irritability. Infants with an ALTE have an appropriate ventilatory response to rebreathing. This is consistent with the majority of findings on ventilatory studies in ALTE infants. ALTE may not represent a near-miss SIDS episode or it may not always be caused by an underlying respiratory abnormality. (Figure)