Hypercarbic ventilatory responses of infants at risk for SIDS

We examined the hypercarbic ventilatory responses (HVR) of 143 infants at risk for sudden infant death syndrome (SIDS) and 34 normal control infants. Sixty-five of the at-risk infants had experienced apparent life-threatening events (ALTE), and 78 were siblings of SIDS victims. Twenty-three (35%) of the ALTE infants experienced subsequent apnea; one died of SIDS. Seven (9%) of the SIDS siblings experienced subsequent apnea; two ultimately died of SIDS. In the HVR studies, we measured tidal volume (VT), minute ventilation (VE), frequency of breathing (f), and end-tidal PCO2 (PETCO2) at rest and while breathing 2% and 4% CO2. Mean HVR vales for the ALTE, sibling, and control groups were all similar. The mean HVR values for those at-risk infants who experienced subsequent apnea were not different from those who did not experience subsequent apnea. However, those infants experiencing subsequent apnea had higher mean VT/kg values (P less than 0.01) and lower mean PETCO2 values (P less than 0.001) than those who did not. The SIDS siblings had significantly lower resting VT/kg values than either the near-miss infants or normal controls (P less than 0.01). We did not find depressed HVR values in infants at risk for SIDS. On the contrary, those infants who experienced subsequent apnea had evidence suggesting relative hyperventilation. SIDS siblings had evidence suggesting relative hypoventilation. These findings are interesting and thought-provoking. However, HVR studies do not appear to be sensitive, specific, or appropriate for the general screening of infants at risk for SIDS.