Multiple causes of asphyxia in infants at high risk for sudden infant death.

A wide range of clinical findings was present in 58 near-miss sudden infant death syndrome (SIDS) infants and 6 surviving twins of SIDS siblings. Specific investigations included: studies of gastro-oesophageal reflux and aspiration (24-hour oesophageal pH recordings, barium swallow, radionuclide 'milk-scan'); polygraphic studies of breathing, reflux, and sleep state; studies of upper airways disease (lateral airways radiography and endoscopy); detection of seizure activity by electroencephalography; evaluation of thiamine status by erythrocyte transketolase activity of venous blood. Thiamine deficiency was found in 12 of 43 tested infants; 5 of the deficient infants had a familial history of SIDS. Many potential mechanisms for asphyxia were found: idiopathic central apnoea (7 infants), tracheal obstruction from minimal tracheomalacia or aberrant innominate artery (4 infants), temporal lobe or generalised seizures (6 infants), gastro-oesophageal reflux (55 infants) with intrapulmonary aspiration (11 infants). The high incidence, severity, and timing of reflux were new findings. Reflux occurred in active and indeterminate sleep, but not in quiet sleep. The depression of respiratory reflexes by active sleep stresses the vulnerability to asphyxia. Two factors suggest that near-miss episodes are related to SIDS: the similar age distribution but earlier occurrence of near-miss episodes compared with age at death of SIDS infants, and the subsequent sudden death of 2 infants whose necropsies were consistent with SIDS.