Upper respiratory obstruction and cot death.

In this country cot death or sudden unexpected death in infancy is the commonest cause of infant death outside the neonatal period. Any theory of its cause must take into account the established facts: it is a condition that occurs most frequently during the winter months-76% of cases occur between October and March, i.e. in 50% of the year, and it also occurs most frequently in babies from the first to the fourth month of life (Froggatt, Lynas, and Marshall, 1968; Ministry of Health (1965). Though the theory of cow's milk anaphylaxis will account for a proportion of cases, it does not seem adequate for many of those that have been appropriately investigated, nor does it explain the seasonal occurrence of the disease. Signs of respiratory infection were present in 68% of cot death cases, and in 3200 of controls (Ministry of Health, 1965, 1970). We suggest that a common march of events may be as follows. First, there is a mild nasal infection in a baby who is an obligate nose breather. Babies react differently from adults to upper airway obstruction, for the baby can show a diminished tidal volume with no increase in respiratory frequency, in the face of increasing upper airway obstruction. Second, this is particularly dangerous during the winter months, for in a cool environment the demand for oxygen is increased even in a baby who is dressed and in a cot (Hey and 0 'Connell, 1970). Thus with a simultaneous increase in oxygen requirement and decrease in ventilation, lethal hypoxia could develop insidiously but rapidly. We also suggest that the infant of 1 to 4 months is particularly at risk, because during this period he has not learnt to mouth breathe, and is emerging from the relative isolation of the neonate to meet more sources of infection, and he is being encouraged to sleep through the night without waking for a feed. Shaw (1968, 1970) has similarly suggested nasal infection and obstruction as the cause of sudden death. Shaw's suggestion arose from close and astute clinical observation, while our proposal is based on experimental findings incidental to work