Sudden infant deaths: arousal as a survival mechanism.

The mechanisms responsible for sudden infant death syndrome (SIDS) are still largely unknown. To explain what factors contribute to the deaths, we suggest a model: the '3 S model for SIDS' that includes 'sicknesses', 'stages of development' and 'surroundings': (1) 'sicknesses' refers to infectious diseases or other medical condition. (2) 'Stages of development' relates to the maturation of vital systems including respiratory, neurovegetative or sleep-wake behavioral controls. (3) 'Surroundings' refers to environmental conditions that enhance the deficiency of cardiorespiratory, vegetative and/or arousal controls. Such conditions were identified by epidemiological studies and include the following main risk factors: the prone body position during sleep, high environmental temperature, maternal smoking or sleep deprivation. An infant could be at higher risk for SIDS because of a deficiency in breathing and cardiac autonomic controls during sleep, inducing repeated episodes of hypoxia and hypoxemia. The risk is increased when the infant has a lower propensity to arouse from sleep and so, to autoresuscitate. The accident has a greater probability to occur when an infection, or an unfavorable environmental factor aggravates the immature cardiorespiratory and sleep/wake behaviors of the infant. The clinical findings could be related to the changes reported in the brainstems of SIDS victims.