Objective: To determine whether rebreathing of expired air is a plausible lethal mechanism of sudden death in infants sleeping face down on sheepskins.
Design: Case reports of infants who died on sheepskins combined with a controlled study of effects of their respiratory microenvironment at death.
Setting: Research laboratory.
Materials: Rabbits used experimentally to assist in simulation of an infant's respiratory microenvironment. Rabbits breathed into sheepskin through the airway of an infant mannequin.
Intervention: None.
Measurements/main results: Rebreathing of expired air was documented by carbon dioxide analysis of airway gas. Arterial blood gas analysis showed hypoxemia, hypercarbia, and acidosis in all experimental rabbits but not in controls. Rebreathing expired air was lethal for three of four experimental rabbits.
Conclusions: Infants sleeping prone on a sheepskin, with their faces straight down, experience potentially lethal rebreathing of expired air. Avoidance of the prone position would markedly reduce the risk of rebreathing expired air. The pronounced decrease in sudden infant death syndrome in southern New Zealand that followed a campaign to eliminate prone sleeping may have been attributable to reduced fatal rebreathing, as deaths of infants sleeping face down on sheepskins were common before the campaign.