Hypoxemia, rather than hypercarbia, may be the more important factor when death occurs in infants sleeping with their faces covered by soft porous bedding

Bethesda, MD The incidence of sudden infant death syndrome (SIDS) has decreased markedly over the past decade since recommendations were made in several countries to place infants in a nonprone position when sleeping. However, SIDS remains the leading cause of infant death beyond the neonatal period in the United States, and 20 percent of US infants continue to sleep prone. Despite the established increased risk of SIDS with prone sleep, the cause of death is still under debate. One proposed reason for infant mortality is that when an infant sleeps facedown, rebreathing of expired air caught in the soft porous bedding occurs.

Background

The rebreathing theory has been criticized because, although increased CO2 is biologically significant, this condition is unlikely to cause nonspecific reversible depression of neuronal excitability or rapid death. Another condition, hypoxemia (subnormal oxygenation of arterial blood) has been noted in animal models of rebreathing; however, no direct measurements of environmental oxygen (O2) in animal or human models have been made. O2 content of inspired air during rebreathing has been assumed to reciprocate CO2 levels, such that inspired O2 = room air O2 minus end-inspiration CO2. The effects of factors such as the respiratory exchange ratio on CO2 and O2 are unknown.

The observations found in previous studies suggest that complex interactions of several factors influencing gas exchange between infant and environment may influence the degree of hypercarbia and hypoxia that develop in inspired air. To further explore the consequences of infants sleeping facedown on soft bedding, a team of researchers evaluated four aspects of gas exchange: (1) infants' gas exchange with the external environment through air-channel formation
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Contact: Donna Krupa
djkrupa1@aol.com
703-527-7357
American Physiological Society
10-Jan-2002