Fatal asphyxial episodes in the very young: classification and diagnostic issues.

Infants and young children are exposed to a relatively limited range of circumstances that may result in accidental or inflicted asphyxial deaths. These usually involve situations that interfere with oxygen uptake by the blood, or that decrease the amount of circulating oxygen. Typically infants and toddlers asphyxiate in sleeping accidents where they smother when their external airways are covered, hang when clothing is caught on projections inside cots, or wedge when they slip between mattresses and walls. Overlaying may cause asphyxiation due to a combination of airway occlusion and mechanical asphyxia, as may inflicted asphyxia with a pillow. The diagnosis of asphyxiation in infancy is difficult as there are usually no positive findings at autopsy and so differentiating asphyxiation from sudden infant death syndrome (SIDS) based purely on the pathological features will usually not be possible. Similarly, the autopsy findings in inflicted and accidental suffocation will often be identical. Classifications of asphyxia are sometimes confusing as particular types of asphyxiating events may involve several processes and so it may not be possible to precisely compartmentalize a specific incident. For this reason asphyxial events have been classified as being due to: insufficient oxygen availability in the surrounding environment, critical reduction of oxygen transfer from the atmosphere to the blood, impairment of oxygen transport in the circulating blood, or compromise of cellular oxygen uptake. The range of possible findings at the death scene and autopsy are reviewed, and the likelihood of finding markers/indicators of asphyxia is discussed. The conclusion that asphyxiation has occurred often has to be made by integrating aspects of the history, scene, and autopsy, while recognizing that none of these are necessarily pathognomonic, and also by excluding other possibilities. However, even after full investigation a diagnosis of asphyxia may not be possible and a number of issues concerning possible lethal terminal mechanisms may remain unresolved.