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What is the Role of Body Position in SUDEP?

Sleeping person
Wednesday, March 4, 2015

Factors Contributing to SUDEP

The underlying mechanisms of sudden unexpected death in epilepsy (SUDEP) are not yet well understood but a conceptual model has emerged over the past decade influenced by research on another poorly understood cause of sudden death, sudden infant death syndrome (SIDS). The model suggests that there are three necessary components for SUDEP:

  • a seizure, likely a tonic-clonic seizure, and its impact on cardiac and breathing function;
  • a susceptible individual with genetic and acquired factors that predispose to fatal consequences of seizures; and
  • environmental or external circumstances.

The necessity of all three factors for a death to occur may explain why even in people with frequent, poorly controlled seizures, SUDEP is relatively infrequent. This model also provides potential avenues for SUDEP prevention despite the fact that the exact mechanisms for how a seizure leads to death are not entirely certain. 

Body Position and SUDEP

Body position has been implicated as an important environmental contributor to SUDEP. Several prior observational studies of SUDEP cases have reported that a high proportion of individuals who died were found prone (lying face down), including the 11 cases of SUDEP recorded in video-EEG monitoring units published as part of the MORTEMUS study.

A recently published systematic review and meta-analysis by Liebenthal and colleagues synthesized the data from the available literature on body position and SUDEP. The authors reviewed studies that included a total of 413 cases of SUDEP from 25 publications; body position at the time of death reported for 253 SUDEPs. Based on the analysis of the studies, the authors estimated that approximately 73% of all SUDEPs are found prone.

Based on a subset of studies where demographic data was reported, being found prone was more common among SUDEPs occurring in people 40 years old or younger. These results suggest that body/head position, either before or after a seizure may be an important factor in sequence of events that lead to SUDEP.

How prone position may predispose a person with epilepsy to the fatal consequences of a seizure is not entirely known, but one possibility is that it may exacerbate the respiratory consequences of a seizure. Being face down in bed may lead to rebreathing of exhaled CO2 and worsen elevated arterial CO2 levels resulting from seizure-related respiratory dysfunction. Elevated CO2 levels can, in turn, prolong post-ictal coma and predispose individuals to fatal arrhythmias.

This finding also points the way to potential strategies for intervention by either repositioning during or immediately after a seizure or simple devices, such as special pillows or harnesses that prevent patients from turning completely prone during sleep or following a seizure. The ability of such interventions to prevent SUDEP is unknown and deserves further study.

Authored by: Daniel Friedman MD | epilepsy.com SUDEP Editor on 3/2015

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