Prone Position a Risk Factor for SUDEP

Pauline Anderson

January 21, 2015

Being in the prone position — on one's stomach — is a risk factor for sudden unexpected death in epilepsy (SUDEP), a new systematic review suggests.

James Tao, MD, PhD, associate professor, neurology, and director, electroencephalography (EEG) laboratory, University of Chicago, Illinois, and colleagues carried out a systematic review and meta-analysis that showed patients with epilepsy, especially those under age 40, are at increased risk for SUDEP when in a prone position.

"From our study, it's clear that turning into the prone position after a convulsive seizure is definitely contributing to SUDEP," said Dr Tao. "There's no doubt that the prone position should be considered a risk factor for SUDEP along with other risk factors. In my opinion, this is probably why sleep is such a risk factor for SUDEP."

Dr James Tao

Other risk factors for SUDEP included generalized tonic-clonic seizures (GTCS), early-onset and chronic refractory epilepsy, age 20 to 40 years, antiepileptic drug polytherapy, poor compliance with antiepileptic drug, and nocturnal seizures.

Their findings are published online January 21 in Neurology.

SIDS Similarities

Circumstances of SUDEP are remarkably similar to those of sudden infant death syndrome (SIDS), the researchers noted. Both occur during sleep, in bed, and as an unwitnessed event. A widespread drive to get parents to put their babies down on their back, known as the '"Back to Sleep" campaign, has been a huge success in preventing SIDS.

For the review, the researchers searched the literature for studies of possible, probably, or definite SUDEP that documented the total number of SUDEP patients found in various body positions and the number of SUDEP patients found in the prone position.

The review included 25 studies, 14 single case reports, and 11 case series. Of the 413 cases of SUDEP reported in the 25 studies, body position was documented in 253 patients. Of these, 73.3% (95% confidence interval [CI], 65.7% - 80.9%) were found in the prone position compared with 26.7% (95% CI, 16.3% - 37.1%) in nonprone positions.

In 11 of the 253 cases, SUDEP occurred during video EEG monitoring. The prone position was observed during SUDEP in all 11 patients. Four of the 11 were sleeping prone before the terminal seizure onset and 3 turned to the prone position during seizures.

The prone position was more significant for younger people. In a subgroup of 88 patients whose demographic characteristics and circumstances of death were documented, the study showed that in those younger than 40 years, 85.7% (95% CI, 74.6% - 93.3%) died in the prone position compared with 60% (95% CI, 38.7% - 78.9%) of those older than 40 years.

The prevalence difference was statistically different (odds ratio, 3.9 [95% CI, 1.4% - 11.4%]; P = .009).

The finding that the chances of dying in the prone position are 4 times higher in young people was "puzzling" to Dr Tao. Although experts have speculated that young people are more likely to drink alcohol, which may compromise their ability to wake up during a seizure, studies show that alcohol is not a significant risk factor for SUDEP. "A lot of patients have been advised by their physician not to drink alcohol at all," said Dr Tao.

A likely explanation is that young people often live alone, with nobody around to turn them on their back in the event of a seizure to prevent airway obstruction, said Dr Tao. "Otherwise, how do you explain this? This group should be healthier than older people, so it's counterintuitive."

Risks did not differ between men and women. As well, although sleep is a well-defined risk factor for SUDEP, there were no statistically significant differences between those who died during sleep (82.5% of 63 cases) and those who died while awake (61.9% of 21 cases).

So it looks like it's being in the prone position, not necessarily being asleep, that raises the risks for SUDEP. "We still don't know for sure why the prone position is such a risk factor," although there are several theoretical mechanisms, commented Dr Tao.

Such mechanisms could include central nervous system shutdown with impaired autonomic regulation, a cardiac cause such as an arrhythmia, or a respiratory cause.

He feels strongly that the airway obstruction is probably the most likely mechanism, although this is difficult to prove, said Dr Tao.

Airway Obstruction

The airway doesn't have to be completely blocked to pose a risk, he added. "When the mouth and nose are even partially buried in the pillow or bedding, you create an environment where you don't get a significant exchange of fresh air; you exhale carbon dioxide and inhale it back, creating hypoventilation."

Just as parents of babies are told to lay their infants on their back in their crib, so too should doctors tell their patients with epilepsy to lie on their backs, according to Dr Tao.

This message is particularly important for vulnerable, high-risk patients with epilepsy, such as those with GTCS, he said. "The reason why GTCS is such risk factor is because the vast majority, after a convulsive seizure, become comatose, or unresponsive," said Dr Tao.

Turning someone on his or her back and freeing the airway in such circumstances "is not rocket science" and is standard protocol in the emergency room [ER], he said. "When someone's unconscious, the first thing ER personnel do is protect the airways and sometimes intubate."

But this tactic probably won't be as successful in preventing SUDEP in adults as it is in preventing SIDS in babies. The highest incidence of SIDS is before the age of 3 months, when babies still don't have the muscle power to turn themselves over, so if placed on their back, they will stay in that position, explained Dr Tau. "But adults tend to change sleeping positions during the night, many times probably."

Although it's important to educate epileptic patients about the risks of sleeping in the prone position, it also might be helpful to develop some sort of alarm that inhibits this position. "I think certain devices could be developed to prevent patients from turning into a prone position during a seizure," said Dr Tao.

He pointed out that patients with sleep apnea, who have a different medical issue and should sleep on their front, can strap a bag onto their back to prevent them from turning to that position.

Modifiable Risk Factor?

An accompanying editorial by Barbara Dworetzky, MD, Brigham and Women's Hospital, Boston, Massachusetts, and Stephan Schuele, MD, Northwestern University, Chicago, noted that the study had no control group of patients with tonic-clonic seizures sleeping in the prone position who did not succumb to SUDEP.

"We're curious about that too," said Dr Tao. "We are now looking at patients having a convulsive seizure who end up on their stomach and survive without any intervention. There's no data at all on that."

According to Dr Dworetzky and Dr Schuele, discovering a possible modifiable risk factor for SUDEP, such as sleeping in the prone position, is "clearly important" because it implies the possibility of preventing a substantial number of deaths. It will be "critical," they write, to identify patients at high risk for SUDEP.

These high-risk groups would include "those with PGES [postictal generalized EEG suppression] during their epilepsy monitoring unit stay, those with intellectual disability and frequent uncontrolled tonic-clonic seizures, or possibly carriers of specific potassium channel genes linked to sudden death in animals," they said.

Asked to comment, Elson So, MD, professor, neurology, Mayo Clinic College of Medicine, Rochester, Minnesota, said the article yields much-needed and important information supporting the thinking that SUDEP is multifactorial, and that mechanical factors are as important as biological ones.

"Information regarding the potential role of the prone position in SUDEP has been largely circumstantial — you can even say it has been anecdotal — having been reported here and there in articles with limited numbers of patients. The authors of the current article made quite a big effort to successfully derive more convincing evidence implicating prone positioning in SUDEP, even when their meta-analysis was largely based on retrospective data."

Dr So reiterated that the study results don't necessarily mean that sleeping prone raises the risk for SUDEP, pointing out that a SUDEP victim who is found prone may have turned to that position because of seizure activity. "So favoring sleeping in the supine position may not be an effective SUDEP prevention measure."

Nonetheless, said Dr So, "it would be reasonable and wise" to advise that patients at high risk for SUDEP keep to a minimum objects such as extra pillows, stuffed animals, towels, fluffy linens, and extra blankets that could contribute to suffocation in the event of a seizure in bed.

The effectiveness in preventing SUDEP of antisuffocation pillows, which claim to have increased "breathability," is unknown, added Dr So.

The study received no targeted funding. Dr Tau has disclosed no relevant financial relationships. Dr Dworetzky has consulted for SleepMed (interpreting ambulatory EEGs). Dr Schuele serves on the speakers' bureau for Sunovion and GSK and has been a medical consultant for Supernus. Dr So has disclosed no relevant financial relationships.

Neurology. Published online January 21, 2015. Abstract Editorial

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