If a person with epilepsy dies suddenly and no obvious reason is found at post-mortem, this is described as Sudden Unexpected Death in Epilepsy (SUDEP). In the UK approximately 500 people die of SUDEP each year, but the exact mechanisms are not known.

In an attempt to discover the cause, scientists at the UC Davis Medical Centre, California, USA, studied recordings of 300 seizures in 57 patients with chronic, recurrent, unprovoked seizures. Within this group they compared the people who had severe, convulsive seizures, with those who had milder symptoms, such as temporary confusion and lip smacking.

The researchers found that one-third of the seizures analysed caused a drop in blood oxygen level to below 90% saturation (healthy saturation is between 97 and 99%). Moreover, in 12% of the patients, their blood oxygen level had fallen to below 70% saturation during their seizures.

The group also discovered that temporal lobe seizures produced more significant drops in blood oxygen level than other types of partial seizure.

What does this mean?

As has been shown before in smaller studies, the scientists concluded from these findings that seizures can disturb the normal signals from the brain that tell a person to breathe. As a result, the oxygen level in their blood starts to drop. It is possible that if a seizure continues for an extended period, blood oxygen levels can fall dangerously low, contributing to SUDEP.

The best way to prevent SUDEP is to control a person's seizures, and approximately two-thirds of people with epilepsy successfully control their condition with medication. However the remaining third require alternative interventions, and experience recurrent seizures whilst the best treatment is being sought. This can lead to repeated seizures or hospital admissions.

At the UC Davis Medical Centre, blood oxygen levels were not previously monitored as a priority in patients who were hospitalised due to their epilepsy. However as a result of these findings, practices are changing. Constant monitoring of patients' breathing is also being encouraged in intensive monitoring units.

This study provides valuable information regarding oxygen saturation in seizures and provides some insight into possible mechanisms of SUDEP. However in order for us to develop interventions in the future, research into exactly how and why seizures can affect breathing is now needed

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