Tonic seizures are a particular risk factor for drowning in people with epilepsy

British Medical Journal, April 21, 2001 by Frank M C Besag

Tonic seizures pose a high risk of drowning because expulsion of air from the lungs causes rapid submersion

It is accepted that people with epilepsy should be supervised when swimming. However, there is little or no guidance about special precautions that should be taken for particular types of seizures. During a tonic seizure the muscles of the chest wall contract and much of the air from the lungs may be expelled. If such a seizure occurs while a person is swimming, the average body density may become higher than the density of the water, causing rapid submersion. When the muscles of the chest wall relax, the person will still be submerged, with the result that water, not air, will enter the respiratory tract and the person will not rise to the surface. We present a case of fatal drowning in a 14 year old boy with epilepsy who had seizures with a marked tonic phase. This case raises an important question with regard to safety: should special precautions be taken to minimise the risk of drowning in patients with tonic seizures?

Case report

A 14 year old boy who had had epilepsy from 7 years of age drowned in a lake on a school outing. His early development was normal. The seizures were all of a similar form: his head and eyes deviated up and to the right; his trunk could either be flexed or straight; he was blue around the mouth; facial twitching was followed by twitching or jerking of the limbs. His parents commented that because he was so rigid it sometimes needed three people to lift him off the floor. He had been treated with sodium valproate and carbamazepine. He stopped taking carbamazepine three months before he died and had had only two seizures during that period. These seizures followed the form already described.

He had always previously been accompanied by his parents when he went swimming. On this occasion he went on an unplanned swim in a lake with 10 or 11 other children and about 15 teachers. He was observed playing happily with the other children, throwing water about. He then disappeared from sight. The teachers did not suspect that he had drowned until the party was about to leave. Divers were called and they found him in about 1.5 m of water. There was a small cut above one eye but no other sign of trauma. His arms were crossed over his chest, as had previously been observed by his parents when he had a tonic seizure. The coroner's verdict was death by drowning secondary to epilepsy.

His parents contacted the British Epilepsy Association and were informed that swimming is good for people with epilepsy and should be encouraged but should be supervised. They asked the question: "What does this mean?"

His parents said, "The supervision should be one-to-one. He should have had someone in water with him. There was no chance for anyone to save him. I think we were blissfully ignorant. I know now he could have had a seizure in the water and I would have been totally unprepared for it. I'm not sure even now that I'd know what to do to resuscitate him. The whole business of epilepsy should be explained properly. You almost need someone to go through it with you." His parents also commented that children with obvious physical disability tend to be better supervised than those who are able, like their son was.

Discussion

Several published papers have acknowledged that drowning is an important cause of death in people with epilepsy?[1-3] Cass et al carried out a population based study of childhood drowning in New South Wales. A total of 132 children aged 0-14 drowned during 1990-5.4 The researchers confirmed the recommendation that all children with epilepsy should be supervised adequately when swimming. Kemp and Sibert studied the records of 306 children who drowned or nearly drowned in the United Kingdom in 1988-9.[5] Four children with epilepsy had drowned. Although Kemp and Sibert found that children with epilepsy had more incidents of submersion, no child participating in supervised swimming drowned. Two children drowned in the bath. These authors emphasised the importance of a high level of supervision while swimming and added that advice should be given on an individual basis, according to what is considered to be realistic for that child. Diekema et al estimated that the relative risk of drowning for children with epilepsy compared with those without epilepsy was 96 in the bath and 23.4 in the swimming pool.[6] Ryan and Dowling identified 25 people with epilepsy whose death by drowning was considered to be directly related to seizures.[7] Fifteen of the 25 deaths (60%) occurred while the person was taking an unsupervised bath. One person died while taking a shower. Four drowned in a river or lake, two in a private pool, two in a public pool, and one in a Jacuzzi. Two fell out of moving boats while having a seizure; they were not wearing a flotation device at the time.

Although these papers rightly emphasise the need for supervision of people with epilepsy when in the bath or while swimming, none of the authors highlights the importance of assessing the risk according to type of seizure. Any seizure that involves impaired awareness or notable loss of control of motor function must be considered to place the person at great risk in the water. Tonic seizures might pose a particular risk because air may be expelled from the chest with the result that the person may sink quickly and be out of sight before appropriate rescue action can be taken. In our case, the history suggests that the boy had a tonic seizure and sank quickly to the bottom of the lake. The additional factors that the water was murky and that he was not supervised by a responsible adult in the water would have added to the risk.