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  • AutorenbildMichael Mutter

Plura cave disaster - the third. Analysis and comment

After 2006 and 2014, another fatal dive happened on April 3 this year in the Norwegian Plura cave system. The cave diver involved was very well-known in the diving community, highly experienced and well-trained. DAN quickly investigated the background of the incident and published a preliminary analysis. The findings are as enlightening as they are consternating.


Mols harbour. Image template: Sidonia Ackermann.

My first thought when I read the story was: it wasn't the oxygen. The exposure was too short and the highly experienced diver was using a perfectly functioning rebreather, which meant he was barely diving in the oxygen-toxic range. My second thought was: Of course it was the oxygen. But not only. But let's first look at the DAN analysis:


Medical history

In talking to the family, it was revealed that the deceased had suffered an unprovoked epileptic seizure for the first time the year before and that there very rarely occured epileptic seizures in his family which were still medically unexplained. These were associated with physical overexertion, stress and dehydration.


On the morning of the dive, the diver felt fit, well-rested and had no jet lag despite traveling on an intercontinental flight to Norway. However, in the week before the trip, he suffered from a viral infection with flu symptoms and gastrointestinal complaints, which may have led to an electrolyte imbalance and dehydration. The latter could have been worsened by the intercontinental flight.


Comment

An unprovoked epileptic seizure occurs without any clear trigger. Thus, from a medical point of view one fact must be stated: The person affected was not fit to dive. And fundamentally not. Certainly not for cave diving, which is the most demanding form of non-commercial and non-military diving.


Because such a seizure can occur again anytime and anywhere, the guidelines of the SUHMS (Swiss Underwater and Hyperbaric Medical Society) state that diving may be resumed after 5 years at the earliest, provided that all of the following 3 criteria are met: Freedom from seizures for 5 years, normal EEG (electroencephalogram = measuering electrical brain activity), no need for antiepileptic medication.


The reason for this is the high risk of recurrence of such an attack. It is 27%, 36% and 43% after 6, 12 and 24 months respectively. This is also the reason why a driving ban of at least (!) 6 months for passenger cars and 2 years for higher categories applies in Switzerland after a first event.


Based on the history and presentation, DAN concludes that this was a medical event while diving and not the result of oxygen toxicity. But was the event really just the result of a tragic circumstance?


There is little doubt that the deceased suffered a grand mal seizure underwater. This is the most dramatic manifestation of epilepsy with unconsciousness in combination with uncontrolled convulsions of the extremities. It is suspected that a focal seizure initially occurred, in which the electrical brain activity only got out of control in a limited area (so-called focal seizure). Presumably, this was the moment when the diver tried to draw attention to himself by screaming. The seizure then became generalized, i.e. the uncontrolled electrical activity spread to the entire brain, resulting in loss of consciousness and generalized convulsions.


Electrical brain activity and the role of oxygen

The control of electrical brain activity is a miracle of nature. Various circumstances increase it and thus the risk of an epileptic seizure. Typical triggers are lack of sleep, certain medications and flickering light. And this is also where oxygen comes into play. As we know, an increased partial pressure of oxygen can trigger an epileptic seizure as a manifestation of CNS toxicity (Paul Bert effect). An O2 partial pressure below 1.3 bar is considered safe. However, nobody knows whether this also applies to people who have a predisposition to epileptic seizures. Clinical common sense tells us that in this case oxygen can possibly trigger an epileptic seizure even within a supposedly safe range. In fact, a recent study, which has already been discussed in the dekoblog, used an EEG to demonstrate hyperexcitability of the cerebral cortex even at the level of a "safe" oxygen partial pressure. This underlines the fact that hyperbaric oxygen does indeed "do something" to the brain even in the accepted partial pressure range and that the maximum values must be strictly adhered to. The process described above with secondary generalization of an initial focal seizure would fit well with oxygen toxicity as a trigger for the epileptic seizure in the plura.


If several risk factors come together, they potentiate each other and the risk increases further. It is therefore not a good idea to party all night on vacation, dehydrate yourself with alcohol and then go on a nitrox dive the next morning to push your MOD to the limit.

In the Plura case risk factors were oxygen, probably also stress and exertion (a cave dive means stress), despite the subjective feeling of being rested, also lack of sleep as a result of the transatlantic flight and, as mentioned, dehydration and possibly also an electrolyte imbalance.


Incident while diving or diving incident?

So, was the death an incident while diving or a diving incident? I believe that it was also the latter and that the assessment of the DAN analysis must be put into perspective. There were too many circumstances that specifically favored the seizure while diving, especially the oxygen.


Many unanswered questions

Finally, other pressing questions arise: Why was the victim in the water in the first place? Did he not know that he was not allowed to dive? How can it be that such a highly certified instructor was not aware of this, especially as he comes from a family with an affinity for diving and a predisposition to epileptic seizures? What about the diving medical counseling after his first epileptic seizure? Did this take place at all? If not, why not? Does this incident reveal a worrying lack of knowledge, even among supposedly highly qualified diving instructors, about the health risks associated with diving? If this is true for diving instructors who have acquired basic medical knowledge but are still medical laymen, what about divers without any medical training?


I don't know the answers to these questions. But DAN seems to be thinking along similar lines, as the organization has launched a fundraising campaign for a program to raise awareness of the consequences of epileptic seizures while diving in order to prevent such tragic incidents in the future.

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