Loss of consciousness, altered awareness, epilepsy and sleep disorders (ILO/IMO Guidelines Appendix E G40-40)

Impairment and risk

Alterations to the state of consciousness will prevent many activities being performed. When the onset is sudden or awareness of the changed state is not present the person may put themselves, others and the vessel at risk.
In some cases loss or alteration of consciousness is recurrent. When this is the case the probability of a future event will determine the likelihood of harm.

Rationale and justification

There are many predisposing factors to alteration or loss of consciousness:

• A blow or other injury to the head.
• Any circulatory condition that severely reduces blood flow and hence oxygen transport to the brain. Causes include pooling of blood in lower limbs (simple syncope), arrhythmias, narrowing of the aortic valve, heart attack, cough syncope.
• Seizures, most commonly from epilepsy but also associated with alcohol and some medications, after head injury or cranial surgery or from intracranial tumours or other lesions.
• Metabolic causes. The commonest of these is hypoglycaemia from the use of insulin.
• Extreme fatigue including that cause by sleep disorders.

Diagnostic methods vary depending on the cause. Observation of an episode can be an important initial clue.

There is good prognostic data for recurrence rates in some conditions such as epilepsy and after a head injury.

Seizures/epilepsy/ seizure risk factors (head injury, intracranial surgery, tumour or risk of cerebral metastasis)

Rationale and justification – risks from seizure
Note – most of the available evidence on the effects of seizures on safety critical tasks comes from studies on drivers.

• It is methodologically difficult to perform studies: those with poorly controlled epilepsy are normally excluded from safety critical tasks. There are big personal incentives not to declare a seizure
• A long period since the last seizure seems to be the best predictor of lack of excess risk of recurrence. A number of large population studies have been the source of estimates of future risk. While there is some evidence of reductions in recurrence rates from better therapy of epilepsy and from better treatment of head injuries and other predisposing factors there are insufficient recent data to improve the current estimates.
• Cessation of anti epilepsy medication is associated with a period when there is an increase in risk.
• The relative risks from different forms of seizure disorder have not been well investigated. Some persistent patterns, such as seizures showing a well established pattern of only occurring during sleep, may indicate a low level of risk while at work
• Approximately 2% of the population will have a seizure during their lifetime. There is a 30-40% likelihood of a recurrence after a first seizure. The probability is greatest soon after the initial event and then declines progressively. Hence a period of observation during the highest recurrence risk period can be justified. A formal diagnosis of epilepsy is not usually made until there have been at least two seizures. The data from large studies of people with epilepsy is good enough to make quantitative risk estimates.
• One year after the last seizure, either on maintenance antiepileptic medication or untreated the risk of a seizure in the next year is c.20%. If medication is stopped the risk will increase for several months.
• Ten years after the last seizure with ten years not on any anti-epileptic treatment the risk of a seizure in the next year is below 2%.
• In most cases there is no obvious provoking factor but the threshold for a seizure may be reduced by alcohol or alcohol withdrawal, by sleep deprivation and by some medications such as tricyclic antidepressants or by the withdrawal of others like benzodiazepines which are protective. In this situation it can be difficult to assess whether the provoking factor was the sole cause or whether it was coincidental with a first seizure for unrelated reasons. This means that a precautionary approach to see if there is a further seizure after removal of the provoking agent may be indicated.
• Local effects affecting the surface of the brain can trigger seizures. They may occur at the time of a head injury or after one if there is persisting damage. Tumours in and around the brain can present as seizures. These may either be primary growths or metastatic cancers from sites such as the lung, breast and skin (melanoma). The infarcted scar created by a stroke can be the location for seizure initiation. Infections – encephalitis or abscess - can also be triggers. Where the predicted seizure risk is high e.g. after severe head injury or with lung cancer, this may be sufficient to restrict a person from safety critical work even in the absence of a first seizure. Estimates of seizure probabilities based on severity of head injury and on the type of cancer and the stage at which it was diagnosed can be made and used as the basis for decisions on suitability for safety critical tasks, assuming there are no other impairments from the underlying condition
• In most people seizures are always of the same type, but there are occasions where there is a mixed or progressive pattern. At the extreme this can take the form of 'status epilepticus' when seizures follow each other without full recovery. There may be specific provoking factors. In some people seizures only occur during sleep. Stroboscopic lighting can provoke photosensitive epilepsy in susceptible individuals.
• Seizures associated with fever are frequent in children. Provided these do not persist after the age of five they do not predict an increased future risk.
• Diagnosis in equivocal cases needs the expertise of a neurologist. The Electroencephalogram can indicate an abnormal focus of electrical activity or the characteristic patterns from some seizure disorders. They may be used with provoking stimuli such as sleep deprivation or stroboscopic lights. However a negative EEG is not evidence of the absence of a seizure risk. Various forms of brain scan can be used to look for local lesions such as tumours or scars.
• A range of medications are used to reduce the risk of seizures. Some are sedating. Compliance is essential if the risk is to be reduced and cessation of medication will result in a period when risk may be raised.

Clinical assessment and decision taking

Once a pattern of episodes has been observed a clinical diagnosis of epilepsy can be made. However often the first episode will be an unexplained and sometimes unwitnessed loss of consciousness (2 above). There may be clues indicating whether the likely cause is syncope, a cardiac problem or a seizure but at times a period of observation may be needed, or where a seizure is the most likely cause it will need to be treated as if this was the cause.

Given that anyone can have a first seizure or other sudden loss of consciousness at any time a criterion based on the level of excess risk which is considered tolerable would be appropriate and it might be set at differing levels depending on whether the consequences of a seizure posed a risk just to the individual or could harm others.

The <2% risk of seizure in the next year noted above is a level that fits well with current practice for safety critical work, that is used in other modes of transport and is not dissimilar to the levels used for risks of sudden incapacity from a cardiac event. The level used should be consistent for seizure risks from all causes.