In July a Quebec truck plowed into cars that were stationary on the highway, killing 1 and maiming half-a-dozen others. Did the experienced, professional driver suddenly become ill or did he fall asleep at the wheel?

I reviewed the ill-driver cases on which I have consulted during the last 10 years. Two major themes emerged: 1) the focus was sometimes misplaced - on medical rareties rather than the mundane issue of driver drowsiness, for example; 2) when considering whether accidents can be attributed to illness, some attending physicians and medical experts need to take a more scientific approach.

Rarely, physicians make a substandard assessment of fitness to drive. Sometimes defendants fail to disclose known conditions, or drive without the knowledge of their attending physicians. Occasionally, physicians attribute accidents to medical conditions when such opinions are unsupportable.

As with other aspects of personal injury, MVAs occur in a medical context that may impact the Quantum of Damages and even the rights and liability of the parties to the litigation. Counsel on both sides should require routine access to pre-accident medical records and exercise the right to examine those records in detail.

Illness caused by accidents

Complex personal injury litigation is frequently concerned with exacerbation of pre-existing illness, and the de novo provocation of medical conditions. There is, for instance, mixed empirical evidence for traumatic causation of and deterioration in common illnesses, such as rheumatoid arthritis, multiple sclerosis, diabetes and cancer.

Psychological consequences of Motor Vehicle Accident (MVA) are frequently under-diagnosed and may be mis-diagnosed. Claimant and Defence counsel may be the first professionals to question their clients’ assumptions about the origins of their symptoms and ask attending physicians to re-evaluate.

“Inevitable accident” can be a legitimate driver defence - but can also be effectively challenged. Unheralded sudden illness and death of drivers do occur and may cause injury and death of others. However, clinicians are generally unconcerned with causation issues, and they may attribute a MVA to illness simply because the proposition is plausible. Both claimant and defence counsel should determine how well- or poorly-supported are such causal attributions.

Preventing driver illness accidents is not that easy. The sixth edition of “Determining Medical Fitness to Drive”, published by the Canadian Medical Association in 2000, uses Evidence Based Medicine to update physician assessment of drivers. However, some sudden complications of common illnesses are so rare, unpredictable and unforeseeable that large numbers of drivers would have to be denied licensing to prevent a few accidents.

Conversely, there are risky conditions that are far from rare and that often go undiagnosed or untreated.

Falling asleep at the wheel is common - and likely grossly under-recognised as a cause of MVA. Perhaps at least as important as alcohol in causing driver impairment, drowsiness has been implicated in 15-30% of all MVAs.

Many physicians fail to consider sleep disorders. Even when trauma centres routinely investigate unexplained MVAs for medical causes, sleep disorders are generally not included in the testing.

Obstructive Sleep Apnea (OSA) occurs in 2% of women and 4% of men in the general population. Depending on the severity of the condition, risk of MVA in drivers with OSA is increased 2-10 times. When they have all three common symptoms - heavy snoring, sleep disturbances and daytime sleepiness - drivers are 12 times as likely to be involved in single vehicle accidents.

Treatment fixes the problem. Performance on long-distance driving simulation tests is impaired in patients with diagnosed OSA, and standard surgery (UvuloPalatoPharyngoPlasty, UPPP) fixes the deficits. Proven compliance with standard medical treatment (Continuous Positive Airways Pressure, CPAP) similarly permits a return to safe driving.

Compared with OSA, Narcolepsy is considerably less common (3-16 per thousand of the general population) but the condition may account for 10% of sleep-related crashes and increases risk of MVA four-fold.

Even less well documented is the contribution of shift work and jet-lag to MVA. Given the commonness of these conditions, such “situational” sleep disorders may be more important than OSA and narcolepsy in causing crashes.

Counsel should be sceptical when medical experts attribute MVAs to sudden illness of an elderly driver. When older drivers cause unexplained MVAs, medical investigation often reveals possible causes of sudden loss of consciousness. However, “possible” is not the same as “balance of probability”. For example, abrupt onset of an abnormal heart rhythm can result in syncope (sudden unconsciousness), but the commonest heart rhythm abnormality, atrial fibrillation, is no more common in drivers who experience syncope than in the general elderly population.

Diabetes is the commonest medical predictor of increased MVA risk in the elderly. It is unclear whether hypoglycemia (low blood sugar) or the complications of long-standing diabetes are responsible for the increased rate of crashes.

A number of failing faculties - vision, hearing, concentration, reaction time - may contribute to the increased accident rates per mile. That MVA rates are not higher still in the elderly is attributable to considerably lesser average mileage driven.

A variety of prescription (and recreational) drugs impair driving ability. Long-acting benzodiazepine sedatives such as Valium (diazepam) are particularly prone to increase MVA risk in the elderly driver.

Perhaps surprisingly, most mental illnesses are not associated with an increased accident risk. Dementia of the Alzheimer type is likely an exception - particularly when the disease progresses beyond the mildest stages.

Death at the Wheel

Sudden death while driving is extremely rare and causes remarkably few serious injury accidents. Most of such deaths are caused by heart attacks, and it appears that there is usually sufficient warning for the driver to stop the vehicle.

Counsel who are litigating and defending MVA claims should be aware and keep abreast of clinical research into the causal contribution of medical conditions. Armed with a greater knowledge and understanding of driver illness, Personal Injury litigators can more effectively challenge medical expert opinion.