SUMMARY: Sudden death at the wheel and psychiatric conditions are far less important than sleep disorders in causing Motor Vehicle Accidents. In the elderly driver, major contributory factors are diabetes, medical causes of sudden loss of consciousness and prescription drugs.
Sudden natural death at the wheel is extremely rare and is even more rarely a cause of serious injury to other road users1,2,3. At autopsy, most victims prove to have had heart attacks1,4.
Perhaps surprisingly, drivers with psychiatric conditions5 do not generally have an increased risk of Motor Vehicle Accident (MVA). Exceptions may include those with Dementia of the Alzheimer Type (DAT)6, though this greater hazard remains uncertain for mild degrees of dementia7,
By contrast, falling asleep at the wheel because of Obstructive Sleep Apnea (OSA) is probably common and grossly under-recognised8. Though MVAs are commonly unexplained, and some trauma centres routinely investigate for sudden loss of consciousness, OSA is rarely considered9.
OSA is diagnosed in 2% of women, 4% of men in the general population10. Increased risk of MVA is 2-10 times, depending on severity of the condition.
Practice PointAs a cause of traffic accidents, falling asleep may be more important than alcohol |
If, as has been suggested, 15-30% of MVAs are associated with drowsiness11, this may be a bigger public health problem than drunk driving. For drivers with all 3 typical symptoms of OSA, single-vehicle accidents were nearly 12 times as common12:
Practice PointTypical symptoms of Obstructive Sleep Apnea Syndrome:
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Not only were long-distance driving simulation tests impaired in patients with diagnosed OSA, but standard surgery (UvuloPalatoPharyngoPlasty, UPPP) normalised the abnormalities13. Proven compliance with standard medical treatment (Continuous Positive Airways Pressure, CPAP) similarly permits a return to safe driving10.
Narcolepsy is considerably less common (3-16 per 1000) than OSA but may account for 10% of sleep-related crashes, and a four-fold increase in risk of MVA.
Situational sleep disorders such as shift work14 and "jet lag" probably the commonest cause of falling asleep at the wheel.
In the elderly driver, major contributory factors are diabetes, medical causes of sudden loss of consciousness and prescription drugs. Among elderly drivers, diabetes mellitus is the disease most predictive of increased motor vehicle collision risk15. It is unclear whether hypoglycemia or complications of diabetes are responsible for the increased risk.
If they are looked for, medical causes of syncope (sudden loss of consciousness) are commonly found in elderly drivers who have have an unexplained MVA16. These are generally neurological or cardiac conditions.
Disturbances of heart rhythm can cause syncope, particularly if they result in bradycardia (pathological slowing of the heart) or temporary cessation of pumping. By contrast, tachycardia (pathological speeding of the heart) is more likely to cause breathlessness. Uncontrolled atrial fibrillation is the commonest such tachycardia and is no more common in elderly people who have syncope or unexplained falls than in those that do not17.
A wide range of prescription medications and recreational drugs can cause drowsiness, and long-acting benzodiazepine sedatives such as Valium (diazepam) are particularly prone to increase MVA risk in the elderly driver18.
Practice PointIn unexplained MVA, claimant or defendant counsel may be the first professionals to raise the question of underlying medical Causation |
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