Section 9

Sleep disorders

Somnolence (sleepiness), with its associated reduction in vigilance, is an important contributor to driver error and motor vehicle crashes. Somnolence can be due to lifestyle issues, a sleep disorder, or both.

The 3rd edition of the International Classification of Sleep Disorders (American Academy of Sleep Medicine, 2014) outlines six categories of sleep disorders: insomnia, sleep-related breathing disorders, central disorders of hypersomnia, circadian rhythm sleep–wake disorders, parasomnias, and sleep-related movement disorders.

The recommendations that follow relate primarily to obstructive sleep apnea (OSA) and narcolepsy, the two sleep disorders for which there is a reasonably clear association between the disorder and the risk of a motor vehicle crash.

Patients reporting excessive somnolence should be questioned in detail about the adequacy and regularity of their sleep–wake cycle, as attention to this may improve symptoms and reduce driving risk.

The following are some risk factors for sleep-related crashes:

• holding multiple jobs
• working a night shift
• nighttime driving (between midnight and 6 am)
• less than 6 hours of nighttime sleep
• long-duration driving or driving after being awake for more than 15 hours
• history of drowsy driving
• daytime sleepiness
• recent (within a year) at-fault motor vehicle crash.

Patients with various sleep disorders may also have one or more of these risk factors and, as a result, have varying levels of sleepiness. This may partly explain observed differences in the risk associated with operating a motor vehicle. The appropriateness of and need for medical intervention in the management of these disorders also varies.

Patients with excessive daytime somnolence should be questioned about and examined for the following risk factors for OSA:

• chronic heavy snoring
• nocturnal snorting and gasping
• witnessed apnea
• uncontrolled hypertension
• significant cardiovascular disease
• morning headaches
• craniofacial abnormalities (e.g., macroglossia, retrognathia)
• large neck size (≥ 43 cm [17 in])
• obesity.

Men and patients older than 40 years of age are also at increased risk of OSA.

Patients with excessive somnolence and one or more risk factors for OSA, as well as those with persistent sleepiness and a history consistent with another sleep disorder (e.g., narcolepsy), should be considered for assessment in a sleep laboratory. When sleep laboratory resources are not available, portable monitoring devices can be used to confirm a diagnosis of OSA if monitoring is performed and interpreted according to published guidelines (Blackman et al., 2010).

OSA is characterized by repetitive upper airway obstruction during sleep, leading to recurrent episodes of hypoxemia and arousal from sleep and resulting in disturbed sleep patterns. The relative risk of motor vehicle crashes among patients with symptomatic OSA is about two to three times that of control groups (Mulgrew et al., 2008), with a risk for single and multiple crashes increasing with sleep apnea severity (Komada et al., 2009; Gottlieb et al., 2018). In severe cases of OSA, the risk of a motor vehicle crash may be increased as much as 10-fold (Arita et al., 2015). However, determining individual risk remains difficult because of individual variations in susceptibility to sleepiness, use of countermeasures, or driving avoidance.

Treatment of OSA with continuous positive airway pressure (CPAP) has been successful in reducing crash risk to control levels (George, 2001), particularly in patients with adequate treatment adherence (Karimi et al., 2015). Reassessment of patients using CPAP, with a compliance-metering device on the CPAP unit, should be done 1 to 2 months after diagnosis. The effectiveness of upper airway surgery is less clear (Haraldsson et al., 1995; Alkan et al., 2021), and patients treated by this method may require re-evaluation by sleep study.

Some patients with mild cases of OSA may be treated through behavioural modification (e.g., weight reduction [Ng et al., 2017], modification of sleeping position, elimination of alcohol and sedatives before sleep) or through the use of oral appliances (Phillips et al., 2013). These interventions may be sufficient, but patients require reassessment for efficacy of treatment before resumption of driving.

Narcolepsy is characterized by recurrent lapses into sleep that are often sudden and irresistible and that typically last 10–15 minutes. Narcolepsy may be accompanied by cataplexy (sudden bilateral loss of muscle tone) during wakefulness, sleep paralysis (generalized inability to move or to speak during the sleep–wake transition), and vivid hallucinations at sleep onset.

Although there is a clear association between crash risk and narcolepsy, this association is not as well studied as that between crash risk and OSA.

Up to 40% of people with narcolepsy may report sleep-related motor vehicle crashes. Their risk for crashes is about four times that of control groups (Aldrich, 1989). Patients with cataplexy and sleep paralysis are believed to be at greatest risk for crashes, based on the relative unpredictability of these symptoms. In an online registry of patients with narcolepsy (with assessments completed every 6 months), almost 20% of patients reported a motor vehicle crash or near miss while driving (Ohayon et al., 2018). Younger age, higher score on the Epworth Sleepiness Scale, and presence of a psychiatric condition were associated with higher probability of a crash or a near miss. There is little information about the effect of treatment on risk for crashes.

Although short- and long-term insomnia may be the most common category of sleep disorder, there are no data linking increased motor vehicle crashes with insomnia.

Circadian rhythm sleep disorders, which are related to sleep loss from disruption of the daily sleep cycle, as seen with shift work or the jet lag experienced with transmeridian flights, are common and might easily be associated with a large number of crashes.

However, there are again no clear data linking them with crashes.

Accordingly, physicians can make only general recommendations about the hazards of drowsy driving due to these other sleep disorders.