Falling asleep at the wheel doesn’t make headlines like speeding or drink driving, but it can be just as deadly.

Fatigue is one of the “Fatal Five” causes of deadly motor vehicle accidents, alongside speeding, alcohol or drug impairment, failure to wear a seatbelt, and distraction. While often linked to shift work or long hours, fatigue can also indicate an underlying sleep disorder such as obstructive sleep apnea (OSA).

OSA is common but often difficult to detect because it presents with non-specific symptoms such as tiredness, low energy, or poor concentration that are not always clearly linked to a sleep disorder.

Although OSA is often seen as a sleep quality issue, its impact on driving, cognition, and public safety makes early identification and management essential.

Understanding the risk

Driving risk increases significantly when OSA goes untreated, with affected individuals estimated to be 2–7 times more likely to be involved in a motor vehicle accident. These “fall-asleep” incidents often occur late at night or in the early morning. They typically involve a single vehicle veering off the road, and show no signs of braking, indicating the driver was fully asleep. Such accidents are more likely to be severe or fatal, particularly when the driver is alone.

Recognising the signs of OSA

OSA affects up to 10% of adult men and 5% of women when both symptoms and sleep study findings are considered. It is characterised by repeated upper airway obstruction during sleep, causing intermittent hypoxia, sleep fragmentation, and increased sympathetic activity. Risk is higher in men and people with obesity, type 2 diabetes, hypertension, or atrial fibrillation.

Symptoms vary but often include habitual loud snoring, witnessed apneas, and episodes of choking or gasping during sleep. Many patients wake unrefreshed despite adequate sleep and report excessive daytime sleepiness, especially during passive activities such as reading, watching TV, or sitting in traffic. Other symptoms may include morning headaches, difficulty concentrating, memory issues, and frequent nighttime urination (nocturia).

A patient who reports either falling asleep while driving or another sleepiness-related incident should be assessed urgently. These are strong indicators for further investigation, even if other symptoms seem mild.

Other causes and compounding factors for daytime sleepiness

Excessive daytime sleepiness is the primary symptom linked to driving risk. However, not all sleepiness is caused by OSA. Contributing factors include sleep restriction, extended wakefulness, shift work, circadian disruption, sedative medications, depression, and other medical conditions like diabetes or neurological disorders.

Fatigue and daytime sleepiness are often used interchangeably, but have different clinical meanings. Daytime sleepiness refers to a tendency to doze off in passive or even active situations, such as watching TV or driving. Fatigue is a general sense of low energy or exhaustion, without the urge to sleep.

When patients report either, particularly in the context of driving, further questioning is warranted. Both states can affect driving, but sleepiness (especially from sleep disorders like OSA) is more directly linked to crashes.

What to ask in the consultation

Patients may not mention sleep concerns unless prompted, as fatigue is often seen as normal and signs of sleepiness can be subtle. Ask direct, targeted questions to uncover symptoms patients may not recognise or report.

Consider asking:

• Do you feel sleepy during passive activities like driving or watching TV?
• Do you regularly feel unrefreshed, even after a full night’s sleep?
• Has anyone told you that you snore loudly or stop breathing during sleep?
• Do you have difficulty concentrating, poor memory, or mood changes during the day?

Keep in mind that patients with obesity, type 2 diabetes, hypertension, or atrial fibrillation require a lower threshold for suspecting OSA due to the strong association with sleep-disordered breathing.

Screening and assessing risk

When OSA is suspected, use validated screening tools such as the STOP-BANG, Berlin, or OSA-50 questionnaires to stratify risk and guide further investigation.

The Epworth Sleepiness Scale (ESS) is an additional subjective measure of daytime sleepiness. A score of 8 or more suggests abnormal sleepiness, while 11 or higher indicates moderate to severe levels. A positive questionnaire combined with an elevated ESS supports direct referral for a Medicare-funded Level 1 (in-lab) or Level 2 (home-based) sleep study, without needing specialist review.

It’s important to note that quantifying the apneic events per hour using the Apnea-Hypopnea Index (AHI) is not always reflective of daytime function or driving risk. Some patients with high AHI may feel well, while others with mild OSA may report serious sleepiness. Both objective and subjective findings should be considered.

Treatment options and patient considerations

Once OSA is confirmed, management depends on severity and clinical context. Mild cases may be managed in general practice, provided there is no significant sleepiness or occupational driving risk. Patients with moderate to severe OSA, particularly those in safety-critical roles or with ongoing symptoms, should be referred to a sleep specialist.

CPAP is the first-line therapy for moderate to severe OSA. It effectively reduces sleepiness, with benefits often noticeable within days. However, adherence is a common barrier with up to half of patients ceasing CPAP use within a year. Outcomes can be improved by providing education, support, and regular follow-ups to patients.

Mandibular advancement splints are an alternative for patients with mild to moderate OSA who cannot tolerate CPAP. Other interventions such as weight loss, positional therapy, and in selected cases, upper airway surgery may also be appropriate.

When to refer

Not all patients respond predictably to treatment. Even with optimal CPAP use, fewer than 10% may continue to experience residual sleepiness. These patients should be referred to a sleep physician for further evaluation.

Referral is also recommended when the diagnosis is unclear or if there are complicating cardiovascular, respiratory, metabolic, neurological, or psychiatric conditions, as well as in cases where the OSA is moderate or severe.

Referral is also advised for commercial or safety-critical drivers. In some cases, the sleep specialist may perform a Maintenance of Wakefulness Test (MWT) to objectively assess alertness in a quiet, low-stimulation environment. In certain jurisdictions, commercial drivers require annual review and documentation of CPAP use, with objective testing when necessary.

Assessing fitness to drive

Before confirming a patient is fit to drive, especially after starting CPAP, verify compliance, symptom improvement and treatment effectiveness. Ideally, CPAP should be used for at least six hours per night, with low residual AHI and clear improvement in alertness. The best way to assess compliance and treatment effectiveness is to ask for the CPAP data download – or ask the patient to show you the CPAP data on their device. This enables objective confirmation and includes usage time, pressure settings, leak rates, and residual respiratory events.

Practice tip: CPAP providers can supply a usage report, or patients may access it via connected apps. Ask them to bring a recent download to their review to support decision-making.

If the patient feels well, reports no daytime sleepiness, and the CPAP data shows good control, driving can usually resume. If concerns remain, further questioning is needed.

Questions to consider before clearing a patient to drive:

• Are they using CPAP consistently (ideally for six or more hours per night)?
• Is the residual AHI low, as confirmed on CPAP download?
• Do they report improved alertness and no longer feel sleepy during the day, including while driving?
• Have they experienced any recent episodes of drowsiness at the wheel, near misses, or crashes?
• Are there other potential contributors to daytime sleepiness, such as medications, shift work, or unmanaged mental health conditions?

What your patient needs to know about driving

Patients with untreated or symptomatic OSA should avoid long-distance, night-time, or monotonous driving until symptoms are under control. If a patient reports falling asleep at the wheel, restrict driving immediately and arrange further assessment.

For private licence holders, driving can resume once symptoms are well managed and adherence to treatment is established. Commercial drivers must meet stricter criteria and require confirmation of ongoing treatment effectiveness through specialist review.

Key takeaways

• Untreated OSA can increase the risk of motor vehicle accidents by 2–7 times.
• Daytime sleepiness is a stronger predictor of driving risk than AHI, so it’s essential to assess functional alertness during clinical evaluation.
• Validated screening tools combined with the ESS can support direct referral for sleep studies, even without specialist input.
• Only clear a patient to drive if CPAP is used consistently, residual AHI is low, and daytime alertness has improved.
• Refer patients in complex or safety-sensitive roles to a sleep specialist.