13 Nov 2015

Driving and Obstructive Sleep Apnoea

In Australia each year, more than 1,500 people are killed on roads and approximately 22,000 are seriously injured. The total economic cost of Motor Vehicle Accidents (MVA) is estimated to be greater than $15 billion per year.Now there is increasing recognition that sleep issues have a role to play in contributing to this toll.

Driving is one of the most complex and potentially dangerous tasks we perform; we must rapidly process our driving environment, make split second decisions, and our motor response requires precise movement through hand-eye coordination.

While past road safety campaigns have espoused the evils of excessive speed, driving under the influence of alcohol, travelling without a seat belt, and avoiding distractions such as mobile phones, there is increasing emphasis and recognition of the impact of fatigue and sleepiness on driving.

Sleep shortage and fatigue are estimated to cause 20-30% of all Motor Vehicle Accidents2-4, either directly or through cognitive impairment, poor judgement, impaired memory, impaired hand-eye coordination and impaired response to external stimuli (such as audible line markers).

It is now known that prolonged wakefulness results in impairment similar to that of alcohol consumption.5 Sleep restriction, poor sleep hygiene, sleep phase disorders and shift work disorder are just some of the conditions that can cause fatigue and sleepiness.

What is Obstructive Sleep Apnoea?

Obstructive sleep apnoea (Sleep Apnoea) is the most common sleep disorder, and when defined as an apnoea hyponoea index (AHI) >5 and daytime somnolence, 5% of adults have Sleep Apnoea syndrome.6

In recent years, the prevalence of obstructive sleep apnoea has been on the rise, due to the obesity epidemic, an aging population and increased recognition by health professionals.

Symptoms of obstructive sleep apnoea include:

  • mechanical obstruction of the oropharynx during sleep, causing repeated arousals
  • fragmented sleep
  • marked swings in blood pressure
  • repeated hypoxemia and hypercapnoea

This results in poor sleep quality, and patients wake unrefreshed, suffering daytime somnolence, depression and irritability, reduced libido, poor memory and concentration. In severe cases, patients will fall asleep involuntarily such as when talking to people or eating meals.

Sleep Apnoea and drivers

Not surprisingly, sleep apnoea is associated with a two- to seven-fold increased risk of a Motor Vehicle Accident.7-10

Commercial drivers are of particular concern due to their increased amount of kilometres driven, the long duration of wakefulness required, monotonous highway driving, and the shifts that are worked including overnight shifts.

Furthermore, the size of the vehicles, limited ability to take evasive action resulting in impact often at full speed, and carriage of hazardous substances, means there is greater potential for injury should an accident occur.

Studies confirm that the prevalence of sleep apnoea in commercial drivers is significantly higher than the general population.11 This is because most commercial drivers are male, overweight due to their sedentary occupation, and middle- to older-age, which are all factors that increase Sleep Apnoea risk. In an Australian study by Howard et al, 60% of commercial drivers undergoing PSG had an AHI >5 and 11% had an AHI >30, but only 16% admitted to symptoms of sleep apnoea.8  

Assessing the risk of Sleep Apnoea

Predicting who has sleep apnoea based on history and clinical examination is imperfect, however specific examination findings (such as BMI, mallampati score and neck circumference) can improve sensitivity and specificity.

Using standardised questionnaires, such as the Epworth Sleepiness Scale, the BERLIN Questionnaire, and the Multivariate Apnoea Prediction index, can also further increase the reliability with which sleep apnoea is predicted. The definitive diagnosis is made by either an at-home or in-laboratory polysomnogram.12,13

Understanding Your Sleep - ResSleep

Assessing driving risk once Sleep Apnoea is diagnosed

Patients who have had a previous accident or near miss due to falling asleep at increased risk of having another accident/near miss, whether it be because they cannot recognise the signs of tiredness or because they choose to ignore these signs.14 Patients with a high ESS (>16) are also at increased risk of having a fall asleep motor vehicle accident,15,16 however one study found an inverse relationship between ESS and sleep apnoea diagnosis, presumably due to underreporting of symptoms.17


The main problem with these measures are that they are subjective, rely on self-reporting and hence are open to manipulation, particularly with the perceived threat of licence revocation.18 Importantly, Sleep apnoea severity alone is not a reliable predictor of motor vehicle accident risk and should be considered in the context of other factors when assessing fitness to drive and overall risk of motor vehicle accidents.19  

Evidence suggests that drivers tend to underestimate the severity of their symptoms when their licence, and employment (in the case of commercial drivers), is under threat from the results of a sleep study.20 Better education is vital in allaying these concerns.   

Objective measures to assess accident risk include maintenance of wakefulness test (MWT), visual vigilance21,22 and driving simulator tests.

Maintenance of wakefulness tests

During an MWT, patients are placed in a non-stimulating environment for 40 minutes at a time and asked to stay awake for as long as possible; this is repeated 4 times throughout the day. The problem with the MWT is that "normal" reference ranges are wide. Nonetheless, several studies show that drivers with a highly pathological MWT sleep latency (0-19 mins) displayed a significantly worse performance on a driving simulator (inappropriate line crossings) than those with a sleep latency of >19 minutes.23-25

Visual vigilance tests

With visual and psychomotor vigilance testing, patients are instructed to respond to visual or psychomotor stimuli as quickly as possible, with reaction time being used as a surrogate marker for driving impairment. Studies show that patients with Sleep Apnoea have a lower hit rate than controls, and this correlates with increased driver errors on a simulator.21 Further studies are needed to prove that poorer performance on vigilance testing is indicative of increased real-world crash risk.

Driving simulator tests

Driving simulators are another type of functional testing increasingly being used to assess a person’s fitness to drive. As the name suggests, simulators recreate the driving environment in a laboratory or clinic, devoid of actual safety risks. Measures include unintentional line crossing, steering deviation, tracking, reaction time, braking times, and crashes. Studies show that patients with Sleep Apnoea demonstrate worse performance on driving simulators compared to healthy controls, however there is no yet robust evidence that performance on a driving simulator accurately translates to real-world accident risk.26

In essence, no one questionnaire, diagnostic test or medical examination is sufficiently sensitive and specific to reliably identify those at highest risk of driving accidents. Thus, the American College of Chest Physicians state that individualised assessment by an experienced medical practitioner synthesising both subjective and objective data is the best way to assess driving risk; this approach is not overly scientific and this highlights the difficulty in determining which patients with sleep apnoea are safe to continue driving.27


Treating Sleep Apnoea and motor vehicle accident risks

Just as there is good evidence that treatment of Sleep Apnoea reduces daytime somnolence, improves neurocognitive functioning, and improves quality of life, several studies show that Motor Vehicle Accident risk decreases once patients with Sleep Apnoea are adequately treated with CPAP.

Two meta-analyses of studies patients with at least moderate Sleep Apnoea found a risk reduction in Motor Vehicle Accident of 0.278 (0.22-0.35) and 0.21 (0.12-0.35) respectively in patients with sleep apnoea before and after treatment with CPAP,7,28 with improvement occurring as early as 2-7 days after starting treatment.

A study by Findley et al showed the importance of compliance, with Motor Vehicle Accident risk only being reduced in those who were compliant with CPAP.29 Despite evidence for its efficacy, one study using a driving simulator showed that patients who are compliant on effective CPAP still have worse driving performance compared to healthy controls,30 however this did not translate into an increased crash risk.

Understanding Your Sleep - ResSleep

Although there have been no definitive studies showing that mandibular advancement splints (MAS) reduce motor vehicle accident risk, it would be reasonable to assume that this was the case as long as the Sleep Apnoea was controlled; a study by Phillips et al shows as much, however driving performance was not a primary endpoint and hence was not powered to demonstrate a difference.23

Should all commercial drivers be screened for Sleep Apnoea?

Currently the answer to this is no, due to the excessive resources that would be needed. Furthermore Sleep Apnoea severity does not predict Motor Vehicle Accident risk, and it is impractical to prevent all commercial drivers with Sleep Apnoea from driving, particularly as up to 2/3 of drivers with Sleep Apnoea never have any objective evidence of crashes.31,32

Increasingly though, trucking corporations are enforcing mandatory medical fitness checks by occupational physicians to ensure the safety of their drivers as well as reducing their legal liability should an accident occur. Usually employees with an increased body mass index, previous history of near miss or fall asleep accidents or high risk safety workers will be asked to proceed onto a diagnostic sleep study and sleep physician review. There is increasing evidence that this proactive approach to driver safety results in a significant long term cost savings.33

Driving licensing systems for medical conditions

"Assessing Fitness To Drive Guidelines" published by Austroads, the association of Australasian road transport and traffic agencies, is an indispensable free publication to assist health professionals in determining whether a patient needs a conditional or unconditional licence for a wide range of medical and surgical conditions. General driving safety information is provided as well as licensing standards for both private and commercial licence holders.

Provision of a conditional licence is determined by the Driver’s Licence Authority (DLA), taking into account recommendations by the treating health professional. A conditional licence identifies that certain treatments or restrictions are needed to ensure the driver and those around him/her are safe on the roads. Conditional licences are subject to periodic review, and may revert back to an unconditional licence if the medical condition improves to the point that they no longer require a licence condition - for example, subjective and objective improvement of Sleep Apnoea after tonsillectomy for tonsillar hypertrophy.

With regards to sleep apnoea, the Austroads guidelines, published by Austroads and the National Transport Commission and approved by the Australian Transport Council, state that a person is not fit to hold an unconditional licence:

  • if the person has established sleep apnoea syndrome (sleep apnoea on a diagnostic sleep study and moderate to excessive daytime sleepiness); or
  • if the person has frequent self reported episodes of sleepiness or drowsiness while driving; or
  • if the person has had motor vehicle crash/es caused by inattention or sleepiness; or
  • if the person, in the opinion of the treating doctor, represents a significant driving risk as a result of a sleep disorder.

The only difference between private and commercial standards is that the latter is subject to periodic review by a specialist in sleep disorders whereas the former requires periodic review by the treating doctor (who doesn't necessarily need to be a specialist in sleep disorders). Of course there may be minor variations in rules between states and territories and hence it is advisable to contact your state or territory driver licensing authority for further guidance regarding fitness to drive.


Dealing with underreporting of Sleep Apnoea symptoms

Drivers will often underreport symptoms for fear of having their licence suspended. In the vast majority of cases, however, the patient can continue to drive so long as the patient remains compliant with effective treatment, whether this be CPAP or a MAS.

To prevent underreporting, some states have introduced laws making it mandatory for drivers to report any medical condition that affects their ability to drive as soon as they become aware of it, or risk significant fines or even imprisonment. It is the doctor’s responsibility to make patients aware of their legal responsibility in relation to driving with medical conditions.

It is a rare but nonetheless very challenging situation when a patient refuses to heed the advice of his/her doctor to limit or cease driving until adequate and efficacious treatment is in place. The dictum of doctor-patient confidentiality must be weighed against the greater good of public safety however "the duty to maintain confidentiality is legally qualified in certain circumstances in order to protect public safety".1

In all states except South Australia and the Northern Territory, statute provides that health professionals are protected from civil and criminal liability should they make such reports to the DLA in good faith without the patient's consent. South Australia and Northern Territory legislation imposes mandatory reporting. However it is preferable that any action taken in the interests of public safety is done so with the consent of the patient wherever possible, and should be done so with the patient's knowledge of the intended action. Remember that the treating doctor only makes recommendations to the DLA about one's fitness to drive; the DLA makes the final decision about whether a patient’s licence is revoked.


In summary, significant fatigue and somnolence due to any cause increases the risk of a Motor Vehicle Accident and is a major concern not only to the individual, but also to the public at large.

Sleep Apnoea is a common and easily treatable cause of daytime somnolence, and treatment with CPAP reduces Motor Vehicle Accident risk to that of healthy controls. However, the majority of patients with Sleep Apnoea will not have any Motor Vehicle Accident due to inattention/sleepiness, and with our current limited investigations, it remains challenging to identify which patients with Sleep Apnoea are most at risk of having fall asleep accidents or near misses. There is no single metric that will consistently identify those at risk, and an integrated assessment of subjective and objective measures by an experienced health professional is currently recommended. Health professionals are advised to familiarise themselves with the Austroads publication "Assessing Fitness to Drive", and to contact their local DLA or sleep physician should they have any queries.

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