18 - Sleep disorders - CCMTA Medical Standards
Sleep disorders and medical fitness to drive.
- 18.6.1 OSA – All drivers
- 18.6.2 Narcolepsy – Non-commercial drivers
- 18.6.3 Narcolepsy – Commercial drivers
18.1 About sleep disorders
Sleep disorders involve any difficulties related to sleeping, including:
- Difficulty falling asleep (insomnia) or staying asleep
- Falling asleep at inappropriate times
- Excessive total sleep time, or
- Abnormal behaviours associated with sleep
This chapter focuses on the most common forms of sleep disordered breathing - obstructive sleep apnea - and on narcolepsy.
In addition to sleep disorders, a number of other factors such as work schedules or lifestyle choices may result in inadequate nocturnal sleep. Regardless of the cause, the risks of excessive sleepiness for driving safety are similar*.
(* Canadian Sleep Society. https://css-scs.ca)
Sleep disordered breathing
Sleep disordered breathing consists of three distinct clinical syndromes:
- Obstructive sleep apnea-hypopnea syndrome (OSAHS): apnea-hypopnea caused by repeated closure of the throat or upper airway during sleep. This is the most common form of sleep disordered breathing. In the medical standards in this section, obstructive sleep apnea-hypopnea syndrome is referred to as OSA.
- Central sleep apnea-hypopnea syndrome (CSAHS): includes types of apnea- hypopnea caused by a neurological problem that interferes with the brain’s ability to control breathing during sleep, as well as high altitude periodic breathing and apnea-hypopnea due to drug or substance abuse.
- Sleep hypoventilation syndrome (SHVS): a type of sleep disordered breathing characterized by insufficient oxygen absorption during sleep. It usually occurs in association with restrictive lung disease in morbidly obese individuals, respiratory muscle weakness or obstructive lung disease such as COPD.
Obstructive sleep apnea-hypopnea syndrome (OSA)
With OSA, the tissue and muscles of the upper airway repetitively collapse during sleep, reducing or preventing breathing. As oxygen levels in the blood fall, arousal causes the airway to re-open. Although individuals with OSA often remain asleep, their sleep patterns are disrupted. These sleep disturbances result in excessive daytime sleepiness. Impairments in cognitive function are common in individuals with OSA and these may include difficulties in attention, concentration, complex problem solving, and short-term recall of verbal and spatial information.
Sleep monitoring is used to confirm a diagnosis of OSA. The preferred test used in diagnosis is nocturnal polysomnography. This test involves monitoring a number of physiological functions, such as brain activity, respiration, heart activity and oxygenation of the blood, while an individual is sleeping. A diagnosis of sleep apnea is based on the apnea-hypopnea index (AHI), where apnea is defined as a cessation of airflow lasting at least 10 seconds and hypopnea is defined as a reduction in airflow with a decline in blood oxygen level lasting at least 10 seconds. Generally, an individual is diagnosed with sleep apnea if they have greater than 5 apnea/hypopnea episodes per hour of sleep.
There are a number of scales used to measure the severity of OSA. A scale based on the AHI describes the following levels of severity:
- Mild: 5 to 14 events per hour
- Moderate: 15 to 30 events per hour
- Severe: more than 30 events per hour
Although nocturnal polysomnography is considered to be the best test for the diagnosis of OSA, a number of other tests may be used by sleep specialists to assist in evaluation or diagnosis. Overnight oximetry is similar to polysomnography, but only measures oxygen level and heart rate. Results from overnight oximetry alone are not considered adequate to diagnose OSA.
A number of tests are used to evaluate daytime sleepiness. These include the Maintenance of Wakefulness Test (MWT), the Multiple Sleep Latency Test (MSLT) and the Epworth Sleepiness Scale (ESS). MWT measures the level of daytime drowsiness based on how long a person can remain awake during the day under controlled conditions. The MSLT is similar to the MWT, but measures how long it takes a person to fall asleep when taking daytime naps, rather than how long they can stay awake. The ESS is a subjective test in which a person is asked to rate on a scale of 1 to 4 the likelihood that they would fall asleep in different situations, such as when watching TV, riding in a car or engaging in conversation.
Treatment options for OSA include:
- Lifestyle changes such as weight loss, alcohol abstinence or change in sleep position
- The use of oral appliances
- The use of a nasal continuous positive airway pressure (CPAP) device,
- Bariatric surgery (for morbidly obese individuals), and
- In rare cases, corrective upper airway surgery
CPAP is the most effective treatment, and the only one which has been shown to reduce the risk of motor vehicle crashes. A CPAP machine blows heated, humidified air through a short tube to a mask worn by the individual while sleeping. As the individual breathes, air pressure from the CPAP machine holds the nose, palate and throat tissues open.
An immediate reduction (usually within 2 weeks) in daytime sleepiness is often reported with CPAP treatment, although studies indicate that approximately 6 weeks of treatment are required for maximum improvement in symptoms. Medical consensus supports the resumption of driving after 2 weeks of treatment. Estimates of compliance with CPAP treatment vary depending on how it is measured.
Subjective rates of compliance based on self-report are higher than objectively determined rates. Using objective measures, a 1993 study found that 46% of individuals were acceptably compliant with their CPAP treatment. The study defined acceptable compliance as the use of the CPAP machine for at least four hours per night for more than 70% of the observed nights.
All commercial drivers must file periodic mandatory medical reports to assess their fitness to hold a commercial licence. Non-commercial drivers are assessed for fitness to drive on a case by case basis, taking into account the treating physicians specific recommendations.
During periodic medical assessments it is essential the examining physician screen for sleep disorders risk factors. The FMCSA Expert Panel Recommendations on Obstructive Sleep Apnea and Commercial Motor Vehicle Driver Safety (2008) reflected the following on OSA.
Symptoms suggestive of OSA:
- Chronic loud snoring
- Witnessed apneas or breathing pauses during sleep
- Daytime sleepiness
Risk factors for OSA:
- Advancing age
- BMI>28 kg/m2 (BMI - Body Mass Index)
- Small jaw
- Large neck size (>17 inches male, >15.5 inches female)
- Small airway
Conditions associated with OSA:
- HBP (High Blood Pressure) or HTA (Hipertension Arterial)
- Type 2 diabetes
Patients with severe OSA, who have been involved in a crash in which their medical condition was a causal factor, are at high risk of having more accidents if they are not treated successfully. Even without having experienced a crash, severe sleep apnea has been identified as a factor that increases crash risk. Consequently, commercial drivers who have experienced a crash associated with falling asleep, or report they have experienced excessive sleepiness while driving, should be advised to stop driving immediately pending completion of sleep studies and effective treatment.
Furthermore, licensing agencies must decide if commercial drivers with OSA risk factors associated with the symptoms listed are fit to hold class 1, 2, 3 or 4 driver licences pending a sleep expert assessment given current waiting times for sleep studies.
Treated OSA is subject to annual medical review by the licensing agency for all Class 1, 2, 3 and 4 driver licence holders.
Narcolepsy is a chronic neurological disorder in which the brain is unable to regulate sleep-wake cycles normally. It is characterized by excessive daytime sleepiness and may also cause cataplexy (abrupt loss of muscle tone), hallucinations and sleep paralysis.
There is no known cure. The symptoms of narcolepsy relevant to driving are sleepiness and cataplexy.
The excessive daytime sleepiness of narcolepsy comprises both a background feeling of sleepiness present much of the time and a strong, sometimes irresistible, urge to sleep recurring at intervals through the day. This desire is heightened by conducive or monotonous circumstances, but naps at inappropriate times, such as during meals, are characteristic. The naps associated with narcolepsy usually last from minutes to an hour and occur a few times each day. Potential secondary symptoms related to sleepiness may include visual blurring, diplopia and cognitive impairment. Cognitive impairment may include difficulties with attention and memory.
Cataplexy refers to an abrupt loss of skeletal muscle tone. It is estimated that 60% to 90% of individuals with narcolepsy experience cataplexy. During a cataplexy attack, which can last up to several minutes and occur several times a day, an individual remains conscious but is unable to move. Generalized attacks can cause an individual to completely collapse, although the muscles of the diaphragm and the eyes remain unaffected. Partial attacks, which affect only certain muscle groups, are more common than generalized attacks. Laughter or humorous events are a common trigger of cataplexy attacks, although anger, embarrassment, surprise or sexual arousal can also trigger an attack.
As there is no cure, treatment for narcolepsy is focussed on the control of sleepiness and cataplexy where present. Medications used for treatment may include:
- Stimulants such as Modafinil (AltertecTM)
- Tricyclic antidepressants
- Selective serotonin reuptake inhibitors
- Venlafaxine (EffexorTM), or
- Reboxetine (EdronaxTM)
See Chapter 15, Drugs, Alcohol and Driving, for more information about medications and driving.
OSA affects at least 2% of women and 4% of men. It is more prevalent among middle aged and older individuals and those who are obese. It commonly remains undiagnosed, with estimates suggesting that 93% of women and 82% of men with moderate to severe sleep apnea are undiagnosed.
Canadian data on the prevalence of narcolepsy are lacking. Research in the United States indicates a prevalence rate of 47 per 100,000 individuals (.05%). It is more common in men than in women.
18.3 Sleep disorders and adverse driving outcomes
Numerous studies have investigated the relationship between OSA and adverse driving outcomes. OSA may cause daytime drowsiness and reduced concentration that are symptoms that can negatively affect driving safely. OSA is also of special concern for the commercial driver who often drives long distances with few breaks and whose work schedule may not be conducive to healthy sleep hygiene.
The majority of studies indicate that individuals with OSA have a 2 to 4 times greater risk for a crash, and the crashes result in more severe injuries. Although numerous tests are available to measure daytime sleepiness, the research also indicates that measures of daytime sleepiness and the severity of sleep apnea are not consistent predictors of impairments in driving performance.
Unlike OSA, there are few studies on narcolepsy and adverse driving outcomes. Although limited, this research suggests that narcolepsy is also associated with elevated crash rates.
18.4 Effect on functional ability to drive
|Condition||Type of driving impairment and assessment||Primary functional ability affected||Assessment tools|
|Episodic impairment: Medical assessment – likelihood of impairment||
All – sudden incapacitation
Cognitive – reduced alertness
Persistent impairment: Functional assessment
Drivers with sleep disorders are not able to compensate for their impairment.
Recently, a number of warning systems for drowsy drivers have been developed. These systems are designed to detect drowsiness by monitoring the driver’s eye movement, head movement or other physical activity, or by sensing when a vehicle is drifting on the road. When drowsiness is suspected, a warning system alerts the driver. These systems are in various stages of development and production.
Research on the effectiveness of drowsy driving warning systems is limited. The existing research indicates that these technologies show promise as a means to warn drivers of fatigue or drowsiness. However, it is recognized that alertness is a complex phenomenon, and no single measure alone may be sensitive and reliable enough to quantify driver fatigue. Further research and development is required before the use of these warning systems can be applied in driver licensing decisions.
18.6 Guidelines for assessment
All drivers eligible for a licence if
|Conditions for maintaining licence||
RoadSafetyBC will impose the following condition:
The following exceptions to CMMTA reassessment standards apply:
|Information from health care providers||
The primary concerns with OSA are daytime sleepiness (risk of sleep while driving) and persistent cognitive impairment.Determining who is at risk of adverse driving outcomes due to daytime sleepiness is problematic. Because existing measures of daytime sleepiness and the severity of sleep apnea are not consistent predictors of impairments in driving performance, the standard looks to driver history of sleep at the wheel for identifying current risk of sleep while driving. The standard also emphasizes the responsibility of the driver to be attentive to the risk for daytime sleepiness*
Non-commercial drivers eligible for a licence if:
|Conditions for maintaining licence||None|
|Information from health care providers||
The general approach of the standard for drivers with narcolepsy is that attacks must be controlled as a prerequisite to driving. Where a driver is treated, the standard includes a requirement for an attack- free period to establish the likelihood that
The episodic risk of a sleep attack or cataplexy while driving is addressed in the requirement for a 12 month period without an episode prior to driving. The length of this no driving period is based on consensus medical opinion in Canada
This standard applies to drivers who are diagnosed with narcolepsy.
Commercial drivers generally not eligible for a licence. May be eligible if:
|BC Guidelines||RoadSafetyBC will not generally request further information|
|Conditions for maintaining licence||
|Information from health care providers||
Consensus medical opinion in Canada indicates that the risks from increased driving exposure associated with commercial driving are such that drivers with narcolepsy may not drive. However CMA Driver’s Guide 8th Ed also indicates people with narcolepsy, who are able to maintain a regular sleep-wake cycle, may be able to drive commercial vehicles during the day, over short routes. The recommendation for licensing commercial drivers with narcolepsy in the CMA Guide is a consensus recommendation based on clinical grounds