It is now well established that sleepiness while driving markedly increases an individual’s risk for a motor vehicle accident. Not only can sleepiness lead to falling asleep at the wheel, but sleepiness while driving can have other insidious or less obvious consequences as well.
Sleepy drivers have longer reaction times, demonstrate impaired judgment, and inattention often resulting from brief “micro sleeps” where the individual’s brain wave activity slows even though the eyes may still remain open. Some may call this effect “road hypnosis” in the trucking industry. Indeed, recent research has now shown that 24 hours of sleep deprivation has the same effects on a driving simulator as a blood alcohol concentration of 0.1%, a level at or above what is considered intoxicated. The dangers of sleepiness while driving, as well as tips to maximize safety, are covered in the section Sleep and Driving.
Commercial motor vehicle drivers are required to have a commercial drivers license (CDL) and undergo yearly Department of Transportation (DOT) physical evaluations. Any medical disorder that may potentially impair the driver should be identified during DOT physicals. These evaluations are meant to determine the eligibility of the driver to obtain a CDL and to ensure that any potentially dangerous medical condition is properly treated.
Why should commercial drivers undergo yearly DOT physical evaluations?
Commercial motor vehicle operators are held to a higher standard than the general population regarding driving privileges for several reasons. Not only do these drivers tend to have long hours behind the wheel, but they also tend to operate larger vehicles which may contain hazardous chemicals or they may transport large numbers of passengers. Moreover, commercial drivers often have economic incentives to drive farther without stopping or even under unsafe driving conditions such as bad weather. The consequences of a motor vehicle accident for commercial drivers can obviously be devastating. Yearly DOT evaluations help ensure that commercial drivers are fit to handle the challenges they face and to maximize public safety.
Sleep disorders as a cause of sleepiness while driving
There are many sleep disorders that may either disrupt sleep or lead to excessive sleepiness and, as a result, can place drivers at an increased risk for a motor vehicle accident. Obstructive sleep apnea (OSA), for example, is one of the most common sleep disorders and arises when the upper airway collapses during sleep, causing the individual to either wake up or go to a lighter level of sleep to re-establish the airway and resume normal breathing. Snoring is a typical sign of upper airway resistance and commonly present in patients with OSA (see Snoring and Obstructive Sleep Apnea). Upper Airway Resistance Syndrome (UARS) is a precursor to OSA, characterized by frequent snore-arousals. Repetitive awakenings to open the airway during sleep cause fragmentation of sleep even though the individual is typically unaware of these many awakenings. As a result of the disrupted sleep, excessive daytime sleepiness occurs and can become dangerous when operating a motor vehicle.
Other sleep disorders such as narcolepsy, restless legs syndrome (RLS), periodic limb movement disorder (PLMD) and disorders causing insomnia all can have excessive daytime sleepiness as a potential consequence. Narcolepsy is a neurological disorder that causes prominent excessive sleepiness no matter how much sleep is obtained at night and is one of the only sleep disorders that may prohibit an individual from obtaining a CDL to drive a commercial motor vehicle. Other sleep disorders are generally easily treated and do not impose any driving restrictions as long as the driver is adhering to the prescribed therapy.
Chronic sleep deprivation is very common in our 24-hour society and can cause a level of excessive daytime sleepiness that is as severe as in patients with narcolepsy. Sleep deprived individuals can often “get by” by staying active and engaged in an activity. However, such individuals typically have difficulty staying awake when sitting still or inactive for longer periods of time, such as driving behind the wheel for hours at a time. As noted above, sleep deprivation increases the risk for motor vehicle accidents. Unfortunately, there is no road-side test currently available like a “breathalizer” to evaluate an individual’s level of alertness. All drivers need to respect their need for sleep and to make a concerted effort to drive only when rested (see Sleep and Driving).
Sleep disorders are very common in the general population, but some sleep disorders are even more common in commercial motor vehicle operators. Obstructive sleep apnea, for example, is found in approximately 15% of all middle-aged men, but present in 30% of all truck drivers. Long-haul truckers in particular tend to have a very sedentary lifestyle and eat fast food or have unhealthy nutrition leading to obesity, a known risk factor of obstructive sleep apnea. Because of the high prevalence of sleep disorders in the commercial driver population, screening for sleep disorders is an essential component in DOT evaluations.
DOT sleep evaluations
If you are asked to undergo a DOT evaluation that includes a consultation at the Ohio Sleep Medicine Institute, you will undergo a comprehensive interview with one of our sleep medicine physicians. This interview is necessary to obtain a thorough history and to screen for any potential underlying sleep disorders that may place the commercial driver at risk for a motor vehicle accident. The most common reason for a sleep medicine consultation in the commercial driver population is for an evaluation of obstructive sleep apnea.
Following the initial consultation, you may be requested to return to the clinic to undergo an overnight sleep study or polysomnogram to monitor your sleep and breathing. This objective testing procedure provides a comprehensive assessment regarding the severity, if any, of obstructive breathing in sleep or the presence of other sleep disorders.
If you are found to have obstructive sleep apnea, you will be required to return for a second night in the sleep laboratory for a nasal CPAP titration. CPAP stands for Continuous Positive Airway Pressure and involves a small mask placed over the nose which is connected to a blower unit that applies a low level of air pressure to the airway to keep it open during sleep (see What is nasal CPAP?). To be successful with CPAP, it is essential to identify the ideal pressure that is specific to your needs and is the reason why a second night in the sleep lab is required. If the pressure is too low, obstructive breathing events will persist. However, if the pressure it too high, the individual may have difficulty adjusting to the pressure. Nasal CPAP is typically well tolerated if the appropriate pressure, mask type and patient education are pursued.
Once nasal CPAP is initiated, you may be asked to return for a Maintenance of Wakefulness Test (MWT) to evaluate your ability to stay awake in a standardized testing procedure. This procedure involves four testing sessions on a single day performed at two-hour intervals. During each of these 40-minute testing sessions, you will be asked to sit in a dimly lit room with the instruction to maintain wakefulness throughout each session. The MWT provides an objective measure as to your ability maintain wakefulness in a very boring or soporific situation.
Compliance with therapy and ability to drive
Other than a few exceptions such as in patients with narcolepsy, commercial motor vehicle drivers generally may be cleared to drive as long as they adhere to the prescribed medical therapy. The newer nasal CPAP units, for example, have a memory card that objectively monitors the number of hours per day the unit has been used and thus provides objective data regarding adherence or compliance. Commercial drivers are required to follow-up with the sleep medicine specialist after the first month of therapy and at least on a yearly basis to monitor compliance with the prescribed therapy and to evaluate interim changes in their health status.
There is still some controversy as to when repeat overnight or daytime testing in the sleep laboratory may be needed, but any decision in this regard should be based on a history and physical evaluation and not simply on a “cookie cutter” approach that requires all drivers to repeat sleep studies on a yearly basis, as is done in many sleep labs. At the Ohio Sleep Medicine Institute, we believe in placing emphasis on a thorough history and physical examination when considering any further sleep laboratory testing.
In summary, commercial drivers should always remember to maximize their total sleep time to avoid any unintentional self-imposed sleep deprivation. This recommendation should be followed by all drivers, irrespective of their medical status, to minimize fatigue and sleepiness when operating motor vehicles or heavy machinery. All drivers have a risk of nodding off behind the wheel if they are sleep-deprived, even if they do not have an underlying sleep disorder. However, as long as commercial drivers with obstructive sleep apnea are compliant with their medical regimen and use their nasal CPAP whenever sleeping, there is no legal or medical necessity to restrict their activities above that of any other commercial driver. On the other hand, a commercial driver who has an accident and is not adhering to CPAP therapy may carry an increased level of personal liability and the likelihood for future driving restrictions.