Published ahead of print on September 6, 2007, doi:10.1164/rccm.200605-629PP
© 2007 American Thoracic Society doi: 10.1164/rccm.200605-629PP
Sleep Apnea, Alertness, and Motor Vehicle Crashes1 University of Western Ontario, London Health Sciences Centre, South Street Hospital, London, Ontario, Canada Correspondence and requests for reprints should be addressed to Charles F. P. George, M.D., F.R.C.P.C., University of Western Ontario, London Health Sciences Centre, South Street Hospital, London, ON, Canada N6A 4G5. E-mail: cgeorge{at}uwo.ca ABSTRACT Sleep apnea causes impairment in performance and is associated with an increased risk of motor vehicle crashes compared with the general population of drivers. Despite this increased risk, the actual number of accidents is still quite low, although the implications are significant in commercial vehicle drivers. It is difficult for physicians to assess risk and ability to drive in many patients with sleep apnea, yet physicians are often mandated to make these assessments with obvious implications for patients. Because many patients may never have a crash, it is not practical or feasible to restrict all untreated patients from driving, unless they operate commercial vehicles. Thresholds of disease severity that prompt driving restriction need to be established for sleep apnea much like they have been for alcohol. Until more data emerge, continued educational efforts about sleep apnea are needed to convince government and insurance organizations to provide appropriate resources for diagnosis and treatment of sleep apnea, because apnea risk is minimized with successful apnea treatment.
Key Words: sleep apnea • driving • motor vehicle crashes • sleepiness • inattention Driving a motor vehicle is a complex task that involves distinct cognitive, perceptual, motor, and decision-making skills. Because sleepiness can influence some or all of these skills, it is not surprising that patients with excessive daytime sleepiness would have increased motor vehicle crashes (MVCs). Inattention has been previously been shown to be a major factor in MVCs (1), and again in a recent naturalistic driving study (2). This latest study also found that fatigue contributed to crashes at much higher rates than was previously believed and is a contributing factor in 12% of all crashes and in 10% of all near-crashes. Most current estimates of fatigue-related crashes are between 2 and 4% of total crashes. Sleep apnea, with its repeated episodes of nocturnal hypoxemia and sleep fragmentation, will increase feelings of fatigue and sleepiness, which in turn increase inattention while driving. This impairment goes beyond simply falling asleep. The driver must be able to survey the surrounding environment, stay in his or her driving lane, and make adjustments in speed and position, which makes driving a divided-attention task. As a result, increased collision rates are expected in sleep apnea sufferers. EVIDENCE FOR INCREASED MVC RISK A majority of research supports the finding that obstructive sleep apnea (OSA) is a significant risk factor for MVCs (3–9). Data supporting an increased MVC risk in sleep apnea are based either on subjective, self-reported crashes or objective accident records obtained from Departments of Motor Vehicles. Both types of data are subject to bias. The occurrence of an MVC could have negative implications for certain occupations and continued employment; as such, self-reports are likely to underestimate risk and bias against an association. Using objective accident data helps to minimize reporting bias but may not remove it completely. If crashes are either not reported or not attributed to sleepiness or sleep apnea, then the rate of crashes due to sleep apnea would again be lower and biased against an increased MVC risk. Most of the data supporting increased MVCs in sleep apnea come from cross-sectional studies involving patients referred to a sleep clinic for assessment (3, 4, 7–9). These reports are based on subjective and/or objective data. Conclusions based solely on data arising from patients referred to sleep clinics are subject to a number of biases. Many of the studies involved small numbers and, although not reported, probably did not control for confounding factors such as drugs, alcohol, and driving exposure. In addition, it can be argued that many patients are referred to a clinic only because of an MVC, falsely elevating the likelihood of an MVC. Still, despite these limitations, the results of virtually all of these clinic-based studies are in the same direction, supporting an increased crash risk in sleep apnea. The study by Young and colleagues (6) provides objective data on crashes (using records from the Wisconsin Department of Transportation accident database) in a population-based sample of government workers with sleep apnea. Using a population-based sample removes the selection biases inherent in a sleep clinic–based sample and allows for control of factors such as drugs, alcohol, and driving exposure. Using this approach, an increased risk of MVCs remains in patients with OSA with an increased odd ratio for MVCs seen in men with an apnea–hypopnea index (AHI) greater than 5, and for men and women combined with an AHI greater than 15. The authors concluded that their "results, in a sample free of clinic bias, were comparable in magnitude to the clinic-based studies indicating that impaired drivers with sleep apnea were not over represented in clinic populations." Therefore, this study points in the same direction as the majority of other studies, lending further support to the finding that OSA is a significant risk factor for MVCs (3–9). A recent systematic review of the literature provides a concise compilation of studies in this area (10). MAGNITUDE OF RISK If we rely only on objective accident data, the risk of crashes associated with OSA is increased between two- and tenfold compared with control groups, with the odds ratio and precision of the estimate being inversely related to the sample size. Our study involving nearly 600 patients with OSA had the lowest overall odds ratio for an accident (3). However, the actual accident rate per patient per year (0.11 ± 0.15, mean ± SD) was double that of the Ontario provincial average of over 6 million drivers (0.05 ± 0.05 per driver per year). Looking at these numbers another way suggests that crashes are still not very common events. A population rate of 0.05 ± 0.05 means that each driver will have, on average, one accident every 20 years. Doubling that means, on average, one accident every 10 years for a patient with OSA, which is still uncommon given the number of patients with this condition. Despite this analysis, the crash risk estimate is likely to be always inexact because previous (retrospective) accident data are being used to correlate with the current clinical state and then predict future events. Although sleep apnea undoubtedly influences some crashes, crashes are multifactorial and influenced by previous sleep and working schedules, medications, and other clinical conditions interacting with circadian factors. It has been suggested, "A more precise estimate of the magnitude of crash risk associated with OSA based on prospective data is critically needed to determine the risk of motor vehicle crashes attributable to OSA at different severity levels and identify vulnerable subgroups" (11). Although such data would remove current uncertainties about managing driving risk, in practical terms this would be difficult if not impossible to obtain, especially in commercial vehicle drivers. All such drivers must now be assessed, and/or treated for sleep apnea (the details of which are outlined in Reference 12). By virtue of their vehicular size and cargo, there is a greater potential for injury, damage, and death with a commercial motor vehicle (CMV) crash. Because of this, and in the interest of public safety, CMV drivers are held to a higher medical standard than the general public. This may relate to recent reports (13–15) indicating that OSA is present in a greater prevalence in CMV operators than in the general population. However, it is very important to highlight that, although the prevalence of OSA may be increased in this population, there are no data to suggest that their crash risk is any different from the general population. Still, it is in this population where the effects of crashes, however uncommon, are potentially the most important both in terms of fatalities and overall costs. The total costs attributable to sleep apnea–related crashes are estimated to be very high, as reported by Sassani and colleagues (16). In 2000, there were 800,000 collisions that could be attributed to sleep apnea. These cost $15.9 billion and 1,400 lives in the 2000. In the United States, treating all drivers suffering from OSA with continuous positive airway pressure (CPAP) would cost $3.18 billion, but based on 70% effectiveness of CPAP treatment, would save $11.1 billion in collision costs and save 980 lives annually (16). HOW TO ASSESS ABILITY TO DRIVE The use of driving simulators as an assessment tool has become popular because they provide a safe, controllable, and low-cost environment in which to assess effects of sleepiness on driving. There are many studies from both Europe and North America of patients with OSA using simulators of variable sophistication (see Reference 10 for summary of studies). All show worse performance in one or more variables in patients compared with control subjects. The difficulty is that none of these studies have been able to predict real-world driving. A recent study in sleepy, nonapneic subjects was the first to compare an in-lab driving simulator with on-road driving with an examiner and instrumented car (17). Real driving and driving simulators were comparable for measuring line crossings but the effects were of higher amplitude in the simulated condition, leading the authors to conclude that results that may not be generalized to real-life driving, except perhaps on a group level. The recent naturalistic driving study (2) was the first instrumented vehicle study undertaken with the primary purpose of collecting precrash driving data. Drivers were selected by advertisement and there was no effort made to determine if they had major medical conditions that could affect their driving. The drivers used these vehicles in their normal daily routines, they were given no special instructions, no experimenter was present, and the data collection instrumentation was unobtrusive. This is the first study to prospectively evaluate factors predictive of crashes or near-crashes and would seem to be an ideal method for prospectively assessing driving ability in sleep apnea. The ethics of doing such a study present a problem because there are already data pointing to increased risk in this population. Moreover, when it comes to public safety, it is well accepted that commercial vehicle drivers must be held to a higher standard than private license holders, and these patients/drivers could never be (medicolegally) included in such a study. This approach, however, could be useful in milder cases. Thus, at present, physicians are left with assessing clinically the ability to drive and relying on patient self-report. This may not always be reliable (18), but it is currently the best we can do. HOW TO MANAGE RISK In simplistic terms, we could reduce crash risk from sleep apnea to zero simply by removing all untreated patients with sleep apnea from the road. In practical terms, however, this is neither possible nor justifiable—either ethically or on the basis of current data. In previous studies, up to two-thirds of clinic patients with sleep apnea never have any objective evidence of crashes (3, 19). If we were to restrict their driving simply because of a diagnostic label (their condition may make it dangerous to operate a motor vehicle), then we should surely do the same for every other condition that may cause some impairment in daytime function (e.g., a sleepy nightshift worker). Society has established and accepted a clear cutoff for driving impaired by alcohol, recognizing that a blood alcohol concentration of 0.08% does not have perfect predictive value—some individuals are impaired well below this level whereas a few others are not as impaired at this or a higher level. We must also become comfortable with some sort of cutoff in terms of sleep apnea, recognizing that, in noncommercial drivers, we will reduce but not eliminate the risk completely. The difficulty with this concept is the lack of an accurate metric in quantifying severity of sleep apnea. Despite its imperfection as an overall measure of disease severity, the AHI is an accepted marker for risk of hypertension and other cardiovascular disease. But can we or should we use this as a cutoff marker for driving in sleep apnea? Except in commercial vehicle drivers, where there is little or no margin for error, and given the lack of extensive evidence, I would argue that patients with mild sleep apnea (defined arbitrarily as an AHI < 30) and without sleepiness (however defined) or history of any crashes should neither be reported nor restricted from driving. And although this statement will clearly invoke a visceral reaction from many, the lack of evidence makes both sides of the position equally tenable (or untenable). My own practice is influenced both by my role as a patient advocate and the laws of my jurisdiction. I discuss the risk of driving with each and every patient that I see, and advise them not to drive if they feel sleepy. This applies to patients in whom the diagnosis is suspected but not yet confirmed as well as known cases of sleep apnea. Patients who are obviously sleepy in clinic and with a history of sleepiness-related crashes are at high risk for another crash (20) and should not be driving. These patients are told not to drive and, unless they cannot be studied, their diagnosis confirmed, or their treatment initiated within a very short time (e.g., <10–14 d), they are reported to the Ministry of Transportation in accordance with local laws. For patients in whom sleep apnea is confirmed, those with no daytime sleepiness are advised about my obligations under the Highway Traffic Act and a report is made. In the report, however, I indicate that I do not believe that the patient is at risk to drive. This applies regardless of AHI score. In situation in which patients are going to be treated (either because of symptoms or concerns about comorbidities), a report is made once the patient begins treatment. Once treated, a patient's risk for crashes should decrease. Treatment with nasal CPAP reduces crash risk to levels seen in the population at large (19, 21). This, of course, applies only when patients are compliant with treatment. Yet, access to care is far from being readily available (22). And, even when the diagnosis is established and treatment available, insurance companies may not universally pay the up-front costs for CPAP, even though they continue to pay overall much greater ongoing monthly costs for many secondary preventive drug therapies. Education remains a key ingredient to any risk management. Not only must we continue to educate the public and industry about the dangers of drowsy driving, whatever the cause, but educate governments and insurance companies about the need to support the diagnosis and treatment of sleep apnea. The physician is expected to diagnose sleep apnea and, through history, assess the patient's risk for crashes. He or she must also inform the patient of these risks and institute treatment in an expeditious fashion. In addition, the physician must have a follow-up plan in place to determine if the treatment has decreased the patient's risk for crashes. We need more data to help us make these decisions. There is an increasing public awareness of the risks of drowsy driving and there are now state laws that make it a criminal offense (New Jersey has an established law, and bills are pending in Illinois, Kentucky, and Massachusetts). But we must be clear not to tar all patients with apnea with the same brush. Not all cases are sleepy or have crashes and more data are needed for society to establish and accept a "safe" sleep apnea cutoff for driving, akin to that for alcohol. FOOTNOTES Originally Published in Press as DOI: 10.1164/rccm.200605-629PP on September 6, 2007 Conflict of Interest Statement: C.F.P.G is a member of the medical advisory board of SleepTech LLC, Kinnelon, NJ. Received in original form May 8, 2006; accepted in final form September 6, 2007 REFERENCES
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