Automobile Accidents in Patients with Sleep Disorders

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1 Sleep 12(6): , Raven Press, Ltd., New York 1989 Association of Professional Sleep Societies Automobile Accidents in Patients with Sleep Disorders Michael S. Aldrich Department of Neurology, University of Michigan Hospitals, Ann Arbor, Michigan, U.S.A. Summary: Sleep-related motor vehicle accidents are a serious safety hazard both for the driver who falls asleep and for others on the road. Sleep disorders may be significant contributing factor in some of these accidents. We reviewed data on sleep-related accidents from 70 control subjects and 424 adults with four categories of sleep disorders: sleep apnea, narcolepsy, other disorders of excessive sleepiness, and sleep disorders without excessive sleepiness. The proportion of individuals with sleep-related accidents was times greater in the hypersomnolent patient groups than in the control group. In patients with hypersomnia, the incidence of sleep-related accidents per year of excessive sleepiness was 3-7%. Although the proportion of patients with sleeprelated accidents was highest in narcoleptics, apneics were involved in more sleep-related accidents because of their greater number. Apneics and narcoleptics accounted for 71 % of all sleep-related accidents. The proportion of severe apneics who had sleep-related accidents was almost twice that of patients with mild or moderate apnea. Mean sleep latency by Multiple Sleep Latency Test did not differ significantly in patients with accidents and those without. Patients with a wide variety of sleep disorders appear to be at increased risk for sleep-related accidents. The severity and duration of hypersomnia are probably not the only factors that contribute to that risk. These findings have implications for the management of patients with sleep disorders. Key Words: Driving-Accidents-Sleepiness-Sleep disorders-narcolepsy Sleep apnea. Of the more than 50,000 deaths each year in the United States from motor vehicle accidents, as many as 13% may be due to falling asleep at the wheel (1). Sleepiness without actually falling asleep may lead to additional accidents because of impaired vigilance and driving errors. In susceptible persons, falling asleep and excessive sleepiness are most likely to occur during long-distance driving in low traffic-a monotonous task with little motor activity. Address correspondence and reprint requests to Dr. M. S. Aldrich, Department of Neurology, 1920/0316 Taubman Center, University of Michigan Hospitals, 1500 East Medical Center Drive, Ann Arbor, MI , U.S.A. Presented in part at the Association of Professional Sleep Societies Annual Meeting, Copenhagen, Denmark, June

2 488 M. S. ALDRICH Sleep deprivation, shift work schedules, circadian variations in alertness, medical conditions, alcohol use, and medications all can contribute to sleepiness and falling asleep while driving. Complete sleep deprivation for just one night leads to an increase in sleepiness and a marked reduction in sleep latency (2), whereas partial sleep deprivation, or insufficient sleep, induces a more gradual, but just as severe, sleepiness. In persons who customarily sleep at night and are awake during the day, alertness reaches a nadir at about 3:00 a.m., with a lesser trough in midafternoon. In a study of locomotive drivers, electroencephalographic (EEG) and electrooculographic changes consistent with drowsiness occurred much more frequently while driving a train at night than during the day (3). When insufficient sleep is combined with a shift in schedule, the consequent sleepiness can be even more severe. The two most common medical causes of daytime sleepiness in patients seen at sleep disorders centers are narcolepsy and sleep apnea. Among patients with sleep apnea, accident rates of 31-93% have been reported (4-6). In studies of narcoleptics, 40-48% reported falling asleep at the wheel and 25% had accidents due to falling asleep (7,8). In this study, we attempted to determine (a) the relative frequency of accidents in patients with various types of sleep disorders and (b) whether or not the incidence of accidents is related to the severity of narcolepsy or sleep apnea. METHODS We reviewed clinical and questionnaire data, nocturnal polysomnograms, and Multiple Sleep Latency Tests (MSLTs) of 424 consecutive adults (over age 16) referred to a sleep disorders center over a 3-year period ( ). Patients who did not drive were excluded. The study group included 279 men and 145 women. All patients were asked to complete a standardized questionnaire at the time of the initial visit. Seventy healthy adult control subjects matched approximately for age and gender also completed the questionnaire. The control subjects were mainly Medical Center employees and spouses of patients with sleep disorders. There were two questions that assessed daytime alertness and sleepiness: "How often do you have a major problem with sleepiness (feeling sleepy or struggling to stay awake) in the daytime?" and "How often do you feel extremely alert and energetic during the whole day?" Possible answers were never, seldom, occasionally, often, and almost always. We also determined the duration of excessive sleepiness as reported by the patients. The questionnaire included two questions related to motor vehicle accidents: "How many times have you ever been involved in automobile accidents?" and "How many times have you had near automobile accidents (driving off the shoulder of the road, etc.) because of sleepiness?" Polysomnographic recordings were performed at night in the University of Michigan Sleep Disorders Laboratory. Recordings began between 9:30 and 11:30 p.m., depending on the patient's usual bedtime. Mean recording time was 467 ± 3.8 min (mean ± SEM). All nocturnal polysomnograms included chin electromyogram, EEG, electrocardiogram, and measurements of eye movements, respiratory effort, air flow, leg movements, and pulse oximetry by ear or finger probe (Ohmeda; Boulder, CO). Polysomnograms and MSLTs were scored for sleep stages and sleep latency using standard criteria (9,10). Apneas were defined as apneic intervals lasting 10 s or more and were classified as obstructive, mixed or central. Hypopneas were defined as intervals of 10 s or more associated with 50% or greater reduction in airflow or respiratory effort and either 4% or greater drop in oxygen saturation or followed by an arousal. The respira-

3 AUTOMOBILE ACCIDENTS AND SLEEP DISORDERS 489 tory disturbance index (RDI) was calculated as the number of apneas plus hypopneas per hour of sleep. Of the 424 patients, 407 had nocturnal polysomnograms and 161 had MSLTs. None of the patients was taking stimulant medications at the time of the sleep studies. Statistical comparisons were made with Analysis of Variance using the Bonferroni correction for multiple pairwise tests. RESULTS Based on clinical evaluation and results of sleep studies, male and female patients were divided into four diagnostic groups: (Group 1) sleep apnea, (Group 2) narcolepsy, (Group 3) other disorders of excessive daytime sleepiness (EDS), and (Group 4) sleep complaints and sleep disorders without EDS (Tables 1 and 2). On average, the apnea group was older than other groups (p < 0.05 versus all other groups) and was predominantly male, whereas the other groups were fairly well matched for age and gender. The 61 patients in Group 3 included 26 with periodic leg movements or restless legs, 10 with insufficient sleep, 4 with sleepiness due to medication, 3 with sleepiness due to medical illnesses, and 18 with idiopathic or uncertain causes. The 79 patients in Group 4 included 31 with insomnia, 6 with subjective sleepiness only, 2 with schedule disturbances, 20 with parasomnias, and 20 with complaints of sleep disturbance for whom no sleep pathology was found. We analyzed the data on accidents separately in men and women because of known gender differences in automobile accident rates. Whereas 200 male patients (72%) and 96 female patients (66%) reported involvement in a total of 814 motor vehicle accidents, none of the patient groups had a significantly higher overall accident rate than the control group (Tables 1 and 2). Sleep-related accidents, however, occurred in 31% of male patients and 20% of female patients compared to 11 % of male controls and 6% of female controls. Of the 60 men and 29 women who reported sleep-related accidents, the sleep disorder diagnoses were sleep apnea (n = 41), narcolepsy (n = 22), EDS with periodic leg movements or restless legs (n = 4), EDS with medication use (n = 2), EDS TABLE 1. Frequency of accidents and near-accidents-men Number of subjects Mean age Percent of subjects with MV A from any cause No. of MVA per subject Percent of MV A that were due to sleepiness MV A due to sleepiness Percent of group with MV A due to sleepiness No. of MV A due to sleepiness per subject Near accidents due to sleepiness Percent of group with near-mv A No. of near MY A per subject Mean duration of sleepiness (years) No. of MY A due to sleepiness per year of EDS Group I apnea % % 19% % Group 2 narcolepsy % % 52%b.d J.OOb,d 72% 19.1a,c Group Group Group other-eds other-no EDS control % 74% 79% % 4% 5% 29%a.c 8% 11% 0.86 b. d % 34% 51% a p < 0.01 versus patients without EDS. b P <~O.OOI versus patients without EDS. c p < 0.01 versus controls. d p < versus controls. MY A, motor vehicle accident; EDS, excessive daytime sleepiness.

4 490 M. S. ALDRICH TABLE 2. Frequency of accidents and near-accidents-women Group Group Group Group Group apnea narcolepsy other-eos other-no EOS control Number of subjects Mean age Percent of subjects with MV A from any cause 68% 48% 62% 80% 74% No. of MV A per subject Percent of MV A that were due to sleepiness 9% 30% 20% 11% 4% MV A due to sleepiness Percent of group with MV A due to sleepiness 15% 29%" 15% 22% 6% No. of MV A due to sleepiness per subject " Near accidents due to sleepiness Percent of group with near MV A 40% 74% 54% 49% 34% No. of near MV A per subject b Mean duration of sleepiness (years) No. MVA due to sleepiness per year of EOS a p < 0.01 versus controls. b p < 0.01 versus all other groups. due to insufficient sleep (n = 3), EDS due to medical illness (n = 1), EDS due to schedule disturbance (n = 1), EDS of undetermined cause (n = 3), subjective sleepiness only (n = 3), parasomnias (n = 2), and insomnia (n = 7). The proportion of narcoleptics reporting sleep-related accidents was more than four times as great as controls and was higher than any other patient group. Thirteen of the 28 patients with more than one sleep-related accident were narcoleptic. The incidence of sleep-relateq accidents per year of excessive sleepiness was 3% in apneics, 4% in narcoleptics, and 7% in patients with other causes of hypersomnia. Fifty-six percent of all patients reported one or more near accidents due to sleepiness. Results of polysomnography are shown in Tables 3 and 4. Male apneics with sleeprelated accidents had significantly more respiratory events and lower mean minimum oxygen saturation than did male apneics without such accidents. A similar, but not significant, trend was apparent among female apneics. Thirty percent of male apneics and 20% of female apneics with RDI >60 reported involvement in sleep-related acci- TABLE 3. Po[ysomnographic findings-men Apnea Narcolepsy Other EOS Other-no EOS -MVA +MVA -MVA +MVA -MVA +MVA -MVA +MVA mean mean mean mean mean mean mean mean Number of subjects Age Total recording time (min) Total sleep time (min) Percent of wakefulness Percent stage 1 sleep Percent stage 2 sleep Percent stage 3-4 sleep Percent stage REM sleep No. of apneas plus hypopneas " Apneas + hypopneas per hour (R0l) 40 49" Minimum 02 saturation (%) 75 68" MV A, no sleep-related accidents; + MV A, one or more sleep-related accidents. a p < 0.05 versus - MV A in same patient group.

5 AUTOMOBILE ACCIDENTS AND SLEEP DISORDERS 491 TABLE 4. Polysomnographic findings-women Apnea Narcolepsy Other-EDS Other-no EDS -MVA +MVA -MVA +MVA -MVA +MVA -MVA +MVA mean mean mean mean mean mean mean mean Number of subjects Age Total recording time (min) Total sleep time (min) Percent wakefulness a Percent stage 1 sleep Percent stage 2 sleep Percent stage ~ sleep Percent stage REM sleep II No. of apneas plus hypopneas Apneas + hypopneas per hour (RDl) Minimum 02 saturation (%) a p < 0.01 versus - MVA in same patient group. dents compared to 15% of male apneics and 12% offemale apneics with RDI <60 (p < 0.02 for men). In patients with sleep disorders without EDS (Group 4), women with accidents had more disturbed sleep, with higher percentage of wakefulness, than women without accidents. A similar trend wa" apparent in Group 4 men. In each of the four patient groups and the control group, we compared measures of sleepiness in those with sleep-related accidents to those without (Tables 5 and 6). In the control group, but not in any of the patient groups, subjects with sleep-related accidents reported higher levels of daytime sleepiness. Within each group, there were no significant differences in mean sleep latency by MSLT between subjects with sleep-related accidents and those without. For all patients with sleep-related accidents, the mean sleep latency by MSLT was 6.6 min compared to 7.3 min in those without such accidents, a difference that was not statistically significant. Among patients with mean sleep latency <3 min, the proportion with sleep-related accidents was 37% compared to 24% in those with mean sleep latency >3 min. This difference was also not statistically significant. TABLE 5. Measures of sleepiness-men Apnea Narcolepsy Other-EDS Other-no EDS Control -MVA +MVA -MVA +MVA -MVA +MVA -MVA +MVA -MVA +MVA mean mean mean mean mean mean mean mean mean mean Number of subjects QI: How sleepy? Percent often or almost always a Q2: How alert? Percent seldom or never a Number of subjects with MSLT Mean latency to sleep by MSLT(min) a p < 0.05 versus - MV A in same group. Q1: How often do you have a major problem with sleepiness (feeling sleepy or struggling to stay awake) in the daytime? Q2: How often do you feel extremely alert and energetic during the whole day?

6 492 M. S. ALDRICH TABLE 6. Measures of sleepiness-women Apnea Narcolepsy Other-EDS Other-no EDS Control -MVA +MVA -MVA +MVA -MVA +MVA -MVA +MVA -MVA +MVA mean mean mean mean mean mean mean mean mean mean Number of subjects QI: How sleepy? Percent often or almost always Q2: How alert? Percent seldom or never Number of subjects with MSLT Mean latency to sleep by MSLT(min) QI: How often do you have a major problem with sleepiness (feeling sleepy or struggling to stay awake) in the daytime? Q2: How often do you feel extremely alert and energetic during the whole day? DISCUSSION Our data support the results of previous studies that have shown a high frequency of accidents in narcoleptics (7,11) and apneics (4). Based on a review of driving records, Findley et al. (12) found that patients with severe sleep apnea had more frequent accidents than patients with mild sleep apnea. Although mistakes in judgment due to cognitive impairment from sleep apnea (13) may lead to accidents, our data suggest that falling asleep at the wheel is a major contributor to the increased risk of accidents in these patients. The accident rates in our study were based on patient reports; actual accident rates might be higher if these patients do not recall or report all accidents or lower if some patients exaggerate the number of accidents. The data also suggest that patients with a wide variety of other sleep disorders associated with excessive sleepiness are at increased risk of sleep-related motor vehicle accidents. Furthermore, the high rate of self-reported sleepiness in our control subjects who reported sleepiness-related accidents suggests that some of the control subjects may have had undiagnosed disorders of excessive sleepiness. Although the proportion of apneics with sleep-related accidents is lower than that of narcoleptics, in our study, they accounted for more sleep-related accidents because of their greater numbers. The apneics were older than the other groups, and this difference may have accounted for some of the accidents and near accidents. Although patients with severe sleep apnea were more likely to have sleepinessrelated accidents than those with milder apnea, we did not find evidence by MSLT that narcoleptics or apneics who have had accidents are more sleepy than those who have not. These findings suggest that sleepiness is not the only factor that contributes to sleep-related accidents. In narcoleptics, cataplexy may affect driving and can occur while driving in more than one-fourth of all narcoleptics (11). Poor judgment of one's ability to drive safely and impaired reaction time are additional factors that may playa role. Our clinical experience suggests that many patients with disorders of excessive sleepiness have voluntarily limited their driving time before presenting at a sleep disorders center, whereas others with similar conditions have continued to drive daily despite repeated near accidents. A change in driving habits with less total driving could account for our finding that for hypersomnolent patients, the frequency of all accidents

7 AUTOMOBILE ACCIDENTS AND SLEEP DISORDERS 493 was not increased despite more sleep-related accidents. Other reports have also indicated that hypersomnolent patients may change their driving habits to reduce the risk of sleepiness while driving (14). The patient's awareness of sleepiness may be another significant factor that affects the risk of accidents while driving. Although a patient who is fully aware of his sleepiness may be able to drive safely provided he is willing to pull off the road when he recognizes that sleepiness is becoming severe or uncontrollable, some patients do not always recognize that they are sleepy and some hyper somnolent patients describe "attacks" of sleep that occur without warning. Apneics do not always accurately report the severity of their sleepiness, and in some cases, they may not be fully aware of it (2). Denial may also contribute to lack of awareness of sleepiness (15). A patient with a less severe condition who denies or does not perceive his sleepiness may be a more dangerous driver than one with a severe condition who takes appropriate precautions. Forty-two percent of the narcoleptics in this study reported no accidents at all, suggesting either that they drove rarely, or not at all, or that they had developed strategies for safe driving. Although the proportion of narcoleptics with sleep-related accidents was the highest of all the groups, the incidence of such accidents per year of sleepiness was similar in the three groups of patients with EDS. The high rate of accidents in these patients raises the question of whether or not driving privleges should be restricted in chronically sleepy persons (16). Although the sleepy driver is clearly at risk for sleep-related accidents, the identification of all such drivers is difficult. Persons with sleep apnea, narcolepsy, and other disorders of excessive sleepiness are not the only ones who become sleepy while driving. Sleep-deprived "normal" persons and persons who drive through the night, when the circadian peak of sleepiness is reached, probably are just as sleepy as most narcoleptics or sleep apneics (2). Sleep apnea has a range of severity, and although some authorities have suggested that no patient with untreated sleep apnea should be allowed to drive, not all apneics are sleepy or cognitively impaired. Our data suggest that the risk of an accident increases with increasing severity of sleep apnea and that the advice given to patients with sleep apnea should be tailored to the severity of the problem. A question that often arises for the patient with a sleep disorder who is being treated is: when is it safe to drive? Objective measures of sleepiness and alertness, such as the MSLT, are expensive, and the findings in a laboratory setting may not be applicable to the patient when driving. Although George et ai. (5) suggested that MSLTs might be helpful in determining whether or not a patient should be allowed to drive, we did not find that MSLTs differentiated patients with accidents from those without. As sleepiness is probably not the only important factor in safe driving, measures of sleepiness should not be the only criterion used to make decisions concerning driving. Spudis et ai. (17) have suggested that narcoleptics should be able to drive safely once they have determined their tolerance for this activity. REFERENCES 1. Bartel EC, Kusakciosiu O. Narcolepsy: a possible cause of automobile accidents. Lahey Clin Found Bull 1965 ;14: Dement WC, Carskadon MA, Richardson G. Excessive daytime sleepiness in the sleep apnea syndrome. In: Guilleminault C, Dement W, eds. Sleep apnea syndromes. New York: A. R. Liss, 1978: Torsvall L, Akerstedt T. Sleepiness on the job: continuously measured EEG changes in train drivers. Electroencephalogr Clin NeurophysioI1987;66:

8 494 M. S. ALDRICH 4. Findley LJ, Unverzagt ME, Suratt PM. Autmobile accidents involving patients with obstructive sleep apnea. Am Rev Respir Dis i988;i38: George CF, Nickerson PW, Hanly PJ, Millar TW, Kryger MH. Sleep apnoea patients have more automobile accidents. Lancet 1987;ii: Guilleminault C, van den Hoed J, Mitler M. Clinical overview of the sleep apnea syndrome. In: Guilleminault C, Dement W, eds. Sleep apnea syndromes. New York: A. R. Liss, 1978: Broughton R, Ghanem Q. The impact of compound narcolepsy on the life of the patient. In: Guilleminault C, et ai., eds. Narcolepsy. New York: Spectrum Publications, 1976: Parkes JD. The sleepy driver. In: Godwin-Austen RB, Espir MLE, eds. Driving and epilepsy and other causes of impaired consciousness. London: Royal Society of Medicine, 1983: Rechtschaffen A, Kales A. A manual of standardized terminology, techniques, and scoring systems for sleep stages of human subjects. Washington, DC: US Government Printing Office (NIH Publication no. 204), to. Carskadon MA, Dement WC, Mitler MM, Roth T, Westbrook PR, Keenan S. Guidelines for the Multiple Sleep Latency Test (MSLT): a standard measure of sleepiness. Sleep 1986;9: Broughton R, Ghanem Q, Hishikawa Y, Sugita Y, Nevsimalova S, Roth B. Life effects of narcolepsy in 180 patients from North America, Asia and Europe compared to matched controls. J Can Sci Neural 1981 ;8: Findley LJ, Fabrizio M, Thommi G, Suratt PM. Severity of sleep apnea and automobile crashes. New Engl J Med 1989;320: Findley L, Barth J, Powers D, Wilhoit S, Boyd D, Suratt P. Cognitive impairment in patients with obstructive sleep apnea and associated hypoxemia. Chest 1986;90: Schwartz BA. Hypersomnia and car driving. Electroencephalogr Clin Neurophysiol 1970;29: Aldrich CK, Aldrich MS, Aldrich TK, Aldrich RF. Asleep at the wheel. Postgrad Med J 1986;80: Findley LJ, Bonnie RJ. Sleep apnea and auto crashes. What is the doctor to do? Chest 1988;94:225-{i. 17. Spudis EV, Penry JK, Gibson P. Driving impairment caused by episodic brain dysfunction. Restrictions for epilepsy and syncope. Arch NeuroI1986;43: Sleep, Vol. ]2, No.6, 1989

Excessive Daytime Sleepiness Associated with Insufficient Sleep

Sleep, 6(4):319-325 1983 Raven Press, New York Excessive Daytime Sleepiness Associated with Insufficient Sleep T. Roehrs, F. Zorick, J. Sicklesteel, R. Wittig, and T. Roth Sleep Disorders and Research