Self‐reported automobile accidents involving patients with obstructive sleep apnea

Automobile accidents are the third leading cause of death and injury in the United States, accounting for 40 to 50 thousand deaths and 2 million accidents per year. ^l Sleep loss and sleep disturbance are thought to play a major role in automobile accidents. ² Among patients with sleep apnea syndrome (SAS), numerous studies found an excessive tendency to fall asleep while driving, which could increase their risk of having a motor vehicle accident (MVA), especially if they have untreated SAS. ^3,4

Several studies demonstrated that patients with SAS compared with non-SAS patients had greater automobile accidents that resulted in serious injuries or deaths; ⁴ tended to have worse performance on driving simulation tests, particularly on both highway and city or rural driving; and hit a greater number of obstacles during their simulated drive. ⁵ In another study, patients with SAS compared with non-SAS patients had poorer brake reaction time, lateral position deviation, and off-road episodes when tested with an advanced driving simulator during a 90-minute rural drive at twilight conditions. ⁶ However, in both studies, the authors found that the driving performance of patients improved once they were treated with continuous positive airway pressure (CPAP) ⁵ or uvulopalatopharyngoplasty. ⁶

Other studies also demonstrated that individuals with SAS may not compensate for their condition by driving more carefully. Haraldsson et a1. ⁸ conducted two studies to determine the impact of SAS on driving. In the first study, they surveyed 140 patients and 142 control subjects without symptoms associated with SAS. They found that 73 patients had a complete triad of SAS-associated symptoms (heavy snoring, sleep disturbances, and daytime somnolence) and that 52% of patients reported habitual sleeping spells while driving compared with less than 1% of the control subjects. ⁷ In the second study, the authors used data from a national random sample of 1,214 persons in Sweden and found that diurnal hypersomnia was only prevalent among 2.2% of respondents. ⁸

Furthermore, studies conducted in Canada, ⁹ the University of Virginia Sleep Disorders Center, ¹⁰ and the Sleep Disorder Center in Michiganll demonstrated that patients with diagnosed SAS compared with control subjects experienced a greater number of accidents (ranging from two times up to a seven-fold increase) and also had a greater rate of more than one accident compared with control subjects. ^9–11

In the present cross-sectional study, we surveyed 253 subjects to assess whether patients with SAS have a higher ratio of self-reported MVAs than patients without SAS to determine what characteristics distinguish those who have MVAs from those who do not have MVAs.

Methods

Results

From the original 295 that were eligible for the study, we received 253 surveys for a response rate of 85.8%. Among these 253 subjects, most were diagnosed with sleep apnea (68%), were men (71%), and were mainly between the ages of 20 to 64 years of age (83%). As noticed in table 1, when the subjects were stratified according to diagnosis of SAS, we found that both the SAS patients and the non-SAS patients were very similar, although SAS patients were mostly men and had a significantly higher proportion of accidents than the control subjects. In addition, SAS patients evidenced a higher proportion of snoring and reports of falling asleep at inappropriate times.

We analyzed groups based on whether they self-reported having an accident. Sixty-six subjects (26%) reported having had at least one accident. Among those who reported at least one car accident, 52 (82%) were diagnosed with sleep apnea. Among individuals who reported either having or almost having an accident, sleep apnea, history of severe dizziness (D.), Parkinson's disease (P.), seizures/epilepsy (S.), and loss of consciousness (L.), report of passing destination with little awareness, and falling asleep at inappropriate times were significantly higher among this group than the nonaccident group. The crude OR of having an accident among those with sleep apnea was 2.57 (95% CI = 1.22 to 5.51, p <0.0063).

We determined the OR_M-H of having a motor vehicle accident in SAS patients relative to those without SAS adjusted for the following covariates: sex, age, shift worker, alcohol intake, coffee intake, daytime nap, history of D.P.S.L., history of passing destination, and falling asleep at inappropriate times. There was an increased ratio of self-reported MVA among patients with polysomnographically confirmed SAS, even after controlling for the different covariates. All variables with the exception of falling asleep at inappropriate times put patients compared with control subjects at relatively increased risk of having an MVA. A history of these variables increased the risk of MVAs among patients compared with control subjects from 2.41 to 2.73 (CI from 1.18 to 5.59).

Table 2 presents unconditional multiple regression analyses that evaluate the adjusted ORs of having an MVA after controlling for the presence of multiple covariates simultaneously. We note that three factors are significantly related to an individual's history of self-reported MVAs, which include history of passing destination, falling asleep at inappropriate times, and diagnosis of SAS. We also note that alcohol intake and history of other medical conditions increase the risk, whereas coffee intake diminishes the risk of WAS in these individuals. Additional multiple logistic regression analyses were conducted using various models to ascertain the impact that different factors would have on the overall OR. The results of those analyses were similar to those demonstrated in table 2.

Discussion

We found a positive relationship between diagnosed SAS and self-reported MVAs among our population of sleep apnea patients. Among SAS patients, there was a greater proportion of men, individuals reporting greater frequency of snoring, and falling asleep at inappropriate times. The literature has found that men generally have a higher risk of car accidents than do women. Even though in our study there was a higher proportion of men than women in the patient population, the OR of having an MVA among SAS patients, after controlling for sex, was still significantly high (OR_M-H = 2.58, 95% CI = 1.29 to 5.17). Patients with SAS also had a higher proportion of reports of falling asleep at inappropriate times than did the non-SAS patients, which has been found to be associated with sleep apnea in other studies. ^3,14 Furthermore, similar to other studies, ⁷ we found that a greater proportion of our patient population reported snoring (OR = 4.17, 95% CI = 1.98 to 8.86). This is important considering that snoring is one of the symptoms of SAS.

The OR between answering affirmatively that they have passed a destination with little awareness and having an MVA was 7.16, whereas the OR for answering positively that they fell asleep at inappropriate times and that they had or almost had an MVA was 5.28. Using multiple logistic regression analysis, we found that even when we adjusted these variables, the adjusted ORs were 5.72 and 4.69 (table 2). This suggests to us that even in the absence of a clear diagnosis of SAS, the characteristics of falling asleep at inappropriate times and passing destinations with little awareness of doing so are good indicators of increased risk of probably having an MVA.

This study demonstrated that patients with polysomnographically confirmed SAS had an increased ratio of self-reported MVAs even after controlling for numerous covariates. As noted in table 2, even after controlling for various factors simultaneously, the risk of having an MVA was 2.58 among those with a diagnosis of SAS. These results suggest an association between sleep apnea and self-reported MVAs and confirms results found previously by others. For example, Findley et al. ¹⁰ reported that the percentage of car accidents among 29 patients with confirmed SAS was greater than that of 35 patients without confirmed SAS (31% versus 6%, p <0.01). In addition, a study conducted in Canada found that 93% of 27 patients with SAS and 53% of control subjects matched by age and sex reported MVAS. ⁹

The logistic regression analysis also demonstrated that alcohol intake enhances the possibility of MVAs for drivers suffering from SAS. This could be because ethanol could reduce sleep latency and attention performance. ¹⁵ Thus, patients with SAS should be more particular about avoiding alcohol before driving and should allow a greater interval between alcohol consumption and driving. We also found that drinking coffee had a reverse effect, allowing patients to stay more alert while driving (OR = 0.43, CI 0.21 to 0.85, p <0.01).

As with any self-reported surveys, there are problems with using a self-administered questionnaire to determine MVAs. Subjects may not recall almost having a car accident or may fail to report an accident. In addition, verifying the information with the Department of Motor Vehicles (DMV) presents a bias because not all accidents are reported to the DMV and also because the DMV does not record who is at fault. Other potentially confounding variables such as driving mileage, duration of driving, weather conditions? and so on should also be controlled when analyzing the relationship between SAS and MVAs. We, however, only used self-reported data on driving accidents or near accidents due to sleepiness so that we could more reasonably analyze the association between SAS and MVA.

The interpretation of the data is also limited by the cross-sectional nature of the survey and also by our inclusion of a clinical population. The findings, however, demonstrate that patients with SAS have a significantly higher ratio of self-reported MVAs than did control subjects, that alcohol intake enhances the possibility of having an MVA among these patients, and that falling asleep at inappropriate times and driving past destination with little awareness in patients with SAS were good indicators of increased risk of having a motor vehicle accident. Nevertheless, sleep apnea is a very treatable condition, and once treated, the risk factors diminish considerably.

Acknowledgments

We thank Dr. Jess F. Kraus for providing guidance to the first author on the statistical analyses and to Ms. Rosa Elena Garcia for clerical assistance.