CÁCERES, SPAIN, AND SAN FRANCISCO--Drivers who are habitually sleepy have a 13-fold higher risk of having a car accident than do well-rested drivers, according to a recently published study.[1] Other findings, presented in preliminary reports at CHEST 2000, showed that among patients with obstructive sleep apnea (OSA), a disproportionate number of car accidents (and other major adverse events) occurred during the waiting period between referral to a sleep disorders center and performance of nocturnal polysomnography.

"When someone drives on a busy highway, one in 30 of their fellow drivers is chronically sleepy--and potentially dangerous. These sleepy drivers may be as impaired as intoxicated drivers, since previous studies have shown that they may perform as poorly on simulators as legally drunk drivers," said Juan F. Masa, MD, in a recent interview with RESPIRATORY REVIEWS.

Dr. Masa and colleagues spoke with 4,002 randomly selected drivers from western Spain. Of this group, 145 people (3.6%) reported being habitually sleepy while driving. These subjects were typically male and middle-aged. Compared with a control group of nonsleepy drivers, the sleepy drivers had a significantly higher prevalence of car accidents in the past five years (5% vs 32%, respectively; adjusted odds ratio, 13.3).

UNRECOGNIZED SLEEP DISORDERS

A total of 90 sleepy drivers and 44 control subjects agreed to participate in stage 2 of the trial--nocturnal polysomnography. The results revealed that the sleepy drivers were more likely to have unrecognized respiratory disorders during sleep. An apnea-hypopnea index of 10 or greater was found in 24% of sleepy drivers but in only 9% of control subjects. In addition, 42% of sleepy drivers but only 13% of controls had a total respiratory event index (ie, the number of apneas, hypopneas, and respiratory effort-related arousals per hour of sleep) of 15 or more. The sleepy drivers also had a higher prevalence of characteristics that are associated with respiratory disorders during sleep: being overweight or a habitual snorer and having morning fatigue, hypertension, or apneas while sleeping.

Among the sleepy drivers, the respiratory event index independently predicted the risk for a car accident. Although scores on the Epworth Sleepiness Scale (a measure of overall excessive daytime sleepiness) were higher among the sleepy drivers than among the nonsleepy drivers, they did not predict the risk for a car accident. In fact, only 50% of the sleepy drivers reported excessive daytime sleepiness on the Epworth Sleepiness Scale. The findings suggest that "sleepiness while driving can occur without significant sleepiness in other daily activities," said Dr. Masa, who is Head of the Pulmonary Division and Director of the Sleep Laboratory at San Pedro de Alcantara Hospital in Cáceres.

Thus, asking patients whether they experience excessive sleepiness while driving (rather than asking about overall daytime sleepiness) may be a more effective way of predicting which subjects with breathing disorders during sleep are at risk for car accidents, the researchers concluded. "Since these respiratory disorders during sleep are treatable, many automobile accidents may be preventable," said Dr. Masa, who is also President of the Sleep Disorders Area in the Spanish Respiratory Society.

WAIT PERIOD LINKED TO ADVERSE EVENTS

In the second study, researchers from the United States examined 124 subjects who were referred to a sleep disorders center for evaluation with nocturnal polysomnography. The subjects were asked to complete a questionnaire documenting adverse events secondary to daytime hypersomnolence that had happened since the time of their referral. The mean waiting time between referral and nocturnal polysomnography was 36 days.

According to the polysomnography results, 111 of the subjects had OSA. "Among these patients with OSA … 50% had one or more major adverse events while waiting to be studied," explained Michel N. Chalhoub, MD, who is a Pulmonary Fellow at the University of Texas Health Science Center in Houston. These adverse events included car accidents (6%), near car accidents (18%), falling asleep while driving (18%), falling asleep at work (34%), and being fired or demoted at work because of daytime sleepiness (12%).

Subjects who were young or who had high scores on the Epworth Sleepiness Scale were at particularly high risk of adverse events. The young subjects were probably at higher risk because they are more active than older subjects and are more likely to be working, Dr. Chalhoub said. Subjects with high Epworth Sleepiness Scale scores are at higher risk because they have a greater degree of daytime hypersomnolence, he added.

The one- to two-month delay between referral to a sleep lab and polysomnography is well known. In the past, this lag time was considered acceptable because studies have documented that the cardiovascular/pulmonary complications of OSA take years to develop.

"However, now we have shown that if you wait four to six weeks, you are going to have a significant number of adverse events related to daytime sleepiness," Dr. Chalhoub said.

--Kristin Della Volpe

Reference
1. Masa JF, Rubio M, Findley LJ. Habitually sleepy drivers have a high frequency of automobile crashes associated with respiratory disorders during sleep. Am J Respir Crit Care Med.2000;162:1407-1412.