This analysis offers an empirical basis for a per se limit for THC that allows identification of drivers impaired by cannabis. The limited epidemiological data render this limit preliminary.

To assist in determining ability to drive in patients with obstructive sleep apnea (OSA), we developed a divided attention driving test (DADT) based on the work of Moskowitz and Burns (6). We first examined its ability to detect impaired performance by testing normal subjects both sober and impaired by alcohol (mean blood alcohol level, 95 +/- 25 mg/dl). Subsequently, 21 male patients with OSA (age 49.3 +/- 12.7 [SD] yr; apnea hypopnea index [AHI] 73 +/- 29) and 21 age- and sex-matched control subjects underwent polysomnography followed by daytime sleep latency testing (MSLT). Before each day-time nap, subjects were given the DADT for 20 min. Patients who performed much worse than control subjects in all measures, with the largest difference noted in tracking error (OSA, 228 +/- 145 cm versus control 71 +/- 31 cm, p < 1 x 10(-9)). Half of the patients were worse than any control subject, with some showing performance worse than control subjects impaired by alcohol. However, MSLT and AHI explained less than 25% of the variance in tracking error, making individual prediction problematic. We concluded that in laboratory driving performance skills are markedly impaired in over half our group with sleep apnea. Further testing and comparing on-road performance should aid in predicting ability to drive.

Abstractbeing asked to make recommendations about a patient's ability to drive and, in some jurBackground -Many patients with obstructive sleep apnoea (OSA) have diffi-isdictions, are required by law to report sleepy patients. While the recent ATS statement on culty in driving and experience increased automobile accidents. It has previously sleep apnoea and driving makes recommendations on driving, 5 it would be helpful to been shown that patients with OSA perform poorly on a laboratory based divided have a safe, reliable and valid laboratory based test of driving performance to aid in the process. attention driving test (DADT). Methods -Seventeen men with OSA of Recently we have been using a laboratory based divided attention driving task (DADT) 6 which mean (SD) age 49.7 (11.2) years and an initial apnoea/hypopnoea index (AHI) of is sensitive to impairment due to alcohol. When given to a group of patients with OSA we found 73.0 (28.9) were restudied from one to 12 (mean (SD) 9.2 (4.2)) months after ini-that at least half of the group performed as poorly, if not worse, than controls impaired by tiating treatment with nasal continuous positive airway pressure (CPAP) to ex-alcohol. Since most patients report improvement or even resolution of their OSA amine the effects of treatment on DADT performance. Eighteen age and sex symptoms with treatment, we wondered whether continuous positive airway pressure matched controls were also retested 8.4 (3.4) months after their initial tests. Fol-(CPAP) might improve and/or normalise DADT performance and sleepiness. lowing a practice session, all subjects were given the DADT for 20 minutes before each daytime nap of the standard multiple sleep latency test (MSLT).Methods Results -Untreated patients with OSA,  who performed much worse than controls Control subjects and patients with OSA from in all measures, improved significantly on a previous protocol 6 made up the study popuall measures of performance, particularly lation. Entry criteria were as previously rein tracking error which returned to the ported, the patient group comprising subjects level of controls in all but one patient. presenting with snoring and/or daytime sleepChanges in performance were much iness to the London Health Sciences Centre greater for patients with OSA than for Sleep Disorders Clinic for evaluation of poscontrols in tracking error (mean difference sible sleep apnoea. Following history and phys-106 (95% CI 75 to 135) cm), sleep latency/ ical examination, those patients suspected MSLT (5.3 (95% CI 2.7 to 8.0) min), num-clinically of having sleep apnoea were invited ber of correct responses (1.2 (95% CI 0.4 to participate in the study. In an attempt to to 1.9)), number of missed responses (1.7 minimise selection bias, consecutive new (95% CI 0.9 to 2.3)), and number out of patients were invited to participate. Exclusion Department of bounds (10.0 (95% CI 7.9 to 13.6)), but not criteria were: (a) no driver's licence (currently, laboratory evidence of hypothyroidism; and (g) sleepiness accou...

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