Pauline Anderson

February 13, 2015

NASHVILLE, TENNESSEE — Patients who have sustained a recent mild ischemic stroke may have performing cognitively challenging driving tasks, such as maintaining a safe distance behind a bus on the highway, a new study suggests.

The results highlight the importance of discussing driving issues with stroke patients, said study author Megan Hird, a Masters student and researcher at St. Michael's Hospital, Toronto, Ontario, Canada.

Although guidelines in some jurisdictions recommend that stroke patients refrain from driving for at least a month, about 35% patients resume driving sooner after a minor stroke, she said.

"They are not receiving driving advice from physicians very consistently," said Hird. The research shows that as few as 9% of patients report receiving recommendations from their physician about driving after a stroke.

"In fairness to physicians, though, there are currently no assessments to help them determine driving fitness," she noted.

The results were presented here at the International Stroke Conference (ISC) 2015.

Simulated Driving

The study included 10 patients who had sustained a mild stroke (National Institutes of Health Stroke Scale score <7) within the previous week and 10 healthy controls matched for age and years of driving experience.

Participants were tested on two 30-minute simulated driving scenarios. The first, which mimicked city driving, involved relatively straightforward driving with routine right- and left-hand turns without traffic, and then a cognitively more demanding task of turning left with traffic.

Turns into busy intersections are when most accidents occur. "When making a left turn in traffic, there is a lot of visual processing going on and you also have to judge when there's an appropriate gap to make that turn safely," said Hird.

The second scenario was more akin to highway driving. It involved staying behind a bus that was constantly changing speed, which requires a degree of sustained attention. "Patients have to maintain a safe distance from the bus while matching the speed of the bus," said Hird.

In total, the stroke patients committed over twice as many errors as controls (12.4 vs 6.0; P <.01). They committed more errors during left turns with traffic (2.4 vs 1.3; P < .05) and during the bus-following task (8.2 vs 2.1; P < .05).

The groups did not differ for number of errors committed during routine turns.

In a separate paper presented here, Kristin A. Vesely, also a researcher at St. Michael's Hospital, looked at driving errors in patients who had sustained an aneurysmal subarachnoid hemorrhage. The 9 patients and 9 matched controls completed the same simulated driving scenarios.

Although the mean number of total errors was the same between the two groups, patients committed more hazardous errors, including collisions (2.4 vs 0.1; P < .05). Further, total errors at intersection turns were greater for patients (7.7 vs 3.2; P < .05).

"We believe that this is the first empirical evidence of driving impairment specific aneurysmal subarachnoid hemorrhage," Vesely concluded.

"This study highlights the need for future larger-scale studies of driving simulation in addition to on-road studies so we can understand how the observations we're seeing in the driving simulation actually translate into on-road driving," she said.

Delicate Issue

The Canadian Medical Association recommends a minimum 1-month wait following a stroke before patients get back behind the wheel. Similar guidelines exist in the United Kingdom. But the American Medical Association does not indicate a specific time frame, said Hird.

The issue of driving following a stroke is a "delicate" one for physicians because they want to maintain a relationship with their patients for whom driving important to their independence, Hird said.

Having paralysis and a visual field defect are "pretty reliable contraindicators" for driving, so would certainly be flagged for driving assessment, she noted. However, she said, "it's trickier when patients have cognitive impairment," because it's unclear how that affects driving performance.

Over 70% of patients exhibit some cognitive impairment following a stroke.

The study was funded by the Heart and Stroke Foundation of Canada and Ontario Ministry of Research & Innovation. The researchers have disclosed no relevant financial relationships.

International Stroke Conference (ISC) 2015. Abstracts TP123, MP54. Presented February 11, 2015.

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