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Diabetes NewsApril 2010

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Driving Mishaps Among Individuals with Type 1 Diabetes

Diabetes Care • December 2009

Hypoglycemia is the major barrier to type 1 diabetes intensive insulin therapy, in part because of its disruptions on cognitive-motor functioning. One practical implication is its adverse effect on vehicular driving performance, resulting in collisions and citations. These potential disruptive effects are further problematic because some individuals with diabetes decide to drive when their blood glucose is low.

Retrospective studies have documented that individuals with type 1 diabetes  compared with those with type 2 diabetes have more collisions and citations. The current study presents the first prospective data documenting the occurrence of different types of hypoglycemia-related driving mishaps.

Objective - Hypoglycemia-related neuroglycopenia disrupts cognitive-motor functioning, which can impact driving safety. Retrospective studies suggest that drivers with type 1 diabetes experience more collisions and citations than their nondiabetic spouses. The first prospective data is presented documenting the occurrence of apparent neuroglycopenia-related driving performance impairments. The initial screening of 452 drivers was completed from three geographic centers who then reported monthly occurrences of driving ‘mishaps’ including collisions, citations, losing control, automatic driving, someone else taking over driving and moderate or severe hypoglycemia while driving.

Research Design and Methods - Drivers with type 1 diabetes (48% male) from three geographically diverse clinical regions (Virginia, Boston and Minneapolis) completed all data collection in a study investigating factors that promote driver safety among individuals with diabetes. Subjects were recruited through newspaper and other media and compensated $250 for their participation. Inclusion criteria were type 1 diabetes >12 months, legal drivers license, driving >5,000 miles per year and blood glucose measurement >twice daily. At screening, 21% retrospectively reported being involved in collisions and 15% reported receiving a moving citation in the previous two years. This is similar to the 19% collision and 15% violation rates reported in our multi-national retrospective study of consecutive patients attending diabetes clinics, suggesting that the current data are representative of the diabetes community in general.

After signing an institutional review board-approved consent form, subjects were instructed on the definition of the seven different types of hypoglycemia-related driving mishaps listed in Table 1.

Table 1 - Seven different hypoglycemic-related driving mishap situations

Since your last entry, while driving how many times:

  1. Did you experience severe hypoglycemia where it was impossible to treat yourself because of low blood glucose?
  2. Did you experience disruptive moderate hypoglycemia where you could still treat yourself but you could no longer drive safely?
  3. Did you experience automatic driving due to hypoglycemia where you became disorientated, got lost, or arrived at your destination with no memory of driving there?
  4. Did you hit something with your vehicle due to hypoglycemia?
  5. Were you stopped by the police for reckless driving or speeding due to hypoglycemia?
  6. Did you lose control of your car, but did not hit anything due to hypoglycemia?
  7. Did someone else take over your car due to hypoglycemia?

Subjects were then asked how often such events occurred in the past two years, how often they carried fast-acting glucose in their car and at what blood glucose threshold they would chose not to drive. For prospective data collection, subjects were given data sheets to record whether and/or when any of the seven types of hypoglycemia-related driving mishaps occurred, whether they measured their blood glucose within thirty minutes of starting to drive and what that blood glucose reading was. For the next twelve months, subjects were contacted monthly by either email or telephone to report their mishaps.

Results - Over twelve months, 52% of the drivers reported at least one mishap, 32% reported two or more mishaps and 5% reported six or more mishaps. On average, 35% of the time drivers performed self monitoring of blood glucose within thirty minutes of initiating their drive when a mishap occurred; 78% of the time self monitoring of blood glucose was <90 mg/dl and 48% of the time it was <70 mg/dl. Disruptive moderate hypoglycemia that impaired driving was the most common event and was reported by 41% of the subjects. While 22% of the subjects prospectively reported some type of collision during the year, only 2.4% reported a collision attributed to hypoglycemia.

Modified Poisson regression analyses were used to estimate the relative risk of the occurrence of hypoglycemia-related driving mishaps. To correct for this exposure, all relative risk ratios were adjusted for the reported total number of miles driven during the twelve month study. The occurrence of future driving mishaps was significantly associated with using insulin pump therapy and a history of severe hypoglycemia, vehicular collisions and hypoglycemia-related driving mishaps. Participants using pump therapy to manage their blood glucose were 35% more likely to experience a hypoglycemia-related driving mishap than those using insulin injections. Having one retrospectively reported episode of severe hypoglycemia, collision, hypoglycemia-related driving mishap or mild symptomatic hypoglycemia while driving increased the risk of a driving mishap in the next twelve months by 6, 20, 6, and 3% respectively. Risk increased exponentially with additional driving episodes; e.g., if two episodes of severe hypoglycemia occurred in the previous twelve months, risk would increase by 12%, or if two episodes occurred in the previous two years, risk would go up 40%.

Conclusions - Hypoglycemia is a common (when monitored prospectively) and unique risk factor for driving mishaps among drivers with type 1 diabetes that is not found among the general population. In this prospective study, these mishaps were not related to sex, duration of the disease, A1C, self-reported hypoglycemic awareness, ability of fast acting glucose in the car or blood glucose thresholds for when to treat or when not to drive. Mishaps were related to the use of insulin pumps, history of collisions, severe hypoglycemia and hypoglycemia-related driving mishaps. Therefore it would be prudent to routinely query patients about experiences concerning hypoglycemia and driving mishaps. If such events have occurred, steps to avoid hypoglycemia while driving should be encouraged, such as measuring blood glucose before driving, encouraging a higher blood glucose threshold for when not to begin driving (e.g., >90 mg/dl), and, when hypoglycemia is detected when driving, safely ceasing driving, eating fast-acting carbohydrates and not resuming driving until blood glucose and cognitive functioning have recovered. Despite the consistency of findings in this and the multi-national retrospective study, similar to that in the Diabetes Control and Complications Trial, a limitation of this is its subject selection/dropout and reliance on the subjects’ attributions as to whether hypoglycemia caused their mishaps, which could contribute to an over or underestimation of hypoglycemia-related driving mishaps.      

Reprinted with permission from the American Diabetes Association

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