Physicians should assess cognitive and psychomotor ability because these functions are essential for driving a motor vehicle. Some factors, in combination with opioids, threaten these functions, e.g.,
- Consistent severe pain rating (i.e., >7/10 most of the time)
- Sleep disorder (chronic poor sleep, sleep apnea) and/or daytime somnolence
- Pre-existing medical conditions that result in cognitive decline
- Concomitant medications that increase sedation, such as benzodiazepines and anticholinergics, tricyclic antidepressants, anticonvulsants, antihistamines, breakthrough pain medication.
Requirements regarding a physician’s duty to report a patient as unsafe to drive vary by province. Prescribers have an obligation to be aware of their provincial legislation about reporting concerns regarding the patient’s ability to drive safely. A useful resource is “Determining Medical Fitness to Operate Motor Vehicles.” (Canadian Medical Association 2009).
Also see Recommendation 7 for titration and driving.
R14. Summary of Peer-Reviewed Evidence
1. Pain itself affects cognitive function.
A recent review by Seminowicz and Davis showed that there is evidence that chronic pain can impair cognitive abilities. One possible mechanism for this effect is based on cortical plasticity and involves impairment of brain function. Another possible mechanism, not exclusive of the first, is based on the concept of limited processing capacity, whereby ongoing pain demands attention and limits the amount of resources available for task performance. Several studies have reported an association between chronic pain and hypervigilance (Seminowicz 2007).
Eccleston suggested that there is competition for attentional resources, reflected in attenuated task performance when a task is very demanding and pain is high (Eccleston 1996).
2. Associations between opioid use and impaired driving.
The evidence for association between opioid use and impaired driving is sparse, heterogeneous, and of poor quality. Some authors attempted to summarize this literature; however, no firm conclusions can be made because of the problems with the primary studies, and because of flaws in the reviews themselves.
Fishbain et al. conducted a systematic review of epidemiological evidence of an association of opioid use and intoxicated driving (6 studies), motor vehicle accidents (MVA) (9 studies) and MVA fatalities (10 studies). The authors concluded that opioids do not appear to be associated with intoxicated driving, MVA, and MVA fatalities (Fishbain 2003). However, there were many flaws in the studies included in this review; also the methods to compare the prevalence rates among the various studies were subject to bias.
Another systematic review by the same author included 41 studies of opioid dependent/tolerant patients and evaluated the following outcomes: psychomotor abilities; cognitive function; effect of opioid dosing on psychomotor abilities; motor vehicle driving violations and MVAs; and driving impairment as measured in driving simulators and off/on road driving. This review concluded that opioids do not impair driving-related skills. However, the majority of the studies included in this review included populations on methadone for addiction, or healthy volunteers. Only five studies were conducted in a population with CNCP. It is known that pain itself interferes with psychomotor and cognitive function; therefore it is difficult to generalize the results of this review to the population for which this guideline is recommended (Fishbain 2003).