Our trial confirms that the Canadian CT Head Rule is highly sensitive (100%) for identifying clinically important brain injuries in patients with minor head injury.6
However, it did not show that implementation of the rule led to a reduction in emergency department use of CT imaging. In fact, there was an increase over time in use of CT scans at 10 of 12 sites, most notably at community hospitals. Many factors likely account for these findings, including our use of simple, inexpensive interventions, suboptimal compliance, crowding in Canadian emergency departments, increased ease of access to CT scans in emergency departments, and an overall secular trend toward increased use of CT imaging.
This implementation study, designed and conducted according to strict methodologic standards, represents the final stage in the development of a clinical decision rule.11,13,15
Our previous studies to derive, validate and implement the Ottawa Ankle Rules, the Ottawa Knee Rule and the Canadian C-Spine Rule all resulted in large reductions in rates of imaging.20,28–31
In these studies, we also achieved higher levels of physician compliance with the protocol (86%–95%).20,28–30
It is unclear why this study, whose methods closely mirrored those used in the Canadian C-Spine Rule implementation study conducted contemporaneously in the same sites, failed to achieve the desired reduction in use of CT scans. Physicians responded differently to the same intervention for different clinical conditions, suggesting that the condition itself had a modifying effect on the implementation of rules in emergency departments. Our study directly replicated interventions in the same settings, which highlights the potential importance of the interaction of attributes of the targeted behaviour with the effects of interventions.32
Perhaps more intensive interventions were required to alter use of CT imaging compared with radiography for injuries of the cervical spine, knee and ankle.
Given that baseline rates of CT imaging were lower than the potential rate predicted in the validation study, the increase in rates of CT imaging at intervention sites may simply reflect correction of unwarranted variation in practice. The increase may also signal a secular trend in increasingly congested emergency departments, where ordering a CT scan and discharging the patient is perceived as being more expedient than conducting a thorough clinical evaluation. Access to CT scanning has increased substantially in recent years, and it can now be ordered quickly and easily at most medium and large hospital emergency departments. Finally, our findings may also be a symptom of increased use of emerging technologies in medicine, where CT imaging of the head is considered the standard of care.33
We observed frequent use of CT imaging for patients with minimal head injury when there is no evidence of neurologic disturbance.
We evaluated potential barriers to successful implementation before the start of the study and found that the most common concerns expressed by clinicians were inability to remember the rule, belief that trauma services would order a CT scan even if the physician did not, and expectations by patients and families that a CT scan would be ordered. In our post-study interviews, physicians identified other potential barriers. Some were not comfortable with the definition of clinically unimportant injury and believed that even trivial findings on CT imaging should be documented. Others stated that CT imaging has become the local standard of care for patients with minor head injury. A common comment was that emergency department overcrowding led to expedient over-testing in the belief that this approach would lead to earlier discharge of patients. Finally, many physicians felt that they could easily circumvent the rule without consequences from study or hospital staff, suggesting that mandatory use of decision rules at the point of requisition for imaging may not be an effective strategy.
Our study had limitations. The baseline imaging rates were not as balanced between intervention and control sites as planned. In addition, the baseline rates were far lower than expected, making the prospect of further reductions unlikely. Perhaps these low rates at baseline were a reflection of prior passive dissemination of the rules or of participation by seven of the sites in previous studies of the Canadian CT Head Rule.6,14
Two sites had unusual results. At one intervention site, almost twice as many patients were seen and a large increase (to 94%) in CT imaging was evident. One control site tripled its rate of imaging from an exceptionally low baseline rate of 22%. Physician compliance with the requisition form was lower than anticipated, and it is difficult to ascertain if this finding reflects a weakness of the implementation strategy or other barriers to use of the decision rule.
Our findings indicate a need for further research to understand the specific barriers to implementing the Canadian CT Head Rule and to evaluate interventions to overcome them. The findings of this and the sister study of the Canadian C-Spine Rule showed that apparently identical interventions targeting the same emergency departments for different conditions had dramatically different results. This difference highlights the importance of replication using knowledge translation trials that would allow exploration of the factors involved.34
The Canadian CT Head Rule again proved to be accurate and reliable, and can be used with confidence by clinicians to determine which patients with minor head injury would benefit from use of CT imaging. Its usefulness is particularly applicable to sites where getting access to CT imaging is difficult or transfer of patients to a large centre is required.
Our knowledge translation trial of the previously validated and highly sensitive Canadian CT Head Rule did not reduce rates of usage of CT imaging in Canadian emergency departments. Future studies should identify strategies to deal with barriers to implementation of the rule and explore more effective approaches to knowledge translation.