Canadian Head CT Rule

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Should US physicians use the Canadian head CT rule?
Are the standards of care in Canada and the U.S. different with regard to ordering CT scans for minor head trauma? Does practicing defensive medicine ignore evidence-based best practice or is it just our American reality.


Should US physicians use the Canadian head CT rule?

 “Use the rule to cut costs and radiation without litigation exposure.”
Per capita, the US currently spends twice as much as Canada, yet ranks behind on many quality measures. Undoubtedly, the US malpractice environment contributes to this fiscal conundrum. In caring for anyone, anyplace, anytime EM physicians sit at the forefront of the defensive medicine frontier. Rarely, do EM physicians benefit from well-established science to augment clinical gestalt. Deciding whether or not to obtain a head CT on head injury patients is one exception.
Mild traumatic brain injury can be defined as loss of consciousness (LOC), amnesia, or witnessed disorientation with initial GCS ≥ 13. The Canadian Head CT (CHCT) rule was developed to guide decision making about the use of CT-head ordering excluding those less than16 years old, pregnant, on Coumadin, suffering seizures, lacking clear trauma, LOC, obvious skull fracture, or hemodynamic instability. The primary outcome was the need for an intervention (craniotomy, skull fracture elevation, ICP monitoring, intubation for head injury), while the secondary outcome was clinically important brain injury on CT as defined by a consensus of 129 neurosurgeons, radiologists, and EM physicians. Insignificant CT findings included: solitary cerebral contusion < 5mm; localized subarachnoid blood < 1mm; thick smear subdural hematoma <4 mm; isolated pneumocephaly; and closed depressed skull fracture not through the inner table. After being derived and validated on over 3000 Canadian patients, the CHCT rule has subsequently been validated in Germany and England. Ironically, in contrast to the US debate about whether to utilize the CHCT rule to decrease head CT ordering, British physicians debated whether to incorporate it into their guidelines fearing it might increase CT use! Other blunt head injury clinical decision rules (CDR) have been developed, but none explicitly followed the guidelines for CDR development and subsequently none have been externally validated. While the CHCT rule has not been demonstrated cost-effective or widely acceptable, no US legal literature demonstrates appropriate use of the CHCT rule missing a clinically significant, successfully litigated intracranial injury. Nonetheless, no sane physician wants to be the first. Therefore, the CHCT rule should not replace clinical judgment. Instead, the rule should augment the intuition experience garners. If a seasoned EM physician’s insight suggests that central nervous system imaging is merited despite a negative CHCT rule, the patient should definitely be scanned. If the clinician’s gestalt is that no significant intracranial injury exists, concern about the medical-legal implications of the rare (0.6% neurosurgically significant – all detected by the CHCT Rule) clinically significant injury should not drive decision making. Practicing knee-jerk, counterintuitive, defensive medicine drives up the cost of health care for everyone and negates the value of clinical expertise. The clinically insignificant CT findings represent the central argument against the CHCT rule. Dr. Klauer has argued that if one of these injuries is missed by one physician only to be found by another physician, a lawyer will portray the patient as a major corporate CEO if only the first physician had ordered the scan even if few surgeons in the world would intervene on the injury. If detecting any abnormality regardless of the cost to the individual or society is top priority, recognize that a brain injury can exist despite a normal head CT. If we are to take a fully defensive posture and toss the evidence out with the tort reform, should we not order more sensitive head injury tests such as MRI, PET scans, serum biomarkers, and formal cognitive testing before any of these patients leave the ED?  Most EM physicians would not advocate this extreme viewpoint, but what distinguishes unnecessary head CT ordering from other unnecessary brain injury testing? Tort reform is past due to alleviate counterintuitive over-testing. Intracranial injuries, missed or recognized, often have devastating results for individuals and families. The CHCT rule, or future worthy substitutes, ought to continue to be the focus of research until cost-effectiveness and acceptability can be demonstrated. If physicians are being legally persecuted for appropriately applying these rules, the case details and testimony should be reported in venues such as EP Monthly.  Lacking an effective alternative, cost-conscious, evidence-based physicians are left with two choices: augmenting clinical decision making with the CHCT rule or substituting best-evidence practice for uniform testing of all head injury victims at tremendous cost to society with no proven benefit to the individual patient.
Christopher Carpenter, MD, is an Assistant Professor at Washington University School of Medicine.


Should US physicians use the Canadian head CT rule?

“A miss is a miss. Juries don’t care if you’re saving cost!”
by Kevin Klauer, DO
The Canadians have demonstrated a unique expertise in developing evidence-based rules that make sense. However, as a risk manager, board member of our group’s risk retention group and a practicing emergency physician, clinical application is where the rubber meets the road.


At journal club, this is an academic discussion. In the ED, we need to make certain we are practicing safe, appropriate and efficient, risk-averse emergency medicine. Which would you prefer to do? Avoid a lawsuit and all the fun this will add to your life for 18 months; or use an evidence-based guideline to convince a jury of laypersons why it was OK to miss a small subdural.
We could have an academic discussion. However, how does that help the average doc working a shift? Many research-oriented discussions focus on the quality of the research. Unfortunately, they fall short with how or if the included recommendations should be implemented clinically and how to do so.

For most of us, this is not an academic discussion. It’s a matter of how to get through the next shift, practicing high quality emergency medicine, avoiding a lawsuit, walking away with some sense of gratification for the care we provide.

The issues I have with the Canadian CT Head rule are a lack of external validity, the exclusion of “clinically unimportant” lesions and the use of a utilization reduction tool that may result in missed intracranial injuries.

External validity is key. Can the study results be reproduced elsewhere, or is it only valid in the environment in which the original study was conducted. In example, an excellent head CT rule was studied at Louisiana State University (LSU) in 2000. It reduced CT utilization without any additional missed injuries. Unfortunately, attempts to reproduce the same results in other environments have been unsuccessful. Thus, rendering application of their rule to LSU only.


Some might say that the Canadian CT head rule has stood the test of external validity. Well, the devil is in the details. Boyle, et al., British investigators, noted a substantial increase in utilization of CTs, without any additional benefit. In Australia, the New Orleans criteria and the Canadian CT head rule were tested. Neither performed well. Rosengren, et al., from down under, reported that if the high-risk Canadian criteria were utilized, 74% of the normal scans could have been avoided, and the one patient requiring “neurosurgical intervention” would have been identified. However, with addition of the medium-risk (2 additional) criteria were used, only a 46.7% reduction in scans would be noted. Unfortunately, two “clinically significant” abnormalities would have been missed. Their conclusion was that such studies have no applicability outside the environment in which they were developed. Hence, they lack external validity. I agree with them!

If you feel external validity has been proven by these studies, conducted in Europe and Australia, how does that apply to apply to those of us practicing in the U.S.? When’s your next shift in Canada, England or Australia?

A fundamental challenge applying the many utilization-driven guidelines, generated by Canadian researchers, to EDs in the United States is that our medical malpractice climate does not afford any forgiveness for medical error. The Canadian CT head rule was 92% sensitive for identifying traumatic neurosurgical lesions. CT utilization could have been reduced to 32%. Unfortunately, only 320 of the 348 patients with positive CT scans would have been identified. Stiell was proud to report that they did not miss any of the lesions requiring neurosurgical intervention. However, they don’t talk much about the 28 “clinically important” and “clinically unimportant” lesions the rule would have missed.

In the malpractice climate in the United States, there is no such thing as a “clinically unimportant” intracranial injury. Any such miss is an opportunity for a lawsuit. If a claim is made, convincing a jury of laypersons that the lesion was “unimportant” will be nearly impossible. Furthermore, average defense costs will be at least $100,000, and that’s just to get you to your first day of trial.

Great concept. But, it falls way short on practical application. Plaintiffs and jurors don’t commend a physician for reducing utilization and saving healthcare costs when they have an injured patient in front of them. I agree that we spend far too much on unnecessary tests in this country. However, until our legal system accepts misses in exchange for controlling costs, we can’t put ourselves at risk.

Kevin Klauer, DO, is the Director of Quality and Clinical Education at EMP & the Director of the Center for Emergency Medicine Education

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