What Canada Can Teach Us About CAT Scans
Joe Habbousche is the CEO of MDCalc, the world's most used online medical calculator. Chances are, you've used it yourself. Joe is a passionate advocate for the practice of evidence based medicine and the proper use of clinical decision tools. In this episode, we dissect one of his favorites: the Canadian CT Head Injury/Trauma Rule
Canadian CT Head Injury Rule
- Derived and validated in a large patient population
- Overall 8% of patients had positive CTs, but only 1.5% required intervention
Two sets of criteria
High Risk/Major Criteria
- Designed to capture patients that went on to require intervention.
Medium Risk/Minor Criteria
- Added on to the high risk criteria to capture those with clinically important brain injury- CT findings that require admission or observation
Who does this not apply to?
- Patients on blood thinners/bleeding disorder
- Under 16 years old
- Seizure after trauma
- No clear history of trauma
- Obvious penetrating skull injury or obvious depressed fracture
- Acute focal neurological deficit
- Unstable vital signs associated with major trauma
- Returned for reassessment of the same head injury
This is a one directional rule
- Designed to be sensitive but not necessarily specific
- This decision rule was designed because when CT imaging is done in all comers with head injury, it has very low yield
- The CT Head Injury/Trauma rule asks, "Can I carve out a cohort of patients who we know will not have a need for this test."
- If you fall in this group (the cohort that the rule says doesn't need the test), then you don't need the test
- Here's the one directional part: If you fall outside that group, the group the rule says does not need the test....the rule DOES NOT COMMENT. It is not studying anyone outside the group that has been deemed safe to not have the test done
Canadian CT Head Rule
Applies to this group of patients
- Blunt trauma to the head resulting in witnessed loss of consciousness
- Definite amnesia or witnessed disorientation
- Initial emergency department GCS score of 13 or greater as determined by the treating physician
- Injury within the past 24 h
High Risk Criteria: Rules out need for neurosurgical intervention
Fails rule with any of the following
- GCS
- Suspected open or depressed skull fracture
- Any sign of basilar skull fracture? Hemotympanum, raccoon eyes, Battle’s Sign, CSF otorrhea/rhinorrhea
- ≥ 2 episodes of vomiting
- Age ≥ 65
Fails rule with any of the following
- Retrograde amnesia to the event ≥ 30 minutes
- “Dangerous” mechanism: Pedestrian struck by motor vehicle, occupant ejected from motor vehicle, or fall from > 3 feet or > 5 stairs.
If all criteria are met/the patient does not fail the rule, the Canadian Head CT Rule suggests a head CT is not necessary for this patient (sensitivity 83-100% for all intracranial traumatic findings, sensitivity 100% for findings requiring neurosurgical intervention). The confidence intervals for these sensitivities range from low 90's so 100%. Since it's unlikely the test is actually 100% sensitive, I'd say it's 'close to' 100% sensitive.
Papers mentioned in this podcast
Original CT Head Rule Study
Stiell, Ian G., et al. "The Canadian CT Head Rule for patients with minor head injury." The Lancet 357.9266 (2001): 1391-1396.PMID: 11356436
Validation Study
Stiell, Ian G., et al. "Comparison of the Canadian CT Head Rule and the New Orleans Criteria in patients with minor head injury." Jama 294.12 (2005): 1511-1518PMID: 16189364
