Written by Clay Smith
The CHIP rule performed better than other head injury rules in patients >16 years old in striking the balance between avoiding CT in 21% of patients while missing only 2 potential neurosurgical lesions on CT. Dive deeper if you want.*
Why does this matter?
There are several head injury decision rules than can be applied in adults (>16y): New Orleans Criteria (NOC), Canadian CT Head Rule (CCHR), NICE, and CHIP. Many argue that the NOC optimizes sensitivity over specificity to the degree that everyone gets a CT with this rule. CCHR is often touted as the best, with higher specificity, allowing some to avoid CT, though sensitivity has ranged from the mid 80s to 100% on validation studies. NICE has low sensitivity. CHIP adds +/- anticoagulation and +/- loss of consciousness and would have reduced CT scanning by 23% but has not been externally validated until now. Which rule should you choose to make decisions about scanning?
A Canadian went to New Orleans with a NICE CHIP on his shoulder
This was a prospective, multi-center study of 4,557 patients externally validating the 4 rules mentioned above in patients over age 16 years with head injury and GCS 13-15. Clinicians prospectively recorded all clinical variables for each rule in real time. Of these patients, 82% underwent head CT; there were no neurosurgical interventions at 30 days on any patients who did not have CT. For the primary outcome of “any finding on CT”, NOC had the highest sensitivity (98.8%) and lowest specificity (4.4%). There was almost no difference in using NOC and just scanning every patient. NICE had the lowest sensitivity for “any finding on CT” at 72.5%, but specificity was highest at 61%. For “potential neurosurgical injury on CT”, sensitivity was: NOC, 100%; CHIP, 97.3%; CCHR, only 87.8% (markedly worse than recent validation studies…); NICE 85.1%. In terms of actual patients with missed neurosurgical lesions on CT: NOC, 0% (0/74); CHIP, 2.7% (2/74) - both small non-op EDHs but one had surgery for depressed fx); CCHR, 12.2% (9/74); NICE, 14.9% (11/74). The study was limited by the fact that not all patients had CT. It was also performed in some centers where the CHIP rule was already commonly used, which could have biased it in favor of the CHIP rule. The authors concluded that if clinicians have an extremely low threshold to CT, NOC was best, but offered little benefit over simply scanning everyone. If the threshold to CT was slightly higher, CHIP offered the best balance of reducing CT scans by about 21% vs missing serious head injury.
*Dive deeper - Here is a way to understand this and explain it to patients.
Does your patient population have a similar prevalence of 1.62% (74/4557) of patients with potential neurosurgical lesion on CT?
If so, take the pretest probability of 1.62% and (using a formula) take the negative LR of CHIP, 0.13. You’ll find the posttest probability of disease to be 0.2%, or 2/1000.
Use shared decision making and talk about these risks with your patient. Then decide if you’re going to CT or not.
For any lesion on CT, pretest prob was 8.4%; NLR 0.27; posttest prob 2.4%. That may be important to your patient as well.
External validation of computed tomography decision rules for minor head injury: prospective, multicentre cohort study in the Netherlands. BMJ. 2018 Aug 24;362:k3527. doi: 10.1136/bmj.k3527.
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Journal Watch had a helpful commentary, stating, “The NOC and CCHR were designed to identify patients who don't need head CT, not to mandate head CT for every patient with a single positive finding.” Subscription required, unlike JournalFeed :)
EMLoN has another perspective on this article you may want to read.