Into the the world of PECARN, CHALICE, and CATCH, we add NEXUS II. Why? Good question.
This is a planned secondary analysis of the NEXUS Head CT decision instrument among enrolled patients less than 18 years of age. Like most decision instruments, this rule classifies patients into “high risk” or “low risk”, with “low risk” being free of any mandated imaging. Their rule, which I will not recount, was tested in 1,018 blunt head trauma patients, and their rule picked up all 27 of those who required neurosurgical intervention. Unfortunately, it also only classified 330 patients as “low-risk” – for an abysmal 33% specificity.
The authors state it may yet have value, despite this poor specificity, as a one-way decision rule. Unfortunately, one-way decision rules are fraught with peril, as the inability to classify a patient as “low risk” is difficult to ignore. This leads clinicians to ultimately use the one-way instrument as a two-way, despite the bleak positive predictive value. This rule also missed one of 49 patients with “significant intracranial injuries”, meaning it is reasonable to expect it may not actually be 100% sensitive. Considering clinical judgement is vastly superior to this product, and there are enough alternative options, it is reasonable not to give this product another thought.
“Validation of the Pediatric NEXUS II Head CT Decision Instrument for Selective Imaging of Pediatric Patients with Blunt Head Trauma”
https://www.ncbi.nlm.nih.gov/pubmed/29665151
Excellent post Ryan…
In particular, I like your comment about one-way decision instruments. Although one can make rational arguments in favor of them, they often fail in their real world implementation- possibly causing more harm than good!
Yeh, it’s too bad – they make sense in academia, but in the real world, “not low risk” always translates to “too high of risk”.