Saturday 15 October 2016

Clearing the C-spine in intoxicated trauma patients. Is a negative CT good enough?

Wouldn’t it be nice to remove the cervical spine collar in an intoxicated trauma patient after negative CT? No more thrashing around, shouting and hassle...

These physician assistant authors out of Portland, Oregon enrolled 1668 adult patients with blunt trauma who underwent cervical spine CT scans in their level 1 trauma centre.

632 (44%) of tested patients were found to be intoxicated. (Intoxication was deemed to positive if the BAL was greater than 0.08g/dl or a positive urine drug screen... ok, not perfect.)


In these intoxicated patients, the CT missed 5 patients with clinically relevant injury. 4 patients had central cord syndrome and one had an unstable ligamentous injury. All of these patients had obvious neurologic deficits and underwent MRI.

The authors conclude the CT had an overall negative predictive value of 99% for injury. Therefore spine clearance based on a negative CT in intoxicated patients with no gross motor deficit appears to be safe and avoids prolonged and unnecessary immobilization.

My heart wants to believe this conclusion but unfortunately there are some major methodological issues with this paper.

The biggest is incorporation bias. The way they identified cervical spine injury was mostly by CT. So of course the CT will have good test characteristics when it forms a substantial part of the gold standard. Only a minority of patients got MRI’s and clinical status was only followed to discharge. It is quite possible that injuries were missed or declared themselves later.  

The authors seemed to emphasize the negative predictive value (NPV) of the CT. But in cohorts with low prevalence of disease, the NPV always looks good. In fact, the NPV before doing anything was 90%.

A better test characteristic that does not depend on disease prevalence is sensitivity. Obviously it is important for screening tests to be highly sensitive especially when the stakes are high.

What was the sensitivity of the CT?

Only 92%. 

Some might argue that this is not good enough and this paper actually proves the opposite of what it is trying to conclude.

Let the controversy continue!


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