In penetrating trauma, sometimes it's very simple to predict operative intervention. However, sometimes, the perfusion states of our patients are less easy predict – vital signs frequently obfuscate the underlying clinical picture as the body compensates.
This is a prospective study that indirectly aims to validate end-tidal CO2 as a predictor of operative intervention in penetrating trauma by correlating it to serum lactate levels. And, as their primary outcome, these investigators observed a strong correlation between ETCO2 and lactate levels (R^2 = 0.74). For secondary endpoints – unsurprisingly, considering it was correlated with lactate – ETCO2 was also predictive of operative intervention. In fact, the authors report ETCO2 was more predictive of intervention than lactate, although it seems a little odd to significantly outperform lactate, given the strength of their linear correlation.
Compared with systolic blood pressure, the test performance characteristics essentially tell us what we already know: normal blood pressure isn't helpful, low blood pressure is obviously helpful (98% specificity). Lactate and ETCO2 are more sensitive to hypoperfusion states not reflected in vital signs, although, in this small study, even elevated ETCO2 would miss 1 in 5 operative interventions (sensitivity 82%) and would incorrectly predict 1 operative intervention for every 4 correct predictions (specificity 82%).
If prospective study confirms that ETCO2 outperforms lactate levels as an indicator of hypoperfusion, perhaps it adds something to the trauma bay evaluation. Otherwise, it seems the most useful function might be to add to prehospital triage protocols – an environment where lactate wouldn't be available.
"Nasal cannula end-tidal CO2 correlates with serum lactate levels
and odds of operative intervention in penetrating trauma
patients: A prospective cohort study"