In a series, the authors found that low end-tidal carbon dioxide (PETCO₂) at the onset of trauma is associated with nonsurvival (Roman et al, Anesthesia & Analgesia 2017, July 10). This is a retrospective study of patients admitted and transferred to the operating room directly from the resuscitation bay. The patients were identified using the Ryder Center trauma registry over a period of  years. The maximum PETCO₂ values within  5 and 10 minutes of the onset of mechanical ventilation in the operating room were determined for patients undergoing general anesthesia with mechanical ventilation.  The trauma patients were divided into two groups: those patients who were discharged from the hospital alive (survivors) and those patients who died in the hospital before discharge (nonsurvivors).  From the graphical analysis of the data, the threshold PETCO₂  giving a positive predictive value of 100% for in-hospital deaths was determined.  Association of threshold and mortality was analyzed using the 2-tailed Fisher exact test.

The authors determined that if PETCO₂ value was <=20 mm Hg with the five minutes of the onset of mechanical ventilation in the operating room, the hospital mortality was 100% (21/21, 95% binomial confidence interval, 83.2% to 100%).  The conclusion of the authors is a maximum PETCO₂ <=20 mm Hg within 5 minutes of the onset of mechanical ventilation in the operating room may be a useful factor in decision making  related to the termination of resuscitative efforts during emergent trauma surgery. They advocate a larger study to corroborate their findings. 

Comments by Bhavani Shankar Kodali MD

I am extremely delighted to see this study highlighting the value of capnography and its relation to cardiac output in trauma victims. Many clinicians underestimate the clinical importance of the relationship between cardiac output and PETCO_2. Whenever I am called into the operating room for an emergency, I look at the capnograph. If the PETCO2 is reasonable, I know that the cardiac output seems reasonable. If PETCO₂ is below 20 mm Hg, I consider an impending catastrophe in the horizon, and thus act quickly. The golden number PETCO₂ to predict survival seems to be 20 mm Hg.  The recommendation to maintain PECCO2 over 20 mm Hg during CPR is based on the poor survival of patients during CPR, particularly when PETCO₂ is lower than 10 mm Hg.  In general, 20 mm Hg of PETCO₂ corresponds to a cardiac output of 2 L. If the end-tidals are below 20 mm Hg, the cardiac output is probably lower than 2 L.