End-tidal Carbon Dioxide Concentration during Cardiopulmonary Resuscitation.

Falk JL, Rackow EC, Weil MH New England Journal of Medicine 1988 Vol 318(10) Pages 607-611

The authors prospectively measured the end-tidal carbon dioxide concentration during 13 episodes of cardiac arrest in 10 critically ill patients being mechanically ventilated, in order to evaluate its usefulness as an indicator of circulatory status during resuscitation. The end-tidal carbon dioxide concentration decreased from a mean (+/- SD) of 1.4+/-0.9 to 0.4+/-0.4% after the onset of cardiac arrest. During precordial compression, it increased to 1.0+/-0.5%. Spontaneous circulation was restored on 7 occasions. This was heralded by a rapid increase in the end-tidal carbon dioxide concentration, from 1.3+/-0.5% to an overshoot value of 3.7+/-2.1%, within approximately 30 seconds. The concentration then declined to a stable value of 2.4+/-1.8% four minutes after resuscitation. However, it remained 0.7+/-0.4% in the 6 patients in which resuscitation failed to restore spontaneous circulation. These observations are consistent with studies of CPR in pigs, in which end-tidal carbon dioxide concentration varied directly with the cardiac output produced by CPR. The authors therefore regard end-tidal carbon dioxide as a quantitative indicator of the volume of blood flow produced during CPR. The assessment of end-tidal carbon dioxide is a reliable noninvasive way to monitor the effectiveness of CPR, except immediately after the injection of bicarbonate, which itself may transiently increase the carbon dioxide concentration.