In this paper from washington state, levine and associates studied end-tidal carbon dioxide levels (ET CO2) in 150 patients suffering out-of-hospital cardiac arrest to determine whether ET CO2 levels could predict which patients would fail resuscitation. If this could be predicted early enough to be of clinical significance, then prolonged, futile resuscitation could be avoided.
Only patients with pulseless electrical activity (PEA) were studied; PEA was defined as a wide or narrow complex of any rate without the presence of a pulse. Based on earlier studies in humans and animals, an ET CO2 level of 10 mmHg was selected as a threshold that, after 20 minutes of CPR, would separate survivors from nonsurvivors. A survivor was defined as one who survived to hospital admission. Those who survived to hospital discharge were followed for six weeks, and an assessment of neurologic recovery was made.
Spontaneous circulation was restored in 35/150 patients, all in less than 20 minutes from initiation of advanced life support. None of the patients who had PEA after 20 minutes of CPR were resuscitated. At 20 minutes, the ET CO2 in nonsurvivors averaged 4.4 mmHg, and the ET CO2 in survivors averaged 32.89 mmHg. However, the 20-minute ET CO2 did not predict who would survive to hospital discharge. Sixteen patients survived to hospital discharge, and 14 survived to six weeks, eight of whom were neurologically intact.
Levine et al therefore conclude that the level of ET CO2 during CPR can be a predictor of death from cardiac arrest in patients with PEA. (Levine RL, et al. End-tidal carbon dioxide and outcome of out-of-hospital cardiac arrest. N Engl J Med 1997;337:301-306.)
COMMENT BY JEFFREY W. RUNGE, MD, FACEP
After reading this article, my conclusions are very different from those of Levine et al. This paper is one more piece of evidence that patients who do not respond to resuscitative efforts after 20 minutes of state-of-the-art advanced life support are not going to survive. This merely restates the fact that has been shown repeatedly in much larger studies. What this paper does add is some additional technological evidence that, in spite of state-of-the-art hospital resuscitation efforts, it is simply impossible to maintain blood and nutrient flow to vital organs over a 20-minute period of time.
Every patient who experienced a return of pulse in this study did so within the 20-minute time period. No one who was persistently pulseless at 20 minutes survived. Those who did achieve a return of spontaneous circulation did have a higher ET CO2 than those who did not. It is hardly surprising that people whose hearts begin beating will have a higher ET CO2 than those without a beating heart. This study simply reinforces earlier work showing that ET CO2 documents low-flow or no-flow states during CPR.
Interestingly, Levine et al mention a worthwhile finding in the discussion section of the paper. In all 35 patients in whom spontaneous circulation returned, ET CO2 rose to at least 18 mmHg before the return of clinically detectable vital signs. This statement is not supported by data cited in the paper but would be a very useful parameter for gauging the success of a resuscitation.
While this technology may help document that death has occurred, it adds little to the body of knowledge about survival from out-of-hospital cardiac arrest. Like every other study of this subject, failure to achieve a prompt response with advanced life support is a harbinger of poor outcome. Certainly if a patient has had 20 minutes of properly delivered advanced life support and has not responded, they are extremely unlikely to survive. This technology may offer some measure of comfort for those who would otherwise carry out prolonged resuscitation of persons with PEA, but for the rest of us, clinical evidence and knowledge of the physiology of CPR is sufficient to decide when to terminate CPR in these patients.
You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
- Award-winning Medical Content
- Latest Advances & Development in Medicine
- Unbiased Content