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A resuscitation quickie. Should we aim for, a better depth or just increase the rate in chest compressions during resuscitation? In a study just published in Resuscitation(1) they looked at how chest compression rate and depth affected end-tidal CO2 (ETCO2).

I recently wrote about ACLS probably being no better than BLS. Apart from quality CPR and defibrillation, nothing else matters as much. Adrenaline perhaps, if given early and not in large quantities can help and certainly ECMO has been found to be useful. However for most departments ECMO or REBOA are not really available.

We need to concentrate on the quality of CPR:

  • The right rate
  • The right depth
  • Paying attention to the duty cycle to allow for adequate recoil

Should we use a metronome for rate? Chest compression depth monitoring is useful, primarily as we aren’t always aware that with time the depth of our compressions is decreasing. Do you monitor depth of compressions? Should we monitor these variables, or simply alter them to achieve the most important outcome; diastolic blood pressure?

The effectiveness of resuscitation is measured ideally, with invasive blood pressure monitoring in the form of an arterial line. In cases where this isn’t possible, ETCO2 can be used as a surrogate marker of cardiac output. It’s non-invasive and gives us an indication of organ perfusion and pulmonary blood flow.

We know that at best, during cardiac arrest, we can achieve about 50% of normal cardiac output with good CPR. Although the rate of compressions can be altered, it’s not as easy to do, especially if the rates is increases, without mechanical devices. The influence of rate adjustment has been shown to be limited (2).

The study just published (1) was a retrospective analysis of monitor defibrillator recordings, which included capnography, compression depth, transthoracic impedance and ECG, in cases with at least 1000 compressions.

As ventilation can affect ETCO2, as well as have effects on cardiac return and thus cardiac output, a mathematical method was used, where the ETCO2 was independent of the ventilation rate.

They demonstrated that compression depth is a good predictor of ETCO2 variations with rate of compressions contributing less.

We know that depth of compression decays during the CPR cycle, as the operator tires. Perhaps we need to monitor not only the rate, but the depth of chest compressions during CPR (3) and alter these variables with either invasive blood pressure monitoring or non-invasive CO2 measurements.


  1. Gutierrez JJ et al. Contribution of chest compression to end-tidal carbon dioxide levels generated during out-of-hospital cardiopulmonary resuscitation. Resuscitation 2002;179:225-232
  2. Steak KR et al. Quantitative relationship between end-tidal carbon dioxide and CPR quality during both in-hospital and out of hospital cardiac arrest. Resuscitation 2015;89:149-54
  3. Meaney PA et al. Cardiopulmonary resuscitation quality: improving cardiac resuscitation outcomes both inside and outside the hospital: a consensus statement from the American Heart Association. Circulation 2013; 128:417-35

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