ACLS Training – CPR or Defibrillation First?

A question that often arises, particularly in ACLS training, is whether providers should administer CPR first or defibrillation. Let’s see what the studies say!

ACLS Training – CPR or Defibrillation First?

There have been many significant advances in resuscitation over the past decade or so, but the foundation remains CPR and defibrillation.

According to the AHA ECC Guidelines, the attributes of high-quality CPR are as follows:

  • Ensuring adequate rate (100-120 compressions per minute)
  • Ensuring adequate depth (2 to 2.4” or 5 to 6 cm)
  • Allowing full chest recoil (avoid leaning)
  • Minimizing interruptions to chest compressions
  • Avoiding excessive ventilations

A question that often arises, however, particularly in ACLS training, is whether providers should administer CPR first or defibrillation. Let’s examine this question in greater detail.

Does CPR first make sense?

In the case of a witnessed arrest, either by a bystander who has a manual defibrillator or AED, or a trained first responder, the critical nature of early defibrillation is indisputable.

If you’ve spent any time around medical professionals, you’ve probably heard it mentioned plenty of times that early defibrillation can save a life.

Initially, the assumption was that delivering 1 ½ to 3 minutes of CPR prior to defibrillation was effective in providing oxygen and nutrients to the heart, thereby increasing the likelihood of success of defibrillation.

Recent evidence suggests, however, that doing chest compressions only while setting up the defibrillator and charging the capacitor may be sufficient.

The concept of “CPR first” got its roots from evidence that suggests the existence of three time-sensitive phases of cardiac arrest:

  1. The electrical phase, which is 0-4 minutes
  2. The circulatory phase, which is 5-10 minutes in
  3. And the Metabolic Phase, which is greater than 10 minutes

Researchers had suggested that the application of CPR prior to defibrillation might be beneficial during the circulatory phase of cardiac arrest.

The Evolution of AHA Recommendations

Due to the fact that it’s rare for an EMS to arrive at the scene of a cardiac arrest during the electrical phase, in 2005 the AHA ECC Guidelines made the following recommendation:

When an out-of-hospital cardiac arrest is not witnessed by EMS personnel, they may give about 5 cycles of CPR before checking the ECG rhythm and attempting defibrillation (Class IIb). One cycle of CPR consists of 30 compressions and 2 breaths. When compressions are delivered at a rate of about 100 per minute, 5 cycles of CPR should take roughly 2 minutes (range: about 1½ to 3 minutes).

This recommendation regarding CPR prior to attempted defibrillation is supported by 2 clinical studies (LOE 2, LOE 3) of adult out-of-hospital VF SCA. In those studies when EMS call-to-arrival intervals were 4 to 5 minutes or longer, victims who received 1½ to 3 minutes of CPR before defibrillation showed an increased rate of initial resuscitation, survival to hospital discharge, and 1-year survival when compared with those who received immediate defibrillation for VF SCA. One randomized study, however, found no benefit to CPR before defibrillation for non-paramedic-witnessed SCA.

Fast-forward to today’s AHA Guidelines

Observational clinical studies and mechanistic studies in animal models suggest that CPR under conditions of prolonged untreated VF might help restore metabolic conditions of the heart favorable to defibrillation…others have suggested that prolonged VF is energetically detrimental to the ischemic heart, justifying rapid defibrillation attempts regardless of the duration of arrest.

A ROC PRIMED study of patients who experience cardiac arrest outside of the hospital concluded that there was no significant difference in the outcomes of those who had been administered CPR for a brief period versus a longer period.


The collective evidence gathered to date suggests that, in most cases, defibrillation performed as soon as practicable is equivalent to an interval of CPR delivered prior to the initial shock.

This is with the caveat that high-quality chest compressions are performed during the defibrillator set up, a process which typically takes about one minute.

At the end of the day, the quality of the CPR being delivered is more important than when the first shock takes place.