ACLS guide to out-of-hospital cardiac arrest

ACLS guide to out-of-hospital cardiac arrest

Ahmed Raza


The number of out-of-hospital cardiac arrests (OHCA) is more than 356,000 in the US annually, out of which 90% are fatal. This sounds scary, but let’s put it into perspective. Based on the Cardiac Arrest Registry to Enhance Survival (CARES) data, the survival rate remains low. OHCA is the third major contributor to significant morbidity in the US.

In 2017, laypersons delivered a shock in only ~2% of cases, used AEDs in 6% of cases, while they initiated CPR in 39% of the cases. Folks witness OHCA in 69.5% of cases at home, 18.8% of cases in public, and in 11.7% of cases at nursing homes. Individuals lost, on average, 20.1 healthy years who experienced out-of-hospital cardiac arrest resulting in the loss of 4.3 million healthy life years nationally in the US.

Ventricular Fibrillation

Ventricular fibrillation (VF) is the most common initial rhythm in the cases of out-of-hospital sudden cardiac arrest. Thankfully, ventricular fibrillation has ten times the survival rate than any other cardiac arrest defibrillated in a timely manner. Time is the most important factor. As time passes, the chances of successful defibrillation decrease rapidly.

According to the new recommendations for treating ventricular fibrillation (VF), rescuers must integrate the use of AED with the CPR. After calling 911, the caller should start CPR while using the AED to increase the survival chances of the victim. If two rescuers are available on the scene, calling EMS and initiation of CPR can be done simultaneously.

When VF persists, the myocardium is depleted of oxygen and metabolic substrates when VF is present for more than a few minutes. In this case, chest compressions are helpful in resolving the ventricular fibrillation and returning to a perfusing rhythm by delivering oxygen and metabolic substrates. In the case of out-of-hospital VF while preparing for defibrillation and checking the ECG rhythm an EMS professional may initiate CPR. As there is insufficient evidence that 90–180 seconds of CPR should be provided before defibrillation, CPR should be given when AED is being readied. For more details take a look at our CPR course and learn a life-saving skill.

Why is immediate resuscitation important?

A study conducted in Sweden on 14,065 people suggests, “With increasing time to defibrillation, the survival rate fell rapidly from ≈50% with a minimal delay to 5% at 15 min”. The survival rate from collapse to defibrillation decreases more gradually with the average of 3%–4% per minute when bystanders provide CPR. Chances of survival can be doubled or tripled if CPR is provided in the first few minutes. People in white or high-income neighborhoods are more likely to receive CPR by bystanders than black, low-income, and Hispanic communities.

About 7 out of 10 cases of OHCA occurs at home, but half of these people don’t get CPR from bystanders. As we have already discussed, the survival rate of the patient is highly dependent on the timely response by the bystanders. Therefore, if you witness a cardiac arrest, call 911 immediately, and then start giving CPR until the emergency medical professionals arrive on the scene. CPR and defibrillation should be given as soon as possible to restart the heart. CPR also increases the time window for defibrillation. Although CPR helps to prolong ventricular fibrillation (VF) and delay asystole, however, it is pertinent to consider that CPR alone is unlikely to terminate ventricular fibrillation, the patient still needs professional medical assistance.

Any delay in CPR or the start of defibrillation will reduce the chances of survival. It is important to note that the use of AEDs only doesn’t improve the chances of survival, it is found that survival rate fell when more emergency medical service providers were equipped with AEDs in Seattle because the emphasis on CPR was reduced. The study on 639 victims of out-of-hospital ventricular fibrillation concluded that the provision of 90 seconds of CPR before the delivery of the shock(defibrillation) increases the chances of survival when the response time is 4 minutes or longer.

If a cardiac arrest is witnessed out-of-hospital, CPR should be provided immediately and should use AEDs as soon as available. However, the outcomes of 2 other randomized controlled trials were different. These trials suggest that in the out-of-hospital ventricular fibrillation patients, administration of CPR for 90–180 seconds before the use of AEDs does not improve survival to hospital discharge rate in comparison to immediate defibrillation, regardless of response time.

Shock defibrillation protocols

Studies reveal that, among two different types of shock defibrillation protocols for treating cardiac arrest, single-shock defibrillation protocol has significant survival benefits as compared to 3-stacked-shock protocols. Rescuers should give an initial shock of 360 J if using monophasic defibrillators. If, after the first shock, ventricular fibrillation persists, then the rescuer should give the second shock of 360 J. After delivering the shock, the rescuer should continue chest compressions to keep the rhythm or pulse in check. Decreasing the interval between the shock and the last compression can elevate the chances of successful delivery of the shock, the decrease might be of a few seconds. Thus, healthcare providers should build effective coordination between CPR and defibrillation to reduce the interval between stopping CPR and providing shock.


Adequate compressions followed by prompt defibrillation is the prominent factor for the survival and return of spontaneous circulation (ROSC) in people with VF. Instant CPR along with single shocks are recommended now due to new biphasic defibrillators with higher efficiency instead of 3-shock sequences, which were recommended before 2005, to treat VF.

While attempting defibrillation, to reduce interruptions, and to ensure the timely resumption of chest compressions after shock delivery, rescuers should practice coordination while providing high-quality CPR with defibrillation. This is the prime factor to increase the survival rate of the patient.


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Last reviewed and updated by on May 1, 2020

Caitlin Goodwin, DNP, RN, CNM, is a Board Certified Nurse-Midwife, Registered Nurse, and freelance writer. She has over twelve years of experience in nursing practice.

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