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Category: Cardiology

Topic: Basic Life Support

Level: EMR

Next Unit: CPR in the Infant

18 minute read

CPR is used to maintain blood flow through the body in the event of cardiac arrest. This has a dual function, it provides oxygen to vital tissues such as the brain, which rapidly dies without oxygen and increases the preload reaching the right side of the heart which stimulates it to resume beating. 

For these reasons CPR is the cornerstone of cardiac arrest management, all cardiac arrest protocols center around effective and timely CPR. This section will review CPR using the algorithm CAB which is a rearrangement of the ABCs proposed by the American Heart Association given the importance of initiating CPR rapidly if no pulse is present. 

Remember, Scene safety is paramount in all situations, even a cardiac arrest. Ensure that you and your team is safe prior to attempt any rescue!


The C.A.B Protocol for CPR in Adults

"CAB" is a rearrangement of the traditional EMS "ABCs" that better meets the needs of a patient that is unconscious and suspected of being in cardiac arrest. The placement of "C" at the front of the acronym is meant to communicate that effective and uninterrupted chest compressions are the most vital intervention in this patient population. Followed by positioning the airway to allow for maximal airflow and the delivery of effective rescue breaths. 


Chest compressions are delivered at a rate of 100-120 compressions per minute, over the mid-sternum, to a minimum depth of 2 inches. For a patient that does not have an advanced airway in place, you will deliver 30 compressions before giving 2 rescue breaths from a bag valve mask, this is known as a 30:2 ratio. If a patient has been intubated or had an advanced airway placed by an ACLS provider, you will provide continuous chest compressions as pausing for breaths is no longer required to deliver effective ventilation.

Every 2 minutes of CPR you will check for a pulse. Attach an AED as soon as it becomes available, it is best to wait for the natural pause between cycles of CPR while breaths are being delivered.


After every 30 compressions in an un-intubated patient, you will deliver 2 rescue breaths. 

The patient should be placed in the "sniffing position" with the head tilted back and the chin lifted upwards and two breaths delivered by bag valve mask with 1 second in between each breath, watch for chest rise to ensure the breaths are effective. Dual rescuer CPR is more effective as it allows you to maintain this position and not have to re-set the patient's airway in between cycles. 


As above, two breaths are delivered after every 30 compressions via a bag valve mask connected to 100% oxygen. If a bag valve mask is not available use a barrier mask with one way valve to deliver "mouth to mouth" breaths. A basic tenant of rescuer safety is to never be without a barrier device for CPR. 

If you are working with advanced life support (ALS) providers they may intubate the patient or place an advanced airway device during CPR, after this is done you no longer need to pause CPR to give breaths. At this time you will switch to giving one breath every 6 seconds.


Single Rescuer CPR

Responsive vs. Unresponsive

First, determine if the patient is responsive or not via a good shout of "ARE YOU OK?" then firmly tap on their shoulders. If they respond, evaluate for any other potential life threats. If there is no response, move to check for a pulse. Activate the emergency response system by radioing for ACLS support and if available, obtain an AED.

Pulse Check

If unresponsive, simultaneously check for a carotid pulse and visible breathing via chest rise for no more than 10 seconds. Note that Gasping or grunting is not breathing.

  • Definite pulse + inadequate breathing: 1 rescue breath 3-5 seconds.
  • Definite pulse + breathing effectively: monitor until ALS unit arrives.
  • Pulseless + apneic: remove clothes from the chest and begin CPR.

Get an AED

The AED will guide you through each step once powered on. Be sure to listen carefully to each command and follow accordingly. Each AED has defibrillator pads. Follow the instructions and utilize the pictures on the pads if you forget placement.

AED's are becoming increasingly available to EMS services and the public. Nearly all basic life support (BLS) teams will carry an AED, if one is not available in your ambulance there will often be AED's available in many public places such as malls, airports, gyms, college campuses, and retirement homes. 

If it is not immediately obvious where to obtain an AED, you should activate the emergency response, initiate CPR, and specifically instruct one or more bystanders to search for an AED. 

For witnessed cardiac arrest, attach the AED pads to the patient’s bare chest. Do not touch the patient during this time as the AED is determining if a shock is advised. If a shock is not advised, quickly begin high-quality chest compressions for 2 minutes and recheck a rhythm every 2 minutes until an ALS crew arrives or the patient begins to move. The AED should prompt you to do this.

Shock Advised!

If a shock is indicated, resume compressions while the AED is charging. 

AED's will not deliver a shock until the button is pressed, as a matter of safety, the individual giving chest compressions at that moment should be the one to press the shock button. Once the AED has charged, STAND CLEAR then press the button to deliver the shock. Immediately resume chest compressions for 2 minutes. The AED prompts you when to stop to re-analyze the rhythm.


Dual Rescuer CPR vs. Single Rescuer CPR

In previous guidelines, it was recommended to switch from a 30:2 compression/breath ratio to a 15:2 compression breath ratio when a second rescuer was present. Current research shows that minimizing the interruption of high-quality chest compressions was the most important factor in the survival of cardiac arrest. As such, it is recommended to use a 30:2 ratio for ALL adult CPR, in children the ratio still changes given their higher need for oxygen. 

  • Additionally, the 2nd rescuer may:
    • activate the emergency response system;
    • be an extra set of eyes for scene safety;
    • obtain the AED and first aid kit;
    • attach AED pads while breaths are being administered between compressions;
    • alternate every 2 minutes in performing high-quality chest compressions;
    • perform pulse checks when indicated by the AED;
    • encourage you to do better chest compressions, ensuring high-quality CPR;
    • assist in other tasks as needed to optimize patient survival.

Be sure to assign responsibilities and stick with them. Communication is key here. No one wins a prize for being a "better rescuer." Someone's life depends on you working together as a TEAM.