• Tim

Cardiac Arrest

Updated: Apr 26, 2021

Of all of the problems that you may have to deal with, Cardiac Arrest is by far the most important.

There are around 60,000 cases of suspected out of hospital cardiac arrest (OOHCA) in the UK each year, with approximately half of these receiving a resuscitation attempt from the Ambulance Service. The other half usually does not receive resuscitation either because the person has been dead for some time, or because there has been no bystander CPR.

In the UK, the average survival rate from OOHCA is poor when compared to some other countries. The main reasons for this are the lack of immediate good quality CPR and a lack of defibrillation in the first few minutes. It is thought that bystander CPR and use of an Automatic External Defibrillator (AED) at least doubles the chances of survival and could save thousands of lives each year.

The Chain of Survival

The Chain of Survival is a series of steps that need to be in place to maximise the chance of a good outcome.

Early Recognition and Call for Help

  • Unresponsive and not breathing, or not breathing normally = Cardiac Arrest

  • Call 999 for help immediately

  • Send for an AED

Early CPR

  • Immediate high quality CPR massively increases the chance of a good outcome

  • CPR buys time until the cause of the cardiac arrest can be reversed

Early Defibrillation

  • Defibrillation within 3-5 minutes of collapse can produce survival rates of 50-70%

  • Each minute of delay in defibrillation reduces the probability of survival by 10%

Post Resuscitation Care

  • Advanced Life Support may be able to reverse the cause

  • Post resuscitation care can affect the outcome

Basic Life Support Sequence


  • Check for safety

  • Call for help - shout or 999


  • Ensure the mouth is clear and head is tilted back


  • Look, listen and feel for breathing for up to 10 seconds

  • Barely breathing, infrequent or slow noisy gasps are not normal breathing

  • If no breathing, not normal or unsure...

Start CPR

  • 30 chest compressions

  • 2 attempted ventilations

  • Repeat

Call/update 999

  • Ask a helper to call if possible

  • Stay with the casualty if possible

  • Use speaker function if on own

Send for an AED

  • If on your own, start CPR

  • Do not leave them for the AED

  • Use the AED as soon as it arrives

Cardio-Pulmonary Resuscitation (CPR)

CPR involves taking over the function of the heart and lungs through chest compressions and ventilations (sometimes called rescue breaths). Start with chest compressions.

The ratio of chest compressions to ventilations is now 30:2 for adults and children during basic life support.

Chest Compressions

Immediate, high quality chest compressions with minimal interruptions are the backbone of any resuscitation attempt. Move the person on to their back on a hard surface.

'High quality' is defined as:

  • Position (heel of hand on centre of the chest, lower half of sternum, not on ribs)

  • Depth (5-6cm in an adult, 1/3rd of the depth of the chest in a child)

  • Release (ensure that you just break contact with the chest in-between each compression)

  • Rate (approximately 100-120/minute or 2 per second, use a metronome app)

If possible, change the person doing chest compressions at least every 2 minutes to maintain quality. Minimise any interruption to compressions by swapping when the AED is analysing or when someone else is doing ventilations.

If you're doing chest compressions, count out loud so that you and anyone else present know how many have been given. This will help minimise the interruption when ventilating the patient. Don't worry if you lose count, just guess where you are and carry on.

Ventilations (or Rescue Breaths)

Ventilations are critical to get oxygen in to the patient and to get carbon dioxide out. How you ventilate the patient depends on the equipment you have, but it will involve a version of 'mouth-to-mouth', with or without a face shield or pocket mask.

There is a small risk of cross infection when giving mouth-to-mouth. Some form of barrier is recommended to minimise this risk, and will also be useful if the person has been sick, has lots of saliva around their mouth, or has blood on them.

See bottom of page for Covid-19 update.

Aim for two effective ventilations, but never interrupt chest compressions by more than 10 seconds. If one or both fail, go back to chest compressions, and change something next time - make sure you're tipping the head right back.

To give an effective mouth-to-mouth ventilation:

  • Open the airway, using a Head Tilt, Chin Lift technique

  • Pinch the nose shut

  • Seal your lips over their mouth

  • Breathe in to them until the chest begins to rise (about 1second)

  • Release to allow the air to come back out - maintain the airway

  • Repeat


  • Too much volume may cause the person to vomit - clear the airway if necessary by tipping them on their side

  • 'Blowing' too hard may cause damage to their airways - be gentle


The cause of OOHCA for the majority of people is a heart attack, and in this case the heart will often fibrillate in the early stages of Cardiac Arrest.

Fibrillation is caused by chaotic electrical activity in the heart muscle, which stops it from being an effective mechanical pump.

In order to stop fibrillation, a shock must be passed across the heart using a defibrillator. For the first aider, this will usually be a public access AED, known as a PAD. PADs can be found in many public places and the 999 control room may be able to tell you where the nearest one is.

An AED will assess the electrical rhythm of the person's heart. If it detects fibrillation, it will charge itself up and then allow a shock to be delivered to the patient. Some AEDs are 'semi-automatic' and require someone to press a button to deliver a shock, but others are fully automatic and will deliver a shock after giving an audible warning.

The shock will stop the electrical activity of the heart, in the hope that it restarts in a normal rhythm. However, this is not always the case and even if a normal rhythm is achieved, it may soon deteriorate in to some other rhythm.

If the person has any other rhythm than fibrillation, it will not shock.

Use the AED as soon as it arrives, whilst minimising interruptions to chest compressions if more than one rescuer is present.

  • Open AED

  • Attach pads to bare chest, quickly dry and/or shave if necessary

  • Follow directions from AED

  • Do not touch patient while analysing

  • Do not touch patient when shocking

  • If shock delivered or no shock indicated, continue CPR

Stopping CPR

Only stop a resuscitation attempt if:

  • A health professional tells you to stop

  • You become exhausted or are at risk from a hazard

  • The person is definitely waking up, moving, opening eyes and breathing normally


If the person is definitely waking up, moving, opening eyes and breathing normally:

  • Stop resuscitation

  • Leave the pads attached

  • Manage the person's airway if necessary

  • Be prepared to re-start CPR and defibrillation if the person stops breathing


Perceived problems that may occur during a resuscitation attempt include:

  • Vomiting - stop, clear the airway by tipping them on their side, then continue

  • 'Cracked ribs' - occasional cracking is normal, consider compression depth


If possible, the following modifications should be made to the protocol. If the modifications cannot be recalled, use the standard protocol.

Children and Infants

Children (defined as those who have not yet reached puberty) and infants (under 1 year old) tend to go in to Cardiac Arrest due to respiratory causes, rather than heart disease as with most adults. Therefore, the following modifications are made:

  • Start with 5 ventilations before compressions

  • Use less force to do compressions - 1 hand for a child or 2 fingers for an infant will do

  • Use paediatric AED pads or use the selector switch on the AED - if none available use adult pads

  • Use the front and back positions for the pads


If the person has gone in to cardiac arrest due to drowning, the following modifications are made:

  • Start with 5 ventilations before starting compressions

  • Be prepared for to clear vomit or frothy secretions from the mouth


If the person is in traumatic cardiac arrest, it is unknown whether it is better to start CPR or not. Guidelines still state that CPR should be started, but that chest compressions should be 'de-emphasised'.

Follow the normal trauma primary survey. Identify and stop any catastrophic bleeding, manage the airway and then check for breathing. If they are unconscious and not breathing, or not breathing normally, start CPR. If the start bleeding significantly when you start compressions, get someone to deal with this whilst carrying on CPR.

Now try our 1 minute quiz about Cardiac Arrest.

Covid-19 Update

As a result of the Covid-19 pandemic, the UK Resuscitation Council and Public Health England (PHE) have provided updated guidelines for first aider CPR. As these guidelines are likely to change with our understanding of this disease, here's links to the latest information:

UK Resuscitation Council Resuscitation in First Aid and Community Settings

UK Resuscitation Council for those Teaching CPR

PHE Guidance for First Responders


In summary, you can significantly increase the chance of survival in out of hospital cardiac arrest.

Start CPR send for an AED and call 999. Maintain great quality chest compressions with minimal interruptions, and use the AED as soon as it arrives.


If you'd like to know more about how to maximise the chances of survival in cardiac arrest, why not book one of our First Aid Courses.