Updated 17/4/25
Causes and Effects Of Cardiac Arrest
Cardiac arrest is when the heart stops contracting effectively or stops completely. The most common cause of cardiac arrest is heart attack, but there are other causes, see later on.
Note – a heart attack is a cause of a cardiac arrest, but it is not the same thing. Heart attack is described in the Heart Attack and Angina section.
When a cardiac arrest occurs, all blood flow ceases in the body. The effect on the brain is loss of consciousness and cessation of all breathing*. Brain injury and brain death occur rapidly if the cardiac arrest is left untreated for 3-4 minutes because the brain cannot tolerate more than about 4 minutes without oxygen before becoming irreversibly damaged. If the casualty has severe hypothermia (e.g. a temperature of 25 degrees c) when they have their cardiac arrest, their brain will survive for longer.
*Agonal breathing may occur, this is abnormal looking gasps that sometimes occur in the first few seconds after a cardiac arrest. These rapidly cease. Agonal breathing must not be confused with normal breathing.
EARLY DEFIBRILLATION IS THE KEY TO SURVIVAL
The best chance of survival is immediate treatment via defibrillation, if indicated by the AED. The effectiveness of defibrillation decreases the longer you wait to deliver a shock. Therefore, the AED must be applied as soon as a cardiac arrest is diagnosed (whilst someone else is doing chest compressions). CPR (cardiopulmonary resuscitation) is used for circulatory support until a rhythm can be restored: in most circumstances CPR by itself will not restore a normal rhythm !!!
Only some cardiac rhythms will respond to defibrillation. These are called “shockable rhythms”. Those that will not respond are called “Non-shockable rhythms”. During resuscitation, the rhythm shown on the ECG (electrocardiogram) can change back and forth between these two.
For more details on cardiac arrest see ‘Casualty Care in Mountain Rescue’.
The following video shows the different contraction patterns of a normal heart and some of the most common types of cardiac arrest.
Unfortunately the survival rate of individuals suffering out-of-hospital cardiac arrest is poor. In our situation where we are unlikely to be present at the time of the arrest, survival is very unlikely.
Symptoms and Signs
No breathing
Look, feel (the diaphragm) and listen for breathing for 10 seconds.
When To Attempt Resuscitation
Resuscitation should be started immediately if:
Witnessed collapse (by MR)
Bystander CPR is taking place
For asystole in the presence of hypothermia or avalanche, see the relevant sections.
Resuscitation should not be started if:
Other injuries incompatible with life are present
It has been over 20 minutes since the collapse, no bystander CPR has taken place
Sustained CPR and timely evacuation would be impossible
Treatment
Remember: EARLY DEFIBRILLATION IS THE KEY TO SURVIVAL
1) The focus upon arrival at the Cas site is to diagnose the casualty as not breathing and to immediately place the AED pads on their chest and turn the AED on. In reality it’s likely that a bystander will be performing CPR. If their CPR is effective then ask them to continue whilst you attach the AED. In the time the machine is analysing start getting the BVM and oxygen out of the medical sac.
2) After the initial shock, or if the AED instructs you that no shock is advised, continue with CPR at the ratio of 30:2. The focus here is good quality chest compressions. If you lose count, don’t panic, just stop when you think you have delivered somewhere near 30 compressions.
In children (0 - 18 yrs) and victims of drowning, it is essential to start with five rescue breaths. NB Chest compression-only CPR is now advocated if there is no medical airway equipment available (e.g. i-gel, pocket mask).
How to do effective chest compressions:
Kneel by the side of the victim. If on your own, kneel at the casualty’s head, as in the video below.
Place the heel of one hand in the centre of the victim’s chest (which is the lower half of the victim’s breastbone (sternum))
Place the heel of your other hand on top of the first hand Interlock the fingers of your hands and ensure that pressure is not applied over the victim's ribs
Keep your arms straight
Do not apply any pressure over the upper abdomen or the bottom end of the bony sternum (breastbone)
Position your shoulders vertically above the victim's chest and press down on the sternum to a depth of 5–6 cm
After each compression, release all the pressure on the chest without losing contact between your hands and the sternum;
Repeat at a rate of 100–120 minute
See video below produced by Nick to give you an overview of the use of the AED, CPR and the i-gel with Bag Valve. This is what you will be assessed on when you do your BLS assessment for the exam.
CPR & AED
Attaching the AED:
Turn on the machine
Cut away clothing using trauma shears
Check that there are no ‘5 P’s’ and remove before placing the pads: Patches, Pendants, Piercings, Pacemakers and Perspiration (wipe skin dry) and excessive body hair. (razor in the ‘Airway & Defibrillator’ pouch)
Apply the defibrillator pads as shown on the outer packaging and connect the lead to the machine. Follow voice prompts.
5. The machine will either tell you to press the ‘blue button’ to start analysing or will automatically start analysing (New AED). Stop chest compressions and do not touch the casualty whilst the AED is analysing.
6a. If no shock is advised immediately restart chest compressions.
6b. If a shock is advised, wait whilst the AED charges.
7. Once charged, the person delivering chest compression MUST ENSURE that everyone is standing clear of the casualty before delivering the shock. If oxygen is being delivered by a mask, it must be removed prior to delivering the shock. However if an i-gel is being used, there is no need to remove oxygen before delivering the shock as the i-gel and Bag Valve form a closed system.
8. After delivering the shock, immediately resume chest compressions. There must be no delay in getting back on the chest. Do not wait hoping to see a response and do not check the pulse at this stage.
9. As soon as possible ventilate the casualty. Use the BVM (ideally 2 person technique, one handed BVM is really difficult and requires practice.) Remember to fully tilt the head back to open the airway. Placing an OPA can help. If you don’t see the chest rise and fall, then consider using an i-gel, to achieve a total of two effective rescue breaths. Do not interrupt compressions by more than 10 seconds to deliver two breaths. Then return your hands without delay to the correct position on the sternum and give a further 30 chest compressions. Give high flow oxygen by connecting the cylinder to the bag.
10.Listen out for the AED commands. It will automatically re-analyse after a further 2 mins. Don’t touch the casualty and follow instructions.
11. In reality you will tire quickly if operating alone. We work much better as a team. If other rescuers arrive on scene, the person performing chest compressions should be swapped out every two minutes. Use the time the AED is reanalysing to swap around efficiently.
12. You’ll notice that Nick is working at the head of the casualty. This is a good position for the solo responder as you can manage the airway effectively from here, be in a position to better seal the BVM and to reach over to perform CPR.
Beware – The FRED AED can be fooled by movement, on one occasion an earlier model being used as a monitor (no longer team practice) advised team members to deliver a shock to a wet and shivering casualty who was sat up and talking. Do not deliver shocks to fully conscious talking casualties!
Remember – As soon as practicable switch from delivering chest compressions manually to using the Autopulse (an automated machine to deliver effective chest compressions). The AutoPulse is calibrated to continue at 30:2.
Urgent evacuation is always warranted
Setting up the FRED AED and voice prompts:
NB We have acquired a new type of AED the ‘FRED Easy Port Plus’. Our current ‘FRED Easy Port’ AEDs are no longer produced) so we will be changing them all when they need to be replaced. Demos for team members will be arranged soon and a video of it functioning put here.
VIDEO OF NEW EASY PORT PLUS
Look for and treat reversible causes of Cardiac Arrest
Some causes of cardiac arrest are reversible. Whilst resuscitation is ongoing, as part of the management of cardiac arrest, you must identify and treat these if possible.
Look for and treat the 4 H’s and T’s. The ones in bold are the most relevant to MR and these are the ones you need to remember:
Hypothermia. Follow the MREW Hypothermia Protocol.
Hypoxia e.g. from drowning, anaphylaxis. Give oxygen.
Hypovolaemia e.g. from blood loss, anaphylaxis. Will need IV fluids.
Hyper/hypokalaemia – severely abnormal levels of potassium in the blood. This is included for information only. There is no intervention available to MR with cas care skills or the equipment we carry.
Toxic e.g. from drugs. Give oxygen. Support breathing. Monitor for cardiac arrest.
Thrombosis e.g. a blood clot lodged in the heart muscle (heart attack), a blood clot lodged in the lungs (pulmonary embolism).
Tension pneumothorax. Air collecting between the lung and the chest wall, resulting in lung collapse which then puts pressure on the heart and can result in cardiac arrest.
Tamponade – trapping of fluid (usually blood) under the the sack in which the heart is enclosed. This compresses the heart and prevents it beating effectively. NB this is included for information only.
When To Stop CPR
There are three reasons to stop CPR.
1). The casualty recovers:
Spontaneous breathing & a pulse returns
Remember – spontaneous breathing takes longer to return than the pulse so continued respiratory support may be necessary
The casualty regains consciousness
If the casualty recovers, monitor the ECG, (using the Viatom) pulse, BP, oxygen saturation and respiration, as it will provide early warning if they start to deteriorate again.
2). Practicalities:
You are too exhausted to continue
CPR cannot be continued during the evacuation (less of a problem if the AutoPulse is used)
The area becomes unsafe
3). The casualty has died
CPR for 20 minutes (except in the case of hypothermia with no contraindications to starting CPR such as injuries incompatible with life)
Injuries become incompatible with life, e.g. prolonged severe bleeding
Before stopping, always make sure there are no treatable reversible causes e.g. hypoxia, severe hypothermia.
See the Resuscitation Decision Tree protocol to aid your decision making. This is in the back of the Cas Care book and also in all the Cas Card folders in the medical sac for use on the hill. If you decide to end CPR or do not start the Recognition Of Life Extinct (ROLE) Protocol will need to be completed. Again this protocol is at the back of the Cas Care book and also in all the Cas Card folders in the medical sac for use on the hill.
Signs and symptoms that a cardiac arrest is about to occur
Whilst cardiac arrest can strike without warning, there are also circumstances when it’s more likely to occur. Being prepared to react quickly in these situations can make the difference between life and death.
There is a higher risk of an arrest occurring:
after (or during) a myocardial infarction (Heart Attack)
when moving a severely hypothermic casualty
tension pneumothorax
drowning
when suffering from severe hypoglycemia
during prolonged fitting (due to lack of oxygen)
In these circumstance it is sensible to apply (but not connect) the defibrillator pads in case they become necessary. Monitor closely and ensure the AutoPulse is on scene and an i-gel and bag are to hand. Organise the Team into roles.
Watch for the most commonly observed symptoms preceding an arrest, shortness of breath with no other causes is the commonest symptom
chest pain
fainting (syncope)
cold sweat
casualty has a feeling that they are going to die
ECG Rhythms - for interest
Knowledge of ECG rhythms is useful, but not necessary for diagnosing and attempting to treat cardiac arrest. The AED will determine whether a rhythm is responsive to defibrillation for you and prompt you accordingly.
Below are examples of:
1) normal (sinus) rhythm;
2) the two most common shockable rhythms (ventricular fibrillation (known as VF) and ventricular tachycardia (known as VT); and °
3) no rhythm, called asystole (commonly known as flat line). Contrary to its common name, in individuals whose heart has recently stopped pumping, asystole will show as a flat, slightly undulating line, not a completely horizontal line as you see on TV.
CPR and defibrillation being done for real.
Note the following about this video:
Immediate call for help
Early CPR instituted (straight on the chest)
AED on chest as soon as available
Shock delivered
Uninterrupted CPR
Minimal off-chest time (only pauses for rhythm checks & delivering shock)
Each person can only do 2 minutes good quality CPR
ROSC means Return of Spontaneous Circulation
The man delivering the breaths is using an i-gel or similar plus Bag-Valve