Understanding defibrillators

The most common cause for the heart to stop (cardiac arrest) is a heart attack, though it is worth noting that a heart attack does not always cause a cardiac arrest. The majority of people who suffer a heart attack stay conscious and survive. Sudden cardiac arrest (SCA) however, can happen at any time and can affect anyone. If a heart attack results in a cardiac arrest, it is usually because it has interrupted the heart’s own electrical impulses, causing the heart to act chaotically (VF or VT) instead of beating in a rhythm. 

If a casualty suffers a cardiac arrest, there is a sequence of events that must happen in order for them to stand a chance of survival. This is known as the chain of survival.

The heart

The heart is a cone-shaped, hollow muscular organ, and is the only muscle that can create its own electrical impulses. The two top chambers of the heart (atria) collect blood from the two largest veins in the body and squeeze it into the chambers below (ventricles). The heart has its own primary pacemaker, situated at the top right-hand side, which fires electrical impulses through the atria first, making them contract. They then pass through the ventricles, causing them to contract, which pumps the blood out of the heart. The cells recharge, ready for the next wave of electricity. 

The AED will analyse the heart’s rhythm, which is likely to be; normal (normal sinus rhythm), ventricular fibrillation (VF), ventricular tachycardia (VT), no activity (asystole).

In an asystole reading the heart is still. There is no electrical activity at all and occurs after the heart has run out of oxygen. This is commonly referred to as ‘flatline’. The AED cannot deliver a shock because the heart has stopped.

The AED can only work if the heart is in a shockable rhythm. The defibrillation shock does not jump-start a heart once it has stopped. The shock is designed to make the heart’s electrical cells recharge, which can stop the fibrillation and brings the heart to a standstill. Once fibrillation is stopped, the heart’s pacemaker should send impulses once again. Maybe the best way of describing it is as similar to rebooting a computer.

Who can use an AED?

The Resuscitation Council (UK) recommends ‘All healthcare professionals should consider the use of an AED to be an integral component of BLS. Untrained employees working in healthcare establishments should not be prevented from using an AED if they are confronted with a patient in cardiac arrest. The administration of a defibrillatory shock should not be delayed while waiting for trained personnel to arrive.

‘An AED can be used safely and effectively without previous training. Therefore, the use of an AED should not be restricted to trained rescuers. However, training should be encouraged to help improve correct pad placement.’ 

Types of AED

Although AEDs are designed to do the same thing, they can vary in design, colour, size, number of buttons and use of voice prompt language. If you are considering obtaining an AED, the following may be useful when making a decision:

  • Buttons – While some AEDs only have one button that will deliver the shock, some units can have up to three
  • Size – AEDs are about the size of a small laptop computer and can weigh approximately 2kg. Units have either a carrying handle attached or come in a carry case
  • Electrodes – These are stored with the AED and are wrapped in foil. Some AEDs have the electrodes already attached, while others are separate and need connecting once the AED is switched on. The electrodes have a shelf life of around two years
  • Battery – Most AEDs have a lithium battery that needs replacing every two-seven years depending on the unit
  • Status indicator – Most AEDs have some form of status indicator, which shows that the machine is ready for use. AEDs perform a variety of daily, weekly and monthly self-checks to ensure battery levels are OK, that electrodes are attached properly, that software isn’t malfunctioning and whether a service is due or not. The AED will flash or beep to indicate that a fault has been located.

Step by step

  1. Make sure that the casualty, bystanders, and you are safe
  2. Check for a response. If no response, shout for help
  3. Carefully open the airway by using ‘head tilt’ and ‘chin lift’
  4. Keep the airway open, look, listen and feel to see if the breathing is normal
  5. If the casualty is breathing normally place them into the recovery position. If the casualty is not breathing normally…
  6. If you are on your own, call the emergency services and get the AED
  7. If you have help – start CPR immediately while your helper calls the emergency services and get the AED. If there is anyone else available, send them for the oxygen and breathing apparatus
  8. Continue CPR using a ratio of 30 compressions to two inflations until the AED arrives
  9. Switch on the AED immediately and follow the prompts
  10. Attach the pads to the casualty’s bare chest while the other rescuer(s) continue CPR if possible
  11. Peel one pad from the plastic backing and place it to the right of the sternum (breast bone) just below the casualty’s right clavicle (collarbone) as shown on the pad
  12. Peel the second pad from the backing and place on the lower chest wall on the left, just below the apex of the heart
  13. While the AED analyses the rhythm stop CPR and ensure no one is touching the casualty. If a shock is advised…
  14. Ensure that nobody touches the casualty. The AED will take a few seconds to fully charge. Shout: ‘Stay clear’
  15. Once the AED advises you to press the button to deliver the shock check the casualty to ensure everyone is clear, shout: ‘Shocking now,’ and press the button
  16. Continue as directed by the voice/visual prompts
  17. Minimise interruptions to chest compressions
  18. If a shock is not advised…Immediately resume CPR using the ratio of 30 compressions to two inflations. Continue as directed by the voice/visual prompts until qualified help arrives and takes over, the casualty shows signs of regaining consciousness and starts to breath normally, or you become exhausted.

These instructions follow the latest Resuscitation Council (UK) guidelines published in October 2010. Some older AEDs (pre 2006) may use older guidelines. If your AED follows older guidelines it is still acceptable to use it as defibrillation using older guidelines is better than no defibrillation at all.

Wendy Berridge delivers CPR, medical emergencies and AED (defibrillation) training to dental practices throughout Yorkshire and Lincolnshire.

Contact details: Email: [email protected]; Telephone: 07771590513; Website: www.berridgemedicaltraining.com.

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