Automated external defibrillators (AED)

• in the UK coronary heart disease (CHD) remains one of the principle causes of death with more than 135,000 people dying each year following acute myocardial infarction:
  • about 2/3 of these deaths occur suddenly outside hospital and complicate the early stages of myocardial infarction
  • most deaths are due to ventricular fibrillation
• defibrillation by an electrical countershock from a defibrillator is the only treatment shown to be effective in the treatment of ventricular fibrillation. The crucial determinant of success is the time interval between the onset of the arrhythmia and the delivery of the countershock; survival falls by approximately 7-10% for every minute after collapse for patients in ventricular fibrillation. This time window can be extended by Basic Life Support
• the Automated External Defibrillator (AED) automates the process of ECG interpretation and preparation for administration of the defibrillatory shock. Little is required of the operator other than to recognise that cardiac arrest may have occurred and attach 2 adhesive electrodes to the chest wall of the casualty. The AED operator is guided through a programmed protocol by written instruction and audible voice prompts. If the AED's electronic algorithm detects a rhythm likely to respond to a defibrillator shock (ventricular fibrillation or tachycardia), it will charge itself to a pre-set level and indicate to the operator how it should be delivered. The AED incorporates recording facilitie for later playback and analysis for audit or training purposes
• there has been changes in the guidance regarding use of AEDs (2)
  • 1) the axillary electrode pad is placed vertically to improve efficiency
  • 2) if possible, continue CPR whilst the pads are being applied
  • 3) program AEDs to deliver a single shock followed by a pause of 2 min for the immediate resumption of CPR
  • sequence of actions when using an AED (2)
    • 1) make sure the victim, any bystanders, and you are safe
      • if two rescuers are present, assign tasks
    • 2) If the victim is unresponsive and not breathing normally:
      • send someone for the AED and to call for an ambulance
      • If you are on your own do this yourself; you may need to leave the victim
    • 3) Start CPR according to the guidelines for BLS
    • 4) As soon as the AED arrives:
      • switch on the AED and attach the electrode pads. If more than one rescuer is present, continue CPR whilst this is done. (Some AEDs may automatically switch on when the AED lid is opened)
      • follow the voice / visual prompts
      • ensure that nobody touches the victim whilst the AED is analysing the rhythm
    • 5a) if a shock is indicated:
      • ensure that nobody touches the victim
      • push the shock button as directed. (Fully-automatic AEDs will deliver the shock automatically)
      • continue as directed by the voice / visual prompt
    • 5 b) if no shock is indicated:
      • immediately resume CPR using a ratio of 30 compressions to 2 rescue breaths
      • continue as directed by the voice / visual prompts
    • 6) continue to follow the AED prompts until:
      • qualified help arrives and takes over,
      • the victim starts to breathe normally, or
      • you become exhausted

Notes:

• placement of AED pads:
  • place one AED pad to the right of the sternum, below the clavicle. The other pad is placed in the mid-axillary line, approximately level with the V6 ECG electrode position or the female breast. This position should be clear of any breast tissue. It is important that this electrode is placed sufficiently laterally. Place the mid-axillary pad with its long axis vertical in order to improve efficiency
  • although most AED pads are labelled left and right, or carry a picture of their correct placement, it does not matter if they are reversed. It is important to teach that if an ‘error’ is made, the pads should not be removed and replaced as this wastes time and they may well not adhere adequately when re-attached

Reference:

1. British Heart Foundation, Factfile 2/2001.
2. Resuscitation Council (UK). The use of Automated External Defibrillators - Resuscitation Guidelines 2005.