If someone’s heart stops, their chances of survival are greatly increased if they receive good CPR and early defibrillation.
An AED is a device that gives a high energy electric shock to the heart.
Defibrillation is the passage of an electrical current across the myocardium to depolarise a critical mass of heart muscle simultaneously, enabling the natural “pacemaker” tissue to resume control.
Following the onset of ventricular fibrillation (VF) or pulseless ventricular tachycardia (pVT) cardiac output ceases and cerebral hypoxic injury starts within 3 minutes.
In VF the ventricular myocardium depolarises randomly.
The ECG shows rapid bizarre irregular waves, of widely varying frequency and amplitude.
Ventricular Tachycardia, particularly at higher rates or when left ventricle is compromised, may cause profound loss of cardiac output.
Pulseless VT is managed in the same way as VF.
The ECG shows a broad, complex tachycardia.
In monomorphic VT (showing little or no variation) the rhythm is regular (or almost regular) at a rate of 100-300 bpm.
Successful defibrillation is defined as absence or VF or pVT at 5 seconds after shock delivery, although the ultimate goal is Recognition Of Spontaneous Circulation (ROSC).
Ensure there is good contact with the skin.
AED Prep Kit
For adults, place one pad on the right side of the chest, just below the collarbone (mid clavicular). Place the other pad on the lower left side of the chest (mid axiliar)
Check manufacturers guidelines for your AED
For all cardiac arrests start CPR and use the AED to assess the rhythm as soon as it arrives:
The aim is to ensure that chest compressions are performed continuously throughout the resus attempt, pausing briefly only to enable specific interventions. Every 5 second increase in the pre-shock pause (analysing stage) almost halves the chance of successful defibrillation. Consequently defibrillation must always be performed quickly and efficiently in order to maximise the chances of ROSC
Do not deliver a shock if anyone is touching the patient
Do not touch any equipment such as IV stands or beds when a shock is being administered
Safe use of oxygen during defibrillation
Sparks in an oxygen rich environment can cause a fire – although no fires have been reported in association with the use of self adhesive pads.
However, we should still take thorough precautions to minimise risk
Can I use an AED on a patient who has a pacemaker?
When a patient needs external defibrillation, effective measures to try to restore life take priority over concerns about any implanted device such as a pacemaker, implantable cardioverter defibrillator (ICD), implantable events recorder or neurostimulator.
Current Resus Council (UK) guidelines are followed, but awareness of the presence of an implanted device allow some additional measures to optimise outcome:
During a shockable rhythm, external defibrillation should be attempted in the usual way.
Start CPR as explained in the previous lesson.
Watch this video to see how to perform CPR and use an AED on an adult:
Most AED’s have either paediatric pads to attach to the chest or a paediatric setting which reduces the size of the shock delivered.
The reason that children’s pads are smaller and placed in a different position is to obtain the correct transthoracic impedence
NOTE: For babies under 1 year check manufacturers guidelines before using an AED