VOL: 98, ISSUE: 24, PAGE NO: 41
PHIL JEVON, RESUSCITATION OFFICER, MANOR HOSPITAL, WALSALL; CATHERINE BALDOCK, RESUSCITATION OFFICER, WALSGRAVE HOSPITAL, COVENTRY
Sponsored by PfizerA number of factors determine whether or not defibrillation will be successful. These include:
A number of factors determine whether or not defibrillation will be successful. These include:
- The time between cardiac arrest and defibrillation. A successful outcome is reduced by about 7-10% for each minute defibrillation is delayed (Cobbe et al., 1991) Defibrillation within three minutes is associated with an increased chance of survival (Gwinnutt et al., 2000)
- Placing the paddles in the correct position (see Part 1)
- The shock sequence: 200J, 300J and 360J, or their biphasic equivalents are recommended (Resuscitation Council (UK), 2000)
- Transthoracic impedance: this is reduced if shocks are delivered in close sequence and at the end of expiration. Transthoracic impedance is also reduced when defibrillation pads are used and adequate paddle pressure (10kg force) is applied.
Conventional defibrillators deliver current with monophasic waveforms - that is, the current flows from one paddle to the other in one direction. However, most modern defibrillators deliver current with biphasic waveforms - the current flows in a positive and then negative direction for a specified duration (Jevon, 2002). The main advantage of biphasic waveforms is that lower energy levels may be required, although currently there are no agreed optimum energy levels.