- application of an electrical current across the heart to convert VF/VT -> sinus rhythm
- single most important modality for cardiac arrest management.
- likelihood of these rhythms reverting with defibrillation is inversely proportional to time.
- the chance of successful reversion declines at a rate of 7-10% per min from onset of VF.
- current pulse causes synchronous contraction of the heart muscle, hopefully allowing SR to occur following refractory period.
- capacitor (potential difference between plates of up to 8000V, energy released during discharge is proportional to the potential difference)
— 360J external defib
— 50J internal defib
- after first shock thoracic impedance is reduced -> second shock will deliver greater energy to the heart.
- energy at discharge is released in a waveform (monophasic or biphasic)
- voltage rises rapidly and then returns to baseline (0 -> +ve -> 0)
- voltage rises, then reverses its direction below baseline before returning to baseline (0 -> +ve -> 0 -> -ve -> 0)
- biphasics have been shown to defibrillate as effectively as monophasic but at a lower energy.
- smaller (more portable)
METHOD OF INSERTION AND/OR USE
- apply paddles to patients as directed
- ‘stand clear’
- pacemaker function
- synchronised or non-synchronised shocks
Suggested commands during CPR
- We are about to perform a 2 minute rhythm check
- Stand clear, continue compressions (charging)
- Stop CPR (rhythm check)
- Everyone clear (compression stands back with hands in air, “I’m clear”)
- (deliver shock) Shock delivered, start compressions
- DC more effective & less damaging than AC
- repeated shocks -> myocardial damage
- electrocution of members of resuscitation team
- biphasic less myocardial damage
- arcing to other metal (backs of GTN patches, implanted defibrillators)