Defibrillators
USES
- application of an electrical current across the heart to convert VF/VT -> sinus rhythm
DESCRIPTION
- 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)
Monophasic
- voltage rises rapidly and then returns to baseline (0 -> +ve -> 0)
Biphasic
- 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)
- cheaper
METHOD OF INSERTION AND/OR USE
- apply paddles to patients as directed
- charge
- ‘stand clear’
- discharge
OTHER INFORMATION
- 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
COMPLICATIONS
- DC more effective & less damaging than AC
- repeated shocks -> myocardial damage
- electrocution of members of resuscitation team
- biphasic less myocardial damage
- burns
- arcing to other metal (backs of GTN patches, implanted defibrillators)
Critical Care
Compendium
Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.
After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.
He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.
His one great achievement is being the father of three amazing children.
On Twitter, he is @precordialthump.
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