4 J per kg and resume — shockable arrest

Structured clinical encounter — resuscitation leadership

This station tests whether the candidate leads a team to the right decision under time pressure, delivers the shock correctly, and runs the shockable-arrest algorithm without error. Marks reward confirming the rhythm and the pulse, the correct mode and dose, correct pad placement, immediate resumption of compressions, and the structured drug sequence. [1] [6]

Stem

An eight-year-old weighing 25 kilograms collapses in the waiting room while waiting to be seen. He had complained of chest discomfort an hour earlier. He is unresponsive and apnoeic. A nurse begins cardiopulmonary resuscitation. The monitor shows ventricular fibrillation. There is no pulse. The team looks to you. [1] [2]

Candidate tasks

1. Lead the rhythm and pulse assessment (2 minutes). Confirm ventricular fibrillation on the monitor and the absence of a pulse during a brief pause in compressions. State the rhythm and the decision aloud: shockable arrest, unsynchronised defibrillation. [1]
2. Select the mode and dose and place the pads (2 minutes). Select 4 joules per kilogram (100 joules). Confirm SYNC is off. Apply pads anterolateral or anteroposterior, firm and gel-coupled, not touching, clear of any device. [1] [3]
3. Deliver the shock and resume compressions (1 minute). Charge while compressions continue, call stand clear, confirm no contact, deliver, and resume cardiopulmonary resuscitation immediately without a pulse check. [1]
4. Run the shockable-arrest drug sequence (ongoing). After the second shock give adrenaline 10 micrograms per kilogram; after the third give amiodarone 5 milligrams per kilogram; reassess after each two-minute cycle. [1]

Examiners' discussion points

• Why unsynchronised and not synchronised? Ventricular fibrillation has no organised R wave to synchronise to, so an unsynchronised shock fires instantly; a synchronised machine would hunt for an R wave that does not exist and never fire. [1] [6]
• Why 4 joules per kilogram? The dose is weight-based to overcome the higher transthoracic impedance of children relative to their mass; it is the biphasic standard taught by the European Resuscitation Council and APLS, with the American Heart Association accepting an initial 2 to 4 joules per kilogram. [1] [3]
• Why resume compressions without a pulse check? The shock can stun the myocardium; the mechanical pump keeps the brain and coronaries perfused while the rhythm recovers, and the pulse is reassessed after the next two-minute cycle. [1]
• What if the child had a pulse and a perfusing tachyarrhythmia instead? The shock would be synchronised at 1 joule per kilogram escalating to 2 joules per kilogram, with SYNC on, to avoid an R-on-T shock. [1] [6]
• What if the child had symptomatic bradycardia unresponsive to adrenaline? Transcutaneous pacing at 80 to 100 per minute, increasing output to capture, with analgesia, as a bridge to a transvenous wire. [5]

Marking grid (out of 20)

Pitfalls the examiners will probe

Leaving SYNC on for ventricular fibrillation (the machine never fires); placing pads that touch on a small chest (use anteroposterior); pausing for a pulse check immediately after the shock; and forgetting adrenaline after the second shock or amiodarone after the third. Each is prevented by the structured algorithm and by calling the mode and the dose aloud. [1] [3]