Reversible Causes of Cardiac Arrest

Concept

In every cardiac arrest — especially non-shockable rhythms and those refractory to treatment — the team must identify and treat reversible causes, because many arrests will not respond until the underlying cause is corrected. These are memorised as the ‘4 Hs and 4 Ts’.

Applying Them

Each is actively considered and treated:

• oxygenate/ventilate (hypoxia)
• give fluids/blood and stop bleeding (hypovolaemia)
• correct potassium and metabolic abnormalities
• rewarm (hypothermia)
• decompress a tension pneumothorax
• drain a tamponade
• treat toxins (antidotes)
• address thrombosis (coronary — consider revascularisation; pulmonary embolism — consider thrombolysis).

WHY They Matter

The reversible causes deserve their prominent place in resuscitation because, unlike the drugs and shocks that support the circulation, correcting them can actually reverse the arrest: a tension pneumothorax relieved by decompression, a massive haemorrhage treated by transfusion and surgical control, a severe hyperkalaemia corrected, or a major pulmonary embolus thrombolysed can all restore a circulation that would otherwise never return. This is especially true of the non-shockable rhythms, in which there is no chaotic electrical activity to defibrillate and the arrest is usually the end-result of a profound physiological insult, so the systematic search for and treatment of the four Hs and four Ts is often the only route to a successful outcome.

Systematically exclude all eight during every resuscitation.

• Always seek & treat reversible causes in arrest — the 4 Hs & 4 Ts.
• 4 Hs: Hypoxia, Hypovolaemia, Hypo-/hyperkalaemia & metabolic, Hypothermia.
• 4 Ts: Tension pneumothorax, Tamponade, Toxins, Thrombosis (coronary/pulmonary).
• Treat each specifically (oxygenate, fluids, correct K⁺, rewarm, decompress, drain, antidote, revascularise/thrombolyse).