Reversible causes for cardiac arrest mnemonic
Reading File
Finding Sources
Searching the Web
reversible causes cardiac arrest mnemonic 4H 4T
Reading File
Reading File
The classic mnemonic for reversible causes of cardiac arrest is the 4 Hs and 4 Ts (sometimes called 5 Hs and 5 Ts in expanded versions). These are particularly important when managing PEA (pulseless electrical activity) and asystole.
The 4 Hs and 4 Ts (AHA / Resuscitation Council)
🅷 The 4 Hs
| H | Cause | Key Action |
|---|---|---|
| Hypoxia | Most common non-cardiac cause of arrest | Ensure airway, high-flow O₂, ventilation |
| Hypovolemia | Hemorrhage, dehydration, distributive shock | IV fluids, blood products, stop bleeding |
| Hypo/Hyperkalemia (+ other electrolytes/metabolic) | K⁺ imbalance, acidosis (H⁺ ions), Ca²⁺ disorders | 12-lead ECG, electrolytes, correct metabolic derangement |
| Hypothermia | Core temp <30°C can cause refractory VF | Active rewarming ("not dead until warm and dead") |
🅣 The 4 Ts
| T | Cause | Key Action |
|---|---|---|
| Tension pneumothorax | Tracheal deviation, absent breath sounds, raised JVP | Needle decompression → chest drain |
| Tamponade (cardiac) | Beck's triad, muffled heart sounds, raised JVP | Pericardiocentesis |
| Toxins | Drug overdose (digoxin, β-blockers, CCBs, TCAs), poisoning | Antidotes, activated charcoal, supportive care |
| Thrombosis | Pulmonary embolism or coronary thrombosis (MI) | Thrombolytics / PPCI / surgical embolectomy |
Expanded Version: 5 Hs and 5 Ts
Some sources (including Miller's Anesthesia and the AHA algorithm) split thrombosis and/or electrolytes further:
| Extra | Cause |
|---|---|
| Hydrogen ions (acidosis) | Counted separately from electrolytes |
| Thrombosis – Pulmonary | PE |
| Thrombosis – Coronary | ACS/MI |
Quick Memory Aid
"Hot Docs Give Help" (less common) or simply remember:4 Hs: Hypoxia · Hypovolemia · Hypo/Hyperkalemia (+ H⁺ acidosis) · Hypothermia
4 Ts: Tension pneumo · Tamponade · Toxins · Thrombosis
These causes matter most in PEA and asystole — the non-shockable rhythms where identifying and correcting the underlying etiology is the primary treatment strategy, since no electrical shock is effective. VF/pulseless VT should also have these causes considered if refractory to defibrillation.
(Miller's Anesthesia, 10e — Pulseless Electrical Activity section; Goldman-Cecil Medicine — Asystole, Bradyarrhythmias, and PEA section)
This is a shared conversation. Sign in to Orris to start your own chat.