Cardiac Arrest & ACLS
Shock the shockable, hunt the H's and T's
High-quality CPR
C-A-B: compressions come first. Adult BLS order is Compressions, then Airway, then Breathing. Start chest compressions immediately on an unresponsive, pulseless patient without delaying for the airway, and attach an AED or defibrillator as soon as it arrives.
Push hard, push fast, let it recoil. Minimize interruptions and rotate compressors every 2 minutes, before fatigue degrades quality. Once an advanced airway is placed, compressions continue without pauses and one breath is given every 6 seconds; overventilation raises intrathoracic pressure and cuts venous return.
Minimize hands-off time. Survival tracks the chest-compression fraction: keep hands-on time above 60% by pre-charging the defibrillator, planning rhythm checks, and limiting pulse-check pauses to under 10 seconds. Every interruption drops coronary perfusion pressure and survival.
Rhythms, shocks, and drugs
Two shockable, two not. Pulseless arrest splits into SHOCKABLE rhythms (ventricular fibrillation and pulseless VT) and NON-shockable rhythms (pulseless electrical activity and asystole). Shockable rhythms get immediate defibrillation; non-shockable rhythms get CPR plus epinephrine, never a shock.
| Feature | Shockable: VF, pulseless VT | Non-shockable: PEA, asystole |
|---|---|---|
| First action | Unsynchronized shock, then 2 minutes of CPR | CPR |
| Epinephrine | After the second shock, then every 3–5 min | As soon as possible, then every 3–5 min |
| Antiarrhythmic | Amiodarone 300 mg, then 150 mg (or lidocaine) if refractory | None |
| Survival hinges on | Early defibrillation | Finding and fixing the cause |
Defibrillation. For VF or pulseless VT, early defibrillation is the single most important intervention and the strongest predictor of survival in a witnessed arrest; every minute of delay lowers survival. Deliver one unsynchronized biphasic shock (120–200 J, or the device maximum if the recommended dose is unknown), then immediately resume CPR for 2 minutes before rechecking the rhythm. Do not pause for a pulse check right after a shock. Synchronized cardioversion is for unstable tachycardia WITH a pulse, never for VF.
Epinephrine 1 mg IV/IO every 3–5 minutes in any arrest. Its α-agonism raises coronary and cerebral perfusion pressure during CPR. Vasopressin has been removed from the algorithm, leaving epinephrine as the sole vasopressor, and atropine is no longer used for asystole or PEA.
Amiodarone for shock-refractory VF. For VF or pulseless VT that persists after CPR, defibrillation, and epinephrine, give amiodarone 300 mg IV (then 150 mg), or lidocaine as an alternative. Antiarrhythmics are only for refractory shockable rhythms, not for PEA or asystole. Magnesium is reserved for torsades de pointes rather than given routinely.
Reversible causes: the H's and T's
PEA is a search for a cause. Search for reversible causes throughout every code. Because PEA and asystole cannot be shocked, fixing the underlying H or T is the only path to ROSC. Bedside ultrasound can reveal tamponade, an empty ventricle, or a dilated right ventricle.
| Cause | Clue | Fix |
|---|---|---|
| Hypovolemia | Bleeding, trauma, flat neck veins | Fluids or blood |
| Hypoxia | Respiratory arrest, airway obstruction | Oxygen, secure the airway |
| Hydrogen ion (acidosis) | DKA, renal failure, prolonged arrest | Ventilation; bicarbonate in selected cases |
| Hypo-/hyperkalemia | Dialysis patient, peaked T waves, wide QRS | Calcium, bicarbonate, insulin-glucose for hyperkalemia; replace potassium if low |
| Hypothermia | Cold exposure | Active rewarming |
| Toxins | Overdose history | Specific antidote (e.g., bicarbonate for tricyclics) |
| Tamponade | JVD, muffled heart sounds (Beck triad) | Pericardiocentesis |
| Tension pneumothorax | Absent breath sounds, tracheal deviation | Needle decompression |
| Thrombosis, coronary | Chest pain before collapse, STEMI | PCI |
| Thrombosis, pulmonary | Recent immobilization, JVD, clear lungs | Thrombolysis |
Monitoring during resuscitation
Capnography grades CPR and flags ROSC. Continuous waveform capnography confirms endotracheal tube placement and gauges compression quality; an end-tidal CO₂ below 10 mmHg during CPR calls for better compressions. An abrupt rise in ETCO₂ toward 35–40 mmHg signals return of spontaneous circulation (ROSC), because pulmonary blood flow has been restored. Persistent ETCO₂ under 10 mmHg after 20 minutes of CPR portends a poor outcome.
Post-cardiac arrest care
Cool the comatose survivor. After ROSC in a patient who does not follow commands, use targeted temperature management (TTM): hold a constant temperature between 32 and 37.5 °C for at least 24 hours with active fever prevention (AHA 2023), and keep preventing fever afterward. TTM improves neurologic outcome; a patient who is awake and following commands does not need it.
Post-arrest fever independently worsens neurologic outcome, so preventing hyperthermia matters as much as the exact target; the older 32–36 °C range was widened to 37.5 °C after trials showed fever prevention works as well as deeper cooling.
Open the artery, tune the physiology.
- Coronary: obtain a 12-lead ECG; emergent angiography and PCI for STEMI or a suspected cardiac cause.
- Oxygenation: SpO₂ 92–98%, avoiding both hypoxia and hyperoxia.
- Ventilation: normocapnia (PaCO₂ 35–45 mmHg); routine hyperventilation is harmful.
- Circulation: MAP at least 65 mmHg.
- Cause: treat the precipitating H or T.
Prognosis. Defer neurologic prognostication until at least 72 hours after return to normothermia, because sedation and cooling depress the exam.