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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- Cardiac arrest = unresponsive + no normal breathing + no definite pulse within 10 seconds.
- First actions: activate emergency response, start high-quality CPR, attach defibrillator/monitor, give oxygen, and establish IV/IO access.
- Shockable rhythms are VF and pulseless VT: defibrillate immediately, then resume CPR without a pulse check.
- Non-shockable rhythms are PEA and asystole: CPR plus epinephrine every 3-5 minutes; defibrillation is not useful.
- Search for Hs and Ts: hypovolemia, hypoxia, hydrogen ion acidosis, hypo/hyperkalemia, hypothermia; tension pneumothorax, tamponade, toxins, thrombosis pulmonary/coronary.
Overview
Cardiac arrest is abrupt cessation of effective circulation. Adult ACLS divides management into shockable rhythms (ventricular fibrillation and pulseless ventricular tachycardia) and non-shockable rhythms (pulseless electrical activity and asystole). The survival-critical interventions are early recognition, high-quality chest compressions, early defibrillation when appropriate, minimization of interruptions, and correction of reversible causes. Rhythm checks occur every 2 minutes and pulse checks should be brief.
Epidemiology
Out-of-hospital cardiac arrest affects hundreds of thousands of adults each year in the United States. Survival is highest when the arrest is witnessed, bystander CPR begins immediately, defibrillation is early, and the presenting rhythm is VF/pVT. Common causes include acute coronary occlusion, respiratory failure, pulmonary embolism, severe electrolyte disturbance, toxicologic exposure, trauma, drowning, hypothermia, and sepsis.
Clinical Features
Symptoms
Sudden collapse with loss of responsiveness
Absent normal breathing or agonal gasps
No definite carotid or femoral pulse within 10 seconds
Preceding chest pain, dyspnea, palpitations, syncope, overdose, trauma, seizure, or drowning history
Post-ROSC coma, hypotension, recurrent arrhythmia, or respiratory failure
Signs
VF/pVT on monitor: chaotic ventricular activity or wide-complex tachycardia without pulse
PEA: organized electrical activity without palpable pulse
Asystole: near-flatline; confirm in two leads and check monitor connection/gain
Signs of reversible cause: unilateral absent breath sounds, JVD, hemorrhage, track marks, hypothermia, or hyperkalemic ECG changes
ROSC signs: sudden rise in end-tidal CO2, palpable pulse, blood pressure, or purposeful movement
Investigations
First-line
Cardiac monitor / defibrillator rhythm assessmentClassify as shockable (VF/pVT) or non-shockable (PEA/asystole). Do not delay compressions for prolonged interpretation.
Pulse checkCheck carotid or femoral pulse for no more than 10 seconds during rhythm check; if uncertain, resume CPR.
End-tidal CO2Confirms advanced airway placement and reflects CPR quality. Abrupt rise suggests ROSC.
Point-of-care glucoseRapidly identify hypoglycemia as a reversible contributor to altered mental status or peri-arrest state.
Second-line
Point-of-care ultrasoundUse only during pulse checks. Evaluate tamponade, RV strain, severe hypovolemia, pneumothorax, and cardiac standstill without prolonging pauses.
Blood gas and electrolytesAssess acidosis, hyperkalemia, hypoxia, and ventilation after airway placement; do not delay ACLS.
12-lead ECG after ROSCIdentify STEMI or ischemia; STEMI after ROSC requires urgent coronary angiography.
Specialist
Post-arrest ICU evaluationTemperature control/fever prevention, coronary evaluation, CT head if neurologic cause suspected, EEG if coma/seizures, serial lactate and organ support.
1
High-quality CPR and BLS foundation
- Start compressions immediately: rate 100-120/min, depth 2-2.4 inches, full recoil, minimal pauses.
- Compression-to-ventilation ratio 30:2 until advanced airway; after advanced airway, continuous compressions with 1 breath every 6 seconds.
- Rotate compressor every 2 minutes or sooner if fatigued.
- Attach defibrillator/monitor as soon as available.
- Avoid hyperventilation, prolonged pulse checks, and unnecessary pauses.
2
Shockable rhythm: VF / pulseless VT
- Defibrillate immediately; use biphasic energy per manufacturer, commonly 120-200 J, and escalate if needed.
- Resume CPR immediately after shock for 2 minutes before rhythm/pulse check.
- Epinephrine 1 mg IV/IO every 3-5 minutes after the second shock.
- Amiodarone 300 mg IV/IO after the third shock, then 150 mg if refractory; lidocaine is an alternative.
- Magnesium sulfate 2 g IV for torsades de pointes or suspected hypomagnesemia.
3
Non-shockable rhythm: PEA / asystole
- Do not defibrillate asystole or PEA.
- CPR immediately and epinephrine 1 mg IV/IO as soon as possible, then every 3-5 minutes.
- Check rhythm every 2 minutes; if rhythm becomes shockable, switch to VF/pVT pathway.
- Confirm true asystole in two leads; check cable connection and monitor gain.
- Aggressively search for and correct Hs and Ts.
4
Post-ROSC care
- Optimize oxygenation and ventilation; avoid hypoxemia, hyperoxia, and hyperventilation when possible.
- Treat hypotension with IV fluids and vasopressors to maintain adequate perfusion.
- Obtain 12-lead ECG and pursue emergent coronary angiography for STEMI or strong suspicion of coronary occlusion.
- Prevent fever and consider targeted temperature management for comatose adult survivors.
- ICU care with delayed neurologic prognostication until confounders resolve.
Complications
- Hypoxic-ischemic brain injury: Major determinant of long-term outcome after ROSC
- Recurrent arrest: Ongoing ischemia, electrolyte disturbance, hypoxia, or shock can cause re-arrest
- Rib and sternal fractures: Common after high-quality compressions; do not stop CPR solely because of suspected fracture
- Aspiration and ARDS: Common after prolonged arrest, drowning, or overdose
- Post-cardiac arrest syndrome: Myocardial stunning, systemic inflammation, vasoplegia, and multi-organ dysfunction
USMLE Step 2 CK Exam Tips
- 1VF/pulseless VT = shock first. PEA/asystole = CPR + epinephrine, no shock.
- 2Epinephrine in VF/pVT is given after the second shock; in PEA/asystole give it as soon as possible.
- 3Amiodarone is for refractory VF/pVT, not asystole.
- 4Asystole must be confirmed in two leads and with monitor/cable/gain check.
- 5Abrupt rise in end-tidal CO2 during CPR is a clue for ROSC.
- 6Do not pause CPR for ultrasound, intubation, IV placement, or prolonged pulse checks.
- 7Torsades with arrest = defibrillation plus magnesium.
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