Cardiac arrest Study Guide

📖 Core Concepts Cardiac arrest = abrupt loss of effective heart pumping → no pulse, no meaningful blood flow → brain ischemia → loss of consciousness within seconds. Shockable vs non‑shockable rhythms: Shockable: ventricular fibrillation (VF) & pulseless ventricular tachycardia (pVT). Non‑shockable: pulseless electrical activity (PEA) & asystole. Chain of Survival – early recognition → by‑stander CPR → rapid defibrillation → advanced life support → post‑resuscitation care. Hs and Ts – mnemonic for reversible causes (hypovolemia, hypoxia, acidosis, …, tension pneumothorax, tamponade, thrombosis, trauma). Return of Spontaneous Circulation (ROSC) – restoration of a palpable pulse & measurable blood pressure; the primary goal of resuscitation. 📌 Must Remember Incidence: ≈ 535 k arrests/yr in the U.S. (13/10 000); 61 % out‑of‑hospital, 39 % in‑hospital. Survival: Out‑of‑hospital ≈ 10 %; in‑hospital ≈ 22 % to discharge. Compression quality: 100‑120 /min, depth 5‑6 cm, full recoil, minimize pauses (<10 s). Epinephrine dose: 1 mg IV/IO every 3‑5 min (adult). Amiodarone regimen: 300 mg rapid IV bolus → 150 mg (or 600 mg total) if needed. Defibrillation energy: biphasic 150 J (adult) first shock; monophasic 200‑360 J if biphasic unavailable. Targeted Temperature Management: cool to 32‑36 °C for 24 h, then rewarm over 12‑24 h. ICD indication: LVEF ≤ 30 % in severe ischemic cardiomyopathy or other high‑risk criteria. 🔄 Key Processes Basic Life Support (BLS) Cycle 30 compressions → 2 rescue breaths (or continuous compressions if no breaths). Re‑assess rhythm every 2 min; deliver shock if VF/pVT. Advanced Cardiac Life Support (ACLS) Algorithm Identify rhythm → Shockable? Defibrillate, then resume CPR, repeat every 2 min. Non‑shockable? Give epinephrine 1 mg q3‑5 min, continue CPR, consider reversible causes (Hs/Ts). After ROSC → airway protection, hemodynamic optimization, TTM, coronary angiography if indicated. Medication Timing Epinephrine: after the first 2‑min CPR cycle (or after first shock if shockable). Amiodarone/Lidocaine: after the third unsuccessful shock for VF/pVT. Sodium bicarbonate: only for confirmed severe acidosis, hyper‑K⁺, or specific toxics. 🔍 Key Comparisons VF vs VT (pulseless) VF: chaotic, no organized QRS; immediate shock required. VT: wide‑complex, rate > 100 bpm; may be perfusing (rare) or pulseless → shock. Biphasic vs Monophasic Defibrillators Biphasic: lower energy, higher first‑shock success, standard of care. Monophasic: higher energy needed, less efficient. Epinephrine vs Vasopressin Epinephrine: proven to increase ROSC; no neurologic benefit advantage. Vasopressin: no outcome superiority alone; may help in combination with steroids. Amiodarone vs Lidocaine Amiodarone: preferred for refractory VF/pVT; improves ROSC admission rates. Lidocaine: alternative when amiodarone unavailable; similar ROSC, no mortality benefit. ⚠️ Common Misunderstandings “More epinephrine = better outcome” – higher than 1 mg does not improve survival and may worsen neurologic recovery. “All cardiac arrests need intubation” – routine ET tube does not improve survival; bag‑valve‑mask or supraglottic airway is acceptable. “Defibrillation works for any rhythm” – only VF and pulseless VT are shockable; PEA/asystole require CPR & meds. “Heart attack = cardiac arrest” – MI is a cause of arrest; arrest is the loss of circulation. 🧠 Mental Models / Intuition “The 5‑minute rule” – every minute without CPR/defibrillation ≈ 10 % drop in survival → act fast. “Shock first, then meds” – if rhythm is shockable, shock ASAP, then resume CPR; drugs come after the first shock cycle. “Hs and Ts = look‑aside checklist” – when ROSC not achieved, mentally run through reversible causes before adding more meds. 🚩 Exceptions & Edge Cases Pre‑cordial thump – only for witnessed, monitored unstable VT when a defibrillator is unavailable; never for unwitnessed out‑of‑hospital arrests. Pediatric arrests – most common cause is respiratory failure → focus on ventilation; compress depth = 1/3 chest depth, rate 100‑120/min. Pregnancy – shift hand position slightly upward & left uterine displacement to relieve aortocaval compression. Temperature management – avoid initiating TTM in the pre‑hospital setting unless protocols explicitly allow (risk of re‑arrest). 📍 When to Use Which Defibrillator type – use biphasic AED/monitor whenever available; monophasic only if no biphasic present. Medication choice – VF/pVT refractory: first amiodarone 300 mg, second 150 mg → if unavailable, lidocaine 1‑1.5 mg/kg. Asystole/PEA: epinephrine 1 mg q3‑5 min; consider vasopressin + methylpred if protocol allows. Torsades de pointes: magnesium sulfate 2 g IV. Airway device – bag‑valve‑mask or supraglottic airway if intubation would pause compressions > 10 s. 👀 Patterns to Recognize Sudden loss of pulse + agonal breathing → immediate CPR & rhythm check. Wide‑complex tachycardia on monitor → consider pulseless VT → shock. Flat ECG with no activity → asystole → continue high‑quality CPR, epinephrine, look for reversible causes. Hyper‑kalemia labs + arrest → give calcium chloride and consider sodium bicarbonate. 🗂️ Exam Traps “Give epinephrine every minute” – guideline is every 3‑5 min, not every minute. “Defibrillation energy is always 200 J” – modern biphasic devices use 150 J (adult). “All cardiac arrests need atropine” – atropine is not recommended for PEA/asystole. “IV amiodarone dose is 300 mg total” – first dose 300 mg, second dose 150 mg (or 600 mg total if using the 2‑dose scheme). “Cooling below 32 °C improves outcome” – target is 32‑36 °C; deeper hypothermia lacks proven benefit and may cause harm. --- Keep this guide handy for quick recall before your exam – it condenses the highest‑yield facts, steps, and pitfalls for cardiac arrest assessment and management.