2.1 Adult Cardiac Arrest & ACLS Pharmacotherapy Protocols

2.1 Adult Cardiac Arrest & ACLS Pharmacotherapy Protocols

Sudden cardiac arrest represents one of the most critical clinical emergencies encountered by emergency medicine pharmacists. Resuscitation outcomes hinge on high-quality cardiopulmonary resuscitation (CPR), rapid rhythm analysis, timely defibrillation, and evidence-based pharmacotherapeutic interventions. Pharmacists on resuscitation teams must rapidly differentiate between shockable and non-shockable arrest pathways, prepare and administer critical vasoactive and antiarrhythmic agents, anticipate line compatibility challenges, and systematically investigate reversible etiologies.

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Rhythm Stratification: Shockable vs. Non-Shockable Pathways

Adult cardiac arrest rhythms fall into two distinct therapeutic categories:

1. Shockable Rhythms: Ventricular Fibrillation (VF) and Pulseless Ventricular Tachycardia (pVT). The primary intervention is immediate, unsynchronized electrical defibrillation paired with uninterrupted cycles of high-quality CPR (compression rate 100–120 bpm, depth 2–2.4 inches, complete chest recoil, minimizing hands-off time to <10 seconds). Pharmacotherapy serves an adjunctive role to facilitate successful defibrillation and prevent recurrent arrhythmia.
2. Non-Shockable Rhythms: Pulseless Electrical Activity (PEA) and Asystole. Defibrillation is ineffective and contraindicated. Resuscitation centers on continuous high-quality CPR, early vasoactive support, and rapid identification and reversal of underlying physiological derangements.

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Epinephrine Pharmacotherapy & Administration Timing

Epinephrine is the primary vasopressor utilized in adult cardiac arrest. It acts as a non-selective agonist at alpha-1, alpha-2, beta-1, and beta-2 adrenergic receptors. In cardiac arrest, its beneficial therapeutic effect is mediated predominantly through alpha-1 adrenergic peripheral vasoconstriction, which elevates systemic vascular resistance, increases aortic diastolic pressure, and augments coronary perfusion pressure (CPP). A CPP threshold of $\ge 15\text{ to }20\text{ mmHg}$ during resuscitation is strongly correlated with achieving return of spontaneous circulation (ROSC).

Standard Dosing & Route

• Dose: 1 mg IV/IO (10 mL of 0.1 mg/mL [1:10,000] solution) administered every 3 to 5 minutes.
• Administration: Administer via rapid IV/IO push, immediately followed by a 20 mL 0.9% sodium chloride flush and brief extremity elevation to accelerate central venous transit.

Timing Nuances: Shockable vs. Non-Shockable Rhythms

The clinical timing of initial epinephrine administration differs substantially based on presenting rhythm:

• Non-Shockable Rhythms (PEA/Asystole): Administer epinephrine as soon as vascular access is established. Large observational registries and clinical trial data (including the PARAMEDIC-2 trial) demonstrate that earlier epinephrine administration (within 3 to 5 minutes of arrest onset) is associated with higher rates of ROSC, survival to hospital admission, and survival to hospital discharge in non-shockable arrest.
• Shockable Rhythms (VF/pVT): Withhold epinephrine initially! The first-line interventions are immediate defibrillation and CPR. Epinephrine is administered after the second defibrillation shock (during the second cycle of CPR) if VF/pVT persists, and every 3 to 5 minutes thereafter. Early epinephrine administration before initial shocks can stimulate beta-1 adrenergic receptors, increasing myocardial oxygen consumption, worsening subendocardial ischemia, and triggering recurrent refractory ventricular dysrhythmias.

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Antiarrhythmic Therapy in Shock-Refractory VF/pVT

Antiarrhythmic pharmacotherapy is indicated for shock-refractory VF or pulseless VT—defined as ventricular dysrhythmias that persist or recur after at least two defibrillation shocks and at least one dose of epinephrine.

Amiodarone

• Mechanism: Class III antiarrhythmic with broad electropharmacologic effects: blocks potassium outward channels (prolonging action potential duration and effective refractory period), blocks fast inward sodium channels (Class I effect), inhibits L-type calcium channels (Class IV effect), and produces non-competitive alpha- and beta-adrenergic blockade (Class II effect).
• ACLS Dosing:
  • First Dose: 300 mg IV/IO rapid push (diluted in 20 to 30 mL of D5W or 0.9% NaCl, or given undiluted).
  • Second Dose: 150 mg IV/IO rapid push after 3 to 5 minutes if VF/pVT persists.
• Formulation Considerations: Conventional amiodarone intravenous solutions contain polysorbate 80 and benzyl alcohol as solubilizing excipients, which produce peripheral vasodilation and negative inotropy upon ROSC. Aqueous amiodarone formulations (using sulfobutylether beta-cyclodextrin/captisol) eliminate these cosolvent-induced hemodynamic depressions.

Lidocaine

• Mechanism: Class Ib antiarrhythmic that selectively binds to and blocks fast inward voltage-gated sodium channels in phase 0 of the cardiac action potential. It preferentially binds to open and inactivated channels in ischemic, depolarized, or rapidly firing ventricular myocardium.
• ACLS Dosing:
  • Initial Bolus: 1 to 1.5 mg/kg IV/IO rapid push.
  • Repeat Bolus: 0.5 to 0.75 mg/kg IV/IO every 5 to 10 minutes for refractory VF/pVT, up to a maximum cumulative dose of 3 mg/kg.
  • Post-ROSC Maintenance: 1 to 4 mg/min continuous IV infusion if lidocaine successfully terminated the arrest rhythm.

Amiodarone vs. Lidocaine: The ALPS Trial

The randomized, double-blind ALPS trial (Resuscitation Outcomes Consortium) compared amiodarone, lidocaine, and placebo in adult shock-refractory out-of-hospital cardiac arrest (OHCA). The trial demonstrated that neither amiodarone nor lidocaine showed a statistically significant difference in survival to hospital discharge or favorable neurological outcome compared to placebo overall. However, in the prespecified subgroup of witnessed cardiac arrests, both active antiarrhythmics demonstrated significantly higher rates of hospital survival compared to placebo. The 2025 AHA guidelines state that amiodarone or lidocaine may be considered for shock-refractory VF/pVT (Class 2b); routine calcium, sodium bicarbonate and magnesium are not recommended (Class 3: No Benefit), and steroids are of uncertain benefit.

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Summary Matrix: ACLS Cardiac Arrest Pharmacotherapy

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Targeted Electrolyte and Buffer Therapies

Magnesium Sulfate

Magnesium acts as an essential cofactor for the sodium-potassium ATPase pump and regulates inward calcium flux through L-type channels. In cardiac arrest, magnesium sulfate is indicated exclusively for Torsades de Pointes (polymorphic VT associated with baseline prolonged QTc) or confirmed severe hypomagnesemia. The recommended dose is 1 to 2 g IV/IO push diluted in 10 mL of D5W or 0.9% NaCl over 1 to 2 minutes. Routine administration in undifferentiated cardiac arrest or monomorphic VF has been evaluated in randomized clinical trials and showed zero improvement in ROSC or hospital survival.

Sodium Bicarbonate

Routine administration of sodium bicarbonate in cardiac arrest is not recommended and may cause significant physiological harm:

1. Paradoxical Intracellular Acidosis: Exogenous bicarbonate buffers hydrogen ions to produce carbonic acid, which dissociates into water and carbon dioxide ($CO_2$). Lipophilic $CO_2$ diffuses rapidly across myocardial and cerebral cell membranes, whereas charged bicarbonate remains extracellular, paradoxically worsening intracellular and cerebral acidosis.
2. Impaired Oxygen Delivery: Alkalinization shifts the oxyhemoglobin dissociation curve to the left, impairing oxygen release at ischemic capillary beds.
3. Hyperosmolality & Hypernatremia: Standard 8.4% sodium bicarbonate is severely hypertonic (2,000 mOsm/L; 1 mEq/mL sodium and bicarbonate).

Specific Legitimate Indications:

• Preexisting documented severe metabolic acidosis (e.g., diabetic ketoacidosis, prolonged downtime with severe lactic acidosis).
• Severe preexisting hyperkalemia.
• Overdose of sodium-channel blocking medications (tricyclic antidepressants, flecainide, quinidine, cocaine).
• Dose: 1 mEq/kg IV/IO push (typically 50 to 100 mEq).

Calcium Formulations: Chloride vs. Gluconate

Routine calcium administration in cardiac arrest increases ischemic cell death by exacerbating intracellular calcium overload, activating lytic proteases, and uncoupling mitochondrial oxidative phosphorylation upon reperfusion.

Specific Legitimate Indications:

• Documented or strongly suspected severe hyperkalemia.
• Severe hypocalcemia (e.g., following massive transfusion secondary to citrate toxicity).
• Severe hypermagnesemia.
• Severe calcium channel blocker overdose.

Formulation Comparison:

• Calcium Chloride 10%: Contains 100 mg/mL of calcium chloride dihydrate ($1\text{ g} = 13.6\text{ mEq} = 272\text{ mg}$ elemental calcium). Because it delivers more calcium per milliliter, it is usually chosen when calcium is indicated during arrest, through a central line or a well-running large vein.
• Calcium Gluconate 10%: Contains 100 mg/mL of calcium gluconate ($1\text{ g} = 4.65\text{ mEq} = 93\text{ mg}$ elemental calcium), roughly one-third the elemental calcium of the chloride salt per gram, so about 3 g of gluconate matches 1 g of chloride. The old teaching that gluconate needs the liver to release its calcium is wrong: both salts ionize rapidly. Gluconate is preferred for peripheral administration because it is far less irritating if it extravasates.

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Reversible Causes: The Hs and Ts Framework

During CPR, the emergency medicine pharmacist must systematically assess and recommend pharmacologic reversals for the reversible causes of arrest:

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Pharmacotherapy-Specific Reversal Strategies

• Hyperkalemia: Calcium chloride 1 g IV push (membrane stabilization) + Sodium bicarbonate 50 to 100 mEq IV push + Regular insulin 10 units IV with 25 g D50W (intracellular shifting).
• Local Anesthetic Systemic Toxicity (LAST): 20% intravenous lipid emulsion (ILE) bolus 1.5 mL/kg over 2 to 3 minutes (about 100 mL in patients over 70 kg), followed by 0.25 mL/kg/min; repeat the bolus and double the infusion to 0.5 mL/kg/min if instability persists, up to about 12 mL/kg (ASRA 2020 checklist).
• Suspected Massive Pulmonary Embolism: If cardiac arrest is caused by documented or highly suspected pulmonary embolism, administer intravenous tenecteplase (weight-based bolus) or alteplase (50 mg IV push, may repeat 50 mg in 15 minutes). Once a fibrinolytic is given, continue CPR long enough for it to work: European Resuscitation Council guidance suggests considering 60 to 90 minutes of CPR after fibrinolytic administration.