Drugs Used in Shock - Shocking Start!
Shock: critical circulatory failure causing tissue hypoperfusion. Early goal-directed therapy is key; target Mean Arterial Pressure (MAP) often >65 mmHg.
Types of Shock & Primary Hemodynamic Problem:
| Shock Type | Primary Problem | Example(s) |
|---|---|---|
| Hypovolemic | ↓ Preload (↓ circulating volume) | Hemorrhage, Dehydration |
| Cardiogenic | ↓ Contractility (pump failure) | MI, Arrhythmia |
| Distributive | ↓ SVR (vasodilation, leaky vessels) | Sepsis, Anaphylaxis |
| Obstructive | ↓ CO (physical obstruction to flow) | PE, Tamponade |
Key Adrenergic Receptors Targeted:
- α1: Vasoconstriction (arterial & venous) → ↑SVR, ↑BP.
- β1: Heart → ↑Heart rate (chronotropy), ↑Contractility (inotropy).
- β2: Smooth muscle relaxation → Vasodilation (skeletal muscle), Bronchodilation.
- D1 (Dopamine): Renal & mesenteric vasodilation (low "renal dose" dopamine - use is controversial).
⭐ Septic shock is the most common type of distributive shock, characterized by profound vasodilation and increased capillary permeability, leading to relative hypovolemia.
Drugs Used in Shock - Pressure Up!
| Drug | Receptor Activity | MAP | CO | HR | SVR | Key Indications | Major Side Effects |
|---|---|---|---|---|---|---|---|
| Norepinephrine | α1 > β1 | ↑↑ | ↔/↓ | ↔/↓ | ↑↑ | Septic shock (1st line), other vasodilatory shock | Peripheral ischemia, Arrhythmias |
| Epinephrine | α1, β1, β2 (dose-dep.) | ↑ | ↑ | ↑ | ↔/↑ | Anaphylaxis, Cardiac arrest, Septic shock (adjunct) | Tachyarrhythmias, HTN, Myocardial ischemia |
| Dopamine | D1 > β1 > α1 (dose-dep.) | Var | Var | Var | Var | Shock (2nd line if NE unavailable/bradycardia), Symptomatic bradycardia | Tachyarrhythmias, Nausea, Ischemia |
| Phenylephrine | α1 (pure agonist) | ↑ | ↓ | ↓ | ↑ | Neurogenic shock, Sepsis-induced hypotension (if tachyarrhythmias with NE) | Reflex bradycardia, Reduced CO, Ischemia |
| Vasopressin | V1 (vascular smooth muscle) | ↑ | ↔ | ↔ | ↑ | Refractory septic shock (adjunct), GI hemorrhage | Myocardial/Splanchnic ischemia, Hyponatremia |
- Low (1-5 mcg/kg/min): D1 (Renal)
- Moderate (5-10 mcg/kg/min): β1 (Cardiac)
- High (>10-20 mcg/kg/min): α1 (Vasopressor)
⭐ Norepinephrine is the first-line vasopressor for septic shock.
Simplified Vasopressor Strategy in Shock:
Drugs Used in Shock - Pump Power!
Key inotropes improve cardiac contractility in shock.
| Feature | Dobutamine | Milrinone | Levosimendan |
|---|---|---|---|
| Mechanism | $\beta_1$ agonist (📌 Do-Beta-mine); ↑ cAMP | PDE3 inhibitor (📌 Mill-PDE-none); ↑ cAMP | Ca2+ sensitizer (📌 Levo-Sensi-dan), K+ATP opener |
| Effects | ↑ Inotropy, mild ↑ Chrono, mild ↓ SVR | ↑ Inotropy, Lusitropy; Vasodilation (↓SVR/PVR) | ↑ Inotropy; Vasodilation (coronary/systemic/pulmonary) |
| Indications | Cardiogenic shock (low CO, ok BP), severe HF | Acute HF, shock (if $\beta$-blocked) | Acute decomp. HF; shock |
| Side Effects | Tachycardia, Arrhythmias, Hypotension (if hypovolemic) | Hypotension, Arrhythmias, Thrombocytopenia | Hypotension, Headache, HypoK+, Arrhythmias |
Drugs Used in Shock - Helper Heroes!
- Corticosteroids (for Septic Shock):
- Indication: Septic shock with persistent hypotension despite adequate fluids & vasopressors.
- Drug: Hydrocortisone IV is preferred.
- Dose: 200-300mg/day (e.g., 50mg IV q6h or as a continuous infusion).
- Mechanism: Modulate inflammation, ↑vascular reactivity to vasopressors.
- Goal: Earlier shock reversal, ↓ vasopressor duration.
- Taper gradually once vasopressors weaned.
⭐ Corticosteroids are considered in septic shock refractory to fluids and vasopressors, particularly if vasopressor requirements are escalating.
High‑Yield Points - ⚡ Biggest Takeaways
- Norepinephrine is the first-line vasopressor in septic shock.
- Dobutamine is the inotropic agent of choice in cardiogenic shock with low cardiac output.
- Epinephrine is the drug of choice for anaphylactic shock and second-line in septic shock.
- Vasopressin is an adjunct in refractory septic shock to spare norepinephrine.
- Phenylephrine is used in neurogenic shock or if tachyarrhythmias are a concern.
- Milrinone (PDE3 inhibitor) is an inodilator for refractory cardiogenic shock.
- Target MAP >65 mmHg and monitor lactate clearance with vasopressors.
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