Dobutamine - Dosing Guide

Standard Dose Range

• Fischer's Mastery of Surgery, 8th ed., p. 339
• Braunwald's Heart Disease, 15th ed.

Dose-Specific Effects

Special Scenarios

• Dobutamine Stress Echo (DSE):
  • Low dose: 5-10 mcg/kg/min (viability assessment, biphasic response)
  • High dose: up to 40 mcg/kg/min (ischemia detection)
• Patients on beta-blockers: Competitive antagonism occurs; doses of 10-20 mcg/kg/min may be needed to achieve desired hemodynamic effect.
• Cardiogenic shock: Start at 5-10 mcg/kg/min; titrate up as needed.

Pharmacokinetics

• Half-life: ~2 minutes
• Clearance: Largely hepatic
• Onset: Rapid (within minutes of infusion start)
• Tachyphylaxis: Can occur with infusions lasting more than 24-48 hours (receptor desensitization)

Key Adverse Effects

• Tachycardia (especially at higher doses - limits usefulness in pre-existing tachycardia)
• Atrial and ventricular arrhythmias
• Increased ventricular response in atrial fibrillation
• Myocardial ischemia (increases oxygen demand)
• Hypotension at low doses (beta-2 vasodilation)

Clinical Indications & Notes

• Preferred inotrope in cardiogenic shock with significant hypotension, and when significant renal dysfunction is present (since milrinone is renally cleared)
• Use the lowest effective dose with continuous BP and telemetry monitoring
• Wean gradually - do not abruptly discontinue
• Effect is attenuated in patients on beta-blockers (beta-1 stimulation is the main mechanism)
• Does NOT affect pulmonary vascular resistance (no direct pulmonary vasodilating properties)

Sources: Braunwald's Heart Disease (9780323722193), Fischer's Mastery of Surgery 8th ed. (9781975176433), Fuster and Hurst's The Heart 15th ed. (9781264257560), Textbook of Clinical Echocardiography (9780323882088)

Drugs for Hypotension

Overview

• Distributive shock (sepsis, anaphylaxis, neurogenic) - primarily vasopressors
• Cardiogenic shock - inotropes + vasopressors
• Hypovolemic shock - fluids first, then vasopressors if needed
• Obstructive shock - treat cause + temporary vasopressors

1. VASOPRESSORS

Norepinephrine (First-line for most shock states)

• Mechanism: Alpha > Beta-1 agonist - potent vasoconstriction + mild inotropy/chronotropy
• Dose: 1-30 mcg/min IV (or 0.01-3 mcg/kg/min), titrated to MAP
• Use: First-line for septic/distributive shock and cardiogenic shock
• Key point: Preferred over dopamine - SOAP II trial showed fewer arrhythmias and improved survival in cardiogenic shock subgroup
• Goldman-Cecil Medicine; Fuster & Hurst's The Heart, 15th ed.

Vasopressin (Second-line adjunct)

• Mechanism: V1 receptor agonist - increases systemic vascular resistance via smooth muscle constriction (non-adrenergic)
• Dose: 0.04-0.1 units/min IV (fixed dose, not titrated)
• Use: Second-line agent when norepinephrine alone is inadequate; vasodilatory shock; post-cardiopulmonary bypass
• Key point: Does not increase heart rate or myocardial oxygen demand; reduces norepinephrine requirements
• Goldman-Cecil; Sabiston Textbook of Surgery

Dopamine (Selective use)

• Mechanism: Dose-dependent - dopaminergic (low), beta-1 (medium), alpha-1 (high)
• Dose ranges:

• Use: Only in select patients with bradycardia and hypotension; low arrhythmia risk
• Key point: No role for "renal-dose dopamine"; more arrhythmias than norepinephrine
• Schwartz's Principles of Surgery 11th ed.; Goldman-Cecil Medicine

Phenylephrine

• Mechanism: Pure alpha-1 agonist - pure vasoconstriction, no beta effects
• Dose: 20-200 mcg/min IV infusion; bolus 40-100 mcg IV for peri-intubation hypotension
• Use: Vasodilatory shock; best choice when tachyarrhythmias must be avoided; cardiogenic shock from hypertrophic cardiomyopathy (HOCM)
• Key point: No chronotropy - safe in SVT; NOT recommended routinely in septic shock (reduces cardiac output)
• Goldman-Cecil; Tintinalli's Emergency Medicine

Epinephrine

• Mechanism: Alpha = Beta agonist - equal vasoconstriction + inotropy/chronotropy
• Dose: 0.01-1 mcg/kg/min IV infusion
• Use:
  • Anaphylaxis (IM 0.3-0.5 mg 1:1000 first-line)
  • Cardiac arrest (IV 1 mg every 3-5 min)
  • Salvage in extreme cardiogenic shock when other agents fail
• Key point: Greater risk of splanchnic ischemia than vasopressin; reserved for refractory situations
• Fuster & Hurst's The Heart; Schwartz's Principles of Surgery

2. INOTROPES (for Cardiogenic Shock / Low Cardiac Output)

Dobutamine

• Mechanism: Beta-1 >> Beta-2, weak Alpha-1 - increased contractility + mild vasodilation (reduces afterload)
• Dose: 2-20 mcg/kg/min IV
• Use: Cardiogenic shock with low CO; heart failure with reduced EF
• Key point: Blunted response in patients on beta-blockers; may need 10-20 mcg/kg/min in those patients
• Fuster & Hurst's The Heart, 15th ed.

Milrinone

• Mechanism: Phosphodiesterase-3 inhibitor - increases cAMP - inotropy + vasodilation (inodilator)
• Dose: 0.375-0.75 mcg/kg/min IV (loading dose: 50 mcg/kg over 10 min, often omitted)
• Use: Cardiogenic shock, especially in patients on chronic beta-blockers (mechanism independent of beta receptors)
• Key point: Renally cleared - use with caution in renal failure; can worsen hypotension

3. ADJUNCTIVE AGENT

Hydrocortisone (for Refractory Vasodilatory Shock)

• Dose: <300 mg/day IV
• Use: Septic shock refractory to fluids and vasopressors (possible relative adrenal insufficiency)
• Schwartz's Principles of Surgery 11th ed.

Summary Table

Sources: Goldman-Cecil Medicine (9780323930345), Fuster & Hurst's The Heart 15th ed. (9781264257560), Schwartz's Principles of Surgery 11th ed. (9781259835346), Sabiston Textbook of Surgery (9780443124341), Tintinalli's Emergency Medicine (9781260019933)