Overview
This lecture explains the use of vasopressors and inotropic agents in critical care, focusing on indications, dosing, preparation, titration, and monitoring for drugs like norepinephrine, vasopressin, epinephrine, dobutamine, and dopamine.
Vasopressors vs Inotropic Agents
- Vasopressors cause blood vessel constriction and raise blood pressure (e.g., norepinephrine, vasopressin, phenylephrine, epinephrine, dopamine).
- Inotropic agents increase heart muscle contractility (e.g., dobutamine, milrinone, isoproterenol, epinephrine, dopamine).
- Epinephrine and dopamine can act as both, depending on the dose.
Key Receptors & Actions
- Alpha-1: Vasoconstriction (main receptor for norepinephrine).
- Beta-1: Increased heart contractility and rate (main for epinephrine, dobutamine).
- Beta-2: Bronchodilation (epinephrine also acts here).
- V1: Vasoconstriction (targeted by vasopressin).
- D1: Renal/splanchnic vasodilation (dopamine, less relevant clinically).
General Principles for Use
- Always use a central line for continuous vasopressor infusion in acute scenarios.
- Regularly assess ECG, mean arterial pressure (MAP), urine output, and lactate.
- Start vasopressors promptly; avoid stopping abruptly.
- Target MAP ≥ 65 mmHg.
Drug Preparation & Dosing
- Norepinephrine: 4 mg in 50 ml (2 ampules); start at 0.05 mcg/kg/min (~2.5 ml/hr for 70 kg pt); max 1 mcg/kg/min.
- Vasopressin: 40 units in 40 ml (2 ampules); fixed dose 0.03 units/min (1.8 ml/hr); max 2.4 ml/hr.
- Epinephrine: 4 mg in 50 ml (4 ampules); start at 0.01 mcg/kg/min (~0.53 ml/hr for 70 kg); max 1 mcg/kg/min.
- Dobutamine: 250 mg in 50 ml (1 ampule); start at 2 mcg/kg/min (1.68 ml/hr); max 20 mcg/kg/min.
- Dopamine: 400 mg in 50 ml (2 ampules); start at 5 mcg/kg/min; max 20 mcg/kg/min; less commonly used due to arrhythmia risk.
Clinical Application and Titration
- Start norepinephrine in septic or most shock cases (except cardiogenic shock).
- If norepinephrine >10–15 ml/hr is needed, add vasopressin.
- Add epinephrine if further support is needed.
- In cardiogenic shock or low ejection fraction, use dobutamine (+norepinephrine if hypotensive).
- For refractory shock, consider IV hydrocortisone 200 mg/day.
- Assess fluid responsiveness with IVC collapsibility, PPV, or stroke volume variation.
Key Terms & Definitions
- Vasopressor — Medication that constricts blood vessels to raise blood pressure.
- Inotropic agent — Drug that increases heart muscle contractility.
- Mean arterial pressure (MAP) — Average pressure in arteries during one cardiac cycle, target ≥65 mmHg.
- Central line — Large intravenous catheter used for reliable drug delivery.
Action Items / Next Steps
- Review preparation and dosing protocols for each vasopressor/inotrope.
- Practice calculating infusion rates for standard patient weights.
- Monitor MAP, ECG, urine output, and lactate regularly during infusions.
- Read up on fluid responsiveness parameters (IVC, PPV, SVV) and their clinical use.