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# Norepinephrine
## Overview
Norepinephrine is a potent vasopressor and inotropic agent that acts primarily on alpha-adrenergic receptors, causing vasoconstriction and increasing blood pressure. It also has beta-1 adrenergic effects, increasing heart rate and contractility, though these are less pronounced than its alpha effects.
## Primary Indications
* Treatment of hypotension (low blood pressure) characterized by a low systemic vascular resistance, typically in the setting of septic shock or other distributive shock states.
* Restoration and maintenance of blood pressure.
## Adult Dosing
* **Intravenous Infusion:** Typically initiated at **2 mcg/min to 4 mcg/min**.
* **Titration:** Gradually titrate infusion rate upwards based on patient's response (e.g., target mean arterial pressure [MAP] of 65 mmHg or higher) in increments of **2 mcg/min to 4 mcg/min** every 5-15 minutes.
* **Maximum Dose:** Doses up to **30 mcg/min** may be required in severe cases. Higher doses are generally not recommended and are associated with increased adverse effects. Local protocols may vary.
## Pediatric Dosing
* **Intravenous Infusion:** Typically initiated at **0.05 mcg/kg/min to 0.1 mcg/kg/min**.
* **Titration:** Gradually titrate infusion rate based on patient's hemodynamic response in increments of **0.05 mcg/kg/min to 0.1 mcg/kg/min** every 5-10 minutes.
* **Maximum Dose:** Doses up to **1 mcg/kg/min** may be used in refractory hypotension. Higher doses are generally not recommended. Dosing depends heavily on local protocol and patient condition.
## Dose Adjustments
No specific dose adjustments are typically required for renal or hepatic impairment, as norepinephrine is primarily metabolized in the liver and extremities. However, close monitoring is crucial in these populations due to potential altered pharmacokinetics and increased susceptibility to adverse effects.
## Contraindications
* Hypersensitivity to norepinephrine.
* Use during general anesthesia with cyclopropane or halothane (can sensitize the myocardium to the effects of norepinephrine, leading to severe arrhythmias).
* Should not be used in patients with mesenteric or peripheral vascular thrombosis, as it may further decrease blood flow to these areas and increase the size of infarcts.
## Adverse Effects
* **Cardiovascular:** Hypertension, reflex bradycardia, arrhythmias (including ventricular arrhythmias), peripheral ischemia, necrosis (especially with extravasation), angina, palpitations, decreased cardiac output.
* **Central Nervous System:** Headache, anxiety, dizziness, tremors, cerebral hemorrhage.
* **Respiratory:** Dyspnea.
* **Other:** Pale skin, sweating, nausea, vomiting, extravasation leading to tissue necrosis.
## Key Drug Interactions
* **MAO Inhibitors & TCAs:** Potentiate the pressor response to norepinephrine, leading to severe hypertension. Discontinue MAOIs at least 14 days before norepinephrine initiation.
* **Alpha-adrenergic Blockers:** May decrease the pressor response.
* **Beta-adrenergic Blockers:** May reduce the cardiac stimulant effects and potentially unmask unopposed alpha-receptor stimulation, leading to severe hypertension.
* **Ergot Alkaloids:** Can potentiate the vasoconstrictive effects.
* **Oxytocin:** May potentiate the pressor effect.
* **General Anesthetics (e.g., cyclopropane, halothane):** Increased risk of arrhythmias.
## Monitoring
* **Hemodynamics:** Continuous monitoring of blood pressure (arterial line preferred), heart rate, and rhythm.
* **Urine Output:** Monitor for adequacy of renal perfusion.
* **Central Venous Pressure (CVP) / Pulmonary Artery (PA) pressures:** May be helpful in guiding fluid management and assessing cardiac function.
* **Peripheral Circulation:** Assess for signs of ischemia (e.g., cool extremities, diminished pulses, color changes).
* **Infusion Site:** Monitor closely for signs of extravasation.
* **Serum Lactate:** Monitor for signs of adequate tissue perfusion.
## Clinical Pearls
* Administer via a central venous catheter to minimize risk of extravasation and tissue necrosis. If peripheral administration is necessary, use a large vein, monitor the infusion site vigilantly, and discontinue immediately if signs of extravasation occur.
* Have phentolamine readily available for local infiltration in case of extravasation.
* Norepinephrine is a potent vasoactive agent; titrate slowly and cautiously to achieve desired hemodynamic goals while minimizing adverse effects.
* Consider underlying causes of hypotension; norepinephrine is a temporizing measure.
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*Disclaimer: This information is intended for clinical decision-making support and does not replace professional medical judgment. Always verify current prescribing information, guidelines, and patient-specific factors before making treatment decisions.*
