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# Norepinephrine
## Overview
Norepinephrine is a potent alpha-1 adrenergic agonist and a weaker beta-1 adrenergic agonist. It primarily causes vasoconstriction, leading to increased systemic vascular resistance and blood pressure. It also increases myocardial contractility and heart rate to a lesser extent.
## Primary Indications
* Severe hypotension and shock, particularly when unresponsive to fluid resuscitation.
* Cardiogenic shock.
* Septic shock.
## Adult Dosing
* **Initial Dosing:** Typically initiated at 0.01 to 0.02 mcg/kg/min as a continuous intravenous infusion.
* **Titration:** Doses are titrated upward to achieve the desired hemodynamic effect, usually a mean arterial pressure (MAP) of 65 mmHg or higher, or as per local protocol.
* **Maximum Dosing:** Doses can be titrated up to 0.1 mcg/kg/min or higher, but doses exceeding 0.3 mcg/kg/min are rarely required and associated with increased risk of adverse events. Specific maximums may depend on local protocol.
## Pediatric Dosing
* **Initial Dosing:** Typically initiated at 0.05 to 0.1 mcg/kg/min as a continuous intravenous infusion.
* **Titration:** Doses are titrated upward to achieve the desired hemodynamic effect, often targeting MAP greater than gestational age (in weeks) plus 5 mmHg in neonates, or a target MAP based on age/weight in older children, or as per local protocol.
* **Maximum Dosing:** Doses can be titrated up to 1 mcg/kg/min or higher, but higher doses may be associated with increased adverse effects. Specific maximums may depend on local protocol.
## Dose Adjustments
* **Renal Impairment:** No specific dose adjustments are routinely recommended, but cautious titration is advised due to potential for accumulation or altered response.
* **Hepatic Impairment:** No specific dose adjustments are routinely recommended, but cautious titration is advised.
## Contraindications
* Hypersensitivity to norepinephrine.
* Severe hypotension with peripheral vasoconstriction and inadequate tissue perfusion, especially in the presence of mesenteric or peripheral arterial thrombosis (as it can further compromise blood flow to these areas).
* Cyclopropane and halogenated hydrocarbon anesthetics (risk of severe hypertension and arrhythmias).
## Adverse Effects
* **Cardiovascular:** Hypertension, bradycardia (reflex), tachycardia, arrhythmias, myocardial ischemia, peripheral ischemia, extravasation leading to tissue necrosis.
* **Central Nervous System:** Headache, anxiety, tremor, dizziness.
* **Respiratory:** Dyspnea.
* **Other:** Palpitations.
## Key Drug Interactions
* **Anesthetics (Cyclopropane, Halogenated Hydrocarbons):** Increased risk of severe hypertension and arrhythmias.
* **Beta-Blockers:** Can blunt the beta-1 effects of norepinephrine (inotropy) and unopposed alpha-1 stimulation can lead to severe hypertension.
* **MAO Inhibitors and Tricyclic Antidepressants:** Prolong and intensify the pressor effects of norepinephrine. Discontinue MAOIs or TCAs at least 14 days before initiating norepinephrine.
* **Alpha-Blockers:** Can antagonize the pressor effects of norepinephrine.
* **Ergot Alkaloids and Oxytocics:** Can cause severe, persistent hypertension.
## Monitoring
* **Hemodynamics:** Continuous electrocardiogram (ECG), blood pressure (invasive arterial monitoring is preferred), heart rate.
* **Urine Output:** To assess renal perfusion.
* **Central Venous Pressure (CVP) or Pulmonary Artery Catheter (PAC) Data:** If available, to guide fluid management and assess cardiac function.
* **Perfusion:** Skin color and temperature, capillary refill time.
* **Infusion Site:** For signs of extravasation.
## Clinical Pearls
* Norepinephrine should be administered via a central venous catheter to reduce the risk of peripheral tissue necrosis due to extravasation.
* If extravasation occurs, discontinue the infusion, do not flush the line, and infiltrate the affected area with phentolamine.
* Titrate to the lowest effective dose to achieve target hemodynamics and minimize adverse effects.
* Consider concurrent use of vasopressin in septic shock for potential synergistic effects and reduced risk of myocardial ischemia compared to very high-dose norepinephrine.
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*Disclaimer: This information is intended for clinical use and does not replace comprehensive drug information resources. Always consult the current prescribing information and institutional protocols before making any medication decisions.*
