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# Norepinephrine
## Overview
Norepinephrine is a potent sympathomimetic amine that acts as a vasopressor. It primarily stimulates alpha-1 adrenergic receptors, causing vasoconstriction and increasing systemic vascular resistance and blood pressure. It also has some beta-1 adrenergic receptor activity, increasing heart rate and contractility.
## Primary Indications
* Severe hypotension and shock (e.g., septic shock, cardiogenic shock) refractory to fluid resuscitation.
## Adult Dosing
* **Initial Bolus:** Not typically recommended.
* **Continuous Infusion:** Initiate at 0.01 to 0.02 mcg/kg/min. Titrate to maintain target systolic blood pressure (often 90-100 mmHg) or mean arterial pressure (MAP) (often >65 mmHg).
* **Maximum Dose:** Doses can be escalated significantly based on patient response, sometimes exceeding 1 mcg/kg/min in refractory shock. Dosing is highly individualized and guided by hemodynamic response.
## Pediatric Dosing
* **Continuous Infusion:** Initiate at 0.05 to 0.1 mcg/kg/min. Titrate to achieve target blood pressure.
* **Maximum Dose:** Typically up to 1 mcg/kg/min, but may be higher in specific situations. Dosing is highly individualized and guided by hemodynamic response.
## Dose Adjustments
* No specific dose adjustments are required for hepatic or renal impairment, but prolonged use may lead to accumulation and increased risk of adverse effects.
## Contraindications
* Hypersensitivity to norepinephrine.
* Hypotension due to absolute hypovolemia without adequate fluid replacement.
* Obstructive shock (e.g., tension pneumothorax, cardiac tamponade) where vasoconstriction may worsen perfusion.
## Adverse Effects
* **Cardiovascular:** Hypertension, reflex bradycardia, arrhythmias, peripheral ischemia, angina, cardiac arrest, myocardial infarction.
* **Extravasation:** Tissue necrosis, sloughing, and gangrene at the infusion site due to potent vasoconstriction.
* **Other:** Headache, anxiety, tremor, dyspnea, nausea.
## Key Drug Interactions
* **MAO Inhibitors:** Potentiate hypertensive crisis. Avoid concurrent use or use with extreme caution and reduced doses.
* **Tricyclic Antidepressants (TCAs):** May potentiate the pressor response. Use with caution.
* **Beta-blockers:** May blunt the beta-1 effects of norepinephrine, leading to unopposed alpha-1-mediated vasoconstriction and potentially severe hypertension.
* **Ergot Alkaloids:** May cause severe hypertension and peripheral ischemia.
## Monitoring
* Continuous hemodynamic monitoring: Blood pressure (intra-arterial preferred), heart rate, EKG.
* Urine output.
* Peripheral perfusion (e.g., skin color, temperature, capillary refill).
* Infusion site for signs of extravasation.
* Serum lactate.
## Clinical Pearls
* Always ensure adequate intravascular volume resuscitation before or concurrently with initiating norepinephrine.
* Administer via a central venous catheter to minimize the risk of extravasation.
* If extravasation occurs, stop the infusion immediately and administer phentolamine locally to counteract vasoconstriction.
* Norepinephrine is typically prepared as a dilute infusion (e.g., 16 mcg/mL or 40 mcg/mL). Verify concentration carefully.
* Protocols for specific shock states (e.g., septic shock) may dictate specific target MAP goals.
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*Disclaimer: This information is for educational purposes only and does not constitute medical advice. Always consult the most current prescribing information and relevant clinical guidelines for complete and up-to-date drug information, including indications, contraindications, warnings, precautions, and adverse reactions, before making any treatment decisions.*
