Noradrenaline, also known as Norepinephrine, is a hormone and medication crucial for maintaining blood pressure and perfusion in critical care settings. It is primarily used in managing severe hypotension, particularly in septic shock, cardiogenic shock, and severe hypotension unresponsive to fluid administration.
Mechanism of Action
Noradrenaline acts predominantly on adrenergic receptors:
- Alpha-1 Adrenergic Receptors:
- Vasoconstriction: Increases vascular tone and systemic vascular resistance, leading to an increase in blood pressure.
- Beta-1 Adrenergic Receptors:
- Cardiac Effects: Increases heart rate and myocardial contractility, enhancing cardiac output.
Half-Life
- Intravenous (IV) Administration: The plasma half-life of noradrenaline when administered intravenously is approximately 2 to 2.5 minutes. This short half-life necessitates continuous infusion to maintain its effects.
Bioavailability
- Intravenous (IV) Administration: Noradrenaline has 100% bioavailability when administered intravenously as it directly enters the systemic circulation.
- Intramuscular (IM) and Subcutaneous (SC) Administration: These routes are not typically used for noradrenaline due to poor absorption and the risk of local tissue necrosis.
Clinical Uses
- Septic Shock:
- Mechanism: Increases vascular tone and cardiac output, counteracting the profound vasodilation and hypotension associated with sepsis.
- Dosage: Typically, 0.01-0.5 mcg/kg/min IV infusion, titrated based on blood pressure response and clinical condition.
- Cardiogenic Shock:
- Mechanism: Improves blood pressure and perfusion by increasing systemic vascular resistance and cardiac output.
- Dosage: Similar to septic shock, with infusion rates adjusted based on hemodynamic response.
- Severe Hypotension Unresponsive to Fluid Administration:
- Mechanism: Provides vasoconstriction and support to blood pressure in patients who do not respond adequately to fluid resuscitation.
- Dosage: Typically 0.01-0.5 mcg/kg/min IV infusion, titrated based on clinical response.
Preparation and Administration in ICU
- Stock Solution: Noradrenaline typically comes in ampoules of 4 mg/4mL. (UK)
- Dilution: To prepare an 8 mg dose in 100 mL of dextrose solution:
- Example: Add 8 mg of noradrenaline (8 mL of 1 mg/mL solution) to 92 mL of 5% dextrose. This results in a final concentration of 0.08 mg/mL (80 mcg/mL).
Administration
- Route: Continuous IV infusion via a central venous catheter (CVC) to ensure rapid and consistent delivery.
Monitoring
- Hemodynamic Monitoring: Continuous monitoring of blood pressure, heart rate, and ECG is essential.
- Urine Output: Indicator of renal perfusion.
- Serum Lactate Levels: To monitor tissue perfusion and metabolic state.
- Clinical Response: Regular assessment of the patient’s clinical status.
- Peripheral and visceral vasoconstriction can reduce blood flow to extremities and organs, potentially leading to tissue ischemia and necrosis. (e.g – Fingertip Necrosis Due to High Dose of Noradrenaline)
- Reasons for Holding Nasogastric (NG) Feeding Due to High Dose of Noradrenaline (Norepinephrine)
- High doses of noradrenaline cause significant vasoconstriction to maintain blood pressure in shock states. This vasoconstriction can reduce blood flow to the splanchnic circulation (the blood vessels supplying the gastrointestinal tract).
Adverse Effects
- Common: Tachycardia, hypertension, headache, anxiety, and palpitations.
- Serious: Arrhythmias, ischemic injury, extravasation leading to tissue necrosis, and severe hypertension.
Contraindications
- Absolute: None in emergency situations where noradrenaline is lifesaving.
- Relative: Use with caution in patients with mesenteric or peripheral vascular thrombosis, as increased vasoconstriction could exacerbate ischemia.