Norepinephrine, also known as noradrenaline, is a medication used in emergency and intensive care settings to manage extremely low blood pressure. It belongs to a class of drugs called vasopressors, meaning it works by stimulating receptors that cause blood vessels to constrict or narrow. This constriction increases resistance to blood flow, raising overall blood pressure in the circulatory system. Following a cardiac arrest, the body often enters a state of severe hypotension (low blood pressure), requiring immediate intervention with a pressor like norepinephrine to maintain life-sustaining circulation.
The Physiological Need for Vasopressors
The severe drop in blood pressure after the return of spontaneous circulation (ROSC) is a central feature of Post-Cardiac Arrest Syndrome (PCAS). PCAS is a complex condition involving brain injury, myocardial dysfunction, and a systemic inflammatory response similar to severe sepsis. This systemic response causes widespread vasodilation, where blood vessels relax and widen.
This vasodilation drastically lowers the systemic vascular resistance (SVR), the primary resistance the heart must pump against to maintain pressure. Simultaneously, the heart muscle is often temporarily weakened, a condition called post-arrest myocardial dysfunction. The combination of low SVR and reduced pumping capacity leads to profound shock.
Correcting this systemic hypotension is important because low blood pressure limits the flow of oxygen and nutrients to all organs. The brain and kidneys are particularly vulnerable to inadequate perfusion immediately following a cardiac event. Norepinephrine counteracts vasodilation by constricting the vessels, restoring SVR, and raising blood pressure to perfuse these vital organs.
Guiding Principles of Norepinephrine Dosing
Determining the appropriate norepinephrine dose is a dynamic process of continuous adjustment, not a fixed dose. The medication is delivered via a continuous intravenous infusion, usually through a central venous catheter, to ensure rapid and consistent delivery. Adjusting the infusion rate based on the patient’s real-time blood pressure response is known as titration.
The initial dosing range for post-cardiac arrest hypotension typically falls between 8 to 12 micrograms per minute (mcg/min) for adults. Some protocols use a weight-based initial dose of 0.05 to 0.1 micrograms per kilogram per minute (mcg/kg/min). This starting dose quickly achieves the target blood pressure while the patient is stabilized.
Once the initial target pressure is reached, the infusion rate is lowered to a maintenance dose, often 2 to 4 mcg/min. The actual dose is highly individualized, influenced by factors such as the patient’s existing medical conditions and fluid status. Patients with underlying cardiac issues or those taking beta-blockers may respond differently.
In cases of refractory hypotension, clinicians may need to increase the infusion significantly, sometimes requiring doses much higher than the standard range. Before substantially escalating the dose, the medical team must address uncorrected volume depletion. Vasopressors are less effective if the patient lacks adequate circulating blood volume.
Defining Hemodynamic Goals
The objective of norepinephrine infusion is to achieve and maintain a specific numerical target. The primary measurement used to gauge sufficient organ perfusion is the Mean Arterial Pressure (MAP), which represents the average pressure in the arteries. Current consensus suggests aiming for a MAP of at least 60 to 65 millimeters of mercury (mmHg) in patients after cardiac arrest.
Maintaining pressure above this threshold is important because the brain’s blood flow regulation mechanisms may be impaired after cardiac arrest. Adequate MAP helps maintain Cerebral Perfusion Pressure (CPP), the pressure gradient that drives blood flow to the brain tissue. Low MAP readings are associated with increased mortality and poor neurological results.
Clinical trials have investigated whether targeting a higher MAP, such as 71 to 100 mmHg, offers better outcomes, but current evidence does not support a universal recommendation for these higher targets. For patients who were previously hypertensive, the target blood pressure may be adjusted slightly higher to ensure adequate perfusion, though it is usually kept no more than 40 mmHg below their typical systolic pressure. Additionally, an older guideline suggests maintaining a Systolic Blood Pressure (SBP) greater than 90 mmHg.
Monitoring and Managing Drug Effects
Because norepinephrine has powerful effects, patients must undergo continuous and intensive monitoring while receiving the infusion. Continuous arterial line monitoring provides the most accurate, real-time blood pressure measurement, allowing the care team to adjust the infusion rate instantly. Cardiac rhythm monitoring is mandatory, as norepinephrine can increase the risk of arrhythmias (irregular heartbeats) and tachycardia.
While life-saving, norepinephrine carries risks if the dose is too high or monitoring is insufficient. Excessive vasoconstriction can lead to peripheral ischemia (reduced blood flow to the extremities). Tissue necrosis is a serious concern if the drug leaks out of the vein (extravasation), necessitating administration through a central line whenever possible.
The goal of treatment is to stabilize the patient so the need for vasopressor support diminishes. Once cardiovascular stability is achieved, the process of weaning the drug begins. The infusion is reduced gradually over time, rather than stopped abruptly, to prevent rebound hypotension (a sudden and dangerous drop in blood pressure).