Vasopressors in Emergencies: Norepinephrine, Epinephrine, Vasopressin

Hemodynamic stabilization of critically ill patients is a core competency in emergency and intensive care medicine. When volume resuscitation alone is insufficient to maintain an adequate perfusion pressure, vasopressors are the decisive pharmacological tool. However, choosing the right vasopressor is not automatic – it depends on the underlying type of shock, the hemodynamic profile, and individual risk factors. This article examines the three most commonly used agents – norepinephrine, epinephrine, and vasopressin – with regard to their mechanisms of action, indications, dose ranges, and clinically relevant side effects. The goal: a well-founded basis for decision-making in daily practice.

Fundamentals of Vasopressor Therapy

Before you reach for the syringe pump, it's worth taking a brief look at the physiology. Mean arterial pressure (MAP) is the product of cardiac output (CO) multiplied by systemic vascular resistance (SVR). A state of shock can result from failure of both components – or just one:

• Distributive shock (e.g., sepsis, anaphylaxis): pathologically decreased SVR with initially preserved or even increased cardiac output
• Cardiogenic shock: primarily reduced CO with often reflexively increased SVR
• Hypovolemic shock: reduced preload with consecutive CO decrease
• Obstructive shock (e.g., pulmonary embolism, cardiac tamponade): mechanical obstruction of blood flow

Vasopressors work primarily by increasing SVR (α₁-receptors on vascular smooth muscle), but depending on the agent, they can also have inotropic (β₁) and chronotropic effects. The art lies in securing the MAP without compromising organ perfusion through excessive vasoconstriction.

General Treatment Principles

Some basic rules apply regardless of the chosen agent:

• Volume first: Vasopressors are not a substitute for adequate volume therapy. Before starting, a volume bolus (e.g., 500–1000 mL crystalloid solution in sepsis) should have been administered – or at least initiated – if the clinical situation permits.
• MAP target: Based on current evidence, a MAP of ≥ 65 mmHg is recommended as the initial target. A higher target may be appropriate in patients with pre-existing hypertension or specific organ perfusion concerns.
• Central access preferred: Administration via a central venous catheter (CVC) is standard. In acute situations, short-term peripheral administration through a large-bore IV cannula is acceptable – provided the infusion site is closely monitored to prevent necrosis from extravasation.
• Titrate, don't bolus: Vasopressors are administered as a continuous infusion via syringe pump and titrated to effect.

Norepinephrine – The Gold Standard

Norepinephrine is the first-line vasopressor in septic shock and in most forms of distributive shock. This status is clearly confirmed by the current Surviving Sepsis Campaign and AHA guidelines.

Mechanism of Action

Norepinephrine acts predominantly via α₁-adrenoceptors, producing potent arterial and venous vasoconstriction. Moderate β₁-activity provides a degree of positive inotropic effect without massively increasing heart rate. β₂-activity is clinically negligible.

Dosing

• Starting dose: 0.05–0.1 µg/kg/min
• Titration: in increments of 0.05–0.1 µg/kg/min every 2–5 minutes based on MAP
• Maximum dose: in practice, doses up to 1–2 µg/kg/min are reached; from approximately 0.5 µg/kg/min, this is generally considered a high vasopressor requirement, suggesting the addition of a second agent
• Preparation (example): 5 mg norepinephrine in 50 mL normal saline = 100 µg/mL

Indications

• Septic shock (first-line therapy)
• Distributive shock of other etiology (e.g., post-spinal anesthesia, neurogenic shock)
• Adjunctive in cardiogenic shock in combination with inotropes
• Vasoplegia after cardiopulmonary bypass

Side Effects and Pitfalls

• Peripheral ischemia: Fingers, toes, and acral regions are at risk with prolonged high-dose administration
• Splanchnic vasoconstriction: Mesenteric hypoperfusion with the risk of non-occlusive mesenteric ischemia (NOMI)
• Arrhythmias: Less common than with epinephrine, but possible – especially in the setting of hypokalemia
• Extravasation necrosis: Peripheral administration can cause tissue necrosis. Countermeasure: local infiltration with phentolamine (5–10 mg in 10 mL normal saline)

Epinephrine – The Broad-Spectrum Catecholamine

Epinephrine is the agent with the broadest receptor profile among catecholamines and is indispensable in resuscitation. In vasopressor therapy, it takes a second-line role but has clear indications as a first-line agent.

Mechanism of Action

Epinephrine stimulates all adrenoceptor subtypes in a dose-dependent manner:

• Low doses (< 0.1 µg/kg/min): Predominantly β₁ and β₂ effects → positive inotropic, chronotropic, and bronchodilatory. β₂-mediated vasodilation in skeletal muscle may even slightly decrease SVR.
• High doses (> 0.2 µg/kg/min): Increasing α₁ dominance → pronounced vasoconstriction that overrides the β₂ effect.

Dosing

In shock (continuous infusion):

• Starting dose: 0.01–0.05 µg/kg/min
• Titrate to effect; dose ranges up to 0.5 µg/kg/min and beyond are possible
• Preparation (example): 3 mg epinephrine in 50 mL normal saline = 60 µg/mL

In cardiac arrest (bolus):

• Epinephrine 1 mg IV every 3–5 minutes for non-shockable rhythms starting from the first cycle
• For shockable rhythms: epinephrine 1 mg IV after the third unsuccessful shock

In anaphylaxis (intramuscular):

• Adults: 0.3–0.5 mg IM (anterolateral thigh), repeat every 5–15 minutes if no improvement

Indications

• Anaphylactic shock: Clear first-line therapy – there is no alternative here
• Cardiac arrest: The only vasopressor per the current AHA algorithm
• Cardiogenic shock with profound hypotension: When the inotropic effect is desired and tachycardia can be tolerated
• Septic shock as a second-line agent: When norepinephrine alone does not adequately raise the MAP
• Severe bronchospasm: β₂-mediated bronchodilation

Side Effects and Pitfalls

• Tachycardia and tachyarrhythmias: Epinephrine is more arrhythmogenic than norepinephrine – this is highly clinically relevant, especially in patients with coronary artery disease or atrial fibrillation
• Lactate elevation: Epinephrine stimulates hepatic glycogenolysis and can increase lactate levels independently of tissue hypoxia. This significantly complicates the interpretation of lactate as a perfusion marker.
• Myocardial ischemia: Increased myocardial oxygen demand from inotropic and chronotropic effects can be problematic in patients with pre-existing coronary artery disease
• Hyperglycemia: Via β₂-mediated glycogenolysis and inhibition of insulin secretion

Epinephrine-induced lactate elevation is a common pitfall: A rising lactate level during epinephrine administration does not necessarily indicate worsening tissue perfusion. In this context, you should always assess the overall clinical picture, urine output, capillary refill time, and central venous oxygen saturation (ScvO₂).

Vasopressin – The Non-Adrenergic Player

Vasopressin (arginine vasopressin, AVP) stands out through its completely non-catecholaminergic mechanism of action. It acts via V1a receptors on vascular smooth muscle to cause vasoconstriction and via V2 receptors in the kidney to produce an antidiuretic effect.

Mechanism of Action in Detail

• V1a receptors (vascular smooth muscle): Direct vasoconstriction, independent of adrenergic signaling pathways. This is particularly relevant in sepsis, where downregulation of adrenergic receptors ("catecholamine-refractory vasodilation") can occur.
• V2 receptors (renal collecting duct): Water retention through insertion of aquaporin-2 channels
• V1b receptors (pituitary gland): ACTH release – clinically less relevant

A key advantage: Vasopressin increases SVR without raising heart rate. It can even induce moderate bradycardia through a baroreflex-mediated mechanism.

Dosing

• Fixed dose: 0.03–0.04 U/min (equivalent to 1.8–2.4 U/h)
• Per current recommendations, vasopressin is not titrated but administered at a fixed dose as an adjunct to norepinephrine
• Doses above 0.04 U/min are associated with an increased rate of ischemic complications (skin, bowel, myocardium)
• Preparation (example): 20 U vasopressin in 50 mL normal saline = 0.4 U/mL; infusion rate of 4.5–6 mL/h corresponds to 0.03–0.04 U/min

Indications

• Septic shock: As an add-on to norepinephrine to reduce the norepinephrine dose (catecholamine-sparing effect) or when the MAP target cannot be achieved with norepinephrine alone
• Vasoplegic syndrome after cardiac surgery: The non-adrenergic mechanism is particularly valuable here
• Cardiac arrest: In the current AHA algorithms, vasopressin is no longer recommended as a routine agent during resuscitation, although older guideline versions included it as an alternative to epinephrine

Side Effects and Pitfalls

• Digital and mesenteric ischemia: Vasopressin can also cause end-organ ischemia – particularly at higher doses
• Hyponatremia: The V2-mediated antidiuretic effect can lead to dilutional hyponatremia
• Coronary vasoconstriction: Rare but described – use caution in patients with severe coronary artery disease
• No abrupt discontinuation: Vasopressin should be tapered, as abrupt discontinuation can lead to rebound hypotension

Comparison at a Glance

Property	Norepinephrine	Epinephrine	Vasopressin
Primary receptor	α₁ > β₁	α₁, β₁, β₂ (dose-dep.)	V1a
Vasoconstriction	+++	++ to +++	+++
Inotropy	+	+++	–
Chronotropy	±	+++	– (tends toward bradycardia)
Arrhythmia risk	+	+++	±
Lactate confounding	–	+++	–
Role in septic shock	First-line	Second-line	Adjunct
Role in anaphylaxis	Second-line (infusion)	First-line (IM bolus)	Case reports only
Cardiac arrest	No routine role	Standard agent	No routine role (currently)

Clinical Decision Algorithms

Septic Shock

1. Volume resuscitation (30 mL/kg crystalloid as initial bolus, reassessment)
2. Start norepinephrine if MAP < 65 mmHg despite volume
3. MAP target not achieved → add vasopressin 0.03 U/min
4. Persistent hypotension → consider epinephrine as a third-line agent or hydrocortisone 200 mg/day
5. In the presence of myocardial dysfunction: consider dobutamine as an inotrope (separate topic)

Anaphylactic Shock

1. Epinephrine 0.3–0.5 mg IM – immediately, without delay
2. Aggressive volume replacement (1–2 liters crystalloid rapidly)
3. For refractory hypotension: epinephrine infusion (0.05–0.5 µg/kg/min IV)
4. As adjuncts: norepinephrine infusion or vasopressin can be added

Cardiogenic Shock

1. Identify the cause and treat it causally if possible (e.g., PCI for STEMI)
2. Careful volume status assessment (caution: volume overload)
3. Norepinephrine for severe hypotension as first-line (current evidence favors norepinephrine over epinephrine due to lower arrhythmia rates and lower mortality)
4. Dobutamine for reduced CO without severe hypotension
5. Consider mechanical circulatory support (IABP, Impella, ECMO)

Special Practical Considerations

Peripheral Vasopressor Administration

In the emergency department or prehospital setting, a CVC is often not available. Peripheral administration of norepinephrine through a well-functioning large-bore IV cannula (≥ 18G) in a proximal vein (antecubital vein, cephalic vein) is considered acceptable for a limited period (hours, not days) based on current evidence. Close monitoring of the insertion site every 30 minutes is mandatory.

Terlipressin as an Alternative

In German-speaking countries, terlipressin (a synthetic vasopressin analogue with V1a selectivity) is occasionally used as an alternative to vasopressin, particularly in hepatorenal syndrome and esophageal variceal bleeding. However, in vasopressor therapy for septic shock, terlipressin is not established as a standard agent and has a longer half-life that limits its controllability.

Combination and Escalation

There is no fixed upper limit for norepinephrine at which you "have to stop." However, the rule is: if you are at > 0.5 µg/kg/min norepinephrine and the MAP remains insufficient, you should:

• Add vasopressin (if not already done)
• Question the diagnosis: Is it truly distributive shock? Is there an occult hypovolemic or obstructive component?
• Consider relative adrenal insufficiency: hydrocortisone 200 mg/day as stress-dose supplementation
• Use echocardiography to evaluate cardiac function

Practical Training

The safe use of vasopressors requires more than theoretical knowledge – it demands routine in rapid decision-making, handling syringe pumps, and hemodynamic interpretation under stress. In the ACLS course at Simulation Tirol, you train exactly these situations in realistic scenarios: from catecholamine-dependent shock to resuscitation with epinephrine administration to structured root cause analysis. Simulation-based training allows you to practice dose calculations, escalation strategies, and team communication in a safe learning environment – before it matters at the patient's bedside.