What norepinephrine infusion rate should be started for a 55‑kg patient (in µg·kg⁻¹·min⁻¹ and the corresponding mL·h⁻¹)?

Norepinephrine Infusion Rate for a 55-kg Patient

For a 55-kg patient requiring norepinephrine, start with 0.05 µg·kg⁻¹·min⁻¹ (2.75 µg/min), which corresponds to approximately 8.25 mL/h using a standard 4 µg/mL concentration.

Standard Preparation and Dosing

The FDA-approved preparation is 4 mg norepinephrine diluted in 1000 mL of 5% dextrose, yielding a concentration of 4 µg/mL 1. This is the standard concentration used in clinical practice.

Initial Dosing Strategy

Start at 0.05 µg·kg⁻¹·min⁻¹ based on converging evidence:

• The Surviving Sepsis Campaign guidelines recommend norepinephrine as first-choice vasopressor, typically initiated at low doses and titrated to MAP ≥65 mmHg 2
• Recent high-quality data from 2026 demonstrates that starting doses of 0.05 µg·kg⁻¹·min⁻¹ provide optimal balance between efficacy and safety 3, 4
• The FDA label recommends starting at 2-3 mL/min (8-12 µg/min) of the standard dilution, then adjusting to maintain adequate blood pressure 1

Calculation for 55-kg Patient

Weight-based calculation:

• 0.05 µg·kg⁻¹·min⁻¹ × 55 kg = 2.75 µg/min

Converting to mL/h (using 4 µg/mL concentration):

• (2.75 µg/min ÷ 4 µg/mL) × 60 min/h = 41.25 mL/h
• Round to 41 mL/h for practical pump programming

Alternative starting range: 0.025-0.1 µg·kg⁻¹·min⁻¹ (1.4-5.5 µg/min or 21-83 mL/h for this patient)

Titration Algorithm

Adjust every 2-5 minutes based on MAP response:

1. If MAP remains <65 mmHg after 2 minutes: Increase by 0.025 µg·kg⁻¹·min⁻¹ increments (approximately double the infusion rate)
2. Target MAP: 65-70 mmHg (or 40 mmHg below pre-existing baseline in previously hypertensive patients) 5
3. Maximum typical dose: 0.2-0.4 µg·kg⁻¹·min⁻¹ before considering additional agents 6

Recent 2026 data shows that failure to achieve MAP ≥65 mmHg within 60 minutes is associated with increased mortality, particularly when baseline MAP is severely depressed 3. If starting at 0.05 µg·kg⁻¹·min⁻¹ fails to achieve target within 15 minutes, escalate more aggressively.

Critical Dosing Thresholds

Based on 2024 research defining severity of cardiovascular failure 6:

• Low dose: <0.2 µg·kg⁻¹·min⁻¹ (<11 µg/min or <165 mL/h)
• Intermediate dose: 0.2-0.4 µg·kg⁻¹·min⁻¹ (11-22 µg/min or 165-330 mL/h)
• High dose: >0.4 µg·kg⁻¹·min⁻¹ (>22 µg/min or >330 mL/h)

Doses exceeding 1.13 µg·kg⁻¹·min⁻¹ (62 µg/min or 930 mL/h) predict significantly increased mortality and should prompt consideration of additional vasopressors (vasopressin 0.03 units/min or epinephrine) 2, 7.

Administration Essentials

Route and monitoring:

• Administer through central venous access whenever possible 1
• If peripheral access only, use large vein and monitor closely for extravasation
• Place arterial catheter for continuous blood pressure monitoring 2

Extravasation management:

• If extravasation occurs, immediately infiltrate site with phentolamine 0.1-0.2 mg/kg (up to 10 mg) diluted in 10 mL normal saline 8

Common Pitfalls

1. Starting too low in severe hypotension: If baseline MAP <50 mmHg, consider starting at 0.1 µg·kg⁻¹·min⁻¹ (5.5 µg/min or 83 mL/h) as lower doses may be insufficient to achieve target within critical 60-minute window 3

2. Using saline alone as diluent: Always use dextrose-containing solutions to prevent oxidation and loss of potency 1

3. Inadequate fluid resuscitation: Correct volume depletion before or concurrent with vasopressor initiation 2, 1

4. Delayed escalation: If no response within 2-5 minutes, increase dose promptly rather than waiting 3

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