What is the initial noradrenaline (norepinephrine) dose and infusion rate for a 100‑kg adult male in shock to maintain a mean arterial pressure of at least 65 mmHg?

Noradrenaline Dosage Calculation for a 100kg Male in Shock

For a 100kg male in shock, start noradrenaline at 0.5 mg/h (approximately 8 mcg/min or 0.08 mcg/kg/min) via continuous IV infusion through central venous access, targeting a mean arterial pressure (MAP) of at least 65 mmHg. 1

Preparation and Initial Infusion Rate

• Standard concentration: Add 4 mg of noradrenaline to 250 mL of D5W to yield 16 μg/mL 1
• Starting dose: 0.5 mg/h (8.3 mcg/min or 0.08 mcg/kg/min for a 100kg patient) 1
• Alternative weight-based calculation: 0.1–0.5 mcg/kg/min translates to 10–50 mcg/min (0.6–3 mg/h) for this 100kg patient 1

Practical Infusion Rate Calculation

For a 100kg patient using the standard 16 μg/mL concentration:

• 0.5 mg/h = 31.25 mL/h on the infusion pump 1
• This delivers approximately 8.3 mcg/min or 0.08 mcg/kg/min 1

Critical Pre-Administration Requirements

• Fluid resuscitation first: Administer a minimum of 30 mL/kg (3,000 mL for this 100kg patient) crystalloid bolus before or concurrent with noradrenaline initiation 1, 2
• Central venous access strongly preferred to minimize extravasation risk and tissue necrosis 1, 2
• Arterial catheter placement as soon as practical for continuous blood pressure monitoring 1, 2

Hemodynamic Target and Titration

• Primary target: MAP ≥ 65 mmHg for most patients 1, 2
• Titration protocol: Increase by 0.5 mg/h every 4 hours as needed, up to a maximum of 3 mg/h 1
• Monitor blood pressure and heart rate every 5–15 minutes during initial titration 1

Monitoring Beyond Blood Pressure

• Lactate clearance: Obtain baseline and repeat within 6 hours if elevated 1
• Urine output: Target ≥ 0.5 mL/kg/h (≥50 mL/h for this 100kg patient) 1
• Clinical perfusion markers: Mental status, capillary refill, skin perfusion 1
• Watch for excessive vasoconstriction: Cold extremities, decreased urine output 1

Escalation Strategy for Refractory Hypotension

• Add vasopressin 0.03 units/min when noradrenaline reaches 0.25 mcg/kg/min (25 mcg/min or 1.5 mg/h for this 100kg patient) and MAP remains <65 mmHg 1, 2
• Never exceed vasopressin 0.03–0.04 units/min except as salvage therapy, as higher doses cause cardiac, digital, and splanchnic ischemia 1, 2
• Add epinephrine 0.05–0.3 mcg/kg/min (5–30 mcg/min for this 100kg patient) if MAP cannot be achieved with noradrenaline plus vasopressin 2
• Add dobutamine 2.5–20 mcg/kg/min when MAP is adequate but tissue hypoperfusion persists, especially with myocardial dysfunction 1, 2

Special Consideration for Obesity

• Obese patients require lower weight-based doses of noradrenaline compared to non-obese patients 3
• For this 100kg patient, if obese (BMI ≥30), expect to use approximately 0.09 mcg/kg/min (9 mcg/min or 0.54 mg/h) at 60 minutes, which is lower than the typical weight-based calculation 3
• Non-weight-based dosing may be more appropriate in obese patients, as total dose requirements are similar between obese and non-obese patients (approximately 8–9 mcg/min) 3

Critical Pitfalls to Avoid

• Do not delay noradrenaline while pursuing excessive fluid resuscitation in profound hypotension (systolic <70 mmHg or diastolic ≤40 mmHg); start as an emergency measure while fluid resuscitation continues 1, 4
• Do not use dopamine as first-line therapy—it increases mortality by 11% absolute risk and causes significantly more arrhythmias 2
• Do not use phenylephrine as first-line—it may raise blood pressure while worsening tissue perfusion 2, 5
• If extravasation occurs, infiltrate phentolamine 5–10 mg diluted in 10–15 mL saline at the site immediately 1