What is the initial low dose of norepinephrine (vasopressor) for a patient weighing 45 kg with hypotension?

Initial Low Dose of Norepinephrine for a 45 kg Patient with Hypotension

For a 45 kg patient with hypotension, the initial low dose of norepinephrine should be 0.1-0.5 mcg/kg/min, which translates to 4.5-22.5 mcg/min. 1, 2

Preparation and Administration

Dilution

• Add 4 mg (4 mL) of norepinephrine to 1,000 mL of 5% dextrose solution
• This creates a concentration of 4 mcg/mL 2
• For a 45 kg patient:
  • At 0.1 mcg/kg/min: 4.5 mcg/min = approximately 1.1 mL/min (67 mL/hr)
  • At 0.5 mcg/kg/min: 22.5 mcg/min = approximately 5.6 mL/min (337 mL/hr)

Administration Route

• Administer through a large vein, preferably via central venous catheter 2
• If central access is unavailable, peripheral administration can be considered for short-term use (less than 24 hours) with careful monitoring for extravasation 1

Titration and Target

• Initial observation period: Monitor response to initial dose for 2-3 minutes (8-12 mcg of base) 2
• Target mean arterial pressure (MAP): 65 mmHg 3, 1
• Adjust in increments of 0.05-0.2 mcg/kg/min every 10-15 minutes based on blood pressure response 1
• For previously hypertensive patients, aim for a systolic blood pressure no higher than 40 mmHg below their baseline 2

Dosing Considerations for Weight

• Weight-based dosing is appropriate for initial dosing in patients of all body sizes 4
• Research shows that obese patients require lower weight-based doses but similar total doses compared to non-obese patients 4
• The average maintenance dose typically ranges from 2-4 mcg/min (0.5-1 mL/min of the standard dilution) 2

Monitoring

• Continuous cardiac monitoring is essential
• Frequent blood pressure measurements
• Regular assessment of tissue perfusion
• Monitor for adverse effects:
  • Tachyarrhythmias
  • Increased myocardial oxygen consumption
  • Lactic acidosis
  • Hyperglycemia 1

Important Caveats

• Always correct hypovolemia before or concurrently with norepinephrine administration 2, 5
• Consider fluid bolus (5-10 mL/kg) if hypovolemia is suspected 1
• In profound, life-threatening hypotension, earlier administration of norepinephrine simultaneously with fluid resuscitation may be beneficial 5
• Avoid abrupt withdrawal; taper gradually when discontinuing 2
• Low doses (<0.2 mcg/kg/min) are associated with lower mortality compared to intermediate (0.2-0.4 mcg/kg/min) or high doses (>0.4 mcg/kg/min) 6

Alternative Vasopressors

• If norepinephrine is ineffective or contraindicated:
  • Epinephrine can be added or substituted 3
  • Vasopressin (0.03 units/minute) can be added to norepinephrine to raise MAP or decrease norepinephrine requirements 3
  • Dopamine may be considered only in selected patients with low risk of tachyarrhythmias 3, 1