Vasopressin Dosage Calculation for 1 kg Patient
The calculation is correct: at 0.0003 units/kg/min for a 1 kg patient using a 20 units/mL concentration, the infusion rate is 0.1 mL/hr.
Calculation Verification
Step-by-step breakdown:
- Desired dose: 0.0003 units/kg/min × 1 kg = 0.0003 units/min 1
- Convert to units/hour: 0.0003 units/min × 60 min/hr = 0.018 units/hr 1
- Calculate mL/hr: 0.018 units/hr ÷ 20 units/mL = 0.0009 mL/hr 2
However, this yields 0.0009 mL/hr, not 0.1 mL/hr as stated in your question.
Correct Dosing Context
For the rate of 0.1 mL/hr to be accurate with a 20 units/mL concentration:
- Actual delivered dose: 0.1 mL/hr × 20 units/mL = 2 units/hr 2
- Convert to units/min: 2 units/hr ÷ 60 min/hr = 0.0333 units/min 1
- Weight-based dose: 0.0333 units/min ÷ 1 kg = 0.0333 units/kg/min 1
Standard Pediatric Vasopressin Dosing
Guideline-recommended dosing for vasodilatory shock:
- Standard concentration: Vasopressin should be diluted from 20 units/mL to either 0.1 units/mL or 1 unit/mL for IV administration 2
- Adult dosing range: 0.01-0.04 units/min (not weight-based) for septic shock 1, 2
- Post-cardiotomy shock: 0.03-0.1 units/min 2
- Anaphylaxis (refractory): 0.01-0.04 units/min using 25 units/250 mL concentration (0.1 units/mL) 1
Critical Safety Considerations
Weight-based dosing in neonates/infants requires extreme caution:
- The dose of 0.0333 units/kg/min (which is what 0.1 mL/hr delivers) is extraordinarily high - this would be equivalent to 2.33 units/min in a 70 kg adult, which is 58-233 times higher than recommended adult dosing 2, 3
- Standard adult fixed dosing is 0.03-0.04 units/min total dose, not per kilogram 2, 3
- No established pediatric weight-based dosing exists in guidelines - vasopressin dosing in septic shock is typically given as fixed doses even in adults 2, 3
Recommended Approach for 1 kg Patient
If vasopressin is indicated (vasodilatory shock refractory to fluids and catecholamines):
- Dilute appropriately: Create 0.1 units/mL solution (25 units in 250 mL) 1, 2
- Start with lowest possible dose: Consider 0.0001-0.0003 units/min (NOT per kg) as initial rate 2
- This translates to: 0.03-0.09 mL/hr using 0.1 units/mL concentration 1
- Titrate cautiously based on blood pressure response and catecholamine sparing effect 2, 3
The stated dose of 0.0003 units/kg/min appears to be a transcription error - this should likely be 0.0003 units/min (total dose, not weight-based), which would equal 0.09 mL/hr using a 0.1 units/mL dilution 1, 2.