What is the drop rate per minute for norepinephrine in a 35 kg patient?

Norepinephrine Drop Rate Calculation for a 35 kg Patient

For a 35 kg patient requiring norepinephrine in 500 ml NS with a drop factor of 20 drops/ml, the appropriate drop rate is 21-42 drops per minute.

Preparation of Norepinephrine Infusion

1. Standard Dilution:

   • According to FDA labeling, norepinephrine should be diluted in dextrose-containing solutions 1
   • Standard preparation: 4 mg (4 mL) of norepinephrine in 1000 mL of dextrose solution = 4 mcg/mL 1
   • For the specified 500 mL NS preparation: 4 mg in 500 mL = 8 mcg/mL concentration

2. Initial Dosing Calculation:

   • Starting dose for hypotensive states: 0.05-0.1 mcg/kg/min 2
   • For a 35 kg patient:
     • Low dose: 0.05 mcg/kg/min × 35 kg = 1.75 mcg/min
     • High dose: 0.1 mcg/kg/min × 35 kg = 3.5 mcg/min

3. Converting to Drop Rate:

   • With 8 mcg/mL concentration:
     • Low dose: 1.75 mcg/min ÷ 8 mcg/mL = 0.22 mL/min
     • High dose: 3.5 mcg/min ÷ 8 mcg/mL = 0.44 mL/min
   • With drop factor of 20 drops/mL:
     • Low dose: 0.22 mL/min × 20 drops/mL = 4.4 drops/min (round to 4-5 drops/min)
     • High dose: 0.44 mL/min × 20 drops/mL = 8.8 drops/min (round to 9 drops/min)

Titration and Adjustment

• Initial rate should be 4-9 drops/min based on the standard dosing range
• Titrate upward by 2-3 drops/min every 5-10 minutes based on blood pressure response 2
• Target mean arterial pressure (MAP) of 65 mmHg 2
• Maximum dose may reach up to 3 mcg/kg/min in severe cases, which would correspond to approximately 42 drops/min for this patient 2

Important Considerations

• Administer through a central venous line whenever possible to prevent extravasation 2
• If using peripheral access, monitor the IV site frequently for signs of extravasation
• Continuous cardiac monitoring and frequent blood pressure measurements are essential 2
• Assess for hypovolemia before and during vasopressor therapy; correct volume depletion when present 1
• For pediatric patients (35 kg suggests a child/adolescent), close monitoring is particularly important due to higher sensitivity to vasopressors

Cautions

• Avoid abrupt withdrawal; taper gradually when discontinuing 1
• Monitor for adverse effects including tachyarrhythmias, increased myocardial oxygen consumption, and tissue ischemia 2
• Dosing should be adjusted based on individual patient response rather than strictly adhering to weight-based calculations 3, 4

Remember that norepinephrine is a potent vasopressor that requires careful monitoring and titration based on clinical response.