Nitroglycerin Infusion Rate Calculation for 5 mcg/hour
To deliver 5 mcg/hour of nitroglycerin from a 50 ml solution with vials containing 25 mg in 5 ml, the infusion pump should be set at 0.06 ml/hour.
Calculation Process
To determine the correct infusion rate, we need to follow a systematic approach:
Step 1: Determine the concentration of the prepared solution
- Each vial contains 25 mg NTG in 5 ml
- For a 50 ml total volume infusion:
- Concentration = 25 mg ÷ 50 ml = 0.5 mg/ml
- Converting to mcg/ml: 0.5 mg/ml = 500 mcg/ml
Step 2: Calculate the required flow rate
- Desired dose: 5 mcg/hour
- Flow rate = Desired dose ÷ Concentration
- Flow rate = 5 mcg/hour ÷ 500 mcg/ml = 0.01 ml/hour
Step 3: Verify the calculation
- At 0.01 ml/hour, the delivered dose would be:
- 0.01 ml/hour × 500 mcg/ml = 5 mcg/hour
Clinical Considerations
When administering nitroglycerin infusions, it's important to note:
- According to ACC/AHA guidelines, standard IV nitroglycerin dosing typically starts at 5 mcg/min (300 mcg/hour) with increases in increments of 5 mcg/min every 3-5 minutes to a maximum of 20 mcg/min 1
- The dose being prepared (5 mcg/hour) is significantly lower than typical therapeutic doses used for hypertensive emergencies or acute coronary syndromes
- For acute coronary syndromes, nitroglycerin is typically initiated at 10 mcg/min and increased by 10 mcg/min every 3-5 minutes until symptom relief or blood pressure response 1
Important Precautions
- Ensure the infusion pump can accurately deliver such a low flow rate (0.01 ml/hour)
- Many standard infusion pumps have minimum flow rate limitations that may exceed this value
- Consider using a syringe pump designed for low-flow applications if available
- Double-check all calculations before administration to prevent medication errors
- Monitor the patient closely for hypotension, especially if they are receiving other antihypertensive medications
Verification
To ensure accuracy, always have a second qualified healthcare provider independently verify the calculation before administration.