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Difficulty: Very hardPharmacological and Parenteral Therapies

During a shift in the cardiac intensive care unit, a nurse receives an order to titrate a continuous dobutamine infusion for a client in cardiogenic shock. The client's documented weight is 92 kg92\text{ kg}. The medication is infusing from a 250 mL250\text{ mL} bag of 5% dextrose in water (D5W) containing 500 mg500\text{ mg} of dobutamine. The current pump rate is displayed as 18 mL/hr18\text{ mL/hr}.

The prescribed titration parameter dictates: "Increase dobutamine dose by 2.5 mcg/kg/min2.5\text{ mcg/kg/min} every 15 minutes to maintain a mean arterial pressure (MAP) >65 mmHg> 65\text{ mmHg}."

The last titration was 20 minutes ago, and the client's current MAP is 58 mmHg58\text{ mmHg}. What new rate, in mL/hr\text{mL/hr}, must the nurse program into the infusion pump? Record your answer using one decimal place.

Answer: 24.9 mL/hr

Answer

24.9
To safely perform an upward titration of a continuous weight-based vasoactive infusion, the nurse must accurately calculate the incremental volume increase and add it to the current baseline rate. First, find the concentration: \(500\text{ mg} = 500,000\text{ mcg}\); \(500,000\text{ mcg} \div 250\text{ mL} = 2,000\text{ mcg/mL}\). Next, calculate the increase needed: \(2.5\text{ mcg/kg/min} \times 92\text{ kg} = 230\text{ mcg/min}\). Convert this to an hourly dose: \(230\text{ mcg/min} \times 60\text{ min/hr} = 13,800\text{ mcg/hr}\). Determine the pump volume for this increase: \(13,800\text{ mcg/hr} \div 2,000\text{ mcg/mL} = 6.9\text{ mL/hr}\). Finally, add this volume to the current rate: \(18\text{ mL/hr} + 6.9\text{ mL/hr} = 24.9\text{ mL/hr}\).

Step-by-Step Solution

1
Calculate the concentration of the dobutamine infusion in mcg/mL.
\(2,000\text{ mcg/mL}\)
Converting to mcg/mL establishes the baseline concentration needed to calculate volume for the weight-based dose, since dobutamine is dosed in mcg/kg/min.
2
Determine the required dose increase per minute based on the client's weight.
\(230\text{ mcg/min}\)
The protocol requires an increase of 2.5 mcg/kg/min. Multiplying by the client's weight (92 kg) gives the total mcg per minute to add.
3
Convert the dose increase from a per-minute rate to a per-hour rate.
\(13,800\text{ mcg/hr}\)
IV pumps are programmed in mL/hr, so the medication dose must be converted to an hourly rate before calculating the corresponding fluid volume.
4
Calculate the additional volume rate (mL/hr) required to deliver the dose increase.
\(6.9\text{ mL/hr}\)
Dividing the hourly dose (13,800 mcg/hr) by the concentration (2,000 mcg/mL) determines how much additional fluid volume is needed per hour.
5
Add the calculated additional volume rate to the current infusion pump rate.
\(24.9\text{ mL/hr}\)
The question asks for the NEW rate on the IV pump, which is the sum of the current continuous rate (18 mL/hr) and the calculated titration increase (6.9 mL/hr).

Key Concept

Continuous IV Infusion Titration and Weight-Based Dosage Calculation
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Topics

Pharmacological and Parenteral Therapies

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