A registered nurse in the cardiovascular intensive care unit is caring for a client with s… — NCLEX-RN

A registered nurse in the cardiovascular intensive care unit is caring for a client with severe decompensated heart failure.

Client data:
- Weight: $176\text{ lb}$
- Current cardiac index (CI): $1.8\text{ L/min/m}^2$
- Current dobutamine infusion rate: $12\text{ mL/hr}$
- Intravenous fluid bag: Dobutamine $500\text{ mg}$ in $250\text{ mL}$ of $5\%\text{ Dextrose in Water (D5W)}$

The unit's hemodynamic titration protocol states: "If CI is $< 2.0\text{ L/min/m}^2$ , increase dobutamine infusion by $2.5\text{ mcg/kg/min}$ every 30 minutes until CI is $\geq 2.0\text{ L/min/m}^2$ . Maximum dose: $20\text{ mcg/kg/min}$ ."

The nurse evaluates the client's current status and determines a titration is required. Based on the protocol, what should the nurse set the new infusion rate to in $\text{mL/hr}$ ? Record your answer to the nearest whole number.

Answer: 18 mL/hr

Answer

The correct infusion rate is 18 mL/hr. This is determined by first converting the client's weight to kilograms (80 kg) and finding the medication concentration (2000 mcg/mL). The current dose is calculated by multiplying the rate (12 mL/hr) by the concentration and dividing by time and weight, yielding 5 mcg/kg/min. Based on the low cardiac index, the protocol requires a 2.5 mcg/kg/min increase, making the new target dose 7.5 mcg/kg/min. Multiplying this target dose by the client's weight (80 kg) and time (60 minutes) yields 36,000 mcg/hr. Dividing by the concentration (2000 mcg/mL) provides the final pump setting of 18 mL/hr.

Step-by-Step Solution

Convert the client's weight from pounds to kilograms.

176\text{ lb} \div 2.2\text{ lb/kg} = 80\text{ kg}

Weight-based continuous medication infusions require the client's weight in kilograms for accurate dosing.

Calculate the concentration of the dobutamine solution in

\text{mcg/mL}

500\text{ mg} = 500,000\text{ mcg}

;

500,000\text{ mcg} \div 250\text{ mL} = 2000\text{ mcg/mL}

Establishing the concentration is necessary to convert between liquid volume (mL) and drug mass (mcg).

Calculate the current rate in

\text{mcg/min}

to determine the current weight-based dose.

12\text{ mL/hr} \times 2000\text{ mcg/mL} = 24,000\text{ mcg/hr}

;

24,000 \div 60 = 400\text{ mcg/min}

The protocol dictates titration based on the current dose in

\text{mcg/kg/min}

, requiring a reverse calculation from the current pump setting.

Divide the

\text{mcg/min}

by the client's weight to find the current

\text{mcg/kg/min}

400\text{ mcg/min} \div 80\text{ kg} = 5\text{ mcg/kg/min}

This confirms the baseline dose before applying the hemodynamic titration protocol.

Determine the new target dose based on the client's cardiac index.

CI is

1.8

(which is

< 2.0

), so add

2.5\text{ mcg/kg/min}

;

5 + 2.5 = 7.5\text{ mcg/kg/min}

The protocol mandates a specific incremental dose increase to improve cardiac output when CI is below target.

Calculate the total new dose required in

\text{mcg/hr}

7.5\text{ mcg/kg/min} \times 80\text{ kg} = 600\text{ mcg/min}

;

600 \times 60 = 36,000\text{ mcg/hr}

Pump rates are set in

\text{mL/hr}

, so the target dose must be converted to an hourly amount.

Divide the hourly dose by the concentration to find the new rate in

\text{mL/hr}

36,000\text{ mcg/hr} \div 2000\text{ mcg/mL} = 18\text{ mL/hr}

This yields the final volume per hour to program into the intravenous infusion pump.

Key Concept

Titrating weight-based vasoactive infusions requires calculating the baseline dose from the existing rate, applying clinical parameters to determine the new target dose, and calculating forward to find the final pump setting in mL/hr.

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