The calculation requires three steps. First, determine the concentration of the vasopressin solution: 40 units divided by 100 mL equals 0.4 units/mL. Second, convert the ordered dose rate from minutes to hours: 0.03 units/minute multiplied by 60 minutes/hour equals 1.8 units/hour. Finally, calculate the infusion rate in mL/hr by dividing the hourly dose by the concentration: (1.8 units/hr) / (0.4 units/mL) = 4.5 mL/hr. This is the correct rate to deliver the prescribed dose.

A. 4.0 ml/hr: This rate is incorrect and would result in underdosing the patient. It may stem from a miscalculation of the hourly dose or the drug concentration.

B. 4.9ml/hr: This is a calculation error. This rate does not align with the prescribed dose and available concentration.

D. 3.5ml/hr: This is a calculation error. This rate would deliver an insufficient amount of medication to the patient.

E. 6ml/hr: This rate is incorrect and would result in overdosing the patient. It would be the correct rate for a dose of 0.04 units/min, not the prescribed 0.03 units/min.

1. University of Washington

School of Pharmacy. (n.d.). Pharmaceutical Calculations: Infusion Rate Calculations. In PHARM 559 Course Materials. This type of university courseware outlines the standard dimensional analysis method for calculating intravenous infusion rates. The formula used is Rate (mL/hr) = [Dose (units/hr)] / [Concentration (units/mL)].

2. Evans

L.

et al. (2021). Surviving Sepsis Campaign: International Guidelines for Management of Sepsis and Septic Shock 2021. Critical Care Medicine

49(11)

e1063-e1143. In Recommendation 31

the guidelines state

"For adults with septic shock on norepinephrine with inadequate mean arterial pressure levels

we suggest adding vasopressin (up to 0.03 U/min)." This peer-reviewed source validates the clinical appropriateness of the dose used in the question. (DOI: 10.1097/CCM.0000000000005337)

3. Stoklosa

M. J.

& Ansel

H. C. (2012). Pharmaceutical Calculations (14th ed.). Lippincott Williams & Wilkins. Chapter 11

"Isotonicity

Osmolality

and Intravenous Infusion Calculations

" provides the foundational principles and formulas for determining the rate of flow for intravenous infusions based on the volume of solution

quantity of drug

and desired dose.