IV Dilution Problem Help!

Music in My Heart · Jan 9, 2012

Hey everyone! I need some help with this problem. I want to know how to work it out, not just the answer please! Any help would be very much appreciated!
A 10 year old child is to receive Zosyn 750 mg IVPB q12h. The drug book states: dilute 10-20 mg/ml and administer over 30 minutes. The pharmacy has sent up Zosyn 800 mg in 15 ml. How should the nurse dilute and administer this medication?
A. Add medication to a 25 ml bag of fluid and administer at 80 ml/hr with a VTBI of 40.
B. Add medication to a 50 ml bag of fluid and administer at 100 ml/hr with a VTBI of 50.
C. Add medication to a 100 ml bag of fluid and administer at 230 ml/hr with a VTBI of 115.

This is a lousy problem because none of the choices is actually correct... However, answer {C} is arguably the best of the three.

For simplicity, I'll just brute-force it and solve each choice...

{A}

Find the concentration

800 mg

----------------

15 mL + 25 mL

800 mg/40 mL = 20 mg/mL (acceptable, at the high end of the range)

Calculate the quantity (mass, actually) of medicine given:

20 mg/mL x 40 mL = 800 mg (too much... by 7%)

Calculate the administration time:

40 mL

-----------

80 mL/hr

40/80 = 0.5 hours or 30 mins (acceptable)

{B}

Following same approach:

Concentration = 800 / (50 + 15) = 12.3 mg/mL (acceptable)

Quantity = 12.3 mg/mL x 50 mL = 615 mg (too low by 18%)

50/100 = 30 min (acceptable)

{C}

Following same approach:

Concentration = 800 / (100 + 15) = 7 mg/mL (too low... though not really problematic)

Quantity = 7 mg/mL x 115 mL = 805 mg (too high by 7%)

230/115 = 30 min (acceptable)

I pick choice {C} because the lower concentration is easier on the veins but still delivers the requisite amount of medication in the ordered time. One could argue in favor of {A} by stating that the smaller volume is preferable in a child but a 10-year-old probably weighs about 35 kg or so and a volume of 3 mL/kg is pretty minimal and not likely to create any issues in a kid without renal or cardiac problems.

I wouldn't be cool giving a dose 7% higher than the one ordered, though... would have to seek MD clarification before I gave it...

Or better yet, just add the 15 mL dose to a 50 mL bag and give 61 mL at 122 mL/hr... and say "pshaww" to stupid multiple-choice questions....

MrChicagoRN, RN · Jan 9, 2012

a 10 year old child is to receive zosyn 750 mg ivpb q12h. the drug book states: dilute 10-20 mg/ml and administer over 30 minutes. the pharmacy has sent up zosyn 800 mg in 15 ml. how should the nurse dilute and administer this medication?
a. add medication to a 25 ml bag of fluid and administer at 80 ml/hr with a vtbi of 40.
b. add medication to a 50 ml bag of fluid and administer at 100 ml/hr with a vtbi of 50.
c. add medication to a 100 ml bag of fluid and administer at 230 ml/hr with a vtbi of 115.

not sure what is meant by the highlighted text, except as a primary dilutent (which the pharmacy does). official fda information is:

"reconstituted zosyn solution should be further diluted (recommended volume per dose of 50 ml to 150 ml) in a compatible intravenous solution listed below. administer by infusion over a period of at least 30 minutes. during the infusion it is desirable to discontinue the primary infusion solution."

[color=#333333]

that information instantly eliminates one answer. of the other two choices, the rates would would infuse one in exactly 30 minutes, while the other would infuse in at a little more than 1/2 hours.

is this question purely math,or does it involve critical thinking? i.e. how much & how fast do you want to infuse into a 10 year old?