My Reviewer: Dosage and Calculations

Before going to the topic, here's an addendum to my previous blog about what's written at the back of San Mig Light's label: "When the work is done and it's time for rest, Let there be San Mig Light." Ngayon ko lang naalala :)

In our previous lecture, we discussed again dosage and calculations. Everything about this topic seemed much clearer to me now. We had a post-test, as usual, and I'm happy to pass all the exams.

Here are some of the questions on dosage and calculations:

1. IVF 1.5 liters to run for 94 cc/hr
a. no. of hours to be infused
b. gtts/min

2. IVF 1 liter to run for 25 gtts/min
a. no. of hours to be infused
b. cc/hr

3. 1 liter of an IVF to run for 3 hours with an infusion set that delivers 10 gtts/ml. 400 ml remains after infusing for 1 hr and 15 mins. Find the gtts/min needed so that the IVF finishes in the required time

4. 100ml of an IVF to run for 2 hours via soluset.

5. Dopamine* 2 amps (ampules) in 500 ml D5W to run for 12 mcg/kg/min. Patient's weight is 60 lbs.

6. ISDN* (Isosorbide Dinitrate or Isoket) 2 amps in 100 ml D5W to run for 2 mg/hr.

7. KCl* (Potassium Chloride) 30 mEqs in 1,000 ml IVF. How many ml of KCl will you incorporate?

8. Drug available is 20 mg/5 ml. Prescription is 40 mg. How many ml will you give?



*In answering items #5-7, you must know by heart the stock dose of those emergency drugs:

Dopamine is 200mg in 2ml ampule
ISDN/Isoket is 20mg/ampule
KCl is 40mEqs in 20ml vial


Solution #5:

Formula:

Order (mcg/kg/min) x weight (in kg) x 60 min/hr)
---------------------------------------------------------
concentration of drug in IVF

Order: 12 mcg/kg/min
Pt's. weight (must be converted into kg): 60 lbs /2.2 kg = 27.2 kg
Dopamine 2 amps (must be converted into mcg):
200mg x 2 amps x 1,000 mcg = 400,000 mcg
Concentration of Dopamine in 500 ml D5W:
400,000mcg
--------------- = 800 mcg/ml
500ml

Solution:
12 mcg/kg/min x 27.2 kg x 60 min/hr
--------------------------------------- = 19,584 / 800 = 24.48 or 24 ml/hr
800 mcg/ml

Your final answer needs to be rounded off to eliminate the decimal numbers because we're talking about the drip rates here (there's no such thing as 24.4 drops, right?)

Tips: So you won't be bugged by what formula to be used in solving these IV drip rates of emergency drugs, just look at the units of measurement in the order. In this case, the order is "12 mcg/kg/min,"

so the formula will be:

mcg x kg x min
-------------------
concentration

the divisor, which is the concentration is always solved by:
drug x no. of amps (x 1,000 if needs to be converted from mg to mcg)
--------------------------------
no. of ml of IVF



Solution #6:

Order: ISDN 2 mg/hr
Concentration: 2 amps of ISDN 20 mg in 100 ml in D5W = 20 x 2 =40 mg / 100 = 0.04 mg/ml

2 mg/hr
--------- = 50 cc/hr
.04 mg/ml


Now, try answering the other items :)