## Monday, January 4, 2016

### Dosage Calculation - Volume/Time - IV Drop Rate Questions

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Volume/Time - IV Drop Rate Questions

Given a certain amount of liquid, a time period, and a drop factor (gtts/mL), what is the necessary IV flow rate in gtts/min? Measurement used when IV is regulated manually. Because it is not possible to give a patient a fraction of a drop, it is typical to round answers for these problems up or down to the nearest whole number.

Formula:

$\overline{)\frac{{\mathbf{Volume \left(mL\right)}}}{{\mathbf{Time \left(min\right)}}}x{\mathbf{Drop Factor \left(gtts/mL\right)}}={\mathbf{Y\left(Flow Rate in gtts/min\right)}}}$

Example: Calculate the IV flow rate for 1200 mL of NS to be infused in 6 hours. The infusion set is calibrated for a drop factor of 15 gtts/mL.
$\frac{{\mathbf{Volume \left(mL\right)}}}{{\mathbf{Time \left(min\right)}}}x{\mathbf{Drop Factor \left(gtts/mL\right)}}={\mathbf{Y\left(Flow Rate in gtts/min\right)}}$
Convert 6 hours to minutes.
min ← hr    ( x by 60 )
6 hr x 60 = 360 min

$\frac{{\mathbf{1200 mL}}}{{\mathbf{360 min}}}x{\mathbf{15 gtts/mL}}=\overline{){\mathbf{50 gtts/min}}}$

Example: Calculate the IV flow rate for 200 mL of 0.9% NaCl IV over 120 minutes. Infusion set has drop factor of 20 gtts/mL.
$\frac{{\mathbf{Volume \left(mL\right)}}}{{\mathbf{Time \left(min\right)}}}x{\mathbf{Drop Factor \left(gtts/mL\right)}}={\mathbf{Y\left(Flow Rate in gtts/min\right)}}$
$\frac{{\mathbf{200 mL}}}{{\mathbf{120 min}}}x{\mathbf{20 gtts/mL}}=\overline{){\mathbf{33 gtts/min}}}$

Question (16): (From Ngee Ann Polytechnics Dosage Calculation Worksheet)
ORDER: I/V Normal Saline 1000 mL over 24 hours. Drop Factor = 60 gtts/mL.

${\mathbf{\text{Rate:}}}\overline{)\phantom{\rule{30pt}{12pt}}}{\mathbf{\text{gtts/min}}}$
$\frac{{\mathbf{Volume \left(mL\right)}}}{{\mathbf{Time \left(min\right)}}}x{\mathbf{Drop Factor \left(gtts/mL\right)}}={\mathbf{Y\left(Flow Rate in gtts/min\right)}}$
Convert 24 hours to minutes.
min ← hr    ( x by 60 )
24 hr x 60 = 1440 min

$\frac{{\mathbf{1000 mL}}}{{\mathbf{1440 min}}}x{\mathbf{60 gtts/mL}}=\overline{){\mathbf{41.7 gtts/min}}}$
Answer rounded to the nearest whole number = 42 gtts/min

Question (18): (From Ngee Ann Polytechnics Dosage Calculation Worksheet)
I/V D5% 1000 mL over 8 hours. Drop Factor = 20 gtts/mL.
${\mathbf{\text{Rate:}}}\overline{)\phantom{\rule{30pt}{12pt}}}{\mathbf{\text{gtts/min}}}$
$\frac{{\mathbf{Volume \left(mL\right)}}}{{\mathbf{Time \left(min\right)}}}x{\mathbf{Drop Factor \left(gtts/mL\right)}}={\mathbf{Y\left(Flow Rate in gtts/min\right)}}$
Convert 8 hours to minutes.
min ← hr    ( x by 60 )
8 hr x 60 = 480 min

$\frac{{\mathbf{1000 mL}}}{{\mathbf{480 min}}}x{\mathbf{20 gtts/mL}}=\overline{){\mathbf{41.7 gtts/min}}}$
Answer rounded to the nearest whole number = 42 gtts/min

Question (19): (From Ngee Ann Polytechnics Dosage Calculation Worksheet)
ORDER: I/V gentamycin 80 mg/100 mL N/Saline over 1 hour. Drop Factor = 60 gtts/mL.

${\mathbf{\text{Calculate Rate:}}}\overline{)\phantom{\rule{30pt}{12pt}}}{\mathbf{\text{gtts/min}}}$
$\frac{{\mathbf{Volume \left(mL\right)}}}{{\mathbf{Time \left(min\right)}}}x{\mathbf{Drop Factor \left(gtts/mL\right)}}={\mathbf{Y\left(Flow Rate in gtts/min\right)}}$
Convert 1 hours to minutes.
min ← hr    ( x by 60 )
1 hr x 60 = 60 min

$\frac{{\mathbf{100 mL}}}{{\mathbf{60 min}}}x{\mathbf{60 gtts/mL}}=\overline{){\mathbf{100 gtts/min}}}$

Question (20): (From Ngee Ann Polytechnics Dosage Calculation Worksheet)
ORDER: I/V Osmofundin 20% 100 mL over 30 Minutes. Drop Factor 60 gtts/mL.

${\mathbf{\text{Rate:}}}\overline{)\phantom{\rule{30pt}{12pt}}}{\mathbf{\text{gtts/min}}}$
$\frac{{\mathbf{Volume \left(mL\right)}}}{{\mathbf{Time \left(min\right)}}}x{\mathbf{Drop Factor \left(gtts/mL\right)}}={\mathbf{Y\left(Flow Rate in gtts/min\right)}}$
$\frac{{\mathbf{100 mL}}}{{\mathbf{30 min}}}x{\mathbf{60 gtts/mL}}=\overline{){\mathbf{200 gtts/min}}}$

Continue (Go to Volume/Time - IV mL Rate Questions)

Reference