## Tuesday, January 5, 2016

### Dosage Calculation - Mass/Time - IV mL Rate Questions

By Dosagehelp.com

Mass/Time - IV mL Rate Questions

Give an order in quantity of mass per time, determine the necessary IV flow rate in mL/hr based on the given mass per volume. These types of problems are often used in critical care nursing.

Formula:
$\overline{)\frac{{\mathbf{Ordered Per Hour}}}{{\mathbf{Have}}}x{\mathbf{Volume \left(mL\right)}}={\mathbf{Y\left(Flow Rate in mL/hr\right)}}}$

Example: Give patient 500 mg of dopamine in 250 mL of D5W to infuse at 20 mg/hr. Calculate the flow rate in mL/hr.
$\frac{{\mathbf{Ordered Per Hour}}}{{\mathbf{Have}}}x{\mathbf{Volume \left(mL\right)}}={\mathbf{Y\left(Flow Rate in mL/hr\right)}}$
$\frac{{\mathbf{20 mg/hr}}}{{\mathbf{500 mg}}}x{\mathbf{250 mL}}=\overline{){\mathbf{10 mL/hr}}}$
Alternatively 500 mg = 250 mL
Therefore, 20 mg/hr = 250 mL/500 mg x 20 mg/hr = 10 mL/hr

Example: Aggrastat at 12.5 mg in 250 mL is prescribed to be infused at a rate of 6 mcg/kg/hr in a patient who weighs 100 kg. At what flow rate in mL/hr will you set the pump?
$\frac{{\mathbf{Ordered Per Hour}}}{{\mathbf{Have}}}x{\mathbf{Volume \left(mL\right)}}={\mathbf{Y\left(Flow Rate in mL/hr\right)}}$
The first step is to convert the order per time to the amount required for this particular patient. This is a Dosage By Weight Question. 6 mcg/kg/hr is a dosage in terms of kg.
${\mathbf{Weight in Kg}}x{\mathbf{Dosage Per Kg}}={\mathbf{Y\left(Required Dosage\right)}}$
${\mathbf{100 Kg}}x{\mathbf{6 mcg/kg/hr}}={\mathbf{600 mcg/hr}}$
Convert 600 mcg/hr to mg/hr.
mcg → mg → g → kg    ( ÷ by 1,000 )
600 ÷ 1,000 = 0.6 mg/hr

$\frac{{\mathbf{0.6 mg/hr}}}{{\mathbf{12.5 mg}}}x{\mathbf{250 mL}}=\overline{){\mathbf{12 mL/hr}}}$
Alternatively 12.5 mg = 250 mL
Therefore, 0.6 mg/hr = 250 mL/12.5 mg x 0.6 mg/hr = 12 mL/hr

Question (22): (From Ngee Ann Polytechnics Dosage Calculation Worksheet)
ORDER: I/V Dopamine 5 mcg/kg/min. Dilution - 200 mg/100 mL Normal Saline. Patient Weight:
50 kg.
Calculate: __________ mL/hr = 5 mcg/kg/min.

$\frac{{\mathbf{Ordered Per Hour}}}{{\mathbf{Have}}}x{\mathbf{Volume \left(mL\right)}}={\mathbf{Y\left(Flow Rate in mL/hr\right)}}$
The first step is to convert the order per time to the amount required for this particular patient. This is a Dosage By Weight Question. 50 kg is the weight in kg and 5 mcg/kg/min is a dosage in terms of kg.

1 min Dosage = 5 mcg/kg
1 hour Dosage = 5 mcg/kg x 60 = 300 mcg/kg
5 mcg/kg/min = 300 mcg/kg/hr

${\mathbf{Weight in Kg}}x{\mathbf{Dosage Per Kg}}={\mathbf{Y\left(Required Dosage\right)}}$
${\mathbf{50 Kg}}x{\mathbf{300 mcg/kg/hr}}={\mathbf{15,000 mcg/hr}}$
Convert 15,000 mcg/hr to mg/hr.
mcg → mg → g → kg    ( ÷ by 1,000 )
15,000 ÷ 1,000 = 15 mg/hr

$\frac{{\mathbf{15 mg/hr}}}{{\mathbf{200 mg}}}x{\mathbf{100 mL}}=\overline{){\mathbf{7.5 mL/hr}}}$
Alternatively 200 mg = 100 mL
Therefore, 15 mg/hr = 100 mL/200 mg x 15 mg/hr = 7.5 mL/hr

Question (23): (From Ngee Ann Polytechnics Dosage Calculation Worksheet)
ORDER: I/V Dopamine 1 mcg/kg/min. Patient Weight: 50 kg.
Calculate: Amount of Dopamine in 100 mL diluent to deliver 1 mL/hr = 1 mcg/kg/min

The first step is to convert the order per time to the amount required for this particular patient. This is a Dosage By Weight Question. 50 kg is the weight in kg and 1 mcg/kg/min is a dosage in terms of kg.

1 min Dosage = 1 mcg/kg
1 hour Dosage = 1 mcg/kg x 60 = 60 mcg/kg
1 mcg/kg/min = 60 mcg/kg/hr

${\mathbf{Weight in Kg}}x{\mathbf{Dosage Per Kg}}={\mathbf{Y\left(Required Dosage\right)}}$
${\mathbf{50 Kg}}x{\mathbf{60 mcg/kg/hr}}={\mathbf{3,000 mcg/hr}}$
Convert 3,000 mcg/hr to mg/hr.
mcg → mg → g → kg ( ÷ by 1,000 )
3,000 ÷ 1,000 = 3 mg/hr
$\frac{{\mathbf{Ordered Per Hour}}}{{\mathbf{Have}}}x{\mathbf{Volume \left(mL\right)}}={\mathbf{Y\left(Flow Rate in mL/hr\right)}}$
$\frac{{\mathbf{3 mg/hr}}}{{\mathbf{Amt. of Dopamine}}}x{\mathbf{100 mL}}={\mathbf{1 mL/hr}}$
${\mathbf{Amt. of Dopamine}}=\frac{{\mathbf{3 mg/hr}}x{\mathbf{100 mL}}}{{\mathbf{1 mL/hr}}}=\overline{){\mathbf{300 mg}}}$
Alternatively,
To deliver, 1 mL = 3 mg of Dopamine
Therefore, 100 mL diluent = 3/1 x 100 = 300 mg of Dopamine

Question (24): (From Ngee Ann Polytechnics Dosage Calculation Worksheet)
Patient Weight:
50 kg.
Calculate amount diluent for 200 mg Dopamine to deliver 1 mL/hr = 1 mcg/kg/min (Dosage).

The first step is to convert the order per time to the amount required for this particular patient. This is a Dosage By Weight Question. 50 kg is the weight in kg and 1 mcg/kg/min is a dosage in terms of kg.

1 min Dosage = 1 mcg/kg
1 hour Dosage = 1 mcg/kg x 60 = 60 mcg/kg
1 mcg/kg/min = 60 mcg/kg/hr

${\mathbf{Weight in Kg}}x{\mathbf{Dosage Per Kg}}={\mathbf{Y\left(Required Dosage\right)}}$
${\mathbf{50 Kg}}x{\mathbf{60 mcg/kg/hr}}={\mathbf{3,000 mcg/hr}}$
Convert 3,000 mcg/hr to mg/hr.
mcg → mg → g → kg ( ÷ by 1,000 )
3,000 ÷ 1,000 = 3 mg/hr
$\frac{{\mathbf{Ordered Per Hour}}}{{\mathbf{Have}}}x{\mathbf{Volume \left(mL\right)}}={\mathbf{Y\left(Flow Rate in mL/hr\right)}}$
$\frac{{\mathbf{3 mg/hr}}}{{\mathbf{200 mg}}}x{\mathbf{Volume of diluent \left(mL\right)}}={\mathbf{1 mL/hr}}$
${\mathbf{Volume of diluent \left(mL\right)}}={\mathbf{1 mL/hr}}x\frac{{\mathbf{200 mg}}}{{\mathbf{3 mg/hr}}}=\overline{){\mathbf{66.7 mL}}}$
Alternatively,
To deliver, 3 mg of Dopamine = 1 mL
Therefore, 200 mg of Dopamine = 1/3 x 200 = 66.7 mL of diluent

Question (25): (From Ngee Ann Polytechnics Dosage Calculation Worksheet)
0.02 mcg/kg/min. Dilution - 1.5 mg/50 mL. Patient Weight: 50 kg.
Calculate: __________ mL/hr =
0.02 mcg/kg/min.
$\frac{{\mathbf{Ordered Per Hour}}}{{\mathbf{Have}}}x{\mathbf{Volume \left(mL\right)}}={\mathbf{Y\left(Flow Rate in mL/hr\right)}}$
The first step is to convert the order per time to the amount required for this particular patient. This is a Dosage By Weight Question. 50 kg is the weight in kg and 0.02 mcg/kg/min is a dosage in terms of kg.

1 min Dosage = 0.02 mcg/kg
1 hour Dosage = 0.02 mcg/kg x 60 = 1.2 mcg/kg
0.02 mcg/kg/min = 1.2 mcg/kg/hr

${\mathbf{Weight in Kg}}x{\mathbf{Dosage Per Kg}}={\mathbf{Y\left(Required Dosage\right)}}$
${\mathbf{50 Kg}}x{\mathbf{1.2 mcg/kg/hr}}={\mathbf{60 mcg/hr}}$
Convert 60 mcg/hr to mg/hr.
mcg → mg → g → kg    ( ÷ by 1,000 )
60 ÷ 1,000 = 0.06 mg/hr

$\frac{{\mathbf{0.06 mg/hr}}}{{\mathbf{1.5 mg}}}x{\mathbf{50 mL}}=\overline{){\mathbf{2 mL/hr}}}$
Alternatively 1.5 mg = 50 mL
Therefore, 0.06 mg/hr = 50 mL/1.5 mg x 0.06 mg/hr = 2 mL/hr

Congratulations: You have completed the Dosage Calculation Worksheet From Ngee Ann Polytechnics.

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