Pediatric Med
Math Review
Dr. McBride ­ November 2022 cohort
Important
Conversions
Review of common conversions used
in the pediatric setting
Important Conversions – Peds
30 mL
=
1 oz
15 mL
=
1 Tbsp
5 mL
=
1 mL
=
1 kg
=
1g
=
1000 mg
1L
=
1000 mL
NS
=
0.9% NaCl
1 tsp
1 gm (of H2O or urine)
2.2 lb
Maintenance Therapy
Body Weight
First 10 kg
ml of fluid/kg/24 hour
100 ml/kg
Second 10 kg
50 ml/kg
Each additional kg
20 ml/kg
Safe Pediatric Dosages
1. Convert weight from lb. to kg. (if needed)
2. Calculate the safe dose (range) based on the pediatric
recommended dose (provided)
3. Compare ordered dose to the recommended safe dose
Remember Fractional
Dosage Calculations
D/H x Q
D = Ordered Dose Amount (usually in g/mg/mcg)
H = On Hand Amount (usually in g/mg/mcg)
Q = Quantity (usually in mL)
DILUTION
Dilution required in tubing or piggyback to administer the drug (mL)
●
WHY?
After calculating the fractional dose, you need to dilute the IV med the
prevent vein irritation or serious side effects
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UNITS?
mg / mL
●
HOW?
Use cross multiplication to calculate safe mL based on med
dose (mg) & subtract fractional dose
Total Dilution Volume — Fractional Dose Volume = Diluent Volume (NS or sterile H2O)
IV Drugs: STEPS
1. Calculate safe therapeutic dose (in mg)
2. Calculate fractional dose (volume of med in mL)
3. Dilution required (mL)
4. Length of time for med to be administered (usually 10-60 min)
5. Flush required for tubing (20 mL)
6. Total volume to be infused
7. Rate of IV per hour
DILUTION Steps – Summary
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Weight (kg) :
Therapeutic dose :
FD :
Total Dilution (TD) :
○ TD - FD = Diluent (D) :
Time :
Flush : 20 mL
IV Rate : TD / Time (mL/hr)
Practice
Questions
A child weighs 18.60 lb. What would be this patient’s daily
fluid maintenance needs?
845 mL/day
18.6 lb / 2.2 = 8.454545 kg
First 10 kg of body weight ­ 8.454545 kg x 100 mL/kg/day = 845.4545
A child weighs 45 kg. What would be this patient’s daily
fluid maintenance needs?
2000 mL/day
First 10 kg of body weight ­ 10 kg x 100 mL/kg/day = 1000 mL/day
Second 10 kg of body weight ­ 10 kg x 50 mL/kg/day = 500 mL/day
Anything above 20 kg of body weight ­ 25 kg x 20 mL/kg/day = 500 mL/day
Total: 2000 mL/day
Doctor orders Zithromax for a child that weighs 82 lbs. The
safe dose range for this medication is 10-12 mg/kg/day. What
is the maximum safe daily dose for this child?
446.3 mg
82 lb / 2.2 = 37.272 kg
Low: 10 mg x 37.272 kg = 372.7 mg
High: 12 mg x 37.272 kg = 446.264 mg
Doctor orders 200 mg of Ibuprofen every 8 hrs. The child weighs
49 lbs. The safe dosage range for this medication is 5-10
mg/kg/dose. What is the safe dosage range for this particular
child?
111.4 ­ 222.7 mg/dose
49 lb / 2.2 = 22.272 kg
Low: 5 mg x 22.272 kg = 111.36 mg/dose
High: 10 mg x 22.272 kg = 222.72 mg/dose
Doctor’s Order: Amoxicillin 50 mg po q6h
Child weighs 15 lbs.
Safe range is 25 – 30 mg/kg/24 hr
Bottle on hand 125 mg/5 mL
A. What is the safe dose for this child?
170 mg/24 hr ­ 204 mg / 24 hr
B. Is this order safe?
Yes ~ 50 mg x 4 = 200 mg/24 hr
C. If safe, what is the fractional dose?
2 mL = 50 mg/125 mg x 5 mL
Ordered: Ciprofloxacin 200 mg IV q12h
Available in vial: 200 mg in 1.6 mL
Safe concentration: 10 mg/mL
How many mL of normal saline would you need to add to dilute
200 mg of Ciprofloxacin and have the correct concentration?
FD:
TD:
200 mg/200 mg x 1.6 mL = 1.6 mL
10 mg
1 mL
200 mg
X
X = 20 mL
Diluent: TD - FD = D → 20 mL ­ 1.6 mL = 18.4 mL
For TD ~ you can also
use D/H x Q equation
using ordered amount
(D) & safe
concentration (H, Q)
A pediatric patient weighs 22 kg. The patient will receive two 90
mL, PO feeds on your shift. He will get one antibiotic which
requires 30 mL of dilution and 20 mL of flush during your shift. It
will run over 60 minutes.
A.
What is the patient’s ⅔ fluid requirement for:
a.
b.
B.
C.
D.
24 hours?
8 hours?
What is the patient’s p.o. intake for your shift?
How much IV fluid will the patient need for medication administration on
your shift?
What IV flow rate, on the pump (mL/hour) will needed to achieve ⅔ fluid
maintenance when the abx is not running during your shift?
A pediatric patient weighs 22 kg. The patient will receive two 90 mL, PO feeds on your shift. He will get
one antibiotic which requires 30 mL of dilution and 20 mL of flush during your shift. It will run over 60
minutes.
Weight:
22 kg
24h Fluid Requirement: 1000 mL + 500 mL + 2(20 mL) = 1540
⅔ 24 h:
1540 mL x 2 / 3 = 1026.667 = 1027 mL
⅔ 8 h:
1027 / 3 = 342.333 = 342 mL
P.O. intake:
90 mL + 90 mL = 180 mL
IV fluid for med:
30 mL + 20 mL = 50 mL
IV flow rate to achieve ⅔ fluid maintenance:
342 mL - 180 mL - 50 mL = 112 / 7 = 16 mL/hr
Ordered: Ampicillin 250 mg IV TID
Patient weight: 20 kg
Available in vial: 500 mg in 1.6 mL
Safe dose is 50 100 mg/kg/24 hours
Safe concentration: 50 mg/mL
How many mL of normal saline would you need to add to dilute 250 mg of Ampicillin and
have the correct concentration? The medication is to be administered over 30 minutes,
what is the hourly rate of IV infusion?
Weight (kg) : 20 kg
Therapeutic dose : 250 mg
FD : 250 mg / 500 mg x 1.6 mL = 0.8 mL
Total Dilution (TD) : 250 mg/50 mg x 1 mL = 5 mL
TD - FD = Diluent (D) : 5 mL ­ 0.8 mL = 4.2 mL
Time : 30 min = 0.5 hr
Flush : 20 mL
IV Rate : TD / Time (mL/hr) = 5 mL / 0.5 hr = 10 mL /hr
More Practice & Other Resources
SMU Peer Tutoring:
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Upswing Instructions
Request a Tutor Form
Videos:
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Daily Maintenance Fluid Requirement
Pediatric Maintenance Fluid Requirements Calculations
Safe Dosage Calculation for IV Meds
Weight-Based Dosage Calculations
Registered Nurse RN Pediatric dosage