Body surface area & advanced

Pediatric calculations

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Dosage based on

body weight

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EXAMPLE : Rx EryPed 150 mg Sig: q6h po.

The infant weighs 15 lb, 6 oz today. The literature states that the Safe dosage range (SDR) is 30 – 100 mg/kg / day in four divided doses. Do u dispense this medication or not???

1. Convert wt to kg.. • 6 oz = 6/12 lb = 0.5 lb • Wt = 15.5 lb = 15.5 / 2.2 = 7 kg

2. Calculate the SDR using drug procure, hospital formulary, handbook of drugs, or ped. Recommendations in drug literature.. • Low SDR = 30 X 7 = 210 mg • High SDR = 100 X 7 = 700 mg

ANSWER

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Answer:

3. Compare with the prescribed order.. • Dose per day = 150 X 4 = 600 mg • Dose is within the SDR

4. Calculate the dose and dispense… • 200 mg …………………….. 5 ml • 150 mg …………………….. ??? = 3.75 ml

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Dosage based on Body

surface area method

(BSA)

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The BSA method is an important measure in calculating dosage for infants , children and for selected adult populations, e.g. Patient undergoing open heart surgery or radiation therapy, severe burn victims and renal diseased pts. BSA is a mathematical estimate using the patient’s height and weight . BSA is expressed in (m2). Type of BSA Calculations: 1. Formula calculation 2. Nomogram chart

Body surface area

method (BSA)

using metric measurement of height and weight

using household measurement of height and weight

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Formula calculation

Example :Use the metric formula and the household formula to calculate the BSA of an infant whose length is 50 cm (20 in) and weight is 6.8 kg (16 lb).

metric : Household :

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BSA West Nomograqm

for normal height child use

rectangle chart

for abnormal connect

height/weight to cross at SA.

Refer to pediatric standard

growth charts and developmental

grids for normal height and weight

ranges for pediatric groups.

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Example : A child 126 cm tall and weighs 23 kg . The drug order reads : vincasar 1.8 mg IV At 10 am • Is this dosage safe for this child ?? Knowing that the recommended dosage as noted on the package insert is 2 mg/m2 • Supply: see label..

Answer: • determine BSA .. • Calculate SDR … SDR = 2 X 0.9 = 1.8 mg • Decide if the dose is safe… yes • Calculate one dose … 1mg ……………………..1 ml 1.8 mg …………………. ??? = 1.8 ml

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Children’s oral,

subcutaneous, and IM

medication

• Assignment for next week

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Children’s IV

medication

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Intermittent IV medication infusion

via volume control set

Injection port

Drug and Fluid administration

chamber

Clamp

Clamp

Injection port

Capped needle

Drip chamber

The fluid chamber holds 100 – 150 ml to be infused in specified time period , usually 60 min or less. The IV bag acts only as a reservoir to hold future fluid infusions. An electronic controller or pump may be used to control the flow rate, which alarms when the chamber empties. After the chamber has emptied and the medication has infused, a flush of IV fluids is given to be sure all the medication has cleared the tubing. The amount of fluid used in flushing ranges from 15 – 50 ml according to overall length of the tubing…(verify with hospital policy) Volume control sets are microdrip sets with a drop factor of 60 gtt/ml.

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Example 1: • ordered antibiotic 1 g q6h. • supplied : 2g powder form of antibiotic that requires reconstitution . pediatric direction from pharmacy: dilute to 100mg / ml, withdraw ordered amount , then further dilute to 30 ml, and administer over 20 min. Answer: 1. Reconstitute to 100mg/ml 100 mg ………………………. 1 ml 2000 mg …………………….. ??? = 20 ml 2. Withdraw the ordered amount 2 g …………….. 20 ml 1 g …………….. ??? = 10 ml 3. Place medication into volume control device and IV solution till 30 ml N.B. Don’t forget to add extra 15 ml flush fluid after the medication empties at the same rate.

4. Electronic flow rate set • 30 ml……… 20 min

??? ……….. 60 min = 90 ml / hr

4. Manual flow rate set • 60 gtt……….1 ml • ??? ……….30 ml/hr = 1800 gtt/hr

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Example 2: • order: D5 NS IV at 30 ml/hr for continuous infusion and gentamicin 30mg IV q8h over 30 min • supplied : as label Answer: 1. Calculate the dilution required to administer gentamicin at flow rate of 30

ml/h 30 ml ………………………. 60 min ??? ………………………….. 30 min = 15 ml 2. Withdraw the ordered amount 40 mg …………….. 1 ml 30 mg …………….. ??? = 0.75 ml 3. Place 0.75 ml medication into volume control device and IV solution till 15 ml 4. Set the flow rate at 30ml /h or 1800 gtt / hr N.B. : Don’t forget to add extra 15 ml flush fluid after the medication empties at

the same rate.

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Preparing Pediatric IV

example : • Order : D5 ½ NS IV KCl 20 mEq / L to infuse at 30ml/h. The child length is 64 cm and weigh 7.2 kg

1. Should you choose a 1 l or 500 ml bag of IV ? • Volume of infusion needed = 30 X 24 = 720 ml • use 500 ml bag rather than 1 liter , otherwise the same 1 liter bag of IV fluid

would be infusing for more than 24 hrs, which is unsafe (sterility) and costy. 2. How many mEq KCl should you add to the 500 ml bag?

• 20 mEq …………….. 1000 ml ??? ……………….…..500 ml = 10 mEq

3. How much KCl should you add to the 500 ml bag? Knowing that KCl is available in 2 mEq/ml • 2 mEq …………….. 1 ml • 10 mEq …………… ??? = 5 ml

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4. How many mEq of KCl would the child receive per hour?

• Total IV volume = 500 + 5 = 505 ml, infusion rate = 30 ml/h • 10 mEq ……………. 505 ml

???........................ 30 ml = 0.6 mEq / hr

5. The recommended child dose is up to 3 mEq /kg / day or 40 mEq/m2/

day, based on child BSA, is the dosage ordered safe?

• KCl the child will receive per day = 0.6 X 24 = 14.4 mEq/day

• Child BSA = = 0.36 m2

• SDR = 0.36 X 40 = 14.4 mEq /day , therefore the dose is safe.

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Minimal / maximal dilution for IV

medications

IV medication are often ordered to be given in the smallest volume or maximal safe conc. To prevent fluid overload. pediatric IV medications state a minimum and maximum allowable conc. a solution of lower conc. Is called minimal safe conc., maximal dilution, or largest volume. a solution of higher conc. Is called maximal safe conc., minimal dilution, or smallest volume.

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Example: the physician orders Claforan 1.2 g IV q8h for a child who weighs 36 kg. the recommended safe dose for intermittent IV administration is a final conc. Of 20 – 60 mg/ml to infuse over 15 – 30 min. 1. What is the minimal amount of IV fluids to safely dilute this dosage ? 2. What is the maximal amount of IV fluids to safely dilute this dosage to the minimal

safe conc.?

Answer: 1. Minimal amount of IV fluid

• 60 mg …………… 1 ml • 1200 mg ……….. ??? = 20 ml • Therefore dissolve 1.2 g claforan in 20 ml to give 60 mg/ml (maximal safe conc.)

2. Maximal amount of IV fluid • 20 mg ………….1 ml • 1200 mg ……… ??? = 60 ml • Therefore dissolve 1.2 g claforan in 60 ml to give 20 mg/ml (minimal safe conc.)

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Calculation of Daily Volume for

maintenance fluids

Use this formula to calculate the daily rate of pediatric maintenance IV fluids • 100 ml/kg/day ………….. 1st 10 kg of body wt • 50 ml/kg/day ………….. 2nd 10 kg of body wt • 20 ml /kg/day ………….. for each kg above 20 kg of body wt

This formula use the child wt to estimate 24 – hour total fluid need, including oral intake It doesn’t include replacement for losses e.g. Vomiting , diarrhea,…etc Pediatric IV soln. That run over 24 hrs usually includes a combination of:

• Glucose / dextrose for energy between 5 – 12 % • Saline between 0.225 – 0.9 % (1/4 ns – ns) • 20meq / l of kCl

Any dextrose and saline combination without potassium should be used only as intermittent or short term IV fluid in children. Be ware of isotonic solution like 5% dextrose in water or 0.9% NaCl , if running continuously on an infant or child … as they don’t contribute enough electrolytes and quickly lead to water intoxication.

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Example :

1.Child who weighs 6 kg ……………… 100 X 6 = 600 ml / day

2.Child who weighs 12 kg ……………. (100 X 10) + ( 50 X 2 ) = 1100 ml

3.Child who weighs 24kg ……………..

(100 X 10 ) + ( 50 X 10 ) +( 20 X 4 ) = 1580 ml/day

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