Academic Day Seminars

ADS – Fluids and Sodium balance Part 1

Prior to this session, I had the opportunity to calculate a patient’s fluid balance during clinical orientation. Though I had a decent grasp on the actual calculations, I felt that I did not have a firm understanding of the rationale to why this is important.

After the ADS these are the following notes that I will be actively carrying with me throughout my rotations:

  • Body composition varies throughout life, in particular:
    • Preterm neonates are 85% TBW (basically watery sacs!)
    • Infants are 60% TBW; 25-30% is ECF, 30-35% is ICF
    • Adults are 60% TBW; 20% is ECF, 40% is ICF
If you give 1 L of:

Where does it go?

Intracellular (2/3) Extracellular (1/3 of TBW)
Interstitial (3/4 of ECF) Intravascular (1/4 of ECF)
D5W 666 mL 250 mL 84 mL
0.9 NaCl (NS) 0 750 mL 250 mL
D5NS 0 750 mL 250 mL
½ NS 333 mL 500 mL 168 mL
D5-½NS 333 mL 500 mL 168 mL
3% NaCl 0 ~750 mL *some H2O moves here from ICF ~ 250 mL *some H2O moves here from ICF
Albumin, blood, pentaspan 0 0 1000 mL

How to calculate maintenance fluid requirements: 4/2/1 method

  Holliday-Segar Method (/day) Estimate (/hr)
First 10 kg 100 ml/kg 4ml/kg
Second 10kg 50 ml/kg 2 ml/kg
Every kg thereafter 20 ml/kg 1ml/kg

Maintenance Needs:

Sodium ~ 3mmol/kg/day (this is likely to be an underestimate, as sick kids need more, and by only giving 3 mmol/kg/day you may cause iatrogenic hyponatremia)

Potassium: 2 mmol/kg/day

Orders would look like this: D5-1/2NS + 30 mmol/L KCl IV at 63 ml/hr

Deficit Needs: to “fix” a deficit – these are fluids lost prior to medical care and should be assessed by degree of dehydration, for every 1 kg of weight loss = 1 liter of fluid loss

Degree of dehydration = (pre-illness weight- illness weight)/pre-illness weight * 100%

Replacement Needs: fluids given to meet ongoing losses due to medical tx (e.g. continuous emesis/diarrhea in hospital)

***Super important: you must give maintenance fluid in the treatment of deficit, otherwise you’ll never “catch up” (Specifically in Phase II and III of the management of severe dehydration)


A great ADS to tease out the nuances of fluid replacements, which are very common in the pediatric realm. I am looking forward to part 2, to further learn about sodium, SIADH, diabetes insipidus!



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