IV fluid calculation for 6 year old 18kg

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Here is the complete IV fluid calculation for a 6-year-old, 18 kg child, based on the Harriet Lane Handbook (23rd ed.).

1. Maintenance Fluids - Holliday-Segar Method

Weight Segment	Rate	Daily Volume
First 10 kg	4 mL/kg/hr	100 mL/kg/day = 1000 mL
Next 8 kg (10-18 kg)	2 mL/kg/hr	50 mL/kg/day = 400 mL
TOTAL	56 mL/hr	1400 mL/day

Hourly rate: 56 mL/hr Daily volume: 1400 mL/day

Maximum recommended rate in the absence of cardiac/hepatic/renal pathology: 120 mL/hr.

2. Fluid Choice (AAP Guideline)

For most hospitalized children, isotonic fluids (0.9% NaCl or Lactated Ringer's) are now recommended as maintenance fluid. The older practice of using 1/4 NS (hypotonic) is no longer recommended due to the risk of hospital-acquired hyponatremia from inappropriate ADH release.

Typical order: 0.9% NaCl + 5% dextrose (D5NS) or LR + D5%, with 20 mEq/L KCl added once urine output is confirmed.

3. Dehydration / Deficit Replacement (if applicable)

Step 1 - Estimate deficit:

Deficit (mL) = % dehydration × 10 mL/kg × weight (kg)
Example: 5% dehydration in 18 kg child = 0.05 × 10 × 18 × 10 = 900 mL deficit
Example: 10% dehydration = 10 mL/kg × 18 kg = 1800 mL deficit

Dehydration Grade	Signs	Deficit
Mild (5%)	Slightly dry mucosa, thirst	~900 mL
Moderate (10%)	Tachycardia, decreased turgor	~1800 mL
Severe (15%)	Shock signs, sunken fontanelle	~2700 mL

Step 2 - Three-phase replacement:

Phase	Action
Phase I (initial bolus)	20 mL/kg isotonic fluid (NS or LR) IV over 20-60 min = 360 mL for 18 kg
Phase II (first 8 hrs)	Replace 1/2 remaining deficit + maintenance over 8 hr
Phase II (next 16 hrs)	Replace 2nd 1/2 deficit + maintenance over 16 hr

Sample calculation - 10% dehydration, 18 kg, after 20 mL/kg bolus:

Deficit = 1800 mL; Bolus given = 360 mL; Remaining deficit = 1440 mL
First 8 hr: (720 mL ÷ 8 hr) + 56 mL/hr maintenance = 90 + 56 = 146 mL/hr
Next 16 hr: (720 mL ÷ 16 hr) + 56 mL/hr maintenance = 45 + 56 = 101 mL/hr

4. Ongoing Losses Replacement

If losses are unmeasurable, replace:

10 mL/kg per watery stool = 180 mL per episode
2 mL/kg per episode of vomiting = 36 mL per episode

Administer these in addition to maintenance, replaced 1:1.

5. Quick Reference Summary for This Child

Parameter	Value
Weight	18 kg
Maintenance rate	56 mL/hr
Maintenance/day	1400 mL/day
Resuscitation bolus	360 mL (20 mL/kg NS or LR)
TBW (total body water)	18 × 0.6 = 10.8 L

Source: The Harriet Lane Handbook, 23rd ed. (Johns Hopkins Hospital), Chapter 11 - Fluids and Electrolytes

Clinical note: Always reassess fluid status frequently. Adjust rate in patients with cardiac, renal, hepatic disease, or those at risk for SIADH (post-op, CNS disease, respiratory illness, pain/stress). Oral rehydration is preferred whenever feasible.

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