Nutrition, Fluid, and Electrolyte Balance
Core concepts
Infants have higher water content and greater surface area, making them vulnerable to dehydration and fluid overload. Calculate maintenance fluids by weight (e.g., 4-2-1 rule: 4 mL/kg/hr for first 10 kg, 2 mL/kg/hr for next 10 kg, 1 mL/kg/hr thereafter). Recognize dehydration severity by clinical signs and use oral rehydration solution when possible; IV fluids for severe dehydration or inability to tolerate oral intake.
Electrolytes: know hyponatremia, hypernatremia, hypokalemia, and hyperkalemia causes and signs. Potassium must never be given as a bolus-always dilute and infuse with a pump. Monitor for fluid overload (edema, crackles, weight gain).
Nutrition: breast milk or formula for infants, iron-rich foods after 6 months, and age-appropriate diet for children. Recognize failure to thrive and obesity. Understand special diets (CF: high-calorie, pancreatic enzymes; renal disease: restricted protein, potassium, phosphorus).
Traps
- Giving potassium IV push-fatal error; always dilute and infuse.
- Using adult maintenance fluid calculations for children.
- Overlooking ongoing losses (vomiting, diarrhea, fever) when calculating fluids.
- Assuming all dehydration needs IV fluids-mild-moderate dehydration responds to oral rehydration.
- Missing signs of fluid overload.
Rule of thumb
4-2-1 for hourly maintenance. For dehydration, replace deficits plus ongoing losses plus maintenance, and reassess frequently.
Worked example
A 15 kg child: maintenance = (4×10) + (2×5) = 50 mL/hr. If dehydrated, add deficit replacement over the prescribed period plus ongoing losses, and monitor urine output and weight.