Maintenance Fluid Calculator

The 4-2-1 rule (Holliday-Segar method) calculates hourly maintenance fluid requirements based on weight: 4 mL/kg/hr for the first 10 kg, 2 mL/kg/hr for the next 10 kg (10–20 kg), and 1 mL/kg/hr for each kg above 20 kg. For a 25 kg child: (4×10) + (2×10) + (1×5) = 40+20+5 = 65 mL/hr.

Daily maintenance = hourly rate × 24. Using the 4-2-1 rule, first calculate hourly rate then multiply by 24. For a 70 kg adult: (4×10)+(2×10)+(1×50)=40+20+50=110 mL/hr, daily total = 110×24 = 2640 mL/day.

The Holliday-Segar method is a weight-based formula for calculating maintenance fluid requirements in children. It uses the 4-2-1 rule and estimates caloric expenditure to determine fluid needs. It is the standard for pediatric maintenance fluid therapy.

Neonates (day 1): 60–80 mL/kg/day; Infants (1–6 months): 100–150 mL/kg/day; Children (< 20 kg): 100 mL/kg/day for first 10 kg + 50 mL/kg/day for next 10 kg; Older children/adults: 1500–2000 mL/m²/day or ~30–35 mL/kg/day.

Common maintenance fluids include D5 1/2NS (for children), D5 1/4NS (neonates), D5 1/2NS + 20 mEq KCl/L (standard pediatric), Lactated Ringer’s (surgical patients), and Normal Saline 0.9% (adults). Choice depends on age, electrolytes, and clinical status.

Potassium (KCl) is added to maintenance fluids to replace daily potassium losses and prevent hypokalemia. Standard is 20 mEq KCl/L for most children. Neonates may not need K+ until urine output is established (first 24–48 hours).

Maintenance fluids cover normal daily losses (urine, insensible loss, stool). Replacement fluids correct existing deficits from dehydration, ongoing losses (vomiting, diarrhea, NG suction), or third-spacing. The total fluid rate is maintenance + replacement.

Using 4-2-1: 4×10=40 mL/hr for first 10 kg, 2×5=10 mL/hr for next 5 kg. Total = 50 mL/hr. Daily = 50×24=1200 mL/day. Use D5 1/2NS + 20 mEq KCl/L at 50 mL/hr.

Using 4-2-1: 4×5=20 mL/hr (all in first tier). Daily = 20×24=480 mL/day (96 mL/kg/day). Use D5 1/4NS or D5 1/2NS without KCl initially, add KCl after urine output confirmed.

There is no strict maximum, but the 4-2-1 rule caps at 1 mL/kg/hr above 20 kg. For large adults, alternative methods use 1500 mL/day for the first 20 kg + 20 mL/kg/day above 20 kg (less than the 4-2-1 rule).

Excessive fluids can cause fluid overload, pulmonary edema, peripheral edema, electrolyte dilution, increased intracranial pressure, and worsening of heart failure. Monitor I/O, daily weights, and signs of overload.

Insufficient fluids lead to dehydration, oliguria, acute kidney injury, electrolyte imbalances, hypernatremia or hyponatremia, hypotension, and in severe cases, hypovolemic shock.

In oliguric renal failure, maintenance fluids should be restricted to insensible losses (300–500 mL/day) plus urine output. Use D5W or minimal electrolyte solutions; avoid potassium-containing fluids if hyperkalemic.

In heart failure, restrict fluids to ~1–1.5 L/day to reduce preload. Use isotonic solutions (NS or LR) to avoid hypotonicity. Monitor daily weights and signs of pulmonary congestion.

Burn patients require significantly more fluids than maintenance due to capillary leak. The Parkland formula (4 mL/kg/%TBSA) is used for resuscitation. Maintenance fluids alone are insufficient for burn shock.

Dextrose (D5 or D10) prevents hypoglycemia and starvation ketosis in children. Adults typically do not need dextrose in maintenance fluids unless there is risk of hypoglycemia (e.g., NPO status, neonates, liver disease).

Isotonic fluids (NS, LR) are recommended by recent guidelines (AAP 2018) to reduce risk of hyponatremia. Hypotonic fluids (D5 1/4NS, D5 1/2NS) were historically used but carry higher risk of iatrogenic hyponatremia.

NICE recommends using isotonic crystalloids (NS, LR) for maintenance in children and adults. Daily maintenance: 100 mL/kg for first 10 kg, 50 mL/kg for next 10 kg, 20 mL/kg for remaining weight (not the traditional 4-2-1).

NICE uses lower volumes for patients > 20 kg (20 mL/kg/day vs 24 mL/kg/day by 4-2-1). NICE recommends isotonic fluids exclusively. Holliday-Segar used hypotonic fluids based on caloric expenditure which may be outdated.

Insensible loss is ~300–500 mL/day in adults (skin and lungs). Increases with fever (~10% per °C above 37°C), tachypnea, burns, and radiant warmers. Decreases with humidified air and mechanical ventilation.

Neonates use D10W (day 1), D10 1/4NS (day 2+), then D10 1/2NS as tolerated. Start at 60–80 mL/kg/day on day 1, increase by 10–20 mL/kg/day up to 150 mL/kg/day by day 5. Add TPN if prolonged.

For each 1°C elevation above 37°C, increase maintenance fluids by 10–15% to compensate for increased insensible losses. High fevers (≥39°C) may require 20–30% increase.

The 100/50/20 rule is the NICE equivalent: 100 mL/kg/day for first 10 kg, 50 mL/kg/day for next 10 kg, 20 mL/kg/day for each kg above 20 kg. It gives lower volumes for larger patients compared to 4-2-1.

Drip rate (gtts/min) = (mL/hr × drop factor) / 60. For 65 mL/hr using microdrip (60 gtts/mL): (65×60)/60 = 65 gtts/min. For macrodrip (15 gtts/mL): (65×15)/60 = 16.3 ≈ 16 gtts/min.

DKA resuscitation uses NS (0.9% saline) initially, then transition to D5 1/2NS or D5 NS when glucose < 250–300 mg/dL. Maintenance fluids are calculated based on deficit and ongoing losses, not standard 4-2-1.

Monitor: urine output (goal 0.5–1 mL/kg/hr in adults, 1–2 mL/kg/hr in children), daily weights, serum electrolytes (Na, K, Cl, HCO3), signs of overload (edema, crackles, JVD), and clinical hydration status.

Third-spacing is the shift of fluid from intravascular to interstitial space (e.g., in burns, sepsis, pancreatitis, surgery). These patients require higher fluid volumes to maintain intravascular volume despite appearing edematous.

Postoperative maintenance uses isotonic fluids (NS or LR) at maintenance rate plus replacement of third-space losses. Use D5 1/2NS with KCl after patient is tolerating PO intake. Avoid hypotonic fluids due to ADH elevation.

Use ideal body weight (IBW) rather than actual weight for maintenance calculations in obesity. Using actual weight overestimates needs in non-edematous states. IBW = (Height in cm – 100) + (Age/10) × 0.9 for men, 0.85 for women.

Using 4-2-1: (4×10) + (2×10) + (1×10) = 40+20+10 = 70 mL/hr hourly, 1680 mL/day daily. Using NICE 100/50/20: (100×10) + (50×10) + (20×10) = 1000+500+200 = 1700 mL/day, equivalent to ~71 mL/hr.

Albumin is a colloid solution used for volume expansion in specific cases: large-volume paracentesis, spontaneous bacterial peritonitis, burns after 24 hours, and hepatorenal syndrome. Not routinely used for maintenance fluids.