Calculate 4-2-1 hourly and daily maintenance, dehydration deficit replacement, and initial bolus for pediatric patients using the Holliday-Segar rule and AAP 2018 isotonic fluid guidance.
The 4-2-1 rule (Holliday-Segar, 1957) is a simple method to calculate pediatric maintenance fluid requirements. For hourly rates: first 10 kg at 4 ml/kg/hr, next 10 kg at 2 ml/kg/hr, and >20 kg at 1 ml/kg/hr. The equivalent daily formula (100-50-20 rule) calculates total daily volume: 100 ml/kg for first 10 kg, 50 ml/kg for next 10 kg, and 20 ml/kg above 20 kg. For example, a 25 kg child requires (10×4) + (10×2) + (5×1) = 65 ml/hr or approximately 1560 ml/day.
Per AAP 2018, isotonic fluids (normal saline [NS], Ringer's lactate [LR], or Plasmalyte) are now preferred for pediatric maintenance over hypotonic solutions. Hypotonic fluids (like 0.45% NS in 5% dextrose) were historically used but increase the risk of hyponatremia and symptomatic hyponatremic encephalopathy, especially with prolonged use. Isotonic fluids are safer for routine maintenance and reduce this complication. Dextrose (5%) can be added to the IV fluid solution for nutritional support if needed.
Dehydration deficit is calculated based on the percentage of body weight lost. The calculator uses clinical estimates: mild dehydration (~5% loss), moderate (10%), and severe (15%). The deficit volume is calculated as: deficit (ml) = weight (kg) × percent dehydration × 10. For example, a 20 kg child with 10% dehydration has a deficit of 2000 ml. The deficit is replaced over 24 hours: ½ over first 8 hours, ½ over next 16 hours (after shock is corrected if present). This is added to the maintenance requirement.
A bolus is a rapid administration of fluid (typically over 15-30 minutes) given to patients in shock or hypovolemia to restore intravascular volume and tissue perfusion. The standard recommendation is 20 ml/kg of isotonic crystalloid (NS or LR). For shock from dehydration, this bolus is given BEFORE calculating the deficit replacement portion of ongoing maintenance. For example, a 20 kg child in hypovolemic shock would receive 400 ml NS bolus rapidly, then continue with maintenance + remaining deficit over the subsequent 24 hours.
The Holliday-Segar 4-2-1 rule and this calculator provide baseline maintenance + deficit replacement only. In clinical practice, you must also account for ongoing losses: nasogastric tube output, diarrhea, vomiting, ileostomy, sweat from fever, insensible losses from hyperventilation, or surgical drains. As a rough estimate, add 10 ml/kg/day for each degree of fever, or quantify actual losses and replace them separately. The total IV rate = maintenance + deficit + ongoing losses. Always monitor urine output (goal ~1 ml/kg/hr) and adjust as needed.
Yes. In adolescents and adults, maximum maintenance is approximately 125 ml/hr or 3000 ml/day, even if the 4-2-1 formula calculates higher. For example, a 150 kg adult would formula-calculate to much higher, but is capped at 3000 ml/day total. This calculator flags with a warning banner if the maintenance exceeds 125 ml/hr, which typically occurs around 50 kg body weight. This cap is a practical limit to avoid fluid overload and hyponatremia in larger patients who do not need the full weight-adjusted volume.