function calculateMaintenanceFluid() {
// Get input values
var weightInput = document.getElementById('patientWeight').value;
var unit = document.getElementById('weightUnit').value;
var resultBox = document.getElementById('resultBox');
// Validation
if (weightInput === "" || isNaN(weightInput) || weightInput <= 0) {
alert("Please enter a valid positive number for patient weight.");
resultBox.style.display = "none";
return;
}
var weightKg = parseFloat(weightInput);
// Convert lbs to kg if necessary
if (unit === 'lbs') {
weightKg = weightKg / 2.20462;
}
var hourlyRate = 0;
// 4-2-1 Rule Logic
if (weightKg <= 10) {
// First 10kg: 4 mL/kg/hr
hourlyRate = weightKg * 4;
} else if (weightKg <= 20) {
// First 10kg @ 4mL, next 10kg @ 2mL
// 40 + (weight – 10) * 2
hourlyRate = 40 + ((weightKg – 10) * 2);
} else {
// First 10kg @ 4mL, next 10kg @ 2mL, remaining @ 1mL
// 60 + (weight – 20) * 1
hourlyRate = 60 + ((weightKg – 20) * 1);
}
// Calculate Daily Volume (Holliday-Segar)
var dailyTotal = hourlyRate * 24;
// Display Results
document.getElementById('displayWeight').innerText = weightKg.toFixed(2) + " kg";
document.getElementById('hourlyRate').innerText = hourlyRate.toFixed(1) + " mL/hr";
document.getElementById('dailyVolume').innerText = Math.round(dailyTotal) + " mL/day";
resultBox.style.display = "block";
}
Understanding Maintenance Fluid Calculation
The maintenance fluid rate determines the amount of intravenous (IV) fluids required to maintain hydration in a patient who is unable to take fluids orally (NPO). This calculator primarily uses the widely accepted "4-2-1 Rule", which is mathematically equivalent to the Holliday-Segar method for calculating daily requirements.
The 4-2-1 Rule Explained
This method calculates the hourly infusion rate (mL/hr) based on the patient's weight in kilograms. It is the standard approach in pediatrics and general medicine for patients with normal kidney function and no excessive fluid losses.
Weight Category
Calculation Logic
Example
First 10 kg
4 mL/kg/hr
5 kg patient = 20 mL/hr
Next 10 kg (11-20 kg)
+ 2 mL/kg/hr
15 kg patient = 40 + (5 × 2) = 50 mL/hr
Every kg > 20 kg
+ 1 mL/kg/hr
50 kg patient = 60 + (30 × 1) = 90 mL/hr
Holliday-Segar Method (Daily Volume)
While the 4-2-1 rule calculates the hourly rate, the Holliday-Segar method is often referenced for daily total fluid volume requirements. The math results in the same totals:
0-10 kg: 100 mL/kg/day
10-20 kg: 1000 mL + 50 mL/kg for every kg over 10
> 20 kg: 1500 mL + 20 mL/kg for every kg over 20
Clinical Considerations
While this calculator provides a baseline for maintenance fluids, clinical judgment is essential. Adjustments must be made for specific conditions:
Dehydration: Patients with fluid deficits require rehydration therapy (boluses) in addition to maintenance fluids.
Fever: Fluid requirements generally increase by 10-12% for every degree Celsius rise in temperature above 37.8°C.
Renal Failure: Patients with compromised kidney function require strict fluid restriction and monitoring.
Cardiac Issues: Patients with heart failure may require volume restriction to prevent fluid overload.
Medical Disclaimer: This calculator is intended for educational and reference purposes only for medical professionals. It should not be used as a substitute for professional clinical judgment. Always verify calculations before administering medication or fluids.