4–2–1 Hourly Maintenance Fluid Rate: Clinical Guide

Overview

Calculates estimated hourly maintenance fluid using the 4–2–1 rule.

Clinical Significance

The 4–2–1 rule is an estimate and must be adapted to the clinical setting and contemporary fluid guidance.

When to Use

• Use when the calculation is relevant to the clinical question.
• Confirm that the population and units match the validated method.
• Use current and reliable measurements.

How It Is Calculated

• 4 mL/kg/h for first 10 kg, 2 mL/kg/h for next 10 kg, then 1 mL/kg/h.

Interpretation

• The 4–2–1 rule is an estimate and must be adapted to the clinical setting and contemporary fluid guidance.
• Interpret alongside the full clinical picture and current guidance.

Worked Example

Enter the required measurements in the stated units. MedicalC then applies: 4 mL/kg/h for first 10 kg, 2 mL/kg/h for next 10 kg, then 1 mL/kg/h.

Patient Considerations

• Consider age, body size, pregnancy, organ function and treatment effects where relevant.
• Repeat the calculation when inputs or clinical status materially change.

Limitations

• Accuracy depends on the quality and units of the entered data.
• The equation may not be validated in every patient population.
• This tool does not replace clinical judgement or specialist advice.

Clinical Pearls

• Check units before calculating.
• Document the source and timing of each input.
• Use trends where clinically appropriate.

Common Mistakes

• Mixing SI and conventional units.
• Using non-contemporaneous measurements.
• Treating the output as a diagnosis or prescription.

Evidence Base

The implemented calculation follows the published or guideline-based relationship: 4 mL/kg/h for first 10 kg, 2 mL/kg/h for next 10 kg, then 1 mL/kg/h.

References

1. Derived from Holliday–Segar maintenance requirements. — Primary publication, guideline or established source supporting the calculation.