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Maintenance Fluid Calculator - Based on 4-2-1 Rule
A maintenance fluid calculator helps determine hourly intravenous fluid requirements in patients who cannot maintain hydration orally. The most widely used approach for estimating these needs in pediatric and some adult cases is the 4-2-1 rule, a weight-based formula that standardizes fluid dosing to maintain baseline physiological balance. The 4-2-1 rule simplifies calculations by assigning hourly fluid volumes based on weight brackets, making it easy to apply in routine clinical care. Although originally developed for pediatrics, it is sometimes used in adults, particularly when standardized fluid management is needed in perioperative or inpatient settings. While the calculator automates these steps, the underlying formula remains the same and should be interpreted in clinical context. It supports safe, consistent fluid prescribing but does not replace judgment in patients with altered fluid needs due to comorbid conditions or evolving clinical status.
Maintenance Fluid Calculator
Weight (kg)
Value
Value
Value
4-2-1 Rule for Maintenance Fluid Calculation
The 4-2-1 rule calculates hourly IV fluid requirements as follows:
• For 0-10 kg: 4mL/kg/hr
• For >10-20 kg: 40 Ml + 2 mL/kg/hr for every kg >10kg
• For >20 kg: 60mL + 1mL/kg/hr for every kg > 20kg
For example:
• A 25 kg child: 60mL + (1mL x 5kg) = 65 mL/hr
• A 70 kg adult: 60mL + (1 mL x 50kg) = 110 mL/hr
This formula provides a consistent framework for ordering maintenance fluids in fasting or hospitalized patients. In practice, clinicians often round to the nearest practical rate, and adjustments may be needed based on age, renal function, or fluid losses.
Clinical Use and Interpretation of Calculator Output
The calculator outputs:
• Maintenance fluids (mL/hr): Standard hourly requirement using the 4-2-1 rule.
• Maintenance x 1.5: Used in perioperative care or patients with increased insensible losses.
• 20 mL/kg bolus: Provided for reference but not part of maintenance; used in fluid resuscitation.
These values are intended for use in patients with stable fluid status who require baseline maintenance. They do not account for insensible losses, electrolyte needs, or abnormal fluid shifts. Patients with renal, cardiac, or hepatic impairment may require rate modifications, and frequent reassessment is necessary in rapidly changing clinical situations. The 4-2-1 rule is a reliable, easy-to-apply formula that helps support consistent fluid management. However, it should not be used for volume resuscitation or as a substitute for condition-specific fluid planning.
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References
[1] Holliday, M. A., & Segar, W. E. (1957). The maintenance need for water in parenteral fluid therapy. Pediatrics, 19(5), 823–832.
[2] Moritz, M. L., & Ayus, J. C. (2003). Prevention of hospital-acquired hyponatremia: a case for using isotonic saline. Pediatrics, 111(2), 227–230.
[3] National Institute for Health and Care Excellence (NICE). (2015). Intravenous fluid therapy in children and young people in hospital (NG29). Retrieved from https://www.nice.org.uk/guidance/ng29
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