Maintenance intravenous (IV) fluids are administered to patients who cannot take oral fluids. They are designed to preserve water and electrolyte balance and provide enough glucose to prevent muscle catabolism.
The 4-2-1 Rule (Holliday-Segar Method)
Developed in 1957 by Malcolm Holliday and William Segar, the 4-2-1 rule is the most widely taught method for estimating a patient's hourly fluid requirement. It estimates water loss based on resting metabolic rate.
| Patient Weight | Fluid Requirement |
|---|---|
| First 10 kg of body weight | 4 mL/kg/hr |
| Next 10 kg (11 to 20 kg) | Add 2 mL/kg/hr |
| Every kg over 20 kg | Add 1 mL/kg/hr |
Clinical Examples
Let's look at how the calculation changes based on a patient's weight.
Example 1: A 8 kg infant
Because the infant weighs less than 10 kg, we only use the first part of the rule.
- 8 kg × 4 mL/kg = 32 mL/hr
Example 2: A 15 kg child
This child's weight falls into the second tier.
- First 10 kg: 10 × 4 = 40 mL/hr
- Remaining 5 kg: 5 × 2 = 10 mL/hr
- Total: 40 + 10 = 50 mL/hr
Example 3: A 70 kg adult
For patients over 20 kg, we use all three tiers.
- First 10 kg: 10 × 4 = 40 mL/hr
- Next 10 kg: 10 × 2 = 20 mL/hr
- Remaining 50 kg: 50 × 1 = 50 mL/hr
- Total: 40 + 20 + 50 = 110 mL/hr
Fluid Composition: What should you prescribe?
Choosing the rate is only half the equation; selecting the appropriate fluid composition is critical.
Isotonic Fluids are Now Standard
Historically, hypotonic fluids (like 0.45% normal saline or 0.2% normal saline) were used for maintenance. However, strong evidence shows this leads to hospital-acquired hyponatremia. The American Academy of Pediatrics (AAP) and most adult guidelines now recommend isotonic fluids for maintenance in the vast majority of hospitalized patients.
- Pediatrics: D5 + 0.9% Normal Saline + 20 mEq/L KCl (D5 NS w/ 20 KCl) is a common choice.
- Adults: 0.9% Normal Saline (NS) or balanced crystalloids like Lactated Ringer's (LR) or Plasmalyte. Dextrose is less commonly added unless the patient is at risk of hypoglycemia.
Limitations and Modifications
The 4-2-1 rule is a starting point, not an absolute rule. It calculates maintenance needs only, assuming a normal metabolic state.
Conditions Requiring INCREASED Fluids
- Fever: Maintenance increases by about 12% for every 1°C above 37.8°C.
- Sweating / Tachypnea: Increased insensible losses.
- Ongoing Losses: Emesis, diarrhea, NG tube output, surgical drains. These should be replaced "mL for mL" with appropriate fluids, in addition to maintenance.
Conditions Requiring DECREASED Fluids
- Heart Failure / Fluid Overload: Avoid excessive fluids to prevent pulmonary edema.
- Renal Failure: Oliguric or anuric patients require strict fluid restriction (insensible losses + urine output).
- SIADH / Meningitis / Severe Pneumonia: Often require fluid restriction to 2/3 of maintenance to prevent hyponatremia.
References
- Holliday MA, Segar WE. The maintenance need for water in parenteral fluid therapy. Pediatrics. 1957;19(5):823-832.
- Feld LG, Neuspiel DR, Foster BA, et al. Clinical Practice Guideline: Maintenance Intravenous Fluids in Children. Pediatrics. 2018;142(6):e20183083.
- Meyers RS. Pediatric fluid and electrolyte therapy. J Pediatr Pharmacol Ther. 2009;14(4):204-211.