IV fluids are generally calculated based on a patient's weight, and sometimes clinical status (e.g., dehydration level) to determine either maintenance fluids or fluid resuscitation needs. For maintenance, a common method uses a weight-based calculation to estimate the daily fluid requirement and then divides by 24 to find the hourly rate.
Maintenance IV Fluid Calculation
Maintenance IV fluids are designed to meet the normal daily fluid needs of a patient who cannot take fluids orally. The most common method for calculating maintenance fluids is based on weight.
Weight-Based Method
This method provides a general guideline and may need adjustment based on the individual patient's clinical condition. The Royal Children's Hospital (RCH) in Melbourne provides the following guidelines:
| Weight (kg) | Full maintenance mL/day | mL/hour |
|---|---|---|
| 3–10 | 100 x weight | 4 x weight |
| 10–20 | 1000 + 50 x (weight - 10) | 40 + 2 x (weight - 10) |
| 20–60 | 1500 + 20 x (weight - 20) | 60 + 1 x (weight - 20) |
| >60 | 2400 mL/day (maximum) | 100 mL/hour |
Example:
- A 7 kg child would need 100 mL/kg/day, totaling 700 mL/day or approximately 28 mL/hour.
- A 15 kg child would need 1000 mL + (50 mL x 5 kg) = 1250 mL/day or approximately 52 mL/hour.
- A 30 kg child would need 1500 mL + (20 mL x 10 kg) = 1700 mL/day or approximately 71 mL/hour.
Considerations
- These calculations provide a starting point. Clinical assessment is always needed to refine the rate based on urine output, hydration status, and electrolyte levels.
- Patients with certain conditions such as heart failure, renal failure or SIADH may require fluid restriction.
- The type of IV fluid used (e.g., normal saline, D5W, lactated Ringer's) will depend on the patient's electrolyte balance and clinical situation.
In summary, IV fluid calculations depend primarily on the patient's weight, with adjustments made according to their clinical status and specific medical needs. These calculations help determine the appropriate hourly rate to maintain adequate hydration and electrolyte balance.
