Maintenance fluid requirements
The commonly used method for approximating water loss (and therefore the water requirement) is the Holliday-Segar nomogram: This formula relates water loss to the caloric expenditure. Holliday and Segar collated information from a number of studies, including their own, and concluded the following:
- Water loss (and therefore water requirement) is a function of caloric expenditure.
- Total daily water requirement to replace insensible and urinary water loss in the hospitalized patient is approximately 100 ml/100kcal/day.
- Caloric expenditure, and therefore the water requirement, for the hospitalized patient can be estimated from the nomogram shown on the next page.
The diagram below is taken from their original publication "The maintenance need for water in parenteral fluid therapy", Pediatrics 1957.
The Holliday-Segard nomogram approximates daily fluid loss, and therefore the daily fluid requirements, as follows:
- 100 ml/kg for the 1st 10 kg of wt. He
- 50 ml/kg for the 2nd 10 kg of wt.
- 20 ml/kg for the remaining wt.
Even though it is correct to think about fluid requirements on a 24-hour basis, the delivery pumps used in hospitals are designed to be programmed for an hourly infusion rate. The 24-hour number is often divided into approximate hourly rates for convenience, leading to the "4-2-1" formula.
- 100 ml/kg/24-hours = 4 ml/kg/hr for the 1st 10 kg
- 50 ml/kg/24-hours = 2 ml/kg/hr for the 2nd 10 kg
- 20 ml/kg/24-hours = 1 ml/kg/hr for the remainder
So, for a 30 kg child, maintenance fluid rate would be:
- 40 ml/hr + 20 ml/hr + 10 ml/hr = 70 ml/hr