An article published in Fluid and Electrolyte Therapy discussed that maintenance fluid calculations assume that fluid loss from sensible and insensible routes is taking place at a normal rate. But a febrile infant will be having a much greater transcutaneous evaporative water loss than one with a normal body temperature. Similarly, a child with tachypnea will lose excess water from the lungs- unless he/she is receiving humidified oxygen.

The authors stated that in patients with kidney disease who have anuria, oliguria or polyuria – maintenance IV fluids will not be written with the standard formula because their urinary losses are at a normal rate. Maintenance fluids using the standard formula would be too much for an anuric child with no urinary losses and too little for those with a concentrating defect in their kidneys causing polyuria. Therefore, before using a standard formula for calculating maintenance fluids, ensure that the child is not having higher or lower losses than usual.

When maintenance fluid for a 10 kg child is prescribed for 24 hours as 1000 ml, it is assumed that loss from the various routes is occurring at a normal rate. However, adjustments are sometimes necessary. In cases with tachypnea – add 20-50% to the respiratory replacement; if a person is receiving humidified oxygen, respiratory water loss is nil. In the case of fever, add 10% to the transcutaneous loss replacement for every degree temperature above 38oC; for patients with anuria exclude urinary loss from replacement; while in oliguria, the actual urine output should be measured every 12 hours and added to the insensible loss for the next 12 hours; whereas, in polyuria, the actual urine output is measured every 1-2 hours and added to the insensible loss for the next 1-2 hours.

Source: Fluid and Electrolyte Therapy. A Chapter in Core Concepts of Pediatrics, 2nd Edition. 2017. Dept. of Pediatrics University of Texas Medical Branch.