Maintenance Iv Fluids Calculator

The 4-2-1 rule converts body weight into an hourly maintenance rate: 4 mL/kg/h for the first 10 kg, 2 mL/kg/h for the second 10 kg, and 1 mL/kg/h for every kilogram beyond 20. A 70 kg adult therefore receives 40 plus 20 plus 50, or 110 mL per hour, about 2640 mL per day. The tiers are not arbitrary. They are the hourly form of a daily caloric estimate of 100 kcal/kg for the first 10 kg, 50 kcal/kg for the next 10 and 20 kcal/kg thereafter, paired with the observation that roughly 1 mL of water is consumed per kilocalorie metabolized to cover urine output and insensible loss through skin and lungs. The same scheme yields electrolyte needs of about 3 mEq of sodium and 2 mEq of potassium per 100 mL of fluid. Maintenance is only the baseline. Fever adds roughly 10 to 12 percent to insensible losses per degree C above 37, burns are resuscitated with the Parkland formula instead, and heart or kidney failure often calls for two-thirds or half the calculated rate. Ongoing losses from nasogastric suction, surgical drains, diarrhea or third-spacing must be replaced separately and are not part of maintenance. Tonicity is the other major caveat: hypotonic maintenance fluid caused iatrogenic hyponatremia often enough that the American Academy of Pediatrics recommended isotonic fluid for most hospitalized children in its 2018 guideline. Dextrose at 5 percent contributes only about 170 kcal per liter, enough to blunt starvation ketosis but far short of nutritional support.

The rule traces to a single paper. Malcolm Holliday and William Segar published The Maintenance Need for Water in Parenteral Fluid Therapy in Pediatrics in 1957. Rather than deriving fluid needs from body surface area, the prevailing method that required nomograms and was awkward at the extremes of size, they plotted energy expenditure against weight and observed that it could be approximated by three straight segments, giving the 100, 50 and 20 kcal per kg tiers. Because water turnover tracks calorie burn, the same tiers described water requirements, and dividing the daily volume by 24 produced the 4-2-1 hourly shorthand that generations of clinicians have memorized. Holliday and Segar also proposed electrolyte contents modeled on the composition of human and cow milk, which led to hypotonic solutions such as 0.2 percent and 0.45 percent saline becoming standard pediatric maintenance fluids for four decades. From the early 1990s, reports of fatal hyponatremic encephalopathy in previously healthy hospitalized children, argued forcefully by Allen Arieff and later by Michael Moritz and Juan Carlos Ayus, showed that antidiuretic hormone secretion driven by illness, surgery, pain and nausea prevents excretion of the free water those fluids deliver. Randomized trials through the 2000s and 2010s favored isotonic fluid, and the American Academy of Pediatrics clinical practice guideline of 2018 recommended it formally, leaving the volume half of the original work intact while replacing its composition.