Parenteral Nutrition Calculator

This calculator works out a starting total parenteral nutrition (TPN) formulation -- the IV route used when a patient cannot be fed enterally -- from a caloric goal and a protein target. Protein (as amino acids) is calculated first, directly from a weight-based dose (commonly 0.8 g/kg/day for maintenance up to 1.5-2.0 g/kg/day in critical illness or burns) using a standard 10% amino acid solution. Protein calories are then subtracted from the total caloric goal to get the remaining "non-protein calories," which are split between lipid emulsion (a chosen percentage, typically 20-30%) and dextrose, using the standard energy densities of 3.4 kcal per gram of dextrose and 2 kcal per mL of a 20% lipid emulsion. Two safety checks are reported alongside the volumes: the glucose infusion rate (GIR, in mg/kg/min), which should generally stay under about 4-5 mg/kg/min in adults to avoid dextrose-driven hyperglycemia, and the non-protein-calorie-to-nitrogen (NPC:N) ratio, a standard check that calories and protein are proportioned appropriately for the patient's stress level (a commonly cited target is roughly 100-150:1 for typical patients, narrower around 80-100:1 for more catabolic, critically ill patients). GIR is calculated over the entered infusion duration, not always a full 24 hours -- cycled or overnight TPN (commonly run over 10-16 hours to free the patient from the pump during the day) delivers the identical daily dextrose dose in less time, which raises GIR for the same prescription, so the infusion-duration input matters even when nothing else about the formulation changes.

Because starting TPN too aggressively in a malnourished or chronically underfed patient can trigger refeeding syndrome (a dangerous shift of phosphate, potassium, and magnesium into cells as the body resumes carbohydrate metabolism), the calculator also flags when GIR exceeds 5 mg/kg/min -- though patients at genuine refeeding risk are often started far more conservatively (closer to 2 mg/kg/min) and advanced slowly with electrolyte monitoring, well below that flag's threshold, so a clean flag here does not rule out refeeding risk in a severely malnourished patient. A separate flag reports when the protein prescription alone already exceeds the caloric goal, leaving no calories to allocate to dextrose or lipid -- a mismatched prescription rather than a valid formulation. The Volume target input on this calculator is informational only in this version -- it does not automatically scale dextrose concentration or any other value to hit a specific total bag volume, so if a specific total volume is required, adjust dextrose concentration manually and re-check the resulting Total Macro Volume against it. Osmolarity, electrolyte content, trace elements, and vitamins are not modeled here at all; every TPN formulation requires pharmacy compounding review and, for peripheral administration, an osmolarity check well below the values a central-line formulation like this one can safely produce.