Parenteral Nutrition Calculator

PN should be started when: (1) the GI tract is non-functional or inaccessible for ≥5–7 days in a previously well-nourished patient; (2) the GI tract is inadequate to meet nutritional requirements for ≥3 days in a malnourished patient; or (3) short-term complete bowel rest is required (e.g., some intestinal fistulae, severe GI bleeding, ileus). Enteral nutrition (tube feeding) is strongly preferred over PN whenever the GI tract is functional, as it maintains gut mucosal integrity, reduces bacterial translocation, and is safer and less expensive.

PN-associated liver disease (PNALD, also called IFALD — intestinal failure-associated liver disease) is a spectrum of hepatic complications from long-term PN including steatosis (fat accumulation), cholestasis (bile flow impairment), fibrosis, and cirrhosis. It occurs in up to 15–40% of long-term PN patients. Risk factors include: duration of PN, lack of enteral stimulation (gut rest), excessive glucose delivery, soybean oil-based lipid emulsions, recurrent line infections, and short bowel syndrome. Modern fish oil-containing or olive oil-based lipid emulsions reduce PNALD risk. Cycled PN (overnight rather than continuous) also reduces cholestasis.

PN complications include: central line-associated bloodstream infections (CLABSI — most common and serious), venous thrombosis, pneumothorax or haemothorax during line insertion, metabolic complications (hyperglycaemia, hypertriglyceridaemia, electrolyte imbalances, refeeding syndrome), and long-term complications (PNALD, metabolic bone disease, trace element deficiency or toxicity). Strict aseptic technique during line care is the most important factor in reducing CLABSI risk — care bundles reduce CLABSI rates by up to 70%.

The maximum glucose oxidation rate in humans is approximately 4–5 mg/kg/min (approximately 6–7 g/kg/day for a 70 kg adult). Above this rate, excess glucose cannot be oxidised and is instead converted to fat (lipogenesis), with consequent CO2 overproduction, hypertriglyceridaemia, hepatic steatosis, and worsening of respiratory failure in patients with limited ventilatory reserve. In PN prescription, the glucose rate should always be calculated and confirmed to be within this maximum.

Standard PN formulations include: sodium (60–150 mmol/day), potassium (40–120 mmol/day), phosphate (20–40 mmol/day), magnesium (8–20 mmol/day), calcium (5–10 mmol/day), and chloride (as counterion). A complete multivitamin preparation and trace element solution (zinc, selenium, copper, manganese, chromium, molybdenum, iodine) are added daily. Requirements change significantly in disease states — renal failure reduces phosphate and potassium needs; critical illness increases phosphate and zinc demands; short bowel syndrome increases zinc losses.

Yes — supplemental PN can be given alongside enteral nutrition when enteral intake is insufficient but some GI function is present. This 'combined' approach avoids the disadvantages of sole reliance on PN (gut disuse, cost) while ensuring adequate macronutrient delivery. ESPEN recommends considering supplemental PN if full target enteral intake cannot be achieved by day 3–4 of ICU admission in patients who are at high nutritional risk (NRS-2002 ≥5 or severely malnourished).

Total Parenteral Nutrition (TPN) is delivered via a central venous catheter (PICC, subclavian, or internal jugular line) and can provide full nutritional requirements including concentrated glucose solutions (10–50%). It is used for complete GI failure or when full nutritional replacement is needed for extended periods. Peripheral Parenteral Nutrition (PPN) uses a peripheral venous cannula and is limited by osmolarity (≤850 mOsm/L) to prevent peripheral vein thrombophlebitis, allowing only dilute solutions with lower glucose concentration and typically supplementary rather than complete nutritional delivery. PPN is suitable for short-term use (up to 7–10 days).

Refeeding syndrome occurs within 72 hours of starting nutritional support in severely malnourished patients. Starvation causes cellular depletion of phosphate, potassium, and magnesium. When carbohydrates are introduced, insulin secretion stimulates cellular uptake of these electrolytes, causing dangerous extracellular falls. Clinical manifestations include: cardiac arrhythmias and cardiac failure (hypophosphataemia — most dangerous), respiratory failure, neuromuscular weakness, peripheral oedema, and Wernicke's encephalopathy (thiamine deficiency). Serum phosphate is the primary monitoring marker — a fall to <0.5 mmol/L requires immediate supplementation and possible feeding pause.