Enteral and parenteral nutrition in critical care

In short

Enteral nutrition (EN) delivers nutrients into the functioning gastrointestinal tract through a tube; parenteral nutrition (PN) delivers them intravenously, bypassing the gut altogether. In critical care, patients are hypermetabolic, catabolic and usually unable to eat, so nutrition support is a prescribed therapy with a route, dose, rate and monitoring plan, not a meal. The governing rule is "if the gut works, use it" — EN preserves gut mucosa and immune function, costs far less and carries fewer infectious complications than PN. This topic is examined in B.Sc Nutrition and Dietetics clinical papers, in RD (Registered Dietitian) examinations of the Indian Dietetic Association, and in technical rounds for clinical dietitian posts in Apollo, Fortis, Max, Manipal, AIIMS and state medical college hospitals, where candidates are asked to calculate a feed, choose a route and troubleshoot intolerance.

Explained

Definitions, indications and route decision

• Enteral nutrition: nutrients delivered into stomach or small bowel via tube. Oral nutritional supplements (ONS) are sometimes counted as enteral in the broad sense; in ICU practice EN means tube feeding.
• Parenteral nutrition: nutrients infused into a vein. TPN (total) meets the entire requirement; PPN/supplemental PN tops up inadequate EN.
• EN indications: functioning gut but inadequate oral intake >3 days expected — mechanical ventilation, stroke with dysphagia, head injury, major burns, head and neck cancer, severe pancreatitis (jejunal), anorexia of sepsis.
• EN contraindications (mostly relative): haemodynamic instability on high-dose vasopressors, complete mechanical bowel obstruction, bowel ischaemia, high-output proximal fistula, paralytic ileus, intractable vomiting or diarrhoea, severe short bowel in early phase.
• PN indications: gut unusable or inaccessible — short bowel syndrome, high-output fistula, prolonged ileus, complete obstruction, severe malabsorption, mesenteric ischaemia, failure to reach ~60% of target by EN after 3–7 days.
• Timing (ASPEN/SCCM and ESPEN broadly agree): start EN within 24–48 h of ICU admission once resuscitated. If EN is impossible, PN in the high-risk/malnourished patient is started early; in the low-risk, well-nourished patient PN is usually deferred to about day 7 because early PN adds infection risk without benefit.
• Route decision ladder: oral → ONS → nasogastric tube → nasojejunal (if gastric intolerance or aspiration risk) → percutaneous (PEG/PEJ) if >4–6 weeks → PN if the gut fails.

Enteral access, formulas and delivery

• Short-term access (<4–6 weeks): nasogastric (NG) — easiest, bedside, confirm position; orogastric in intubated patients; nasoduodenal/nasojejunal (ND/NJ) — placed endoscopically or with electromagnetic guidance, reduces reflux and gastric residual problems.
• Long-term access (>4–6 weeks): PEG (percutaneous endoscopic gastrostomy), PEG-J, surgical gastrostomy, jejunostomy/FJ (feeding jejunostomy, often placed during upper GI surgery).
• Tube position check: the reliable confirmation for a new tube is radiography; pH of aspirate (≤5.5) is used where protocol allows. The auscultation ("whoosh") test is unreliable and no longer recommended.
• Formula types by composition:
  • Polymeric (standard): intact protein, complex carbohydrate, LCT ± MCT; 1.0–1.5 kcal/mL; needs a working digestive capacity. Most ICU patients.
  • Oligomeric/semi-elemental: peptides and MCT; for malabsorption, short bowel, pancreatic insufficiency.
  • Elemental/monomeric: free amino acids; highest osmolarity, poor taste, reserved for severe malabsorption.
  • Disease-specific: renal (low K, Na, phosphate, protein tailored to dialysis), hepatic (BCAA-enriched), diabetic (low glycaemic index, fibre, MUFA), pulmonary, immune-modulating (arginine, glutamine, nucleotides, omega-3 — not advised in severe sepsis).
  • Modular: single-nutrient additions — protein powder, MCT oil, glucose polymer, fibre.
• Energy density and osmolarity: standard feed ~300–500 mOsm/kg; hyperosmolar feeds (>600) given intragastrically are tolerated better than jejunally, where they cause osmotic diarrhoea.
• Delivery methods:
  • Bolus: 200–400 mL over 10–20 min by syringe, 4–6 times a day; gastric only; cheap, physiological, allows mobility; higher cramping/aspiration risk.
  • Intermittent/gravity drip: 300–500 mL over 30–60 min.
  • Continuous pump: 20–150 mL/h over 16–24 h; best tolerance; essential for jejunal feeding; standard in ICU.
  • Cyclic: continuous at night, usually in rehabilitation or home EN.
• Starting and advancing: begin 10–40 mL/h (or 25% of target), advance every 8–12 h to goal in 24–72 h. Kitchen-blenderised feeds are common in Indian public hospitals — cheap but variable in nutrient content, viscous and prone to contamination; commercial powdered or ready-to-hang feeds are preferred where affordable.
• Monitoring: tolerance (distension, vomiting, stool), volume actually delivered versus prescribed, blood glucose, electrolytes (especially K, Mg, PO₄), fluid balance, weight, head-of-bed elevation 30–45°, tube flush 20–30 mL water every 4–6 h and after drugs. Routine gastric residual volume (GRV) measurement is no longer recommended as a standalone trigger to stop feeds; if measured, a cut-off of about 500 mL with no other sign of intolerance does not justify stopping.

Parenteral nutrition: access, components and compounding

• Peripheral PN: osmolarity limit about 850–900 mOsm/L; short term (<10–14 days); causes phlebitis beyond that.
• Central PN: via subclavian/internal jugular central venous catheter, PICC, or tunnelled line (Hickman) / implanted port for long-term home PN; tip in lower superior vena cava; allows high osmolarity. A dedicated lumen for PN reduces infection.
• Components:
  • Dextrose: 3.4 kcal/g (monohydrate) — the only carbohydrate used; stock solutions 5–70%. Maximum oxidation about 4–5 mg/kg/min; exceeding it causes hyperglycaemia, fatty liver, excess CO₂.
  • Amino acids: 4 kcal/g; standard, or disease-specific (BCAA-rich for hepatic encephalopathy, essential-amino-acid formulas for renal failure).
  • Lipid emulsions: 10% = 1.1 kcal/mL, 20% = 2.0 kcal/mL, 30% = 3.0 kcal/mL — soybean (LCT), MCT/LCT physical mix, olive-oil-based, fish-oil-containing (SMOF). Supply essential fatty acids, limit ≤1–1.5 g/kg/day, keep triglycerides below about 400 mg/dL.
  • Electrolytes, trace elements (zinc, copper, selenium, chromium, manganese), vitamins (fat- and water-soluble, including thiamine) added daily; vitamin K needed with many preparations.
• Delivery systems: 2-in-1 (dextrose + amino acids, lipid piggy-backed) and 3-in-1 / total nutrient admixture (TNA) (all three in one bag). Multi-chamber pre-mixed bags are the common Indian hospital practice (Kabiven-type), compounded bags are made in a hospital pharmacy under laminar flow.
• Stability rules: lipid emulsions crack at low pH and high electrolyte load; calcium and phosphate can precipitate — add phosphate early and calcium last, and respect the manufacturer's calcium-phosphate solubility curve. Do not add drugs or bicarbonate to a PN bag unless proven compatible. Use within 24 h once spiked; protect from light.
• Weaning: when EN or oral intake reaches about 60% of needs, taper PN; taper over hours to avoid rebound hypoglycaemia, especially in children.

Estimating requirements in critical illness

• Energy: indirect calorimetry is the reference standard (measures VO₂ and VCO₂). Where unavailable, weight-based estimation of 25–30 kcal/kg/day is used, with 20–25 kcal/kg in the acute phase and up to 30 later. Predictive equations (Harris–Benedict with stress factors, Mifflin–St Jeor, Penn State) are second choice and often inaccurate in ICU.
• Protein: 1.2–2.0 g/kg/day in critical illness; up to 2.0–2.5 g/kg in major burns, polytrauma, open abdomen and continuous renal replacement therapy (CRRT adds amino acid losses). Protein is prioritised over energy.
• Phase-based feeding: acute early phase — hypocaloric/permissive underfeeding (do not exceed about 70% of measured expenditure in the first 2–3 days) because of endogenous energy production; late phase — full feeding 80–100% of target. Overfeeding causes hyperglycaemia, hypertriglyceridaemia, hepatic steatosis, CO₂ retention and difficult weaning.
• Fluid: roughly 30–35 mL/kg/day in adults, adjusted for fever, drains, dialysis and cardiac/renal restriction; count the water in the feed (a 1 kcal/mL feed is about 80–85% water; 1.5–2.0 kcal/mL feeds only 69–78%).
• Obesity: hypocaloric high-protein feeding — 11–14 kcal/kg actual body weight (BMI 30–50) or 22–25 kcal/kg ideal body weight (BMI >50), with 2.0–2.5 g protein/kg ideal body weight.
• Nutritional risk screening for the ICU: NRS-2002 (score ≥3 at risk, ≥5 high risk) and the NUTRIC score (high risk ≥5 without IL-6) identify who benefits most from aggressive early nutrition. Detailed assessment methods belong to the assessment topic; here they are used only to grade urgency.

Complications and their management

• EN mechanical: tube misplacement into the airway (feeding into the lung is catastrophic), nasal/oesophageal erosion, sinusitis, tube blockage (flush; avoid crushing sustained-release tablets), accidental removal, PEG-site infection and buried bumper.
• EN gastrointestinal: diarrhoea (commonest — usually sorbitol-containing drugs, antibiotics, *C. difficile*, hyperosmolar feed, rapid rate, lactose or fat intolerance; not necessarily the feed), constipation, nausea, distension, delayed gastric emptying (treat with prokinetics such as metoclopramide, post-pyloric access), high gastric residual.
• EN pulmonary: aspiration pneumonia — reduce with head-up 30–45°, continuous rather than bolus feeding, post-pyloric tube, oral care.
• EN metabolic: hyperglycaemia, dehydration from hyperosmolar feed with low free water, electrolyte shifts, tube-feed syndrome (high protein, low water → hypernatraemia, azotaemia).
• Drug–nutrient interactions: phenytoin absorption falls markedly with continuous feed (hold feed 1–2 h either side), warfarin versus vitamin K content, fluoroquinolone chelation, no crushing of enteric-coated or modified-release forms.
• PN catheter-related: pneumothorax, haemothorax, arterial puncture, air embolism, thrombosis, and above all central line-associated bloodstream infection (CLABSI) — prevented by aseptic insertion bundle, chlorhexidine skin preparation, dedicated lumen, hub disinfection, early removal.
• PN metabolic: hyperglycaemia and hypoglycaemia on abrupt stop, hypertriglyceridaemia, essential fatty acid deficiency (lipid-free PN >2–3 weeks), azotaemia, electrolyte and acid-base disturbance, trace element deficiency or toxicity.
• PN hepatobiliary and bone: intestinal failure-associated liver disease (IFALD) — cholestasis and steatosis from overfeeding, excess soybean lipid, lack of enteral stimulation and sepsis; biliary sludge and gallstones from gut disuse; metabolic bone disease in long-term PN.
• Refeeding syndrome: on feeding a starved patient, insulin drives potassium, magnesium and phosphate intracellularly → hypophosphataemia (hallmark), arrhythmia, respiratory and cardiac failure, Wernicke's encephalopathy. High risk: BMI <16, >15% unintentional weight loss in 3–6 months, little or no intake >10 days, low baseline K/Mg/PO₄, alcohol use, chronic diuretics. Management: thiamine 200–300 mg (often IV) and B-complex before and for the first days of feeding, start at about 10 kcal/kg/day (5 kcal/kg in extreme cases), advance over 4–7 days, replace electrolytes aggressively and monitor daily.

Indian practice, standards and regulation

• Clinical guidelines used in Indian ICUs: ASPEN/SCCM (2016 critical care guidelines and subsequent updates), ESPEN ICU guideline (2019/2023 update), and the ISCCM (Indian Society of Critical Care Medicine) nutrition recommendations, which adapt protein–energy targets to Indian body weights and the widespread use of blenderised feeds.
• Product regulation: enteral and oral nutritional formulas are regulated by FSSAI under the Food Safety and Standards Act, 2006 — specifically the Food Safety and Standards (Foods for Infant Nutrition) Regulations and the Food Safety and Standards (Health Supplements, Nutraceuticals, Food for Special Dietary Use, Food for Special Medical Purpose, Functional Food and Novel Food) Regulations, 2016, under which a Food for Special Medical Purpose (FSMP) must be used under medical supervision and labelled accordingly. Amendments appear frequently — verify the current amendment before quoting a clause.
• PN products are drugs, licensed under the Drugs and Cosmetics Act, 1940 and its Rules, manufactured to Schedule M GMP; compounding in a hospital pharmacy follows aseptic/laminar-flow practice.
• Infection control: NABH accreditation standards and the ICMR/NCDC hospital infection control guidance drive CLABSI bundles and feed-handling hygiene; blenderised feed must be prepared fresh, hung for a maximum of about 4 hours, and commercial decanted feed for up to 8–12 hours (closed ready-to-hang systems up to 24–48 h per manufacturer).
• Cost reality: blenderised kitchen feed may cost roughly ₹100–300 per day; commercial powdered enteral feed roughly ₹400–900 per day; TPN with a multi-chamber bag plus additives commonly ₹2,500–6,000 per day plus line and monitoring costs. Prices vary widely by hospital and brand — treat these as orders of magnitude.
• Professional practice: the clinical dietitian prescribes the feed plan jointly with the intensivist; RD registration with the Indian Dietetic Association and, increasingly, the Allied and Healthcare Professions Act, 2021 framework governs who may practise clinical dietetics.

Key points

• Gut-first rule - if the GI tract works and is accessible, feed enterally; PN only when the gut fails.
• EN timing - start within 24–48 h of ICU admission after haemodynamic resuscitation.
• EN benefits - maintains mucosal integrity and gut-associated lymphoid tissue, reduces bacterial translocation, fewer infections, far cheaper than PN.
• Access rule of thumb - nasal tubes for under 4–6 weeks, PEG or jejunostomy beyond that.
• Post-pyloric feeding - chosen for gastroparesis, high aspiration risk, severe acute pancreatitis; must be continuous.
• Energy target - 25–30 kcal/kg/day when indirect calorimetry is unavailable; 20–25 kcal/kg in the acute phase.
• Protein target - 1.2–2.0 g/kg/day, up to 2.5 g/kg in burns, trauma and CRRT; protein takes priority over calories.
• Permissive underfeeding - keep to about 70% of target for the first 2–3 days; avoid full feeding too early.
• Overfeeding harms - hyperglycaemia, hypertriglyceridaemia, hepatic steatosis, raised CO₂ production, delayed weaning.
• Formula choice - polymeric for a working gut, semi-elemental for malabsorption, elemental only for severe malabsorption.
• Osmolarity limit for peripheral PN - about 850–900 mOsm/L; above that a central line is mandatory.
• Energy values in PN - dextrose monohydrate 3.4 kcal/g, amino acids 4 kcal/g, lipid 20% emulsion 2 kcal/mL.
• Dextrose infusion limit - about 4–5 mg/kg/min oxidation ceiling in adults.
• Refeeding syndrome - hypophosphataemia with hypokalaemia and hypomagnesaemia; give thiamine first, start at ~10 kcal/kg/day.
• GRV - routine monitoring is not recommended as the sole reason to withhold feed; look at the whole clinical picture.
• Diarrhoea on EN - investigate drugs, antibiotics and infection before blaming the formula.
• CLABSI - the dominant serious complication of PN; prevented by insertion and maintenance bundles and a dedicated lumen.
• Weaning PN - taper when EN/oral intake reaches about 60% of the target to prevent rebound hypoglycaemia.

Formulas and examples

Example 1 — Enteral feed plan for a ventilated patient. Male, 60 kg, 170 cm, day 2 of sepsis on a ventilator. Target 25 kcal/kg and 1.5 g protein/kg. Feed available: 1.0 kcal/mL polymeric, 40 g protein per litre, 84% water. Fluid need 30 mL/kg.

• Energy = 25 × 60 = 1,500 kcal/day; protein = 1.5 × 60 = 90 g/day.
• Volume for energy = 1,500 ÷ 1.0 = 1,500 mL/day.
• Protein supplied = 1.5 L × 40 = 60 g — a shortfall of 30 g, so add a modular whey protein powder (about 80% protein) → 30 ÷ 0.8 ≈ 38 g powder/day, split across flushes.
• Continuous rate over 22 h (2 h for breaks and procedures) = 1,500 ÷ 22 ≈ 68 mL/h; start at 25 mL/h and advance 20 mL/h every 8 h.
• Water: feed gives 1,500 × 0.84 = 1,260 mL; total need = 30 × 60 = 1,800 mL → extra 540 mL/day as flushes (about 90 mL six times a day) minus any IV fluid given.
• Nitrogen = 90 ÷ 6.25 = 14.4 g; non-protein kcal = 1,500 − (90 × 4) = 1,140 → NPC:N ≈ 79:1, below the 100–150:1 stress range, confirming this is a deliberately high-protein, modest-energy prescription.

Example 2 — TPN composition and checks. Female, 50 kg, prolonged ileus. Prescribe 25 kcal/kg and 1.5 g/kg protein; lipid to give 30% of total energy.

• Energy = 25 × 50 = 1,250 kcal/day; protein = 1.5 × 50 = 75 g → 75 × 4 = 300 kcal from amino acids.
• Lipid energy = 0.30 × 1,250 = 375 kcal → 20% emulsion at 2 kcal/mL = 188 mL ≈ 37.5 g fat = 0.75 g/kg (within the 1–1.5 g/kg limit).
• Carbohydrate energy = 1,250 − 300 − 375 = 575 kcal → dextrose = 575 ÷ 3.4 ≈ 169 g.
• GIR = (169 × 1,000) ÷ (50 × 1,440) ≈ 2.35 mg/kg/min — safely under the 4–5 mg/kg/min ceiling.
• Nitrogen = 75 ÷ 6.25 = 12 g; non-protein kcal = 950 → NPC:N ≈ 79:1 (high-protein stress regimen).
• If made up to 1,500 mL: dextrose 113 g/L, amino acids 50 g/L, lipid 25 g/L, electrolytes ~100 mEq/L → osmolarity ≈ (113×5) + (50×10) + (100×2) + (25×1.3) = 565 + 500 + 200 + 33 ≈ 1,298 mOsm/L → central line required.

Example 3 — Refeeding risk. Male, 38 kg, height 168 cm, negligible intake for 14 days, serum phosphate 0.6 mmol/L.

• BMI = 38 ÷ 1.68² = 38 ÷ 2.822 ≈ 13.5 kg/m² → BMI <16, negligible intake for >10 days, low phosphate = high refeeding risk.
• Day 1 energy = 10 × 38 = 380 kcal/day; with a 1 kcal/mL feed that is 380 mL, about 16 mL/h continuous.
• Give thiamine 200–300 mg daily plus B-complex and a multivitamin before feeding starts; correct phosphate, potassium and magnesium intravenously.
• Advance roughly to 15 kcal/kg (570 kcal) on day 3, 20 kcal/kg (760 kcal) on day 5, and full 25–30 kcal/kg (950–1,140 kcal) by about day 7 if electrolytes stay stable, checking K, Mg, PO₄ daily for the first week.

Example 4 — Nitrogen balance. Patient receives 1,800 mL of a feed containing 55 g protein per litre; 24-h urinary urea nitrogen is 14 g.

• Protein intake = 1.8 × 55 = 99 g/day; nitrogen intake = 99 ÷ 6.25 = 15.84 g.
• Losses = 14 + 4 = 18 g.
• Balance = 15.84 − 18 = −2.16 g/day → still catabolic; raise protein. To reach balance, nitrogen intake must be ≥18 g → protein ≥ 18 × 6.25 = 112.5 g/day, i.e. about 245 mL more of the same feed or a modular protein addition.

Example 5 — Obese ICU patient, hypocaloric high-protein feeding. Female, actual weight 110 kg, height 160 cm.

• BMI = 110 ÷ 1.60² = 110 ÷ 2.56 ≈ 43.0 kg/m² → BMI 30–50 band → use 11–14 kcal/kg actual weight.
• Energy at 12 kcal/kg = 12 × 110 = 1,320 kcal/day.
• IBW (Broca, women) = 160 − 105 = 55 kg; protein at 2.0 g/kg IBW = 110 g/day.
• A 1.5 kcal/mL, 68 g/L protein concentrated feed: 1,320 ÷ 1.5 = 880 mL/day, giving 0.88 × 68 ≈ 60 g protein → add about 50 g protein as modular powder (≈63 g of an 80% powder).

Where it is used

• Hospital ICUs and HDUs: clinical dietitians in Apollo, Fortis, Max, Medanta, Manipal, CMC Vellore, AIIMS and state medical colleges write daily EN/PN prescriptions and join nutrition support team rounds.
• Nutrition support teams (NST): intensivist, clinical dietitian, pharmacist and nurse jointly manage TPN compounding, line care and refeeding protocols; NABH accreditation expects a documented nutrition screening and care process.
• Food industry and FSMP manufacturers: product development, regulatory affairs and medical nutrition sales roles at Abbott, Nestlé Health Science, Danone, Fresenius Kabi, B. Braun, Baxter, Pfizer and Indian players for enteral formulas and PN bags.
• Home enteral and parenteral nutrition: PEG-fed stroke, motor neuron disease and head-and-neck cancer patients; home PN for short bowel syndrome, with dietitian-led caregiver training.
• Paediatric and neonatal units: NICU TPN and preterm enteral feeding protocols, where dosing is per kg and far more precise.
• Teaching, research and exams: B.Sc/M.Sc Nutrition and Dietetics clinical papers, internship case presentations, RD examination, and clinical trial coordination in ICU nutrition studies.

Interview questions

• Q: When would you choose parenteral over enteral nutrition? A: Only when the gut cannot be used or accessed — complete obstruction, bowel ischaemia, high-output proximal fistula, prolonged ileus, severe short bowel — or when enteral feeding has failed to deliver about 60% of the target after 3–7 days.
• Q: How soon should enteral feeding start in a ventilated ICU patient? A: Within 24–48 hours of admission once the patient is haemodynamically resuscitated, starting at a low rate and advancing to goal over 24–72 hours.
• Q: Why is enteral feeding preferred even when it meets only part of the requirement? A: Even trophic feeding maintains mucosal integrity and gut immune function, reduces bacterial translocation and infectious complications, and costs far less than PN.
• Q: What is the osmolarity limit for peripheral parenteral nutrition and why? A: About 850–900 mOsm/L; higher osmolarity damages the vein endothelium and causes thrombophlebitis, so a central line with high blood flow is needed.
• Q: How do you calculate energy from a parenteral bag? A: Dextrose monohydrate 3.4 kcal/g, amino acids 4 kcal/g, lipid from the emulsion strength (20% = 2 kcal/mL); add them, and count amino acid calories separately when quoting non-protein calories.
• Q: A tube-fed patient develops diarrhoea. What do you check first? A: Drugs and antibiotics (sorbitol-containing syrups, magnesium, prokinetics), *C. difficile* and other infection, feed rate and osmolarity, and feed hygiene — the formula itself is often not the cause.
• Q: What is refeeding syndrome and how do you prevent it? A: An insulin-driven intracellular shift of phosphate, potassium and magnesium when a starved patient is fed, causing arrhythmia and cardiorespiratory failure; prevent it with thiamine before feeding, starting at about 10 kcal/kg/day, slow advancement and daily electrolyte replacement.
• Q: Should gastric residual volume decide whether to continue feeding? A: No — routine GRV monitoring is not recommended as a sole trigger; a value of around 500 mL without vomiting, distension or other signs of intolerance does not justify stopping the feed.
• Q: Why is post-pyloric feeding chosen in severe acute pancreatitis or gastroparesis? A: It bypasses the stomach, reduces reflux and aspiration risk and tolerates feeding when gastric emptying is delayed; it must be given continuously by pump.
• Q: What is permissive underfeeding and why is it used? A: Deliberately giving about 70% of the measured or estimated energy target in the first 2–3 days of critical illness, because endogenous energy production is high and early full feeding worsens hyperglycaemia and outcomes; protein is still given in full.
• Q: How do you feed an obese critically ill patient? A: Hypocaloric, high-protein — 11–14 kcal/kg actual weight for BMI 30–50 (22–25 kcal/kg ideal weight above BMI 50) with 2.0–2.5 g protein per kg ideal body weight.
• Q: Which regulations govern enteral formulas and PN products in India? A: Enteral and oral formulas are foods regulated by FSSAI, with medical formulas classed as Food for Special Medical Purpose under the 2016 health supplements and nutraceuticals regulations; PN solutions are drugs licensed under the Drugs and Cosmetics Act, 1940 and made to Schedule M GMP.
• Q: Why give phenytoin away from a continuous enteral feed? A: The feed markedly reduces phenytoin absorption, so the feed is held for 1–2 hours before and after the dose and the tube flushed, with levels monitored.

Common mistakes

• Using 4 kcal/g for parenteral dextrose instead of 3.4 kcal/g, which overstates the energy delivered.
• Computing feed volume from energy only and forgetting to check whether the protein target is met — then not adding a modular protein.
• Forgetting that a concentrated feed is only about 70–78% water, leaving the patient dehydrated with hypernatraemia and azotaemia.
• Blaming the formula for every episode of diarrhoea instead of reviewing drugs, antibiotics, infection and feed hygiene.
• Feeding a severely malnourished patient to full target on day 1, precipitating refeeding syndrome, and giving thiamine after rather than before the first feed.
• Running hyperosmolar PN through a peripheral line, or adding calcium and phosphate carelessly to the same bag and causing precipitation.
• Quoting a stress factor from Harris–Benedict as if it were a measured value, and ignoring that indirect calorimetry is the reference standard.
• Writing "NPO, start TPN" for a patient with a working gut simply because they are intubated.

Related topics

Nutritional assessment: anthropometric, biochemical, clinical and dietary · Medical nutrition therapy: gastrointestinal disorders, liver disease and cancer · Therapeutic diets: diabetes, cardiac, renal and obesity · Fluid, electrolyte and acid-base balance · Protein and energy metabolism in stress and sepsis · Food safety and FSSAI regulation of foods for special medical purpose