🍼 What is Parenteral Nutrition?
Parenteral nutrition (PN) is the intravenous delivery of nutrients (carbohydrates, amino acids, lipids, electrolytes, vitamins, trace elements) directly into the bloodstream, bypassing the gastrointestinal tract.
Golden Rule: "If the gut works, use it." Enteral nutrition (EN) is always preferred over PN when the GI tract is functional. PN is indicated only when the enteral route is not feasible, not tolerated, or contraindicated.
Indications for PN
- Prolonged ileus (>5–7 days)
- Short bowel syndrome / massive bowel resection
- High-output enterocutaneous fistula
- Severe acute pancreatitis where EN is not tolerated (rare — EN now preferred even in pancreatitis)
- Obstruction preventing enteral access
- Severe mucositis post-chemotherapy/bone marrow transplant
- Mesenteric ischaemia
- Bowel rest requirements (rare)
When NOT to start PN early: Starting PN within 48 hours in critically ill patients who can tolerate EN is associated with worse outcomes (increased infections, ICU length of stay). Early EN is preferred.
Types of PN
Total Parenteral Nutrition (TPN)
- ALL nutritional needs via IV route
- No enteral intake
- Requires central venous access
- Osmolarity typically >900 mOsm/L
Supplemental / Partial PN
- EN + PN combined
- Used when EN meets <60% of target
- Reduces infection risk vs TPN alone
- Bridge to full EN tolerance
📊 PN Macronutrient Components
| Component | Standard Requirement | Notes |
|---|
| Calories (total) | 25–30 kcal/kg/day | Reduce in acute critical illness (20–25) |
| Carbohydrates (dextrose) | 3–5 g/kg/day | Max glucose infusion rate ~4 mg/kg/min |
| Amino acids (protein) | 1.2–2.0 g/kg/day | Higher in burns, sepsis, critical illness |
| Lipid emulsion (IVFE) | 1.0–1.5 g/kg/day | Max infuse over ≥12 hours; do NOT exceed 2.5 g/kg/day |
| Fluid | 25–35 mL/kg/day | Adjust for fluid balance |
Non-protein calories: Protein (amino acids) should NOT be counted as an energy source in critically ill patients — protein is needed for anabolism, not fuel. Calculate energy from dextrose + lipid only.
🩺 Vascular Access for PN
CRITICAL: PN with osmolarity >900 mOsm/L MUST be administered via a central venous catheter (CVC) or PICC line. Peripheral PN risks thrombophlebitis and chemical burns from hyperosmolar solutions.
Central Venous Access Options
Central Venous Catheter (CVC)
- Internal jugular, subclavian, femoral
- Subclavian preferred for long-term PN (lowest infection rate for tunnelled CVCs)
- Femoral = highest CLABSI risk
- Tip position: lower SVC / cavoatrial junction — confirm by CXR before use
PICC Line
- Peripherally Inserted Central Catheter
- Inserted via antecubital/brachial vein
- Tip: lower SVC — confirm by CXR
- Suitable for weeks to months of PN
- Lower CLABSI risk than short-term CVC
Peripheral PN (PPN)
- Maximum osmolarity: <900 mOsm/L (some guidelines say ≤800)
- Used for short-term PN (≤2 weeks) when central access delayed
- Shorter dwell time per cannula (~72 hours), change site regularly
- Not suitable for high protein or dextrose concentrations
🔒 Central Line Insertion & Maintenance
Insertion Bundle (CLABSI Prevention)
- Hand hygiene (surgical scrub technique)
- Full sterile barrier precautions: gown, gloves, mask, hat, large sterile drape
- Chlorhexidine 2% skin antisepsis — allow to dry completely
- Optimal site selection: subclavian/jugular over femoral
- Daily review and remove when no longer needed
Dedicated PN Lumen
PN must run through a DEDICATED lumen. Do NOT connect blood products, IV medications, or blood sampling to the PN lumen. This significantly increases CLABSI risk and can cause PN incompatibility.
Line Care During PN
- Change IV tubing every 24 hours (lipid-containing PN degrades tubing faster)
- Use inline 1.2 micron filter for lipid-containing PN (0.2 micron for lipid-free)
- Inspect connection sites at every nursing assessment
- Dressing change: transparent semipermeable dressing every 7 days, or gauze every 2 days, or whenever soiled/loose
- Chlorhexidine-impregnated dressing — recommended for all CVCs in ICU
CXR Before First PN Infusion
Mandatory to confirm:
- Catheter tip in lower SVC or cavoatrial junction
- No pneumothorax
- No haemothorax
- No kinked or malpositioned catheter
NEVER start PN without confirmed central line tip position.
💊 Prescribing & Administering PN
PN Preparation
All-in-One (3-in-1 / TNA bags)
- Dextrose + amino acids + lipid premixed in one bag
- Most common in ICU/clinical settings
- Prepared by pharmacy under aseptic conditions
- Standardised or individualised prescriptions
2-in-1 Bags
- Dextrose + amino acids only (no lipid)
- Lipid emulsion (IVFE) infused separately
- 0.2 micron filter for 2-in-1; 1.2 micron for TNA
- Allows adjustable lipid dosing
Administration Rate
- Start PN at 50% of target rate for first 24 hours in malnourished patients (refeeding risk)
- Advance to full rate over 24–48 hours if glucose and electrolytes remain stable
- Continuous infusion over 24 hours standard in ICU
- Cyclic PN (12–14 hours overnight) for stable long-term home PN patients
Blood Glucose Monitoring
| Phase | Monitoring Frequency | Target |
|---|
| First 24–48 hours | Every 1–4 hours | 6–10 mmol/L |
| Stable phase | Every 4–6 hours | 6–10 mmol/L |
| Home PN | Fasting + 2h post-infusion | 4–8 mmol/L |
Hyperglycaemia in PN: Blood glucose >10 mmol/L = start insulin infusion. Target 6–10 mmol/L. Avoid hypoglycaemia (<4 mmol/L) especially in patients on concurrent insulin.
Electrolyte Additives
Standard PN bags should contain:
- Sodium (as NaCl): ~80–100 mmol/day
- Potassium (as KCl): ~60–80 mmol/day
- Phosphate: 20–40 mmol/day (CRITICAL in refeeding risk)
- Magnesium: 10–15 mmol/day
- Calcium (as gluconate): 5–10 mmol/day
Refeeding risk: In malnourished patients, phosphate MUST be added and monitored closely. Check phosphate before starting PN and daily for first week.
🔬 Monitoring During PN
| Parameter | Frequency | Why |
|---|
| Blood glucose | Every 1–6 hours | Hyperglycaemia risk |
| Phosphate | Daily (days 1–5), then 2–3×/week | Refeeding syndrome |
| Potassium | Daily initially | Refeeding, insulin effect |
| Magnesium | Daily initially | Refeeding risk |
| Sodium / Urea / Creatinine | 3×/week | Fluid balance, renal function |
| LFTs (ALT, ALP, bilirubin) | Weekly | PN-associated liver disease |
| Triglycerides | Weekly | Lipid tolerance |
| Weight | 3×/week | Fluid balance vs muscle gain |
Triglycerides >4.5 mmol/L: Stop or reduce lipid infusion. Risk of hypertriglyceridaemia-induced pancreatitis.
⚠️ Complications of PN
1. Catheter-Related Complications
| Complication | Prevention / Management |
|---|
| CLABSI (Bloodstream Infection) | Strict aseptic technique; dedicated lumen; daily CVC review; remove ASAP |
| Pneumothorax (insertion) | CXR post-insertion; ultrasound guidance reduces risk |
| Arterial puncture | Ultrasound guidance; confirm venous blood before dilating |
| Venous thrombosis | Subclavian/PICC preferred; low-dose heparin in selected patients |
| Air embolism | Trendelenburg position during insertion/removal; hum/bear down manoeuvre |
2. Metabolic Complications
Refeeding Syndrome
- Hallmark: severe hypophosphataemia
- Also: ↓K⁺, ↓Mg²⁺, thiamine deficiency, fluid shifts
- Prevent: start low (max 10 kcal/kg/day), give thiamine BEFORE starting PN in malnourished
- Monitor electrolytes daily for first week
Hyperglycaemia
- Most common metabolic complication
- Target BGL 6–10 mmol/L
- Insulin infusion if persistently >10
- Reduce dextrose concentration if uncontrolled
PN-Associated Liver Disease (PNALD)
- Cholestasis, steatohepatitis, cirrhosis with long-term PN
- Early signs: rising ALP, bilirubin, transaminases
- Prevention: minimise duration, use cyclic PN, advance to EN/oral ASAP, avoid overfeeding
- Fish oil–based lipid emulsions (SMOFlipid) may be hepatoprotective
Electrolyte Imbalances
- Hypophosphataemia — most critical (refeeding)
- Hypokalaemia — insulin drives K⁺ into cells with glucose
- Hypomagnesaemia — often concurrent
- Adjust PN additives daily based on results
3. Metabolic Bone Disease
Long-term PN can cause osteoporosis. Ensure adequate calcium, phosphate and vitamin D in PN bag. Annual DEXA scan for home PN patients.
4. Gut Disuse
Prolonged PN causes gut mucosal atrophy, bacterial overgrowth, increased intestinal permeability, and translocation of bacteria. Introduce even minimal enteral feeds ("trophic feeds") whenever possible to maintain gut integrity.
Trophic/trickle feeds: Even 10–20 mL/hour of enteral formula provides enough luminal nutrition to maintain gut mucosa integrity and reduce gut-related complications of PN.
🛑 Stopping PN
Weaning PN
- When EN/oral intake meets ≥60% of nutritional targets, PN can be weaned and stopped
- Reduce PN over 24–48 hours rather than abrupt cessation (avoid rebound hypoglycaemia)
- Monitor BGL for 2–4 hours after PN stopped (risk of hypoglycaemia from continued endogenous insulin)
Hypoglycaemia on stopping PN: If PN must be stopped suddenly (e.g., bag runs out, line problem), infuse 10% dextrose at the same rate until a new PN bag is available. Check BGL every 30–60 minutes.