TPN
Reading File
Finding Sources
Finding Sources
Reading File
Reading File
Reading File
Finding Sources
Reading File
Finding Sources
Reading File
Reading File
Finding Sources
Reading File
Reading File
Here is a thorough, textbook-based overview of Total Parenteral Nutrition (TPN):
Total Parenteral Nutrition (TPN)
Definition
TPN (also called central parenteral nutrition) is the delivery of complete nutritional requirements intravenously via a large-diameter central vein, bypassing the gastrointestinal tract entirely. It supplies all macronutrients and micronutrients through a high-osmolality solution (dextrose 15-25%, amino acids 3-5%).
- Schwartz's Principles of Surgery 11e, p. 101
Indications
TPN is used when the gut cannot or should not be used:
- Severe bowel obstruction or ileus
- Severe shock
- High-output enteric fistula (no distal feeding access)
- Severe GI hemorrhage
- Severe short bowel syndrome
- GI discontinuity (surgical)
Timing rules:
- Low nutrition risk patients: do not start TPN for the first 7 days
- High malnutrition risk or chronically malnourished: start as soon as feasible
- Patients on enteral nutrition who cannot reach 60% of goal calories after 7-10 days: add supplemental TPN
- Current Surgical Therapy 14e, p. 1645
TPN vs. Peripheral Parenteral Nutrition (PPN)
| Feature | TPN (Central PN) | PPN |
|---|---|---|
| Dextrose concentration | 15-25% | 5-10% |
| Protein | Full supplementation | ~3% |
| Access required | Central vein (SVC) | Peripheral vein |
| Osmolality | ~2,000 mOsm/L | Lower |
| Duration | Long-term | Short-term (<2 weeks) |
| Suitable for severe malnutrition | Yes | No |
- Schwartz's Principles of Surgery 11e, p. 101
Composition of a Standard TPN Formulation
| Component | Amount (per ~1050 mL bag) |
|---|---|
| 10% Amino acid solution | 500 mL (50 g amino acids) |
| 50% Dextrose solution | 500 mL (250 g dextrose = 840 kcal) |
| Fat emulsion | Variable |
| Electrolytes + vitamins + minerals | ~50 mL |
| Osmolality | ~2,000 mOsm/L |
Electrolyte ranges (per liter):
-
Sodium: 60 mEq (range 0-150)
-
Potassium: 40 mEq (range 0-80)
-
Acetate: 50 mEq
-
Chloride: 50 mEq
-
Phosphate, Calcium, Magnesium: titrated to need
-
Mulholland & Greenfield's Surgery 7e, p. 142-143
Access
- Short-term: percutaneous 16-gauge catheter into subclavian or internal jugular vein, threaded to SVC
- Long-term/home TPN: tunneled catheter or subcutaneous port via basilic/cephalic vein (PICC) or surgical tunneling
- Solutions must be prepared under laminar flow hoods in pharmacy (sterile conditions)
Initiation and Titration
- Start at lower rates, increase over 2-3 days toward goal
- In critically ill patients (ICU): hypocaloric nutrition is preferred in the first week
- Target: <20 kcal/kg/day or <80% of estimated caloric need
- Protein target: >1.2 g/kg/day
- This reduces hyperglycemia and insulin resistance
- Blood glucose target (ICU): 140-180 mg/dL
- Schwartz's Principles of Surgery 11e, p. 101
Additives and Supplementation
| Additive | Notes |
|---|---|
| Vitamins | IV vitamin preparations added to each bag; vitamin K is NOT in commercial prep - give weekly separately |
| Lipid emulsion | Prevents essential fatty acid deficiency; limit to max 100 g/week in first week (soy-based, divided in 2 doses); omega-3/MCT formulations preferred over omega-6-heavy emulsions |
| Trace minerals | Zinc, copper, chromium, manganese - use commercial preparation; zinc deficiency = eczematoid rash at intertriginous areas; copper deficiency = microcytic anemia; chromium deficiency = glucose intolerance |
| Insulin | Added directly to TPN bag once total daily dose determined |
Monitoring
| Parameter | Frequency |
|---|---|
| Electrolytes | Daily until stable, then every 2-3 days |
| Urine/capillary glucose | Every 6 hours |
| Serum glucose | At least daily initially |
| BUN, LFTs, phosphate, magnesium | At least weekly |
| Vital signs + urine output | Regularly |
| Weight | Regularly |
- Schwartz's Principles of Surgery 11e, p. 101-102
Complications
1. Catheter-Related
- Central line-associated bloodstream infection (CLABSI) - most serious risk
- Patients exclusively on TPN are more susceptible to infections due to loss of gut mucosal barrier function
2. Metabolic
| Complication | Mechanism | Notes |
|---|---|---|
| Hyperglycemia | High dextrose load, insulin resistance | IV insulin infusion preferred; add insulin to TPN bag once dose established |
| Hypokalemia | Glucose-driven K+ shift intracellularly | May cause glycosuria - treat with K+, not insulin; may need up to 240 mEq/day |
| Hypertriglyceridemia | Fat emulsion excess | Limit IV fat emulsions |
| Hypophosphatemia | Rapid cellular uptake at initiation | Common at start of feeding |
| Essential fatty acid deficiency | Fat-free solutions over time | Dry scaly dermatitis, hair loss; prevent with periodic fat emulsion |
| Steatotic (fatty) liver disease | Excess glucose, lack of enteral stimulation | Monitor LFTs |
| Bone disease | Metabolic changes with long-term PN | Monitor calcium metabolism |
3. Hepatobiliary
- TPN-associated liver disease (steatosis, cholestasis) - especially with prolonged use
Refeeding Syndrome
A potentially fatal complication when nutrition is reintroduced after prolonged starvation (>5 days), most commonly described with IV (parenteral) refeeding.
Mechanism: Carbohydrate reintroduction triggers insulin release, driving intracellular shift of phosphate (for ATP synthesis via glycolysis), potassium, and magnesium.
Hallmark: Hypophosphatemia - can cause cardiac arrhythmias, infarctions, cardiac arrest.
Other electrolyte abnormalities: Hypokalemia, hypomagnesemia, thiamin deficiency.
Diagnostic criteria (consensus): Drop in phosphate, potassium, or magnesium of:
- 10-20% = mild
- 20-30% = moderate
- >30% and/or organ dysfunction = severe Occurring within 5 days of initiating feeding.
Management:
- Identify high-risk patients before starting PN
- Start feeding cautiously: 10-20 kcal/kg/day for first 24 hours (or 100-150 g dextrose)
- Increase gradually over 4-7 days
- Supplement B vitamins (especially thiamin) before starting
- Aggressive electrolyte repletion (K, Phos, Mg, Ca)
- Reduce caloric intake if electrolytes drop severely
- Tietz Textbook of Laboratory Medicine 7e; Sabiston Textbook of Surgery; Current Surgical Therapy 14e
Insulin Management in TPN (Diabetes/Hyperglycemia)
- Preferred: IV insulin infusion for rapid dose titration
- Once total insulin dose determined, add a proportion directly into the TPN bag
- For patients with type 1 DM or pancreatogenic DM: add long-acting insulin (0.1-0.2 units/kg/day) in case TPN is interrupted
- Harrison's Principles of Internal Medicine 22e, p. 3264
Enteral > Parenteral (When Possible)
Enteral nutrition is preferred over TPN whenever the gut can be used because:
- Cheaper and safer
- Maintains gut mucosal integrity (enterocyte nutrition via glutamine, short-chain fatty acids)
- Preserves the immunologic barrier function of the gut
- Bypassing the portal circulation in TPN impairs hepatic protein synthesis
- Mulholland & Greenfield's Surgery 7e, p. 143
Summary mnemonic - TPN complications = "CHIEF":
- CLABSI (catheter infection)
- Hyperglycemia
- Infection (gut barrier loss)
- Electrolyte imbalance / Essential fatty acid deficiency
- Fatty liver / reFeeding syndrome
This is a shared conversation. Sign in to Orris to start your own chat.