Overview
Definition:
Total parenteral nutrition (TPN) is an intravenous method of feeding that bypasses the gastrointestinal tract
Patients receive a solution of nutrients, including carbohydrates, proteins, lipids, vitamins, minerals, and electrolytes, administered directly into a vein
It is indicated when the gut is non-functional or inaccessible for prolonged periods, preventing malnutrition and supporting recovery in critically ill patients.
Epidemiology:
TPN is utilized in a significant proportion of hospitalized patients, particularly in intensive care units and in those with severe gastrointestinal disorders or malabsorption syndromes
Incidence varies by hospital and patient population, but it remains a cornerstone of nutritional support for a select group of surgical and medical patients.
Clinical Significance:
TPN is crucial for maintaining nutritional status, preventing catabolism, and promoting wound healing in patients unable to tolerate enteral feeding
Improper initiation or monitoring can lead to severe complications including hyperglycemia, electrolyte imbalances, infections, and organ dysfunction, directly impacting patient outcomes and mortality
Mastery of TPN is essential for surgical residents managing complex surgical patients.
Indications For Tpn
Non Functional Gi Tract:
Conditions such as prolonged ileus, bowel obstruction, short bowel syndrome, severe malabsorption (e.g., inflammatory bowel disease flares, celiac disease), and high-output fistulas.
Inability To Achieve Adequate Enteral Intake:
When enteral nutrition is not feasible or insufficient to meet estimated caloric and protein needs for more than 7-10 days
This includes severe anorexia, catabolic states, and intensive chemotherapy regimens.
Specific Surgical Scenarios:
Perioperative nutritional support in malnourished patients undergoing major surgery, particularly gastrointestinal surgery, where prolonged NPO status is anticipated
Early initiation in critically ill patients with predicted prolonged need for nutritional support.
Tpn Initiation
Assessment And Calculation:
Calculate estimated caloric needs (e.g., 25-30 kcal/kg/day) and protein requirements (e.g., 1.2-2.0 g/kg/day) based on patient's condition, weight, and metabolic state
Assess fluid and electrolyte status thoroughly.
Central Venous Access:
TPN must be administered via a central venous catheter due to the hyperosmolar nature of the solution, which can cause phlebitis in peripheral veins
Preferred sites include subclavian, internal jugular, or femoral veins
Ensure sterile insertion technique and proper catheter care.
Solution Formulation:
TPN solutions are customized
Typically contain dextrose (e.g., 20-50%), amino acids (e.g., 2-7%), lipids (e.g., 10-30%), electrolytes (sodium, potassium, chloride, calcium, magnesium, phosphate), trace elements, and vitamins
Initial initiation may start with a lower dextrose concentration to assess glucose tolerance.
Tpn Monitoring
Fluid And Electrolyte Balance:
Monitor daily intake and output, daily weight
Regularly check serum electrolytes (sodium, potassium, chloride, magnesium, phosphate, calcium) and adjust TPN formulation accordingly
Monitor for signs of fluid overload or depletion.
Glucose Control:
Frequent blood glucose monitoring (e.g., every 4-6 hours initially) is critical
Hyperglycemia can occur, especially with high dextrose loads
Insulin may be added to the TPN bag or administered subcutaneously/intravenously
Hypoglycemia can occur if TPN is abruptly stopped.
Nutritional Parameters:
Monitor serum albumin, prealbumin, triglycerides, and liver function tests (ALT, AST, alkaline phosphatase, bilirubin) regularly (e.g., weekly initially)
Assess for signs of refeeding syndrome if patient has been severely malnourished.
Infection Surveillance:
Monitor for signs and symptoms of infection, including fever, chills, elevated white blood cell count, and local signs of catheter site infection
Strict aseptic technique for TPN administration and catheter care is paramount
Consider blood cultures if infection is suspected.
Complications Of Tpn
Metabolic Complications:
Hyperglycemia, hypoglycemia, electrolyte imbalances (hypokalemia, hypophosphatemia, hypomagnesemia), refeeding syndrome, hypertriglyceridemia, essential fatty acid deficiency, and vitamin deficiencies/toxicities.
Catheter Related Infections:
Central line-associated bloodstream infections (CLABSIs) are a major concern
Other catheter-related complications include catheter occlusion, thrombosis, dislodgement, and pneumothorax/hemothorax during insertion.
Gi Complications:
While TPN bypasses the gut, prolonged TPN can lead to gut atrophy, bacterial overgrowth, cholestasis, and increased risk of C
difficile infection
Early transition to enteral feeding is preferred when possible.
Organ Specific Complications:
Hepatobiliary complications (e.g., steatosis, cholestasis, gallstones), renal complications (e.g., electrolyte disturbances), and cardiac complications (e.g., fluid overload).
Transitioning Off Tpn
Enteral Feeding Introduction:
As GI function returns and tolerance improves, gradually introduce enteral feeding
Start with small volumes of isotonic formula and advance as tolerated
TPN can be reduced as enteral intake increases.
Gradual Weaning:
TPN should be gradually reduced and eventually discontinued as enteral intake meets at least 60-75% of estimated nutritional needs
Abrupt discontinuation can lead to hypoglycemia, especially in patients on high dextrose infusions.
Monitoring During Transition:
Continue to monitor fluid balance, electrolytes, and glucose closely during the transition period
Assess for any signs of intolerance to enteral feeding.
Key Points
Exam Focus:
Indications for TPN are critical
Differentiate TPN from EN
Key monitoring parameters include glucose, electrolytes, and signs of infection
Common TPN complications (metabolic, infectious) are high-yield.
Clinical Pearls:
Always start TPN slowly, especially in malnourished patients
Never abruptly stop TPN
Regular reevaluation of nutritional needs and TPN composition is essential
A multidisciplinary approach involving physicians, dietitians, and nurses is vital.
Common Mistakes:
Failure to adequately assess nutritional needs
Inadequate monitoring of glucose and electrolytes
Poor aseptic technique leading to infection
Not transitioning to enteral feeding when feasible
Incorrect TPN formulation leading to complications.