TPN Care &
Metabolic Monitoring
How to safely administer Total Parenteral Nutrition and monitor patients for metabolic complications.
What Is TPN?
Total Parenteral Nutrition (TPN) delivers complete nutrition directly into the bloodstream through a central venous catheter, bypassing the GI tract entirely.
TPN contains dextrose (high concentration glucose), amino acids, lipids, electrolytes, vitamins, and trace elements.
Why a Central Line?
Key Term: Hyperosmolarity
TPN's high dextrose concentration creates a solution with very high osmolarity. A standard formula approximation:
A typical TPN with \( 250 \) g/L dextrose and \( 50 \) g/L amino acids gives:
Core Rule: Monitor Blood Glucose
High dextrose load is the greatest metabolic risk. Glucose is monitored frequently, especially when initiating TPN.
The Three Glucose Dangers
Refeeding Syndrome
When a malnourished patient is suddenly fed, insulin surges and drives electrolytes into cells, causing dangerous serum drops.
Prevention: start TPN slowly, advance gradually, and replace electrolytes before and during initiation.
TPN vs PPN
| TPN | PPN | |
|---|---|---|
| Access | Central line | Peripheral IV |
| Dextrose | High (up to \( 25\% \)) | Low (\( \leq 10\% \)) |
| Osmolarity | \( > 900 \ \text{mOsm/L} \) | \( < 900 \ \text{mOsm/L} \) |
| Duration | Long-term | Short-term |
| Calories | Full nutrition | Partial / supplement |
Nursing Care Steps
What to Monitor
Worked Example: Bag Runs Out
Scenario: The next TPN bag has not arrived from pharmacy and the current bag will empty in \( 30 \) minutes.
Why: Abruptly stopping the high glucose infusion would trigger rebound hypoglycemia, because circulating insulin remains elevated.
Worked Example: Glucose Math
A TPN bag contains \( 500 \) mL of \( 25\% \) dextrose. How many grams of dextrose are delivered?
This large carbohydrate load explains why frequent glucose checks and insulin coverage are essential.
Worked Example: Refeeding Risk
Scenario: A severely malnourished patient is started on TPN. On day 2 labs show phosphate \( 1.2 \) mg/dL and the patient reports muscle weakness.
Action: Notify provider, expect orders to slow the rate and aggressively replace phosphate, potassium, and magnesium.
Common Mistakes
Quick Reference
| Issue | Cause | Nursing Action |
|---|---|---|
| Hyperglycemia | High dextrose load | Insulin per order, monitor |
| Hypoglycemia | Abrupt TPN stop | Hang D10W, taper |
| Refeeding | Rapid feeding | Slow rate, replace lytes |
| Infection | Central line/bag | Sterile, change q24h |
| Fluid overload | Rate too high | Daily weight, I&O |
Question 1 of 5
The nurse discovers the TPN bag will be empty in \( 20 \) minutes and the next bag is delayed. What is the best action?
Question 2 of 5
Which lab finding is the hallmark of refeeding syndrome in a TPN patient?
Question 3 of 5
Why must TPN be infused through a central venous catheter?
Question 4 of 5
A TPN bag contains \( 1000 \) mL of \( 20\% \) dextrose. How many grams of dextrose does it deliver?
Question 5 of 5
Which action by a new nurse requires immediate intervention?