Parenteral feeding: TPN and PPN, indications and complications
Parenteral nutrition gives nutrients straight into a vein, bypassing the gut. Use it only when the gut cannot be used.
What parenteral nutrition is
Parenteral nutrition (PN) means giving nutrients by vein, so the digestive tract is not used. It is used when the gut does not work, cannot be used, or cannot absorb enough for more than about a week. The solution contains dextrose, amino acids, fat emulsion, electrolytes, vitamins, trace elements and water, mixed under sterile conditions in the pharmacy. It is life-saving but costly and carries a higher risk of infection than tube feeding.
TPN vs PPN
Lipid emulsion is useful in PPN because it gives many calories without raising osmolarity.
What goes into a parenteral solution
| Component | Purpose | Note |
|---|---|---|
| Dextrose (glucose) | Main energy source | 3.4 kcal per gram (hydrated form) |
| Amino acids | Protein for repair and immunity | 4 kcal per gram |
| Lipid emulsion | Energy and essential fatty acids | 10% gives 1.1 kcal/mL; 20% gives 2 kcal/mL |
| Electrolytes | Sodium, potassium, calcium, magnesium, phosphate | Adjusted daily from blood reports |
| Vitamins and trace elements | Zinc, copper, selenium, chromium, manganese; all vitamins | Added just before use |
| Water | Fluid needs | About 30-35 mL per kg body weight in adults (ESPEN range 30-40 mL) |
Indications, contraindications and complications
| Heading | Points |
|---|---|
| Indications | Severe short bowel syndrome; intestinal obstruction; prolonged paralytic ileus; high-output fistula; severe malabsorption; severe acute pancreatitis not tolerating tube feeds; uncontrolled vomiting; when enteral feeding cannot meet needs for more than about 7 days |
| Contraindications | A working gut that can be used; need expected for less than about 5-7 days; unstable blood pressure or severe fluid overload; no safe venous access; patient refuses |
| Catheter complications | Pneumothorax or bleeding while inserting the line; blocked line; clots (thrombosis); line infection and sepsis, the most serious risk |
| Metabolic complications | High blood sugar; low blood sugar if stopped suddenly; electrolyte imbalance; refeeding syndrome (low phosphate, potassium and magnesium); fatty liver and liver dysfunction; essential fatty acid deficiency if no lipid is given |
| Gut complications | The unused gut lining thins (atrophy), which may let bacteria cross into the blood |
Enteral vs parenteral feeding
| Point | Enteral | Parenteral |
|---|---|---|
| Route | Gut, by mouth or tube | Vein, central or peripheral |
| Gut function needed | Yes | No |
| Effect on gut | Keeps the gut lining healthy | Gut lining may thin |
| Infection risk | Lower | Higher (line sepsis) |
| Cost | Low; kitchen feeds possible | High; sterile pharmacy mix |
| Main danger | Aspiration | Sepsis and metabolic upsets |
When a patient on TPN starts to recover, the dietitian begins small tube or oral feeds early and reduces the PN slowly, watching blood sugar, because even a little food keeps the gut lining alive.
2 marks: “Differentiate TPN and PPN.” TPN goes into a central vein and can meet all needs with a concentrated solution; PPN goes into a peripheral vein, is dilute and short-term.
5 marks: “Compare enteral and parenteral feeding.” Table: route, need for gut function, effect on gut, infection risk, cost, main danger, with one line on when each is used.
10 marks: “Explain parenteral nutrition with its indications, contraindications and complications.” Define, TPN vs PPN, components with energy values, indications, contraindications, catheter, metabolic and gut complications, and the move back to enteral feeding.
Parenteral = para (beside) + enteral (gut): it goes around the gut, straight to the blood.