Total parenteral nutrition (TPN) is intravenous nutrition used when the gut cannot be used safely.

It can be life-saving, but also carries significant risks.

The most important rule:

If the gut works, use it.

TPN is always second line.

This guide focuses on when to use it, when not to use it, and what juniors actually need to know on the ward.

✅ What is TPN?

TPN = nutrition given via a central line containing:

Glucose (carbohydrate)
Amino acids (protein)
Lipids (fat)
Electrolytes
Vitamins & trace elements

It bypasses the gut completely.

Used only when enteral feeding is not possible.

✅ First principle (most important)

Before thinking about TPN, always ask:

Can we feed the gut?

Because:

Enteral feeding is safer
Cheaper
Fewer infections
Better outcomes

If the gut works → use oral/NG/PEG feed.

TPN is last resort.

✅ When should you consider TPN? (real-life indications)

Think TPN when:

Gut not usable:

Bowel obstruction
Ileus
Severe pancreatitis not tolerating enteral feed
High-output fistula
Short bowel
Severe malabsorption
Post-op complications
Prolonged NBM with no plan to feed

Or:

Inadequate intake:

Unable to eat >5–7 days
Not meeting needs enterally despite attempts

If patient can tolerate NG feeding → don’t jump to TPN.

❌ When NOT to use TPN

Very common exam + ward mistakes.

Do NOT use TPN for:

Poor appetite
Mild dysphagia
Short-term NBM (1–2 days)
“Convenience”
Working gut

These patients need:

Dietitian input
Supplements
NG feeding

Not TPN.

✅ Step 1 – Always involve the nutrition team

Juniors do NOT independently start TPN.

In real NHS practice:
👉 Refer to dietitian or nutrition team

They:

Calculate requirements
Prescribe TPN
Monitor safely

Your role = recognise need + refer early.

✅ Step 2 – Central access is required

TPN is hyperosmolar.

It must go through:

PICC line
Hickman
Central line

Never peripheral cannula (except special short-term PPN).

Check line position before starting.

✅ Step 3 – Know the risks (very important)

TPN is not benign.

Main complications:

🔴 Infection (most common + most dangerous)

Line sepsis
CLABSI

🔴 Electrolyte problems

Refeeding syndrome
Hypophosphataemia
Hypokalaemia

🔴 Metabolic

Hyperglycaemia
Fluid overload
Liver dysfunction

🔴 Mechanical

Line thrombosis
Pneumothorax (insertion)

This is why we avoid TPN unless necessary.

✅ Step 4 – Monitoring (what juniors actually do daily)

If patient on TPN, you are often the one checking bloods.

Daily:

U&E
Magnesium
Phosphate
Glucose
Fluid balance
Weight

Regularly:

LFTs
Triglycerides

Look for:

Falling electrolytes
Sepsis
Hyperglycaemia

Most complications show up in bloods first.

🚨 When to worry on the ward

Escalate if:

Fever or rigors → possible line sepsis
Line redness/discharge
Hypotension
Rising CRP
Electrolytes crashing
Glucose persistently high
Deranged LFTs

If septic:
👉 treat as line infection until proven otherwise

Do not ignore.

✅ Refeeding risk (important overlap)

Most TPN patients are malnourished.

Always:

Check electrolytes first
Give thiamine
Start slowly
Monitor daily

Refeeding syndrome can happen with TPN too.

✅ Practical ward workflow

If thinking about TPN:

Ask:

Can the gut be used?
If yes → NG/enteral
If no → refer nutrition team
Check electrolytes
Monitor daily

Simple and safe.

✅ Common real-life scenarios

Scenario 1

Post-op ileus, 7 days NBM
→ TPN appropriate

Scenario 2

Elderly patient eating poorly
→ NOT TPN → dietitian + supplements first

Scenario 3

Severe pancreatitis
→ try enteral first → TPN only if not tolerated

Scenario 4

On TPN + fever
→ think line sepsis → escalate urgently

❌ Common junior mistakes

Starting TPN too early
Forgetting NG feeding option
Not involving dietitians
Missing refeeding risk
Ignoring line infections
Not checking daily bloods

TPN problems are often preventable.

✅ Take-home concept

If the gut works, use it.
TPN is last resort, high risk, and needs specialist input.
Your job is to recognise indications, monitor closely, and spot complications early.