24. Total Parenteral Nutrition

Question 1

TPN

Answer 1

Parenteral nutrition is, by definition, administered intravenously. TPN supplies all daily nutritional requirements
to the patient. In general, because TPN solutions are concentrated and therefore have the potential to cause
venous thrombosis in peripheral veins, a central venous catheter is required.

Question 2

What are the indications for TPN?

Answer 2

Where possible,
the enteral route should always
be used in preference to
parenteral nutrition.

However, where this is not possible,
TPN should be considered.

> Anticipation of undernutrition
(<50% of metabolic requirements
achieved enterally)
for >7 days.

> TPN may be indicated for severely 
undernourished patients unable to
ingest large volumes 
of oral feed prior to surgery, 
radiation therapy or
chemotherapy.

> Patients with disorders
requiring complete gastrointestinal
rest, e.g. ulcerative colitis/pancreatitis.

> Post-operative patients
in whom enteral feeding
has either not been
possible or has failed after 5 days.

Question 3

Describe the nutritional content of TPN.

Answer 3

TPN should be considered as a drug.

Most hospitals in the UK now have

a nutrition team comprising 
a physician, 
dietician 
and 
pharmacist, 

with the remit of reviewing patients
with nutritional concerns
and
guiding safe use of parenteral nutrition.

Question 4

Table 24.1 Basic adult requirements for TPN

Answer 4

Water
30–40 mL/kg/day

Energy

Medical patient 30 kcal/kg/day
Post-operative patient 30–45 kcal/kg/day
Hypercatabolic patient 45–60 kcal/kg/day

Amino acids

Medical patient 1 g/day
Post-operative patient 2 g/day
Hypercatabolic patient 3 g/day

Essential fatty acids

Minerals
Acetate/Calcium/Chloride/Copper/Magnesium
Potassium/Selenium/Sodium/Zinc

Vitamins
A/D/E/K/C/Folic acid/Thiamine/Pyridoxine/Niacin

Question 5

Basic TPN solutions are prepared using….

Are they always the same

Answer 5

using sterile techniques.
Solutions may be modified
based on laboratory results
(e.g. electrolyte disturbances),

underlying disorders,
hypermetabolism or
other factors.

Commercially available lipid emulsions
are often added to supply
essential fatty acids
and triglycerides and 20–30%

of total calories are
usually supplied as lipids.

However, withholding lipids
and their calories may help obese
patients mobilise endogenous
fat stores and increase their insulin sensitivity.

Electrolytes can be added to
meet the patient’s needs.

Patients who have renal insufficiency
and are not receiving haemofiltration

or who have hepatic failure

require solutions
with reduced protein content
and a higher
percentage of essential amino acids.

For patients with respiratory failure,

a lipid emulsion must provide
most of the
non-protein calories in order to
minimise CO2 generation.

Question 6

How is TPN administered and monitored?

Answer 6

Ideally, TPN should be administered
through a dedicated port of a
central venous line.

Strict asepsis must be used during administration.

The infusion is started initially at
50% of the calculated requirements.

Insulin may be required to maintain
glycaemic control.

Basic monitoring tests include daily weight,
FBC,
urea and electrolytes,
and liver function tests.

Question 7

What complications may occur with TPN?

Answer 7

With close monitoring by a nutrition team
complication rates should be <5%,

however complications related
either to the central venous catheter
(infection)

or to the nutrition, may occur.

1
Volume overload –
may occur when high daily energy
needs require large volumes of fluid.

2
Glucose abnormalities – 
hyperglycaemia may occur 
(less commonly hypoglycaemia) 
and 
therefore regular blood glucose 
monitoring is essential.

3
Electrolyte disturbances – 
the most clinically important electrolytes 
to be monitored are 
sodium, 
potassium, 
magnesium and 
phosphate.

4
Metabolic bone disease –
bone demineralisation develops in some
patients receiving prolonged TPN (>3 months).

The only remedy is to discontinue the
TPN temporarily or permanently.

5
Hepatic complications – 
transient liver dysfunction 
on starting TPN is common, 
evidenced by increased 
hepatic transaminases, 
bilirubin and
alkaline phosphatase. 

6
Delayed or persistent elevations
may result from excessive quantities of amino acids. The pathogenesis of the hepatic
complications is not known.

7
Gallbladder complications –
include cholelithiasis and cholecystitis.

Question 8

Refeeding syndrome

Answer 8

is a relatively rare but
potentially fatal complication
of TPN and a favoured examination question.

The syndrome describes the
severe hypophosphatemia 
and 
other metabolic complications 
that are seen in malnourished patients 

who receive concentrated calories via TPN.

The syndrome was first described in
Japanese prisoners of war after the Second
World War.

Refeeding syndrome usually occurs within
72 hours of starting the feed.

The syndrome results from a
sudden shift from

fat to carbohydrate metabolism

with a sudden rise in insulin secretion 
leading to an 
increased cellular uptake
of 
phosphate, 
potassium, 
magnesium 
and 
glucose. 

Serum levels of these
electrolytes fall rapidly
causing life-threatening systemic consequences

including acute cardiac failure, 
confusion, 
coma, 
convulsions 
and 
even death. 

Prevention of the syndrome involves 
identifying patients at risk and
introducing slow refeeding along 
with close monitoring and correction of
electrolyte disturbances.