Parenteral nutrition

01Purpose and principlesWhat the treatment does and how it fits into care.

Parenteral nutrition bypasses gastrointestinal digestion and absorption by infusing nutrients intravenously. Appropriate scenarios include prolonged ileus, obstruction without enteral access, severe intestinal failure, high-output fistula in selected anatomy or perioperative inability to use the gut. A functioning intestine should normally be used because enteral delivery preserves a more physiological route and avoids central-line hazards.

The prescription is a changing clinical formulation, not a standard fluid bag. Disease, weight, nutritional depletion, renal and hepatic function, gastrointestinal losses, temperature, insulin response and other infusions determine daily content. Pharmacy compatibility and stability govern what can safely share an admixture; bedside improvisation is dangerous.

Longer-term home PN is a highly specialised treatment for type 3 intestinal failure. It needs trained patients or carers, defined catheter-care practice, reliable supply, emergency advice and a multidisciplinary intestinal-failure service. Monitoring extends beyond sepsis to venous thrombosis, metabolic bone disease, liver injury, micronutrient imbalance and quality of life.

Key points

Parenteral nutrition is indicated when oral and enteral routes are unsafe, inadequate or impossible because the gastrointestinal tract cannot absorb or be accessed sufficiently; it is not a shortcut around feeding difficulties.
Define the intestinal problem, expected duration, treatment goal and exit strategy before insertion of vascular access, involving the nutrition-support team early.
A complete prescription accounts for energy, amino acids, glucose, lipid, electrolytes, vitamins, trace elements and fluid, with daily individualisation during unstable illness.
Central venous access permits more concentrated long-term delivery; peripheral PN is limited by venous tolerance, composition and duration and remains subject to the same metabolic safeguards.
Use a dedicated lumen and strict aseptic technique, minimising manipulation; never connect incompatible medicines or sample blood routinely through a PN line outside the agreed policy.
Identify refeeding risk before the first bag, give vitamin support, initiate energy cautiously and monitor phosphate, potassium, magnesium, glucose and fluid balance.
Suspected catheter-related bloodstream infection requires paired appropriately labelled cultures and early microbiology or intestinal-failure advice; shock needs immediate treatment, while line removal depends on organism and clinical context.
Return to oral or enteral intake whenever useful gut function recovers, reducing PN in a controlled manner rather than maintaining intravenous calories through clinical inertia.

02Indications, selection and cautionsWho may benefit, who needs urgent treatment and important alternatives.

Non-functional gut

Persistent ileus, complete obstruction, severe malabsorption or inaccessible bowel can make enteral delivery unable to meet need despite appropriate attempts.

Acute intestinal failure

Postoperative complications, enterocutaneous fistula, abdominal sepsis or short bowel may create large losses and rapidly changing fluid, electrolyte and nutritional requirements.

Catheter infection

Fever, rigors or malaise during connection or infusion, without another source, raises suspicion for catheter-related bloodstream infection but does not prove it.

Venous complication

Arm, neck or facial swelling, collateral veins, line dysfunction or pain can indicate catheter-associated thrombosis or central venous stenosis.

Metabolic intolerance

Hyperglycaemia, hypertriglyceridaemia, electrolyte shifts, fluid overload or acid-base change often reflects the interaction between formulation, infusion rate and acute illness.

Hepatobiliary effect

Rising liver enzymes, cholestasis, steatosis or gallbladder stasis can accompany sepsis, overfeeding, absent enteral stimulation or long-term intestinal failure.

Red flags requiring action

Rigors with hypotension, confusion, mottling or lactate elevation in a patient with central access requires immediate sepsis treatment after cultures when safe and must not await proof of line infection.
Sudden chest pain, dyspnoea, arrhythmia or cardiovascular collapse during line insertion or manipulation suggests pneumothorax, embolic or malposition complications requiring emergency response.
Rapid oedema, heart failure, respiratory weakness, delirium or arrhythmia after nutrition begins may indicate severe refeeding physiology and demands urgent correction.
Painful swollen limb or face with catheter dysfunction suggests central venous thrombosis; preserve future access by seeking specialist imaging and anticoagulation advice promptly.
Marked hyperglycaemia with ketones, hyperosmolar symptoms or reduced consciousness is a medical emergency, not simply a reason to discard the current PN bag.

03Assessment before treatmentTests and checks that guide safe selection.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Nutrition and intestinal-failure assessmentFirst step
Why
Confirm indication, estimate requirements and identify a feasible route transition.
Interpretation and limitations
Document gastrointestinal diagnosis, residual anatomy, losses, previous enteral trials, weight trend, fluid needs and realistic duration before exposing the patient to line risk.
02
Baseline metabolic panel
Why
Guide the first formulation and identify refeeding or organ-function hazards.
Interpretation and limitations
Glucose, urea, creatinine, sodium, potassium, phosphate, magnesium, calcium, liver tests and triglycerides should be interpreted with fluid balance, inflammation and recent intake.
03
Paired blood cultures
Why
Evaluate suspected catheter-related bloodstream infection while preserving organism and timing information.
Interpretation and limitations
Collect appropriately labelled samples from the catheter and a peripheral vein before antimicrobials if this causes no unsafe delay; differential positivity supports attribution but requires microbiology interpretation.
04
Vascular imaging
Why
Investigate suspected catheter thrombosis, malposition or access failure.
Interpretation and limitations
Ultrasound assesses accessible veins, while central disease may require CT or venographic imaging chosen with vascular-access and intestinal-failure specialists.
05
Micronutrient and bone profile
Why
Detect cumulative deficiency, toxicity and metabolic bone disease during prolonged support.
Interpretation and limitations
Select tests and intervals according to duration, anatomy, losses and formulation; acute inflammation distorts several trace-element concentrations, so trends need specialist context.
06
Liver and sepsis evaluation
Why
Distinguish PN-associated abnormalities from infection, obstruction, medicines and underlying disease.
Interpretation and limitations
Pattern, timing, cultures, imaging and energy delivery matter; attributing cholestasis to PN without excluding sepsis can miss a life-threatening driver.

04Treatment approachPreparation, options, escalation and aftercare.

01INDICATEDecision to start PNFirst stepNutrition goals cannot be met safely through oral or enteral routes because gut function or access is inadequate.

1Define the gastrointestinal mechanism, predicted duration, prior route optimisation, refeeding category and patient-centred objective.
2Refer to the multidisciplinary nutrition-support team to estimate requirements and choose peripheral or central access with a documented rationale.
3Establish baseline biochemistry, fluid balance, vascular-access plan and aseptic responsibilities before ordering the tailored formulation.
4Set review criteria for progression, complication surveillance and transition back toward gastrointestinal feeding.

02PRESCRIBESafe daily formulationParenteral nutrition is indicated and suitable vascular access is available.

1Calculate total input from PN, intravenous medicines, maintenance fluids and losses, avoiding duplicate electrolytes or hidden glucose.
2Specify energy, amino acids, lipid, carbohydrate, vitamins, trace elements, electrolytes, volume and infusion duration with pharmacy compatibility checks.
3Begin cautiously when refeeding risk or metabolic instability exists and adjust the next prescription from clinical response and laboratory trends.
4Protect the dedicated lumen using aseptic connection, authorised filters or equipment and a clear policy for interruptions and line locks.

03FEVERPossible catheter bloodstream infectionFever, rigors, unexplained inflammation or sepsis occurs in a patient receiving PN through central access.

1AlternativeAssess severity immediately, look for alternative sources and obtain paired line and peripheral cultures before antibiotics when this is safe.
2Treat shock promptly using the local sepsis and antimicrobial pathway, involving microbiology and the nutrition or intestinal-failure service early.
3Decide line salvage, antimicrobial lock, exchange or removal from organism, tunnel or exit-site findings, metastatic infection, haemodynamic status and access value.
4Document clearance cultures and future prevention, and never resume routine PN use through an unsafe line without specialist authorisation.

04WEANReturn to gastrointestinal feedingBowel function recovers or oral and enteral intake begins meeting a meaningful proportion of requirements.

1Quantify absorbed oral or enteral intake and ongoing losses rather than inferring recovery from bowel sounds alone.
2Advance gastrointestinal delivery while reducing PN energy and fluid to prevent overfeeding, glucose swings and volume excess.
3Remove unneeded central access promptly when safe, balancing infection prevention against genuine near-term access requirements.
4Communicate the nutritional endpoint, remaining deficiencies and monitoring owner at discharge or transfer.

05Regimens, contraindications and interactionsTreatment details and the circumstances that modify them.

Supply essential macronutrients, micronutrients, electrolytes and fluid when gastrointestinal absorption cannot meet requirements.

Individualised parenteral nutrition admixture

Infuse the pharmacy-approved daily formulation through the designated access at the prescribed rate and duration, using a pump and aseptic connection.

Never add bedside ingredients or run incompatible drugs through the dedicated lumen; account for refeeding risk, organ failure, glucose, triglycerides, fluid status and formulation stability.

Cover vitamin requirements and reduce acute thiamine-deficiency injury during renewed carbohydrate metabolism.

Thiamine and multivitamin preparation

Provide before and during initial nutritional escalation according to refeeding risk, route reliability and the local nutrition protocol.

Ensure the complete PN prescription contains ongoing vitamins and trace elements where indicated; replacement does not remove the need for controlled energy and electrolyte monitoring.

Control clinically important hyperglycaemia while adequate nutrition continues whenever safely possible.

Insulin with parenteral nutrition

Use a protocol-led subcutaneous or intravenous regimen titrated to bedside glucose, illness severity and changing PN delivery.

Interruption or cycling of PN changes hypoglycaemia risk; avoid ungoverned insulin addition to bags and involve diabetes or nutrition teams for unstable requirements.

Treat catheter-related bloodstream infection while source-control and line-preservation decisions are made.

Antimicrobial therapy for suspected CRBSI

Start the local empiric sepsis regimen after appropriate cultures when stable enough, then narrow to organism and susceptibility advice.

Local resistance, allergy, renal function, organism, tunnel infection and haemodynamic instability determine choice and line removal; specialist advice is essential for salvage.

06Complications, monitoring and follow-upAdverse effects, response and longer-term review.

During initiation, review observations, fluid balance, weight, oedema, glucose, renal function, potassium, phosphate and magnesium at a frequency matched to instability and refeeding risk.
Trend liver tests and triglycerides against delivered energy, lipid, sepsis, medicines and enteral stimulation, avoiding reflex attribution to one component.
Inspect the catheter exit site and dressing, observe every connection technique and investigate unexplained fever using the agreed bloodstream-infection pathway.
Compare prescribed with delivered volume because procedures, pump alarms and bag interruptions can create major deficits or insulin-related hazards.
For prolonged PN, assess micronutrients, blood count, coagulation, bone health, venous access, renal status and quality of life through the specialist schedule.
Reassess remaining bowel length or function, stool or fistula losses and oral intake regularly to identify opportunities for intestinal rehabilitation and safe weaning.

07Special situationsVariants, exceptions and circumstances that change the usual approach.

The line is limited capital

Repeated unnecessary removal can exhaust central venous access in chronic intestinal failure, while inappropriate salvage can perpetuate sepsis; organism-specific expertise balances both harms.

Overfeeding is not generosity

Excess carbohydrate and total energy can worsen hyperglycaemia, carbon dioxide production, steatosis and fluid burden without accelerating useful tissue recovery.

Peripheral does not mean trivial

Peripheral PN can still trigger refeeding, hyperglycaemia and prescribing errors, and it adds phlebitis and extravasation limitations.

Liver tests need a differential

Sepsis, biliary disease, drug injury, overfeeding and lack of enteral stimulation may converge; adjusting lipid alone may miss the dominant cause.

Home treatment is a service

A bag prescription without training, compounding quality, catheter support and emergency pathways is not a safe home parenteral nutrition programme.

08Common pitfallsFrequent interpretation and management errors.

01
Do not start PN merely because oral intake is inconvenient; first establish why the gastrointestinal route cannot safely meet need.
02
Do not prescribe calories without vitamins, trace elements, electrolytes and a coherent fluid plan unless a specialist has defined a short exceptional formulation.
03
Do not add potassium, insulin or medicines to a compounded bag at the bedside without pharmacy-controlled compatibility and governance.
04
Do not remove every febrile patient's central line reflexively before obtaining appropriate cultures and considering organism, stability and future access.
05
Do not attempt line salvage in haemodynamic instability or another situation where urgent source control is clinically required.
06
Do not continue full PN unchanged as enteral absorption improves, because combined routes can produce overfeeding and fluid excess.