Parenteral Feeding

"Parenteral feeding" describes the intravenous administration of nutrients. This may be supplemental to oral or tube feeding or it may provide the only source of nutrition as total parenteral nutrition (TPN).¹

Parenteral nutrition should be considered for all patients who are malnourished or at risk of malnutrition and have a non-functioning or inaccessible gastrointestinal tract, preventing enteral feeding.²

Peripheral lines may be used to deliver short-term nutritional support, but central access is necessary for parenteral feeding of more than 2 weeks duration. Lines should be dedicated to feeding and must not be used for drug administration or blood sampling:¹

• Central catheters and ideally tunnelled subclavian vein central lines, inserted using full aseptic technique are the optimal method of access.
  • Parenteral nutrition solution is thrombogenic and an irritant to veins.
  • Central access allows delivery of more concentrated formulations into high flow vessels.¹
• Peripheral administration is achieved through peripherally inserted central catheters (PICC) or standard cannulas, inserted with an aseptic technique.¹
  • Tolerance to peripheral lines is increased with feeds of low osmolality and neutral pH and the use of soft paediatric cannulas.

TPN solutions contain a balanced mix of essential and non-essential amino acids, glucose, fat, electrolytes and micronutrients:

• Iso-osmotic lipid emulsions are used to provide an energy-rich solution and reduce irritation of veins.
• Such preparations also permit a lower concentration of glucose to prevent hyperglycaemia or hyperosmolar dehydration.

A wide selection of preparations are produced under sterile conditions and are available as 3 litre bags of pre-packaged solution.¹

Parenteral nutrition should be introduced at a low rate and gradually increased:²

• TPN is usually delivered at a continuous flow rate but cyclical regimens may suit longer use.¹
• Vitamins including folic acid are infused with the solution, but vitamin B12 must be prescribed separately.

Re-feeding syndrome

During starvation intracellular electrolyte stores, particularly phosphate, are depleted despite normal serum concentrations. Feeding stimulates the cellular uptake of electrolytes and can lead to electrolyte disturbances with profound hypophosphataemia.

Clinical features usually develop within 4 days of re-feeding, but are often non-specific. Later manifestations include rhabdomyolysis, cardiac failure, hypotension, arrhythmias, respiratory failure, seizures and coma.
(See our Nutritional Support record.)

Catheter-related complications¹

• Immediate complications are mainly related to insertion and include haemorrhage, pneumothorax or haemothorax, arrhythmias or cardiac tamponade.
• Long-term catheter complications include thrombosis and pulmonary embolism, pleural or pericardial effusion, subacute bacterial endocarditis, chylothorax and venopulmonary fistula.

Infection

• Septicaemia occurs in 3-7% of patients on TPN, with a mortality rate of catheter-related sepsis of up to 15%.³
• Infections with staphylococcal species and enterococci are common.⁴
• There must be strict adherence to asepsis and solution bags and giving sets must be discarded after 24 hours use.¹

Liver and gallbladder dysfunction¹

• Up to 90% of patients develop mild cholestasis with elevation of transaminases and alkaline phosphatase.
• Gallstones and gallbladder sludging may also occur.

Hyperglycaemia

Up to 30% of patients receiving nutritional support are hyperglycaemic. Tight glycaemic control is important in sick patients and so treatment with oral hypoglycaemic agents or insulin is often required.

Monitoring should include the general observations and laboratory schedule recommended for all forms of nutritional support. The following schedule is recommended for all patients receiving parenteral nutrition:

• Baseline levels should include full blood count (FBC), B12 and folate, urea and electrolytes (U+Es) including magnesium, phosphate and calcium, glucose, liver function tests (LFTs), albumin, prealbumin, C-reactive peptide (CRP), zinc and copper.
• Blood glucose should be monitored every 4-6 hours.
• Daily FBC, U&E plus magnesium and phosphate should be taken if there is a high risk of re-feeding syndrome.
• LFTs, lipid profile, calcium, albumin, prealbumin, transferrin and CRP should be performed once/twice weekly.
• Zinc, iron, selenium and copper levels should be monitored every 2-4 weeks.
• Manganese and 25-OH Vitamin D levels should be taken 3-6 monthly.

The frequency of most tests can be reduced once the patient's condition is stable. In addition there should be daily attention to:

• Peripheral lines for signs of thrombophlebitis
• Centrally sited lines for signs of infection or inflammation

Demand for home parenteral nutrition (HPN) - to facilitate hospital discharge - is rising, but access to local services may be limited.⁵ There are only 2 designated Intestinal Failure Units nationally; St Marks hospital, London and Hope hospital in Salford. They are the only units to receive specific funding for this role, and are now oversubscribed.

Patients must receive training and information on HPN prior to discharge. An individual nutritional care plan is drawn up which includes feeding regimens and the required multidisciplinary input. Patients must be competent in the management of feeding systems and aware of common problems. All patients must be supported by a skilled team, which includes specialist nutrition nurses, dieticians and district nurses. Partnership with homecare companies for provision of HPN solutions and equipment is encouraged. GPs must also be closely involved to liaise with services and recognise potentially life-threatening complications.²