Parenteral nutrition should only be used when it is not possible to meet nutritional requirements via the gastrointestinal tract. Parenteral nutrition is an invasive and relatively expensive form of nutrition support and, in inexperienced hands, can be associated with risks from catheter placement, catheter infections, thrombosis and metabolic disturbance. Careful consideration is therefore needed when deciding to whom, when and how this form of nutrition support should be given (Klek et al. [76], NCCAC [108]). It should be planned and managed by healthcare professionals with the relevant expertise (NCEPOD [110]). Whenever possible, patients should be made aware of why this form of nutrition support is needed and its potential risks and benefits.

Parenteral nutrition may be used in combination with enteral nutrition where some gut function is present but this is insufficient to meet nutritional requirements, for example in intestinal failure, where the patient can eat but absorptive capacity may be insufficient to maintain nutritional status.

Intestinal failure (IF) can be categorized as follows.

Parenteral nutrition provides nutrients in a form that can be used directly by the body when they are infused intravenously. Nitrogen (protein) is provided as free amino acids in a ratio designed to meet the requirements for essential amino acids. Specific amino acid profiles may be used for some disease states. Energy is usually provided from carbohydrate and fat. Carbohydrate is present as glucose and fat is provided as a lipid emulsion of essential fatty acids. The lipid source may be provided by long‐chain, medium‐chain triglycerides or fish oil containing omega‐3 fatty acids, with different manufacturers using different lipid blends. Fluid, electrolytes, vitamins, minerals and trace elements are also provided by parenteral nutrition (Singer et al. [171]).

Parenteral nutrition is usually administered from a single infusion container in which all the requirements for a 24‐hour feed are premixed. Such infusions are available as standard ready‐prepared bags that require mixing, and vitamins, minerals, and trace elements or individual bags may be added to a particular prescription and purchased from a compounding unit.

The regimen for a particular patient should be formulated according to their needs for energy, nitrogen, electrolytes and fluid. The majority of commercial vitamin and mineral preparations aim to meet both short‐ and long‐term requirements although appropriate monitoring is required to ensure that nutritional requirements are met in the longer term as clinically indicated by the monitoring guidelines. Standard parenteral nutrition regimens may be suitable for some patients who require short‐term nutritional support or do not appear to have excessively altered nutritional requirements.

The choice of such regimens depends on the patient's bodyweight and nutritional requirements. To allow for the possible need to vary the constituents of the infusion in response to changes in the patient's electrolyte or nutritional requirements, parenteral nutrition solutions should be ordered daily. Once compounded, parenteral nutrition has a limited lifespan determined by the manufacturers. Bags of parenteral nutrition that have been compounded with vitamins and minerals need to be stored in a refrigerator. However, some triple‐chamber parenteral nutrition bags can be stored at ambient temperatures and require mixing prior to administration. These bags generally require the addition of vitamins, minerals and trace elements under aseptic conditions.

Parenteral nutrition should be introduced slowly in the seriously ill or injured, with no more than 50% of requirements given in the first 24–48 hours due to the risk of refeeding syndrome (NCCAC [108]).

The traditional method of access is via a central venous catheter. Central venous access is required because parenteral nutrition solutions are hyperosmolar and there is a risk of thrombophlebitis associated with feeding into peripheral veins. However, it has been shown that, with care and attention, peripheral veins can be used to provide short‐term parenteral nutrition (NCCAC [108]). This would be via a midline or peripheral cannula. For the administration of parenteral nutrition, the device should be placed in the largest vein possible, usually in the forearm away from a joint, with rotation of the site every 48–72 hours (Shaw [163]).

A skin‐tunnelled catheter is the first choice for long‐term nutrition but peripherally inserted central cannulas (PICCs), non‐tunnelled central venous catheters or venous access ports can also be used in the short term. The number of lumens will depend on the patient's peripheral venous access and the number of additional therapies required. It is recommended that the minimum number of lumens is used but if additional intravenous access is required then a double‐ or triple‐lumen catheter should be inserted and then one lumen should be dedicated for use with parenteral nutrition. If using a single‐lumen device, routine blood sampling and additional infusions should be carried out independently, using a separate cannula if necessary (Das and Bowling [43]).

For setting up an infusion, see Procedure guideline 15.23: Medication: continuous infusion of intravenous drugs.