Parenteral nutrition Feed composition

Carbohydrate is normally provided as concentrated glucose. 30-40% of total calories are usually given as lipid (e.g. soya bean emulsion). The nitrogen source is synthetic, crystalline L-amino acids which should contain appropriate quantities of all essential and most non-essential amino acids. Carbohydrate, lipid and nitrogen sources are usually mixed into a large bag in a sterile pharmacy unit. Vitamins, trace elements and appropriate electrolyte concentrations can be achieved in a single infusion, thus avoiding multiple connections. Volume, protein and calorie content of the feed should be determined on a daily basis in conjunction with the dietitian.

Choice of parenteral feeding route

A dedicated catheter (or lumen of a multi-lumen catheter) is placed under sterile conditions. For long-term feeding a subcutaneous tunnel is often used to separate skin and vein entry sites. This probably reduces the risk of infection and clearly identifies the special purpose of the catheter. Ideally, blood samples should not be taken nor other injections or infusions given via the feeding lumen. The central venous route allows infusion of hyperosmolar solutions, providing adequate energy intake in reduced volume.

Parenteral nutrition via the peripheral route requires a solution with osmolality <800m0smol/kg. Either the volume must be increased or the energy content (particularly from carbohydrate) reduced. Peripheral cannulae sites must be changed frequently.

Complica tions

Catheter related Misplacement




• Fluid excess

• Hyperosmolar hyperglycaemic state

• Electrolyte imbalance

• Hypophosphataemia

Metabolic acidosis Hyperchloraemia

Metabolism of cationic amino acids

• Rebound hypoglycaemia

High endogenous insulin levels

Vitamin deficiency Folate Pancytopenia

Thiamine Encephalopathy Vitamin K Hypoprothrombinaemia

Vitamin excess Vitamin A Dermatitis

Vitamin D Hypercalcaemia

Fatty liver

Nutrition — use and indications, p78; Electrolytes

, p146; Calcium, magnesium and phosphate, p148; Hypernatraemia, p416; Hyponatraemia, p418; Hyperkalaemia, p420; Hypokalaemia, p422; Hypomagnesaemia, p424; Hypocalcaemia, p428; Hypophosphataemia, p430; Metabolic acidosis, p434

^ Ovid: Oxford Handbook of Critical Care

Editors: Singer, Mervyn; Webb, Andrew R.

Title: Oxford Handbook of Critical Care, 2nd Edition

Copyright ©1997,2005 M. Singer and A. R. Webb, 1997, 2005. Published in the United States by Oxford University Press Inc

> Table of Contents > Special Support Surfaces

Special Support Surfaces

Special support surfaces

Pressure sores

Pressure sores occur due to compression of tissue between bone and the support surface and due to shearing forces, friction and maceration of tissues against the support surface. The use of special beds attempts to reduce the pressure at the contacting skin surface to a level lower than the capillary occlusion pressure. In the majority of cases it is sufficient to minimise the time that the support surface contacts any one area of skin by position changes.

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