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The high osmolality of TPN formulations results in rapid development of thrombophlebitis and line failure if infused into peripheral veins. This problem has been overcome by using central venous catheters to deliver TPN solutions into large veins, most commonly via the subclavian or internal jugular veins (see Chapter 3). Getting access to, and the presence of central venous catheters within these veins, can result in a number of complications:

• insertion-related: air embolism, arterial puncture, cardiac arrhythmias, catheter embolus, chylothorax, haemoperi-cardium, haematoma, haemothorax, hydro/TPN-thorax, malposition, neurological injury, pneumothorax;

(a)

Figure 4.4. Witzel jejunostomy. (a) The site of insertion of the catheter into the jejunum is about 30 cm distal to the ligament of Treitz. (b) A fine-bore catheter is inserted through the seromuscular tunnel in the jejunal wall and fastened at the mucosal entrance by an anchor stitch. (c) The incision in the tunnel of the jejunal wall is closed over the catheter. (d) The jejunum is anchored to the anterior abdominal wall.

Figure 4.4. Witzel jejunostomy. (a) The site of insertion of the catheter into the jejunum is about 30 cm distal to the ligament of Treitz. (b) A fine-bore catheter is inserted through the seromuscular tunnel in the jejunal wall and fastened at the mucosal entrance by an anchor stitch. (c) The incision in the tunnel of the jejunal wall is closed over the catheter. (d) The jejunum is anchored to the anterior abdominal wall.

• late complications: catheter infection or sepsis, catheter displacement, central venous thrombosis, luminal occlusion.

Complications occur in up to 5% of catheter placements.

A variety of routes, catheters and techniques of insertion are available. The two main methods of insertion are blind percutaneous puncture of a vein or open surgical exposure. The advantages of the percutaneous technique in experienced hands are that insertion is quick and may be done under local anaesthesia at the patient's bedside as long as sterile procedure is observed. Open surgical exposure is done in an operating theatre and may require general anaesthesia.

This route of insertion should be used for patients with chronic respiratory disease, those on a ventilator, and those with severe clotting disorders because of the risks associated withdevelopmentofcomplications. Strictcathetercareproto-cols should be followed and monitored by an infection control or nutrition nurse to minimize the incidence of catheter-related sepsis. If a patient on TPN develops a pyrexia and leu-cocytosis in the absence of any other focus of infection, then the central venous catheter should be considered to be the source of infection. However, all other possible sources of infection should be considered and cultures of sputum, urine and other sites is mandatory.

TPN is increasingly administered by the peripheral route (peripheral parenteral nutrition (PPN)). A number of methods have been investigated to reduce the incidence of peripheral vein thrombophlebitis, including the use of heparin, in-line filtration, cortisol, buffering, locally applied glyceryl trinitrate patches and fine-bore cannulas. Reducing the osmolality by altering the formulation of carbohydrate energy components and nitrogen source may also have a role and specially formulated commercial mixtures have been shown in clinical studies to be suitable for PPN. Thrombophlebitis cannot be totally abolished, however, but it should be borne in mind that most courses of TPN rarely last more than 10-14 days. TPN can be administered peripherally if it is anticipated that support will be needed for <2 weeks.

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