Secure venous access is required for the successful and safe delivery of Parenteral nutrition (PN).
In considering the type of venous access required it is important to consider:
- The time PN support is likely to be required for
- The nutritional requirements of the patient
Central venous access is required for PN support given over longer periods (>28 days). It is recommended that peripheral PN is only used for a short period of time and only when using nutrient solutions where osmolarity does not exceed 850mosm/l, with a substantial proportion of the non protein calories given as lipid. Peripheral PN demands careful surveillance for thrombophlebitis as parenteral feed is very irritant to veins. Central venous catheters have been extensively used for parenteral nutrition. In many hospitals a dedicated single lumen catheter is inserted for parenteral nutrition use only. These may have a Dacron cuff to retain the catheter in place and cuffed catheters are suitable for use for longer term parenteral nutrition at home. It is probably easier to maintain good catheter care and so low infection rates using single lumen dedicated catheters but in critically ill patients with complex fluid and drug requirements, multi-lumen catheters are used. It is unwise to use a multi-lumen catheter which has been in place for some days and used for other purposes to start parenteral nutrition.
Line insertion technique
All lines placed for PN should be done so using aseptic non touch technique. There is compelling evidence that ultrasound guided venepuncture using real time ultrasonography is associated with a lower risk of complication and higher rate of successful placement than 'blind' venepuncture.
Complications associated with vascular access for PN can be broadly divided into:
- Insertion related
- Line related
- Patient related
Insertion related complications include:
- Bleeding (arterial or venous)
- Misplaced lines (suboptimal tip location*)
- Early infection
* Central venous catheter tip should be sited in the lower third of SVC or upper third of right atrium (at or below the level of the carina on plain chest X-ray imaging). There is evidence of increased risk of malfunction including line associated thrombosis associated with tip position > 4cm from cavoatrial junction.
Line related complications include:
- Line fracture and line occlusion
Line fracture can occasionally occur. It is sometimes possible to repair this without the need for line replacement. Factors that influence the risk of line occlusion include the catheter size and use of positive pressure connectors and fluid locks. Infections are more common when cvcs with more lumens than absolutely necessary are used.
Patient related complications:
The greatest risk is of infection. This may be bloodstream, tunnel site or exit site infection. In many cases the line can be salvaged with appropriate antibiotic treatment but certain infections necessitate line removal, in particular fungal line infection.