Bacterial colonisation of midline and central venous catheters

The provision of parenteral nutrition conventionally requires the insertion of a central venous catheter (CVC) with the attendant risks of pneumothorax, vascular damage and line sepsis [1]. In addition, CVC insertion requires appropriately trained medical staff. It is possible to provide central venous access with peripherally inserted central catheters (PICC) but these are associated with malposition, catheter fracture, leakage and occlusion [2]. An alternative to these is the use of 20 cm single lumen 22 G venous catheters inserted in the antecubital fossa (midlines). This unit provides a 'midline' service for parental nutrition or long-term venous access, and this audit describes the experience of this service to date. All lines were inserted on a general ward by a trained theatre technician using standard sterile techniques including chlorhexidine or iodine (in 70% methylated spirit) skin preparation and a semipermeable film dressing (tegaderm™). At removal, midline tips were sent for microbiological analysis using a Maki roll technique.

There were 160 midlines inserted over an 18 month period, 139 catheters were inserted for parental nutrition and 21 for other reasons. Catheters remained in situ for median of 6 days with a range of 1–60 days. Reasons for catheter removal included blockage (13%), concerns over arm swelling (17.5%) and completion of therapy (39%). Of the 160 midlines inserted, microbiological data were available on 120. There was an overall bacterial colonisation rate of 20.8%. By comparison the colonisation rate for CVC in this unit is 49%. The colonisation rates for midlines and CVCs become significantly different by day 7 (P = 0.03, χ²) and remain so thereafter. For midlines, the majority of catheters that eventually become colonised do so by day 8. In contrast, for CVCs the colonisation rate continues to rise until day 15. The majority of organisms isolated from midline catheters were staphylococcus epidermidis (19/27). Other organisms included β-haemolytic streptococcus (two cases), enterobacter aerogenese (two cases), MRSA (one case), coliform (one case), staphylococcus aureus (one case) and candida (one case).

Midline catheters represent a simple technique that can be performed by nonmedical staff. They can be used for long-term intravenous access with a lower risk of colonisation than central venous catheters.