Editor—It is common practice to flush a central venous catheter (CVC) manually when occlusion is suspected. The manufacturers of one silastic CVC commonly used in neonatal units recommend a maximum flushing pressure of 1.2 bars. (Vygon GmbH & Co KG. Epicutaneo-cave-catheter product insert; 1994.) Excessive pressure may lead to CVC rupture with associated infection, or to avulsion of the distal catheter. We set out to assess whether our current practices are safe. In vitro studies showed that the typical burst pressure of 4 CVCs was between 5.2 and 7 bars.

We then asked 22 doctors and 14 nurses to flush an occluded, fluid filled intravenous pressure line attached to a manometer. Each participant was asked to exert the maximum pressure which they would apply when flushing a CVC. The first 20 subjects were asked to flush using 2.5 ml and 5 ml syringes, and the remaining 16 subjects used only 2.5 ml syringes. Two attempts were made with each syringe, and the higher reading was analysed. Results were expressed in geometric mean (95% CI).

We found that: (i)    maximum pressures were significantly lower using a 5 ml than a 2.5 ml syringe, being 0.76 (0.56, 1.01) bars and 1.0 (0.71, 1.41) bars, respectively (p<0.01). (ii)   doctors exerted significantly higher pressures than nurses (p<0.05). (iii)  for the 22 doctors using a 2.5 ml syringe (the normal situation on our unit) the 97th centile for maximum flushing pressure was 12.2 bars. Fifteen (68%) exceeded the recommended maximum pressure and four (18%) exceeded the likely burst pressure. Smaller syringes exert higher output pressures. A survey of American CVC product leaflets reported that nearly all recommend a 10 ml syringe as the minimum size for flushing.1 Although there would be a reduced risk of rupture if 5 ml rather than 2.5 ml syringes were used, we recommend that training with a manometer should be given to all staff who are likely to flush CVCs. We also suggest that British product leaflets should emphasise the hazards of using smaller syringes to flush CVCs.