The efficacy and safety of epidural filter catheters when used for post-operative intra-articular anaesthesia

There are concerns about the risk of iatrogenic infection when employing local anaesthetic techniques with post-operative intra-articular infusions in total knee arthroplasty. This study aimed to determine the efficacy of intact epidural filters in preventing transit of bacteria and to develop a technique of administration which would prevent membrane rupture.

Filter efficacy was assessed using a standardised test suspension of Pseudomonas aeruginosa. Twenty millilitres of suspension was injected through isolated epidural filters (n = 10) or filters with 40 cm of catheter tubing attached (n = 30). For each filter, injections were carried out at 0, 8 and 24 h. Filtrates were collected, incubated, sub-cultured onto Columbia horse blood agar and examined for bacterial growth.

Three delivery techniques were tested: manually controlled syringe with 5 ml of water at 20 ml/min, forced administration syringe with 5 ml of water at >240 ml/min and an automated syringe driver delivering 40 ml of water at 6.7 ml/min. For the two techniques using syringes, three syringe sizes, 5 ml, 10 ml and 20 ml, were tested. Each test condition was carried out on 10 filters (total n = 70). Filters were examined for rupture.

Intact epidural filters prevented bacterial transit in all cases. Manual controlled and automated syringe driver administration generated no filter ruptures. Manual forced administration generated 93% filter rupture. Ruptures occurred at peak pressures of approximately 620 kPa.

Epidural filters can be used to prevent bacterial transit. These results suggest automated devices remove the risk of filter rupture. This study is relevant to all specialties that utilise these filters during infiltration such as epidurals or other regional anaesthetic techniques.