Technical and light microscopic comparison of four different small-diameter catheters used for continuous spinal anesthesia.

Background and Objectives. Recently several manufacturers developed ultra-thin catheters for continuous spinal anesthesia. Their use may be associated with technical problems. Methods. Four spinal catheters [Preferred Medical 28-gauge and 32-gauge (polyurethane), Kendall CoSpan 28-gauge (nylon), and Microspinal 32-gauge (polyimide)] were compared in 41 patients who underwent knee or hip operations. Difficulties in using the catheters were recorded, and after their removal, the catheters were examined by light microscopy. Results. The insertion of the 28-gauge catheters was always successful. However, five of 11 of the 32-gauge polyurethane and one of ten of the 32-gauge polyimide catheters could not be inserted. Plain 0.5% bupivacaine (2-6.5 ml) was administered, and the median pinprick analgesia level varied between T4 (28-gauge nylon) and T7 (other groups). During removal, one of ten of the 28-gauge nylon, four of the of the 28-gauge polyurethane, and all six 32-gauge polyurethane catheters stretched. Two of six of the 32-gauge polyurethane catheters broke, but no fragment remained in any patient. Microscopic examination revealed deposits of fibrinous material on the tips of all polyurethane and polyimide catheters and on one nylon catheter. One polyimide catheter ruptured 15 cm from the tip. No signs of tearing or lost pieces of catheter material were observed by light microscopy. Conclusion. The use of the 32-gauge polyurethane catheter was associated with problems that limit its clinical usefulness. Nylon and polyimide catheters with stainless steel stylets were more resistant to stretching. The nylon catheter was most resistant to adhesion of fibrinous material.