Epidural administration and analgesic spread: comparison of injection with catheters and needles.

This study was designed to investigate differences in epidural analgesic spread between catheter and needle injections in 48 patients with comparable physical characteristics. The spread of analgesia in the catheter injection group with a 0.24 ml.sec(-1) injection rate (n = 16) was 16.8 +/- 1.5 spinal segments and that in the needle injection group at the same injection rate (n = 16) was 12.5 +/- 1.8 spinal segments ( P < 0.01). Needle injection at the faster rate of 1.2 ml.sec(-1) (n = 16) produced a significantly greater spread of analgesia than with the 0.24 ml.sec(-1) rate through the needle (16.2 +/- 1.6 vs 12.5 +/- 1.8 spinal segments, P < 0.01). Thirteen of 16 patients receiving the fast needle injection complained of back compression or discomfort during the injection. The injection through an epidural catheter and the fast (1.2 ml.sec(-1)) injection through a needle produced extensive and equivalent epidural analgesic spread. However, because of patients discomfort with fast injection through the needle, the authors conclude that when using continuous epidural anesthesia, the initial injection of local anesthetic should be administered through the epidural catheter not the needle.