A test to prevent subarachnoid and intravascular injections during epidural analgesia

Abstract

Not one of the present tests for the correct position of an epidural catheter can reliably detect intravascular, intrathecal and extra-epidural placement. A simple rapid test has therefore been developed. Following placement of the epidural catheter an initial aspiration test for cerebrospinal fluid and blood is performed. Air (1 ml) and then saline (2 ml) are injected through the epidural filter. The test involves 3 steps after removal of the filter: (i) the open end of the epidural catheter is lifted and the liquid meniscus present in the catheter is observed to drop rapidly; (H) the open end of the epidural catheter is lowered and the liquid meniscus is again observed to fill the catheter with clear liquid and no blood; (iii) the presence of air in the catheter during backflow confirms the correct position in the epidural space relative to a position in the subarachnoid space. The combined steps were prospectively examined in 278 cases of surgery under epidural analgesia. The test reliably detected 5 cases of intravascular and 2 cases of subarachnoid placement. No cases of local anaesthetic toxicity or undiagnosed subarachnoid injection were noted. Not one of the 6 failures to establish epidural analgesia could be attributed to intravascular or intrathecal placement. The sensitivity, specificity and positive predictive value for correct epidural placement of the catheter were found to be 95,5%, 63,6% and 98,5% respectively. The  time required to perform the test was less than 30 seconds in 92% of the cases. The test provides an additional easy rapid method of avoiding the two main dangerous misplacements of an epidural catheter, but requires further investigation to determine sensitivity and specificity more accurately.

S Afr Med J 1995; 85: 531-534