Distinguishing cerebrospinal fluid from mepivacaine using the pH test in patients undergoing elective cesarean section with combined spinal-epidural anesthesia

Abstract

Introduction In single-space combined spinal-epidural anesthesia (CSEA), it is important to correctly determine if the fluid coming out of the spinal needle is cerebrospinal fluid (CSF) or the liquid used in the loss of resistance (LOR) technique. In this study, we used mepivacaine for LOR and measured the pH values of CSF and mepivacaine to determine whether the pH test is a reliable method to confirm CSF when performing single-space CSEA. Methods This clinical trial included 47 full-term pregnant women who underwent cesarean section. Single-space CSEA was administered at the lumbar intervertebral space using a small amount of mepivacaine for LOR. The pH values of CSF and mepivacaine were determined by the color of the test strip immediately after dropping. The area under the curve (AUC) for the pH values was calculated to determine the cutoff value for distinguishing between CSF and mepivacaine. Results The median pH values were 7.7 (7.1–8.0) and 6.2 (5.9–6.8) for CSF and mepivacaine, respectively. When the cutoff value of pH for distinguishing CSF from mepivacaine was 7.1 or greater, the AUC was 1.0 (100% sensitivity and specificity). Our result demonstrated that CSF can be correctly distinguished from mepivacaine in patients undergoing cesarean section under single-space CSEA using a cutoff value of pH 7.1. Conclusion The pH test is a simple and reliable method to confirm CSF when performing single-space CSEA with mepivacaine for LOR. Trial registration Accuracy of pH test paper for cerebrospinal fluid during spinal anesthesia: prospective study in healthy pregnant women under scheduled caesarean section; University Hospital Medical Information Network, UMIN000036454. Registered 1 May 2019

Incidental epidural fluid collection – differential approach considerations

“…1 Those older studies cautioned, however, that no single test is perfect, and suggested the use of a combination of tests. In more recent literature, the use of glucose and pH has been revisited, 3,4 to varying degrees of success.…”

“…In this situation, clear fluid at the needle hub may represent either a) iatrogenic fluid, b) cerebrospinal fluid (CSF) that leaked after a previous procedure or c) intrathecal CSF from a new dural puncture. Evolving literature exists on differentiating local anesthetic, [1][2][3] and normal saline 4 from CSF; however, none of the tests discussed are currently standard of care in a major guideline. To our knowledge, there is no mention of fluid from prior CSF collection versus CSF from new dural puncture.…”