A re-evaluation of the ability of thiopental to identify cerebrospinal fluid in epidural catheter aspirate

Jonathan H. Waters, Victor L. Rizzo, Sivam Ramanathan

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


Study Objective: Sodium thiopental has been used to determine whether fluid aspirated from an epidural catheter is previously injected local anesthetic or cerebrospinal fluid (CSF). The purpose of this study was to test the efficacy of this test in distinguishing opioids from CSF. Design: in vitro study. Setting: Laboratory of a university hospital. Measurements and Main Results: Three in vitro studies were performed. The first study tested for precipitation when thiopental was mixed with several commonly used epidural medications. Then, thiopental was mixed in combinations of opioids with local anesthetics to see if the opioid might prevent the precipitation of the local anesthetics. Finally, lidocaine was serially diluted and precipitation with thiopental was assessed. It was found that certain concentrations of opioids as well as normal saline do not precipitate with thiopental. In addition, the ratio of opioids to local anesthetic of 10:1 prevented precipitation when thiopental was added. Local anesthetics combined with cerebrospinal fluid in a 1:10 ratio produced a precipitate on mixing with thiopental. Conclusions: Use of thiopental to differentiate opioids from cerebrospinal fluid is unreliable. In addition, in some simulated situations, opioids may mask the presence of local anesthetic.

Original languageEnglish (US)
Pages (from-to)224-227
Number of pages4
JournalJournal of Clinical Anesthesia
Issue number3
StatePublished - May 1995
Externally publishedYes


  • Anesthetic techniques
  • cerebrospinal fluid
  • epidural
  • epidural aspirate
  • sodium thiopental

ASJC Scopus subject areas

  • Anesthesiology and Pain Medicine


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