February 1999

Labor Epidural Analgesia Without an Intravascular "Test Dose"
Norris MC, Fogel ST, Dalman H, Borrenpohl S, Hoppe W, Riley A.
Anesthesiology 1998;88:1495-1501.
Commentary by Dr. Dwane

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[ see abstract below ]

The most common life threatening problems with epidurals occur as a result of where malpositioned epidural catheters come to rest: most commonly, intravascularly (IV), to a lesser extent, intrathecally (IT), and, rarely, in the subdural space. We employ many different safety steps to define these inadvertent misplacements. These tests are chosen to cause the least physiological impairment of the parturient, and to ensure the clearest endpoint.

In this study, Norris et al performed epidurals on 1029 parturients, placing catheters as either part of combined spinal/epidural blocks, or as continuous lumbar epidurals. Once placed, the catheters were tested by simple aspiration for the return of blood or cerebrospinal fluid. Sixty IV placements and 4 IT placements were identified and managed appropriately. Aspiration-negative catheters were then injected with 2 mL of 0.25% bupivacaine or 0.2% ropivacaine to rule out IT placement. Before the epidural catheters were used they were tested by injecting 10-15 mL of local anesthetic with or without opioid, in divided doses.

All 4 IT catheters in the study were identified by aspiration and only 2 additional IV catheters that were not identified by aspiration were subsequently detected. This false-negative rate compares favorably with those of both Doppler testing and the epinephrine test dose.

Although there were no false-negative tests using aspiration to identify IT placement, even this study protocol specified a small dose of epidural local anesthetic to rule out IT placement. Notably, one patient was felt to have had a subdural placement of the catheter, having a negative (for blood or CSF) aspiration test, no analgesia with 2 cc of local anesthetic but with two 5 mL doses of 0.25% bupivacaine producing analgesia, hypotension, and a sensory level to T2. This complication would not have been detected by other safety steps except incremental injection of the local anesthetic dose. Also, because of the lack of sensitivity of this aspiration test if used when manipulating epidural catheters known to be intravenously placed, the authors recommend the immediate replacement of a known IV catheter rather than attempting epidural catheter manipulation.

In summary, this study demonstrates that simple aspiration through the multiport epidural catheter is as reliable as the Doppler test or epinephrine test dose in detecting intravenous catheter placement. No safety maneuver of itself is 100% reliable. Therefore the use of a secondary safety test coupled with incremental injection of local anesthetic doses is still necessary to insure patient safety.

Note: This study applies to currently used concentrations of local anesthetics for obstetrical analgesia. The use of aspiration alone with epidurals for operative obstetrical anesthesia still requires examination. For a discussion of safety steps for epidural injection of local anesthetics, please see: Mulroy MF, Norris MC, Liu SS. Safety steps for epidural injection of local anesthetics: Review of the Literature and Recommendations. Anesth Analg. 1997.85:1346-1356.



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ABSTRACT