The Epinephrine Test Dose in Obstetrics

Abstract

We commend Dr. Paech for his admirable safety records. We wish that all practitioners would exercise similar diligence and vigilance. We continue to advocate use of an epidural test dose in laboring women, for several reasons. First, many anesthesiologists initiate epidural analgesia with solutions of bupivacaine more concentrated than 0.125%. Second, the observations of Norris et al. (1) do not apply to single-orifice catheters. Third, some anesthesiologists, regrettably, do not remain at the bedside and observe the response to the therapeutic dose of local anesthetic. Finally, failure to give an epinephrine-containing test dose will delay the recognition of intravascular cannulation in some, albeit not all, patients with an IV catheter. Delayed recognition of an IV catheter results in delayed removal and replacement of that catheter, with a consequent delayed onset of satisfactory analgesia. Further, a laboring woman may require emergency cesarean delivery at any time. Bolus IV injection of a large dose of local anesthetic entails a risk of systemic local anesthetic toxicity. Our editorial focused on the importance of the epidural test dose for recognition of an IV catheter. However, the test dose remains equally useful for excluding unintentional intrathecal placement of the catheter. Failure to recognize an intrathecal catheter entails a subsequent risk of high spinal anesthesia, and it may result in an increased risk of respiratory depression after unintentional intrathecal injection of a supposed “epidural” dose of opioid. Paech acknowledges the use of an epinephrine-containing test dose in patients in whom intravascular cannulation is suspected. Thus, he seems to concede the value of the epinephrine-containing test for confirmation of intravascular cannulation in patients with negative aspiration. Dr. Paech also alludes to safety concerns with the epinephrine-containing test dose. However, to our knowledge, there is no published case of adverse clinical outcome resulting from IV injection of an epinephrine-containing test dose. Curiously, Paech advocates partial withdrawal of an IV catheter until aspiration is negative, despite the fact that Norris et al. (1) called attention to the hazards of that practice. Norris et al. (1) concluded: “It may be more prudent simply to replace intravascular catheters instead of trying to reposition them.” We agree that no single test dose is perfect and that there are several different ways to test a catheter. However, published data and clinical experience suggest that the advantages of the epinephrine-containing test dose outweigh the disadvantages and, thus, contribute to the safety of epidural anesthesia. Just as the Apgar score prompts healthcare providers to focus their attention on the newborn infant, the epidural test dose should prompt anesthesiologists to remain at the bedside and focus their attention on the early recognition of an intravascular or subarachnoid catheter. We believe that safety is optimized when anesthesiologists adhere to the following regimen: 1) careful aspiration of the catheter; 2) administration of an epinephrine-containing test dose immediately after a uterine contraction, with simultaneous monitoring of maternal heart rate; 3) incremental injection of the therapeutic dose of local anesthetic; and 4) careful assessment of the maternal response to both the test and the therapeutic dose of local anesthetic. David J. Birnbach MD David H. Chestnut MD