To the Editor:--Weitz and Drasner studied a possible correlation between dermatomal spread of anesthesia from epidural injection of 10 ml 1.5% lidocaine to predict subsequent epidural morphine postoperative pain efficacy (2.5 mg plus continuous infusion). Patients were studied in three groups (minimal, moderate, and extensive local anesthesia from the lidocaine dose) including seven (14% of studied) patients, where no clinical evidence of epidural block developed. The type of catheter (single- vs. multiple-orifice), statistical evaluation of demographic factors, ASA status, and the absolute numbers, means, and standard deviations of dermatomes developing anesthesia were not reported for any group. While a 3-ml pre- and postoperative test dose containing epinephrine was used to "exclude intravenous or intrathecal injection of local anesthetic," in the face of the continuing debate regarding the usefulness of the epinephrine test dose, no exclusion of patients with factors known to mask epinephrine effects (i.e., beta blockade, pacemakers) nor monitors or methodology used to evaluate intravascular effects is mentioned. .
I would question: (1) the validity in assuming catheter localization to the epidural space in the absence of effects from 10 ml lidocaine; (2) why the 10 ml lidocaine test was not done preoperatively (as 3 ml were injected then anyway) before the effects of pain, general/local anesthesia, and epidural morphine compromised the evaluation of either lidocaine's effects or the opioid analgesia in the postanesthesia care unit; and (3) whether any of the group 2 patients had unilateral effects, indicating possibly paravertebral instead of epidural injection?
The authors noted effective analgesia (VAS < 4) only in patients who developed a block to T6 or greater (maximal effect group). Pain relief was, however, "found" in all seven patients who experienced no lidocaine effects "despite relatively high VAS scores" (indicating significant pain?), and the groups exhibiting minimal and moderate lidocaine effects had similar pain scores. Does this study attest to the frequent ineffectiveness of epidural opioids in general (or this particular dosing regimen), patient tolerance of postoperative pain (and the needlessness of this epidural opioid regimen) or merely a very high (> 14%) rate of (resident) nonepidural catheter placement?
Preoperative dosing and maintainence of epidurals (with local anesthetic and then morphine) during combined epidural/general anesthesia provide reduced intraoperative general anesthetic requirements and a pain-free emergence in the recovery room. When morphine is placed in the epidural space in sufficient amounts caudally, effective opioid analgesia results to manage even thoracic pain, which raises the question as to why local anesthetic effect above L1 from 10 ml would be a predictor of morphine effect. [5,6]What is the utility of this method, which only misdiagnoses nonfunctional catheters as epidural catheters and requires patients to unnecessarily experience postoperative pain on emergence.
Paul Martin Kempen, M.D., Ph.D., Department of Anesthesiology, Louisiana State University Medical Center, P.O. Box 33932, Shreveport, Louisiana 71130-3932.