To the Editor:--Weitz and Drasner [1]address a clinically important subject, because epidural analgesia is used frequently to provide postoperative analgesia in patients undergoing extensive and potentially painful operations, which may require general anesthesia due to length of surgery or position of patient during surgery. Some anesthesiologists will not give a preoperative epidural dose of local anesthetic adequate to produce motor or sensory block for fear of intraoperative hypotension. Thus, the patient may arrive in the recovery room with no proof of the proper epidural location of the catheter. We agree with the authors' major conclusion that demonstrable sensory anesthesia is a predictor of good epidural morphine analgesia, because the epidural catheter must be located within the epidural space for epidural analgesia to be effective.

Data by Weitz and Drasner show that, on the operative day, patients with little or no demonstrable sensory block (0-7 points) after testing the epidural catheter with 150 mg lidocaine had mean+/- SEM visual analog (VAS) pain scores of 5.5+/-0.5. These VAS scores were significantly higher than the VAS scores (1.0+/-0.25) of patients whose catheters were clearly demonstrated to be located in the epidural space (16-24 points), judging by extent of sensory analgesia after lidocaine injection. Ranges of the VAS scores were not given, but one can surmise maximum VAS score in the former group of patients were about 7 or 8. In our practice, we would consider VAS pain scores higher than 5 to be an indication that epidural analgesia is not effective. In light of absence of expected sensory block after epidural lidocaine injection, we would assume the epidural catheter is not located in the epidural space. The epidural catheter would be removed and either it would be replaced or the patient would receive intravenous patient-controlled analgesia.

We are surprised at the authors' secondary conclusion that failure to achieve sensory blockade does not necessarily preclude failure of epidural opioid analgesia. It is well recognized that epidural catheters can be misplaced and then found in locations other than in the epidural space. We are aware of only two reliable and practical methods of ascertaining proper epidural position of a catheter: epidurography or demonstration of bilateral sensory and/or motor block after a test injection of an appropriate dose of a local anesthetic. The claim that the results of this latter test can be ignored sends a message that is potentially harmful to the patients of the readers of ANESTHESIOLOGY. We are confident that this was not the intent of Weitz and Drasner.

Rom A. Stevens, M.D., Associate Professor, Director, Division of Pain Management.

Radha Sukhani, M.D., Associate Professor, Director, Ambulatory Surgery Center, Stritch School of Medicine, Loyola University Medical Center, Maywood, Illinois 60153.

Weitz SR, Drasner K: Local anesthetic test dose as a predictor of effective epidural opioid analgesia. ANESTHESIOLOGY 1995; 83:96-100.