In Reply:-We appreciate Dr. Chado's comments and interest in our article. We have reanalyzed the data as suggested by Dr. Chado. The ratio of pre- and posttreatment current perception threshold values were not significantly different (Table 1). There was a trend for the 250- and 5-Hz lumbar groups to have a greater change posttreatment (as would be predicted), but the variability was too great to demonstrate this difference statistically. It is possible that a larger sample size or a crossover study design would have decreased the variability and demonstrated the predicted differences (we have considered both factors in subsequent studies). Another factor may be that the neurometer is not sensitive enough to measure the mild sensory changes effected by intrathecal opioids.

Finally, we agree with Dr. Chado that there is good evidence that the neurometer selectively stimulates various nerve fibers. However, to our knowledge, definitive patch clamp experiments have yet to be performed.

Edward T. Riley, M.D.

Sheila E. Cohen, M.B. Ch.B., F.R.C.A.

Cathy L. Hamilton, M.D.

Department of Anesthesia; Stanford University School of Medicine; Stanford, California 94305;

(Accepted for publication November 24, 1998.)