To the Editor:-The editorial by Kissin [1]rightly calls attention to the many difficulties facing the investigator who seeks to demonstrate the clinical phenomenon of preemptive anesthesia. To his balanced words, I add that I believe semantic confusion has arisen because of misuse of the word "preemptive." Increasingly, this word is equated by those who conduct clinical trials or review the literature with "preoperative" or "pre-incision." In the animal literature, however, the term "preemptive" refers to measures that prevent sensitization of cells within the spinal cord dorsal horn and other key sites within pain pathways. By definition, preemptive interventions in animal models must be accomplished before the onset of nociception. Conversely, preoperative or pre-incisional measures that could not possibly be viewed as preventing dorsal horn sensitization have been tested as if they were preemptive in the preceding sense. For example, the administration of single dose of a nonsteroidal antiinflammatory drug, or a single low dose of an opioid preoperatively, have been evaluated in clinical trial whose results are then discussed as tests of "preemptive analgesia."

It is clear from the preclinical literature that preemptive means "preventive," not simply before Preemptive analgesia, like many other potentially worthwhile advances in medicine, would be abandoned if its initial, sometimes uncritical implementation were viewed as a final test of its value Cardiopulmonary bypass, blood transfusion, organ transplantation, and the use of muscle relaxants are but a few examples. Kissin does well to caution his colleagues that even effects that do exist and that may be of extreme importance are not always evident. For these reasons, we should not allow linguistic imprecision to compound our difficulties when evaluating this important concept.

Daniel B. Carr, M.D., F.A.B.P.M., Saltonstall professor of Pain Research, Vice-Chairman for Research, Medical Director, Pain Management Program, Department of Anesthesiology, Professor of Anesthesiology and Medicine, Tufts University School of Medicine, New England Medical Center, 750 Washington Street #298, Boston, Massachusetts 02111.

(Accepted for publication September 12, 1996.)

Kissin I. Preemptive analgesia: Why its effect is not always obvious. Anesthesiology 1996; 83:1015-9.