To the Editor:—Hugo et al. reported a clinical study of barbiturate-induced hyperalgesia. [1] There are a number of methodologic problems and assumptions in their results that need to be addressed.

A major problem is with the conclusion that barbiturate hyperalgesia, if present, occurs early in the postoperative period. This is based on the finding that pain scores were higher in the thiopental group at the 0–4-h period. However, the authors did not take into account that the morphine use in the thiopental group was less than that in the propofol group during this period. This lower morphine dose may account for the difference in pain scores at 0–4-h period and may be a result of greater postoperative sedation in the thiopental group during this period. The higher morphine intake may indicate that the propofol group may have had greater pain sensation.

Another issue is with the assessment of pain scores and morphine use in the 0–4-h period after a general anesthetic. Variables such as postoperative sedation during emergence from general anesthesia were not controlled for in this study. Perhaps even more important is the lack of reliability in assessing pain in patients emerging from general anesthesia. Every effort should be made to quantify pain in an objective fashion and to eliminate the variable of postanesthetic sedation. This may be difficult, but a more objective pain scoring method should be used in this situation.

For the reasons stated above, we believe that a more complete study is needed before we can refute or support Clutton-Brock [2] and Dundee [3] from 30 yr ago. The following factors are essential in the study of clinically relevant barbiturate hyperalgesia:(1) a quantitative and reproducible nociceptive stimulus, (2) a quantitative and reliable assessment of pain or hyperalgesia, and (3) elimination of variables in general anesthesia or postoperative sedation. With these considerations, a more definitive answer to the question of barbiturate hyperalgesia can be addressed.

Anand Tewari, M.D.; Clinical Fellow; Yale Center for Pain Management; Tong-Yi Yao, B.S.; Medical Student; Lloyd R. Saberski, M.D.; Clinical Director; Yale Center for Pain Management; Yale University School of Medicine; 333 Cedar Street; P.O. Box 3333; New Haven, Connecticut 06510.

(Accepted for publication November 3, 1994.)

Hugo S, Lake APJ, Cooledge BA: Are barbiturates hyperalgesic? ANESTHESIOLOGY 80:1413-1414, 1994.
Clutton-Brock J: Some pain threshold studies with particular reference to thiopentone. Anaesthesia 15:71-72, 1960.
Dundee JW: Alterations in response to somatic pain associated with anesthesia: II. The effect of thipentone and pentobarbitone. Br J Anaesth 32:407-414, 1960.