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A-77
2002
Increased Anesthetic Requirement in Subjects with Naturally Red Hair
Edwin B. Liem, M.D.; Chun-Ming Lin, M.D.; Mohammed I. Suleman, M.D.; Anthony G. Doufas, M.D.; Daniel I. Sessler, M.D.
Outcomes Research Institute and Department of Anesthesiology, University of Louisville, Louisville, Kentucky
Introduction No phenotype correlates with anesthetic sensitivity in humans. Nonetheless, some anesthesiologists believe that patients with red hair require more anesthesia. We therefore tested the hypothesis that desflurane requirement in subjects with red hair exceeds that of those with dark hair.

Methods With IRB approval and informed consent, we studied healthy female Caucasian volunteers, ages 18 to 40 years who had either natural bright red (n = 10) or dark (n = 10) hair. General anesthesia was induced with propofol and maintained with desflurane at an initial concentration randomly set between 5.5 and 7.5%. After an equilibration period of 45 minutes, a noxious electrical stimulation (100 Hz, 70 mA) was transmitted through bilateral intradermal needles. An observer, blinded to the desflurane concentration, evaluated body movement. If the volunteer moved in response to the stimulation, the desflurane concentration was increased by 0.5%; otherwise the concentration was decreased by 0.5%. The up-and-down sequence was continued until volunteers "crossed-over" from movement to non-movement (or vice versa) four times. This procedure, known as the "Dixon up-and-down method," is a standard technique for evaluating anesthetic potency1. Individual responses were plotted as a logistic regression curve. The concentration corresponding to the P50 was considered to be the desflurane requirement. Results in the two groups were compared with unpaired, two-tailed t-tests; P < 0.05 was considered statistically significant.

Results The groups were comparable in terms of height, weight, and age. The volunteers with the red hair had a mean desflurane requirement of 6.19% (95% CI 5.84 -6.54); the mean requirement in the dark haired group was 5.18% (95% CI 4.86-5.49, P = 0.0001, Fig. 1).

Conclusion Data from animal studies suggests that genetic factors might contribute to differences in anesthesia requirements. For example, strains of the nematode Caenorhabditis elegans may differ over a 10-fold range in their anesthetic sensitivities to halothane and isoflurane2. That people with the red hair phenotype have a greater anesthetic requirement is thus not only of practical clinical importance, but suggests that genetic differences contribute to anesthetic requirement in humans.

References

1. Dixon WJ: Quantal-response variable experimentation: The up-and-down method, Statistics in Endocrinology. Edited by McArthur JS, Colton T. Cambridge, MIT Press, 1970, pp 251-267

2. van Swinderen B, Galifianakis A, Crowder M. Common genetic determinants of halothane and isoflurane potencies in Caenorhabditis elegans. Anesthesiology. 1998 Dec; 89(6):1509-17.

Anesthesiology 2002; 96: A77
Figure 1