The effects of surgery on the circadian rhythms of cortisol.

The circadian rhythms of plasma cortisol levels are studied extensively. Frequent sampling techniques are used to examine the effects of surgical trauma on the circadian pattern of plasma cortisol in man. Five patients were studied, 48 hours before and 48 hours after major surgery. The normal preoperative cortisol rhythms of these patients did not disappear after surgical trauma but they were significantly phase-shifted. In addition, the mean cortisol concentrations were significantly elevated and the intracircadian cycles suffered complex changes in the postoperative period.