Corticosteroid-binding globulin and free cortisol in the early postoperative period after cardiac surgery

To characterize concentrations of corticosteroid-binding globulin (CBG), total and free serum cortisol, and free urinary cortisol in patients during the postoperative period of cardiac surgery.

In 24 patients serum was sampled on the first and second postoperative day after cardiac surgery (21 procedures with thoracotomy, 3 thoracoscopic procedures); urine was collected for two 10-h periods (8 P.M. until 6 A.M.) on the respective postoperative days. Total serum cortisol and free urinary cortisol were measured with an automated chemiluminescence assay (analysis of urine after extraction with dichloromethane), and CBG using a coated-tube RIA. Free serum cortisol was calculated from the concentrations of total serum cortisol and CBG as described previously. Thirty healthy volunteers were studied as controls.

CBG was reduced to about one-half of the normal concentration on both postoperative days. Whereas total cortisol was about two-fold increased on the first postoperative day compared to controls extremely high concentrations of free serum cortisol were calculated from CBG and total cortisol [median 136 nmol/L (interquartile range 100-185); controls 21.8 nmol/L (interquartile range 16.9-29.8)]. On the second postoperative day, median total serum cortisol was within the interquartile range of the controls, free serum cortisol in contrast was still two-fold increased. Free serum cortisol and free urinary cortisol were significantly correlated (r = 0.60).

Extremely high concentrations of free serum cortisol are typically found in the postoperative period of cardiac surgery; under these conditions the mere consideration of total cortisol does not appropriately display the activation of the adrenal cortex.