Postoperative circadian rhythms and cortisol stress response to two types of cardiac surgery

Although endocrine stress responses of coronary artery bypass patients have been reported, similar studies have not been conducted in patients undergoing implantation of an automatic cardioverter/defibrillator device.

To compare patterns and magnitudes of intra- and postoperative cortisol stress responses in patients undergoing two types of surgery; rate at which postoperative cortisol levels return to presurgical levels; and whether stressors associated with these two procedures affect postoperative circadian rhythms of cortisol, heart rate, and body temperature.

A time-series, small-group design was used to investigate 16 coronary artery bypass graft and 9 automatic cardioverter defibrillator patients. For the cortisol stress study, blood samples were obtained pre-, intra-, and postoperatively until day 6. For the circadian rhythm aspect, cortisol circadian rhythm aspect, cortisol levels, heart rate, and oral temperatures were measured every 2 hours for 24 hours beginning on postoperative day 1.

Plasma cortisol levels increased significantly toward the latter part of surgery. Generally, no significant group differences were found in cortisol magnitude during and after surgery. Postoperative cortisol levels were significantly elevated from preoperative levels for both groups; however, the automatic cardioverter defibrillator group's cortisol levels declined at a slower rate. The stressors associated with these surgeries were sufficient to disrupt or abolish circadian rhythms for the measured variables.

The elevated postoperative cortisol levels and altered circadian rhythms may contribute to increased vulnerability by dampening patients' anti-inflammatory and immunologic responses and adversely affecting their sense of well-being. The clinical significance of these findings is yet to be determined; more research is warranted.