Background and Purpose of Study

Surgery, particularly cardiac surgery, stimulates a series of hormonal changes that constitute the stress response, in which cortisol plays a key role.1 This stress response to the surgical procedure could be important in the development of postoperative cognitive dysfunction (POCD) following cardiac surgery, given that prolonged exposure to high concentrations of glucocorticoids can be toxic to neural structures, particularly the glucocorticoid receptor-rich hippocampus, which is essential for certain types of memory.2 A recent study reported that patients with higher cortisol levels on the 1st postoperative morning after cardiac surgery exhibited an increased risk of early POCD.3 To gather a deeper understanding of the potential involvement of the stress response to a surgical procedure in the pathogenesis of POCD, we measured the perioperative cortisol levels at multiple time points. We hypothesized that higher postoperative cortisol levels are related to the occurrence of early POCD after cardiac surgery.

Materials and Methods

The current prospective cohort study enrolled 125 patients undergoing elective cardiac surgery with or without cardiopulmonary bypass (CPB). Patient serum cortisol levels were determined one day before surgery (at 08:00) and on the 1st (at 08:00, 16:00 and 24:00), 3rd (at 08:00) and 5th (at 08:00) postoperative days. A battery of nine neuropsychological tests was used to assess the participants two days before the surgical procedure and on the 6th postoperative day. POCD was defined as a decrease in performance of 1 standard deviation or greater between the postoperative and preoperative z scores on at least one neuropsychological test. A mixed-design ANOVA was used to determine the correlations of the perioperative cortisol levels with the occurrence of POCD and with the surgical technique performed.

Results and Discussion

Mixed-design ANOVA showed no statistically significant differences in the cortisol levels between non-POCD and POCD patients (F = 0.52, p = 0.690) or between patients with and without CPB (F = 2.02, p = 0.103) at the six perioperative time points. Therefore, this prospective cohort study which provided a longitudinal assessment of the perioperative cortisol level in cardiac surgical patients shed new light, revealing that the high postoperative cortisol levels merely reflect the stress response to the surgical procedure, while the real cause of POCD after cardiac surgery lies in another mechanism. In addition, we showed that cardiac manipulation during beating-heart surgery may lead to significant haemodynamic impairment reflected by a pronounced cortisol response, which therefore negates the benefits of avoiding CPB in terms of the stress hormone response.

Conclusion

The occurrence of early POCD and the use of CPB were not associated with significantly higher cortisol levels in this study with a repeated measurement design.

References

  1. Gibbison B, Spiga F, Walker JJ, et al. Dynamic pituitary-adrenal interactions in response to cardiac surgery. Crit Care Med 2015; 43:791-800.
  2. Lupien SJ, Maheu F, Tu M, Fiocco A, Schramek TE. The effects of stress and stress hormones on human cognition: Implications for the field of brain and cognition. Brain Cogn 2007; 65:209-237.
  3. Mu DL, Li LH, Wang DX, et al. High postoperative serum cortisol level is associated with increased risk of cognitive dysfunction early after coronary artery bypass graft surgery: a prospective cohort study. PLoS One 2013; 8:e77637.

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