Introduction: The stress response post-operatively increases glucocorticoid concentration and a higher cortisol response is associated with better recovery. The measurement of cortisol concentrations post-operatively can be unreliable due to altered binding protein concentrations. Free serum cortisol is felt to be the better marker of bio-active glucocorticoid concentrations but is difficult to measure. Salivary cortisol and cortisone have been shown to correlate well with serum free cortisol and is independent of binding protein concentrations. We investigated the use of salivary cortisol and cortisone in this group of patients.
Methods: Patients undergoing cardiothoracic surgery without any history of glucocorticoid drug use or adrenal pathology were recruited into the study. Paired saliva and serum samples were collected pre- and post-operatively. Serum total cortisol, serum free cortisol, salivary cortisol and salivary cortisone were all measured by liquid chromatography tandem mass spectrometry. Saliva was collected using a disposable pipette after allowing the saliva to pool in the mouth for a few minutes.
Results: A poor correlation was observed between salivary cortisol serum free cortisol (r = 0.34) and serum free cortisol and salivary cortisone (r = 0.28). A curvilinear correlation was seen between serum free cortisol and serum total cortisol as expected (r = 0.93). The range of pre-operative cortisol concentrations was 55552 nmol/L. The range of post-operative cortisol concentrations was 351233 nmol/L. 70% of post-operative samples which were collected in the morning had cortisol concentrations <500 nmol/L.
Discussion: Despite previous reports promoting the use of salivary cortisol and cortisone as a marker of serum free cortisol a poor correlation was seen in this population. This may be due to the poor quality of saliva collected in this group and different methods for collecting saliva should be investigated. A significant proportion of patients had low cortisol concentrations post-operatively.
Declaration of interest: There is no Conflict of interest that could be perceived as prejudicing the impartiality of the research reported.
Funding: No specific grant from any funding agency in the public, commercial or not-for-profit sector.