Association between lymphocyte expression of the apoptotic receptor Fas and pain in critically ill patients

OBJECTIVE: Lymphocyte apoptosis in critical illness is associated with immunosuppression. We explored for the first time the associations between pain ratings and expression of the apoptotic receptor Fas on B and T cells in critically ill patients and the potential mediating effects of adrenocorticotropic hormone (ACTH), cortisol, and substance P (SP). DESIGN: This is an exploratory correlational study with repeated measurements (14 days followup) and cross-sectional comparisons. SETTING: This study was conducted in a state hospital in the metropolitan area of Athens, Greece. PARTICIPANTS: The participants were 36 consecutive critically ill patients and 36 matched controls. OUTCOME MEASURES: Pain measured by the self-reported numeric rating scale [NRS], the behavioral pain scale, and the pain assessment scale was the primary outcome measure. Flow cytometry (Fas), electrochemiluminescence (ACTH and cortisol) and enzyme-linked immunosorbent assay (SP) were used. Mixed linear models for repeated measurements and bivariable associations at discrete time points were employed. RESULTS: Significant pain at rest was noted. Pain ratings associated with Fas expression on cytotoxic T cells (P=0.041) and B cells (P=0.005), even after adjustment for a number of clinical treatment factors (P=0.006 and P=0.052, respectively). On the day that more patients were able to communicate, Fas on B cells (r=0.897, P=0.029) and cytotoxic T cells (r=0.832; P=0.037) associated with NRS ratings. Associations between pain ratings and ACTH serum levels were noted (P<0.05). When stress neuropeptide levels were added to the model, the statistical significance of the associations between pain ratings and Fas expression was attenuated (P=0.052–0.063), suggesting that stress neuropeptides may partially mediate the association. CONCLUSION: Preliminary evidence for the association between pain and lymphocyte apoptotic susceptibility is provided. The role of pain management in maintaining immunocompetence in critical illness is worth exploring.