Buffering Capacity in Sepsis: A Prospective Cohort Study in Critically Ill Patients.

Background: The concept of buffering generally refers to the ability of a system/organism to withstand attempted changes. For acid-base balance in particular, it is the body's ability to limit pH aberrations when factors that potentially affect it change. Buffering is vital for maintaining homeostasis of an organism. The present study was undertaken in order to investigate the probable buffering capacity changes in septic patients. Materials and methods: This prospective cohort study included 113 ICU patients (96 septic and 17 critically-ill non-septic/controls). The buffering capacity indices were assessed upon ICU admission and reassessed only in septic patients, either at improvement or upon severe deterioration. Applying Stewart's approach, the buffering capacity was assessed with indices calculated from the observed central venous-arterial gradients: a) Delta PCO2/Delta[H+] or Delta pH, b) Delta SID/Delta[H+] or Delta pH. Results: In a generalized estimating equation linear regression model, septic patients displayed significant differences in Delta PCO2/Delta pH [beta coefficient = -47.63, 95% CI (-80.09) - (-15.17), p = 0.004], compared to non-septic patients on admission. Lower absolute value of Delta PCO2/Delta pH (%) on admission was associated with a significant reduction in ICU mortality (HR 0.98, 95% CI: 0.97-0.99, p = 0.02). At septic-group reassessment (remission or deterioration), one-unit increase of Delta PCO2/Delta[H+] reduced the ICU death hazard by 44% (HR 0.56, 95% CI: 0.33-0.96, p = 0.03). Conclusions: In the particular cohort of patients studied, a difference in the buffering capacity was recorded between septic and non-septic patients on admission. Moreover, buffering capacity was an independent predictor of fatal ICU outcome at both assessments, ICU-admission and sepsis remission or deterioration.