Abstract
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) ΔPCO2/Δ[H+] or ΔpH, b) ΔSID/Δ[H+] or ΔpH. Results: In a generalized estimating equation linear regression model, septic patients displayed significant differences in ΔPCO2/ΔpH [beta coefficient = –47.63, 95% CI (–80.09) – (–15.17), p = 0.004], compared to non-septic patients on admission. Lower absolute value of ΔPCO2/ΔpH (%) 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 ΔPCO2/Δ[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.
Highlights
In all body tissues, the microcirculation represents an exchange site for nutrients, oxygen and waste products; being crucial for the preservation of structural and functional integrity of all organs and systems, it affects total body homeostasis
For the whole cohort of patients, in a generalized estimating equations (GEE) linear regression model with ∆PCO2/∆pH as a dependent variable, septic patients on admission displayed significant differences in ∆PCO2/∆pH, compared to non-septic patients: beta coefficient = –47.63, 95% confidence interval (−80.09) – (−15.17), p = 0.004, adjusted for disease severity by the corresponding Sequential Organ Failure Assessment (SOFA) score
In a GEE linear regression model with ∆PCO2/∆[H+] as dependent variable, group B septic patients displayed significant difference in ∆PCO2/∆[H+] on clinical deterioration, compared to non-septic patients: beta coefficient = – 0.58, 95% confidence interval (–0.94) – (–0.23), p = 0.001, adjusted by the corresponding SOFA score
Summary
The microcirculation represents an exchange site for nutrients, oxygen and waste products; being crucial for the preservation of structural and functional integrity of all organs and systems, it affects total body homeostasis. In 1978, Stewart stated that the body’s acid-base status is regulated by three independent variables: strong ion difference (SID), partial pressure of carbon dioxide (PCO2) and total non-volatile weak acid concentration ([ATOT], mainly albumin) [4]. He further suggested that the buffering capacity can be estimated by the change of the above variables per unit change of [H+] or pH [5]. The buffering capacity indices were assessed upon ICU admission and reassessed only in septic patients, either at improvement or upon severe deterioration. Buffering capacity was an independent predictor of fatal ICU outcome at both assessments, ICU-admission and sepsis remission or deterioration
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