The relationship between oxygen extraction and venous pH in sepsis

Area of Science:

• Physiology
• Biochemistry
• Critical Care Medicine

Background:

• The Haldane effect (HE) describes how oxygen binding to hemoglobin influences carbon dioxide (CO2) and proton (H+) binding.
• Understanding HE's impact on acid-base balance is crucial in critical illnesses like sepsis.
• Previous studies have not fully quantified HE's buffering role on venous pH in septic patients.

Purpose of the Study:

• To quantify the impact of the Haldane effect (HE) on the relationship between oxygen extraction (O2Ex) and venous pH in septic patients.
• To assess the buffering capacity of O2Ex on venous pH mediated by HE.
• To evaluate the protective role of HE against excessive decreases in venous pH during circulatory failure.

Main Methods:

• Utilized a recently developed model to quantify blood CO2 exchange and Haldane relationships.
• Analyzed 247 measurements from 91 septic patients with varying sepsis severity.
• Calculated arterio-venous pH difference (a-vDpH) and the HE-mediated moderation of a-vDpH (DpH) using arterial and mixed venous blood gas data.

Main Results:

• Arterio-venous pH difference (a-vDpH) increased with venoarterial CO2 difference (v-aDCO2) but was moderated by O2Ex (a-vDpH = .006 + .017 v-aDCO2 - .009 O2Ex).
• The HE's total moderating effect (total DpH) was strongly related to O2Ex (DpH = -.002 + .009 O2Ex).
• Loss of HE's protective effect contributed to greater venous pH decreases in hypodynamic patients with impaired O2Ex.

Conclusions:

• The Haldane effect significantly moderates the decrease in venous pH relative to arterial pH in septic patients.
• HE provides a quantifiable buffering role against excessive decreases in venous pH, particularly important in circulatory failure.
• This study offers a method to quantify the HE component, separating it from other pH-affecting factors in sepsis.