Mixed venous oxygenation in fatal gram-negative septicemia

Area of Science:

• Critical Care Medicine
• Physiology
• Pathophysiology

Background:

• Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection.
• Accurate assessment of tissue oxygenation is crucial for managing septic patients.
• Mixed venous oxygen partial pressure (SvO2) is often used as an indicator of oxygen delivery and consumption.

Purpose of the Study:

• To investigate changes in arterial and mixed venous oxygen partial pressure (PO2) during fatal gram-negative septicemia.
• To evaluate the reliability of mixed venous PO2 as an index of tissue oxygenation in sepsis.
• To explore the potential role of shunting in altered oxygen values during sepsis.

Main Methods:

• Continuous monitoring of mixed venous and arterial PO2 in seven patients with fatal gram-negative septicemia.
• Analysis of PO2 values across early, middle, and late stages of septicemia.
• Correlation of PO2 changes with hemodynamic parameters and metabolic acidosis.

Main Results:

• Early sepsis showed tachycardia, hypotension, and hypoxemia.
• Middle stage sepsis exhibited severe hypotension with a consistent rise in mixed venous PO2 (mean 50 mmHg) and arterial PO2.
• Late stage sepsis presented normal mixed venous PO2 (mean 42 mmHg) despite persistent metabolic acidosis.

Conclusions:

• Elevated mixed venous PO2 during septicemia may result from systemic arterial-venous shunting.
• Mixed venous PO2 is an unreliable index of tissue oxygenation in the context of sepsis.
• A theoretical model is proposed to explain the relationship between tissue and mixed venous oxygenation in sepsis.