avO2Differenz

avO2Differenz, abbreviated for arteriovenous oxygen difference, is the amount of oxygen extracted by tissues from arterial blood as it circulates. It is defined as the difference between arterial oxygen content (CaO2) and venous oxygen content (CvO2). This parameter reflects how much oxygen tissues take up from the blood to meet metabolic demands.

CaO2 and CvO2 are calculated from hemoglobin concentration (Hb), oxygen saturation, and dissolved oxygen: CaO2 = (Hb × 1.34 × SaO2) + (0.003 × PaO2); CvO2 = (Hb × 1.34 × SvO2) + (0.003 × PvO2). The oxygen content values are expressed in milliliters of O2 per deciliter of blood (ml O2/dL). The avO2Differenz itself is the numerical difference CaO2 − CvO2, representing the O2 extracted per 100 mL of blood.

Typical values and dynamic changes: at rest, CaO2 is about 20 ml/dL and CvO2 about 15 ml/dL, producing an avO2Differenz around 4–5 ml/dL. During exercise, tissues increase oxygen extraction, and the avO2Differenz can rise substantially as cardiac output and metabolic demand grow.

Physiological significance: the avO2Differenz relates to oxygen delivery and consumption via VO2 ≈ CO × avO2Differenz. It is used to assess tissue oxygenation and metabolic adequacy, particularly in clinical settings. In practice, measurements rely on arterial blood samples and venous blood samples to determine CaO2 and CvO2; mixed venous blood from the pulmonary artery is the standard, though central venous oxygen saturation (ScvO2) is often used as an approximation.

Clinical relevance: an increased avO2Differenz may indicate reduced oxygen delivery or heightened extraction (e.g., anemia, hypoxemia, shock), while a small difference with high delivery can raise concerns about mitochondrial dysfunction or impaired utilization.