Oxygen Saturation of Mixed Venose Blood (SvO2 ), reference value 68%-77% mean 75% Clinical significance: The difference in arterial and venous oxygen content can be calculated by measuring SvO2, which is a more accurate reflection of cardiac output. A decrease in SvO2, while arterial oxygen saturation and oxygen consumption are still normal, is evidence that cardiac output is also low. Therefore, oxygen saturation tests of mixed venous blood are now considered to be of great value in the monitoring of severe cardiopulmonary disorders. Inadequate blood circulation due to decreased cardiac output, peripheral circulatory failure, sepsis, cardiogenic shock, hyperthyroidism, anemia and methemoglobinemia, pulmonary disorders, and other causes of reduced oxygenation, an SvO2 of less than 60% usually indicates increased tissue oxygen consumption or poor cardiopulmonary function. Chronic respiratory failure is often caused by bronchopulmonary disorders, such as COPD, severe tuberculosis, bronchiectasis, diffuse interstitial pulmonary fibrosis, and pneumoconiosis, with COPD being the most common. Thoracic lesions such as chest surgery, trauma, extensive pleural thickening, and thoracic deformity can also cause chronic respiratory failure.