Mixed venous blood exhibits an oxygen tension of______________?
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Answer: B. 40 mm Hg
Explanation
Mixed venous blood returning to the right heart has an oxygen partial pressure of approximately 40 mm Hg. This value reflects the average oxygen extraction by metabolically active tissues throughout the systemic circulation. Blood from superior and inferior venae cavae mixes thoroughly within the right atrium and ventricle. Mixed venous blood gas analysis provides valuable insights into overall systemic tissue oxygenation status. Partial pressure of oxygen measures the dissolved oxygen tension within biological fluid compartments. Systemic capillaries release oxygen to tissues, lowering the PO2 from arterial levels down to venous values.
Critically ill patients in intensive care units may undergo central venous catheterization to monitor oxygen extraction. Low mixed venous oxygen saturation indicates inadequate cardiac output or severe tissue hypoperfusion. Pulmonary artery catheterization allows clinicians to sample true mixed venous blood entering the lungs. A partial pressure of 25 mm Hg represents severely desaturated venous blood under extreme metabolic stress. A partial pressure of 55 mm Hg is significantly higher than normal mixed venous oxygen tension levels. A partial pressure of 70 mm Hg approaches arterial oxygen levels and does not reflect mixed venous blood.
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