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Immunology & Autoimmune
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Currently under review
Pending specialist review and validation.
Mixed venous oxygen saturation measures how much of the hemoglobin in your returning venous blood is carrying oxygen after it has circulated through your body. It is typically measured using a co-oximeter on blood drawn from a pulmonary artery catheter, which collects a truly mixed sample from multiple veins.
Because the sample blends blood from the upper body, lower body, and heart muscle, it reflects the overall balance between oxygen delivery and oxygen use by your tissues. This is different from arterial oxygen saturation, which reflects how well oxygen is loaded in the lungs before blood reaches the body.
This test helps your care team understand whether your tissues are getting and using enough oxygen. It is commonly used in critical illness, shock, heart failure, and major surgery to guide decisions about fluids, oxygen, transfusions, and medications that support the heart and circulation. It offers a real-time window into the match between supply and demand for oxygen.
Watching how this value changes over time can show whether treatment is helping or if your condition is becoming more severe. Clinicians interpret it together with arterial blood gases, hemoglobin, lactate, imaging, and bedside assessments of heart and lung function.
Your result is interpreted in the context of your symptoms and other tests. Lower values can indicate that your body is extracting more oxygen because delivery is limited by low cardiac output, low hemoglobin, or reduced oxygen entering the blood. Higher values can occur when tissues extract less oxygen, such as during certain infections, with heavy sedation or paralysis, or when blood bypasses areas where oxygen is normally used.
One result is less informative than a pattern over time. Your team may repeat the test to confirm accuracy, review how the sample was obtained, and look at related results like arterial oxygen levels, hemoglobin, and lactate. Based on the full picture, they will decide whether to adjust oxygen therapy, fluids, medications, or other treatments.
Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.
A true mixed venous sample requires a pulmonary artery catheter; central venous samples are not identical. Accidental arterial contamination, drawing during a catheter flush, or sampling from the wrong port can skew the result.
Changes in inspired oxygen, positive pressure ventilation, and high levels of PEEP can alter oxygen delivery and demand, shifting venous oxygen saturation independently of tissue health.
Anemia lowers oxygen-carrying capacity and can lower the value, while carboxyhemoglobin or methemoglobin from smoke exposure, nitrites, or dyes can affect co-oximeter readings and clinical interpretation.
Exposure of the syringe to air, delays before analysis, temperature changes, or clotting can change the measured saturation. Prompt, airtight handling reduces pre-analytic error.
Vasopressors, inotropes, sedatives, neuromuscular blockers, fever, shivering, and severe pain all modify cardiac output and tissue oxygen use, which can raise or lower the measured value.
Sepsis, cardiogenic shock, congenital heart disease, significant valve disease, pregnancy, and severe lung disease can alter venous mixing or tissue oxygen extraction, affecting interpretation.
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