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01 Characteristics of Venous Blood Gas
Venous blood gas discomfort reflects the function of lung gas exchange, but reflects tissue gas exchange and body acidity. Under normal circumstances, the pO2 of venous blood is significantly reduced, the pH value is similar to that of arterial blood, and the pCO2 is slightly higher than arterial blood (around 4~5mmHg). venous blood gasHowever, in critically ill patients, especially in the state of circulatory failure, arteriovenous blood gas will be separated from arteriovenous blood gas and acid. At this time, arterial blood gas analysis cannot accurately reflect the acidity of the tissue, and only venous blood gas analysis can find serious, even fatal, tissue acidosis.
02 parameters of venous blood gas value
a. The normal value of intravenous pO2 is 40±3 mmHg. If the mixed intravenous pO2 is lower than 28 mmHg, it is often accompanied by lactic acidosis and insufficient tissue perfusion. Therefore, 28 mmHg is commonly used as a critical value in clinical practice.
b. The normal venous pCO2 value is 40-50 mmHg, which is not much different from the arterial pCO2, but the results are different when the cardiac output is reduced.
3. The normal venous pH is 7.35-7.45, which is not much different from the arterial pH. Arterial blood showed hypocapnia and respiratory poisoning, while mixed venous blood showed hypercapnia and respiratory acidosis. The pH and pCO2 difference between arterial and mixed venous blood increased.
4. The normal value of venous oxygen saturation is 65% to 75%.
03Two methods to identify arterial and venous blood gases
Method 1: Distinguish from the appearance
The arterial blood was bright red, and the pulse was visible on the inner surface of the syringe. But when the patient's peripheral circulation is poor, the pulsation is not obvious. In severe hypoxia, arterial blood is also darker and difficult to distinguish.
Method two: monitor blood oxygen saturation
Critically ill patients have ECG monitoring and non-invasive oxygen saturation monitoring, record the non-invasive oxygen saturation value when blood gas is drawn, and compare it with the blood oxygen saturation in the blood gas test result. If the difference is within 5%, the blood drawn is regarded as arterial blood .
related articles:3 ways to distinguish systemic arterial and venous blood gases
