Despite the different name, venous blood gas analysis is a basic but very important test in medical emergencies. After all, it is by means of the test indicators that doctors verify the levels of gases present in the respiratory process and the components of the body's acid-base balance (ph). If you have any doubts about the procedure, we have clarified the main ones below!

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How is the venous blood gas test performed?

The execution is quite simple: all that is needed is a blood sample - approximately 1.5 mL - to analyze the indicators.

What is it used for and when is it indicated?

The venous blood gas test is useful for patients with kidney and lung diseases, and it is also useful for monitoring patients in the intensive care unit, where it is possible to check the levels of gases in the patient's blood:

• Respiratory, kidney and lung diseases - including treatments in progress.
• It detects possible imbalances of gases and acids in the blood.
• It assesses whether therapies such as oxygen therapy are improving a patient's health.
• Identifies possible blood vessel ruptures.
• Finally, it helps in the diagnosis of metabolic diseases and poisoning.

What is the difference between venous and arterial blood gas?

Both tests have the same purpose, however, the difference is in the collection site:

• Venous blood gas: The blood sample is drawn from the patient's vein. In general, venous blood is richer in CO2 (carbon dioxide), because it is returning to the heart.
• Arterial blood gas: is when a blood sample is taken from the patient's artery. Unlike venous blood, this has more O2 (oxygen) because it has just been pumped and is coming out of the heart.

Reference Values

The reference values for venous blood gas analysis are:

• pH: 7.33 - 7.43.
• pO2: 30 - 50 mmHg.
• pCO2: 38 - 50 mmHg.
• HCO3: 23 - 27 mmol/L.
• BE: -3 - +3.
• SO2: 60 to 85%.

What do the values outside the parameters indicate?

First of all, blood gas is not the only test to make a diagnosis; therefore, the situations below require analysis of the clinical context - something that only a physician is capable of doing. So, if in doubt, always consult a professional to interpret the results of a test.

• Difficulty breathing: An oxygen level below normal has difficulty breathing, i.e., there is not enough oxygen.
• Respiratory acidosis: When the pH is below normal and the carbon dioxide is high, the person may have pneumonia, asthma, or another complication in the respiratory system.
• Respiratory alkalosis: if the pH is high and the carbon dioxide pressure is low, it can indicate anything from emotional stress, to brain trauma, to lung disease.
• Metabolic acidosis: Low pH and bicarbonate levels can signal that the blood is too acidic. As a result, the metabolism and the kidneys can become impaired.
• Metabolic alkalosis: with pH and bicarbonate levels above normal can lead to hypokalemia (low potassium in the blood), causing chronic vomiting, cirrhosis, and heart failure.

Source: Jorge Henrique Yoscimoto Koroishi, cardiologist and coordinator of hospitalization and surgeries of the Sirius Group.