How to Read Arterial Blood Gases

Arterial blood gasses are a common test done to measure the acidity and gas content of the blood, primarily the oxygen and carbon dioxide levels 1. Arterial blood gas levels are typically done in pulmonology, because it can give information on lung function 1. Arterial blood gasses are measured by taking a sample of arterial blood, commonly from the radial artery, which can be accessed in the wrist 1.

Look at the acid-base balance. This can be found by looking at the pH. A pH of less than 7.35 means the blood is acidic, whereas one of more than 7.45 indicates the blood is alkalinic (the opposite of acidic).

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Look at oxygen pressure. This will be labeled "PO2." A low PO2 (below 60mm mercury) means that supplemental oxygen should be given, and a PO2 lower than 26 means the patient is near death.

Look at carbon dioxide pressure (PCO2). PCO2 is normally between 35 and 45 mm mercury. Low PCO2 means that the patient is hyperventilating (sometimes to compensate for the blood being acidic), and a low PCO2 means they are under ventilating.

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Look at bicarbonate levels, which are measured as HCO3. A low HCO3 (less than 22 millimoles per liter) can indicate that there is a metabolic condition causing the blood to be acidic, whereas a high HCO3 (greater than 26) means that there is a metabolic alkalosis issue.

Look at the base excess, which can also indicate a metabolic issue. If the base excess is negative (less than negative 3 millimoles per liter) that indicates too much acid in the blood, whereas one that is greater than 3 means that there is too little acid in the blood.