Arterial blood gas analysis is a biochemical test often done for respiratory diseases. To quickly read the blood gas analysis you need to perform the following three steps, which is commonly known as the trilogy. The first step is to look at the pH, or acidity and alkalinity. pH d1 has a normal value of 7.40. If it is less than 7.4 or greater than 7.35, the body is considered to be in acidosis, and if it is greater than 7.4 or less than 7.45, the body is considered to be in alkalosis. If it is less than 7.35, there may be compensatory acidosis, and if it is greater than 7.45, there may also be compensatory alkalosis. The second step is to look at the partial pressure of carbon dioxide. A marked increase in partial pressure of carbon dioxide and a marked decrease in pH is considered respiratory acidosis. If the partial pressure of carbon dioxide is not high and the pH is alkaline, it is considered as alkalosis. The third step is to look at the bicarbonate. If the pH decreases, the partial pressure of carbon dioxide increases, and the bicarbonate increases, then it is respiratory acidosis with metabolic alkalosis. If pH is lowered, partial pressure of carbon dioxide is lowered, and bicarbonate is elevated, or if there may be a complex, compound acid-base imbalance, further exclusion is needed based on high substitution acid. Blood gas analysis requires long-term clinical practice and repeated mapping to accurately determine the specific pathology of respiratory failure.