The ABG is a panel of laboratory values commonly measured in patients to monitor acid-base disturbances. The first thing you’ll see when you see an ABG is a set of three lines. Between these three lines, you’ll see four different numerical values that are usually presented in a linear format. They’re placed from left-to-right as follows: pH is the first on the left, with the partial pressure of CO2 next as the second value. The third value is the partial pressure of O2. The last and final value is the partial pressure of HCO3 and it’s all the way on the right.