It includes pH, PCO2 and HCO3. Notice that the upper part of the map contains values that indicate an alkalosis, the lower part acidosis and the middle part normal values.
These three elements have a fixed relationship (the H-H Equation) to each other. If you know any two of these values you can always calculate the third. Blood gas analyzers actually measure CO2 and pH. HCO3 is then calculated from the first two values.

pH is the value that tells us how acidic or basic our blood is. It is an abreviation for potenz or "power" of hydrogen. Hydrogen is present in minute amounts in blood (about 0.00000008 mEq/L) and is quantified in "pH units" which increase as the H concentration goes down and decrease as the H concentration goes up. The lower the pH, the higher the concentration of H and the more acidic the blood is. The higher the pH, the lower the concentration of H and the more basic (or less acidic) the blood is. Normal pH is 7.40 with a normal range from 7.35 to 7.45. Clinically, pH values as low as 6.80 or as high as 7.80 may be seen for short periods of time.

PCO2 is the value that tells us how much breathing we are doing. It means pressure of carbon dioxide gas in breathing air or dissolved in a liquid like blood. It is measured in millimeters of mercury (mmHg). The respiratory system excretes CO2 and can quickly lower or raise the CO2 as in hyper- and hypo- ventilation. Less breathing means more CO2, more acid and a lower pH. More breathing means less CO2, less acid and a higher pH. Normal CO2 is 40 with a normal range from 35 to 45 mmHg. Clinically, CO2 may go as low as 5 mmHg or as high as 100 mmHg (or more).

HCO3 is the value, measured in milliequivalents (mEq), that tells us how much bicarbonate ion is dissolved in blood. It is a "buffer" (a substance that combines with acid and decreases its ability to lower pH). The kidneys help control pH by excreting or retaining HCO3. There are also many non-renal causes of changes in HCO3 like keto-acidosis, lactic acidosis and NG suction, but kidneys are the main controllers of HCO3. More HCO3 means less acid and a higher pH. Less HCO3 means more acid and a lower pH. Normal HCO3 is 24 mEq with a normal range from 22 to 26 mEq. Clinically, HCO3 may go as low as 5 and as high as 60 mEq.