A practical approach to arterial blood gas analysis is discussed in this section. It will provide basic principles for understanding acid-base disturbances commonly encountered in medical practice Hypoxia refers to reduced oxygen pressure in the alveolus. Hypoxemia refers to low arterial PaO2. Acidemia and alkalemia refer to the alterations in the blood pH. Stepwise approach to assess acid-base disorders is essential. Anion gap acidosis results from accumulation of acidic metabolites and is manifested by a low HCO3- and an anion gap > 12.