Arterial blood gas analysis has become an essential skill for all healthcare practitioners. It provides important information with regard to adequacy of ventilation, oxygen delivery to the tissues and acid-base balance. Although each patient's clinical presentation will be judged individually, situations that warrant analysis of a blood gas sample include respiratory compromise, post-cardiorespiratory arrest, evaluation of interventions such as oxygen therapy, respiratory support and as a baseline before surgery. This article reviews the different parameters that are measured by various machines, with a focus on basic measurement of arterial blood gases. These include partial pressure of carbon dioxide in arterial blood (PaCO(2)), partial pressure of oxygen in arterial blood (PaO(2)), bicarbonate levels (HC0(3)(-)) in arterial blood and base excess/deficit. The physiology of acid-base balance is reviewed and the causes and presentation of the four acid-base disturbances is described. A systematic method to aid arterial blood interpretation is identified, together with discussion regarding the importance of interpreting PaO(2) readings in relation to the amount of inspired oxygen a patient is receiving (FiO(2)), the practice of temperate correction and the relationship between standardized and actual bicarbonate readings.