Jennifer L. Isenhour, MD

The foundation of arterial blood gas (ABG) analysisconsists of determining whether the patient has acidosis or alkalosis;whether it is a respiratory or metabolic process; and,if respiratory, whether it is a pure respiratory process. If the patient'spH and PCO2 are increased or decreased in the same direction,the process is metabolic; if one is increased while theother is decreased, the process is respiratory. In a number ofclinical situations, pulse oximetry is preferred to ABG analysis.However, pulse oximetry may not be accurate in patients whoare profoundly anemic, hypotensive, or hypothermic. Whilevenous blood gas (VBG) analysis does not provide any informationabout the patient's oxygenation, it can help assessthe level of acidosis or alkalosis. VBG analysis may be particularlyuseful in patients with diabetic or alcoholic ketoacidosis.(J Respir Dis. 2008;29(2):74-82)