The foundation of arterial blood gas (ABG) analysis
consists 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's
pH and PCO2 are increased or decreased in the same direction,
the process is metabolic; if one is increased while the
other is decreased, the process is respiratory. In a number of
clinical situations, pulse oximetry is preferred to ABG analysis.
However, pulse oximetry may not be accurate in patients who
are profoundly anemic, hypotensive, or hypothermic. While
venous blood gas (VBG) analysis does not provide any information
about the patient's oxygenation, it can help assess
the level of acidosis or alkalosis. VBG analysis may be particularly
useful in patients with diabetic or alcoholic ketoacidosis.
(J Respir Dis. 2008;29(2):74-82)