Interpretation of arterial blood gases

Arterial blood gas analysis is a frequently used and extremely useful clinical tool. Doctors of all levels understand the results to varying degrees. This article aims to explain some of the more important points and thus help with interpretation of results. Not all of the results produced by a blood gas analyser are measured; the machine calculates some itself. The three things the machine actually measures are the pH of the blood and the partial pressures of both oxygen and carbon dioxide. Doctors within the specialty often run high-dependency units and therefore it is important for surgeons to be able to understand and act on abnormal results. One of the most commonly held misconceptions is the need to withdraw supplemental oxygen in order to establish if a patient is hypoxic. This is not necessary and the reasons are detailed in this short article. Abnormalities in acid–base disturbance and the concepts of buffering, compensation and the effects of altitude are also discussed. The final part of this article is a stepwise guide to interpretation of blood gases.