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Interpreting arterial blood gases

Understanding basic physiology eases arterial blood gas analysis

  • By: Anna Fraser, Yee Ean Ong
  • Published: 20 April 2012
  • DOI: 10.1136/sbmj.e818
  • Cite this as: Student BMJ 2012;20:e818

An arterial blood gas measurement is often an important test in a critically ill patient. Many medical students flounder over the interpretation of arterial blood gas measurements, but they are not especially complicated if you understand the basic physiology and have a step by step process to interpret them. An arterial blood gas measurement provides valuable information about the blood pH and the partial pressures of arterial carbon dioxide (PaCO2) and oxygen (PaO2). Most analysers calculate serum bicarbonate (HCO3-) and the base excess. Some analysers also measure electrolytes, haemoglobin, glucose, lactate, and other analytes.

Patients who typically require an arterial blood gas measurement are those who are in respiratory failure; are critically ill or deteriorate unexpectedly—for example, because of sepsis or multiorgan failure; have uncontrolled diabetes mellitus; or have taken, or are suspected of taking, an overdose or dangerous toxin.1

You should not do an arterial blood gas measurement if

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