Arterial blood gases (ABG’s) represent the ‘gold standard’ method for acquiring patients’ acid base status. Arterial blood sampling potentially can cause spasm, intraluminal clotting, bleeding, haematoma formation and transient obstruction of blood flow. Patients often report this procedure as a painful and unpleasant experience.

Earlobe blood gas (EBG) sampling is a useful alternative to ABG’s. Properly obtained capillary blood samples accurately reflect arterial blood gas measures of PO₂, PCO₂ and pH.

The British Thoracic Society maintain that for most patients who require blood gas sampling, either ABGs or arterialised EBGs may be used to obtain an accurate measure of pH and partial pressure of carbon dioxide (PaC0₂). However, the partial pressure of oxygen (Pa0₂) is less accurate in earlobe blood gas samples especially when on high flow oxygen (FiO₂ >20kPa) (it underestimates the Pa0₂ by 0.5–1 kilopascal (kPa). Therefore, oximetry (oxygen saturations) should be monitored carefully if earlobe blood gas specimens are used and an ABG should be taken if possible if there is any concern about the accuracy of a EBG.

The purpose of this guideline is to outline the minimum standard for Blood Gas Sampling – capillary and arterial for Respiratory Practitioners in primary, community and secondary care settings in Wales.