Sampling for analysing blood gas pressures

Interestingly, as many patients expressed no preference between arterial puncture under local anaesthesia and ear lobe sampling as expressed a preference for ear lobe sampling. 1 Repeated "arterialised" venous samples may be obtained from a cannula in a dorsal hand vein: for partial pressure of carbon dioxide the agreement with arterial values is generally within 0.13-0.26 kPa. 3 I have found, however, that even in the presence of a modest alkalosis causing vasoconstriction (pH about 7.4-7.5) this difference increased to 0.53 kPa (unpublished observations).