Choice of blood sample for blood gas analysis

Venous blood is an acceptable alternative to arterial blood for estimation of bicarbonate by blood gas analysis, according to the results of a recently published Australian study. Over a six-month study period, clinicians at the Emergency Department of Western Hospital in Melbourne simultaneously sampled venous and arterial blood from 246 patients, whose clinical condition warranted blood gas analysis. 

This study population were suffering either acute respiratory disease (195 patients) or suspected metabolic disturbance (51 patients). Blood gas analysis of arterial samples revealed that the bicarbonate concentration for the total study group ranged from 1.2 to 50.7 mmol/L with a mean of 24.9 mmol/L. 

Of the 246 patients, 58 had an arterial bicarbonate result below the laboratory reference range and 34 had a result above the range. On average, arterial blood bicarbonate was 1.2 mmol/L lower than venous blood bicarbonate; the 95% limits of agreement ranged from –2.73 mmol/L to +5.13 mmol/L. 

The authors conclude that the small difference between arterial and venous blood bicarbonate concentration, revealed by their study, is of no clinical significance and that it is therefore acceptable to use venous blood for bicarbonate estimation. 

In the discussion section the authors cite previous work suggesting that venous blood is an acceptable alternative to arterial blood for measurement of pH and argue the case for the use of venous rather than arterial blood gas analysis in the investigation of patients suspected of suffering a metabolic disorder.