Acid–Base Status in Circulatory Failure

To the Editor: Adrogué et al. (May 18 issue)¹ conclude that information about pH partial pressure of carbon dioxide (PCO₂), or plasma bicarbonate level that is obtained from central venous blood (from the superior vena cava) is not different from that obtained from mixed venous blood (from the pulmonary artery). Although this may be true in persons who are hemodynamically and metabolically normal or nearly normal, it may not be true in patients with preexisting renal, pulmonary, or metabolic disease. A patient with chronic obstructive pulmonary disease in whom the effect of respiratory acidosis is compensated by the…