Ionized calcium in blood: studies on patients with pulmonary disease

A new automatic ionized calcium analyser ICA 2 (Radiometer, Copenhagen, Denmark) was used for studies of ionized calcium (cCa2+) in the arterial blood of patients with a compensated respiratory acidosis due to chronic lung disease. The data for 16 patients showed an unexpectedly high level of variation in cCa2+ (range, 1.01-1.25 mmol l-1) despite the fact that there was only a small degree of variability in pH (range, 7.38-7.51). cCa2+ was not correlated with pH as has been observed in acute respiratory disturbances. A highly significant negative correlation was found between cCa2+ and base excess (BE) (r = -0.81, P less than 0.0001), and between cCa2+ and carbon dioxide tension (PCO2) (r = 0.71, P less than 0.002). These correlations differed from those reported previously in acute respiratory disturbances. CCa2+ showed a significant positive correlation with oxygen tension (PO2) (r = 0.71, P less than 0.002). It is concluded that cCa2+ in arterial blood from patients with chronic lung disease is correlated with acid-base and gas quantities in an entirely different manner to that observed in acute acid-base disturbances in normal adults.