Quantitative Acid-Base Dynamics in Chronic Pulmonary Disease

SUMMARY

The defense of the extracellular pH was evaluated in 17 patients with chronic obstructive lung disease and chronic hypercapnia during superimposed acute respiratory acidosis. In group I the chronic stable state Pa_CO2-pH-HCO₃ was not defined; in groups IA and II the stable state was defined. Duration of acute acidosis in groups I and IA was 16 and 23¼ hr, respectively; in group II, 30 min.

The defense of pH in groups I and IA was greater than acute hypercapnia in normal man but less than chronic stable hypercapnia (P < 0.05). The pH in group II approached that of normal man during acute respiratory acidosis. Plasma bicarbonate concentrations paralleled the ( H⁺ ) responses. A wide confidence band based on these observations overlapped the previously established bands for acute and chronic hypercapnia.

In the clinical situation, variable Pa_CO2 exposures create variable in vivo carbon dioxide titration curves. Thus, the defense of the extracellular pH during acute respiratory acidosis superimposed upon chronic hypercapnia is related temporally to renal buffering mechanisms. Under these circumstances, prediction bands for steady state acute or stable chronic hypercapnia are not valid for the interpretation of coexisting metabolic disorders.