Time course of acid-base status in patients hospitalized in a pulmonary department

The aim of this prospective observational study was to evaluate the time course of acid-base status of patients with respiratory failure admitted to a Pulmonary department of a University hospital. Patients with either hypoxemic or hypercapnic acute respiratory failure were included in the study. The acid base status of each patient was assessed using the physicochemical approach. In 66 consecutive patients (36 with hypoxemic and 30 with hypercapnic respiratory failure) arterial blood gases, serum electrolytes and proteins were measured upon admission and discharge in order to derive strong ion difference (SID) and gap (SIG, unmeasured anions). During hospitalization albumin (Alb) significantly decreased [ΔAlb 2 (0-5) gr/l, median (interquartile range)] and SID significantly increased [ΔSID -1 (-4-1) mEq/l]. PaCO2 significantly increased [ΔPaCO2 -5 (-7-0) mmHg] and decreased [ΔPaCO2 2 (-2-10) mmHg], respectively in patients with hypoxemic and hypercapnic respiratory failure. Compared to hypercapnic, hypoxemic group exhibited significant pathologic elevation of SIG [7 (5-9) vs. 11 (9-13) mEq/l], which remained unaltered at hospital discharge [11 (9-12) mEq/l]. In conclusion, the acid-base status of patients with respiratory failure changes significantly during their hospitalization and there are differences in the metabolic acid base disturbances depending on the type of respiratory failure. The cause of continuous pathologic elevation of unmeasured anions in patients with hypoxemic respiratory failure remains to be determined.