RESUMEN
OBJECTIVE: To analyze the methods used in our hospital for obtaining pleural fluid to determine the acid-base balance and to evaluate the clinical repercussions of each method. METHODS: Initially we studied the methods used by physicians in our hospital to collect pleural fluid for determination of the acid-base balance. In a second phase, we performed a prospective, descriptive, comparative study with the participation of 71 patients with pleural effusions in order to compare the acid-base balance according to the technique used to obtain the fluid. RESULTS: Pleural fluid was obtained using 3 methods: a) direct extraction using a heparinized syringe (group 1); b) extraction using a 20 mL syringe with subsequent aspiration from this syringe into a heparinized syringe (group 2); and c) filling a heparinized syringe from the 20 mL syringe (group 3). The only significant differences between group 1 and groups 2 and 3 were an increase in the pleural PO2 and oxygen saturation. The difference in the mean pH between groups 1 and 2 was 0.009 (95% confidence interval: -0.39 to 0.02; P=.5) and between groups 1 and 3 was 0.007 (95% confidence interval: -0.38 to 0.023; P=.6). The correlations between findings for PO2, pH, and PCO2 obtained in the different groups were statistically significant, with values superior to .95 in the last 2 variables. CONCLUSIONS: Physicians who perform thoracentesis in our hospital use different methods for obtaining fluid to determine the pleural acid-base balance. The 3 methods analyzed show no significant differences with regard to pH or PCO2. Pleural fluid may be obtained by a single puncture with a large-volume syringe, subsequently transferring the fluid to a heparinized syringe without this significantly affecting the pH or PCO2, thus reducing the number of manipulations and the risk of complications.