IS DIRECT COLLECTION OF PLEURAL FLUID INTO A HEPARINIZED SYRINGE IMPORTANT FOR DETERMINATION OF PLEURAL PH - A BRIEF REPORT

Introduction: It has long been believed that pleural fluid must be dir ectly aspirated into a heparinized syringe to obtain an accurate value . Many operators aspirate 30 to 60 mt of pleural fluid into a syringe without heparin, and then place 1 mL into a heparinized syringe from w hich the pH is determined. We postulated that this technique does not cause a clinically significant difference in pleural pH values. Method s: Patients undergoing thoracentesis in the outpatient clinic, general ward, and medical ICU were eligible. After the initial entry of the n eedle into the pleural space, a heparinized syringe was used to obtain pleural fluid for pH determination. A 60-mL syringe was then used to aspirate additional pleural fluid for biochemical analysis and culture . At the end of the procedure, a second aliquot of pleural fluid was p laced into a heparinized syringe for pH determination. A difference of 0.1 in pH was taken as clinically important. Results: Twenty-one pleu ral fluid samples were obtained from 20 patients. Pleural fluid pH det erminations were within 0.1 in all but one patient. The mean pH for th e directly collected group was 7.39 (25%: 7.35; 75%: 7.45). The mean f or the indirectly collected group was 7.41 (25%: 7.35; 75%: 1.45). The difference between the two means (0.02; 95% confidence interval, 0.03 68 to 0.00131) was statistically significant but clinically unimportan t (p = 0.037). Conclusions: Pleural fluid can be collected in a large syringe and then placed into a heparinized syringe to assess pH. This is useful information because the use of just one syringe saves time a nd reduces the risk of iatrogenic complications.