Comparing Pleural Fluid Removal Volume and Oxygenation Change in Therapeutic Thoracentesis: Is There a Relationship?

Background: During therapeutic thoracentesis (TT), pleural fluid is typically drained to completion. Fluid removal improves oxygenation, and the amount of fluid removed is directly associated with the risk of serious complications. A relationship between the amount of fluid removed during TT and the change in oxygenation has not been found in the literature. A direct relationship was hypothesized in this study. Differences in the change in oxygenation between sexes, age, and pre-procedure oxygen support were secondarily hypothesized. This information would assist in the guidance of future TT protocols. Methods: Subjects of this retrospective cohort study were males and females aged 26-74 years. Of the 166 patients who underwent inpatient TT between February 4, 2020, and December 10, 2022, at Berkshire Medical Center (BMC), 16 met the inclusion criteria. They were identified using CPT codes in the electronic medical record (EMR). Demographics, amount of fluid removed, and type of oxygen support were recorded. Pre and post-TT arterial oxygen partial pressure (PaO2) and fraction of inspired oxygen (FiO2) values were collected to calculate the P/F, a metric for oxygenation status. T-test and correlation coefficient were calculated to analyze the change in the P/F ratio versus the amount of pleural fluid removed. Correlation coefficients or ANOVA were calculated to compare oxygenation changes to sex, age, and supplemental oxygen types. Results: There was no statistical significance (p=0.87) in the linear relationship between the amount of pleural fluid drained (mean=660 mL, range=150-1500 mL) and the change in oxygenation (mean=162, range=34-300). There were no statistically significant differences in oxygenation changes between sex (p=0.60), age (p=0.81), or types of oxygen support pre-procedure (p=0.07). There was a statistically significant difference in pre and post-procedure P/F ratio (p<0.001). Discussion: We found a statistically significant change in oxygenation before and after TT, with no evidence of a direct relationship between amount of fluid removed and improvement in oxygenation. There were no complications when removing up to 1500 mL of fluid. A protocol that halts pleural fluid drainage once it is complete or when the amount removed reaches 1500 mL, whichever occurs first, may be optimal.