Patterns of pleural pressure amplitude and respiratory rate changes during therapeutic thoracentesis

BACKGROUND: Although the impact of therapeutic thoracentesis on lung function and blood gases has been evaluated in several studies, some physiological aspects of pleural fluid withdrawal remain unknown. The aim of the study was to assess the changes in pleural pressure amplitude (Ppl(ampl)) during the respiratory cycle and respiratory rate (RR) in patients undergoing pleural fluid withdrawal. METHODS: The study included 23 patients with symptomatic pleural effusion. Baseline pleural pressure curves were registered with a digital electronic manometer. Then, the registrations were repeated after the withdrawal of consecutive portions of pleural fluid (200 ml up to 1000 ml and 100 ml above 1000 ml). In all patients the pleural pressure curves were analyzed in five points, at 0, 25%, 50%, 75% and 100% of the relative volume of pleural effusion withdrawn in particular patients. RESULTS: There were 11 and 12 patients with right sided and left sided pleural effusion, respectively (14 M, 9F, median age 68, range 46–85 years). The most common cause of pleural effusion were malignancies (20 pts., 87%). The median total volume of withdrawn pleural fluid was 1800 (IQR 1500–2400) ml. After termination of pleural fluid withdrawal Ppl(ampl) increased in 22/23 patients compared to baseline. The median Ppl(ampl) increased from 3.4 (2.4–5.9) cmH(2)O to 10.7 (8.1–15.6) cmH(2)O (p < 0.0001). Three patterns of Ppl(ampl) changes were identified. Although the patterns of RR changes were more diversified, a significant increase between RR at baseline and the last measurement point was found (p = 0.0097). CONCLUSIONS: In conclusion, therapeutic thoracentesis is associated with significant changes in Ppl(ampl) during the respiratory cycle. In the vast majority of patients Ppl(ampl) increased steadily during pleural fluid withdrawal. There was also an increase in RR. The significance of these changes should be elucidated in further studies. TRIAL REGISTRATION: ClinicalTrial.gov, registration number: NCT02192138, registration date: July 1st, 2014.