Impact of therapeutic thoracentesis and pleural pressure changes on breathing pattern, dyspnea, lung function, and arterial blood gases

INTRODUCTION Therapeutic thoracentesis is highly effective in providing symptomatic improvement in patients with large volume pleural effusion (PE). However, some physiological effects of pleural fluid (PF) withdrawal are still not fully elucidated. OBJECTIVES The study aimed to evaluate alterations in the breathing pattern, pulmonary function, and arterial blood gases (ABG) in relation to both withdrawn PF volume and pleural pressure (P-pl) changes in patients undergoing therapeutic thoracentesis. PATIENTS AND METHODS This prospective, observational, cross-sectional study included 37 patients with large volume PE. Respiratory rate (RR), dyspnea, pulmonary function, and ABG were assessed before the thoracentesis, at the termination of the PF withdrawal and 1, 3, and 24 hours after the procedure. The volume of PF drained, P-pl, and tidal volume (TV) were monitored during the thoracentesis. RESULTS Thoracentesis resulted in a transient but significant increase in RR directly after the procedure, and a transient decrease, followed by subsequent increase in TV. There was a significant and constant increase in forced vital capacity up to 24 hours after thoracentesis (P = 0.001). Oxygen partial pressure (PaO2) significantly improved directly after PF withdrawal (P = 0.01) and returned to baseline values after 24 hours. Thoracentesis was invariably associated with a significant increase in the amplitude of P-pl (P-pl_ampl) changes during the respiratory cycle (P <0.001). CONCLUSION Therapeutic thoracentesis results in a modest improvement in pulmonary function, transient increase in PaO2 and increase in P-pl_ampl. The improvement in pulmonary function and ABG is closely related to the volume of PF drained and pleural elastance. The increase in P(pl_ampl )probably represents a more efficient work of the respiratory muscles.