Ultrasound Evaluation of Hemidiaphragm Function Following Thoracentesis: A Study on Mechanisms of Dyspnea Related to Pleural Effusion.

Background: Dyspnea is the major symptom caused by pleural effusion. The pathophysiological pathways leading to dyspnea are poorly understood. Dysfunction of respiratory mechanics may be a factor. We aimed to study the change in diaphragmatic function following thoracentesis.

Methods: Patients undergoing thoracentesis at a highly specialized pleural center, underwent ultrasound evaluation of hemidiaphragm movement, before and after thoracentesis was performed. The change was compared to the reduction of dyspnea measured at the modified Borg scale.

Results: Thirty-two patients were included. Dyspnea was reduced from 5.01 [95% confidence interval (CI): 4.12-6.04] to 2.6 (95% CI: 1.87-3.4, P<0.0001). Low hemidiaphragmatic movement before thoracentesis on the side of pleural effusion was improved by 17.4 cm (95% CI: 13.04-21.08), equalizing movement to the side without pleural effusion. On average, 1283 mL (SD: 469) fluid was drained. Multiple linear regression analysis showed that prethoracentesis ultrasound evaluation of hemidiaphragmatic function was correlated with successful thoracentesis.

Conclusion: Hemidiaphragm function is reduced on the side of pleural effusion, and thoracentesis restores function. Improvement in diaphragm movement is related to a reduction in dyspnea.