Suction pressures generated during thoracentesis using wall suction-based automated drainage: an in vitro and in vivo analysis

Equipoise exists regarding the optimal method to drain pleural fluid during thoracentesis. While several institutions use wall-based automated suction, others point to the risk of excessively high suction pressures and therefore elevated barotrauma risk as a reason to avoid it. We first performed in vitro experiments involving drainage of a 1-liter saline bag using standard thoracentesis apparatus, a digital manometer, and either manual drainage (using a 60 mL syringe) or automated drainage (using wall suction at the maximum setting). The proceduralist was blinded to measurements during manual aspiration. Separately, in a clinical setting involving consecutive hospitalized adults undergoing thoracentesis, dynamic suction pressures were similarly measured during automated drainage. Total aspirated volume, time-to-evacuation, patient discomfort, and complications were also recorded. In vitro experiments showed that compared to manual aspiration, automated drainage using wall suction resulted in shorter average time-to-evacuation (230 sec vs. 365 sec), lower suction pressures (average maximum: -361±4.5 cmH2O vs. -496±5.1 cmH2O, p<0.0001), and less pressure variation (95% of values within a 20 cmH2O range vs. swings between 0 and -500 cmH2O). Twenty hospitalized adults undergoing thoracentesis via automated drainage (mean aspirated volume: 1649.5±685.5 mL) experienced similar suction pressures to those measured in in vitro experiments using automated drainage (average maximum: -350±59.2 cmH2O) and limited pressure variations (mean interquartile range: 19.3 cmH2O). There were no complications, including pneumothorax, hemothorax, or re-expansion pulmonary edema. Thoracentesis using automated wall suction does not generate excessively high suction pressures and reduces pressure swings. It appears safe and effective and may reduce the time-to-evacuation of a pleural effusion.