Pleural manometry: technique and clinical implications.

INTRODUCTION Pleural manometry during large-volume thoracentesis can prevent the development of excessively negative pleural pressures, which have been associated with re-expansion pulmonary edema; can diagnose an unexpandable lung; and can predict pleurodesis success. We currently perform pleural manometry simultaneously with both a vertical-column water manometer with an interposed resistive element, and a hemodynamic transducer connected to a standard physiologic system. We present the technique as well as the advantages and disadvantages of both systems in measuring pleural liquid pressures. TECHNIQUE A flexible thoracentesis catheter is inserted in the most dependent portion of the pleural effusion. The water manometer consists of two lengths of IV tubing connected through a 22-gauge needle inserted into an injection terminal. The system is connected to the zeroing port of the pressure transducer, and both are carefully purged of air. The electronic system is zeroed at the level the thoracentesis catheter is introduced into the patient. Measurements are performed initially and after each 250 mL of fluid that is withdrawn. ACCURACY OF THE WATER MANOMETER: Forty consecutive patients who underwent therapeutic thoracentesis had pressure measurements. Pleural fluid removed ranged from 50 to 4,200 mL (mean, 1,445 mL). A total of 291 pressure measurements were acquired and analyzed. Mean pleural liquid pressure obtained by the water manometer had a strong positive correlation with the values obtained by a standard physiologic system (r = 0.97, p < 0.001). CONCLUSION An overdamped water manometer is a valid method to measure mean pleural liquid pressure. Coughing invalidates pressure measurements with the water manometer; however, with the electronic method, periods of quiet breathing can be identified, allowing for the measurement of pleural pressure.