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Should you routinely check pleural pressures with bedside manometry during thoracentesis?
David Feller-Kopman of Johns Hopkins says, of course: it's zero risk, zero cost, only seconds of extra time, and provides potentially useful clinical information. Specifically, one can identify people with "entrapped lung" and "trapped lung":
Identifying "Entrapped Lung" by Pleural Pressures
In people with entrapped lung, initial elastance is normal and pleural pressures steadily fall until some fluid (e.g., 1-2 L) are removed, at which time elastance falls and additional fluid removal leads to very negative pleural pressures. This is indicative of the lung failing to expand fully at the end of thoracentesis, and is most common in patients with malignant pleural effusions. It can also be seen in people with a pleural peel, lymphangitic carcinomatosis, or an endobronchial obstruction.
How can identifying entrapped lung with pleural manometry help?
- People with entrapped lung are more likely to have a failure of pleurodesis, as the lung doesn't fully expand and appose the chest wall. Identifying these people may be of benefit when considering pleurodesis and counseling about likelihood of success.
- Manometry can permit maximal fluid removal during thorcentesis by providing the physician confidence to remove large volumes, without fear of inducing re-expansion pulmonary edema (REPE). Some experienced interventional pulmonologists routinely remove as much as 3 L or more during thoracentesis, as long as pleural pressures do not become too negative (-20 cm H2O has been suggested, but this number was guessed/extrapolated from animal studies and has never been correlated with real outcomes or risks in people).
- Also, entrapped lung can explain the presence of a pneumothorax after thoracentesis as likely being due to incomplete lung re-expansion, rather than an iatrogenic complication from punctured lung parenchyma.
"Trapped Lung" on Pleural Manometry
In patients with "trapped lung," elastance is low throughout thoracentesis. Removal of small amounts of fluid (e.g., < 1 L) lead to very negative pleural pressures (e.g., -30 cm H2O) and should prompt termination of the thoracentesis, as fluid removal won't help and might harm.
Arguments Against Overreliance on Pleural Manometry During Thoracentesis
Fabien Maldonado and John J. Mullon of the Mayo Clinic acknowledge the utility of pleural manometry, but point out that (as when using any objective metric in clinical medicine) taking a view of the patient's whole clinical picture and symptoms should take precedence. There is no standard "elastance curve" that has been validated across individuals, nor is there any consensus as to a "dangerous" negative pleural pressure. Therefore, drawing conclusions from pleural manometry is still often a subjective or impressionistic endeavor by the physician.
How to Check Pleural Pressures / Manometry During Thoracentesis
For a detailed description of how to check pleural pressures (manometry) during thoracentesis, read David Feller-Kopman et al's excellent free full-text review in Chest 2009.
Feller-Kopman D. Should Pleural Manometry Be Performed Routinely During Thoracentesis? Yes. Chest 2012;141:844-845.
Maldonado F, Mullon JJ. Should Pleural Manometry Be Performed Routinely During Thoracentesis? No. Chest 2012;141:846-848.
Feller-Kopman D et al. Assessment of Pleural Pressure in the Evaluation of Pleural Effusions. Chest 2009;135:201-209.