Safe and effective bedside thoracentesis: A review of the evidence for practicing clinicians

Measurement of intrapleural pressure using a water manometer during thoracentesis may minimize REPE by terminating fluid drainage when intrapleural pressure begins to drop rapidly.^50,51 A cutoff of -20 cm H₂O has been cited repeatedly as safe since being suggested by Light in 1980, but this is based on animal models.^50,52 In 1 prospective study of 185 thoracenteses in which manometry was performed, 15% of patients had intrapleural pressure drop to less than -20 cm H₂O (at which point the procedure was terminated) but suffered no REPE.⁵⁰

Manometry is valuable in the identification of an unexpandable or trapped lung when pleural pressures drop rapidly with only minimal fluid volume removal.^47,53 Other findings correlated with an unexpandable lung include a negative opening pressure⁴⁷ and large fluctuations in pressure during the respiratory cycle.⁵⁴

While development of symptoms (eg, chest pain, cough, or dyspnea) is often used as a surrogate, the correlation between intrapleural pressure and patient symptoms is inconsistent and not a reliable proxy.⁵⁵ One study found that 22% of patients with chest pain during thoracentesis had intrapleural pressures lower than -20 cm H₂O compared with 8.6% of asymptomatic patients,⁵⁶ but it is unclear if the association is causal.

Thoracentesis is often performed for symptomatic relief and removal of large fluid volume. However, it remains common to halt fluid removal after 1.5 L, a threshold endorsed by BTS.¹⁹ While some investigators have suggested that removal of 2 L or more of pleural fluid does not compromise safety,^57,58 a 4- to 5-fold rise in the risk of pneumothorax was noted in 2 studies.^20,59 when more than 1.5 L of fluid was removed. The majority of these may be related to pneumothorax ex vacuo, a condition in which fluid is drained from the chest, but the lung is unable to expand and fill the space (eg, “trapped lung”), resulting in a persistent pneumothorax. This condition generally does not require treatment.⁶⁰ When manometry is employed at 200-mL intervals with termination at an intrapleural pressure of less than 20 mm H₂O, drainage of 3 L or more has been reported with low rates of pneumothorax and very low rates of REPE.^50,51 However, whether this is cause and effect is unknown because REPE is rare, and more work is needed to determine the role of manometry for its prevention.

POSTPROCEDURAL CONSIDERATIONS

Postprocedure Imaging

Performing an upright CXR following thoracentesis is a practice that remains routinely done by many practitioners to monitor for complications. Such imaging was also endorsed by the American Thoracic Society guidelines.⁶¹ However, more recent data question the utility of this practice. Multiple studies have confirmed that post-thoracentesis CXR is unnecessary unless clinical suspicion for pneumothorax or REPE is present.^36,58,62,63 The BTS guidelines also advocate this approach.¹⁹ Interestingly, a potentially more effective way to screen for postprocedure complications is through bedside US, which has been shown to be more sensitive than CXR in detecting pneumothorax.⁶⁴ In 1 study of 185 patients, bedside US demonstrated a sensitivity of 88% and a specificity of 97% for diagnosing pneumothorax in patients with adequate quality scans, with positive and negative likelihood ratios of 55 and 0.17, respectively.⁶⁵

Thoracentesis remains a core procedural skill for hospitalists, critical care physicians, and emergency physicians. It is the foundational component when investigating and treating pleural effusions. When the most current training, techniques, and technology are used, data suggest this procedure is safe to perform at the bedside. Our review highlights these strategies and evaluates which aspects might be most applicable to clinical practice.

Our findings have several implications for those who perform this procedure. First, appropriate training is central to procedural safety, and both simulation and direct observation by procedural experts have been shown by multiple investigators to improve knowledge and skill. This training should integrate the use of US in performing a focused thoracic exam.

Second, recommendations regarding coagulopathy and a “safe cutoff” of an INR less than 1.5 or platelets greater than 50,000/µL had limited evidentiary support. Rather, multiple studies suggest no difference in bleeding risk following thoracentesis with an INR as high as 3.0 and platelets greater than 25,000/µL. Furthermore, prophylactic transfusion with fresh frozen plasma or platelets before thoracentesis did not alter bleeding risk and exposes patients to transfusion complications. Thus, routine use of this practice can no longer be recommended. Third, further research is needed to understand the bleeding risk for patients on antiplatelet medications, heparin products, and also direct oral anticoagulants, given the growing popularity in their use and the potential consequences of even temporary cessation. Regarding patients on mechanical ventilation, thoracentesis demonstrated no difference in complication rates vs. the general population, and its performance in this population is encouraged when clinically indicated.

Intraprocedural considerations include the use of bedside US. Due to multiple benefits including effusion characterization, puncture site localization, and significantly lower rates of pneumothorax, the standard of care should be to perform thoracentesis with US guidance. Both use of US to mark an effusion immediately prior to puncture or in real time during needle insertion demonstrated benefit; however, it is unclear if 1 method is superior because no direct comparison studies were found. Further work is needed to investigate this potential.

Our review suggests that the location and course of the ICA is variable, especially near the midline, in the elderly, and in higher intercostal spaces, leaving it vulnerable to laceration. We recommend physicians only attempt thoracentesis at least 6 cm lateral to the midline due to ICA tortuosity and, ideally, 12 cm lateral, to avoid the presence of collaterals. Although only 2 small-scale studies were found pertaining to the use of US in identifying the ICA, we encourage physicians to consider learning how to screen for its presence as a part of their routine thoracic US exam in the area underlying the planned puncture site.

Manometry is beneficial because it can diagnose a nonexpandable lung and allows for pleural pressure monitoring.^52,53 A simple U-shaped manometer can be constructed from intravenous tubing included in most thoracentesis kits, which adds little to overall procedure time. While low rates of REPE have been observed when terminating thoracentesis if pressures drop below -20 cm H₂O or chest pain develops, neither measure appears to have reliable predictive value, limiting clinical utility. Further work is required to determine if a “safe pressure cutoff” exists. In general, we recommend the use of manometry when a nonexpandable (trapped) lung is suspected, because large drops in intrapleural pressure, a negative opening pressure, and respiratory variation can help confirm the diagnosis and avoid pneumothorax ex vacuo or unnecessary procedures in the future. As this condition appears to be more common in the setting of larger effusions, use of manometry when large-volume thoracenteses are planned is also reasonable.

Postprocedurally, routine imaging after thoracentesis is not recommended unless there is objective concern for complication. When indicated, bedside US is better positioned for this role compared with CXR, because it is more sensitive in detecting pneumothorax, provides instantaneous results, and avoids radiation exposure.

Our review has limitations. First, we searched only for articles between defined time periods, restricted our search to a single database, and excluded non-English articles. This has the potential to introduce selection bias, as nonprimary articles that fall within our time restrictions may cite older studies that are outside our search range. To minimize this effect, we performed a critical review of all included studies, especially nonprimary articles. Second, despite the focus of our search strategy to identify any articles related to patient safety and adverse events, we cannot guarantee that all relevant articles for any particular complication or risk factor were captured given the lack of more specific search terms. Third, although we performed a systematic search of the literature, we did not perform a formal systematic review or formally grade included studies. As the goal of our review was to categorize and operationalize clinical aspects, this approach was necessary, and we acknowledge that the quality of studies is variable. Lastly, we aimed to generate clinical recommendations for physicians performing thoracentesis at the bedside; others reviewing this literature may find or emphasize different aspects relevant to practice outside this setting.

In conclusion, evaluation and treatment of pleural effusions with bedside thoracentesis is an important skill for physicians of many disciplines. The evidence presented in this review will help inform the process and ensure patient safety. Physicians should consider incorporating these recommendations into their practice.