Recommendations on the Use of Ultrasound Guidance for Adult Thoracentesis: A Position Statement of the Society of Hospital Medicine

5. We recommend that ultrasound should be used to identify the chest wall, pleura, diaphragm, lung, and subdiaphragmatic organs throughout the respiratory cycle before selecting a needle insertion site.

Rationale: The use of ultrasound improves the selection of a safe needle insertion site because sites chosen without ultrasound guidance may be below the diaphragm, over solid organs,^9,19 or in locations that risk puncture of the lung.⁹ Visualization of the chest wall, diaphragm, and lung, which define the boundaries of a pleural effusion, allows the clinician to confirm the presence of a drainable pleural effusion and assess for other pathologies, such as ascites and tumor, that may be mistaken for a pleural effusion.^22,25,26 Hypoechoic lesions can represent small loculated pleural effusions but also pleural plaques, pleural masses, peripheral lung masses, or abscesses.^27,28

6. We recommend that ultrasound should be used to detect the presence or absence of an effusion and approximate the volume of pleural fluid to guide clinical decision-making.

Rationale: The presence and approximate size of pleural fluid collections are important determinants of whether thoracentesis, another procedure, or no procedure should be performed. Ultrasonography has higher sensitivity and specificity for detecting pleural effusions and better differentiates effusions from consolidations compared with chest radiography.^29-42 Ultrasound allows semiquantitative estimation of pleural fluid volume to determine whether thoracentesis should be performed.^41-45 When using ultrasound to choose a site for thoracentesis, the British Thoracic Society Pleural Disease guidelines recommend ≥10 mm of pleural fluid between the visceral and parietal pleura.¹³ Pleural effusions of <10–15 mm are considered too small to tap.^22,23 In a prospective study of 45 patients, a measurement of >9.9 cm by ultrasound between the chest wall and the “V-point,” the intersection of the diaphragm and the collapsed lung, correlated with a pleural fluid volume of >1 liter.⁴⁶ Another prospective study of 73 patients showed that a pleural effusion spanning >3 intercostal spaces by ultrasound also correlated with a pleural fluid volume of >1 liter.⁴⁷ Anticipating the volume of fluid to be removed may aid in preplanning and procurement of larger capacity drainage containers prior to starting the procedure. Lung ultrasound can also change the management if the characteristic of the effusion suggests that an invasive procedure is unsafe or another diagnostic or therapeutic option is more appropriate.³⁹ In a prospective cohort study of 189 mechanically ventilated patients, lung ultrasound guided the management in all patients with suspected effusion, leading to chest tube placement in 7 patients and thoracentesis in 34 patients.⁴⁸

7. We recommend that ultrasound should be used to detect complex sonographic features, such as septations, to guide clinical decision-making regarding the timing and method of pleural drainage.

Rationale: Pleural effusions can be broadly categorized sonographically as simple or complex. Complex effusions are further categorized as with or without septation. Simple effusions are anechoic and are often, but not invariably, transudative.^49-51 The use of sonography and computerized tomography (CT) is complementary, but features of complex pleural effusions (fibrin stranding and septations) may be better visualized by ultrasound than by CT of the thorax.⁵² Detection of complex features should prompt the consideration of pleural fluid sampling.^53,54 Exudative effusions from tuberculosis, malignancy, or other etiologies more often include debris, septations, or other complex features.^55,56 Certain features such as a swirling debris, pleural thickening, and nodularity may be more often associated with malignancy,^54,56 and advanced ultrasound techniques may be used to detect a trapped lung prior to attempting drainage of a malignant pleural effusion.⁵⁷ Two studies found complex septated pleural effusions to be invariably exudative^50,58 and drainage was unlikely to be successful without the placement of a chest tube.^50,58-60 Chest tube placement through fibrinolytic administration or video-assisted thoracoscopic surgery (VATS) may be more appropriate in the management of complex septated pleural effusions,^59-61 and expert consultation with a thoracic specialist is recommended in these cases.

8. We suggest that ultrasound can be used to measure the depth from the skin surface to the parietal pleura to help select an appropriate length needle and determine the maximum needle insertion depth.

Rationale: The distance from the skin to the parietal and visceral pleura can be measured by ultrasound to determine whether thoracentesis can be safely performed and to guide selection of an adequate length needle.³⁸ The length of needle required to penetrate the pleural space varies based on the thickness of the chest wall. Percussion of the chest wall is limited when there is more than 6 cm of subcutaneous tissue,⁶² making physical examination in obese patients unreliable for selecting an appropriate site or needle length for thoracentesis. Ultrasound allows visualization of deep soft tissues, well beyond the limits of percussion, and allows an accurate measurement of the chest wall.⁶³