Ultrasound-based Diagnosis & management
This section will review the use of ultrasound for guidance of pleural effusion drainage. We will review a step-wise process to explore 1. ultrasound-based diagnosis of a pleural effusion 2. common pathologies that may masquerade as a pleural effusion 3. ultrasound guided-quantification and 4. ultrasound-based procedural guidance. Although we have selected a number of pleural devices that are available in the Edmonton zone, the essentials of this procedure remain the same.
For the sake of simplicity, this page will not review the differential diagnosis, decision to whether a patient requires diagnostic or therapeutic drainage, or adjunctive imaging (e.g. CT for pleural enhancement in empyema).
Key references for this approach are at the end of this page.
a Step-wise approach
Step 1: Recognize a pleural effusion on ultrasound
Recognize a pleural effusion
A pleural effusion is characterized by a black (anechoic) space surrounded by clear margins including 1. chest wall, 2. diaphragm and corresponding sub-diaphragmatic viscera, 3. spine (far field) and 4. lung (often compressed). This video clip has been acquired with the patient in the semi-recumbent position.
Acknowledge the patient position
A pleural effusion is traditionally imaged in the coronal plane in a patient sitting or semi-recumbent (As shown in the previous clip). If a patient is laying down (supine) the probe can also be used to acquire a transverse or axial image as displayed screen left. Given that the lung itself may be buoyant atop the pleural fluid, this approach may yield a clearer perspective of the volume of the effusion.
Step 2: Rule out false positives
False positive pleural effusions
In this clip, we can see fluid above and below the diaphragm. It is absolutely essential to ensure you can identify *all* structures on the screen. The free fluid below the diaphragm in this case could be incorrectly identified as a pleural effusion. Note how the spine is also visible ("spine sign") above and below the diaphragm as the fluid provides an "acoustic window".
False positive pleural effusions
In this clip, we can see a dense structure with mixed echogenicity above the diaphragm on the left of the image. This is consolidated lung, which is clearly anatomically distinct from a pleural effusion.
Step 3: Consider ultrasound-based (gross) quantification and characterization of fluid
Typically transudative effusions are anechoic (mostly black). Exudative effusions are often hypo-echoic, with swirling mixed densities or even loculations. Ultimately, determination requires sampling and biochemical analysis. This clip demonstrates multiple strands concerning for an organized complex effusion.
Quantification of a pleural effusion
This video tutorial describes the basics in understanding gross quantification of a pleural effusion. Please note that loculated effusions are considerably more difficult to quantify and is more accurate with assessment by CT.
Step 4: Perform ultrasound-guided drainage
Site-selection for drainage
You can see in this clip the diaphragm is just barely visible below the white dotted line. We would recommend moving at least one interspace above (yellow dotted line), permitting the anechoic space is still visible. Once you have selected a "safe" site with ample anechoic space, above the diaphragm, we suggest you mark the spot with a marker or blunt plastic cannula.
Ensure no underlying vessels
Typically the safest and recommended spot to target is directly above the rib (cephalad) to minimize hitting the neurovascular bundle. Occasionally, vessels can be aberrant and traverse across the intercostal space. A linear probe can be used to rule out vascular aberrancy as as shown in the 2D + color Doppler clip.
Static vs dynamic guidance of procedures
Dynamic guidance refers to directly visualizing a needle as it traverses a tissue. This technique is commonly used in vascular access. Static guidance refers to identification and localization of a structure for "safe" (blind) puncture. Because of the complex nature of the intercostal space, we advocate for a static-guidance based technique. Prior to puncture, we recommend visualizing the space in two orthogonal planes to ensure a safe distance from visceral structures. The use of calipers can be helpful to provide you with information regarding depth of insertion required and depth of nearest visceral structures.
Fuhrman pigtail catheter
The Cook Medical website has a useful video to understand insertion of the Fuhrman (8.5 Fr) pigtail catheter. This catheter is often used for thoracic, pericardial and abdominal drainage. Insertion is performed via the traditional Seldinger technique.
Thal-Quick percutaneous Chest tube
The Cook Medical website also has a useful video to understand insertion of the Thal-Quick percutaneous chest tube. This catheter is used explicitly for thoracic drinage.. Insertion is performed via the traditional Seldinger technique.
This video by "carefusion" describes the use of the Safe-T-Centesis thoracic drainage system.
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Brogi, E., Gargani, L., Bignami, E., Barbariol, F., Marra, A., Forfori, F., & Vetrugno, L. (2017). Thoracic ultrasound for pleural effusion in the intensive care unit: A narrative review from diagnosis to treatment. Critical Care, 21(1), 1–11. https://doi.org/10.1186/s13054-017-1897-5
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