First of all, be sure what you are assessing. At first glance, pericardial and pleural effusions can appear similar on echo, but there are important distinguishing features. Use 2D echo in the parasternal long axis view to assess where the effusion lies in relation to the descending aorta. A pericardial effusion will extend just up to the gap in between the left atrium (LA) and the front of the descending aorta (Fig. 25.2). In contrast, a pleural effusion extends behind the aorta and around the LA (Fig. 25.3). However, bear in mind that some patients will have coexistent pericardial and pleural effusions.

Use 2D echo to assess the extent of the effusion – is it circumferential, filling the entire pericardium, or localized? If localized, record where the effusion lies in relation to the atria and/or ventricles. Very localized effusions can sometimes be difficult to spot – for instance, if they lie within the oblique sinus – and may only be evident through the compression of adjacent structures (e.g. atria or pulmonary veins). Bear in mind
that the patient’s position may affect the distribution of the pericardial effusion – for instance, the effusion may localize posteriorly in a supine patient.

Assess the size of the effusion from several different views using 2D and/or M-mode echo. Record both the depth of the effusion (in cm) and the location where each measurement was taken. The size of an effusion can be gauged by its depth (Table 25.2). It is important to note that effusion size is not the same as clinical severity – small effusions that accumulate quickly can have a greater haemodynamic effect than large effusions that accumulate slowly.

Pericardial effusions can contain a fluid transudate or exudate, blood or pus. It can be difficult to distinguish between these on echo, and the pericardial fluid will usually look echolucent regardless of its nature. However, there may be strands of fibrin visible within the fluid, and these commonly adhere to the outside of the heart. Sometimes masses may be visible within the pericardium (Fig. 25.4). Describe the appearance of any strands or masses, including their size and location.

Once you have assessed the appearances of the pericardial effusion, move on to assess its haemodynamic effects to look for evidence that would support a clinical diagnosis of cardiac tamponade (see below).

Use 2D and M-mode echo to confirm the presence of a pericardial effusion and to assess its extent as described above. Look carefully for signs of chamber collapse during diastole. As pressure within the pericardium rises, the right-sided chambers collapse (at least in part) during diastole (Fig. 25.5). The first chamber to be affected is the
right atrium (RA), which is seen to collapse during atrial systole, followed by the right ventricle (beginning with the right ventricular outflow tract, RVOT). Rarely, LA

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