pneumothorax or pleural effusion from normal tissues and it identifies the level of the diaphragm as it moves with respiration Technique Any probe can be used to interrogate the lung If identifying a pneumothorax, the linear probe is appropriate because it provides the best visualization of the pleural line However, for the actual thoracentesis procedure a phased array or curvilinear probe is preferred because it will provide a wider and deeper view of the chest cavity (Fig 131.24 ) For identifying fluid in the chest, the probe should be placed in the midaxillary line or posteriorly where the intended catheter will be placed If the static technique is used, the level of the diaphragm should be marked along with the deepest pocket of intrathoracic fluid Pitfalls If using the static technique, moving the patient after the area of fluid is marked could lead to fluid shifts and inappropriate placement of the catheter or needle It is also important to identify the level of the diaphragm when diagnosing a pleural effusion to ensure that the visualized fluid is not confused with intra-abdominal free fluid