Ultrasonographic guidance of thoracic drainage and biopsy procedures is an attractive alternative to computerized tomography (CT) or fluoroscopic guidance. While CT scanning is the standard for overall imaging of the chest in all cases of malignancy and many nonmalignant conditions, ultrasound may be used for procedure guidance. Ultrasound guidance eliminates further radiation exposure and is often less time consuming and more comfortable for the patient. The intensivist–sonographer, who engages in thoracic interventions, must possess the cognitive and manual skills required for pleural and lung sonography; and, in the case of anterior mediastinal biopsy, must be familiar with the ultrasound anatomy of the mediastinal organs. The ability to visualize inserted hardware and to recognize and interpret reverberation artifact associated with hardware is required for all but thoracentesis and some simple biopsy procedures.
Convex-array or sector-scanning probes with frequencies between 2 and 5 MHz (typically 3.5 MHz) are most suitable for thoracic sonography and are also the most versatile for thoracic procedure guidance.1 Higher frequency transducers do have better near-field resolution at the expense of penetration depth. We do not recommend probes with a biopsy channel for thoracic interventions due to the common problem of ribcage interference with imaging. Instead, an approach combining imaging with traditional bony landmark detection, that is, finding the upper rib margin with a finder needle prior to insertion of other hardware, is generally preferred. As in general thoracic sonography, the mark on the probe is oriented cephalad and the corresponding mark on the screen is placed at the upper left of the image. Thus, the orientation of standard views, which is imaging in the longitudinal axis, is cephalad left and caudal right on the screen. However, during procedure planning and visualization of hardware, nonstandard imaging planes are routinely used.
Positioning for Procedures
Proper patient positioning is essential in interventional chest sonography. Free-flowing pleural effusions follow the gravitational gradient and collect in the most dependent part of the thoracic cavity. In the patient sitting upright, an effusion will collect in the inferior and posterior chest and is most easily accessed from a position behind the patient. The approach to positioning the critically ill patient varies with the size of the effusion, presence of obesity, number and type of support devices, and physiologic compromise, such as hemodynamic instability. Large effusions may be accessed with the patient in the supine position, which presents few problems during access. However, lateral access may be impossible in the very obese even with very large effusions. Adduction of the ipsilateral arm across the chest greatly improves lateral access and should uniformly be attempted. Posterior access may be facilitated by having the patient held in a sitting position but also by placing the patient at the very edge of the bed or even in the full lateral decubitus position. These positions require assistants to assure safety and prevent inadvertent movement of ...