Chapter 11 Intensive Care Unit

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CHAPTER 11 • Intensive Care Unit Imaging

patients upon arrival in the ICU. The frequency with which radiographs are necessary after stabiliza- tion is much more controversial. General agreement exists that CXRs should be obtained promptly after invasive procedures such as endotracheal (ET) intu- bation, feeding tube placement, transvenous pace- maker insertion, thoracentesis, pleural biopsy, and central vascular catheter placement to ensure proper tube or catheter position and exclude complica- tions. Likewise, a film should probably be obtained routinely after transbronchial biopsy, although the need for such a study in the nonintubated patient is debated. In all but emergency situations, a CXR should follow failed attempts at catheterization via the subclavian route before contralateral placement is attempted. Although many ICUs continue to routinely obtain daily or even more frequent radiographs in patients with cardiopulmonary disease or dysfunc- tion, regularly scheduled films are not necessary in all patients. Despite data indicating that a quarter to two thirds of routine ICU CXRs demonstrate an abnormality or minor change, many of these findings are nonacute or inconsequential. Most important developments are signaled by clinically suggestive signs or careful examination of the patient before obtaining the radiograph. Prospective study indi- cates that fewer than 10% of films demonstrate a new significant finding, and only a fraction of these are not anticipated by clinical examination. A reason- able compromise position is to obtain daily “routine”

radiographs on mechanically ventilated patients who have hemodynamic or respiratory instability. The need for additional films should be dictated by changes in the patient’s clinical condition and by the performance of procedures. In the stable, mechani- cally ventilated patient, especially those with a tracheostomy, studies can safely be obtained less frequently. Obviously, deterioration should prompt reevaluation. Because up to 25% of ET tubes are initially posi- tioned suboptimally, radiographic confirmation of tube location is crucial; positioning the ET tube in the right main bronchus often results in right upper lobe or left lung atelectasis. (Left main intubations are uncommon because the left main bronchus is smaller and angulates sharply from the tracheal axis.) Conversely, if the tube tip lies too high in the trachea (above the level of the clavicles), unin- tended extubation is likely. When the head is in a neutral position, the tip of the ET tube should rest in the midtrachea, approximately 5 cm above the carina. In adult patients, the T6 vertebral level is a good estimate of carinal position if it cannot be directly visualized (Fig. 11-3). The carina is usually located just inferior to the level of the aortic arch. (Another method to locate an unseen carina uses the intersection of the midline of the trachea with a Placement of Tubes and Catheters Tracheal Tube Position

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FIGURE 11-3.  Location of the main carina on the frontal film. The separation between the right and left main bronchi ( arrow ) almost invariably occurs at the level of the 6 and 7 posterior ribs, directionally “southwest” of the aortic knob.