Radiography for the Critical Care Patient

Chapter 5 Radiography for the Critical Care Patient

Introduction of the picture archiving and communication system (PACS) and advances in imaging technology have revolutionized intensive care radiology. PACS has significantly improved the quality of images, accessibility, delivery, and reporting time. The development of multidetector-row computed tomography (CT) scanners with very rapid acquisition times enables even dyspneic patients to be successfully imaged. CT imaging provides more accurate assessment of disease than the supine radiograph and frequently reveals unsuspected pathology. With the introduction of image-guided interventional procedures, the radiologist has become an increasingly active member of the intensive care patient’s clinical team for diagnostic and therapeutic purposes.

The interpretation of the chest radiograph of the intensive care patient is a challenging exercise. A wide spectrum of pulmonary and pleural abnormalities may occur, and their radiographic appearances are complicated by several coexisting pathologies. Unraveling the various components is hindered by the supine projection of most radiographs, the variability of serial radiographs due to technique, and the multitude of tubes, lines, and other devices partially obscuring the underlying lungs.

For a safe and logical approach, the radiologist should first determine the nature and location of all the support devices, such as tubes and lines (Table 5-1). Incorrect positioning is an important cause of morbidity. A systematic review of the lungs, pleura, and mediastinum ensures that all important observations are made. Interpretation may be difficult, because the radiographic features are often nonspecific, and it is therefore important to have as much clinical information as possible and the aid of prior radiographs. Additional radiographic studies, such as decubitus views, ultrasound, or CT, often help to clarify a difficult interpretation or a suspected clinical problem.

Table 5-1 Correct Positioning for Tubes and Lines

Tube or Line Location
Endotracheal tube 5 to 7 cm above the carina
Nasogastric tube Side holes or tip below the left hemidiaphragm in the stomach
Central venous pressure catheter Superior vena cava
Pulmonary artery line Pulmonary artery within 2 cm of the hilum
Intra-aortic counterpulsation balloon catheter Just below the superior aortic knob contour
Cardiac pacemaker (right ventricular lead) Posteroanterior view: projected over the cardiac apex; lateral view: lies anterior and inferior (behind sternum)
Automatic implantable cardioverter-defibrillator Proximal lead: superior vena cava; distal lead: right ventricle; patch: left chest wall or on pericardial surface
Pleural drainage tubes Midaxillary, sixth to eighth interspace directed anterosuperiorly (pneumonectomy) or directed posteroinferiorly (effusion)


Endotracheal Tube

Malposition occurs in about 15% of placements, with emergency intubation having the highest complication rates. Physical examination is an unreliable guide to correct tube location, and a chest radiograph is required for confirmation. Correct placement of the endotracheal tube can be determined by the location of the tube tip relative to the carina. Ideally, the tip should be within 5 to 7 cm of the carina, with the head in the neutral position (i.e., inferior border of the mandible projected over the C5 and C6 vertebra). During flexion and extension of the cervical spine, the tip of the endotracheal tube may vary by a distance of 2 cm. The endotracheal tube should be at least 3 cm distal to the cords. A location that is too high may result in inadvertent extubation or may damage to the vocal cords. A position that is too low results in endobronchial intubation, occurring on the right more frequently than the left (Fig. 5-1). This may result in overinflation and possibly pneumothorax on the intubated side and atelectasis of the opposite lung.

Esophageal intubation may be recognized by the margins of the endotracheal tube lying lateral to the tracheal air column and gaseous gastric distention. A right posterior oblique chest radiograph displaces the trachea to the right of the esophagus and allows recognition of the esophageal intubation (Fig. 5-2). The optimal width of the tube should be one half to two thirds of the width of the tracheal lumen, and the inflated cuff should not distend the tracheal wall. After a tracheostomy, the tube tip is ideally situated between one half and two thirds of the distance from the stoma to the carina. The width of the tube should be approximately two thirds of the width of the trachea, and the tip should not be wedged against the tracheal wall.

Tracheal laceration due to the endotracheal tube may result in pneumomediastinum, pneumothorax, or subcutaneous emphysema, singly or in combination. The tip of the endotracheal tube may be deviated to the right of the tracheal lumen. Inflation of the cuff by more than 2.8 cm (normal diameter is 2 to 2.5 cm) can cause tracheal laceration, as can positioning of the lower margin of the cuff at less than 1.3 cm from the tube tip (normal distance is 2.5 cm). Tracheal stenosis may occur at the tracheostomy stoma or at the endotracheal tube tip (Fig. 5-3). At the stoma, stenosis is caused by the formation of granulation tissue or by fibrosis with destruction of the tracheal cartilage. At the cuff site, stenosis results from a circumferential scar that is 1 to 4 cm long and that is typically 1.5 cm below the stoma.

Nasogastric Tube and Feeding Tube

Incorrect positioning of a nasogastric tube is the most common tube complication (Fig. 5-4). Radiographic confirmation of correct positioning is mandatory before suction or feedings begin. The tube may be seen lodged within the tracheobronchial tree or coiled with the larynx or pharynx. More commonly, the tube lies too high in the esophagus above the gastroesophageal junction (Fig. 5-5). On many tubes, the side holes extend for a distance of 10 cm from the tip, and at least 10 cm of tubing should be seen within the stomach. Side holes above the gastroesophageal junction place the patient at risk for aspiration of gastric contents. Feeding tubes should be positioned in the duodenum to reduce the risk of gastroesophageal reflux of feedings and aspiration. The enteroflex tube is inserted over a wire, and perforation of the esophagus or stomach is a potential hazard. The stiff stylet may inadvertently enter the lung and cause a pneumothorax (Fig. 5-6). Complications associated with the nasogastric and feeding tubes are listed in Box 5-1.

Central Venous Catheter

Central venous catheters are used routinely in the management of critically ill patients for venous access and measurement of intravascular blood volume (i.e., central venous pressure). Up to 40% of catheters are malpositioned. The catheters are usually placed through the subclavian or internal jugular vein. The optimal site for the catheter tip is within the superior vena cava, identified on the frontal view as at the level of the first anterior intercostal space. A catheter within the brachiocephalic veins produces inaccurate central venous pressure measurements due to interference by the proximal venous valves, and positioning within the right atrium is associated with a risk of cardiac perforation and arrhythmias. A catheter that follows a left anterior paramediastinal course is most likely in a left-sided superior vena cava (Fig. 5-7). This venous anomaly occurs in 0.3% of the population, and is usually associated with a right-sided superior vena cava. The left superior vena cava drains into the right atrium by way of the coronary sinus (Fig. 5-8). Catheter placement in an arterial vessel is usually clinically suspected because of the pulsatile flow through the catheter. This may be confirmed on the chest radiograph by the course of the catheter following the major arterial vessels.

Pneumothorax is a common complication of line insertion, occurring in up to 5% of patients, particularly after using a subclavian approach. The pneumothorax is often difficult to detect clinically, and a chest radiograph with the patient preferably erect should be obtained after every line insertion. The pneumothorax may be evident immediately, hours, or rarely, days after insertion. Examination of the lung and pleura opposite to the line insertion is important because bilateral punctures may have been attempted.

Inadvertent puncture of the subclavian or carotid artery may result in an extrapleural hematoma, recognized as a small apical opacity or as mediastinal widening due to more extensive bleeding. Rarely, a pseudoaneurysm of these vessels may develop (Fig. 5-9).

Ectopic infusion of fluid into the mediastinal or pleural space through inadvertent placement of a line outside of a vein produces a radiographic appearance of mediastinal widening, suggesting significant intrathoracic bleeding. The diagnosis is suggested by the temporal relationship with the catheter insertion and is confirmed by thoracocentesis.

Central venous catheter placement is frequently associated with nonobstructing thrombus around the tip, and in 15% of cases, a high-probability ventilation-perfusion scan for pulmonary emboli has been demonstrated.

Catheter fragmentation with subsequent central venous embolization is estimated to occur in 1% of catheter placements (Fig. 5-10). Many cases are unrecognized clinically and may be detected by the astute radiologist. The fragments typically migrate through the central veins and right heart chambers and into the pulmonary artery and its branches. Death, arrhythmias, cardiac or vessel perforation, sepsis, mycotic aneurysm, and pulmonary emboli may result. In many cases, percutaneous retrieval devices can successfully remove the fragment.

Complications of line insertion in part reflect the expertise of the operator. For this reason, the femoral vein approach has gained popularity. There is no risk of a pneumothorax and access is direct and technically easier, and the puncture site is readily compressible. Bleeding from an inadvertent puncture of the femoral artery is easily controlled. Concern over the potentially increased risk of infection and thrombosis using this approach has proved unwarranted. Complications associated with the central venous catheter are reviewed in Box 5-2.

Percutaneous intravascular central catheters (PICCs) are particularly useful for long-term access. They are small (2 to 5 F in diameter) and are routinely placed by way of the antecubital veins. Because of their fine caliber, they may be difficult to visualize radiographically, particularly in the mediastinum. There is obviously no risk of a pneumothorax, and the risk of infection and thrombosis is low. Because these lines are very flexible and may become displaced, they should be monitored by routine radiographs (Fig. 5-11).

Hickman lines are increasingly used in patients after organ transplantation or for prolonged chemotherapy because of the low incidence of line infections. These catheters are inserted surgically through the subclavian vein and are positioned in the distal superior vena cava or proximal right atrium. The catheter may become pinched at the junction of the clavicle and the first rib, resulting in difficult infusions (when the arms are down), thrombosis, or catheter fragmentation. Totally implantable venous access systems or infusaports consist of a disk placed just below the skin port and a catheter that should terminate in the superior vena cava. Infections are rare, but venous thrombosis may occur.

Pulmonary Artery Catheter

Pulmonary artery catheters are frequently used to monitor the hemodynamic status of critically ill patients to aid differentiation of cardiogenic from noncardiogenic pulmonary edema. The complication rate associated with these catheters is low, but the complications may be fatal. The catheter is typically inserted through the subclavian or internal jugular vein and “floated” distal to the pulmonic valve to lie within the right or left main pulmonary artery. An inflatable balloon at the catheter tip is used to obtain a pulmonary capillary wedge pressure that reflects left atrial pressure and left end-diastolic volume. Balloon inflation is required only at the time of obtaining measurements and may be radiographically visible as a 1-cm, round lucency at the catheter tip. On inflation, the catheter floats distally into a smaller arterial vessel; when the balloon is deflated, the tip should lie in the right or left pulmonary artery within 2 cm of the hilum. Coiling or looping of the catheter within the atrium or ventricle may cause arrhythmias, right bundle branch block, complete heart block, or tricuspid valve rupture.

Pulmonary infarction is the most common serious complication; it results from a location of the catheter that is too peripheral or from excessively prolonged inflation of the balloon in a major peripheral pulmonary artery. Obstruction to distal flow results from the catheter itself or clot formation on or around the catheter tip. The extent of the infarct is determined by the size and distribution of the occluded vessel. Typically, infarction is recognized as patchy consolidation involving the region of the lung peripheral to the catheter. Management requires removal of the catheter, which is frequently a sufficient treatment.

Pulmonary hemorrhage, another complication, has a similar radiographic appearance and is more common in patients with pulmonary arterial hypertension and in those receiving anticoagulation (Fig. 5-12). It may be caused by pseudoaneurysm formation, a rare but potentially fatal complication resulting from rupture of the pulmonary artery (Fig. 5-13

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Feb 28, 2016 | Posted by in RESPIRATORY IMAGING | Comments Off on Radiography for the Critical Care Patient
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