7.2 ICU Chest Radiography & Imaging

Interpretation of the ICU Chest Radiograph (CXR)

In the ICU, the portable anteroposterior (AP) chest radiograph is a daily staple. The primary goals of the ICU CXR are twofold: to verify the proper position of indwelling tubes and lines, and to diagnose or monitor cardiopulmonary pathology. The RT must adopt a systematic approach to reading every film.

Verification of Lines and Tubes

Endotracheal Tubes (ETT)

The most frequent assessment an RT will perform on a CXR is verifying ETT placement. The ideal position for the distal tip of the ETT is 3 to 5 cm above the carina in an adult.

• Landmarks: If the carina is not well visualized (often the case in under-penetrated portable films), use the thoracic spine. The tip should be level with the T3 to T4 intervertebral space or roughly at the level of the aortic knob.
• Complications of Malposition:
  • Too deep: The tube will almost always enter the right mainstem bronchus (due to its wider, steeper angle). This results in hyperinflation of the right lung, atelectasis/collapse of the left lung, and profound hypoxemia. The tube must be withdrawn immediately.
  • Too shallow: A tip near the thoracic inlet or vocal cords risks accidental extubation or vocal cord damage. The tube must be advanced.
• Neck Position Effect: Flexion of the neck pushes the ETT deeper (towards the carina). Extension of the neck pulls the ETT out (towards the cords).

Tracheostomy Tubes

The tip of a tracheostomy tube should reside halfway between the stoma and the carina. It should be parallel to the long axis of the trachea, not abutting the anterior or posterior tracheal wall, which could cause necrosis or a tracheoesophageal fistula.

Central Venous Catheters (CVC)

CVCs are typically inserted via the internal jugular (IJ) or subclavian vein. The distal tip must reside in the lower third of the Superior Vena Cava (SVC), right at the cavoatrial junction. If the tip is located inside the right atrium, it risks causing arrhythmias or cardiac perforation. If it is too high in the SVC or innominate vein, it risks thrombosis.

Chest Tubes (Thoracostomy Tubes)

The position of a chest tube depends on its purpose:

• Pneumothorax: Air rises. Therefore, tubes placed for air drainage are directed anteriorly and apically (towards the apex).
• Pleural Effusion/Hemothorax: Fluid falls. Tubes placed for fluid drainage are directed posteriorly and basally (towards the bases).

Radiographic Pathology in the ICU

Acute Respiratory Distress Syndrome (ARDS)

ARDS represents severe inflammatory lung injury. The classic CXR appearance of ARDS includes:

• Bilateral, diffuse, fluffy alveolar infiltrates (often described as "ground-glass" or a "white-out" in severe cases).
• Normal cardiac silhouette (unlike cardiogenic pulmonary edema, where the heart is enlarged).
• Spared costophrenic angles (pleural effusions are not a hallmark of ARDS, whereas they are common in CHF).
• Air bronchograms may be present due to alveolar filling.

Cardiogenic Pulmonary Edema (CHF)

Often confused with ARDS, CHF presents with distinct features:

• Bilateral infiltrates, often radiating from the hila in a "bat-wing" or "butterfly" pattern.
• Cardiomegaly (heart size > 50% of the thoracic width on a PA film, though this is harder to judge on an AP portable film).
• Pleural effusions (blunting of the costophrenic angles).
• Kerley B lines (short, horizontal lines near the periphery indicating interstitial edema).
• Prominent pulmonary vasculature in the upper lobes (cephalization).

Pneumothorax

A pneumothorax is the presence of air in the pleural space.

• Upright Film: Classic findings include an absent bronchovascular markings in the periphery and a visible, thin white line representing the visceral pleura separated from the chest wall.
• Supine Film (ICU Patient): In a supine patient, air collects anteriorly and basally, making the classic pleural line hard to see. Instead, look for the "Deep Sulcus Sign"—an abnormally radiolucent, deep, and wide costophrenic angle on the affected side. The hemidiaphragm may also appear depressed.
• Tension Pneumothorax: A medical emergency characterized by a massive pneumothorax causing a mediastinal shift away from the affected side, flattening of the hemidiaphragm, and compression of the contralateral lung. Immediate needle decompression or chest tube insertion is required.

Atelectasis

Atelectasis (lung collapse) presents as an area of increased opacity (whiteness). Key distinguishing features include:

• Volume Loss: The lung volume is reduced. You will see a shift of mediastinal structures (trachea, heart) toward the side of the atelectasis (unlike a large pleural effusion or tension pneumothorax, which push structures away).
• Elevation of the ipsilateral hemidiaphragm.
• Crowding of the ribs on the affected side.