Diagnostics & Procedures · Topic 3 of 16

Chest X-Ray Interpretation

Diagnostics · chest radiograph

Chest X-Ray Interpretation

Check film quality, then every tube and line — ETT 3–5 cm above the carina, CVC tip in the low SVC, feeding tube below the diaphragm — before the lungs.

Key numbers

ETT tip 3–5 cm above the carina3–5 cm above carina

Cardiothoracic ratio > 50% on PA filmCTR > 0.5 (PA)

IABP tip ~2 cm below the aortic knob~2 cm below arch

01 · The numberETT tip 3–5 cm above the carina

The endotracheal tube tip belongs in the mid-thoracic trachea, 3–5 cm above the carina (carina at T4–T5); a tip at the carina slips into the right mainstem bronchus and collapses the left lung.

02 · DoCVC tip in low SVC, not atrium

Before using a jugular or subclavian line, confirm on radiograph that the tip lies in the SVC at the cavoatrial junction and that there is no pneumothorax; a right atrial tip risks perforation and arrhythmia.

03 · DoFeeding tube: confirm tip below the diaphragm

Confirm a blindly placed nasogastric or feeding tube on radiograph before first use: it runs vertically through the chest, passes below the diaphragm, and its side port lies below the gastroesophageal junction.

Presentation

What you'll see

Pneumothorax: visceral pleural line, no markings beyond must knowPneumothorax shows a visceral pleural line with no lung markings beyond it; on a supine film a large one may show only a deep sulcus sign. Diagnose tension pneumothorax clinically, not by film.

Silhouette sign localizes consolidationLoss of a normal border localizes the opacity: right heart border = right middle lobe; left heart border = lingula; right hemidiaphragm = right lower lobe; left hemidiaphragm = left lower lobe.

Effusion: meniscus; air-fluid level means hydropneumothoraxPleural effusion forms a meniscus rising up the lateral chest wall on an upright film (about 75 mL blunts the posterior costophrenic angle); a straight air-fluid level instead suggests hydropneumothorax.

Trachea shifts away from tension, toward collapseTension pneumothorax pushes the trachea and mediastinum to the opposite side (with a depressed ipsilateral hemidiaphragm); lobar collapse or atelectasis pulls the trachea toward the abnormal side.

Free air under the diaphragm: perforationFree air under the diaphragm on an upright chest film means a perforated viscus (seen in 50–75% of perforations); a lateral film is more sensitive, and CT follows if the film is nondiagnostic.

Cardiogenic edema: cephalization, Kerley B linesHydrostatic edema progresses from upper-lobe redistribution (cephalization) to interstitial edema — Kerley B lines, peribronchial cuffing, effusions — then perihilar alveolar opacities, usually with cardiomegaly and a wide vascular pedicle.

Widened mediastinum: image the aortaA widened mediastinum (with an obscured aortic knob or left effusion) in chest pain or deceleration trauma suggests aortic dissection or injury — get CT angiography; a normal mediastinum does not exclude it.

CVC left of the spine: suspect malpositionA right-sided central line that crosses the midline or runs vertically left of the spine suggests arterial placement, a left-sided SVC or extravascular position — do not use it until position is confirmed.

Diagnosis & monitoring

Work-up

Cardiothoracic ratio > 50% on PA filmOn a PA film the heart should be no wider than 50% of the chest; portable AP films magnify the heart, so call cardiomegaly cautiously — a normal heart on AP is truly normal.

IABP tip ~2 cm below the aortic knobThe intra-aortic balloon pump's radiopaque tip belongs in the proximal descending aorta, about 2 cm below the aortic arch (just past the left subclavian origin); too high threatens cerebral flow, too low reduces support.

Do right now

In this order

First moves

Check rotation, inspiration and penetration first

→

ETT tip 3–5 cm above the carina3–5 cm above carina

→

CVC tip in low SVC, not atrium

→

Feeding tube: confirm tip below the diaphragm

Why each step

Check rotation, inspiration and penetration firstJudge quality first: no rotation (medial clavicle ends equidistant from the spinous processes), adequate inspiration (about 10 posterior ribs visible), and penetration; a poor inspiration crowds vessels and mimics heart failure.

ETT tip 3–5 cm above the carinaThe endotracheal tube tip belongs in the mid-thoracic trachea, 3–5 cm above the carina (carina at T4–T5); a tip at the carina slips into the right mainstem bronchus and collapses the left lung.

CVC tip in low SVC, not atriumBefore using a jugular or subclavian line, confirm on radiograph that the tip lies in the SVC at the cavoatrial junction and that there is no pneumothorax; a right atrial tip risks perforation and arrhythmia.

Feeding tube: confirm tip below the diaphragmConfirm a blindly placed nasogastric or feeding tube on radiograph before first use: it runs vertically through the chest, passes below the diaphragm, and its side port lies below the gastroesophageal junction.

The rules

Know these

PA catheter tip proximal, never past the hilumA pulmonary artery catheter tip belongs in the right or left main pulmonary artery, proximal to the interlobar artery and never beyond the hilum; a distal tip risks pulmonary infarction or hemorrhage.

Cardiogenic edema or ARDS on the film?

Commonly confused

Heart size	Often enlarged
Vascular pedicle	Widened
Opacity distribution	Perihilar, central
Other signs	Cephalization, Kerley B lines, effusions

More detail

Reference

Show 6 reference facts

A skin fold can mimic a pneumothorax on AP or infant films, but lung vessels are seen crossing the apparent edge.

The commonest malposition of a nasogastric tube is the right or left lower lobe bronchus; feeding through it can be catastrophic.

Pulmonary contusion may not opacify on chest radiograph for 24–48 hours after injury; CT is highly sensitive and also shows associated injuries.

In pulmonary embolism the film is usually nonspecific; Westermark sign (focal oligemia) and Hampton hump (pleural-based wedge opacity) are uncommon.

Expiratory films increase the contrast between pleural air and lung and can reveal a small pneumothorax; portable AP films are suboptimal and reserved for patients too ill to travel.

A central line tip too high in the SVC is prone to malfunction, thrombosis and vessel-wall erosion, especially with left-sided insertion; too low increases arrhythmia risk.

Pearl

Tubes and lines first: a perfect read of the lungs is no help if the feeding tube is in the right lower lobe bronchus.