Thoracic Imaging 2003 - Society of Thoracic Radiology

WEDNESDAY
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patients the upper lobes and superior segments of the lower
lobes are affected. Disease may rapidly clear (1-2 d) or
progress over 24-48 hr. If clearing does not occur by 72 hrs
then consider a complication. The three patterns of disease
caused by aspiration are gastric aspiration and chemical tracheobronchitis/pneumonitis,
infection (pleuroparenchymal), and airway
obstruction (9).
Life Support Devices
Much of ICU radiology pertains to life support lines and
devices, to evaluate both the position of the device and for complications
related to the insertion procedure or to the presence of
the device itself. Following are the most important radiologic
features of common life support devices.
Endotracheal (ET) tube: optimal position is 5cm above the
carina in an adult. The tube moves ± 2 cm with flexion/extension
of the neck. Malposition is present in 12-15% of patients.
ET width should be ? to 2/3 the width of the trachea, and the
cuff should fill but not expand the trachea. Misplaced tubes
invariably enter the right mainstem bronchus. A study of 101
intubations found that there were 10 malpositions (1 urgent).
Rupture of the larynx or trachea is suggested by projection of
the ET tip outside and to the right of trachea with cuff overdistention.
Tracheostomy: will not move with flexion/extension of the
neck. The tip should project approximately at T3. The cuff
should hug but not distend the tracheal wall. High-pressure cuffs
may cause pressure erosion of the trachea and eventual TE fistula.
Central venous pressure monitor: tip location should be
between the venous valves (proximal subclavian and IJ veins)
and the right atrium. Subclavian catheters should project medial
to the anterior portion of the 1 st rib. Central venous catheter
placement incurs a PTX rate of 5.6%. A catheter inadvertently
placed into the subclavian artery will project superiorly and
medial to the expected subclavian venous course. Local bleeding
may ensue but is usually easily controlled. Catheter placement
(left subclavian) against the wall of the SVC may lead to
erosion.
Swan-Ganz catheter: The tip should not be distal to the proximal
interlobar pulmonary arteries. There is a 24% malposition
rate on the 1 st CXR (1). Infarct, arterial perforation, knotting,
and endocarditis/sepsis are unusual complications.
Intra-aortic balloon pump: The tip should project just inferior
to the aortic arch. The balloon is inflated during diastole and
may sometimes appear as a long ovoid lucency on the CXR.
Pacer: a lateral film is needed to show the RV tip projecting
anteriorly (cf. posterior deviation if the lead enters the coronary
sinus). Perforation has occurred if the tip is outside the heart
shadow.
Chest tube: should be positioned antero-superiorly for PTX
drainage, and postero-inferiorly for effusions. Malpositioning
may show the tube in a fissure, through the lung parenchyma, or
in the extrapleural tissues (malposition is best seen on CT).
Nasogastric (NG) tube: the side hole should project in the
stomach. If a feeding tube is inadvertently placed into the lung,
a post-removal CXR should be carefully evaluated for PTX.
Use of Chest CT in the ICU
CT scanning is increasingly being used in critically ill
patients who may have multiple medical problems, not easily
discriminated by the CXR. It has been estimated that 24-75% of
ICU chest CTs show “clinically useful” information (10), translating
to a change in management in 22-39% of scanned cases.
A portable CT scanner has been described which could help circumvent
problems with transportation of critically ill patients.
Major categories in which chest CT has proven useful are pleural
disease (especially empyema), lung abscess, life line malpositioning,
complications of mechanical ventilation (unsuspected
PTX was found in 7% of ventilated patients by CT), and pulmonary
embolism.
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