Emergency ultrasound in trauma patients

John P. McGahan, MDa,*, John Richards, MDb, Maria Luisa C. Fogata, MDa

aDivision of Diagnostic Radiology, University of California, Davis, School of Medicine, 4860 Y Street, Suite 3100,

Sacramento, CA 95817, USA

bDivision of Emergency Medicine, University of California, Davis, School of Medicine, 2315 Stockton Boulevard,

PSSB 2100, Sacramento, CA 95817, USA

The chest

Sonography has been shown to detect pleural

effusions [28]. In traumatized patients, sonography

can be used to diagnose pneumothorax or free fluid

within the thorax. More recently, sonography also

has been shown to be helpful in diagnosing pericardial

effusions [29,30] in traumatized patients. The

main reason for diagnosing pericardial effusions is to

prevent patients from having a traumatically induced

pericardial tamponade. We incorporate the subcostal

view of the heart as a portion of the FAST scan in all

patients with blunt abdominal trauma. This is helpful

in diagnosing pericardial effusions (Fig. 7). It must

be emphasized that inexperienced examiners often

have problems diagnosing pericardial effusions. For

instance, Blavias et al [30] set up a study with

emergency medicine residents and fellows trained in

sonography. They had trouble discerning the epicardial

fat, which appeared hypoechoic on US, from a

true pericardial effusion. Sonography had a sensitivity

rate of 73% and a specificity rate of only 44%

in this study [30]. With more experienced examiners,

sonography may be useful in detecting moderate

pericardial effusions.

More recently, sonography also has been proved

to be useful in diagnosing pneumothorax [31,32]. The

parietal pleura adheres to the inner muscle of the thorax,

whereas the visceral pleura adheres to the lung.

During inspiration and expiration the visceral pleura

``slides'' back and forth adjacent to the parietal

pleura. The bright echogenic line of the visceral

pleura, which adheres to the lung as it moves and

slides during normal inspiration and expiration, may

be observed on real-time sonography and is a normal

finding (Fig. 8). Absence of the sliding lung is a

direct sign of pneumothorax (Fig. 9). Remembering

that the free air within the thorax rises to the most

nondependent portion of the thoracic cavity, the US

probe is placed in this area to check for pneumotho-

rax. Either a curved array probe or, better yet, a linear

array probe may be used to detect pneumothorax. The

US probe is placed in the intercostal space. The

normal ``to and fro'' motion of the visceral pleura

against the parietal pleura is observed in a normal

patient. The normal motion of the visceral pleura

against the parietal pleura is absent with pneumothorax,

however. In a normal patient, a ``reverberation

artifact'' usually is noted posterior to the parietal

visceral pleura interface in a normal patient (see

Fig. 8). This is observed as lines that are equally

spaced from one another and gradually decrease in

echogenicity. This is the reverberation of the US

beam as it strikes the interface between the parietal

and visceral pleura and the air in the lung and is

reflected back to the transducer. This reverberation

produces multiple equally spaced echoes. The reverberation

artifact is not identified when there is a

pneumothorax. A pneumothorax may produce acoustic

shadowing. Absence or decrease of the reverberation

artifact also may occur in a normal patient if

the gain settings are set too low.

An article by Rowan et al [33] compared the

accuracy of sonography with that of the supine

chest radiograph in detecting traumatic pneumothorax,

with CT serving as the reference or ``gold''

standard. They studied 27 patients who sustained

blunt thoracic trauma and had US. The radiographic

and US findings were compared with CT findings.

Eleven of 27 patients had pneumothoraces as seen

with CT. All of the pneumothoraces were detected

by sonography, for a sensitivity rate of 100%. The

specificity rate of sonography was 94%, and 1 of

16 patients had a false-positive diagnosis of pneumothorax.

Supine chest radiography had a sensitivity

rate of only 36% (4 of 11 patients), with a specificity

rate of 100%. In their study, US was more sensitive

than chest radiography in the detection of traumatic

pneumothoraces.

Fig. 8. Normal lung. (A) Real-time US examination using linear array probe demonstrates the appearance of the normal lung on

US. Note that the first echogenic line (open arrow) corresponds to the interface between the parietal and the visceral pleura.

Parallel equally spaced lines of decreasing echogenicity are observed posterior to this, which corresponds to reverberation

artifacts (arrows). (B) Drawing of reverberation artifact. The US probe is placed on the skin surface (S). R refers to the interface

between the parietal and visceral pleura. Lines labeled as numbers 1 and 2, which are of decreasing echogenicity posterior to this,

correspond to reverberation artifacts caused by the US beam ``reverberating'' or ``bouncing'' between the pleura and transducer.

(C) Similar pattern is seen with sector scan of the lung in another patient.

Fig. 9. Small pneumothorax.

Real-time US examination of thorax in this patient with a small pneumothorax

demonstrates the echogenic line that corresponds to the parietal and visceral pleura,

which is noted to the left side of image. Note more distal reverberation artifacts. To

the right side of the image there is loss of this pattern because of a small pneumothorax.

[28] Ma OJ, Mateer JR. Trauma ultrasound examination

versus chest radiography in the detection of hemothorax.

Ann Emerg Med 1997;29:312- 6.

[29] Aaland MO, Bryan III FC, Sherman R. Two-dimensional

echocardiogram in hemodynamically stable

victims of penetrating precordial trauma. Am Surg

1994;60:412- 5.

[30] Blaivas M, DeBehnke D, Phelan MB. Potential errors

in the diagnosis of pericardial effusion on trauma ultrasound

for penetrating injuries. Acad Emerg Med

2000;7:1261-6.

[31] Dulchavsky SA, Schwarz KL, Kirkpatrick AW, et al.

Prospective evaluation of thoracic ultrasound in the

detection of pneumothorax. J Trauma 2001;50:201- 5.

[32] Sargsyan AE, Hamilton DR, Nicolaou S, et al. Ultrasound

evaluation of the magnitude of pneumothorax:

a new concept. Am Surg 2001;67:232-6.

[33] Rowan KR, Kirkpatrick AW, Liu D, Forkheim KE,

Mayo JR, Nicolaou S. Traumatic pneumothorax detection

with thoracic US: correlation with chest radiography

and CT. Initial experience. Radiology 2002;225:

210- 4.

J.P. McGahan et al / Radiol Clin N Am 42 (2004) 417-425 425

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