Focus On: Ultrasound Detection of Traumatic Anterior Pneumothorax

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December 2008
 

By Arun Nagdev, MD, and Michael Murphy, MD 

 

 

Learning Objectives

After reading this article, the physician should be able to:

  • Recognize the primary ultrasonographic finding of normal lung tissue (lung sliding).
  • Recognize the ultrasonographic findings present in a pneumothorax (absence of lung sliding, absence of comet tails).
  • Perform an ultrasonographic exam of the chest for the detection of a pneumothorax.
 

Early detection of a pneumothorax may be important in the clinical management of a trauma patient. Supine chest radiographs in the immobilized trauma patient have been shown to be insensitive.1 As bedside ultrasound is more frequently utilized by emergency physicians, detection of pneumothoraces at the bedside by ultrasound has become a valuable aspect of the initial assessment of the trauma patient.

Added to the FAST (Focused Assessment with Sonography in Trauma), rapid evaluation of the chest for the detection of a pneumothorax can offer the emergency physician pertinent clinical information to aid in the management of the trauma patient with undifferentiated injuries.2 

Initial clinical research in ultrasonographic evaluation of the chest in the critically ill patient originated in European intensive care units. These studies demonstrated the superiority of bedside ultrasound in the detection of anterior pneumothoraces, compared with supine chest radiographs (CXR).1,3,4 Although clearly demonstrating increased sensitivity, these initial studies were performed on nontrauma patients.

Recent data from acutely injured patients support the initial studies by demonstrating that bedside ultrasound is more sensitive than chest radiography in the detection of an anterior pneumothorax when computed tomography (CT) is used as the gold standard. In summary, these studies demonstrate that ultrasound has a sensitivity of 92%-100% in detecting pneumothorax, compared with the supine CXR, which has been shown to have a sensitivity of 36%-75%.5,6 

This article will focus on the ultrasound detection of pneumothorax mainly in the setting of trauma. The ultrasound examination techniques described may certainly be extended to use in the diagnosis of pneumothorax in the nontrauma patient.

Pathophysiology

In the normal state, the closed pleural system of the lung is made up of physiologic pleural fluid contained between the visceral and parietal pleura making up the pleural sac. Air introduced into this closed system leads to a pneumothorax by separating the normally apposed visceral and parietal pleura. This separation can potentially alter the mechanisms of respiration.

In the supine trauma patient without previous pleural disease, pathologic air within the pleural space tends to rise to the anterior chest wall at the paracardiac regions and anterior costo-diaphragmatic sulci. It is at these anterior sites that bedside ultrasound is ideal (see image 1).

1208TraumAntPneumothorax1 

Probe Selection

The low-frequency, curvilinear probe (2-5 MHz) has been used by most authors for the detection of anterior pneumothoraces (see image 2, item A). This probe is found on most bedside ultrasound machines and is recommended for use during FAST examinations.

1208TraumAntPneumothorax2 

The curvilinear probe allows for the continuation of the FAST exam to the thoracic cavity, negating the need for a probe change during the exam. In our experience, using the high-frequency, linear probe (5-10 MHz) allows the novice physician to obtain rapid proficiency in the chest ultrasound exam for detection of pneumothorax (see image 2, item B).

After sufficient experience with pattern recognition of positive and negative ultrasonographic signs of a pneumothorax with the linear, high-frequency probe, the clinician may then utilize the curvilinear, low-frequency probe for the complete evaluation of the abdomen and thorax--thus adding the lung component to the standard FAST exam, commonly termed the Extended FAST or EFAST.2 

Procedure

The bedside chest ultrasound exam for the detection of anterior pneumothoraces is performed by placing the probe perpendicular to two ribs spaces in the anterior chest region (see image 2, item C). The hyperechoic (white) ribs, with posterior shadows, act as fixed anatomical landmarks (see image 2, item D). This defined interspace, just deep to the intercostal muscles and soft tissue, is the location of the pleural line.

Sliding of the pleural line indicates the lack of air between the visceral and parietal pleural, and "rules out" an anterior pneumothorax. When pathologic air accumulates in between the parietal and visceral pleura, ultrasound waves are able to image the superficial parietal layer, but cannot visualize the visceral layer. This is because of the small collection of air in the pleural space that causes ultrasound waves to scatter. This is represented as "lack of lung sliding" and can be interpreted as a pneumothorax.

Once the pleural space is interrogated adequately, we recommend utilizing M-mode as an adjunctive imaging modality to confirm the presence or absence of a pneumothorax. Motion mode, or "M-mode," allows the clinician sonographically to evaluate a single line and determine the presence of motion along that singular line.

Again, by leaving the probe in same perpendicular orientation over the rib interspaces, the operator can determine, in a static method, the presence of lung sliding. Lack of motion in the soft tissue region is displayed as horizontal lines, while motion is displayed as unorganized "static" (see image 3).

1208TraumAntPneumothorax3 

Currently, no consensus exists regarding the number of interspaces that need to be interrogated to exclude an anterior pneumothorax. In a supine patient, we recommend scanning 2-3 interspaces in the midclavicular line in the most anterior region of the chest (usually around the nipple line/4th-5th rib space). Also, we recommend evaluating both hemithoraces to differentiate normal from abnormal lung tissue if a pneumothorax is present.

Secondary Signs of an Anterior Pneumothorax

In "B-mode," or "brightness mode," another sign termed "comet tail" artifact can aid the physician in the ultrasound examination of the chest for the detection of a pneumothorax.

Comet tail artifacts are "ray-like" projections off the pleural line thought to be created when ultrasound waves hit the interface between the apposing pleural and visceral layers of the lung (see image 4). These artifacts are not seen when pathologic air is present between the normally apposed pleural layers. Lack of comet tail artifacts can indicate the presence of a pneumothorax.

1208TraumAntPneumothorax4 

The point where normal lung interfaces with air of a pneumothorax in the pleural space is defined as the "lung point." In "B-mode," the physician can scan the anterior chest in search of the dynamic transition between normal pleural sliding and absence of pleural sliding (pneumothorax). This dynamic point moves during the respiratory cycle, and can be found at various locations in the chest. Small pneumothoraces tend to have transitions in the anterior chest, while larger pneumothoraces have areas of transition on the lateral aspect of the chest.

Visualization of the lung point is pathognomonic for the presence of a pneumothorax. Experience is necessary to recognize this specific sign, and it may be necessary to interrogate numerous interspaces to locate the lung point. This limits the recognition of lung point during a rapid EFAST examination.

Limitations

Lack of lung sliding and comet tail artifacts may not always indicate a pneumothorax. Recently intubated patients may have a mainstem bronchus intubation preventing adequate aeration of one lung and not demonstrate either lung sliding or comet tail artifacts, giving the operator a false impression of pneumothorax.

Also, when evaluating the paracardiac regions on the left chest, care must be taken to identify the pleural line. The heart rises and falls with the movement of the diaphragm, and this motion may be misinterpreted as a "lung point," especially if the probe marker is pointed caudad instead of cephalad (as recommended).

In stable trauma patients with ultrasonographic signs of a pneumothorax and a negative supine chest radiograph, we recommend a repeat upright plain film after clearance of cervical immobilization for confirmation of an occult pneumothorax. In patients where cervical immobilization cannot be removed, we recommend computed tomography of the chest to delineate the pneumothorax early in trauma care (before transportation or intubation).

Summary

Continuation of the FAST exam to include the chest for the rapid determination of a pneumothorax can be useful for the emergency physician.

The provider must interrogate the most anterior aspect of the chest wall. The operator must identify pertinent landmarks (rib with resultant shadows) and determine the location of the pleural line. Lack of pleural movement can indicate air between the parietal and visceral pleura, allowing for rapid identification of a pneumothorax. This technique has been shown to be more sensitive for the recognition of anterior pneumothoraces in trauma patients, compared with supine chest radiographs.

Further management should be based on the clinical situation.

References

  1. Lichtenstein D.A., Meziere G., Lascola N., et al. Ultrasound diagnosis of occult pneumothorax. Critical Care Med. 2005;33:1231-8.
  2. Kirkpatrick A.W., Sirois M., Laupland K.B., et al: Hand-held thoracic sonography for detecting post-traumatic pneumothoraces: The extended focused assessment with sonography for trauma (EFAST). J. Trauma 2004;57:288-95.
  3. Lichtenstein D.A., Menu Y.: A bedside ultrasound sign ruling out pneumothorax in the critically ill: Lung Sliding. Chest 1995;108:1345-8.
  4. Lichtenstein D., Mezierre G., Biderman P., et al. The comet-tail artifact: An ultrasound sign ruling out pneumothorax. Intensive Care Med. 1999;25:383-8.
  5. Blavais M., Lyon M., Duggard S.: A prospective comparison of supine chest radiography and bedside ultrasound for the diagnosis of traumatic pneumothorax. Acad. Emerg. Med. 2005;12:844-9.
  6. Soldati D., Testa A., Sher S., et al. Occult traumatic pneumothorax: diagnostic accuracy of lung ultrasonography in the emergency department. Chest 2008;133:204-11.

Contributors

Dr. Arun Nagdev is an assistant professor, department of emergency medicine, at the Warren Alpert School of Medicine of Brown University. Dr. Michael Murphy is an attending physician, department of emergency medicine, at the Warren Alpert School of Medicine of Brown University. Medical Editor Dr. Robert C. Solomon is an attending emergency physician at Trinity Health System in Steubenville, Ohio, and clinical assistant professor of emergency medicine at the West Virginia School of Osteopathic Medicine.

Disclosures

In accordance with the Accreditation Council for Continuing Medical Education (ACCME) Standards and American College of Emergency Physicians policy, contributors and editors must disclose to the program audience the existence of significant financial interests in or relationships with manufacturers of commercial products that might have a direct interest in the subject matter.

Dr. Nagdev, Dr. Murphy, and Dr. Solomon have disclosed that they have no significant relationships with or financial interests in any commercial companies that pertain to this educational activity.

"Focus On: Ultrasound Detection of Traumatic Anterior Pneumothorax" has been planned and implemented in accordance with the Essential Areas and Policies of the Accreditation Council for Continuing Medical Education (ACCME).

ACEP is accredited by the ACCME to provide continuing medical education for physicians. ACEP designates this educational activity for a maximum of one Category 1 credit toward the AMA Physician's Recognition Award. Each physician should claim only those credits that he or she actually spent in the educational activity.

"Focus On: Ultrasound Detection of Traumatic Anterior Pneumothorax" is approved by ACEP for one ACEP Category 1 credit.

Disclaimer

ACEP makes every effort to ensure that contributors to College-sponsored programs are knowledgeable authorities in their fields. Participants are nevertheless advised that the statements and opinions expressed in this article are provided as guidelines and should not be construed as College policy.

The material contained herein is not intended to establish policy, procedure, or a standard of care. The views expressed in this article are those of the contributors and not necessarily the opinion or recommendation of ACEP. The College disclaims any liability or responsibility for the consequences of any actions taken in reliance on those statements or opinions.

 

 

 

 

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