Comparison of Four Views to Single-View Ultrasound Protocols to Identify Clinically Significant Pneumothorax

Background

Ultrasound has become a key adjunct for the initial evaluation of trauma patients in the emergency department (ED), with the eFAST, or extended focused assessment with sonography in trauma examination, including lung evaluation for the presence of a pneumothorax (PTX) or hemothorax. While prior research has shown ultrasound (US) to be very effective at identifying a PTX [1], there is no standardized imaging protocol that has been shown be superior to others. The two most common approaches are a single view of each hemithorax and four views of each hemithorax [2] —this paper sets out to determine if the single view strategy is sufficient to identify a clinically significant PTX.

Comparison of Four Views to Single-view Ultrasound Protocols to Identify Clinically Significant Pneumothorax

 

Clinical Question

Does the single-view or four-view lung US technique have a higher diagnostic accuracy for the identification of clinically significant PTX in trauma patients?

Methods & Study Design

  • Population
    • The study was conducted at a single urban academic ED with an annual volume of 130,000 patients and a dedicated Level I trauma service staffed by trauma surgeons and EM physicians. Adult patients with acute traumatic injury who were undergoing a CT scan of the chest as part of their clinical care were eligible for enrollment.
  • Intervention
    • Patients were assigned to one of two imaging protocols, a single view of each hemithorax or four views of each hemithorax prior to any CT imaging being done, with US images obtained by emergency physicians or the attending trauma surgeon using a 7.5-Mhz (5- to 10-MHz) linear array transducer. US exams were performed by both residents and attending physicians who had been credentialed in both US protocols.
  • Outcomes
    • Researchers looked for the ability of US to identify clinically significant PTX requiring chest tube placement; a PTX was considered clinically insignificant if the radiologist, who was blinded to the US interpretation, read the CT scan as a thin collection of air up to 1 cm thick in the greatest slice or seen on fewer than five contiguous slices.
  • Design
    • This was a randomized, prospective trial on trauma patients.
  • Excluded
    • The study excluded any patient who was too unstable and required clinical care that prevented performing a chest wall US, patients with a chest tube in place prior to arrival, children, pregnant women, and prisoners.

Results

    • For clinically significant PTX, CXR showed a sensitivity of 48.0% and specificity of 100%, a single view US showed a sensitivity of 93.0% and a specificity of 99.2%, and four views showed a sensitivity of 93.3% and specificity of 98.0%. There was no statistically significant difference in either sensitivity or specificity when comparing single view and four-view for clinically significant or any PTX.

Strengths & Limitations

  • Strengths
    • Randomized, prospective trial
    • 100% agreement between the initial US read by the performing provider and the study author, for a Cohen’s kappa of 1
  • Limitations
    • Study was conducted at a single center with a limited number of US operators
    • Standard prehospital approach to spinal immobilization that results in placement of patients supine on a long board - in areas where this approach may differ (e.g., patients arrive semirecumbent or upright), the positioning of a PTX in the chest may be altered, rendering a single view of the anterior chest wall less accurate
    • As this study was a convenience sample that required the treating physician to remember to enroll the patient and randomize them prior to performing the US, there is a possibility of selection bias

Author's Conclusions

"The sensitivities are equivalent for both a single view and four views of each hemithorax when using point-of-care ultrasound to evaluate for a clinically significant pneumothorax in the trauma population.  The additional time required for additional views should be weighed against the lack of additional diagnostic accuracy when evaluating critically ill and time-sensitive trauma patients in the ED."

Our Conclusions

Although not all PTXs are located anteriorly and multiple views of each hemithorax may be thought to maximize sensitivity and/or allow the physician to be able to attempt to quantify the size of the PTX, performing eight views instead of two views during the eFAST requires extra time while adding no diagnostic value.  From this study, it appears that a single view on each side of the thorax is sufficient to detect clinically significant PTXs on trauma patients.

As with any diagnostic tool, it is important to remember its limitations. Specifically, the US exams in this study were done in supine patients, who were brought in by EMS in a supine position, allowing the pneumothorax to move to the most anterior portion of the chest. Caution should be taken when applying the test characteristics of this study to patients that are not in the supine position. There was also one patient who had a significant PTX that was missed by US and required a chest tube. This patient had received a needle decompression by prehospital providers and was randomized to a single anterior US chest view that was performed just lateral to the needle insertion site which may have led to false negative US exam. It appears this specific group of patients may benefit from a more comprehensive four-view lung examination.

 

The Bottom Line

A single anterior view on each side of the chest in a supine patient is sufficient to detect clinically significant pneumothoraces.

Authors

This post was written by Ben Foorman, MS4 at UCSF. It was edited by Michael Macias, MD.

References

    1. Lichtenstein DA, e. (2017). Ultrasound diagnosis of occult pneumothorax. - PubMed - NCBI . Ncbi.nlm.nih.gov. Retrieved 28 July 2017, from https://www.ncbi.nlm.nih.gov/pubmed/15942336
    2. Blaivas M, e. (2017). A prospective comparison of supine chest radiography and bedside ultrasound for the diagnosis of traumatic pneumothorax. - PubMed - NCBI . Ncbi.nlm.nih.gov. Retrieved 28 July 2017, from https://www.ncbi.nlm.nih.gov/pubmed/16141018
    3. Helland G, e. (2017). Comparison of Four Views to Single-view Ultrasound Protocols to Identify Clinically Significant Pneumothorax. - PubMed - NCBI . Ncbi.nlm.nih.gov. Retrieved 28 July 2017, from https://www.ncbi.nlm.nih.gov/pubmed/27428394

Case # 2: A Needle In the Haystack

A 40 year old male presented with 3 days of progressive dyspnea on exertion. He notes he was in a normal state of health prior to this and played basketball daily without issue but now he can no longer walk across the room without becoming winded. He has no chest pain, a normal chest x-ray and an ECG demonstrating sinus tachycardia

Vitals: HR 109 BP 110/72 RR 22 O2 96

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Answer and Learning Point

Answer

There is evidence of severe aortic regurgitation and aortic root dilation (~6 cm) on this parasternal long axis view. In a patient without any previous cardiac history with new aortic regurgitation this is concerning for acute aortic dissection. Cardiac surgery was consulted immediately and the patient was taken straight to CT scan for confirmation of type A aortic dissection. The patient was in the OR within 1 hour and had an excellent outcome.

Learning Point

Aortic dissection is quite uncommon (~5-30 per 1 million people per year) and is often seen in patients with chronic uncontrolled hypertension or other diseases such as bicuspid aortic valve, Marfan Syndrome or Ehlers-Danlos Syndrome. Unfortunately all the "classic" indicators of dissection are actually not that common [1].  Traditionally we are taught that patients with acute aortic dissection will arrive hypertensive, while in actuality up to 1 in 4 patients with Stanford Type A dissection will have a presenting systolic blood pressure below 100 mmHg. Additionally, it is taught that a dissection presents as a “ripping or tearing” pain going to the back.  Looking at the data, while over 90% of patients felt that it was the worst pain they had ever experienced, only 50% of subjects described their pain as ripping or tearing (62% described pain as sharp), only 35% had any posterior chest pain, and only 85.4% of patients described the onset of their pain as ‘acute.’ [1]

The varied presentation of this disease makes aortic dissection difficult to diagnose, and the clinician should have a high index of suspicion for this life-threatening disease process.  This is where ultrasound comes in. Anyone who has a concerning chest pain story, pain above and below the diaphragm, chest pain + a neurological symptom, or signs and symptoms of acute heart failure without any previous cardiac history, should have a bedside ultrasound performed.  While ultrasound cannot rule out aortic dissection, it can rapidly identify complications of dissection and expedite care in these patients whom time is of the essence.

The Approach

Perform standard abdominal aorta ultrasound evaluating for aneurysm or intimal flap. Be sure to evaluate from proximal aorta, in the epigastric region, distally to the iliac vessels. A normal aorta caliber is < 3 cm.

Obtain a parasternal long axis view:

Measure aortic root, this should be less than 4 cm. There are varying opinions on where the best place to take this measurement is, I suggest measuring the largest area you see as it is better to be on the conservative side.
Apply color doppler to evaluate for aortic regurgitation.
Assess global cardiac function. This is useful to see if a patient is compensated or decompensated as well as assist with fluid/pressor management if needed.
Evaluate for pericardial effusion. If there is evidence of effusion and concern for Type A aortic dissection, this suggests that there is communication with pericardial sac.
Evaluate descending thoracic aorta for intimal flap

References

  1. Hagan PG, Nienaber CA, Isselbacher EM, et al. The International Registry of Acute Aortic Dissection (IRAD): New Insights Into an Old Disease. JAMA. 2000;283(7):897-903. doi:10.1001/jama.283.7.897.
  2. Taylor RA, e. (2017). Point-of-care focused cardiac ultrasound for the assessment of thoracic aortic dimensions, dilation, and aneurysmal disease. - PubMed - NCBI Ncbi.nlm.nih.gov. Retrieved 22 July 2017, from https://www.ncbi.nlm.nih.gov/pubmed/?term=22288871
  3. C, K. (2017). Emergency department diagnosis of aortic dissection by bedside transabdominal ultrasound. - PubMed - NCBI Ncbi.nlm.nih.gov. Retrieved 22 July 2017, from https://www.ncbi.nlm.nih.gov/pubmed/19549013
  4. Lang R, Bierig M, Devereux R, et al. Recommendations for Chamber Quantification: A Report from the American Society of Echocardiography’s Guidelines and Standards Committee and the Chamber Quantification Writing Group, Developed in Conjunction with the European Association of Echocardiography, a Branch of the European Society of Cardiology. J Am Soc Echocardiogr 2005; 18: 1440-63.
  5. Rubano E, e. (2017). Systematic review: emergency department bedside ultrasonography for diagnosing suspected abdominal aortic aneurysm. - PubMed - NCBI Ncbi.nlm.nih.gov. Retrieved 22 July 2017, from https://www.ncbi.nlm.nih.gov/pubmed/?term=23406071

Does This Adult Patient Have a Blunt Intra-abdominal Injury?

Background

Trauma is the leading cause of death in those younger than 45 years in the United States. Around 80% of injuries are due to blunt trauma with 20% involving penetrating trauma. It is blunt trauma, however, that carries substantial diagnostic challenges due to complex injury patterns and difficult management strategies. This paper sets out to review and summarize the comparisons of different techniques in diagnosis of intra-abdominal injury via physical exam findings, laboratory values, and imaging including bedside ultrasound. 

Does This Adult Patient Have a Blunt Intra-abdominal Injury? 

Clinical Question

How accurate and reliable are existing symptoms, signs, laboratory tests and bedside imaging studies at diagnosing intra-abdominal injury following blunt abdominal trauma?

Methods & Study Design

  • Population
    • The study analyzed 12 papers that assessed clinical examination and 22 papers to assess role of FAST in identifying intra-abdominal injury. Sample sizes ranged from 117 to 3435 patients. All studies defined inclusion criteria as adult patients with any blunt abdominal trauma except for 2 studies that included only adult patients in motor vehicle collisions.
  • Intervention
    • This particular paper focused on the likelihood ratios of various approaches in predicting intra-abdominal injury including: physical exam findings (i.e rebound tenderness, abdominal distention, guarding, seat belt sign, and hypotension), laboratory tests (i.e.  base deficit, hematuria, elevated transaminases and anemia), and FAST examination.
  • Outcomes
    • Researchers measured specificity, sensitivity, positive likelihood and negative likelihood of the various physical exam, laboratory, and imaging findings associated with blunt trauma.
  • Design
    • This is a meta-analysis of numerous prospective studies looking at blunt abdominal trauma.
  • Excluded
    • The publishers chose to include studies that were prospective, with consecutive enrollment and blinding, and included a reference standard (i.e.  abdominal CT, DPL, laparotomy, autopsy, or clinical course to detect intra-abdominal injury or hemoperitoneum).

Results

Strengths & Limitations

  • Strengths
    • Analyzed the biggest publications from top-trauma centers focusing on strength of statistical analysis.
    • Created subcategories of studies that focused on FAST in order to ascertain if any of the information was skewed.
  • Limitations
    • This is a 2012 study that only focused on papers older than 2007, excluding any new techniques and standards as well as imaging advancements of the last decade.
    • They did not review studies for clinical outcome, so cannot draw conclusions regarding how change in bedside exam and procedures impact patient care post diagnosis.
    • As with all large meta-analysis studies there is always risk of significant heterogeneity from varying study inclusion/exclusion criteria making generalizability complex.

Author's Conclusions

“Bedside ultrasonography has the highest accuracy of all individual findings, but a normal result does not rule out an intra-abdominal injury. Combinations of clinical findings may be most useful to determine which patients do not require further evaluation, but the ideal combination of variables for identifying patients without intra-abdominal injury requires further study.”

Our Conclusions

Overall, this paper reinforces the strength of bedside ultrasonography (adjusted positive LR of 30) as a diagnostic tool of intra-abdominal injury following blunt trauma compared to physical exam and laboratory findings. This reinforces ultrasounds role as the best tool to "rule-in" an intra-abdominal injury. However, it also elucidates a relatively poor sensitivity of the FAST exam, making it a poor tool to "rule-out." This is important as it urges physicians to not rely solely on a negative FAST exam when ruling out intra-abdominal injury but consider other factors including clinical gestalt, mechanism of injury, physical exam and laboratory work up.

Additionally, to better understand the magnitude of this paper's findings it is important to known what a likelihood ratio really tells us. The following image is a quick way to think about likelihood ratios. A positive likelihood ratio of 2 should increase your probability of disease ( resulting in your post test probability) by 15%, 5 by 30% and 10 by 45%. Likewise a negative likelihood ratio of 0.5 should decrease your probability of disease by 15%, 0.2 by 30% and 0.1 by 45%.

The Bottom Line

Bedside ultrasonography is a highly specific diagnostic tool to rule in  intra-abdominal injury following blunt trauma but should be used in conjunction with clinical gestalt, physical exam findings and laboratory values when ruling out injury.

Authors

This post was written by Olga Miakicheve, MS4 at UCSD. It was edited by Michael Macias, MD.

References

    1. Simel, D. (2012). Does This Adult Patient Have a Blunt Intra-abdominal Injury?. JAMA, 307(14), 1517. doi:10.1001/jama.2012.422

Case # 1: The Acutely Winded Traveler

A 65 year old female presents with shortness of breath after a return flight from the Gold Coast of Australia to the United States.

Vitals: HR 107 BP 110/80 RR 22 O2 95

RV+Strain_Mead

Answer and Learning Point

Answer

There is right ventricular dysfunction demonstrated as septal bowing appreciated on this parasternal short axis view. This is concerning for a pulmonary embolism in the setting of the provided clinical context.

Learning Point

Echocardiography can be a useful adjunct to laboratory markers (i.e. BNP and troponin) and CTA for evaluation of right heart strain in normotensive patients presenting with concern for pulmonary embolism.  While there is building evidence that many patients presenting with pulmonary embolism are safe for discharge [1] , those patients that have evidence of right ventricular dysfunction are at higher risk for morbidity and mortality and may also be candidates for more advanced therapies, other than simple anticoagulation, such as catheter directed thrombolysis.  The most up-to-date evidence supports that emergency physicians can accurately perform echocardiography at the bedside to risk stratify patients presenting with concern for pulmonary embolism. In a recent study by Weekes et al, emergency physicians (EP) performed goal directed echocardiography to assess for right ventricular dysfunction. If any of the following criteria below were present, a patient was considered positive by goal directed echocardiography for right ventricular dysfunction:

This study found the EP goal-directed echocardiography sensitivity and specificity for right ventricular dysfunction to be 100% (CI 87% to 100%) and 99% (95% CI 94% to 100%), respectively [2]. Our patient ended up having a saddle embolus and underwent catheter directed thrombolysis and did well.

References

  1. Aujesky D, e. (2017). Outpatient versus inpatient treatment for patients with acute pulmonary embolism: an international, open-label, randomised, non-inferiority trial. - PubMed - NCBI . Ncbi.nlm.nih.gov. Retrieved 8 July 2017, from https://www.ncbi.nlm.nih.gov/pubmed/21703676

  2. Weekes AJ, e. (2017). Diagnostic Accuracy of Right Ventricular Dysfunction Markers in Normotensive Emergency Department Patients With Acute Pulmonary Embolism. - PubMed - NCBI . Ncbi.nlm.nih.gov. Retrieved 8 July 2017, from https://www.ncbi.nlm.nih.gov/pubmed/?term=26973178

FAST Ultrasound Examination as a Predictor of Outcomes After Resuscitative Thoracotomy

Background

The emergency resuscitative thoracotomy (RT), aka The ED Thoracotomy, is a procedure performed as a last-ditch effort during resuscitation of a patient in traumatic arrest or impending traumatic arrest. Unfortunately despite physicians’ best efforts, outcomes for this procedure are generally poor. The largest review of outcomes after RT performed in the emergency department found an overall survival of 7.4% (8.8% for penetrating injury, 1.4% for blunt injury), with good neurological outcomes present in 92.4% of surviving patients [2]. Furthermore, given the lack of high quality evidence on this procedure, there are no universal guidelines that exist to determine optimal candidates [3,4]. Point-of-care ultrasound has become a core adjunct in evaluation of the trauma patient, however there is minimal data evaluating its utility in determining which trauma patients may benefit from RT [5].

FAST Ultrasound Examination as a Predictor of Outcomes After Resuscitative Thoracotomy: A Prospective Evaluation

Clinical Question

Can the Focused Assessment Using Sonography for Trauma (FAST) predict survival after a RT in patients presenting to the emergency department in traumatic cardiac arrest?

Methods & Study Design

  • Population
    • All penetrating trauma patients with absent vital signs and blunt trauma patients with a loss of vital signs en route or in the resuscitation bay that underwent RT.
  • Intervention
    • A FAST exam was performed just prior to RT to assess for the presence or absence of a pericardial effusion and cardiac motion.
  • Outcomes
    • Survival to Discharge or Organ Donation
  • Design
    • Prospective, observational study performed at a single academic level-1 trauma center
  • Excluded
    • Patients who were taken directly to the OR for an emergent or urgent thoracotomy were excluded.
    • Patients who did not have a FAST exam performed prior to RT were excluded from analysis

Results

    • 223 patients underwent RT, 187 underwent analysis (36 had no FAST performed)
      • Primary Outcome
        • Survival: 3.2%
        • Organ Donation: 1.6%

Strengths & Limitations

  • Strengths
    • First large, prospective observation study on emergency RT
    • Sensitivity analysis performed to include patients who had inadequate views obtained
  • Limitations
    • Study performed at a high-volume, single academic level-1 trauma center with which may skew generalizability
    • Residents who had formal training in the FAST exam performed all ultrasound scans. Many emergency medicine physicians are not credentialed in ultrasound or FAST examination

Author's Conclusions

"In summary, for the patients that arrived to hospital and underwent a FAST examination, all survivors and organ donors had visible cardiac motion. If no cardiac motion or pericardial effusion was seen, the survival was zero. Ultrasound was, therefore, able to effectively identify those patients who had the potential to survive the RT and discriminate them from those who did not. Utilizing ultrasound would have resulted in the avoidance of a significant proportion of thoracotomies which were ultimately found to be futile.”

Our Conclusions

This is a well done study examining the utility of the FAST exam in identifying which patients will potentially benefit from emergency RT. One may look at the primary outcomes of this study and think that the very low overall survival rate (3.2%) does not jive with previously reported studies. However, it is important to note that during the study period, 21 patients who had a penetrating cardiac injury and went straight to the OR for thoracotomy, were excluded. All of these patients survived. If we were to incorporate this number into the the final analysis, survival would be ~13% which fits better with previous data. But that isn’t the point of this study. The big question that I feel is appropriately answered is which patient population can we safely avoid undertaking an emergency RT, knowing it is futile. While resource utilization for a procedure of this magnitude may be less burdensome at an academic level-1 trauma center, performing a RT in an emergency department where this is rare occurrence requires a much larger undertaking by the staff. The new data from this study, demonstrates that patients who did not have cardiac motion or a pericardial effusion on initial FAST had a zero survival rate. This is practice changing, especially for providers who rarely perform this procedure. If an experienced trauma team performing this procedure had zero survival rate in patients with no cardiac motion or pericardial effusion, it is safe to say that a provider with less experience will perform better. Furthermore, having real time data to share with the entire resuscitation team during a traumatic arrest can provide closure to the team and a sense that performing any further heroic procedures is futile.

The Bottom Line

The FAST exam is a critical adjunct in traumatic patients and should be applied to all cases of traumatic arrest in order to determine the utility of performing an emergency RT.

References

    1. Inaba K, e. (2017). FAST ultrasound examination as a predictor of outcomes after resuscitative thoracotomy: a prospective evaluation. - PubMed - NCBI . Ncbi.nlm.nih.gov. Retrieved 4 July 2017, from https://www.ncbi.nlm.nih.gov/pubmed/26258320
    2. Rhee PM, e. (2017). Survival after emergency department thoracotomy: review of published data from the past 25 years. - PubMed - NCBI . Ncbi.nlm.nih.gov. Retrieved 4 July 2017, from https://www.ncbi.nlm.nih.gov/pubmed/10703853
    3. Seamon MJ, e. (2017). An evidence-based approach to patient selection for emergency department thoracotomy: A practice management guideline from the Eastern Association ... - PubMed - NCBI . Ncbi.nlm.nih.gov. Retrieved 4 July 2017, from https://www.ncbi.nlm.nih.gov/pubmed/26091330
    4. Burlew CC, e. (2017). Western Trauma Association critical decisions in trauma: resuscitative thoracotomy. - PubMed - NCBI . Ncbi.nlm.nih.gov. Retrieved 4 July 2017, from https://www.ncbi.nlm.nih.gov/pubmed/23188227
    5. Moore EE, e. (2017). Defining the limits of resuscitative emergency department thoracotomy: a contemporary Western Trauma Association perspective. - PubMed - NCBI . Ncbi.nlm.nih.gov. Retrieved 4 July 2017, from https://www.ncbi.nlm.nih.gov/pubmed/21307731