SonoStudy: Contrast Enhanced Ultrasound – the future for trauma assessment? #FOAMed

In a recent article in Critical Ultrasound Journal from July 2013, the authors (Italians, of course! – they always do things ahead of everyone!) discuss the utility of contrast enhancement for solid organ evaluation in trauma patients. So, the FAST scan will assess for free fluid from injury, but we dont know what that injury is through a simple FASt scan. With contrast, we can better visualize the solid organs and assess for injury. The authors say it best, “Computed Tomography (CT) is the standard reference in the emergency for evaluating the patients with abdominal trauma. Ultrasonography (US) has a high sensitivity in detecting free fluid in the peritoneum, but it does not show as much sensitivity for traumatic parenchymal lesions. The use of Contrast-Enhanced Ultrasound (CEUS) improves the accuracy of the method in the diagnosis and assessment of the extent of parenchymal lesions. Although the CEUS is not feasible as a method of first level in the diagnosis and management of the polytrauma patient, it can be used in the follow-up of traumatic injuries of abdominal parenchymal organs (liver, spleen and kidneys), especially in young people or children.”

The thing to keep in mind is that this is actually not new – but evolving and getting spoken about more and more – as the authors state: “The first results in the literature indicates the use of CEUS in patients with blunt abdominal trauma after the FAST (Focused Assessment with Sonography in Trauma) or the US, in hemodynamically stable patients with a history of low-energy trauma [1,4,6]. CT is reserved in cases of severe trauma, with clinical suspicion of multiorgan lesions and cases with inconclusive CEUS [6].”

How does contrast work sonographically? Read on : “The contrast agents eco-amplifiers are able to modify the acoustic impedance of tissues, interacting with ultrasound beams and increasing the echogenicity of the blood. The contrast media (CM) ultrasound (USCA, UltraSound Contrast Agent) consist of microbubbles containing inert gases and surrounded by membrane stabilizers. The power of echogenic microbubbles and acoustic impedance depends on the size of the microbubbles. The microbubbles, unlike the tissues and the free gas, are not simply passive reflectors, but expand and compress in response to the stages of compression and rarefaction of the acoustic wave, with increasingly large hikes in diameter. The non-linear oscillation of microbubbles determines the emission of frequencies of said second harmonic with a frequency which is twice the insonation. Through the use of specific software, low acoustic pressures and an algorithm of specific processing, it is possible to selectively display the signals from the CM, separating the signal of the microbubbles from the one regarding the tissue. This particular signal is identified in real time by means of two main algorithms: Pulse Inversion (PI) and Contrast Pulse Sequence (CPS) [7,8]“

Here are some images from the authors in the article that makes the point:

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The conclusion? What to make of all of this?: “In the low-energy trauma and in hemodynamically stable patients, the US can be used as a first-level examination; when US detect intra-abdominal fluid CT examination is need. In the high-energy trauma the use of US as first line diagnostic is superfluous and damaging and the use of CT without and with i.v.c onstrast material is imperative. In order to reduce the radiation dose, particularly in young people or children, CEUS has an important role in the follow-up of conservatively treated traumatic injuries of the abdominal parenchymatous organs (liver, spleen and kidneys) diagnosed by CT [39,40]“

Read the article to get even more details on how the future of ultrasound will be, hopefully…here.

SonoStudy: 550 pts, prospective study: How good is ultrasound for traumatic pneumothorax? @westjem #FOAMed

In the march 2013 issue of Western Journal of Emergency Medicine, a study done that has been described as having generalizability, as the ultrasound scans were by many different levels of physicians, prospectively, during a trauma assessment for pneumothorax, has caused quite a bit of discussion. Mostly due to some of the limitations of the study. It is great that a prospective study with some generalizability is seen, but I wonder about the details in the methodology. They begin by discussing the importance and relevance of ultrasound for pneumothorax:

“Rapid diagnosis and treatment of traumatic pneumothorax (PTX) is important to prevent tension physiology and circulatory collapse in patients with blunt and penetrating trauma. Supine chest radiograph (CXR) is traditionally employed; however, it misses up to 50% of PTXs.1 Thoracic ultrasound (TUS) was first described in 1995 for diagnosing PTX in humans when Lichtenstein noted that the absence of comet-tail artifacts and lung sliding were associated with PTX.2 Since then ultrasound has become a validated method of examining the pleura in multiple settings. In 2011 the Eastern Association for the Surgery of Trauma gave a level 2 recommendation for the use of ultrasound to identify PTX in its practice management guidelines.3 In most studies TUS has been found to have favorable results. In Lichtenstein’s study,2 TUS had a sensitivity and negative predictive value of 100% and 96.5%, respectively, for the detection of PTX in the intensive care unit setting.4 Dulchavsky5 subsequently demonstrated that this modality has a sensitivity of 95% in the detection of PTX in patients at a Level 1 trauma center. These reports used plain radiography as the gold standard: a diagnostic modality known to be inaccurate in the detection of PTX.6 In subsequent studies using dedicated chest computed tomography (CCT) as a reference standard, sensitivities of TUS have ranged widely from 49% – 98%, while finding that it is still consistently more accurate than supine CXR.713 Studies in which TUS is performed by emergency physicians (EP) for traumatic PTX have reported even higher sensitivities ranging from 86–97% with specificities of > 99%.14 While these latter numbers are desirable, they have the potential limitation of being less applicable due to a higher skill level of the sonologists involved. The actual performance of TUS for PTX would likely vary based on the sonologist’s skill and experience. The current investigation set out to determine the test characteristics of TUS for traumatic PTX in the hands of a large heterogenous group of potential sonologists representative of typical clinicians involved in trauma care.”

The full abstract is shown below:

“Introduction:

Prior studies have reported conflicting results regarding the utility of ultrasound in the diagnosis of traumatic pneumothorax (PTX) because they have used sonologists with extensive experience. This study evaluates the characteristics of ultrasound for PTX for a large cohort of trauma and emergency physicians.

Methods:

This was a prospective, observational study on a convenience sample of patients presenting to a trauma center who had a thoracic ultrasound (TUS) evaluation for PTX performed after the Focused Assessment with Sonography for Trauma exam. Sonologists recorded their findings prior to any other diagnostic studies. The results of TUS were compared to one or more of the following: chest computed tomography, escape of air on chest tube insertion, or supine chest radiography followed by clinical observation.

Results:

There were 549 patients enrolled. The median injury severity score of the patients was 5 (inter-quartile range [IQR] 1–14); 36 different sonologists performed TUS. Forty-seven of the 549 patients had traumatic PTX, for an incidence of 9%. TUS correctly identified 27/47 patients with PTX for a sensitivity of 57% (confidence interval [CI] 42–72%). There were 3 false positive cases of TUS for a specificity of 99% (CI 98%–100%). A “wet” chest radiograph reading done in the trauma bay showed a sensitivity of 40% (CI 23–59) and a specificity of 100% (99–100).

Conclusion:

In a large heterogenous group of clinicians who typically care for trauma patients, the sonographic evaluation for pneumothorax was as accurate as supine chest radiography. Thoracic ultrasound may be helpful in the initial evaluation of patients with truncal trauma.”

So what are the limitations? They describe a few of them:

The technique: “The TUS examination consisted of the consecutive sonographic interrogation of every intercostal space between the clavicle and the diaphragm on each hemithorax. Scans were performed in the mid-clavicular line. On the left side, if cardiac motion was encountered in the mid-clavicular line, the probe was moved laterally to the left anterior axillary line and the pleura seen in the remaining intercostal spaces was evaluated until the diaphragm/spleen was encountered. To use the ribs to assist in the identification of the rib spaces and the pleura, the probe was placed in a longitudinal plane for the entire exam.” So, would this have increased their sensitivity or specificity as they include all rib spaces? Not too sure. Is this truly generalizable if the technique is different than how most perform the quick E-FAST? no. The main reason for the technique, i imagine, is to find the lung point which is far more specific for pneumothorax.

The Probe and Machine – The low frequency curvilinear probe was used on an older ultrasound system – SonoSite Titan. Could this have affecte their results? Would the increased resolution of a linear probe have helped their evaluation on the newer machines? It is possible, but by how much? who knows.

The comparison group: “Not all subjects underwent CCT and instead just had CXR and clinical observation. It is possible that some patients in this latter group had radio-occult PTX that may have been visualized on CCT leading to misclassification bias. Such a bias could result in a lower sensitivity rate for both TUS and CXR, however would likely not affect the accuracy of these tests for determining clinically significant PTX.” It is tough to have a standard and if only the chest CT group were compared, it may have had different results.

Im hoping to see more studies like this one where more generalizability is seen, and not studies done only by the experts, so that we can have a true assessment. It is best done using the technique most commonly performed (using only the second intercostal space and mid clavicular line and trying to ind the lung point if absence of lung sliding is seen) at multiple-sites, with increased power to the study, all compared to a CT as the imaging gold standard. But, i can dream, as that is quite difficult to accomplish, and the authors did a pretty nice job with what they had, got pretty good numbers of subjects – something to ponder….

For a prior post on pneumothorax and a link to the CHEST meta-analysis, go here.

For a SonoTutorial post on pneumothorax ultrasound, go here.

Another study stating that ultrasound can be used to assess post=procedure pneumothorax published in June 2013 of JUM, go here.

SonoStudyReview: The Pneumothorax by @EMLyceum – EBM review on imaging/diagnosis/treatment #FOAMed

If there ever was a post worth reading about pneumothorax, this excellent review by EM Lyceum was too good not to pass along to everyone. Now I don’t know about you, but I always get asked the questions about chest Xray versus Ultrasound, what to do when only the ultrasound shows the pneumothorax (because you know it’s better than Chest Xray! as discussed in a prior post), when to order that CT chest, and how should you treat it: nothing? pigtail? small chest tube? large chest tube? EM Lyceum does a great job in reviewing this using literature to back it up. There have been more studies that haven’t been mentioned with regard to ultrasound and pneumothorax diagnosis, and the sensitivity and specificity of chest xray is stated pretty high as prior studies tend to do (with more accurate and recent ones stated by EM Lyceum to be lower (in the real world that we work in). And, there was a great meta-analysis in Chest Journal speaking of which imaging modality was better, chest Xray or ultrasound. Go to the EM Lyceum site and read-on to grasp the answers to all the questions! Thank you EM Lyceum – this was awesome!

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By BTS 2010 guidelines (Macduff, 2010).

SonoStudy: Thoracic ultrasound in identifying pneumothorax progression in the intubated – the lung point

In the Feb 2013 issue of Chest, Oveland et al studied porcine models, introducing air at incremental levels to identify if thoracic ultrasound is as accurate as CT scanning for the detection pneumothorax progression in the intubated patient. They found that “the accuracy of thoracic ultrasonography for identifying the lung point (and, thus, the PTX extent) was comparable to that of CT imaging. These clinically relevant results suggest that ultrasonography may be safe and accurate in monitoring PTX progression during positive pressure ventilation.”

“Background:  Although thoracic ultrasonography accurately determines the size and extent of occult pneumothoraces (PTXs) in spontaneously breathing patients, there is uncertainty about patients receiving positive pressure ventilation. We compared the lung point (ie, the area where the collapsed lung still adheres to the inside of the chest wall) using the two modalities ultrasonography and CT scanning to determine whether ultrasonography can be used reliably to assess PTX progression in a positive-pressure-ventilated porcine model.

Methods:  Air was introduced in incremental steps into five hemithoraces in three intubated porcine models. The lung point was identified on ultrasound imaging and referenced against the lateral limit of the intrapleural air space identified on the CT scans. The distance from the sternum to the lung point (S-LP) was measured on the CT scans and correlated to the insufflated air volume.

Results:  The mean total difference between the 131 ultrasound and CT scan lung points was 6.8 mm (SD, 7.1 mm; range, 0.0-29.3 mm). A mixed-model regression analysis showed a linear relationship between the S-LP distances and the PTX volume (P < .001).

Conclusions:  In an experimental porcine model, we found a linear relation between the PTX size and the lateral position of the lung point. The accuracy of thoracic ultrasonography for identifying the lung point (and, thus, the PTX extent) was comparable to that of CT imaging. These clinically relevant results suggest that ultrasonography may be safe and accurate in monitoring PTX progression during positive pressure ventilation.”

Full article found here.

To see the lung point, you visualize the pleural line using the linear probe (indicator toward the patient’s head) starting from anterior chest wall (2nd intercostal space, mid-clavicular line) to inferior-lateral chest wall, and look out for the area where the lack of lung sliding or comet tail artifacts reverts back to normal lung sliding with comet tail artifacts. Blaivas, et al, studied this, showing that bedside ultrasound can detect size of pneumothorax through identification of the lung point location. Below is a video fo the lung point:

SonoStudy: >12,000 kids – Identifying factors putting kids at low risk, not needing CT after trauma

There has been quite a bit of press lately on this –  Here and Here – And for good reason. With the ALARA principle, and being a pediatric population which has been studied so many times with regard to trauma and the need for CT, a recent study by Holmes et al published in Annals of Emergency Medicine did a multi-site study enrolling >12,000 kids and identified 7 factors that places children at very low risk for injury not requiring abdominal CT. A prior post discusses a study done by the same author and my thoughts of pediatric US in trauma. BTW – Dr. Holmes also discusses low risk factors for adult patients in a prior study too.

The prediction rule for pediatric patients consisted of (in descending order of importance):
No evidence of abdominal wall trauma or seat belt sign,
Glasgow Coma Scale score greater than 13,
No abdominal tenderness,
No evidence of thoracic wall trauma,
No complaints of abdominal pain,
No decreased breath sounds, and
No vomiting.

Now, I dont know about you, but to me it is quite obvious – we just now have a nicely powered study that we can use for all the doctors who want to CT despite all of the above being negative. The authors say that if any one of the above exist then a decision by the physician should be made as to what the next best management step would be – observation period with serial exams, ultrasound (holla!), CT – are all options depending on clinical judgement. Below is the abstract:

Study objective: We derive a prediction rule to identify children at very low risk for intra-abdominal injuries undergoing acute intervention and for whom computed tomography (CT) could be obviated.
Methods: We prospectively enrolled children with blunt torso trauma in 20 emergency departments. We used binary recursive partitioning to create a prediction rule to identify children at very low risk of intra-abdominal injuries undergoing acute intervention (therapeutic laparotomy, angiographic embolization, blood transfusion for abdominal hemorrhage, or intravenous fluid for ≥2 nights for pancreatic/gastrointestinal injuries). We considered only historical and physical examination variables with acceptable interrater reliability.
Results: We enrolled 12,044 children with a median age of 11.1 years (interquartile range 5.8, 15.1 years). Of the 761 (6.3%) children with intra-abdominal injuries, 203 (26.7%) received acute interventions. The prediction rule consisted of (in descending order of importance) no evidence of abdominal wall trauma or seat belt sign, Glasgow Coma Scale score greater than 13, no abdominal tenderness, no evidence of thoracic wall trauma, no complaints of abdominal pain, no decreased breath sounds, and no vomiting. The rule had a negative predictive value of 5,028 of 5,034 (99.9%; 95% confidence interval [CI] 99.7% to 100%), sensitivity of 197 of 203 (97%; 95% CI 94% to 99%), specificity of 5,028 of 11,841 (42.5%; 95% CI 41.6% to 43.4%), and negative likelihood ratio of 0.07 (95% CI 0.03 to 0.15).
Conclusion: A prediction rule consisting of 7 patient history and physical examination findings, and without laboratory or ultrasonographic information, identifies children with blunt torso trauma who are at very low risk for intra-abdominal injury undergoing acute intervention. These findings require external validation before implementation.

SonoStudy: Flat IVC predictor of poor prognosis in trauma – A-B-C-D-Echo in Trauma!

A recent study on the IVC and trauma and acute surgical patients was done by Ferrada et al, and despite the giggles I get when I read it and how they describe the IVC as “Fat ” or “Flat”, it is an important topic to discuss as it is one of the few articles out there that correlate the iVC to trauma patients and acute surgical patients. First off, it is a retrospective study, which can make it difficult to assess patients with similar factors without other factors coming into play (but when is that NOT the case, honestly?) They did compare the IVC in all patients and studied those patients who seemed sick as well – ICU admission, immediate surgery need, transfusion needed. The power of the study was good but not great – 101 patients studied – varying in type of trauma and surgical need. There was a previous study published in the Journal of Trauma in 2011 that stated CT evidence of flat IVC was an indicator for hypovolemia and  poor prognostic indicator for blunt solid organ injuries – this confirmed a study done in 2010 stating the same thing. Thankfully, ultrasound can get you that information much more immediately than CT!

This month, another study by the same author (Ferrada) in the Journal of trauma and acute care surgery entitled A-B-C-D-Echo (I know, love it!) stated that adding limited transthoracic echo, including the IVC, will benefit trauma patients with results showing “Flat inferior vena cava was associated with an increased incidence of ICU admission (p < 0.0076) and therapeutic operation (p < 0.0001). Of the 148 patients, 27 (18%) had LTTE results indicating euvolemia. The diagnosis in these cases was head injury (n = 14), heart dysfunction (n = 5), spinal shock (n = 4), pulmonary embolism (n = 3), and stroke (n = 1). Of the patients, 121 had LTTE results indicating hypovolemia. Twenty-eight hypovolemic patients had a negative or inconclusive Focused Assessment with Sonography for Trauma examination finding (n = 18 penetrating, n = 10 blunt), with 60% having blood in the abdomen confirmed by surgical exploration or computed tomographic scan. Therapy was modified as a result of LTTE in 41% of cases. Strikingly, in patients older than 65 years, LTTE changed therapy in 96% of cases.”

Below are the Abstracts of the studies highlighted by Ferrada:

“Flat inferior vena cava (IVC) on ultrasound examination has been shown to correlate with hypovolemic status. We hypothesize that a flat IVC on limited echocardiogram (LTTE) performed in the emergency room (ER) correlates with poor prognosis in acutely ill surgical patients. We conducted a retrospective review of all patients undergoing LTTE in the ER from September 2010 until June 2011. IVC diameter was estimated by subxiphoid window. Flat IVC was defined as diameter less than 2 cm. Fat IVC was defined as diameter greater than 2 cm. Need for intensive care unit admission, blood transfusion requirement, mortality, and need for emergent operation between patients with flat versus Fat IVC were compared. One hundred one hypotensive patients had LTTE performed in the ER. Average age was 38 years. Admission diagnosis was blunt trauma (n = 80), penetrating trauma (n = 13), acute care surgery pathology (n = 7), and burn (n = 1). Seventy-four patients had flat IVC on initial LTTE. Compared with those with fat IVC, flat patients were found have higher rates of intensive care unit admission (51.3 vs 14.8%; P = 0.001), blood transfusion requirement (12.2 vs 3.7%), and mortality (13.5 vs 3.7%). This population also underwent emergent surgery on hospital Day 1 more often (16.2 vs 0%; P = 0.033). Initial flat IVC on LTTE is an indicator of hypovolemia and a predictor of poor outcome.”

ABCDEcho:

“BACKGROUND: Limited transthoracic echocardiogram (LTTE) has been introduced as a technique to direct resuscitation in intensive care unit (ICU) patients. Our hypothesis is that LTTE can provide meaningful information to guide therapy for hypotension in the trauma bay.

METHODS: LTTE was performed on hypotensive patients in the trauma bay. Views obtained included parasternal long and short, apical, and subxyphoid. Results were reported regarding contractility (good vs. poor), fluid status (flat inferior vena cava [hypovolemia] vs. fat inferior vena cava [euvolemia]), and pericardial effusion (present vs. absent). Need for surgery, ICU admission, Focused Assessment with Sonography for Trauma examination results, and change in therapy as a consequence of LTTE findings were examined. Data were collected prospectively to evaluate the utility of this test.

RESULTS: A total of 148 LTTEs were performed in consecutive patients from January to December 2011. Mean age was 46 years. Admission diagnosis was 80% blunt trauma, 16% penetrating trauma, and 4% burn. Subxyphoid window was obtained in all patients. Parasternal and apical windows were obtained in 96.5% and 11%, respectively. Flat inferior vena cava was associated with an increased incidence of ICU admission (p < 0.0076) and therapeutic operation (p < 0.0001). Of the 148 patients, 27 (18%) had LTTE results indicating euvolemia. The diagnosis in these cases was head injury (n = 14), heart dysfunction (n = 5), spinal shock (n = 4), pulmonary embolism (n = 3), and stroke (n = 1). Of the patients, 121 had LTTE results indicating hypovolemia. Twenty-eight hypovolemic patients had a negative or inconclusive Focused Assessment with Sonography for Trauma examination finding (n = 18 penetrating, n = 10 blunt), with 60% having blood in the abdomen confirmed by surgical exploration or computed tomographic scan. Therapy was modified as a result of LTTE in 41% of cases. Strikingly, in patients older than 65 years, LTTE changed therapy in 96% of cases.

CONCLUSION: LTTE is a useful tool to guide therapy in hypotensive patients in the trauma bay.”

SonoStudy: >29,000 patients: Utility of cardiac portion of FAST scan: should we be doing it?

Should we keep doing the echo with the FAST scan? What does it truly add? Ill never forget the story I heard about a 35 yr old male blunt trauma victim after single vehicle motor vehicle accident who lost his pulse en route.  The echo part of the FAST scan showed tamponade in the first 5 minutes of evaluation and ACLS/ATLS management. He survived due to early pick up) and walked out of the hospital. Or, the penetrating epigastric stab wound victim who was tachycardic and hypotensive with no tamponade or pericardial effusion seen on FAST (helping us rule out tamponade as the cause of shock). But, when looking at the studies….a recent one from JEM states:

“Background

Focused assessment with sonography in trauma (FAST) is widely used and endorsed by guidelines, but little evidence exists regarding the utility of the cardiac portion in blunt trauma. The traditional FAST includes the routine performance of cardiac sonography, regardless of risk for hemopericardium.

Study Objectives

Our goal was to estimate the prevalence of hemopericardium due to blunt trauma and determine the sensitivity of certain variables for the presence of blunt hemopericardium.

Methods

We performed a retrospective chart review of two institutional databases at a large urban Level I trauma center to determine the prevalence of blunt hemopericardium and cardiac rupture and incidental or insignificant effusions. We evaluated the sensitivity of major mechanism of injury, hypotension, and emergent intubation for blunt hemopericardium and cardiac rupture.

Results

Eighteen patients had hemopericardium and cardiac rupture (14 and 4, respectively) out of 29,236 blunt trauma patients in the Trauma Registry over an 8.5-year period. The prevalence was 0.06% (95% confidence interval [CI] 0.04–0.09%). The prevalence of incidental or insignificant effusions was 0.13% (95% CI 0.09–0.18%). One case of blunt hemopericardium was identified in the emergency ultrasound database out of 777 cardiac ultrasounds over a 3-year period. No patient with blunt hemopericardium or cardiac rupture presented without a major mechanism of injury, hypotension, or emergent intubation.

Conclusion

Blunt hemopericardium is rare. High-acuity variables may help guide the selective use of echocardiography in blunt trauma.”

So, I would ask: is it worth the 20 seconds it takes to look at the heart to pick up those patients who had a positive scan? And, is it worth the 20 seconds it takes to look at the heart to rule it out? – i say – yes. But I get it – it may be negative A LOT of the time.