Comparison of outcomes between pulseless electrical activity by electrocardiography and pulseless myocardial activity by echocardiography in out-of-hospital cardiac arrest; secondary analysis from a large, prospective study.

OBJECTIVE: To measure prevalence of discordance between electrical activity recorded by electrocardiography (ECG) and myocardial activity visualized by echocardiography (echo) in patients presenting after cardiac arrest and to compare survival outcomes in cohorts defined by ECG and echo. METHODS: This is a secondary analysis of a previously published prospective study at twenty hospitals. Patients presenting after out-of-hospital arrest were included. The cardiac electrical activity was defined by ECG and contemporaneous myocardial activity was defined by bedside echo. Myocardial activity by echo was classified as myocardial asystole--the absence of myocardial movement, pulseless myocardial activity (PMA)--visible myocardial movement but no pulse, and myocardial fibrillation--visualized fibrillation. Primary outcome was the prevalence of discordance between electrical activity and myocardial activity. RESULTS: 793 patients and 1943 pauses in CPR were included. 28.6% of CPR pauses demonstrated a difference in electrical activity (ECG) and myocardial activity (echo), 5.0% with asystole (ECG) and PMA (echo), and 22.1% with PEA (ECG) and myocardial asystole (echo). Twenty-five percent of the 32 pauses in CPR with a shockable rhythm by echo demonstrated a non-shockable rhythm by ECG and were not defibrillated. Survival for patients with PMA (echo) was 29.1% (95%CI-23.9-34.9) compared to those with PEA (ECG) (21.4%, 95%CI-17.7-25.6). CONCLUSION: Patients in cardiac arrest commonly demonstrate different electrical (ECG) and myocardial activity (echo). Further research is needed to better define cardiac activity during cardiac arrest and to explore outcome between groups defined by electrical and myocardial activity.

Point-of-Care Ultrasound in Trauma.

The use of point-of-care ultrasound in trauma is widespread. Focused Assessment with Sonography for Trauma examination is a prototypical bedside examination used by the treating provider to quickly determine need for intervention and appropriate patient disposition. The role of bedside ultrasound in trauma, however, has expanded beyond the Focused Assessment with Sonography for Trauma examination. Advancements in diagnostics include contrast-enhanced ultrasound, thoracic, and musculoskeletal applications. Ultrasound is also an important tool for trauma providers for procedural guidance including vascular access and regional anesthesia. Its portability, affordability, and versatility have made ultrasound an invaluable tool in trauma management in resource-limited settings. In this review, we discuss these applications and the supporting evidence for point-of-care ultrasound in trauma.

Using support vector machines on photoplethysmographic signals to discriminate between hypovolemia and euvolemia.

Identifying trauma patients at risk of imminent hemorrhagic shock is a challenging task in intraoperative and battlefield settings given the variability of traditional vital signs, such as heart rate and blood pressure, and their inability to detect blood loss at an early stage. To this end, we acquired N = 58 photoplethysmographic (PPG) recordings from both trauma patients with suspected hemorrhage admitted to the hospital, and healthy volunteers subjected to blood withdrawal of 0.9 L. We propose four features to characterize each recording: goodness of fit (r2), the slope of the trend line, percentage change, and the absolute change between amplitude estimates in the heart rate frequency range at the first and last time points. Also, we propose a machine learning algorithm to distinguish between blood loss and no blood loss. The optimal overall accuracy of discriminating between hypovolemia and euvolemia was 88.38%, while sensitivity and specificity were 88.86% and 87.90%, respectively. In addition, the proposed features and algorithm performed well even when moderate blood volume was withdrawn. The results suggest that the proposed features and algorithm are suitable for the automatic discrimination between hypovolemia and euvolemia, and can be beneficial and applicable in both intraoperative/emergency and combat casualty care.

A retrospective study of pulseless electrical activity, bedside ultrasound identifies interventions during resuscitation associated with improved survival to hospital admission. A REASON Study.

OBJECTIVE: Our objective was to determine whether organized or disorganized cardiac activity is associated with increased survival in patients who present in pulseless electrical activity (PEA) treated with either 1) standard advanced cardiac life support (ACLS) medications or 2) other interventions. METHODS: This was a secondary analysis of a prospective, multi-center observational study utilizing ultrasound in out-of-hospital or inemergency department PEA arrest. Bedside ultrasound was performed as ACLS protocol started and during pulse checks. Only cases with visible cardiac activity on ultrasound were included in the present analysis. Cardiac activity was categorized as disorganized (agonal twitching) or organized (contractions with changes in ventricular dimensions). Patients were categorized as receiving either standard bolus ACLS medications or alternative medications during the resuscitation (continuous adrenergic agents, thrombolytics, others). The primary outcome was survival to hospital admission. The secondary outcome was return of spontaneous circulation (ROSC). Multivariate modeling was performed to assess association between survival to hospital admission in patients with intravenous adrenergic agents and cardiac activity. RESULTS: In our cohort of 225 patients in PEA cardiac arrest with cardiac activity on ultrasound, the overall survival rate was higher in patients with organized cardiac activity than with disorganized cardiac activity. PEA cardiac arrest patients with organized cardiac activity treated with standard ACLS interventions demonstrated improved survival to hospital admission compared to those with disorganized activity (37.7% (95%CI 24.8-50.2%) versus 17.9% (95%CI 10.9-28%). PEA cardiac arrest patients with organized cardiac activity who received continuous adrenergic agents during the resuscitation and prior to ROSC demonstrated higher survival to hospital admission 45.5% (95%CI 26.9-65.4%) and ROSC 90.9% (95%CI 71.0-98.7%) compared to those with disorganized cardiac activity who received continuous adrenergic agents during the resuscitation 0% (95%CI 0-23.0%) and 47.1% (95%CI 26-69%). Regression analysis demonstrates an association between increased survival in patients receiving intravenous adrenergic agents and organized cardiac activity. CONCLUSION: Survival in patients following PEA arrest is higher in patients with organized cardiac activity. The initiation of continuous adrenergic agents during PEA was associated with improved survival to hospital admission in patients with organized cardiac activity on bedside ultrasound, but this improvement was not seen in patients in PEA with disorganized cardiac activity. Bedside ultrasound may identify a subset of patients that respond differently to ACLS interventions.

Emergency department point-of-care ultrasound in out-of-hospital and in-ED cardiac arrest.

BACKGROUND: Point-of-care ultrasound has been suggested to improve outcomes from advanced cardiac life support (ACLS), but no large studies have explored how it should be incorporated into ACLS. Our aim was to determine whether cardiac activity on ultrasound during ACLS is associated with improved survival. METHODS: We conducted a non-randomized, prospective, protocol-driven observational study at 20 hospitals across United States and Canada. Patients presenting with out-of-hospital arrest or in-ED arrest with pulseless electrical activity or asystole were included. An ultrasound was performed at the beginning and end of ACLS. The primary outcome was survival to hospital admission. Secondary outcomes included survival to hospital discharge and return of spontaneous circulation. FINDINGS: 793 patients were enrolled, 208 (26.2%) survived the initial resuscitation, 114 (14.4%) survived to hospital admission, and 13 (1.6%) survived to hospital discharge. Cardiac activity on US was the variable most associated with survival at all time points. On multivariate regression modeling, cardiac activity was associated with increased survival to hospital admission (OR 3.6, 2.2-5.9) and hospital discharge (OR 5.7, 1.5-21.9). No cardiac activity on US was associated with non-survival, but 0.6% (95% CI 0.3-2.3) survived to discharge. Ultrasound identified findings that responded to non-ACLS interventions. Patients with pericardial effusion and pericardiocentesis demonstrated higher survival rates (15.4%) compared to all others (1.3%). CONCLUSION: Cardiac activity on ultrasound was the variable most associated with survival following cardiac arrest. Ultrasound during cardiac arrest identifies interventions outside of the standard ACLS algorithm.

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

OBJECTIVE: Ultrasound (US) has been shown to be effective at identifying a pneumothorax (PTX); however, the additional value of adding multiple views has not been studied. Single- and four-view protocols have both been described in the literature. The objective of this study was to compare the diagnostic accuracy of single-view versus four-view lung US to detect clinically significant PTX in trauma patients. METHODS: This was a randomized, prospective trial on trauma patients. Adult patients with acute traumatic injury undergoing computed tomography (CT) scan of the chest were eligible for enrollment. Patients were randomized to a single view or four views of each hemithorax prior to any imaging. USs were performed and interpreted by credentialed physicians using a 7.5-Mhz linear array transducer on a portable US machine with digital clips recorded for later review. Attending radiologist interpretation of the chest CT was reviewed for presence or absence of PTX with descriptions of small foci of air or minimal PTX categorized as clinically insignificant. RESULTS: A total of 260 patients were enrolled over a 2-year period. A total of 139 patients received a single view of each chest wall and 121 patients received four views. There were a total of 49 patients that had a PTX (19%), and 29 of these were clinically significant (11%). In diagnosis of any PTX, both single-view and four-view techniques showed poor sensitivity (54.2 and 68%) but high specificity (99 and 98%). For clinically significant PTX, single-view US demonstrated a sensitivity of 93% (95% confidence interval [CI] = 64.1% to 99.6%) and a specificity of 99.2% (95% CI = 95.5% to 99.9%), with sensitivity of 93.3% (95% CI = 66% to 99.7%) and specificity of 98% (95% CI = 92.1% to 99.7%) for four views. CONCLUSIONS: Single-view and four-view chest wall USs demonstrate comparable sensitivity and specificity for PTX. The additional time to obtain four views should be weighed against the absence of additional diagnostic yield over a single view when using US to identify a clinically significant PTX.

Carotid Flow Time Changes With Volume Status in Acute Blood Loss.

STUDY OBJECTIVE: Noninvasive predictors of volume responsiveness may improve patient care in the emergency department. Doppler measurements of arterial blood flow have been proposed as a predictor of volume responsiveness. We seek to determine the effect of acute blood loss and a passive leg raise maneuver on corrected carotid artery flow time. METHODS: In a prospective cohort of blood donors, we obtained a Doppler tracing of blood flow through the carotid artery before and after blood loss. Measurements of carotid flow time, cardiac cycle time, and peak blood velocity were obtained in supine position and after a passive leg raise. Measurements of flow time were corrected for pulse rate. RESULTS: Seventy-nine donors were screened for participation; 70 completed the study. Donors had a mean blood loss of 452 mL. Mean corrected carotid artery flow time before blood loss was 320 ms (95% confidence interval [CI] 315 to 325 ms); this decreased after blood loss to 299 ms (95% CI 294 to 304 ms). A passive leg raise had little effect on mean corrected carotid artery flow time before blood loss (mean increase 4 ms; 95% CI -1 to 9 ms), but increased mean corrected carotid artery flow time after blood loss (mean increase 23 ms; 95% CI 18 to 28 ms) to predonation levels. CONCLUSION: Corrected carotid artery flow time decreased after acute blood loss. In the setting of acute hypovolemia, a passive leg raise restored corrected carotid artery flow time to predonation levels. Further investigation of corrected carotid artery flow time as a predictor of volume responsiveness is warranted.

Multi-Institution Validation of an Emergency Ultrasound Image Rating Scale-A Pilot Study.

BACKGROUND: As bedside ultrasound (BUS) is being increasingly taught and incorporated into emergency medicine practice, measurement of BUS competency is becoming more important. The commonly adopted experiential approach to BUS competency has never been validated on a large scale, and has some limitations by design. OBJECTIVE: Our aim was to introduce and report preliminary testing of a novel emergency BUS image rating scale (URS). METHODS: Gallbladder BUS was selected as the test case. Twenty anonymous BUS image sets (still images and clips) were forwarded electronically to 16 reviewers (13 attendings, 3 fellows) at six training sites across the United States. Each reviewer rated the BUS sets using the pilot URS that consisted of three components, with numerical values assigned to each of the following aspects: Landmarks, Image Quality, and Annotations. Reviewers also decided whether or not each BUS set would be "Clinically Useful." Kendall τs were calculated as a measure of concordance among the reviewers. RESULTS: Among the 13 attendings, image review experience ranged from 2-15 years, 5-300 scans per week, and averaged 7.8 years and 60 images. Kendall τs for each aspect of the URS were: Landmarks: 0.55; Image Quality: 0.57; Annotation: 0.26; Total Score: 0.63, and Clinical Usefulness: 0.45. All URS elements correlated significantly with clinical usefulness (p < 0.001). The correlation coefficient between each attending reviewer and the entire group ranged from 0.48-0.69, and was independent of image review experience beyond fellowship training. CONCLUSION: Our novel URS had moderate-to-good inter-rater agreement in this pilot study. Based on these results, the URS will be modified for use in future investigations.

Learning curves in emergency ultrasound education.

OBJECTIVES: Proficiency in the use of bedside ultrasound (US) has become standard in emergency medicine residency training. While milestones have been established for this training, supporting data for minimum standard experience are lacking. The objective of this study was to characterize US learning curves to identify performance plateaus for both image acquisition and interpretation, as well as compare performance characteristics of learners to those of expert sonographers. METHODS: A retrospective review of an US database was conducted at a single academic institution. Each examination was scored for agreement between the learner and expert reviewer interpretation and given a score for image quality. A locally weighted scatterplot smoothing method was used to generate a model of predicted performance for each individual examination type. Performance characteristics for expert sonographers at the site were also tracked and used in addition to performance plateaus as benchmarks for learning curve analysis. RESULTS: There were 52,408 US examinations performed between May 2007 and January 2013 and included for analysis. Performance plateaus occurred at different points for different US protocols, from 18 examinations for soft tissue image quality to 90 examinations for right upper quadrant image interpretation. For the majority of examination types, a range of 50 to 75 examinations resulted in both excellent interpretation (sensitivity > 84% and specificity > 90%) and good image quality (90% the image quality benchmark of expert sonographers). CONCLUSIONS: Educational performance benchmarks occur at variable points for image interpretation and image quality for different examination types. These data should be considered when developing training standards for US education as well as experience requirements for US credentialing.

Correlation of corrected flow time in the carotid artery with changes in intravascular volume status.

PURPOSE: Assessment of volume status remains a challenge in critical care. Our purpose was to determine if Doppler waveform analysis of carotid artery blood flow correlates with changes in volume status. MATERIALS AND METHODS: Dehydrated patients receiving an intravenous fluid bolus were enrolled with exclusions including age less than 18 years, pregnancy, vasopressor administration, or atrial fibrillation. Ultrasound examination with Doppler analysis of the carotid artery was performed with measurements taken to calculate corrected flow time (FTc). Corrected flow time, mean arterial pressure, and pulse rate before and after fluid administration were compared using Wilcoxon matched-pairs signed rank test. RESULTS: Fifty-six patients were enrolled with mean fluid administration of 1110 mL. Corrected flow time increased with fluid resuscitation from prefluid mean of 299 milliseconds (95% confidence interval [CI], 282-317 milliseconds) to a postfluid mean of 340 milliseconds (95% CI, 323-358 milliseconds) (P<.0001). Mean percentage change in FTc was 14.9% (95% CI, 8.4-21.3). There were no significant changes in mean arterial pressure or heart rate from pre- to post-fluid administration. CONCLUSION: Intravenous fluid administration in dehydrated patients resulted in significant changes in FTc in the carotid artery despite no change in vital signs. Corrected flow time measured from carotid arterial blood flow may be a useful means of assessing volume status in volume-depleted patients.

The Massachusetts abscess rule: a clinical decision rule using ultrasound to identify methicillin-resistant Staphylococcus aureus in skin abscesses.

OBJECTIVES: Treatment failure rates for incision and drainage (I&D) of skin abscesses have increased in recent years and may be attributable to an increased prevalence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA). Previous authors have described sonographic features of abscesses, such as the presence of interstitial fluid, characteristics of abscess debris, and depth of abscess cavity. It is possible that the sonographic features are associated with MRSA and can be used to predict the presence of MRSA. The authors describe a potential clinical decision rule (CDR) using sonographic images to predict the presence of CA-MRSA. METHODS: This was a pilot CDR derivation study using databases from two emergency departments (EDs) of patients presenting to the ED with uncomplicated skin abscesses who underwent I&D and culture of the abscess contents. Patients underwent ultrasound (US) imaging of the abscesses prior to I&D. Abscess contents were sent for culture and sensitivity. Two independent physicians experienced in soft tissue US blinded to the culture results and clinical data reviewed the images in a standardized fashion for the presence or absence of the predetermined image characteristics. In the instance of a disagreement between the initial two investigators, a third reviewer adjudicated the findings prior to analysis. The association between the primary outcome (presence of MRSA) and each sonographic feature was assessed using univariate and multivariate analysis. The reliability of each sonographic feature was measured by calculating the kappa (κ) coefficient of interobserver agreement. The decision tree model for the CDR was created with recursive partitioning using variables that were both reliable and strongly associated with MRSA. RESULTS: Of the total of 2,167 patients who presented with skin and soft tissue infections during the study period, 605 patients met inclusion criteria with US imaging and culture and sensitivity of purulence. Among the pathogenic organisms, MRSA was the most frequently isolated, representing 50.1% of all patients. Six of the sonographic features were associated with the presence of MRSA, but only four of these features were reliable using the kappa analysis. Recursive partitioning identified three independent variables that were both associated with MRSA and reliable: 1) the lack of a well-defined edge, 2) small volume, and 3) irregular or indistinct shape. This decision rule demonstrates a sensitivity of 89.2% (95% confidence interval [CI] = 84.7% to 92.7%), a specificity of 44.7% (95% CI = 40.9% to 47.8%), a positive predictive value of 57.9 (95% CI = 55.0 to 60.2), a negative predictive value of 82.9 (95% CI = 75.9 to 88.5), and an odds ratio (OR) of 7.0 (95% CI = 4.0 to 12.2). CONCLUSIONS: According to our putative CDR, patients with skin abscesses that are small, irregularly shaped, or indistinct, with ill-defined edges, are seven times more likely to demonstrate MRSA on culture.

Inferior vena cava displacement during respirophasic ultrasound imaging.

BACKGROUND: Ultrasound measurement of dynamic changes in inferior vena cava (IVC) diameter can be used to assess intravascular volume status in critically ill patients, but published studies vary in accuracy as well as recommended diagnostic cutoffs. Part of this variability may be related to movements of the vessel relative to the transducer during the respiratory cycle which results in unintended comparison of different points of the IVC at end expiration and inspiration, possibly introducing error related to variations in normal anatomy. The objective of this study was to quantify both craniocaudal and mediolateral movements of the IVC as well as the vessel's axis of collapse during respirophasic ultrasound imaging. METHODS: Patients were enrolled from a single urban academic emergency department with ultrasound examinations performed by sonographers experienced in IVC ultrasound. The IVC was imaged from the level of the diaphragm along its entire course to its bifurcation with diameter measurements and respiratory collapse measured at a single point inferior to the confluence of the hepatic veins. While imaging the vessel in its long axis, movement in a craniocaudal direction during respiration was measured by tracking the movement of a fixed point across the field of view. Likewise, imaging the short axis of the IVC allowed for measurement of mediolateral displacement as well as the vessel's angle of collapse relative to vertical. RESULTS: Seventy patients were enrolled over a 6-month period. The average diameter of the IVC was 13.8 mm (95% CI 8.41 to 19.2 mm), with a mean respiratory collapse of 34.8% (95% CI 19.5% to 50.2%). Movement of the vessel relative to the transducer occurred in both mediolateral and craniocaudal directions. Movement was greater in the craniocaudal direction at 21.7 mm compared to the mediolateral movement at 3.9 mm (p < 0.001). Angle of collapse assessed in the transverse plane averaged 115° (95% CI 112° to 118°). CONCLUSIONS: Movement of the IVC occurs in both mediolateral and craniocaudal directions during respirophasic ultrasound imaging. Further, collapse of the vessel occurs not at true vertical (90°) but 25° off this axis. Technical approach to IVC assessment needs to be tailored to account for these factors.

Sonoelastographic characteristics of abscess induration associated with therapy failure.

OBJECTIVES: Sonoelastography can visualize components of skin and soft tissue abscesses, including the abscess cavity and surrounding induration, related to the patient's response to the infection. We speculate that characteristics of the induration surrounding an abscess may predict which abscesses will eventually fail therapy. METHODS: We conducted a prospective trial of patients with a suspected skin abscess requiring surgical drainage who were enrolled from the emergency department of an urban tertiary care center. In this pilot study, all patients underwent incision and drainage for the suspected abscesses. Abscesses (n = 56) were imaged in orthogonal planes (long-axis and transverse to the body part) using B-mode sonography and elastography before incision and drainage. Telephone follow-up using a standardized questionnaire was performed 7 to 10 days after the initial drainage procedure to determine therapy failure. Physicians blinded to patient outcome analyzed the sonograms for predetermined image characteristics of the abscess induration. RESULTS: All patients underwent incision and drainage, but 16.1% of patients failed therapy. Asymmetry of the surrounding induration was associated with therapy failure. A higher percentage of patients who failed therapy had asymmetry (66%; 95% confidence interval, 35.1%-88.3%) versus those who were successfully treated (12.8%; 95% confidence interval, 5.6%-25.6%; P = .003). In all patients, the mean volumes ± SD of the abscess cavity and induration were 2.2 ± 3.7 and 19.9 ± 24.7 cm, respectively, with a mean volume ratio (induration to abscess cavity) of 31.9 to 1. CONCLUSIONS: We describe sonographic characteristics of the abscess induration imaged with sonoelastography that are associated with therapy failure. We found that patients with asymmetric induration visualized with sonoelastography have higher rates of therapy failure.

Comparison of computerized tomography and ultrasound for diagnosing soft tissue abscesses.

BACKGROUND: The diagnosis of a superficial abscess is usually obtained through history and physical exam but bedside ultrasound (US) and computerized tomography (CT) are sometimes used to assist in the diagnosis. It is unclear which imaging modality is superior for patients with superficial soft tissue infections. We compared the diagnostic accuracy of CT and US in patients with skin and soft tissue infections. METHODS: Patients presenting with a suspected skin abscess that underwent both US and CT imaging were eligible for inclusion. Two physicians blinded to patient characteristics and other imaging results prospectively reviewed the CT and US images for pre-defined image elements, and in circumstances where there was disagreement between these interpretations, a third physician adjudicated the findings. The presence or absence of an abscess cavity was noted on imaging. Imaging detail was summarized using a pre-specified 4-point scale based on the degree of visible detail with higher numbers corresponding to greater detail. The clinical presence of an abscess was defined by surgical evacuation of purulence. Sensitivity and specificity for both CT and US were calculated using Chi square analysis. Comparison between imaging detail was performed using a Student's T-test. Data are presented with (95% confidence intervals) unless otherwise noted. RESULTS: Over an 18 month period 612 patients received a soft tissue bedside ultrasound with 65 of those patients receiving a CT for the same complaint. 30 of these 65 patients had an abscess located in the head and neck (37%), buttock (17%), lower extremity (17%), upper extremity (13%), torso (13%), or hand (3%). US demonstrated a sensitivity and specificity for the diagnosis of abscess of 96.7% (87.0% to 99.4%) and 85.7% (77.4% to 88.0%) respectively. The overall sensitivity and specificity of CT for the diagnosis of an abscess was 76.7% (65.5% to 82.8%) and 91.4% (81.8% to 96.7%) respectively Overall image detail ratings were superior for US compared to CT (3.5 vs 2.3, p = 0.0001). CONCLUSION: US is more sensitive then CT, but CT is more specific for superficial soft tissue abscesses. US demonstrated more visible detail within the abscess cavity compared to CT.

A randomized controlled trial of incision and drainage versus ultrasonographically guided needle aspiration for skin abscesses and the effect of methicillin-resistant Staphylococcus aureus.

STUDY OBJECTIVE: The incidence of skin and soft tissue infections has increased dramatically during the last decade, in part because of increased prevalence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA). Incision and drainage is considered the primary intervention; however, some clinicians prefer ultrasonographically guided needle aspiration because it represents a less invasive alternative. Our hypothesis is that ultrasonographically guided needle aspiration is equivalent to incision and drainage in treating simple skin and soft tissue abscesses. METHODS: This study was a nonblinded randomized controlled trial. Patients with uncomplicated superficial abscesses were randomized to incision and drainage with packing or ultrasonographically guided needle aspiration. Purulence obtained from the abscess was cultured to identify the causative organism. Bedside ultrasonography was performed pre- and postintervention to confirm the presence or absence of an abscess cavity. Patients were followed up at 48 hours (in person by a clinician) and on day 7 (telephone follow-up by research staff). The primary outcome was a combination of sonographic resolution and clinical resolution of the signs and symptoms of ongoing infection at day 7. The signs and symptoms of ongoing infection include increasing pain, erythema, and the presence of pus. Resolution was assessed with both sonographic resolution (day 0 and day 2) and improvement of clinical symptoms (day 2) and resolution of clinical symptoms (day 7) without further intervention. RESULTS: A total of 101 patients were enrolled, 54 incision and drainage and 47 ultrasonographically guided needle aspiration patients. At initial presentation, 60% (95% confidence interval [CI] 45% to 70%) of needle aspirations yielded little or no purulence, despite sonographic visualization of an abscess cavity and sonographic guidance during the procedure. The overall success of ultrasonographically guided needle aspiration was 26% (95% CI 18% to 44%) compared with 80% (95% CI 66% to 89%) success in patients randomized to incision and drainage. The difference between groups was 54% (95% CI 35% to 69%). Overall success of both incision and drainage and ultrasonographically guided needle aspiration was lower in patients with CA-MRSA. Patients with CA-MRSA (n=33) were less likely to receive successful drainage with needle aspiration (8% versus 55%) or incision and drainage (61% versus 89%). The difference for needle aspiration and incision and drainage was 47% (95% CI 15% to 57%) and 28% (95% CI 4% to 45%), respectively. CONCLUSION: Ultrasonographically guided needle aspiration is insufficient therapy for skin abscesses. The presence of CA-MRSA decreases the success of both incision and drainage and ultrasonographically guided needle aspiration.

Incidence of posterior vessel wall puncture during ultrasound-guided vessel cannulation in a simulated model.

OBJECTIVES: The incidence of posterior vessel wall puncture (PVWP) during central line placement with possible subsequent injury to structures lying behind the vein is unknown. At times the internal jugular vein lies immediately anterior to the carotid artery rather than lateral to it, leading to potential arterial puncture should the needle pass through the vein completely. The objective of this study is to evaluate the incidence of PVWP during simulated ultrasound (US)-guided vessel cannulation. METHODS: Enrolled subjects were emergency medicine resident and attending physicians. Subjects performed US-guided venous access on simulated blood vessels within gelatin-based US phantoms. While blinded to the purpose of the study, each subject performed successful cannulation of the vessel on separate phantoms, with wire placement confirmed by expert review of a follow-up US. Each phantom was subsequently deconstructed to manually inspect for PVWP. RESULTS: Thirty-five subjects with a range of experience in the technique participated, each performing both transverse and long-axis approaches for a total of 70 cannulations. The overall incidence of PVWP was 34% (95% confidence interval [CI] = 22.9% to 45.1%). CONCLUSIONS: This study found a high incidence of inadvertent PVWP during simulated US-guided vessel cannulation in this model.

Use of ultrasound elastography for skin and subcutaneous abscesses.

OBJECTIVE: Elastography is a new adjunct to real-time ultrasound imaging that overlays traditional B-mode imaging with a color graphic representation of tissue elasticity. Soft tissue infections are common presenting conditions in the emergency department, and elastography has the potential to help in diagnosis and treatment of evolving soft tissue infections as they progress from induration to fluctuant abscesses, but to our knowledge, no studies of elastography in superficial soft tissue have been published. We hypothesized that elastography would provide increased information regarding skin abscesses. METHODS: This was a prospective study of patients with suspected skin abscesses requiring surgical drainage in the emergency department of an urban tertiary care center. Abscesses were imaged with B-mode imaging and elastography in orthogonal planes. Ultrasound images were analyzed for characteristics of the elastographic images. RESULTS: A total of 50 patients with suspected skin abscesses underwent B-mode imaging and elastography. Elastography accurately differentiated the induration surrounding the abscess from the surrounding healthy tissue, a differentiation that was not visible on B-mode imaging. The elastographic properties of the abscess cavity were variable and not always seen, even with purulence identified during incision and drainage. In some cases, elastography identified abscess cavities not seen on B-mode imaging. When seen, the abscess cavity could be characterized by elastographic color and speckle patterns. CONCLUSIONS: Elastography identified the tissue induration and some abscess cavities not seen on B-mode imaging. It offers a way to characterize abscesses that may be useful clinically, but more research is needed.

Learning curve of bedside ultrasound of the gallbladder.

Existing guidelines for the number of ultrasounds required before clinical competency are based not on scientific study but on consensus opinion. The objective of this study was to describe the learning curve of limited right upper quadrant ultrasound. This was a prospective descriptive study. Ultrasounds collected over 1 year were reviewed for interpretive and technical errors. Possible errors during bedside ultrasound of the gallbladder include incorrect interpretation, incomplete image acquisition, and improper or poor imaging techniques resulting in poor image quality. The ultrasound image quality was rated on a 4-point scale, with 1 = barely interpretable and 4 = excellent image quality. Required images were rated on an additional 4-point scale, with 4 = all required images were included and 1 = minimal images were recorded. There were 352 patients enrolled by 42 emergency physicians (35 residents and 7 attendings). Gallstones were identified in 13.9% of the patients, and 4.3% of the ultrasounds were indeterminate. Interpretive and technical error rates decreased as the clinician gained experience. The number of poor quality ultrasounds decreased after an average of seven ultrasounds. Inclusion of all required images increased after 25 ultrasounds. Sonographers who had performed over 25 ultrasounds showed excellent agreement with the expert over-read, with only two disagreements, both from a single individual. It was concluded that clinicians are clinically competent after performing 25 ultrasounds of the gallbladder.

Identification of congestive heart failure via respiratory variation of inferior vena cava diameter.

INTRODUCTION: Rapid diagnosis of volume overload in patients with suspected congestive heart failure (CHF) is necessary for the timely administration of therapeutic agents. We sought to use the measurement of respiratory variation of inferior vena cava (IVC) diameter as a diagnostic tool for identification of CHF in patients presenting with acute dyspnea. METHODS: The IVC was measured sonographically during a complete respiratory cycle of 46 patients meeting study criteria. Percentage of respiratory variation of IVC diameter was compared to the diagnosis of CHF or alternative diagnosis. RESULTS: Respiratory variation of IVC was smaller in patients with CHF (9.6%) than without CHF (46%) and showed good diagnostic accuracy with area under the receiver operating characteristic curve of 0.96. Receiver operating characteristic curve analysis showed optimum cutoff of 15% variation or less of IVC diameter with 92% sensitivity and 84% specificity for the diagnosis of CHF. CONCLUSION: Inferior vena cava ultrasound is a rapid, reliable means for identification of CHF in the acutely dyspneic patient.