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Journal Watch - Emergency Ultrasound Section Newsletter, December 2012

Brian Euerle MD RDMS FACEP
Greg R. Bell MD

Article: Brooke M, Walton J, Scutt D, et al. Acquisition and interpretation of focused diagnostic ultrasound images by ultrasound-naive advanced paramedics: trialing a PHUS education program. Emerg Med J. 2012;29(4):322-326.

Reviewer: Alisa Sato MD, Emergency Ultrasound Fellow, Harbor-UCLA Medical Center

Objective: To investigate whether paramedics can acquire and interpret lung ultrasound (US) images accurately after a brief educational course.

Methods: This was a prospective observational cohort study performed through the University of Liverpool and the North West Ambulance Service NHS Trust. Ten of 36 advanced paramedics volunteered for the study and underwent 2 days of training on thoracic US. The participants were taught how to identify pleural sliding, comet tail artifacts, and a lung point using two-dimensional (2D) ultrasound imaging and how to use M-mode to identify “seashore” signs and “stratosphere” signs. After the training, the paramedics underwent a two-part examination that assessed their ability to 1) evaluate video clip images for the presence or absence of a pneumothorax and 2) obtain images of sufficient quality to identify a pneumothorax. These results were compared with those of two blinded ultrasound experts to determine overall accuracy.

Results: For part I (evaluating prerecorded lung ultrasound video clips), the paramedics assessed a total of 30 images and answered 3 questions for each image. The paramedics demonstrated accuracy similar to that of the experts in identifying a pneumothorax in M-mode clips (0.94 vs 0.93), and 2D mode clips (0.78 vs 0.76). For part II (objective structured clinical examination assessment), all advanced paramedics engaged in a direct clinical examination and were assessed by two expert sonographers, with a 100% success rate. All paramedics obtained excellent US images and interpreted them correctly.

Discussion: This study proposes that paramedics can achieve excellence in acquiring and interpreting lung US images compared with expert sonographers with 2 days of basic education and US training. This very small pilot study involved only 10 advanced paramedics, which is a limitation. It is difficult to anticipate how well the paramedics may implement these US techniques during the pressured environment of the real prehospital setting. Nonetheless, this study implies that paramedics are capable of rapidly learning thoracic US and identifying a pneumothorax, which could be life-saving in the field.

Article: Weiner SG, Sarff AR, Esener DE, et al. Single-operator ultrasound-guided intravenous line placement by emergency nurses reduces the need for physician intervention in patients with difficult-to-establish intravenous access. J Emerg Med. 2012 Oct 25. [Epub ahead of print]

Reviewer: Gregory R. Bell MD, Assistant Clinical Professor and Director of Emergency Ultrasound, University of Iowa

Objective: To determine if ultrasound-guided IV (USIV) placement by emergency nurses (EN) who undergo a brief training session can be performed with less physician intervention than standard IV line placement.

Methods: This was a prospective two-center non-blinded pilot study of 50 conveniently enrolled patients who had either a history of difficult IV placement or two failed standard IV attempts by ENs. The patients were randomly assigned to undergo either USIV placement or institutional standard-of-care (SOC) methods for difficult IV placement (not including USIV). The two centers were a large city ED (42,000 patients/year) and a medium-sized city ED with a large rural catchment (106,000 patients/year). Nurses received the same 2-hour didactic instruction and simulation training and exposure to the ultrasound machines at their respective facilities. They were taught the single-operator, out-of-plane approach. Enrollment into the study was granted when they were successfully able to cannulate using a training phantom. Nurses used their choice of needle sizes at both facilities. Patients were randomly enrolled when one of four trained researchers and a trained nurse were working in the emergency department. Parameters included total skin punctures, time from randomization, the result, and patients’ perception of pain and level of satisfaction.

Results: The cohort included 21 (42%) in the SOC arm and 29 (58%) in the USIV arm. Physicians were asked to help in 11/21 (52.4%) of SOC patients and 7/29 (24.1%) of the USIV patients (p=0.04). Other findings, not significantly different between groups, included the number of punctures, time taken for IV placement, pain perception, and patient satisfaction. Satisfaction was higher, however, in the USIV group.

Discussion: With a nominal amount of instruction, ultrasound guidance for IV placement has been an effective tool for physicians, nurses, and emergency medical technicians. This pilot study found that with 2 hours of instruction, nurses using USIV were significantly more successful and required less physician back-up than those not trained in this procedure. The authors point out that this is likely to free up physician time to tend to other matters, and it may reduce the need for central venous access. The authors point out the selection biases in the study.

Article: Sim SS, Lien WC, Chou HC, et al. Ultrasonographic lung sliding sign in confirming proper endotracheal intubation during emergency intubation. Resuscitation. 2012;83:307-312.

Reviewer: Adrea Lee MD, Emergency Ultrasound Fellow, Department of Emergency Medicine, University of Maryland School of Medicine

Objective: To assess the accuracy and timeliness of the use of ultrasound to confirm proper endotracheal tube (ETT) positioning in the trachea (and not in the mainstem bronchus) after intubations performed in the emergency department (ED).

Methods: This prospective, single-center, observational study enrolled 115 adult patients who were intubated in the ED for respiratory failure or cardiac arrest. After endotracheal intubation was confirmed by auscultation, pulse oximetry, and continuous waveform capnography, ultrasound was used to identify the presence or absence of lung sliding in the midaxillary line at the fourth or fifth intercostal space bilaterally. Bilateral lung sliding was interpreted as an ultrasonographic sign of correct placement. The primary outcome of the study was accuracy of ultrasound compared with the standard of chest radiography to confirm endotracheal and not endobronchial (ie, mainstem or one-lung intubation) placement. The secondary outcome was the timeliness of ultrasound compared with chest radiography.

Results: Of the 115 patients included in the study, 9 (7.8%) had one-lung intubations. The overall accuracy of ultrasound in confirming proper ETT placement was only 88.7%. The positive predictive value (PPV) was 95.7% in patients intubated for non-cardiac arrest reasons, but 100% in patients who were intubated for cardiac arrest. The negative predictive values (NPVs) were poor (overall 35.7%). The median operating time for ultrasound was 88 s, while that of chest radiography was 1349 s.

Discussion: This study did not find that ultrasound was equivalent to chest radiography in confirming proper positioning of the ETT after intubation. In subgroup analysis, however, the PPV of ultrasound in cardiac arrest patients was 100%, warranting further investigation, as the number in the cardiac arrest group was relatively low (n=31). In addition, the authors point out that ultrasound can be especially useful in this population, as these patients are unlikely to have chest radiography performed unless there is return of spontaneous circulation. The unilateral absence of lung sliding was insufficient to diagnose one-lung intubation, which the authors felt was in part due to the multiple anatomic causes of false negatives (malignancy, pneumothorax, effusions). The authors concluded that ultrasound is a reasonable adjunct to the standard clinical exam when assessing ETT position and that more investigation is needed to determine which populations may benefit the most from this time-saving technique.

Article: Major R, Girling S, Boyle A. Ultrasound measurement of optic nerve sheath diameter in patients with a clinical suspicion of raised intracranial pressure. Emerg Med J. 2011;28:679-681.

Reviewer: Alisa Sato, MD, Emergency Ultrasound Fellow, Harbor-UCLA Medical Center

Objective: To determine if bedside ultrasound measurement of optic nerve sheath diameter (ONSD) can accurately predict the presence or absence of raised intracranial pressure (ICP) and acute pathology in the emergency department.

Methods: This was a prospective 3-month observational study at a large urban teaching hospital in Norwich, UK, conducted from November 2007 to February 2008. After a brief training session, a group of emergency department middle grades measured the ONSD in both eyes of patients referred for a CT scan for evaluation of acute traumatic and non-traumatic pathology. A positive ONSD measurement was taken as an average of greater than 5 mm in both eyes. Two independent radiologists reviewed the CT scan images. The criteria for the diagnosis of raised ICP included one or more of the following: mass effect with midline shift of 3 mm or more, collapsed third ventricle, hydrocephalus, effacement of sulci with evidence of significant edema, or abnormal mesencephalic cisterns. The primary outcome measure was the sensitivity and specificity of ONSD measurement in identifying raised ICP evident on CT scan, and the secondary outcome measure was identifying any acute intracranial pathology evident on CT scan.

Results: Twenty-six patients were enrolled in the study; six of them had raised ICP on ONSD measurement. The radiologists confirmed signs of raised ICP on CT scans for all six of these patients. One patient had a positive CT scan without evidence of raised ICP on ONSD measurement. For the primary outcome measure (identifying increased ICP), ONSD had a specificity of 100% and a sensitivity of 86%. For the secondary outcome measure (identifying acute intracranial pathology), ONSD had a specificity of 100% and sensitivity of 60%.

Discussion: The authors concluded from this small study that, with minimal training, ONDS is a specific and sensitive measure of raised ICP and acute intracranial pathology in patients referred for CT scan in the emergency department. There were several limitations to this study, however. First, the middle grades were not blinded from the overall clinical state of their patients, which may have introduced some bias in acquiring the OSND measurement. Also, the study was very small and the patient characteristics were highly different between the trauma and non-trauma groups (for example, the non-trauma patients were much older with a worse Glasgow Coma Scale score compared with the trauma patients). Larger observational studies, possibly separating trauma from non-trauma patients, may be helpful in confirming that ONDS is indeed a helpful diagnostic tool to evaluate patients for increased ICP and acute intracranial pathology.

Article: Parri N, Crosby BJ, Glass C, et al. Ability of emergency ultrasound to detect pediatric skull fractures: a prospective, observational study. J Emerg Med. 2012 May 10 (Epub ahead of print).

Reviewer: Brian D. Euerle MD RDMS, Associate Professor, Department of Emergency Medicine, University of Maryland School of Medicine

Objective: To determine the sensitivity, specificity, and predictive values of ultrasound for identifying skull fractures in pediatric patients with minor head trauma.

Methods: This was a prospective, observational study done at a single pediatric emergency department. Children less than 18 years of age with a history of head trauma and localizing signs of trauma, such as hematoma, abrasion, or focal tenderness, who were determined to require a head CT were considered for enrollment into the study. Exclusion criteria included hemodynamic instability, neurologic deterioration, Glasgow Coma Scale score <14, open deformity, or a depressed fracture. The ultrasound assessment was performed by a study investigator who was either an emergency medicine ultrasound fellow or a pediatric emergency physician and was blinded to the clinical scenario. All study investigators had completed a 16-hour ultrasound training curriculum as well as practice cranial scanning on pediatric volunteers. Ultrasound scans were performed in the area of localized trauma using a 7.5-MHz linear probe. Entire head scanning was not done as it was felt to be impractical. Ultrasound-visible fractures were defined as cortical defects seen in two orientations not correlating with anatomic, symmetric sutures. The ultrasound study was performed before head CT whenever possible. Ultrasound findings were reported as either positive or negative for fracture and were compared with the CT scan results, which were obtained with a 40- or 64-slice scanner.

Results: Serial enrollment of eligible patients yielded 55 patients for analysis. CT scan showed 35 (63.6%) patients with cranial fractures and 20 (36.4%) without fractures. The ultrasound scan correctly identified each fracture, in the correct location with no false negatives, giving a sensitivity of 100% (95% CI, 88.2‒100). One ultrasound scan was interpreted as positive for fracture and the CT was negative, yielding a specificity of 95% (95% CI, 75‒99.9). The positive predictive value of ultrasound for cranial fractures was 97.2% (95% CI, 84.6‒99.9) and the negative predictive value was 100% (95% CI, 80.2‒100).

Discussion: In this study, cranial ultrasound had excellent accuracy in diagnosing skull fractures compared with the gold standard of CT scan. The authors commented that the ultrasound examinations were brief, painless, and relatively simple to perform by emergency physicians with varying levels of training. In an era in which physicians are increasingly mindful of the radiation exposure of patients, this is an important area for further research. It remains unclear as to how this technique might be incorporated into the overall management of head injury patients; it must be kept in mind that CT, of course, evaluates the skull as well as the underlying brain.
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