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Portable Ultrasound Devices in Emergency Departments

Last updated: March 10, 2006
Issue: 63
Result type: Report

Context and Policy Issues

In the emergency department (ED), prompt and accurate diagnoses made by physicians are a prerequisite for the effective and timely treatment of patients with serious illnesses and injuries. Modern diagnostic methods such as ultrasonography (U/S) and computed tomographic (CT) scanning play a role in enhancing the quality of medical care. The machines that are used are often located in imaging departments, are complicated to operate, and may be unavailable outside regular daytime working hours. A survey conducted in 2002 reported that after-hours U/S was available to Canadian emergency physicians (EPs) in 94% of hospitals, and 75% of these scans were performed by radiologists or ultrasound technicians. Although 88% of the radiologists regarded the emergency service as “good or excellent,” only 48% of the EPs agreed, and 29% of them thought that the emergency radiology service was “poor.”

Smaller, portable ultrasound (pU/S) devices, which can easily be brought to the bedside, have been introduced. EPs, surgeons, and other non-radiologists have started to perform emergency ultrasound examinations with the intent of improving the certainty of diagnoses and potentially reducing the use of certain invasive examinations. Because these non-radiologists may receive limited or no U/S training, and do not have the same knowledge of U/S as radiologists, the chances of misdiagnosis may increase. It is unclear if and how much training is required; and what the minimum requirements of reporting are to ensure accountability.

Portable devices need to be distinguished from hand-held machines for U/S. The latter do not have the technical capabilities of the larger devices.

Research Questions

1a. What is the evidence of effectiveness (improved technical outcomes, improved clinical decision making, improved patient-relevant outcomes, and reduced harm) when non-radiologists use pU/S devices for assessing abdominal trauma, abdominal aortic aneurysm (AAA), and ectopic pregnancy?
1b. What is the evidence regarding the effect of diagnostic accuracy on the effectiveness of these interventions?
1c. What is the evidence regarding the effect of user-dependent variables on the effectiveness of the intervention, specifically for the user (general practitioners, EPs, and other non-radiologists), the type of training, the length of training, and previous experience in emergency U/S examinations?
2a. What guidelines exist regarding the use of these devices for the indications?
2b. What is the level of evidence supporting these guidelines?
2c.Are the recommendations in the guidelines consistent with the evidence?
3. What are the ethical and legal implications of using and reporting information from pU/S and other ultrasound imaging technologies?

Methods

A protocol was developed a priori, and clinical questions were developed in consultation with methodological and clinical experts. Published literature was obtained by searching multiple databases using a defined search strategy and by searching the bibliographies of selected papers. For Research Questions 1a and 2a, two reviewers independently and systematically applied inclusion and exclusion criteria to all available literature, and performed data extraction. One reviewer rated the quality of the included studies. For Research Question 3, a qualitative-review approach was adopted. A quantitative review of the clinical effectiveness of pU/S use in EDs was conducted. Summary likelihood ratios (LRs) and post-test probabilities in clinical scenarios were calculated, based on the data from individual studies, to evaluate the clinical effectiveness of ED pU/S.

Findings

From 1,020 initial citations, 135 were identified as potentially meeting the selection criteria. After the full reports were reviewed, 49 were judged to have met the inclusion criteria. Of the 49 reports, 29 addressed Research Question 1a (clinical effectiveness of pU/S). The included studies were two comparative studies and 16 case series reports of pU/S for abdominal trauma; one case series report for AAA; three comparative studies and four case series reports for ectopic pregnancy; and three case series reports detailing more than one use. The quality of the identified primary studies was impaired by potential selection bias, differential use of a reference standard, or failure to use a blinded reference standard. For Research Question 1c, we identified six training guidelines and nine training programs. For Research Question 2a, two clinical practice guidelines and three systematic reviews were identified.

Research Question 1a: We did not identify any studies that reported mortality rates or patient survival rates for any condition. One retrospective comparative study examined the effect of emergency U/S on time to diagnosis and on time to operative treatment. A statistically significant difference was shown in favour of pU/S in EDs. False-positive and false-negative diagnosis data were routinely reported. The most frequently reported outcome measures in the included studies were sensitivity and specificity. Among patients with abdominal trauma, most of the values of sensitivity for detecting free fluid were between 0.80 and 0.90; a similar range of sensitivity for detecting free fluid plus organ injury was observed. The values of specificity were typically 0.96 to 1.00, for the detection of intraperitoneal free fluid. For patients with AAA, the sensitivity of emergency U/S was reported to be 1.00. Emergency U/S had a sensitivity of 0.82 to 1.00, and a specificity of 0.88 to 1.00 in detecting ectopic pregnancy. The summary estimates of positive LRs were 61.76, 14.57, and 14.55 for blunt abdominal trauma, ectopic pregnancy, and AAA respectively. The summary estimates of negative LRs were 0.20, 0.08, and 0.06 for blunt abdominal trauma, ectopic pregnancy, and AAA respectively.

Results from one prospective comparative study showed that the accuracy of the diagnosis is associated with greater observer education. The U/S training courses for EPs and other non-radiologists usually consisted of a didactic session, followed by a hands-on practical session with live human models. In the primary studies identified, previous training experience of eight to 12 hours of didactic sessions and 15 to 50 supervised U/S scans were reported by most researchers. The minimum number of pU/S scans ranged from 50 to 500, while the minimum number of accurate scans recommended in the training guidelines ranged from 15 to 25.

All the identified trials were conducted in metropolitan hospitals, so we could not differentiate, based on the available evidence, between emergency pU/S in a rural location and that in an urban location.

Research Question 2a: Two clinical practice guidelines suggested that focused abdominal sonography for trauma (FAST) was useful as an initial screening tool when used by surgeons for patients with blunt abdominal trauma. The recommendations from these guidelines were inconsistent with the findings of three systematic reviews. One concluded that more trials should be conducted before ultrasound is accepted as a standard test for the evaluation of blunt trauma. Another review concluded that in terms of clinically suspected abdominal trauma, other effective assessment (i.e., CT) should be performed regardless of the initial sonographic findings. The third review concluded: “There is insufficient evidence from RCTs to justify promotion of ultrasound-based clinical pathways in diagnosing patients with suspected blunt abdominal trauma.”

In six guidelines that describe training and credentialing requirements, the minimum number of pU/S scans ranged from 50 to 500, while the minimum number of accurate scans recommended ranged from 15 to 25. Recommendations about documentation suggested that pU/S reports be labelled as “limited ED ultrasound,” to differentiate it from the formal U/S examinations performed by a radiologist in the imaging department. We did not find evidence of ongoing experience or continuous training on clinical effectiveness. All recommendations in the six guidelines seemed to be consensus-based with some unstructured consideration of the literature. Standards for the amount of training of non-radiologists were generally higher than reported in the included primary studies. Documentation standards were generally more elaborate than those reported in the primary studies.

Research Question 3a: The ethical responsibilities of non-radiologists with respect to ED pU/S are similar to those required of radiologists. Patients should be informed that ED pU/S is a focused, limited examination. Greater adherence to specialty-specific guidelines for emergency U/S, such as those developed by the Canadian Emergency Ultrasound Society (CEUS), will minimize misdiagnosis and potential litigation.

Conclusions and Implications

The results of this review suggest that the demonstrated benefits of ED pU/S performed by non-radiologists are limited to improving diagnostic certainty. We did not find convincing evidence that ED pU/S administered by a non-radiologist has an impact on outcomes that is relevant to patients’ health. In this report, we were unable to identify compelling evidence of improving time to diagnosis or time to operative treatment. These patient-relevant outcomes are reported so infrequently that statements for or against ED pU/S are impossible to make.

There is enough evidence from studies of blunt abdominal trauma, AAA, and ectopic pregnancy to suggest that ED pU/S performed by non-radiologists is an effective tool for improving diagnostic certainty. pU/S is likely to improve the certainty of diagnosis in an ED. These results are robust – the estimated effect remains similar even when only studies of a higher quality are considered. The non-therapeutic advantages of using this technique are that it is easier to use and repeat, it is inexpensive to perform with the available technology, and it is non-invasive.

There is evidence of misdiagnosis with pU/S, which is associated with inexperience. There is additional evidence of improved performance from non-radiologist physicians who undergo training. Training programs that use didactic and practical sessions (a minimum of 50 scans for each medical use) have shown improved effectiveness. Misdiagnoses with pU/S scans that are performed by trained non-radiologist physicians can still occur, but at rates akin to those observed in similar studies of radiologist-performed U/S scans.

We were able to identify clinical practice guidelines for emergency U/S examinations for patients with abdominal trauma. None of the guidelines are specifically intended for non-radiologist physicians. Decisions to implement ED pU/S will need to be based on tacit knowledge and local guidance.

Training and credentialing guidelines are important with respect to the ethical and legal requirements for emergency pU/S examinations that are performed by EPs, because guidelines for other specialties include topics that are not pertinent to emergency medicine. Training programs exist for the performance of U/S examinations. A training standard for physicians who use pU/S in the ED is important to ensure patient safety. Recommendations regarding the amount of continuing experience needed to maintain competence are essential.

Additional prospective, comparative, high quality studies, designed to measure the impact of ED pU/S on efficiency, while monitoring clinical efficacy, would be helpful for making evidence-based decisions. The body of evidence describing diagnostic performance needs to be supplemented with results that demonstrate the effect of this intervention on diagnostic reasoning and time to definitive care.