Mass casualty incidents
Preparation for mass casualty incidents (from natural or other disasters) has become a major focus of training for prehospital providers around the globe in recent years. Triage of casualties to an appropriate level of care or disposition is paramount; EMS providers are often faced with an overwhelming number of injured that must be assessed rapidly. Several studies have examined the role that ultrasound may play in enhancing existing triage systems during multicasualty incidents.
In 1988 an earthquake in Armenia killed over 25,000 people and injured over 150,000 [
32]. Within 72 h after the disaster, 750 patients were admitted to the large receiving hospitals in the capital city of Yerevan. Although there was only a single computed tomography (CT) scanner available, many ultrasound machines were utilized to perform trauma evaluations on admitted patients; 530 ultrasound examinations were performed on 400 patients in this study. Of these, 96 patients were found to have a clinically significant pathological condition. There were 16 patients in this study who were taken to the operating room based on ultrasound findings and physical examination. There were only three patients in the study who received a CT scan as part of their evaluation if they were not head injury cases; all others were managed based on physical examination and ultrasound. The authors noted four false-negative ultrasound examinations, including kidney rupture, subcapsular splenic hematoma, retroperitoneal hematoma, and an obese patient with hemothorax.
A Turkish earthquake in 1999 was the setting for another study of ultrasound use as a triage tool. In this natural disaster, 17,000 deaths and over 100,000 injuries were reported [
33]. Renal ultrasound was utilized by physicians in this study to evaluate nine patients with crush injury. The resistive index (a measure of renal vasoconstriction) was measured using Doppler ultrasonography. The authors found that the resistive index was increased in patients with acute crush injury and correlated with the need for hemodialysis and the duration of dialysis dependence. Ultrasound impacted care of patients with regards to fluid resuscitation and other management options.
In the aftermath of mudslides which killed over 1,000 people in Guatemala, a hand-carried ultrasound unit was brought on-site by relief workers to evaluate injured patients [
34]; 137 ultrasound examinations were performed on 99 patients. A wide range of scans were performed, including pelvic, right upper quadrant, cardiac, thoracic, and soft tissue scans. The authors report that for 12% of patients, ultrasound confirmed the presence of an emergent disorder. In 42% of patients, ultrasound was able to rule out disease. Although this study was set during the relief effort after a natural disaster, many patients were evaluated for illnesses which were not acute; 23% of patients presented with illnesses less than 24 h in duration, and 44% were greater than 14 days in duration. Thus, it may be difficult to generalize all of the data to an acute multi-casualty scenario.
During the Second Lebanon War, casualties received by a level I trauma center were triaged according to the Injury Severity Score (ISS) [
35]. A FAST examination was performed in 102 of 281 admissions with suspected abdominal injury. The authors report that five hemodynamically unstable patients were taken for operative intervention based on a positive FAST examination; 28 hemodynamically stable patients were managed solely with ultrasound and did not undergo CT scan (based on the negative ultrasound and low suspicion for injury). The authors report that ultrasound was useful as a screening tool in determining which patients should be dispositioned to laparotomy, CT scan, or clinical observation during multicasualty incidents. However, it should be noted that not every casualty was screened with ultrasound, and the study was retrospective in nature.
Another retrospective study examined the role of ultrasound as an adjunct to the simple triage and rapid treatment (START) mass casualty triage system [
36]. In the START system, patients are triaged to ambulatory (green), delayed (yellow), immediate (red), and expectant (black) based on clinical criteria such as vital signs and the Glasgow Coma Scale. The charts of 570 patients from the trauma registry at a level I trauma center were reviewed, and each patient was assigned a START triage classification of yellow, red, or black. FAST examination results were available for 359 patients; 27 were positive. The authors found 22.2% of positive FAST exams represented false positives, which would have resulted in overtriage of yellow patients to the red category. In addition, 12.9% of the negative studies were false negatives. Reliance on ultrasound alone would have undertriaged this group. Although it is difficult to draw conclusions based on this retrospective study, there did not appear to be a benefit of using the FAST examination as a tool to alter triage disposition.
One important question regarding ultrasound deployment in disaster scenarios is the number of ultrasound units which would be required to truly speed triage decisions [
36]. A single ultrasound operator would create a triage bottleneck when many patients were being assessed; thus multiple providers with multiple machines would need to be deployed to effect any time savings from the technology. No prospective, controlled studies of ultrasound use in triage have been described and the results of retrospective reviews have been mixed. While the technology holds promise for improved triage assessment in the field, it is difficult to draw conclusions regarding the utility of the technique given current published data.
Telemedicine
Another emerging area for prehospital care is telemedicine, which allows clinicians from remote sites (such as base medical centers) to review images and diagnostic data from EMS providers on-scene or en route. The concept of image data transmission from ambulances is not new; in 1987, a study demonstrated the feasibility of 12-lead ECG transmission via cellular telephone [
37]. In the decades that followed, EMS performance, interpretation, and transmission of ECGs has become commonplace and has been shown to positively impact patient care [
38]. In 1996, remote review of inhospital echocardiography studies transmitted to laptop computers via standard telephone lines was described [
39]: 187 studies were transmitted and reviewed remotely; 153 were abnormal, 19 were technically limited. The authors reported 99% agreement between telemedicine laptop interpretation and conventional workstation interpretation.
The feasibility of real-time wireless transmission of ultrasound images was examined in 2003 [
40]. FAST exam images were obtained on an ambulance and transmitted wirelessly to a line-of-sight antenna, then sent via satellite for review at a remote location. The authors noted antenna (line-of-sight) images were of comparable quality to those viewed on-site. There was a reduction in image quality noted when images transmitted via satellite were reviewed remotely (32% reduction for still and 42% for video clips). In another study, prerecorded cardiac scans were transmitted from an ambulance in the field via 2.5-GHz spread-spectrum radio transmitter [
41]. Transmitted images were compared side-by-side (in real time) at the base hospital. Recorded (and not live) images were transmitted to allow for the most direct comparison of image quality. In this series, 32 studies were transmitted while the ambulance was in motion (50–75 mph). Findings of left ventricular function, effusion, and inferior vena cava anatomy had the highest image quality ratings (mean 97–100% equivalent to original videos). In contrast, wall motion assessment (mean 13% equivalent) and valvular anatomy (mean 27–60% equivalent) were not well visualized on transmitted images.
Improved image quality upon transmission was demonstrated in a study from 2004; echocardiograms performed in the field were transmitted via wireless microwave signal to a satellite transmission for off-site review [
42]. In this study, 12 transmitted studies were compared to on-site images as well as formal echocardiography performed on standard, non-portable equipment. Blinded cardiologist reviewers graded good agreement in technical quality (83%), left ventricle size (92%), pericardial effusion (100%), and ejection fraction (100%).