Interpretation Accuracy and Theoretical Decision Impact of Prehospital Ultrasound for Paramedics - Analysis of a Rural Pilot Program

Abstract

OBJECTIVES:

Focused, limited-scope prehospital ultrasound (PHUS) has become increasingly feasible for paramedics to learn and implement. However, the impact of ultrasound findings on paramedic clinical decisions has not been well examined. In this pilot program, we investigated the accuracy of paramedic interpretation and theoretical impact of ultrasound findings on clinical decisions in a small rural pilot program of PHUS in the state of New Hampshire.

METHODS:

In this prospective observational cohort study, five experienced paramedics performed 47 total exams during patient care, including focused assessment with sonography in trauma (eFAST) (n=15), focused pulmonary (n=20), and cardiac arrest echocardiography (n=12). Paramedics were instructed to follow existing protocols and not use PHUS findings to change decisions. Paramedics completed online forms post-call, which included their diagnostic exam interpretation and perceived impact of PHUS on treatment, transport, and receiving facility decision if PHUS was integrated into care. The program medical director performed an independent review of the associated PHUS exam image clips and made a “gold standard” interpretation. Then, paramedic interpretations were compared as accurate, indeterminate due to poor window quality, or inaccurate. Statistical differences between the three different exam types were examined using contingency tables.

RESULTS:

Among all exam types, 39 (83%) were accurately interpreted with adequate windows, 7 (15%) were indeterminate from incomplete windows, and only one (2%) was truly inaccurate. Paramedics reported that 10 (8%) exams would have impacted their decisions if integrated into care, 55 (46%) would have supported the decision that they made without PHUS, and 54 (45%) would not have impacted their decision. Overall, 32 (63%) pulmonary, 23 (64%) eFAST, and 10 (31%) cardiac exams would support or impact their decisions (p=0.04).

CONCLUSIONS:

Trained, experienced paramedics can acquire and accurately interpret focused PHUS exams in the field. Incomplete windows were the most frequent source of interpretation error. Paramedics reported that PHUS findings would support or impact their clinical decisions in the majority of uses, with pulmonary and eFAST providing the most decision support of exams studied. These results support growing evidence that PHUS may support prehospital decisions and patient care in focused, protocolized use cases in rural settings.

INTRODUCTION

Point of Care Ultrasound (POCUS) has been integrated into emergency department (ED) care in the United States (U.S.) since the 1990s given its accessibility at the bedside and ability to visualize and help diagnose common pathologies. Multiple studies demonstrate that with appropriate training, the use of POCUS by emergency clinicians can improve diagnostic accuracy, time to diagnosis, and decrease procedural complications (1,2).

Since integrating ultrasound into the ED, there has been parallel interest to incorporate POCUS into emergency medical services (EMS). The mobile, unpredictable nature of the prehospital environment brings minimal availability of diagnostic tools, forcing paramedics to make critical decisions with limited information (4–6). Despite this diagnostic uncertainty, accurate prehospital decisions improve patient outcomes and care coordination, and POCUS has been investigated as a fast and actionable tool to support clinical decisions in the field (7–11). The need for improved diagnostic information is pronounced in rural environments, such as those common to New Hampshire, where paramedics face long transports and difficult, impactful destination decisions between local critical access facilities versus Helicopter EMS (HEMS) intercept or lengthy ground transport to a tertiary care facility (12–13).

Studies of prehospital ultrasound (PHUS) from the early 2000s, primarily performed in Europe, established that HEMS flight physicians could accurately perform and interpret extended focused assessments with sonography in trauma (eFAST) exams in the field which might help reduce iatrogenic injuries and alert trauma centers earlier of incoming injuries (14). Similarly, a study of Dutch HEMS physicians found that POCUS impacted treatment decisions in 26% of trauma patients and 65.4% of non-trauma patients (15). These prior studies reinforce the feasibility and applicability of POCUS in the prehospital setting. However, most of these studies were limited due to POCUS performance and interpretation being performed by EMS physicians, who are typically not present in prehospital care in the U.S., and may not translate to paramedic level training. Additionally, these programs were limited by lack of defined non-physician prehospital protocols, easy access to training, and most notably high-quality portable ultrasound equipment.

Technological advancements throughout the 2010s introduced multiple high quality handheld ultrasound machine models which increased accessibility of the technology into the prehospital environment. Recently, small pilot studies have demonstrated that both ground EMS and HEMS paramedics are able to learn, perform, and accurately interpret POCUS when used in the prehospital setting including echocardiography in cardiac arrest, eFAST in trauma, and lung ultrasound in respiratory distress (10,11,16–18). Our 2024 study addressed the impact of paramedic PHUS training in a purely simulated environment and demonstrated that PHUS can improve paramedics’ clinical decisions and confidence in undifferentiated patients (19). Though evidence, quality, and volume of PHUS programs are increasing, few have integrated PHUS into their prehospital decision-making paradigm through formalized EMS protocols.

At the time of this program, a proposed New Hampshire Statewide EMS PHUS protocol had been drafted based on best evidence but not yet implemented into paramedic scope of practice. Building on a prior study regarding PHUS education by our research group, we instituted a rural EMS PHUS pilot program with POCUS trained paramedics which would not deviate clinical care from current EMS protocols (19). Our primary aims were to 1) quantify the theoretical impact of PHUS findings on paramedic prehospital care decisions and 2) assess paramedic interpretation accuracy in the course of clinical care via a robust quality assurance program, with the ultimate aim of informing future implementation of the Statewide PHUS protocol.

METHODS

Study Design

This was a prospective observational cohort study designed to evaluate the accuracy of PHUS image acquisition and interpretation among trained paramedics as well as perceived, theoretical impact of image findings on clinical decisions. The study was created in conjunction with a newly implemented, independently operated small-scale rural pilot program of PHUS in New Hampshire. Our study aimed to observe the impacts of introducing PHUS to analyze ultrasound performance characteristics among the paramedics and estimate impacts on their clinical decisions if the PHUS findings had theoretically been integrated into care. During the year-long observational period, trained paramedics conducted and interpreted eFAST, focused pulmonary, and cardiac arrest echocardiography exams on EMS calls when indications were met as part of the existing pilot program. Paramedics completed a brief quality assurance (QA) worksheet after each exam as part of the pilot protocol which included their field interpretation, exam setting and length, and theoretical decision impact of the findings. These worksheets were reviewed with image overread and feedback from the program medical director who is a boardcertified emergency physician with extensive ED POCUS experience. We retrospectively analyzed the paramedic surveys and physician QA forms to establish an observational dataset for analysis. The operational pilot program that implemented and regulated paramedic use of PHUS in the field was distinct from our study and administered by the local EMS agencies and district medical director. The pilot program was overseen and approved by the State of New Hampshire Medical Control Board as a prerequisite pilot program in April, 2023 prior to implementation. Our associated study that analyzed the de-identified observational survey data generated by the cohort of paramedics in the pilot program was reviewed and given an exempt determination by the Committee for the Protection of Human Subjects at Dartmouth College (#00032581). Two members of the study team also served on the pilot program implementation team.

Setting and Participants

The pilot program was conducted within a single regional EMS district of New Hampshire and included five experienced, full-time paramedics from three different fire-based EMS services. The primary transport destination for this service area is a small critical access hospital with a transport time of approximately 5–30 minutes. This facility serves as the medical resource hospital providing EMS medical direction and physician oversight for this pilot program. Due to limited specialty services at this local hospital, paramedics may choose to bypass the local ED and transport patients directly to a Level II trauma center (1–1.5 hours by ground, 15–25 minutes by air) or the only large academic tertiary hospital/Level 1 trauma center in the State (1.5–2 hours by ground, 15–25 minutes by air). Comprehensive pilot program characteristics are available in Table 1.

Table 1:

Pilot Program Overview

Paramedics Included	5
Paramedic Experience, years of employment
11–15	1
16–20	1
21+	3
Exams Completed by Paramedic, number of exams (%)
Paramedic #1	22 (46.8)
Paramedic #2	13 (27.7)
Paramedic #3	5 (10.6)
Paramedic #4	5 (10.6)
Paramedic #5	3 (6.38)
Fire-Based EMS Agencies Included	3
Communities Served by EMS Agency
Rural (<2,500 residents)	2
Suburban (2,500–25,000 residents)	1
Combined 2023 Call Volume, # EMS calls	2,469
Local Hospital ED Volume, Avg. Annual ED Census	13,000

Pilot Program Procedure

Prior to the pilot program, the paramedics completed a 13-hour PHUS course covering eFAST, focused pulmonary, and cardiac arrest echocardiography exams described in our prior study (19). The course included 10 proctored exams of each exam type on standardized patients. After completing the course, paramedics completed 15 proctored exams for each of the three exam types with direct oversight from the program medical director during teaching shifts at the medical resource hospital. The combined proctored exams totaled 25 for each exam type with the goal of maintaining consistency with American College of Emergency Physicians POCUS education recommendations. Each paramedic received an orientation to pilot program operations and then was approved to begin the program. During the pilot program, paramedics maintained handheld ultrasound units on their ambulance for use in the field during routine EMS shifts. The program used two ButterflyiQ+ units (Butterfly Network Inc, Burlington, MA) and one Clarius HD portable ultrasound unit (Clarius Mobile Health Corp, Vancouver, BC, Canada).

Paramedics attended (2) 2-hour continuing education sessions distributed throughout the pilot program that focused on maintenance of image acquisition and interpretation skills.

Paramedics followed a pilot program protocol which included indications for each exam type, exam procedure, and QA follow up which is available in Supplemental File Appendix 1. Briefly, the eFAST exam was indicated for major/multisystem trauma and included a full eFAST with abdominal, cardiac, and lung windows evaluating for intra-abdominal and intrathoracic free fluid, pericardial effusion, and pneumothorax. The focused pulmonary exam was indicated for respiratory distress where congestive heart failure (CHF) vs. chronic obstructive pulmonary disease (COPD)/reactive airway disease was suspected and included apical and lateral lung views evaluating specifically for diffuse A or B-line pattern and lung sliding. Focused cardiac arrest echocardiography was indicated in non-shockable arrest and included a brief subxiphoid or parasternal long axis view during standard pulse/rhythm checks evaluating for presence or absence of organized cardiac activity. Paramedics were trained to obtain windows without impacting pulse check time or pausing compressions (20). The completion of indicated Advanced Cardiac Life Support (ACLS) interventions and any compression interruptions were part of the program protocol and tracked QA metrics. Cardiac arrest echocardiography was also indicated for cases where termination of resuscitation parameters had been met, evaluating for absence of organized cardiac activity. Paramedics were permitted to conduct a cardiac exam to obtain sonographic windows on patients not currently in cardiac arrest who were at high risk of cardiac arrest (i.e. shock, high-risk chest pain, return of spontaneous circulation after resuscitation). This provision was made during the pilot program with the goal of providing paramedics with adequate opportunities to acquire and interpret cardiac exams as the volume of out-of-hospital cardiac arrests was relatively low among all of the rural EMS agencies enrolled in the study.

When indications for an exam were met during an EMS call, paramedics could choose to conduct a PHUS exam at any point during the call as long as they believed that it would not significantly impact on scene time or other care priorities. They were instructed to use judgment to determine if and when an exam would be appropriate during a call with guidance to only perform exams during idle time (ie. during transport once all interventions are complete, while waiting for a needed operational or clinical task to occur), and not to delay transport or any indicated action in favor of a PHUS exam. Paramedics conducted and interpreted exams in the field, though per the protocol of this initial observational phase of the pilot program, they did not integrate any exam findings into their clinical decision making, prehospital care, or transport plan. We aimed to first assess perceived PHUS impact. As such, the program did not impact the provision of EMS care and paramedics continued to work strictly within the routine state patient care protocols. Paramedics uploaded each set of image clips without any patient information to the de-identified secure cloud platform provided by the respective device manufacturer.

Within 24 hours after the call, paramedics completed a 14-question electronic worksheet that took 5–10 minutes. Each worksheet was de-identified, did not include any patient data, and used the generic fire department incident number for tracking. There was a unique worksheet specific to each exam type which included questions on exam indications, setting (scene vs. transport), and interpretation of findings. While paramedics did not use the exams for any clinical decisions, the worksheets included a question set regarding their perception of the theoretical impact of PHUS on treatment, transport, and receiving facility decisions if they had integrated the exam findings into their clinical decisions. Worksheets also included questions related to perceived impact to on-scene time and estimated exam duration, but these values were purely used for QA and not integrated into the study dataset due to their subjective nature. Each worksheet included a unique web link to the de-identified cloud platform so that the form could be linked with the associated image clips for QA review. Worksheets are available in Supplemental File Appendix 2.

The program medical director conducted a physician QA overread of each exam. Feedback focused on accuracy of interpretation, image quality, and windows acquired, detailed in Supplemental File Appendix 3. Interpretations were graded as 1) accurate, 2) indeterminate due to incomplete windows, or 3) inaccurate. Scans were graded as indeterminate due to incomplete windows when the paramedic did not obtain and/or record the full sonographic window needed to make a complete interpretation, though interpreted the recorded portion correctly. A common example of this error was failing to include the liver tip in a right upper quadrant eFAST view but appropriately determining there was no free fluid present in the remainder of the window obtained.

Measurements

The post-scan worksheets completed by paramedics were used to obtain data on the 1) frequency of each exam type and setting, and 2) theoretical decision impact reported by paramedics across each exam type. Each worksheet was matched to the associated QA overread by the program medical director to obtain paramedic interpretation accuracy data using physician interpretation as the gold standard. Theoretical decision impact was established using questions in the QA worksheet that asked paramedics to rate the impact of the PHUS results if they had integrated their findings into prehospital care. Paramedics rated their perceived impact across categories of treatment, transport modality, and receiving facility decisions using categories of influence on decisions depicted in Table 4. Seven QA forms included data only from category 1 above because the QA form did not include decision-impact questions in the initial testing phase of use, however, these were later added. Additionally, one question regarding treatment decision impact on one pulmonary exam QA form was left incomplete by a paramedic, yielding a decrease of one treatment decision response in the dataset.

Table 4:

Perceived Impact of Prehospital Ultrasound on Paramedic Decisions

Medical Decision Making Type	All Exams	Pulmonary Totals	Cardiac Totals	eFAST Totals	ap-value
All Decision Types, n (%)
Did not contribute to decision	54 (45.4)	19 (37.3)	22 (68.8)	13 (36.1)	0.04
Supported decision without PHUS	55 (46.2)	27 (52.9)	8 (25.0)	20 (55.6)
Impacted decision	10 (8.4)	5 (9.8)	2 (6.3)	3 (8.3)
Transport Modality, n (%)
Did not contribute to decision	21 (52.5)	8 (20.0)	8 (80.0)	5 (41.7)	0.37
Supported decision without PHUS	17 (42.5)	9 (22.5)	2 (20.0)	6 (50.0)
Impacted decision	2 (5.0)	1 (2.5)	0 (0.0)	1 (8.3)
Receiving Facility Choice, n (%)
Did not contribute to decision	21 (52.5)	8 (42.1)	8 (72.7)	5 (41.7)	0.32
Supported decision without PHUS	19 (47.5)	9 (47.4)	3 (27.3)	7 (58.3)
Impacted decision	0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)
Treatment, n (%)
Did not contribute to decision	12 (30.8)	3 (18.8)	6 (54.5)	3 (25.0)	0.40
Supported decision without PHUS	19 (48.7)	9 (56.3)	3 (27.3)	7 (58.3)
Impacted decision	8 (20.5)	4 (25.0)	2 (18.2)	2 (16.7)

^aExact Chi-Square p-value

Statistical Analysis

Exam characteristics, post-scan worksheet responses, and interpretation accuracy were summarized for descriptive statistics using frequencies and percentages. All associations between exam types across these categories were evaluated using contingency tables using an exact probability Chi-square test (Fisher’s exact test). This method was selected because of some cells having low counts (<5). Inter-rater reliability between the paramedic and the program medical director exam findings were calculated and represented as weighted Cohen’s Kappa scores. All descriptive statistics and association assessments were performed using SAS/STAT v.9.4 (SAS Institute Inc., Cary, NC) using the FREQ procedure. Significant differences were declared at P≤0.05.

RESULTS

Exam Characteristics

Exams Acquired

A total of 47 different exams were performed across the five paramedics, including 12 cardiac exams (26%), 20 pulmonary exams (43%), and 15 eFAST exams (32%) (Table 2).

Table 2:

Paramedic Prehospital Ultrasound Exam Characteristics

Exam Characteristic	All Exams	Pulmonary Totals	Cardiac Totals	eFAST Totals	ap-value
Exam Count, n (%)	47	20 (42.6)	12 (25.5)	15 (31.9)
Accuracy, n (%)
Accurate Interpretation	39 (83.0)	17 (85.0)	12 (100.0)	10 (66.7)	0.06
Indeterminant, incomplete windows	7 (14.9)	2 (10.0)	0 (0.0)	5 (33.3)
Inaccurate	1 (2.1)	1 (5.0)	0 (0.0)	0 (0.0)
Exam setting, n (%)
On Scene	13 (27.7)	5 (25.0)	4 (33.3)	4 (26.7)	0.92
During Transport	34 (72.3)	15 (75.0)	8 (66.7)	11 (73.3)

^aExact Chi-Square p-value

Exam Findings

A variety of normal and pathological findings were identified across exam types, including 8 (40%) pulmonary exams with a diffuse or focal B-line pattern and 3 (25%) cardiac exams with pericardial effusion. Among cardiac exams, 4 (25%) were conducted during cardiac arrest resuscitation and 1 (25%) of these exams demonstrated organized cardiac activity during resuscitation. There were no pathological findings identified among eFAST exams, and a minority of eFAST exams did not include pericardial and/or lung sliding windows (Table 3).

Table 3:

Prehospital Ultrasound Exam Findings

Finding by Exam Type	Count	Percentage
Pulmonary
Apical and Lateral Windows (n=20)
A-Pattern	12	60%
Widespread/Bilateral B-Pattern	4	20%
Focal B-Pattern	4	20%
Apical Lung Sliding (n=20)
Lung Sliding Present	20	100%
Lung Sliding Absent	0	0%
Cardiac Arrest Echocardiography (n=4)
Cardiac Standstill	3	75%
Organized Cardiac Wall Motion	1	25%
Pericardial Effusion Present	1	25%
All ACLS Interventions Completed Prior to POCUS	4	100%
Rhythm Checks Prolonged/Interrupted by POCUS	0	0%
Echocardiography Total (n=12)
Cardiac Standstill	3	25%
Organized Cardiac Wall Motion	9	75%
Pericardial Effusion Present	3	25%
eFAST
Intra-abdominal Windows (n=15)
Free Fluid Negative	10	67%
Free Fluid Positive	0	0%
Free Fluid Indeterminate	5	33%
Pericardial Window (n=9)
Pericardial Effusion Negative	6	67%
Pericardial Effusion Positive	0	0%
Pericardial Effusion Indeterminate	3	33%
Apical Lung Sliding (n=11)
Lung Sliding Present	10	91%
Lung Sliding Absent	0	0%
Lung Sliding Indeterminate	1	9%

Accuracy

Among all exam types, 39 (83%) had an accurate finding that matched the physician overread, 7 (15%) were indeterminate due to incomplete or poor quality windows, and only 1 exam (2%) was truly inaccurate where findings did not match the physician overread. Among cardiac exams, 12 (100%) had an accurate finding that matched physician overread, while none were either indeterminate or inaccurate. Among pulmonary exams, 17 (85%) had an accurate finding that matched physician overread, 7 (15%) were indeterminate due to incomplete or poor quality windows, and only 1 (5%) was truly inaccurate where findings did not match the physician overread. Lastly, among eFAST exams, 10 (67%) had an accurate finding that matched physician overread, 5 (33%) were indeterminate due to incomplete or poor quality windows, and none were inaccurate. The rate of accurate findings did not significantly differ between the three exam types (p = 0.06). The agreement on exam findings, including indeterminate, between the paramedic and program medical director was excellent for cardiac (Kappa = 1.00), moderate for pulmonary (Kappa = 0.75), and weak for eFAST exams (Kappa = 0.53). The total agreement on all exams between the paramedics and program medical director was moderate (Kappa = 0.77).

Setting

Among all types of exams, 34 (72%) were performed during transport while 13 (28%) were performed while on scene. The rate of performing exams during transport was 67% for cardiac, 75% for pulmonary, and 73% for eFAST (p = 0.92).

Perceived Impact on Decision Making

Overall Decision Making

Among all 119 individual post-scan clinical decision questions completed across all decision types, paramedics indicated that 10 (8%) exams would have impacted their overall decision making, 55 (46%) exams would support the decisions made without PHUS, and 54 (45%) exams would have no impact on their overall decision making (Table 4). Paramedics indicated that 31% of cardiac exams, 63% of pulmonary exams, and 64% of eFAST exams would support or impact overall decision making. Paramedics indicated that a significantly higher proportion of cardiac exams would have no impact on overall decision making (p = 0.04).

Treatment Decisions

Among the 39 QA worksheet questions completed on treatment decisions, paramedics indicated that 8 (21%) exams would have impacted their treatment decisions, 19 (49%) exams would support the treatment made without PHUS, and 12 (31%) exams would have no impact on treatment. Paramedics indicated that 45% of cardiac exams, 81% of pulmonary exams, and 75% of eFAST exams would support or impact treatment decisions (p = 0.35).

Transport Modality

Among the 40 worksheet questions completed on transport modality, paramedics indicated that 2 (5%) exams would have impacted their transport decisions, 17 (43%) exams would support the transport decisions made without PHUS, and 21 (53%) exams would not contribute to their transport decisions. Paramedics indicated that 20% of cardiac exams, 56% of pulmonary exams, and 58% of eFAST exams would support or impact their transport decisions (p = 0.37).

Receiving Facility Choice

Among the 40 worksheet questions completed on receiving facility choice, paramedics indicated that 0 (0%) exams would have impacted their receiving facility choice, 19 (47%) exams would support the facility choice made without PHUS, and 21 (53%) exams would not contribute to their facility choice. Paramedics indicated that 27% of cardiac exams, 53% of pulmonary exams, and 58% of eFAST exams would support or impact their receiving facility choices (p = 0.32).

DISCUSSION

Over the past three decades, POCUS has grown from a tool with limited scope used only by emergency physicians and trauma surgeons to a broad array of applications practiced by an ever-growing number of specialties and professions (21). A precedent to train a variety of providers such as associate providers, nurses, and physical therapists to use POCUS for focused applications is well established in the literature (22–25). Compact and high-quality ultrasound units, increased penetration in healthcare, and interest by prehospital providers has led to a rapidly evolving body of PHUS literature. To date, the majority of PHUS studies in the U.S. have focused on knowledge retention, image acquisition and interpretation, and curriculum design and implementation (9,26,27). Only recently have studies begun to explore the effects of PHUS on paramedics’ medical decision making and safety profile (10,16,19). Before broadly developing and deploying EMS protocols, especially in rural, critical access areas, it is imperative to determine how this skill performs clinically in the field without putting patients at risk of harm.

Our study suggests that experienced paramedics with training consistent with American College of Emergency Physicians guidelines are able to accurately perform and interpret PHUS and safely integrate these skills into modified pre-existing protocols in New Hampshire. We focused on the use of limited eFAST, pulmonary, and cardiac ultrasound exams because they are common in current PHUS literature and field use, and involve use cases with the potential for actionable, impactful decision support. In addition, training for these applications had already been established in our prior study (19).

In this study, interpretation accuracy was high (83%) across all exam types suggesting that paramedics are able to perform the limited procedure and interpret findings well in the field without direct physician oversight. Accuracy was highest for cardiac (100%) and pulmonary (85%) exams but lowest for eFAST (67%). However, only one study among the 47 completed exams (2%) had a definitively inaccurate finding. This single identified inaccuracy was a pulmonary exam interpreted as an A-line pattern by the paramedic that was determined to have a B-line pattern by physician overread. This exam represents a false negative interpretation by the paramedic and was therefore inaccurate. Seven (15%) exams were indeterminate due to incomplete windows (necessary anatomy not fully included) and/or poor image quality windows (necessary anatomy not captured clearly) which is consistent with prior studies which also found incomplete windows to be the major barrier to accurate findings in the field (10, 11). Incomplete windows were most common in the eFAST exam, which has a total of six windows spanning multiple organ systems from the upper chest to low pelvis requiring more nuanced manipulation of the probe and greater exposure of the patient. We believe that tight quarters, stretcher straps, body habitus, and clothing all make image acquisition significantly more difficult in a moving ambulance than in hospital settings. Difficulty obtaining complete windows for eFAST exams suggests the need to focus training on image acquisition within the ambulance and potentially during movement while an instructor observes and provides feedback on ways to optimize skills.

According to the paramedics, performing PHUS would have changed 8.4% of overall clinical decisions. Treatment decisions had the highest perceived impact (21%) followed by transport modality decisions (5%), while paramedics indicated that PHUS would not have changed any receiving facility decisions. These findings are important, demonstrating that in the hands of experienced paramedics trained in ultrasound, PHUS in a rural setting could theoretically change care in one of every 12 patients with these common prehospital presentations. Additionally, PHUS supported 46.2% of overall medical decisions which may be quite valuable in the prehospital environment. As discussed above, paramedics often face diagnostic ambiguity due to limited availability of accurate diagnostic data in the field (4–6). PHUS may provide a fast, actionable additional datapoint that when congruent with other findings may improve accuracy of decisions. Paramedics in this study identified that the addition of PHUS supported a majority of their decisions, despite these findings not being implemented into patient care at this stage of the pilot program. Though these findings are limited by the theoretical nature of our decision impact data and small sample size, they present a framework to understand how PHUS may inform specific decisions and support recent studies demonstrating that PHUS improves prehospital diagnosis and management across multiple applications (10,16). In 45% of the responses, PHUS had no influence on decision making, which may be influenced by the extensive experience of our paramedics. All paramedics practiced for at least 11 years with three practicing for greater than 21 years. As such, this cohort may be more comfortable than less experienced paramedics regarding making decisions with limited information. This may have contributed to a reduction in the perceived value and impact of PHUS findings. We expect that PHUS may be more helpful in well-trained paramedics with less clinical experience. Additionally, the value added by PHUS may be particularly helpful for paramedics of all experience levels in clinical contexts where traditional data points are unavailable or unreliable such as patients with altered mental status, low health literacy, language barriers, or care in austere environments.

Of the 47 unique exams performed, pulmonary (43%) exams were most prevalent and had the highest theoretical impact and support of treatment decisions among all exam types. This might highlight the diagnostic value of PHUS in differentiating primarily cardiac from primarily pulmonary etiology, which is often difficult in the prehospital setting due to overlapping symptomatology, limited history, and barriers to clear auscultation (5). Differentiation of these two common pathologies is important as treatments beneficial for COPD and asthma patients, such as beta agonists, could potentially be harmful in CHF, and correct prehospital identification and treatment improves outcomes in acute heart failure (9,16,28). This importance of diagnostic accuracy in context of our finding that 81% of pulmonary exams would impact or support treatment decisions compliments the growing body of evidence that PHUS improves prehospital diagnosis and management of undifferentiated respiratory distress and showcases a mechanism by which PHUS may improve patient outcomes in future investigations (16,29).

While PHUS had a high 69% perceived support or impact on treatment decisions, the perceived impact on transport modality and receiving facility choice was relatively low across all exams. This likely reflects that experienced rural providers following established EMS protocols are able to determine which patients may benefit from a helicopter intercept and which patients are appropriate for local hospitals. For example, performing focused echocardiography on patients in cardiac arrest is unlikely to change their transport mode or receiving facility as these decisions are clearly stipulated in the EMS protocol. However, finding a large pericardial effusion or organized cardiac activity in PEA arrest may change treatment decisions such as following return of spontaneous circulation protocols or transporting to the ED rather than terminating in the field. Similarly for the focused pulmonary exam, PHUS evidence supporting a primary cardiac versus pulmonary cause of respiratory distress may influence the decision to follow the appropriate EMS treatment protocol and provide the associated interventions. However, these findings are less likely to impact the decision to transport to a local facility versus a tertiary center which is defined by the EMS protocol based parameters of patient stability rather than presumed etiology. Prior to the analysis, we hypothesized that the eFAST exam may have the greatest impact on receiving facility choice and transport mode as identifying intra-abdominal or intrathoracic free fluid in a trauma patient is a clear indication for transfer to a trauma center. Our study did not capture any eFAST exams positive for free fluid, so we were unable to assess the impact of this PHUS finding.

LIMITATIONS

Despite promising results, this project does have some limitations. First, paramedics only performed 47 exams across 3 exam types, which resulted in a relatively low volume of abnormal exam findings and types of pathology identified by PHUS, limiting analysis of interpretation accuracy across normal vs abnormal exams. The dataset may also have been too small to drive statistical power. Therefore, we cannot conclude that true differences in measured parameters between exam types do not truly exist for non-significant results. (Table 2 and 4). We used QA review by a single emergency physician to establish a gold standard to analyze interpretation accuracy. The lack of additional reviewers could introduce bias and reduce the internal validity of this dataset. Additionally, the majority of these exams (75%) were also performed only by two paramedics so these results must be replicated in a larger cohort of providers. Second, these preliminary results may only be generalized to paramedics working in rural-suburban areas. Prior studies suggest that EMS agencies in rural areas are more likely to have longer response times, on-scene times, and hospital transport times than EMS agencies in urban areas (31,32).

However, this limitation is considered minor as PHUS may be particularly beneficial in rural EMS. Third, results can only be generalized to experienced paramedics. Studies suggest that experienced paramedics rely less on tools and more on provider judgment, often termed the “gut feeling,” compared to inexperienced paramedics, which may have impacted these results (33,34). Fourth, paramedics could not incorporate PHUS findings into their actual decision making. Therefore, paramedics may have been more likely to under-report findings that “would have impacted” their decision-making process. This under-reporting may be particularly prevalent among the 75% of cardiac exams that were conducted in patients that were not in cardiac arrest. The binary finding of presence or absence of cardiac activity has low relevance in these clinical scenarios. Although these exams had educational value, they may be less likely to have a perceived impact on decision making compared to exams with actionable findings. Additionally, completing the worksheet after the entire call was completed may have also contributed to under-reporting and recall bias given that paramedics completed forms up to 24 hours after each exam and may have been more aware of the patient outcome and disposition. This problem will be mitigated in the next phase of this program, which allows paramedics to incorporate PHUS findings into decisions real time.

FUTURE DIRECTIONS

The next phase of this program is currently underway and is prospective and interventional in design. Paramedics will use PHUS to inform decisions in the field under direction of a recently published New Hampshire Statewide EMS protocol (Section 7.7 “Point of Care Ultrasound”). This phase will incorporate medical record review to measure congruence between PHUS-informed paramedic decisions and ultimate disposition at the receiving hospital. We will use this data to determine if the PHUS-supported decision made by the paramedic in the field was consistent with the patient’s definitive diagnosis and treatment. This phase will also determine if PHUS improves prehospital diagnosis and management by case-matching calls where PHUS was used to similar calls where PHUS was not used across the three indications and exams included in the pilot program. Additionally, medical record review can collect objective temporal data to examine differences in paramedic on-scene time between matched PHUS and non-PHUS cases. Together, this will help to build external validity to the self-reported impact of PHUS on paramedic decision making discussed in this current phase of the PHUS pilot program, and establish the clinical yield of integrating PHUS into prehospital care.

CONCLUSIONS

To our knowledge, no prior studies have specifically implemented and investigated a small-scale PHUS pilot program in a rural area, not associated with an academic medical center, and overseen by local community-based emergency medicine physicians. Overall, this preliminary pilot program suggests that experienced, PHUS trained paramedics can acquire and accurately interpret focused PHUS exams in rural areas, and even during patient transport to the hospital. Paramedics reported that PHUS findings might impact or support their clinical decisions in about half of uses among the specific, narrow-focus of indications studied, with pulmonary and eFAST exams providing the most decision support in this study. These results inform growing evidence that PHUS may improve prehospital decision making in focused, protocolized programs and may be feasible and beneficial when implemented in rural parts of the U.S.

DATA SHARING STATEMENT:

The raw dataset for this study is available from the corresponding author upon request. The associated program protocol and processed data is available in the appendix.