Prehospital POCUS: Ultra-Portable Ultrasound in the Field

Shifting the Diagnostics Boundary

In high-acuity trauma, finding the bleeding we can't see changes where the patient goes and how fast. Point-of-Care Ultrasound (POCUS) has been part of hospital trauma care since the FAST exam went mainstream, but cart-based machines never made sense in an ambulance.

Handheld probes changed that. The Butterfly iQ+ puts a whole-body, single-probe ultrasound on a semiconductor chip that plugs into a phone or tablet; GE HealthCare's Vscan Air is a wireless, dual-headed alternative. The question for us is no longer whether we can carry ultrasound, but what it can and can't tell us in the field.

Performing the eFAST Exam on the Street

The Extended Focused Assessment with Sonography for Trauma (eFAST) looks for three things:

• Free fluid: blood in the peritoneal, pleural, or pericardial spaces.
• Pneumothorax: normal lung sliding at a given probe position rules out a pneumothorax at that spot. Absent sliding raises suspicion. It does not replace the clinical diagnosis of tension physiology, and a needle decompression is still a decision based on the patient, not the screen.
• Pericardial effusion: fluid around the heart in a penetrating chest wound changes the destination and the pre-alert.

What the Field Accuracy Data Actually Say

This is the part that matters most for how we use it.

• A positive scan is reliable; a negative scan is not. A 2024 meta-analysis of six prehospital studies (1,356 patients) found pooled specificity of 97% but sensitivity of only about 60% for abdominal free fluid. A negative field FAST in a patient with a mechanism and abnormal vitals does not mean they aren't bleeding.
• It changes management. A 2019 systematic review of nine prehospital studies (2,889 patients) found that every study measuring it reported changes in polytrauma management, ranging from 6% to 49% of cases, and generally adequate diagnostic accuracy for pneumothorax and free fluid.
• Paramedics can do it. A 2026 German cohort of 21 paramedics, after structured training, performed 169 handheld exams over two years. eFAST showed 100% sensitivity and 96.5% specificity against hospital diagnoses, and lung ultrasound 91.7% and 100%. Ultrasound findings changed transport urgency in 36% of missions and hospital destination in 18%. Abdominal exams outside eFAST were much weaker, around 71% each.

Cardiac Activity in Arrest

Ultrasound during a PEA or asystole code also has evidence behind it. The multicenter REASON study (Resuscitation, 2016) enrolled 793 patients in out-of-hospital or ED arrest and scanned them in the ED at the start and end of ACLS. Cardiac activity on ultrasound was the variable most associated with survival. With no cardiac activity, 0.6% still survived to discharge. Patients whose scans found a pericardial effusion and who got pericardiocentesis did markedly better than everyone else.

That gives medical directors objective data to build into field termination-of-resuscitation protocols, but it is one input, not the trigger. The scan also has to fit inside a pulse check without stretching the pause; that is a pit-crew skill, not just an imaging skill.

Tele-Ultrasound Over Wireless Networks

Some handheld systems support live remote viewing; Butterfly calls its version TeleGuidance. In principle, a physician at the receiving facility can watch the scan and coach the probe in real time while we transport. In practice, whether that works depends on cellular coverage along your transport corridor and whether anyone at the other end is staffed to watch. I have not seen outcome data showing it changes trauma care yet, so treat it as a QA and training tool first.

The Implementation Roadmap

The accuracy data above come from crews with structured training, so that is where implementation starts:

• Training to a protocol: a defined eFAST and lung sequence, with competency sign-off before field use.
• QA on stored images: every clip reviewed against the hospital outcome, which is how the German program generated its accuracy numbers.
• Image storage and privacy: clips are patient data. Cloud upload, device storage, and retention need the same governance as the ePCR.
• Clear rules on what a scan can change: destination and pre-alert, yes; delaying transport for a better image, no.

Sources

• BMC Emergency Medicine (PMC) — Prehospital ultrasound for abdominal free fluid in trauma: systematic review and meta-analysis
• Injury (PubMed) — Prehospital ultrasound in the management of trauma patients: systematic review
• Scand J Trauma Resusc Emerg Med (PMC) — Feasibility and diagnostic accuracy of paramedic-performed prehospital POCUS
• Resuscitation (PubMed) — REASON: point-of-care ultrasound in out-of-hospital and in-ED cardiac arrest
• Butterfly Network — Butterfly iQ+ single-probe, whole-body handheld ultrasound