Point-of-care ultrasound (POCUS) — FAST, echo, lung, vascular access

Overview

Point-of-care ultrasound (POCUS) is a targeted, clinician-performed diagnostic tool used at the bedside to answer specific clinical questions in real time. Unlike departmental radiology, POCUS does not replace comprehensive imaging; it provides rapid, actionable information to guide immediate management.

In the UK, the Focused Acute Medicine Ultrasound (FAMUS) accreditation structures POCUS competency into three modules: thoracic, abdominal (liver, renal, bladder), and vascular. For ACRRM rural generalists, competency is expected across FAST/eFAST, focused echocardiography, lung ultrasound, and ultrasound-guided vascular access.

In rural and remote Australia, POCUS is strategically essential, CT, MRI, departmental ultrasound, and nuclear medicine are frequently unavailable or delayed by hours to days. A portable handheld or cart-based device allows the rural generalist to assess life-threatening pathology, guide invasive procedures, and determine urgency of retrieval.

Physics and Equipment Fundamentals

Ultrasound imaging relies on piezoelectric transducers that emit high-frequency sound waves and detect reflected echoes. Time-of-return is converted to depth; echo amplitude is converted to brightness (echogenicity). Gel eliminates air pockets between probe and skin, air blocks ultrasound transmission entirely and prevents image generation. Ultrasound does not involve ionising radiation.

Minimising the distance between transducer and target organ reduces energy loss in tissue and improves image quality.

Probe Selection

In resource-limited remote settings, a single phased array or curvilinear probe can serve most emergency applications. Handheld devices offer reasonable image quality suitable for RFDS pre-hospital and remote community clinic use.

FAST and eFAST Examination

Indications

FAST (Focused Assessment with Sonography in Trauma) is an adjunct to the primary survey in haemodynamically unstable trauma patients. Extended FAST (eFAST) adds bilateral pleural views for pneumothorax and haemothorax detection.

• Blunt or penetrating thoraco-abdominal trauma
• Unexplained haemodynamic instability
• Suspected cardiac tamponade
• Mechanism suggesting intra-abdominal or pericardial injury

FAST evaluates for haemorrhage in both the abdomen and pericardium. Diagnostic peritoneal lavage (DPL) evaluates only the abdomen and is used as an alternative where ultrasound technology is unavailable or FAST is technically limited (e.g. obesity, intraluminal bowel gas).

FAST Views and Findings

Interpretation

• Positive FAST: Anechoic free fluid in any peritoneal or pericardial window. In the haemodynamically abnormal patient this mandates urgent surgical consultation. In haemodynamically normal patients a surgeon should still be consulted to direct care.
• Negative FAST: Does not exclude injury, retroperitoneal haemorrhage (pelvic fracture, renal pedicle) is not reliably detected. Sensitivity improves with serial examination.
• eFAST, pneumothorax: Loss of lung sliding, absence of comet-tail artefacts, A-lines only, and the lung point sign (transition between sliding and non-sliding pleura) confirm pneumothorax. Tension pneumothorax remains a primarily clinical diagnosis; do not delay decompression to perform eFAST.
• eFAST, haemothorax: Anechoic or complex fluid above the diaphragm.

Neither FAST nor DPL effectively evaluates the retroperitoneum.

Obstetric Modification

A fetal FAST may be performed alongside the standard exam when qualified personnel are available:

Maternal resuscitation must not be delayed to perform fetal FAST. In the absence of fetal FAST capability, Doppler measurement of fetal heart rate is sufficient.

Rural Context

A positive FAST in an unstable patient at a remote facility may be the sole objective finding justifying:

• Immediate RFDS or retrieval activation with pre-notification of surgical receiving team
• Pericardiocentesis for tamponade as a temporising measure prior to transfer
• Emergency damage-control laparotomy if an operating theatre is locally available

FAST should never delay haemorrhage control or resuscitation.

Focused Echocardiography

Clinical Applications

TTE (transthoracic echocardiography) is non-invasive, more readily available, and guides most haemodynamic queries. TOE (transoesophageal echocardiography) offers superior image clarity for complex structural assessment or poor acoustic windows but is invasive and requires specialist expertise.

Core Echo Windows

• Subxiphoid (subcostal) four-chamber: Best initial window in trauma (performed as part of FAST); visualises pericardial effusion and gross biventricular function.
• Parasternal long axis (PLAX): Left sternal border, 3rd-4th ICS. Assesses LV size and function, mitral and aortic valves, aortic root, posterior pericardium.
• Parasternal short axis (PSAX): Rotated 90° from PLAX. Assesses RV:LV ratio and interventricular septal flattening ("D-sign" of RV pressure overload).
• Apical four-chamber: Over cardiac apex. Comprehensive biventricular size and systolic function; requires practice to obtain consistently.

IVC Assessment for Volume Status

$$\text{IVC collapsibility index} = \frac{\text{IVC}{\max} - \text{IVC}{\min}}{\text{IVC}_{\max}} \times 100\%$$

Caution: IVC assessment is less reliable in elderly patients with chronically elevated baseline right atrial pressure, and in mechanically ventilated patients (where distensibility index is used instead).

Rural Context

Focused echo enables the rural generalist to:

• Distinguish cardiogenic from non-cardiogenic shock without invasive monitoring
• Detect tamponade and perform guided pericardiocentesis
• Choose between volume loading and inotropic support in the shocked patient
• Transmit images via secure telehealth to retrieval teams and receiving hospitals to support shared decision-making

Lung Ultrasound

Principles

Normal aerated lung reflects nearly all ultrasound, generating characteristic artefacts. Pathological change alters the pleural acoustic interface, producing recognisable patterns. POCUS can identify pneumothorax (absent lung sliding, absence of comet-tail artefacts, lung point), pleural effusion, pulmonary oedema (B-lines), and consolidation.

Systematic Scan Protocol

Divide each hemithorax into zones (anterior, lateral, posterior; upper and lower), commonly 6 zones per side (12 total). This characterises:

Differentiation of Acute Dyspnoea

Important: Lung ultrasound can also be used to confirm and mark the drainage site for pleural effusions (as per British Thoracic Society guidance) and to assess for underlying consolidation in suspected pneumothorax before NIV initiation. An undrained pneumothorax is an absolute contraindication to CPAP/BiPAP.

Rural Context

Distinguishing pneumonia from acute pulmonary oedema without CXR or laboratory results has direct, immediate management consequences (antibiotics vs. diuretics vs. NIV). Lung POCUS also enables:

• Safe initiation of NIV after excluding pneumothorax
• Guided drainage of symptomatic pleural effusions (including in palliative community patients)
• Monitoring treatment response (B-line reduction following diuresis)
• Assessment of childhood pneumonia in remote clinics where CXR is unavailable

Abdominal and Renal POCUS

Beyond FAST, POCUS has defined roles in the acute abdominal/renal assessment:

POCUS confirms the presence of ascites and marks the drainage site. Departmental ultrasound provides detailed organ assessment for hepatic cirrhosis, portal hypertension, hepatic vein thrombosis, or liver metastases. CT (contrast-enhanced) is preferred where malignant ascites is suspected.

The serum-ascites albumin gradient (SAAG) guides aetiology of ascitic fluid:

$$\text{SAAG} = \text{serum albumin} - \text{ascites albumin}$$

• $\text{SAAG} \geq 11\ \text{g/L}$: portal hypertension-related
• $\text{SAAG} < 11\ \text{g/L}$: non-portal hypertension cause

Ascitic neutrophil count $\geq 250\ \text{cells/mm}^3$ is diagnostic for spontaneous bacterial peritonitis (SBP).

Ultrasound-Guided Vascular Access

Principles

Real-time ultrasound guidance significantly improves first-pass success, reduces complications (arterial puncture, haematoma, pneumothorax with subclavian approach), and enables access in patients with difficult anatomy, obesity, oedema, hypovolaemia, scarring, or intravenous drug use.

Distinguishing Vein from Artery

Central Venous Access, Internal Jugular Technique

1. Position patient head-down (Trendelenburg); head turned contralateral
2. Linear probe in transverse orientation; identify IJ (lateral to carotid artery, compressible)
3. Confirm vein vs. artery by compression and Doppler
4. Advance needle under real-time visualisation (in-plane or out-of-plane)
5. Confirm guidewire position in vein before dilation, critical safety step (Seldinger technique)
6. Post-insertion: confirm catheter tip position and exclude pneumothorax

Femoral and axillary/subclavian approaches are alternatives; femoral avoids pneumothorax risk and is preferred in coagulopathic patients.

Peripheral Vascular Access

Ultrasound-guided peripheral access using a long catheter (midline or long peripheral IV) via basilic or brachial vein avoids central line complications and can be performed by trained rural generalists when standard peripheral access fails.

Arterial Cannulation

Radial artery cannulation under ultrasound guidance using a linear probe improves success in vasoconstricted, shocked patients. Confirms arterial pulsation prior to insertion; reduces haematoma risk.

DVT Assessment, Three-Point Compression

Compression ultrasonography at three sites (common femoral vein at inguinal ligament, femoral vein at saphenofemoral junction, popliteal vein) can rule in proximal DVT:

A positive DVT finding triggers anticoagulation and may change management from observation to active treatment or urgent retrieval if PE is clinically suspected.

Decision to Retrieve, POCUS-Based Criteria

Transmitting POCUS images or short video clips via secure telehealth to the retrieval team and receiving clinician supports triage categorisation and shared decision-making.

Special Considerations

Paediatric POCUS

• Thinner chest walls provide superior acoustic windows; image quality generally better than adults
• eFAST is reliable in paediatric trauma and should be applied as in adults
• Normal IVC diameter is smaller, collapsibility indices apply but require age-appropriate interpretation
• Lung POCUS is highly sensitive for consolidation in children, valuable in remote clinics where CXR is unavailable for childhood pneumonia assessment

Obstetric POCUS

• FAST applicable in pregnancy; uterus and fetus visible in pelvic views
• Fetal FAST assesses cardiac activity, presentation, placental position, and estimated gestational age (femur length $> 4$ cm suggests viability)
• Maternal resuscitation takes absolute priority, fetal FAST must not delay maternal interventions
• Lung POCUS useful for detecting pulmonary oedema in pre-eclampsia and eclampsia
• Suprapubic view may suggest placenta praevia; transvaginal US is more sensitive but should be used cautiously in known or suspected praevia

Aboriginal and Torres Strait Islander Health

• POCUS offers non-invasive, rapid, culturally adaptable bedside assessment in community settings
• Rheumatic heart disease (RHD) is highly prevalent in remote Aboriginal communities, focused echo can detect mitral and tricuspid valve pathology and guide timely referral for formal echocardiography via specialist outreach
• Renal disease (IgA nephropathy, diabetic nephropathy), chronic suppurative lung disease, and cardiac failure create complex, overlapping presentations amenable to POCUS-assisted assessment
• Interpreter services and culturally appropriate consent are essential; explain the procedure clearly and respect patient comfort, particularly regarding clinician gender and body contact

Aged Care

• Frail elderly patients may have poor acoustic windows (emphysema, obesity, calcified ribs)
• IVC assessment less reliable with chronically elevated right atrial pressure
• POCUS-guided ascitic tap and pleural drainage reduce procedural complications in frail patients managed in community or residential aged care, avoiding unnecessary transfer

Quality, Training, and Governance

ACRRM recognises POCUS as a core rural generalist competency. Credentialling pathways include the ACRRM POCUS Certificate program and emergency POCUS training aligned with ACEM guidelines.

Documentation requirements for every POCUS examination:

• Indication
• Views obtained and technical adequacy
• Key findings
• Clinical decision made based on findings
• Limitation statement if views are suboptimal

Images should be stored (digital export) to support retrieval handover and quality audit. Regular case review and image archiving are components of ongoing quality assurance.

Technical limitations:

• Operator dependent, quality and accuracy improve substantially with supervised practice
• Obesity, surgical emphysema, bowel gas, and subcutaneous emphysema degrade image quality
• POCUS is a focused tool, not a comprehensive study, does not replace departmental imaging when available
• Negative FAST does not exclude retroperitoneal injury
• Lung point may be absent in complete lung collapse; clinical diagnosis of tension pneumothorax must not await POCUS

Sources

• Royal Flying Doctor Service clinical resources
• ACRRM Rural & Remote Medicine resources