What are the implications of Point-of-Care Ultrasound (POCUS) in diagnosing Abdominal Aortic Aneurysm (AAA) and other conditions?

From the Guidelines

Point-of-care ultrasound (POCUS) is recommended as a first-line tool for abdominal aortic aneurysm (AAA) detection and management due to its accuracy, accessibility, and lack of radiation exposure. When performing POCUS for AAA, scan the abdominal aorta from the diaphragm to the bifurcation using a curvilinear probe (2-5 MHz), measuring the outer wall to outer wall diameter in both transverse and longitudinal views. An aortic diameter ≥3.0 cm indicates an AAA, with risk of rupture increasing significantly at diameters >5.5 cm 1.

Key Considerations

• POCUS has valuable applications in trauma assessment (FAST exam), cardiac evaluation (focused cardiac ultrasound), lung assessment (detecting pneumothorax, pleural effusions), and vascular access guidance.
• The primary advantages of POCUS include immediate bedside results allowing for rapid clinical decisions, reduced need for patient transport, decreased radiation exposure compared to CT scans, and cost-effectiveness.
• However, POCUS accuracy depends heavily on operator skill and patient factors such as obesity or bowel gas that may limit visualization.

Imaging Modalities

• Ultrasound is the initial screening test in patients with suspected AAA, as supported by the consensus of the literature 1.
• CT abdomen and pelvis with intravenous (IV) contrast, CT abdomen and pelvis without and with IV contrast, and CT abdomen and pelvis without IV contrast are noninvasive and commonly used to evaluate various abdominopelvic pathologies, including aortic and nonaortic causes of a pulsatile abdominal mass 1.
• Noncontrast CT has been found to be more sensitive than ultrasound (US) in identifying AAAs, and the OTO aortic diameter perpendicular to the long axis of the aorta is recommended for determining maximum aortic diameter on CT 1.

Clinical Implications

• The risk of death from an AAA rupture is estimated to be between 75% and 90%, and up to 5% of sudden deaths in the United States are caused by AAA rupture 1.
• Elective surgical repair is considered the best way to prevent rupture and can be performed using an open surgical or endovascular approach.
• Screening or imaging surveillance is widely used to detect AAA that requires repair, with a generally accepted threshold of an aneurysm diameter exceeding 5.5 cm in men and 5.0 cm in women 1.

From the Research

POCUS Implications for AAA and Other Conditions

• The use of point-of-care ultrasound (POCUS) has been shown to be highly accurate in diagnosing abdominal aortic aneurysm (AAA) in the emergency department, with a pooled sensitivity of 98.33% and specificity of 99.84% 2.
• POCUS can help guide the need for urgent transfer to a vascular center in patients suspected of having ruptured AAA (rAAA) 3.
• Prehospital POCUS has been associated with reduced time to treatment, higher chance of operability, and significantly higher 30-day survival in patients with rAAA, ruptured iliac aneurysm, or impending rupture of an AAA 4.
• POCUS can be used to screen for AAA in the primary care setting, increasing adherence to screening guidelines and preferred by participants to formal ultrasound screening 5.
• Physician assistant students have been shown to be able to acquire adequate AA POCUS images, with 95% able to obtain interpretable transverse images of the distal aorta and longitudinal views of the aorta 6.

Benefits of POCUS for AAA Diagnosis

• Rapid diagnosis and treatment of rAAA can improve patient outcomes 3, 4.
• POCUS can decrease time to diagnosis and improve mortality of those diagnosed with abdominal aortic aneurysms and dissections 6.
• POCUS is a valuable tool that can help guide the need for urgent transfer to a vascular center in patients suspected of having rAAA 3.
• The use of POCUS in the emergency department can accurately detect and manage AAA, even with limited training 2.

Limitations and Future Directions

• Classic clinical symptoms associated with rAAA have poor sensitivity, and their absence does not rule out the condition 3.
• Computed tomography with angiography (CTA) has reasonable accuracy, but misses some cases of rAAA 3.
• Further research is needed to fully assess the applicability of POCUS for AAA screening in the primary care setting 5.
• Residual confounding cannot be excluded in studies evaluating the effectiveness of prehospital POCUS 4.