Table 4 Abdominal ultrasound
From: Head to toe ultrasound: a narrative review of experts’ recommendations of methodological approaches
Condition | Imaging acquisition | Anatomy, findings and measurements | Training and learning curve |
|---|---|---|---|
Abdominal aortic aneurysm (AAA) | - Use a convex probe 3.5–5 MHz - Place the transducer perpendicular to the subcostal area below the xiphoid process with the notch toward the patient’s right and adjust depth to visualize the abdominal aorta (AA) - In this position, measure transverse diameters at the proximal, mid, and distal segments - Rotate transducer to the longitudinal plane with notch pointing toward the patient’s head - In this position, scan the AA in the longitudinal plane from origin (subcostal window) to bifurcation (1–2 cm below the umbilicus) by moving the probe caudally - Pay attention that the transducer is positioned parallel to the long axis of the AA - Measure maximal antero-posterior diameter of AA in proximal, mid (near renal arteries), and distal (above iliac bifurcation) segments - Adjust depth while carrying out the examination since AA becomes more superficial as it courses through the abdominal cavity If AA cannot be optimally visualized, try to apply a gentle pressure with transducer to displace bowel gas, or use lower transducer frequency | - In the transverse view both AA and inferior vena cava (IVC) can be recognized on either side of the spine; also, origins of renal arteries are visualized - AA is visualized in a cross section allowing measurement of the antero-posterior and side-to-side diameters - In the longitudinal view, AA is visualized in its long axis allowing measurement of the antero-posterior and cranial-to-caudal diameters - In this view also the two major proximal branches are visualized: celiac trunk and superior mesenteric artery Upper limit of normal antero-posterior diameter above 50 years - 26.6 mm in men and 23.6 mm in women for the proximal AA - 22.5 mm in men and 18.3 mm in women for the distal AA | - 15-day course - Formal or web-based teaching - Laboratory training on healthy volunteers and simulators - Minimum Passing Score - Learning Curve: 25 up to 50 examinations on average |
Hydronephrosis | - Use a convex probe 3.5–5 MHz - The kidney should be scanned in both long and short axes - To obtain a long axis view of the right kidney, the transducer is placed along the right lower intercostal spaces on the mid-axillary line with the transducer directed posteriorly and the notch pointing towards the head of the patient Please note that, the transducer should be swept anteriorly to posteriorly and cephalad to caudad in order to image the entire kidney - To obtain a long axis view of the left kidney, the transducer is placed on the posterior axillary line along left lower intercostal spaces but more cephalad than the right kidney Please, note that to obtain a long axis view of the left kidney, a more posterior approach is required to avoid stomach or intestinal air - For the short axis view of both kidneys, the transducer is rotated 90° from the long axis with indicator pointing down - Thickness measurement should be made between the surface of the kidney and a point where the parenchyma reaches the renal sinus | - Hydronephrosis appears as anechoic area within the normally echogenic renal sinus. The degree of hydronephrosis is based on visual diagnosis and is graded as mild, moderate or severe - The longitudinal diameter of the kidney ranges from 9 to 12 cm - The normal thickness varies from 1.5 to 1.8 cm, with mean values greater in males | - 2-week course - 25 to 50 proctored examinations → 50 are needed to reach enough accuracy for grading the severity of hydronephrosis |
Bladder evaluation | - Use a convex probe 3.5–5 MHz -The probe should be placed on midline in the suprapubic area with the indicator pointing toward patient’s head Then, the probe may necessitate to be angled slightly downward toward the pelvis until the bladder is visualized In the longitudinal scan antero-posterior and cranial-caudal diameters should be measured - The probe should be then rotated counterclockwise until the probe indicator is pointing to the patient’s right to obtain a transverse view and to measure the latero-lateral diameter | - US measurement of urine volume in the bladder allows to rule out bladder overdistension and to establish catheterization need - The three measured diameters should be used to calculate the bladder volume as follows: [Depth (mm) × length (mm) × width (mm)] × 0.7 = bladder volume (mL) | -5 to 10 proctored examinations |
Acute renal failure (ARF) | -Color and Power Doppler allow to identify vessels at the level of the hilum and in the renal parenchyma - Intrarenal vessels are better assessed by transverse scans that allow a Doppler angle closer to 0° and, thus, a higher sensitivity in detecting slow flow in small vessels - Knobology: (a) assess pulse repetition frequency (PRF) 1.2–1.4 kHz, and (b) velocity of the waveform 25–50 cm/s | - The RI is given by the ratio between systolic peak and diastolic peak/ systolic peak, and the normal value is 0.58 ± 0.10 - Values > 0.70 are considered abnormal, although a major clinical significance is observed only for values > 0.80 which are correlated with a worse outcome | Not yet well defined for critical care setting |
Gastric distension | Low-frequency (2–5 MHz) convex transducer Supine and right lateral decubitus position Semi-recumbent is an alternative if unable to turn lateral Transducer should be placed along the sagittal plane in the epigastrium, perpendicular to skin Landmarks to be observed: - Vertebral bodies - Long axis of abdominal aorta - Pancreas - Liver - Short axis of gastric antrum | Grade 0 - Empty antrum - “Bull’s-eye” appearance - Thick muscularis propriae layer - Low pulmonary aspiration risk Grade 1 - Fluid visible in right lateral decubitus only - Low pulmonary aspiration risk Grade 2 - Fluid visible in both supine and RLD - High pulmonary aspiration risk - Thick fluids - Distended antrum - Recently ingested with ‘frosted glass’ appearance - Later stages associated with hyperechoic, heterogeneous consistency - Highest pulmonary aspiration risk Calculation of antral cross‐sectional area (CSA) CSA (cm2) = antero-posterior diameter × craniocaudal diameter × π∕4 (1) | 33 supervised examinations |