ROUB cheat sheet

Amniotic fluid index (AFI): sum of the deepest vertical pocket in each of four quadrants; normal 5–24 cm, oligohydramnios <5 cm, polyhydramnios >24 cm.

Single deepest pocket (SDP): oligohydramnios <2 cm; polyhydramnios ≥8 cm. SDP is preferred in multiple gestations to avoid overdiagnosis of polyhydramnios.

Crown-rump length 45–84 mm gives the most accurate first-trimester dating; estimated due date = LMP-based date adjusted by CRL when discrepancy exceeds 5–7 days.

Nuchal translucency is measured at 11+0 to 13+6 weeks with CRL 45–84 mm, in a mid-sagittal plane, calipers on the inner borders, neutral neck position.

Estimated fetal weight formulas (Hadlock) use BPD, HC, AC, and FL; AC is the single best predictor of fetal weight and is most affected by growth restriction.

Doppler indices: resistive index RI = (PSV − EDV)/PSV; pulsatility index PI = (PSV − EDV)/TAMX; systolic/diastolic ratio S/D = PSV/EDV.

Umbilical artery Doppler: absent or reversed end-diastolic flow indicates severe placental insufficiency; reversed flow carries the highest stillbirth risk.

Middle cerebral artery PI below the 5th centile suggests fetal anemia or brain-sparing; peak systolic velocity >1.5 MoM is the threshold for anemia workup.

Biophysical profile: 2 points each for fetal breathing, movement, tone, amniotic fluid volume, and reactive NST; score ≥8 is generally reassuring, ≤4 warrants delivery assessment.

Diagnostic ultrasound is first-line for suspected rotator cuff tear in many settings; full-thickness tears show a focal hypoechoic gap with loss of the normal convex bursal contour.

Supraspinatus tendon is examined with the arm in internal rotation (Crass position), hand on ipsilateral buttock, to bring the tendon anteriorly.

Dynamic evaluation: subscapularis is assessed with external rotation; biceps long head in the bicipital groove with the forearm supinated.

Lateral epicondylitis (tennis elbow): common extensor origin shows hypoechoic thickening, loss of fibrillar pattern, and possible intrasubstance tear or calcification.

Median nerve cross-sectional area >10 mm² at the carpal tunnel inlet supports carpal tunnel syndrome; the nerve normally flattens distally.

Plantar fascia thickness >4 mm at the calcaneal insertion supports plantar fasciitis; normal thickness is roughly 2–4 mm.

Achilles tendon: normal is <6 mm anteroposterior diameter; focal hypoechoic thickening with loss of fibrillar pattern suggests tendinopathy or partial tear.

Muscle strain grading: grade I is strain without fiber disruption, grade II is partial tear, grade III is complete tear with retraction; hematoma appears as anechoic to complex fluid.

Anisotropy: tendons and nerves appear falsely hypoechoic when the beam is not perpendicular; correct by heel-toe angling of the transducer.

FAST exam windows: right upper quadrant (Morison's pouch), left upper quadrant (splenorenal), suprapubic (pelvis), and subxiphoid (pericardium).

Free intraperitoneal fluid appears as anechoic fluid in dependent recesses; the right upper quadrant is the most sensitive single window in supine patients.

Lung sliding present rules out pneumothorax at that site; absent sliding plus a lung point sign is highly specific for pneumothorax.

B-lines (≥3 per intercostal space) indicate interstitial syndrome (pulmonary edema, pneumonia, fibrosis); A-lines indicate normal aeration.

IVC assessment: diameter <2 cm with >50% collapse suggests low right atrial pressure; >2 cm with <50% collapse suggests elevated right atrial pressure.

Focused cardiac views: parasternal long axis for pericardial effusion and LV function; apical four-chamber for chamber comparison and gross EF estimation.

Ocular ultrasound: optic nerve sheath diameter >5 mm (measured 3 mm behind the globe) is a screening marker for raised intracranial pressure.

Probe selection: curvilinear (2–5 MHz) for abdomen and lung, linear (5–12 MHz) for vascular access and superficial structures, phased array (1–5 MHz) for cardiac.

Needle guidance: in-plane approach shows the needle shaft and tip; out-of-plane shows the tip as a dot, so confirm tip position before advancing.

Left ventricular ejection fraction by eyeball estimate: normal ≥55%, mildly reduced 45–54%, moderately reduced 30–44%, severely reduced <30%.

Fractional shortening FS = (LVIDd − LVIDs)/LVIDd; normal is roughly 25–45% and correlates with EF.

Cardiac output CO = stroke volume × heart rate; stroke volume = LVOT area × LVOT VTI, with LVOT area = π × (diameter/2)².

Aortic stenosis severity by peak velocity: mild 2.5–3.0 m/s, moderate 3.0–4.0 m/s, severe >4.0 m/s; mean gradient >40 mmHg supports severe disease.

Mitral inflow E/A ratio: normal E > A; E/A reversal suggests impaired relaxation (grade I diastolic dysfunction).

Tissue Doppler e′ <8 cm/s (septal) or <10 cm/s (lateral) supports diastolic dysfunction; E/e′ >14 suggests elevated filling pressures.

Carotid stenosis: peak systolic velocity thresholds approximate <125 cm/s (normal), 125–230 cm/s (moderate), and >230 cm/s (severe) in many labs, correlated with angiography.

Pericardial effusion: anechoic space between pericardium and myocardium; right atrial systolic collapse and right ventricular diastolic collapse suggest tamponade physiology.

Abdominal aortic aneurysm: infrarenal diameter ≥3 cm defines aneurysm; ≥5.0–5.5 cm is the usual threshold for surgical or endovascular referral.