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Introduction to Ultrasound

Definition of Ultrasound

• Ultrasound (US) = sound with a frequency > 20 kHz; diagnostic medical US typically uses 2–15 MHz.
• Modern anaesthesia practice employs US for vascular access, regional blocks, neuraxial mapping, transthoracic (TTE) and trans-oesophageal echo (TOE), lung, gastric and airway scanning, focused obstetric assessments and haemodynamic Doppler studies.

Image Generation

• Ultrasound images are traditionally created using the Piezoelectric Effect. This involves the vibration of a piezoelectric crystal at the tip of the transducer, generating ultrasonic frequencies that create ultrasound waves.
  • Piezoelectric crystals are delicate and costly, with replacements costing thousands of dollars.
• The ultrasonic waves penetrate the body’s soft tissues and reflect back to the transducer. These returning waves are converted into ultrasound images displayed on a screen.
• Understanding the physics of waves is fundamental to grasping how ultrasound images are formed, how ultrasound artifacts occur, and how to use advanced ultrasound applications such as Doppler.

Does Echo Influence Survival Outcome

• Echo improves diagnostic accuracy but is not associated with improved survival or shorter hospital stay.

Evidence for Outcome Impact

• Vascular access–meta-analysis of 20 RCTs shows US guidance halves first-pass failure and arterial puncture during IJ cannulation.
• Regional anaesthesia–US reduces block failure and LAST, accelerates onset and lowers LA dose.
• Peri-operative TOE/TTE–observational data reveal change-of-management rates > 30 %; 2023 stepped-wedge RCT in high-risk non-cardiac surgery showed a 14 % relative reduction in major haemodynamic complications but no mortality signal at 30 days.
• Critical-care TTE–South-African multicentre cohort (ICU Echo SA 2024) linked early POCUS-guided fluid optimisation with shorter ventilator days; mortality benefit remains inconclusive.

Physics

Key Physics

• Frequency (f) = c/λ. Higher f → shorter wavelength → improved axial resolution but greater attenuation.
• Acoustic impedance (Z) = density × propagation speed. Reflection coefficient ∝ (Z₂–Z₁)²/(Z₂+Z₁)².
• Attenuation (dB cm⁻¹) rises with frequency and tissue type (bone ≈ 20, lung ≈ 12, muscle ≈ 1); compensation via time-gain controls.
• Beam interactions–reflection, refraction (Snell’s law), scattering and absorption produce the artefacts below.
• Safety indices–Mechanical Index (MI < 1.9) limits cavitation risk; Thermal Index (TI) guides exposure time (TI < 1.0 for first-trimester obstetrics). Follow ALARA (As Low As Reasonably Achievable) principles.

Frequency and Wavelengths

• Frequency: The number of sound wave cycles per second.
• Wavelength: The length or distance of a single cycle of a wave.
• Equation: Frequency = Speed of sound wave / Wavelength
  • As wavelength increases, frequency decreases (and vice versa).
  • Shorter wavelength = Higher frequency
  • Longer wavelength = Lower frequency

Impact of Frequency on Ultrasound Imaging

• High-Frequency Probes:
  • Emit shorter wavelengths
  • Provide better resolution
  • Have decreased penetration
• Low-Frequency Probes:
  • Emit longer wavelengths
  • Provide deeper penetration
  • Have lower resolution

Types of Probes and Their Characteristics

• Phased Array Probe: Great penetration, moderate resolution
• Curvilinear Probe: Good penetration, good resolution
• Linear Probe: Poor penetration, excellent resolution

Acoustic Impedance

• Definition: Acoustic impedance (Z) is the resistance to ultrasound propagation as it passes through a tissue.
• Equation: Impedance = Density x Propagation Speed of Sound Wave
• Dependence: Acoustic impedance is dependent on the tissue density and the speed of sound through that tissue.
• Effect: As tissue density increases, the impedance (resistance) increases as well.

Reflection of Ultrasound Waves

• Mechanism: Reflection occurs when ultrasound waves encounter the interface of two tissues with significantly different impedance values.
• Proportion: The proportion of reflected ultrasound waves is proportional to the difference in impedance between the two tissues.
• Example: Bone and air appear as bright lines on ultrasound due to the large impedance difference from soft tissue, causing almost all ultrasound waves to reflect back.
  • Impedance Values: Air (0.0004), Bone (12), Soft tissue (1.6).

Refraction of Ultrasound Waves

• Mechanism: Refraction occurs when ultrasound waves encounter tissues with slightly different impedance values.
• Effect: The speed of the ultrasound waves changes, causing a change in direction (refraction).
• Dependence: The degree of refraction depends on the angle of incidence and the change in speed in the second medium.
• Example: Refraction is seen at the rounded interfaces between fluid-filled structures and adjacent soft tissues, causing edge artifacts such as black lines from the edges of structures like the gallbladder, cysts, vessels, and bladder.

Attenuation–Absorption

• Definition: Attenuation is the loss and absorption of ultrasound energy as it passes through a medium.
• Effect: Describes how rapidly a medium reduces the intensity of an ultrasound wave.
• High Attenuation Mediums: Air and bone have the highest attenuation.
• Dependence: Unlike impedance, attenuation is not solely dependent on the density of the material.

Doppler Effect

• Definition: The Doppler Effect (or Doppler Shift) evaluates movement either towards or away from the ultrasound probe/transducer. Commonly used to detect blood movement, but can also evaluate tissue and muscle movement.
• Essentials
  • Doppler shift (Δf) = 2 v f₀ cos θ / c.
  • Keep insonation angle < 20 °; at 90 ° no flow is detected.
  • Aliasing occurs when |Δf| > ½ PRF; increase scale, decrease depth or use CW.

Doppler Shift Equation

• Equation: Doppler Shift = (2 x Velocity of blood x Transducer frequency x cos θ) / Propagation speed
  • θ: Angle of Insonation (angle of incidence between the ultrasound beam and the direction of flow).
• Dependence: The Doppler shift is primarily related to:
  1. The velocity of the blood cells.
  2. The angle of insonation.
• Technique: For accurate Doppler measurements, ensure the movement is parallel to the ultrasound probe (0 degrees). Angles above 25-30 degrees will significantly underestimate measurements. At 90 degrees, the Doppler will read no flow due to the cosine of 90 degrees being 0.

Note: While using the velocity of blood as an example, the same principles apply when measuring muscle movement using tissue Doppler.

Common Artefacts (recognition Prevents misdiagnosis)

Artefact	Cause	Typical appearance
Mirror image	Strong reflector + air	Duplicate organ deep to diaphragm
Acoustic shadow	High attenuation (bone, gallstone)	Black shadow distal to object
Posterior enhancement	Low attenuation fluid	Bright distal field behind cyst/bladder
Edge shadow	Refraction at curved wall	Linear dropout from vessel edge
Reverberation / A-lines	Multiple reflections	Equidistant horizontal lines (lung)
Comet-tail	Closely spaced reflectors	Tapering tri-angular echo (metal needle)
Ring-down / B-lines	Resonant air–fluid	Vertical laser-like line to bottom
Side-lobe / grating	Off-axis beam energy	Ghost echo e.g. “clot” in left atrium

Probes

Foot-print	Array	Usual MHz	Resolution ↑	Penetration ↑	Typical use
Linear	128–256 elements	5–15		–	Vascular, nerve, lung, paediatric
Curvilinear	64–128	2–8			FAST, abdominal, obstetric
Phased-array	64–128	1.5–5			Cardiac, trans-cranial, rib spaces

• Piezo-electric crystals convert electrical ↔ mechanical energy (classically lead-zirconate-titanate).
• Emerging CMUT/PMUT silicon transducers offer wider bandwidth and reduced cable bulk.
• Probe care: avoid alcohol-based wipes on lens; micro-cracks cause delamination and infection-control failure.

Probe Movement

• Only do one movement at a time. 1mm of movement of probe on patient is 2cm on screen
• Depth → centre region of interest at ½–⅔ screen; single focal zone at that depth.
• Overall gain for uniform grey; TGC sliders flatten banding.
• Rock (heel-toe), slide, tilt and rotate–one plane at a time; 1 mm on skin ≈ 20 mm on screen (~×20 magnification).

Modes of Ultrasound

Mode	Information	Anaesthetic application
B-mode (2D)	Brightness map of echo amplitude	Core of all POCUS
M-mode	Motion along a single line vs time	Lung sliding, TAPSE, fetal HR
Colour Doppler	Direction & mean velocity (BART rule)	Valve screening, shunts, IV line patency
Pulse-wave Doppler	Point velocity profile (Nyquist-limited) Measures the velocity of blood flow at a single point using a sample gate. Limitation: Maximum speed detectable is limited by the Nyquist Limit; aliasing occurs if this limit is exceeded. Not suitable for high-velocity applications (>200 cm/s).	LVOT VTI for CO, diastolic function
Continuous-wave Doppler	Unlimited high velocity Measures all points along the cursor line and can detect very high velocities (>1000 cm/s). It does not alias.	Aortic stenosis, severe regurgitation
Tissue Doppler / strain	Low-velocity myocardial or diaphragmatic motion A form of Pulse Wave Doppler designed to measure slower speeds of tissue/muscle movement (1 cm/s–20 cm/s).	Weaning readiness, diastolic grading
Harmonic imaging	Receives at 2f; improves contrast	Obesity, deep nerve blocks
3D/4D TOE	Volumetric valve assessment	Mitral clip, complex cardiac surgery

Pulse Wave (PW) Doppler Mode

Basics of Operation

Positioning

Stand on the left side of the patient with the probe in the right hand. The patient should be in the left lateral position with the arm above the head.

Probe Marker Orientation

Locate the marker on the screen. With echocardiography, the marker is on the right side and corresponds to the marker on the cardiac probe.

Probe Movement

You can slide, rotate, rock (parallel to probe marker—rock the foot), or tilt (perpendicular to probe marker—tilt the tail) the transducer. Attempt to perform only one movement at a time. Note that 1 mm of movement of the probe on the patient equates to 2 cm on the screen.

Optimising the Image

• Depth: A centimetre scale is seen on the side of the screen indicating the depth of tissue being scanned. Adjust the depth to ensure the entire structure being evaluated or the area of interest is visible on the screen.
• Gain: Adjust the intensity of returning echoes shown on the screen. Increasing the gain will brighten the display, while decreasing the gain will darken it.
• Time Gain Compensation: Adjusts the gain at varying depths using multiple slider levers.
• Focus Point: Define the area you want to focus on.

Basic Mode (B-Mode) and Motion Mode (M-Mode)

• Gain (Brightness)
• Depth
• Time gain compensation
• Frequency (use higher frequency for more superficial structures, usually 2-4 MHz)
• Focus point
• I-beam (compounding—smooths the picture)
• Grey map (choose the grey scale)
• Zoom (enhances the view, especially useful for M-mode)

Doppler (Pulse Wave Doppler – PW)

• If the indicator is green, it is active, and you can move it.
• Adjust sample volume (size measured). The sample volume should never be less than the diameter of the vessel and never more than 2/3 of the diameter.
• Steer: Change the direction of measurement.
• Quick angle: Change to 60 degrees and maintain steer.
• Use finite angle adjustment for further angle adjustments.
• I-touch: Automatically adjusts scale and baseline.
• Can invert the image and adjust the baseline.
• Adjust the scale to fit the entire waveform.
• Duplex: Simultaneous live imaging and Doppler.
• Sweep speed: Adjusts the number of waves.

Color Doppler

• BART mnemonic: Blue AWAY, Red TOWARDS.
• Adjust the size and steer the box.
• Gain will adjust color.
• Utilizes pulsed wave Doppler and the Doppler equation to generate colors.
• Aliasing: Blood velocity moving faster than the analyzing frequency shift, leading to misinterpretation.
• Best interpreted when the box is placed inline with blood flow. Aim for cos=0 degrees (cos0=1). If not inline, the angle of observation (cos) will increase and underestimate the velocity of blood flow.
• A larger box will decrease the frame rate, so keep the box as small as possible while including all the areas you want to assess.

CARDIAC and Fluid Responsiveness

• Patient position: Attempt in Left lateral position or place pillow beneath right shoulder. Might require patient to hold breath for more adequate view.

Views

Patient Set-up & Probe Orientation

• Position–left lateral decubitus for parasternal / apical views; supine with knees flexed for subcostal & IVC.
• Probe markers (screen­-left)
  • PLAX 10 o’clock → right shoulder  * PSAX 1 o’clock → left shoulder
  • Apical series 3 o’clock → left flank  * Subcostal 12 o’clock → patient’s hea
• Use phased-array 1.5–5 MHz; depth 16–20 cm (parasternal) or 12 cm (apical).

Core FoCUS Views & Key Questions

View	Probe tips	Binary questions
PLAX	2-4 ICS, LSB, marker right shoulder	LV contractility adequate? RV / LA / aortic root size normal? Pericardial effusion?
PSAX (aortic, mitral, papillary levels)	Rotate 60–90° clockwise	Global LV systolic function? Septal “D-shape” (RV pressure/volume overload)?
Apical 4-/5-/2-/3-chamber	Apex beat, marker 3 o’clock	LV/RV size & function? Valvular regurgitation? Stroke volume / VTI?
Subcostal 4-chamber & IVC	1–2 cm below xiphisternum	Tamponade? IVC calibre & variation?

Qualitative and Semi-quantitative Check-list

Variable	Normal reference	Rapid screen
LV wall thickening	> 40 % systolic thickening	“Eyeball” squeeze & wall inward motion
EPSS	< 7 mm	M-mode PLAX
MAPSE	≥ 12 mm lateral annulus	M-mode apical
RV size	RV ≲ ⅔ LV in A4C	Compare basal widths
TAPSE	≥ 17 mm	M-mode tricuspid annulus
S’ (TDI)	≥ 9.5 cm s⁻¹	PW-TDI RV free wall
IVC (spont. breath)	≤ 2.1 cm or collapsibility > 50 %	Subcostal long axis
IVC (ventilated)	Distensibility > 18 %	Measure during resp. cycle

Quantitative Systolic Assessment

1. Teichholz / fractional shortening (PLAX M-mode) when image quality limits 2D methods.
2. Biplane Simpson (LVEF) from A4C & A2C–gold standard for bedside echo.
3. MAPSE (lateral + septal) average correlates with LVEF; quick surrogate when time-critical.

MAPSE

Stroke Volume & Fluid Responsiveness

• Stroke volume (SV) = π (LVOT ø / 2)² × LVOT VTI
• Measure LVOT diameter (mid-systole, PLAX) once unless physiology changes.
• Acquire PW-Doppler in A5C with sample at LVOT; optimise angle (θ < 20°) & trace VTI.
• Normal VTI 18–22 cm.
• Dynamic tests
  • Passive leg raise (PLR) or 200 mL crystalloid bolus.
  • Responder = ≥ 10–12 % rise in VTI (meta-analysis AUROC 0.88).
  • Combine with IVC distensibility or carotid VTI for ventilated patients when apical window is poor
  • Caution–unreliable in significant aortic or mitral regurgitation, arrhythmias, LVOT obstruction.

Cardiac Output

Right-heart Strain & Pulmonary Hypertension Screen

Sign	Finding
RV/LV basal ratio > 1 (A4C)	Dilated RV
Septal flattening (“D-shape”) in PSAX	RV pressure overload
TAPSE < 17 mm or S’ < 9.5 cm s⁻¹	RV systolic dysfunction
McConnell sign	Akinesis mid-free wall with preserved apex (suggests acute PE)

Left-ventricular Diastolic Dysfunction (LVDD)

Step	Acquisition	Measurement	Key cut-offs*	Interpretation
1	A4C–PW-Doppler at MV leaflet tips	Mitral inflow E/A ratio & E-wave deceleration time (DT)	Normal adult: E/A 1–2 & DT 160–240 ms	E<A ⇒ impaired relaxation (Grade I) • E/A > 2 & DT < 160 ms ⇒ restrictive (Grade III–IV)
2	A4C–TDI at septal & lateral annulus	Early annular velocity e’ (cm s⁻¹)	Septal e’ < 7 or Lateral e’ < 10 → abnormal relaxation	Distinguishes pseudonormal (Grade II) from normal pattern
3	Calculate E/e’ (average e’)	Surrogate LV filling pressure	E/e’ < 8 normal • 8–14 indeterminate • > 15 raised	> 15 suggests LVEDP > 15 mmHg and poor fluid tolerance
4	A4C–planimetry or M-mode	LA volume index (LAVi)	> 34 mL m⁻² chronic elevation	Confirms chronic LVDD when E/e’ equivocal
5	TR jet (CW Doppler)	TR Vmax (m s⁻¹)	> 2.8 m s⁻¹ suggests ↑ pulmonary pressures	Supports Grade II–III if two major criteria positive

• *Cut-offs from ASE/EACVI 2016 guidance, validated in peri-operative cohorts 2019-2024.

Bedside algorithm (simplified for FoCUS)

1. Acquire mitral inflow & septal e’.
2. If E/A < 0.8 and E < 50 cm s⁻¹ → Grade I (relaxation defect).
3. If E/A > 2.0 → Grade III/IV (restrictive).
4. Otherwise calculate E/e’:
   • E/e’ ≤ 8 → normal filling (Grade 0).
   • E/e’ ≥ 15 or LAVi > 34 or TR Vmax > 2.8 m s⁻¹ → Grade II (pseudonormal).
   • If 1 of 3 supportive signs only → indeterminate; reassess with load manipulation or TTE.
     Clinical implications for the anaesthetist

• Raised filling pressure (E/e’ > 15) → low fluid reserve, tolerate higher PEEP poorly; prefer vasopressor over fluid bolus.
• Grade III–IV LVDD associated with two-fold increase in peri-operative pulmonary oedema and ICU length-of-stay.
• In septic shock, high E/e’ predicts failure of liberal fluid strategy—supporting Doppler-guided resuscitation algorithms.
• Consider intra-operative diastolic-tailored goals: MAP > 65 mmHg, pulse pressure < 60 mmHg, heart-rate optimisation (β-blockade or pacing) to prolong filling time.

Evidence Snapshot (2018–2025)

• LVOT-VTI change ≥ 10 % after PLR predicts fluid responsiveness with pooled sensitivity 0.86 & specificity 0.88–2024 systematic review of 34 studies
• Critical-care ultrasound-guided resuscitation in septic shock reduced 28-day mortality and ICU length of stay in 2025 multicentre RCT (n = 480)
• Ultrasound-tailored fluids outperformed usual care in septic shock–2024 ECCM meta-analysis; best performance with IVC + PLR protocols
• EACTS/EACTAIC 2025 guideline endorses goal-directed fluid therapy using Doppler-derived SV change in high-risk cardiac and major vascular surgery
• South-African review (JTCCM 2024) highlights FoCUS as feasible first-line tool in low-resource ICUs

Pitfalls & Tips

• Far-field foreshortening of LV apex gives false-low VTI–slide laterally until true apex.
• Under-filled LV mimics poor contractility; always integrate IVC/clinical picture
• Arrhythmia–average ≥ 5 beats for Doppler measurements.
• LVOTO in severe hypovolaemia; beware spuriously high VTI.

Valvulopathies – Step-by-step Echocardiographic Diagnosis

General Systematic Approach (all valves)

1. Leaflet morphology & motion–assess for thickening, calcification, prolapse, flail, restricted motion.
2. Colour Doppler
   • Antegrade turbulence → suspect stenosis.
   • Retrograde jet → regurgitation; inspect vena contracta and proximal isovelocity convergence (PISA).
3. Optimise spectral Doppler
   • Align beam ≤ 20 ° with flow.
   • Raise velocity scale (Nyquist ≥ 60 cm s⁻¹), shift baseline, shorten sample depth, or choose higher-frequency probe to avoid aliasing.
4. Quantify severity–use at least two quantitative and one supportive parameter (guideline requirement).
5. Look for sequelae–chamber enlargement, ventricular hypertrophy, pulmonary or systemic hypertension.

Aortic Valve

Parameter (TTE)	Mild	Moderate	Severe
Stenosis – measured in ≥ 2 windows (A5C, suprasternal, right parasternal)
Peak velocity (Vₘₐₓ)	2.6–2.9 m s⁻¹	3.0–3.9	≥ 4.0
Mean gradient	< 20 mmHg	20–39	≥ 40
Valve area (AVA, continuity)	> 1.5 cm²	1.0–1.5	< 1.0
Dimensionless index (LVOT VTI / AV VTI)	> 0.5	0.25–0.50	< 0.25
Regurgitation–A5C / PLAX colour + CWD
VC width	< 3 mm	3–6	> 6
Jet/LVOT width	< 25 %	25–65 %	> 65 %
PHT (ms)	> 500	200–500	< 200
Regurgitant vol (ml)	< 30	30–59	≥ 60
Desc. aorta holodiastolic reversal	Absent	—	Present (> 20 cm s⁻¹ end-diastolic)

• Tips
  • Measure LVOT diameter inner-edge to inner-edge in mid-systole (zoomed PLAX).
  • Late-peaking (crescendo) CWD curve ➜ severe AS with low flow.
  • Always calculate stroke volume to confirm “low-flow low-gradient” AS.

Mitral Valve

Parameter	Mild	Moderate	Severe
Stenosis (PLAX/A4C zoom + CW)
Mitral valve area (planimetry)	1.5–2.5 cm²	1.0–1.5	< 1.0
Mean gradient (HR 60–80 bpm)	< 5 mmHg	5–10	> 10
PHT (ms)	< 150	150–220	> 220
SPAP (from TR jet)	< 30 mmHg	30–50	> 50
Regurgitation (A4C/A2C colour + CW)
VC width	< 3 mm	3–7	≥ 7
Effective regurgitant orifice (EROA)	< 0.20 cm²	0.20–0.39	≥ 0.40
Regurgitant volume	< 30 ml	30–59	≥ 60
Pulmonary vein systolic flow	Normal	Blunted	Reversed

• Primary MR–leaflet or chordae pathology; secondary MR–annular dilatation / LV dysfunction: quantify both and report mechanism (Carpentier classification)

Tricuspid Valve

Parameter	Mild	Moderate	Severe
Regurgitation (A4C/S4C/subcostal)
VC width	< 0.5 cm	0.5–0.6	≥ 0.7 cm or non-visualisable because too large
PISA EROA	< 0.20 cm²	0.20–0.39	≥ 0.40
Regurgitant jet area (not stand-alone)	< 5 cm²	5–10	> 10
Systolic hepatic vein flow	Normal	S–blunted	S-flow reversal
Stenosis
Mean gradient (CW)	—	2–5 mmHg	≥ 5 mmHg
Valve area (continuity)	—	1.0–1.5 cm²	< 1.0 cm²

Pulmonary Valve

Parameter	Mild	Moderate	Severe
Stenosis (PSAX PV level + CW)	Peak gradient	36–64 mmHg	≥ 64 mmHg
Regurgitation	VC width	—	≥ 0.6 cm or diastolic flow reversal in PA

Supportive and Integrative Signs (all Regurgitant lesions)

• LV / RV / LA / RA enlargement commensurate with volume overload.
• Pressure overload sequelae–concentric LVH (AS), septal flattening (severe TR / PR).
• Exercise TTE when resting assessment indeterminate but symptoms disproportionate.

Practical Acquisition Pearls

• Use 3–5 continuous-wave envelopes at sweep 50–100 mm s⁻¹; trace the highest waveform.
• Average measurements in sinus rhythm; in AF use ≥ 5 cycles.
• Re-check blood pressure when calculating gradients; systemic hypertension can exaggerate MR/AR severity.

Lung Ultrasound

Scanning Protocol & Normal Artefacts

Zone approach	Probe & depth	Key normal findings
6-point (BLUE) or 12-zone supine/semi-recumbent	Linear (superficial) or curvilinear 3–5 MHz	Pleural line: smooth, ≤ 2 mm
		Lung sliding (“ants marching”) in real time; seashore sign on M-mode
		≥ 2 equally spaced A-lines under each pleural line

• A-lines = horizontal reverberations → normal aeration.
• B-lines = vertical, laser-like artefacts starting at pleura, obliterate A-lines, move with respiration

Key Pathological Signs & Diagnoses

Pattern / sign	Diagnostic implication	Typical probe position
Absent lung sliding ± barcode sign	Pneumothorax (PTX) if coupled with A-lines and lung point	2nd ICS mid-clavicular; sweep laterally
Multiple (≥ 3) B-lines per rib space	Interstitial syndrome (pulmonary oedema, ARDS, fibrosis, early COVID-19)	Anterior & lateral chest
Waterfall B-lines, spared areas	Cardiogenic oedema (diffuse) vs ARDS (patchy)	Whole hemithorax
Sub-pleural consolidation ± dynamic air bronchograms	Pneumonia	Posterior basal & axillary
Shred sign (irregular deep border)	Non-translobar pneumonia or contusion	Dependent zones
Quad sign, spine sign, sinusoid sign	Pleural effusion	Posterolateral 5–8 ICS
Hepatisation + static air bronchograms	Atelectasis	Posteromedial
Re-appearance of pleural sliding with compression	Lung herniation / minimal PTX	Event site

Pneumothorax (BLUE Profile A′)

• Probe: high-frequency linear.
• Hallmark: A-lines + absent sliding + lung point (specificity 99 %).
• M-mode: barcode / stratosphere sign (no granular pattern).
• Quantification: distance from sternum to lung point correlates with PTX size.

Pleural Effusion

• Curvilinear probe mid-axillary 5–7 ICS.
• Anechoic or complex collection deep to parietal pleura.
• Spine sign–vertebral bodies visualised above diaphragm.
• Quad sign (rib shadows, pleura, lung line) confirms pocket.
• Volume estimate (supine): craniocaudal height (cm) × 20 ≈ mL.

Pneumonia / Consolidation

• Patchy B-lines early → shred sign as air bronchograms appear.
• Dynamic air bronchograms distinguish pneumonia from atelectasis.
• Sensitivity ~90 %; superior to CXR for ventilator-acquired pneumonia.

Cardiogenic Pulmonary Oedema

• Bilateral, symmetrical B-lines from bases to apices (“white lung”).
• LUS score (0–3 per zone) correlates with EVLW; fall of ≥ 5 points after diuretic predicts successful wean.

Pulmonary Embolism (PE) Adjunct

• Peripheral wedge-shaped pleural-based consolidation without colour flow (dual-image Doppler).
• Combine with RV strain on echo for bedside PE probability.

Interpretation Pitfalls

• Absent B-lines does not exclude early interstitial oedema if high PEEP.
• Lung pulse (cardiac-synchronised pleural movement) rules out PTX despite absent sliding.
• Rib shadows and mirror artefact can mimic effusion—scan in two orthogonal planes.

Clinical Integration & South-African Context

• LUS halves time-to-diagnosis of PTX and pleural effusion in trauma compared with chest X-ray (UCT trauma service 2022).
• In SARS-CoV-2 waves, SAICU LUS protocol (12-zone score > 15) predicted need for invasive ventilation (AUROC 0.89).
• Recommended training: 25 supervised scans, of which ≥ 5 pathological, for independent practice (SASA POCUS 2023).

VEXUS

Links

• Transoesophageal ultrasound (TOE)
• Electrocardiogram (ECG)
• Cardiac physiology

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