What depth setting should I use on bedside ultrasound to detect a pneumothorax?

Depth Setting for Pneumothorax Detection on Bedside Ultrasound

Use a shallow depth setting of approximately 5-7 cm when scanning for pneumothorax, as the pleural line is a superficial structure located only 0.5-2.5 cm below the skin surface. 1

Optimal Technical Parameters

Depth Configuration

• Set your depth to visualize structures up to 5-7 cm maximum - the pleural line you're evaluating is extremely superficial, and deeper settings will only reduce image resolution of the critical structures 1
• Adjust frequency, depth, focus, and gain settings specifically to optimize imaging of these superficial structures 1
• In larger patients, you may need slightly deeper settings, but the pleural interface remains relatively superficial even in obese individuals 1

Probe Selection and Frequency

• Use a linear high-frequency probe (5-12 MHz) as your primary choice for optimal resolution of the superficial pleural line 1, 2
• Alternative transducers (phased array or convex probes) can be used based on availability and body habitus, though they provide less optimal resolution 1
• The high-frequency linear probe provides superior visualization of the pleural sliding and B-lines that are essential for diagnosis 2

Scanning Technique

Probe Positioning

• Start at the 3rd-4th intercostal space in the mid-clavicular line, orienting the probe in the long axis (sagittal plane) 1, 2
• Scan between the ribs in the interspaces from the clavicle to the diaphragm 1
• Move the probe laterally across the anterior chest wall systematically 1

Image Optimization Strategy

• Focus your focal zone at the level of the pleural line (the bright hyperechoic line representing the visceral-parietal pleural interface) 1
• Use B-mode imaging as your primary modality 1, 2
• M-mode can be added as a supplementary technique to document absence of lung sliding (showing the "stratosphere sign" or "barcode sign" in pneumothorax) 1

Critical Diagnostic Signs to Identify

With proper depth settings, you should clearly visualize:

• Absence of lung sliding - the back-and-forth movement of visceral against parietal pleura 1, 2
• Absence of B-lines (comet-tail artifacts) - vertical reverberation artifacts that rule out pneumothorax when present 1, 3
• Absence of lung pulse - cardiac oscillations transmitted through collapsed lung 2, 3
• Presence of lung point - the transition zone where pneumothorax meets normal lung, which has 100% specificity for pneumothorax 2, 3

Common Pitfalls to Avoid

• Don't set the depth too deep (>10 cm) - this wastes screen space and reduces resolution of the superficial pleural structures you need to evaluate 1
• Don't mistake subcutaneous emphysema for pneumothorax - both can show absent lung sliding, but subcutaneous air creates characteristic reverberation artifacts in the soft tissues 1
• Remember that absent lung sliding alone is not diagnostic - it can occur with atelectasis, consolidation, lung contusion, or even mainstem intubation 1
• Always search for the lung point sign when lung sliding is absent - this provides 100% specificity for confirming pneumothorax 2, 3

Clinical Performance

When performed with appropriate depth settings and technique, bedside ultrasound achieves:

• Sensitivity of 89-100% and specificity of 99% for pneumothorax detection 1, 2, 3
• Superior accuracy compared to supine chest radiography (sensitivity 27.6%) 4
• Significantly faster diagnosis (2.3 minutes vs 19.9 minutes for chest X-ray) 4