Airway Ultrasound

Airway US Basics - Scan & See

• Why Airway US?
  • Non-invasive, real-time, dynamic assessment.
  • Complements static predictors (e.g., Mallampati).

  ⭐ Ultrasound offers a dynamic, real-time assessment of the airway, complementing traditional static predictors like Mallampati score.

• Probe Selection:
  • High-frequency linear (5-12 MHz): Superior resolution for superficial structures (e.g., vocal cords, cricothyroid membrane).
  • Low-frequency curvilinear (2-5 MHz): Better penetration for deeper structures, wider field (e.g., epiglottis, subglottic view).
• Basic Views & Structures:
  • Scan in transverse & sagittal planes.
  • Identify: Hyoid bone, epiglottis, thyroid cartilage, vocal cords (true/false), cricoid cartilage, tracheal rings.

Sonoanatomy - Airway Atlas

• Tongue & Floor of Mouth:
  • Genioglossus muscle: Hypoechoic, bulky, forms tongue base.
  • Mylohyoid muscle: Thin, hypoechoic band inferiorly.
• Hyoid Bone: Key landmark.

  ⭐ The hyoid bone, appearing as a hyperechoic curved line with posterior acoustic shadowing, is a primary landmark for orienting airway ultrasound.

• Laryngeal Structures (Superior to Inferior):
  • Epiglottis: Hypoechoic, leaf-like; anterior pre-epiglottic space (hypoechoic fat).
  • Thyroid Cartilage: Hyperechoic; inverted V-shape (transverse), linear (sagittal). Vocal cord attachment.
  • Vocal Cords: True (hypoechoic, medial) & False (hyperechoic, lateral) - "sandwich sign" at glottis.
  • Arytenoid Cartilages: Hypoechoic, pyramidal, atop posterior cricoid.
  • Cricoid Cartilage: Hyperechoic complete ring; "signet ring" appearance.
• Trachea & Esophagus:
  • Tracheal Rings: Anterior, hyperechoic, C-shaped/inverted U-shapes ("string of beads" sign). Air-mucosa interface (A-line).
  • Esophagus: Typically collapsed, posterior/postero-lateral to trachea; multilayered "target sign".

Prediction Parameters - Crystal Ball Scan

• PTST (Pre-tracheal Soft Tissue):
  • ↑ PTST-VC (Vocal Cords): >2.8 mm predicts difficult laryngoscopy (DL).
  • ↑ PTST-H (Hyoid).
• SED (Skin-to-Epiglottis Distance):
  • ↓ SED is a key predictor of difficult intubation.
• Tongue Dimensions:
  • ↑ Thickness/volume linked to difficult airway.
• Other Distances:
  • ↓ sHMD (Sonographic Hyomental Distance).
  • ↓ Skin-to-Anterior Commissure distance.
• Visibility:
  • Impaired view of hyoid, epiglottis, vocal cords.

⭐ Key predictors of difficult intubation include increased pre-tracheal soft tissue thickness at the vocal cord level and a reduced skin-to-epiglottis distance.

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Clinical Uses - Guided Moves

• ETT Confirmation:
  • Transtracheal: Direct ETT view, cuff inflation, "double tract sign" (trachea anterior, esophagus posterior).
  • Transthoracic: Bilateral lung sliding ("ants marching"), diaphragm movement.
• LMA Confirmation:
  • Verify correct tip placement in hypopharynx.
• Procedure Guidance:
  • Percutaneous Dilatational Tracheostomy (PDT): Midline, vessels (e.g., AJV, ITA), pre-tracheal structures, best puncture site.
  • Cricothyroidotomy: Rapid cricothyroid membrane identification.
  • Nerve Blocks (e.g., SLN, transtracheal): Precise needle guidance, local anesthetic spread.

⭐ Transtracheal ultrasound reliably confirms endotracheal tube placement by visualizing the tube within the trachea, often with a 'double tract' sign if the esophagus is also seen.

High‑Yield Points - ⚡ Biggest Takeaways

• Airway ultrasound rapidly identifies key landmarks: hyoid, epiglottis, vocal cords, trachea, cricothyroid membrane.
• Vocal cord mobility: Assessed by "bilateral shimmering" or symmetrical adduction/abduction.
• ETT confirmation: Direct tracheal visualization (e.g., "bullet sign", tracheal rings) and bilateral lung sliding are crucial.
• Cricothyroid membrane (CTM): Accurately located between thyroid and cricoid for emergency front-of-neck access (FONA).
• Subglottic diameter measurement: Aids in pediatric ETT sizing and detecting potential stenosis.
• Predicts difficult intubation: By assessing anterior neck soft tissue thickness or hyomental distance extended (HMDE).