Airway ultrasound structures (2027)
Stem
Ultrasound application station. A healthy adult volunteer lies supine with the neck in neutral. The examiner has a linear probe connected and runs the machine. The prompt reads: "This 58-year-old man, 104 kg, with a short, thick neck is scheduled for awake tracheal intubation. Using the probe, identify and mark his cricothyroid membrane, naming the structures you use to find it."
Question
Can you show me his cricothyroid membrane and name the structures around it as you go?
Ideal answer
HeadlineThe cricothyroid membrane is the gap between thyroid cartilage and cricoid; I find it in the midline with a linear probe and mark it before the awake intubation.
- High-frequency linear probe, because these structures are superficial.1
- Transverse just above the sternal notch first. The trachea is an inverted U with a bright air-mucosa line;2 the esophagus usually lies to its left and moves when he swallows,2 so I know I am on the airway.
- Longitudinal in the midline, sliding toward the head, so the rings lead me to the cricoid: they make a "string of pearls"; the cricoid is the larger bead above them, the thyroid cartilage above that.2
- Name the gap, point, mark the skin, so the membrane is ready if the awake intubation fails: thyroid cartilage, membrane, cricoid, with the bright air-mucosa line and reverberation artifact deep to the membrane.1
Breaking down the answer
- More only if asked — through the thyroid cartilage the vocal cords move when he says "eee";1 above that, the hyoid is a bright curve with a dark shadow.2 Then I stop, because the task is timed.
- What 2027 adds — the outline lists ten airway structures: trachea, tracheal rings, cricoid, cricothyroid membrane, thyroid cartilage, vocal cords, hyoid, epiglottis, tongue and esophagus.3 Airway blocks (superior laryngeal and transtracheal) arrive in the same year.3
| Structure | Probe position | What identifies it |
|---|---|---|
| Tongue, floor of mouth | Submental, sagittal, curvilinear | Muscle mass above the mentum and hyoid1 |
| Hyoid | Transverse, above the larynx | Bright curve with an acoustic shadow2 |
| Epiglottis | Transverse, thyrohyoid membrane | Dark curved band, pre-epiglottic space in front1 |
| Vocal cords | Transverse, through thyroid cartilage | Paired structures; true cords move with phonation1 |
| Cricoid | Transverse or longitudinal | Dark oval in transverse; a bump in longitudinal2 |
| Cricothyroid membrane | Longitudinal midline | Gap between thyroid cartilage and cricoid; reverberation deep to it1 |
| Tracheal rings | Longitudinal, then transverse | "String of beads"; inverted U2 |
| Esophagus | Transverse at the sternal notch | Usually left of the trachea; peristalsis with swallowing2 |
- Why the membrane matters — DAS advises identifying the trachea and membrane before an anticipated difficult airway, using ultrasound when inspection and palpation fail.4 In a heavy man with a short neck, palpation is exactly what fails, so I mark it before the awake intubation starts.
- Bright line, dark cartilage — cartilage is dark; air under the mucosa makes the bright line and the reverberations below it.2 Calling the reverberations "the posterior wall" is a classic error.
- Changes if the long-axis view will not come — transverse, the cricoid is a dark oval;2 I center it and slide toward the head until it gives way to the membrane.
Follow-up question
Second task: after intubation, the examiner shows a transverse view at the suprasternal notch. Beside the trachea, on the left, a second bright curved line with a shadow appears. What is it, and what do you do?
Follow-up answer
HeadlineThat is the "double tract" sign: a second air-mucosa interface beside the trachea, so the tube is in the esophagus.5,6
A correct intubation shows a single air-mucosa interface inside the trachea.1 I say it out loud, then act: remove the tube, mask ventilate with 100% oxygen, and reintubate, confirming with capnography and with ultrasound. The view helps where capnography may mislead, such as cardiac arrest;2 in one emergency series it identified 16 of 17 esophageal intubations and 94 of 95 tracheal tubes.6 I reassess by watching the tube position and lung sliding on both sides.
Pitfalls that cost points
- Calling the cricoid the thyroid cartilage because it is the first ring you find.
- Marking the membrane without first finding the tracheal rings below it.
Rapid-fire
Q: What skin-to-epiglottis distance suggests difficult laryngoscopy? A: More than about 2.5 to 2.75 cm.1
Q: What hyomental distance ratio suggests difficulty? A: A ratio below 1.2 between neutral and extended positions.1
Q: Can ultrasound size a tube in a child? A: Yes; the subglottic diameter estimates tube size better than age-based formulas.2
Q: What does an "alphabet P" sign mean? A: A thickened epiglottis beside the hyoid shadow in epiglottitis.2
Q: Does marking the membrane change an emergency front-of-neck airway? A: Yes; a vertical skin incision is the default, and a transverse stab alone is acceptable only when the membrane is clearly palpable or ultrasound-marked.7
Numbers to know
| Item | Value |
|---|---|
| Linear probe | 7–15 MHz1 |
| Curvilinear probe | 2–5 MHz1 |
| Skin-to-epiglottis, difficult laryngoscopy | >2.5–2.75 cm1 |
| Hyomental distance ratio, difficult | <1.21 |
| T.R.U.E. (tracheal placement) | Sensitivity 98.9%, specificity 94.1%: 94/95 tracheal, 16/17 esophageal6 |
| Outline airway structures | 10, from 20273 |
Links
- POCUS image acquisition: probe positions and Doppler sectors, The ultrasound application station: format and tasks, Cannot intubate, cannot oxygenate, Airway station: exam, algorithm, device choice (2027), Lung ultrasound: pleura, A/B-lines, effusion, pneumothorax, Abdominal free fluid and gastric ultrasound
- Atlas: Airway blocks: superior laryngeal and transtracheal (2027)
- ABA OSCE Content Outline (current version); DAS guidelines for unanticipated difficult intubation (2015)
Sources
- 1.Airway Ultrasound: A Narrative Review of Present Use and Future Applications in Anesthesia · Healthcare (Basel) (Riveros-Perez, Avella-Molano), 2025 · ebi.ac.ukFull text via Europe PMC (PMC12248689); probe choice, standard views, skin-to-epiglottis cutoffs.
- 2.Role of upper airway ultrasound in airway management · Journal of Intensive Care (Osman, Sum), 2016 · ebi.ac.ukFull text via Europe PMC (PMC4983796); sonoanatomy only (it uses 'double tract' differently, so it is not cited for that sign).
- 3.APPLIED Exam Objective Structured Clinical Examination (OSCE) Content Outline · ABA · theaba.orgPoint-of-care ultrasound: airway-related structures (testing to start 2027).
- 4.Difficult Airway Society 2015 guidelines for management of unanticipated difficult intubation in adults · DAS, 2015 · ebi.ac.ukFull text via Europe PMC (PMC4650961); 'The role of ultrasound' paragraph on identifying the cricothyroid membrane.
- 5.Comments to Role of upper airway ultrasound in airway management · Journal of Intensive Care, 2017 · jintensivecare.biomedcentral.comLien WC. A second air-mucosa interface ('double-tract sign') diagnoses esophageal intubation.
- 6.Tracheal rapid ultrasound exam (T.R.U.E.) for confirming endotracheal tube placement during emergency intubation · Resuscitation, 2011 · scholars.lib.ntu.edu.twChou HC et al., Resuscitation 2011;82:1279-84 (PMID 21684668). 112 emergency intubations, 17 esophageal; sensitivity 98.9%, specificity 94.1% for tracheal placement.
- 7.Difficult Airway Society 2025 guidelines for management of unanticipated difficult tracheal intubation in adults · DAS, 2025 · sea.org.ecAhmad et al., Br J Anaesth 2026;136:283-307 (online 7 Nov 2025), doi 10.1016/j.bja.2025.10.006; full English text hosted by the Sociedad Ecuatoriana de Anestesiología. Plan D: vertical skin incision (up to 8 cm) is the default eFONA incision unless the cricothyroid membrane is clearly palpable or ultrasound-marked; number 10 blade, bougie, 6.0 cuffed tube.
Facts on this page were checked against these sources on Oct 16, 2026. Guidelines change; confirm doses against current institutional protocols.