Point of Care Ultrasound of the Airway

Abstract

Ultrasound of the airway differs from that of other parts of the body in that it leverages on air-filled structures and the resultant hyperechoic air-mucosal interface. POCUS of the airway is noninvasive, portable, employs equipment that has multiple applications (hence is cost-effective), and has a relatively gentle learning curve. It is easily assimilated into a wide range of patient care settings, provides a means to update the traditional assessment of the airway and improves patient airway management and safety.

MCQs: Chose the Single Best Answer

(Read the questions with a book or a paper covering the answer side, try to answer on your own, and then check with the answer)

Questions				Answers
1. A pre-scan prior to performance of a cricothyroidotomy reveals the following structures    Which of the following accurately labels structures 1, 2, and 3?				Answer: A. The cricothyroid membrane (CTM) appears as a bright white line due to the air-mucosa interface, with a reverberation artifact posteriorly. The CTM is 13–15 mm long in adults. In the transverse orientation, scanning from the thyroid cartilage, then to the CTM, followed by the cricoid, and finally back to the CTM helps to visualize the transition and ascertain the identity of the CTM [23]
	1	2	3
A	Cricothyroid membrane	Reverberation artifact	Sternohyoid muscle
B	Cricoid cartilage	Reverberation artifact	Thyroid gland
C	Thyroid cartilage	Endotracheal tube	Sternocleidomastoid muscle
D	Cricothyroid membrane	Endotracheal tube	Sternothyroid muscle
2. A patient who has sustained a penetrating head and neck trauma develops difficulty breathing and is desaturating. Ultrasound of his airway reveals subcutaneous emphysema. Appropriate management includes  A. Monitor the patient closely but do not manipulate the airway at this point as it may worsen the situation  B. Support the patient with bag-mask ventilation  C. Intubate the patient via the oral or nasal route  D. Identify the level of injury and proceed to secure the airway				Answer: D. Subcutaneous emphysema indicates discontinuity in the airway or aerodigestive tract. Nonintervention may miss the window of opportunity for management before the patient becomes more unstable. Positive pressure ventilation should be minimized until the airway is secured. Careful ultrasound examination of the airway is useful to rapidly delineate distorted anatomy and formulate the safest location to secure the patient’s airway, whether by intubation or front of neck access. Bronchoscopy evaluation is indicated as well where possible. Cervical spine immobility is likely to add to the complexity
3. After a difficult intubation, this image is seen on ultrasound of the airway. Appropriate immediate management should include:  A Ventilate the patient with appropriate tidal volumes  B Remove and reinsert the endotracheal tube (ETT)  C Check for ETCO2 using a colorimeter or capnograph  D Deepen the patient using inhalational or intravenous agents				Answer: B. This ultrasound image shows an oesophageal intubation. The air column in the ETT produces a “drop-out” dark area below the air-ETT interface. Stylets or bougies may produce the same, albeit smaller, effect. Monitoring of an intubation in real time using ultrasound allows for immediate identification of esophageal intubation
4. Prior to performing a percutaneous dilatational tracheostomy (PDT), a vascular structure is seen at the level of the fourth tracheal ring. This vascular structure is likely to be the:  A. Thyroid artery  B. Superior laryngeal artery  C. Innominate artery  D. Tonsillar artery				Answer: C. The innominate artery is also known as the brachiocephalic artery. It is the most proximal branch of the aortic arch, originating medial and anterior to the left common carotid artery. This short artery courses superiorly posterior to the aortic arch, bifurcating into the right subclavian artery and right common carotid artery at the level of the sternoclavicular joint. It crosses from left to right anterior to the trachea, usually around the ninth tracheal ring. However, it has a very variable location, and can sometimes be observed at or above the suprasternal notch as a pulsatile structure Avoidance of this artery is paramount as cases of fatal bleeding, or trachea-innominate artery fistulas post tracheostomy, have been described. It should be located prior to both surgical and percutaneous dilatational tracheostomies
5. In a preoperative assessment for an elective surgery, you note that your patient has a hoarse voice. Ultrasound examination reveals the following Appropriate management includes:  A. Continue with surgery with careful intubation technique  B. Assure patient and document voice hoarseness before proceeding with surgery  C. Referral to otolaryngologist for further evaluation  D. Investigate the patient for left recurrent laryngeal nerve palsy				Answer: C. There is a vocal cord cyst at the anterior commissure. On the ultrasound, posterior acoustic enhancement of the area below the fluid cyst hints at its nature. Careful documentation and preoperative evaluation, as well as counselling of patient for potential worsening of voice hoarseness is indicated. The vocal cords are abducted hence vocal cord paralysis is unlikely. Depending on how time-sensitive the surgery is, investigation into the cause of the patient’s hoarse voice is useful but should not prohibit urgent surgery from proceeding
6. A patient is noted to have a left-sided neck fullness just below his chin. Bedside ultrasound revealed the following: The lesion shown is most likely to be:  A. A thyroglossal duct cyst  B. Ectopic thyroid tissue  C. A vocal cord cyst  D. A branchial cleft cyst				Answer: A. Thyroglossal duct cysts are the most common congenital neck mass. They are thin-walled, fluid-filled, usually close to the midline, anterior to the thyroid cartilage, and splaying the strap muscles. They are generally close to the hyoid bone and can be traced to a tail diving under the hyoid. On ultrasound, they appear anechoic, with posterior acoustic enhancement. Stranding within the cyst or thickened walls may indicate inflammation. Thyroid tissue would exhibit a homogenously hypoechoic appearance but can be found in very variable locations. A vocal cord cyst would appear posterior to the thyroid cartilage and branchial cleft cysts tend to be located more laterally. Ultrasound is a useful initial investigation modality due to its noninvasiveness, accessibility, relatively low cost, and avoidance of exposure to radiation
7. Ultrasound features that correlate to a higher likelihood of obstructive sleep apnoea (OSA) include all EXCEPT:   A. Tongue thickness > 60 mm   B. Tongue width > 28 mm   C. Thickened lateral pharyngeal walls   D. Mentohyoid distance < 52 mm				Answer: D. Together with patient history and physical examination, airway ultrasound can help improve the accuracy of OSA screening. Airway ultrasound features include the tongue thickness and width, as well as thickening of the lateral pharyngeal wall. Non-airway parameters include carotid plaque formation and carotid intimal thickening as surrogate markers [24]
8. In a patient with known right recurrent laryngeal nerve palsy, you would expect to see the following on ultrasound in the transverse orientation at the level of the thyroid cartilage during inspiration:				Answer: C. The recurrent laryngeal nerve (RLN) branches from the vagus nerve and supplies all the intrinsic muscles of the larynx, except the cricothyroid muscles. Complete paralysis of the RLN results in a partially adducted vocal cord, while partial paralysis results in a fully adducted vocal cord
	Right vocal cord	Left vocal cord
A	Abducted	Abducted
B	Abducted	Adducted
C	Adducted	Abducted
D	Adducted	Adducted
9. A victim of a road traffic accident where the vehicle caught fire was brought into the emergency department with severe burns to his face, although his neck is relatively unscathed. The potential airway issues include:  A. Lower airway edema  B. Potential cervical spine instability  C. Upper airway injury  D. All of the above				Answer: D. This unfortunate patient will have all the attendant issues of trauma and smoke inhalation, not to mention burns and injuries to his face and upper airway
10. Advantages of a cricothyroidotomy over a tracheostomy in an emergency front of neck access include:  A. Relatively avascular structure  B. More superficial and palpable cricothyroid membrane compared to the deeper tracheal rings  C. Shorter insertion time required  D. All of the above				Answer: D. In an emergency situation, a cricothyroidotomy offers the fastest and least complicated means of front of neck airway access. However, it is thought to be associated with an increased risk of subglottic stenosis, and hence creation of a formal tracheostomy is often performed within 72 h of an emergency cricothyroidotomy
11. Postsurgical tracheostomy creation, a ward nurse notices swelling around the tracheostomy site. Ultrasound evaluation reveals anechoic areas in the subcutaneous and peri-muscular planes The cause of the swelling is likely to be:  A. Blood  B. Subcutaneous emphysema  C. Soft tissue swelling  D. An overly tight tracheostomy strap				Answer: A. Fluid, such as blood, appears anechoic on ultrasound and will cast posterior acoustic enhancement (bright area). Air will cause posterior shadowing (dark area). Ultrasound of the airway is a useful bedside examination that is portable, can be done rapidly and noninvasively, and gives immediate information which can be critical to preventing adverse patient outcomes
12. Structures that may overlie the cricothyroid membrane (CTM) DO NOT include:  A. The cricothyroid artery and vein (in the upper 1/3)  B. The pyramidal lobe of the thyroid gland  C. Recurrent laryngeal nerve  D. Lymph nodes				Answer: C. All the other structures may be found in variable positions overlying cricothyroid membrane and care should be taken in the event a cricothyroidotomy needs to be performed
13. Differences between the ultrasound appearance of the pediatric airway compared to that of an adult include all EXCEPT:  A. A cartilaginous and hypoechoic hyoid bone  B. Measurement of the tracheal diameter for endotracheal tube sizing at the level of the thyroid cartilage  C. Thinner and less echogenic cricothyroid membrane  D. An elliptical rather than circular subglottic airway				Answer: B. The narrowest part of the pediatric airway is at the level of the cricoid cartilage, and airway measurement should take place here. Ultrasound sizing of the airway is more accurate compared to age-based and height-based formulas in estimating ETT size (outer diameter) for pediatric patients [25, 26]
14. A 12-year-old child with cerebral palsy and severe scoliosis requires a spine operation to improve his respiratory function. He has very limited cervical extension. Which of the following ultrasound techniques may help in this situation?  A. Assessment of the tracheal diameter for endotracheal tube (ETT) sizing at the level of the sternal notch  B. Use of ultrasound to perform a superior laryngeal nerve block for an awake intubation  C. Use of a curvilinear probe to assess the mentohyoid distance  D. Use of a small “hockey stick probe” to identify the cricothyroid membrane				Answer: B. This patient is an airway challenge because of his limited range of motion. Ultrasound will be difficult because of his inability to extend his neck, and such patients are generally small for their age. Ultrasound is a reliable tool to predict ETT size for pediatric patients with thoracic or lumbar scoliosis. However, pediatric patients with cervical lateral bending will need an ETT smaller than the size predicted by ultrasonography [27]. Real-time imaging of the airway during intubation can also help to ensure that the ETT is placed at an appropriate depth, but this requires a second operator
15. Ultrasound features of an intubated airway include all except:  A. Reverberation artifacts in the airway  B. Double track lines in the sagittal plane  C. Posterior shadow in the airway  D. Comet-tail artifacts in the airway				Answer: A. The air column within the endotracheal tube causes a linear posterior shadow within the airway. Radial comet-tail artifacts may also be seen. Double track lines indicate the presence of a tube within the airway
16. A 45-year-old patient attempted suicide by drinking a large volume of corrosive fluid and alcohol. He presents to the emergency department. He is extremely agitated, trashing, and has pulled out his intravenous cannulas. His breathing is stridorous and his pulse oximetry reading is 88%. What is the most reasonable plan of action?  A. Avoid sedation, attempt awake bronchoscopic intubation  B. Avoid sedation, perform percutaneous dilatational tracheostomy  C. Sedate with IM or inhalational agents, perform cricothyroidotomy  D. Sedate with IM or inhalational agents, paralyze patient, and attempt nasal or oral intubation				Answer C: The patient likely has upper airway edema and is agitated from a combination of intoxication and hypoxia. He is in respiratory distress and his airway needs to be secured. He is likely to be difficult to manage without sedation but should be kept spontaneously ventilating where possible. He will not be able to cooperate with an awake intubation Rapid focused ultrasound assessment of the airway should be done to identify the cricothyroid membrane as well as to evaluate airway edema and soft tissue swelling. Serial ultrasounds can also be used to monitor progress
17. Which of the following is true about ultrasound appearance of airway structures?  A. Cartilage appears homogenously hypoechoic  B. The cricothyroid membrane appears as a bright line because it is relatively solid compared to cartilage  C. Reverberation artifacts appear as hyperechoic radial lines  D. Air causes posterior acoustic enhancement				Answer: A The air-mucosa interface, such as that at the cricothyroid membrane, appears as a bright line because of the significant difference between soft tissue and air, resulting in a strong reflection of soundwaves Reverberation artifacts are generated due to the reflective properties of the air-mucosa interface and appear as regularly spaced parallel hyperechoic lines deep to the air-mucosa interface Air columns, such as that within an endotracheal tube, will cast an acoustic shadow, obscuring structures deep into it
18. A patient presents with the following lesion on CT scan and is being brought to the operating theatre for intubation and emergency surgery During a pre-intubation ultrasound scan of the patient’s airway, which area do you expect to see the lesion in?				Answer: A. This patient has a large retropharyngeal abscess. Airway anatomy may be distorted, and ultrasound can help especially with ensuring accurate endotracheal tube sizing, as well as with the identification of critical airway structures
19. The best level to measure the airway diameter to select a left-sided double lumen endotracheal tube size is at the:  A. Hyoid  B. Thyroid cartilage  C. Suprasternal notch  D. Cricoid cartilage				Answer: C. The suprasternal notch provides an easily visualized and measured point of the airway for the purposes of sizing of a double lumen endotracheal tube, according to its outer diameter
20. Which of the following ultrasound features may predict a difficult airway?  A. Skin to tracheal distance of 23 mm at the suprasternal notch  B. Tongue width of 27 mm  C. Skin to epiglottis distance of 22 mm  D. Mentohyoid distance of 42 mm				Answer: D. The skin to tracheal distance at the suprasternal notch is not proven to be a marker of airway difficulty, although a larger distance would probably correspond to a prominent chest which may interfere with the handle of a standard laryngoscope It is important to remember that no single parameter can predict airway difficulty well. Multiple ultrasound airway parameters, together with clinical assessment, can help to increase the rate of identification of difficult airways and enable management by informing the clinician of the level at which they are most likely to encounter difficulty

Clinical exam scenarios	Answers
A young man was brought into ED after a bar fight. He is intoxicated and unable to give a consistent history, but you note some mild bruising and swelling over his neck. He has no other injuries His vital signs are as follows:  Blood pressure: 114/74 mmHg  Heart rate: 90 beats/min  Pulse oximetry: 94% on room air Physical examination: No noisy breathing/stridor, not cyanotic, not in respiratory distress 1. What are your airway concerns for this patient? 2. Ultrasound reveals the following. There are no other abnormalities. What is the likely diagnosis? 3. How would you manage this patient?	1. What are your airway concerns for this patient?   • Cervical spine injury   • Airway patency and continuity   • Soft tissue swelling 2. Likely diagnosis?   • Cricoid cartilage injury, indicated by the loss of continuity and depression of the cricoid cartilage   • There may be accompanying soft tissue swelling and edema   • Likely cause in this patient is blunt laryngeal trauma 3. Management?   Laryngeal trauma can be categorized as penetrating or blunt laryngeal trauma. Management can be guided by the Schaefer Classification System of Severity of Laryngeal Injuries in the table below [28, 29]
	Severity	Management
	Group 1: Minor endolaryngeal hematomas or lacerations without detectable fractures	Conservative; Consider medical adjunctive management such as steroids, antibiotics, anti-reflux medication, humidification, and voice rest
	Group 2: More severe edema, hematoma, minor mucosal disruption without exposed cartilage, or nondisplaced fractures	Conservative initially but with serial examination as injuries may progress over time. Medical adjuncts as for Group 1
	Group 3: Massive edema, large mucosal lacerations, exposed cartilage, displaced fractures, or vocal cord immobility	Direct laryngoscopy or esophagoscopy should be performed in the operating room. Tracheostomy, surgical exploration, and repair are often required
	Group 4: Same as group 3, but more severe, with disruption of anterior larynx, unstable fractures, two or more fractures lines, or severe mucosal injuries	Direct laryngoscopy and esophagoscopy must be performed emergently. Tracheostomy mandated and surgical repair may involve stent placement
	Group 5: Complete laryngotracheal separation	Patient will present with severe respiratory distress, necessitating urgent airway evaluation and management. Altered anatomy may make airway management difficult. Close communication and joint management between the surgical and anesthetic teams are critical
	Schaefer Classification System of Severity of Laryngeal Injuries and Suggested Management
An unknown elderly male was knocked down by a motorcycle while crossing the road. He sustained lower limb fractures and focused assessment with sonography in trauma (FAST) shows free fluid in his abdomen. He is hypotensive and tachycardic, and pulse oximetry is 86% on bag-mask ventilation with 100% oxygen. He is noted to have a tracheostomy, which was dislodged in the accident, as well as bilateral neck scars. Medical records are unavailable as he was not carrying any identity documents 1. What are your treatment priorities in this patient? 2. Bag-mask ventilation does not seem to be improving the patient’s oxygenation, and he has become unconscious. Attempts at recanalization of the tracheostomy have failed, and the clinical team decides to intubate orally. Suspecting a difficult airway, an airway ultrasound is performed and reveal the following    What is the implication of this ultrasound finding? 3. What is the most reasonable plan of management to secure the patient’s airway?	1. What are your treatment priorities in this patient?    This patient has sustained polytrauma, and it is imperative to rapidly secure his airway, oxygenate him and improve his hemodynamics with fluid, blood, and pressor support 2. Ultrasound of airway—findings and implications    The airway of this patient appears to terminate at the mid-tracheal level. This implies that the patient likely had a total laryngectomy and that the upper airway is not continuous with the lower airway. Hence, oral intubation will not be possible 3. Plan of management    Careful but rapid exploration of the tracheostomy site can be performed. A bougie or flexible suction catheter may be gently passed into the tracheotomy track. Real-time ultrasound monitoring can help to ascertain intratracheal placement and avoid creating a false passage. A tracheostomy tube or armored endotracheal tube can then be railroaded into the trachea, and ultrasound is used to confirm placement, as well as the depth of insertion
A patient was intubated 6 days ago for airway protection after an episode of torrential epistaxis, which has now resolved. The patient is a 40 kg elderly female of small build. A size 7.5 ETT was used. She is now ready to be extubated, but the clinical team is encountering resistance when attempts are made to withdraw the ETT. The patient is otherwise well and breathing spontaneously on FiO2 0.28. They request for the anesthetic team’s assistance in attempting extubation in the operating theatre 1. How would you assess the patient’s fitness for extubation? 2. What are the risk factors for developing subglottic stenosis? 3. What ultrasound airway parameters are useful in the evaluation of this patient for extubation?	1. How would you assess the patient’s fitness for extubation?    Acronym: MOVEC   • Mental status—GCS >8 (with some rare exceptions)   • Oxygenation—The patient should be able to maintain adequate oxygenation with low levels of support. The PaO2/FiO2 ratio should be more than 150, and FiO2 < 0.4   • Ventilation—Positive End Expiratory Pressure should be <10 cmH2O, and minute ventilation requirements <15 L/min   • Expectoration—Secretions should not be excessive or cause mucous plugging   • Cardiovascular—instability should not be present 2. What are the risk factors for developing acquired subglottic stenosis?   • Paediatric—Prolonged intubation, low birth weight [30]   • Adults—High body mass index, diabetes [31], prolonged intubation 3. What ultrasound parameters are useful in evaluation of this patient?   • Air column width during cuff deflation at the level of the cricothyroid membrane is a predictor of post-extubation stridor (PES) [32]   • Evaluation of vocal cord function and airway edema   • Ultrasound of the lung and diaphragm can also help to predict readiness for extubation
A 6-year-old child presents to the emergency department with a sorethroat, drooling, and stridor. He is distressed and anxious 1. How would you assess patency of this child’s airway? 2. How can ultrasound of the airway help? 3. What are the differential diagnoses? 4. Ultrasound of the airway in the sagittal section using a curvilinear probe at the submental level shows the following appearance. What is the most likely diagnosis?	1. How would you assess patency of this child’s airway?   • Rapid assessment of patient’s airway, breathing, and circulation   • Airway—accessory muscle use, tracheal tug, stridor   • Breathing—respiratory rate, breathing effort, and ability to move air in and out of lungs   • Circulation—presence of cyanosis, hypoxia, heart rate, consciousness 2. How can ultrasound of the airway help?   • Assess patency of airway   • Identify cricothyroid membrane in the event emergency front of neck access is needed   • Right-sizing of an endotracheal tube or tracheostomy tube   • Evaluate potential causes for patient’s symptoms   • Noninvasive, bedside test that can be done with parental presence to encourage child’s cooperation 3. Differential diagnoses?   • Infective—epiglottitis, viral croup, bacterial tracheitis   • Allergy—anaphylaxis, angioedema   • Foreign body inhalation   • Trauma   • Inhalation of corrosive or irritative gas 4. Ultrasound appearance of epiglottitis   • Using a curvilinear probe in the longitudinal orientation and at the level of the hyoid bone, the epiglottis appears as the head of the “alphabet P,” and the acoustic shadow cast by the hyoid bone forms the stem of the letter P. A swollen and oedematous epiglottis is indicative of epiglottis [33]   • Evaluation can also be made in the transverse orientation, just below the hyoid, seeing the hypoechoic cartilaginous epiglottis in the middle of the tongue [34]
A 35-year-old male patient presents to the emergency department with a penetrating neck wound across his neck. The patient is sitting upright. Supplemental oxygen is being administered via a non-rebreather mask, and oxygen saturation is 85–88%. His blood pressure is 95/50 mmHg and heart rate is 102 beats per minute. The subcutaneous tissue below the mandible and oropharynx is grossly traumatized and bleeding heavily. The patient is conscious and able to breath, but there is a bubbling sound in his neck area with each breath 1. What are your initial goals of airway management in this patient? 2. How would you secure this patient’s airway? 3. How would you utilize ultrasound in this scenario?	1. Initial goals of management   • Airway—maintain airway patency   • Breathing—maintain spontaneous ventilation and supplemental oxygen   • Circulation—ensure good vascular access and administer fluids, blood, and vasopressors as needed   • Disability—assess for other injuries 2. How would you secure this patient’s airway?    This is an airway fraught with difficulties. There is likely trauma to the trachea itself, along with blood that will obscure visualization and soft tissue swelling which will worsen    The airway needs to be secured together with surgical expertise, and the management plan would need to be formulated according to the suspected level of injury. The patient may need to be sedated for this, but spontaneous ventilation should be maintained as far as possible. Avoid a cannot intubate, cannot ventilate situation 3. Use of ultrasound    Combination of airway and lung ultrasound can help to evaluate the success of endotracheal tube (ETT) insertion, whether by the oral, nasal, or front of neck access route. Tracheal ultrasound (either in real time or immediately after intubation) can exclude the presence of the ETT in the esophagus and possibly visualize the ETT in the trachea. Confirm the presence of lung sliding on the left, the absence of which may indicate right endobronchial intubation. Finally, confirm the presence of lung sliding on the right [35]
A 48-year-old patient, with a body mass index of 51 kg/m2 requires intubation with a double lumen endotracheal tube for surgical removal of a right lung mass. She has limited neck extension, a small mouth opening, and has hypertension and diabetes. She is unsure if she has symptoms of obstructive sleep apnea 1. What are the ultrasound features that may suggest that the patient has obstructive sleep apnoea? 2. What may help make to optimize the performance of an airway ultrasound examination in this patient? 3. If double lumen tube intubation is not possible, what are the alternatives to achieve lung isolation?	1. What are the ultrasound features that may suggest that the patient has obstructive sleep apnea (OSA)?  • Tongue width (between the lingual arteries) > 28 mm  • Retro-lingual space <37 mm and retropalatal space <30 mm  • Distance between the lateral edge of the pharynx and carotid artery, usually 30–50 mm. A greater distance correlates with greater severity of OSA [4, 24, 36] 2. Optimizing airway ultrasound examination    Ultrasound in morbidly obese patients may be challenging, especially with limited neck extension. Placing the patient’s upper body in a ramped position may help to increase access to the patient’s neck, as well as improve ventilation for the intubation process. Sufficient ultrasound gel is also essentialThe cricothyroid membrane (CTM) is often impalpable in morbidly obese patients. Ultrasound localization of the CTM can be performed faster than palpation. Tube sizing and real-time monitoring of intubation help to avoid airway injury [37] 3. If double lumen tube intubation is not possible, what are the alternatives to achieve lung isolation?    Insertion of a single lumen ETT, followed by the use of a bronchial blocker is one method. Alternatively, the single lumen ETT can be advanced to the left bronchus as an intentional endobronchial intubation