This study was supported, in part, by the National Institutes of Health/National Cancer Institute (Bethesda, Maryland) Cancer Support Grant P30 CA008748.

This scanning protocol is for clinical training and has not been published elsewhere. The ultrasound images were obtained from a volunteer and de-identified. As per the institutional guidelines, this protocol is beyond the Common Rule and FDA definition of the human research subject, and formal IRB approval is not required.
1. Transducer and image optimization
<ol>
	<li>Use a linear array 12-4 MHz transducer. This is a high-frequency transducer for superficial imaging struct...

<ol>
	<li>Apfelbaum, J. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=American+Society+of+Anesthesiologists+Practice+Guidelines+for+Management+of+the+Difficult+Airway.">American Society of Anesthesiologists Practice Guidelines for Management of the Difficult Airway.</a> Anesthesiology. 136 (1), 31-81 (2022).</li><li>Ji, S. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Correlation+between+modified+LEMON+score+and+intubation+difficulty+in+adult+trauma+patients+undergoing+emergency+surgery.">Correlation between modified LEMON score and intubation difficulty in adult trauma patients undergoing emergency surgery.</a> World Journal of Emergency Surgery. 13, 33 (2018).</li><li>Hall, E. A., Showaihi, I., Shofer, F. S., Panebianco, N. L., Dean, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrasound+evaluation+of+the+airway+in+the+ED:+A+feasibility+study.">Ultrasound evaluation of the airway in the ED: A feasibility study.</a> Critical Ultrasound Journal. 10 (1), 3 (2018).</li><li>Chou, H. -. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tracheal+rapid+ultrasound+exam+(T.R.U.E.)+for+confirming+endotracheal+tube+placement+during+emergency+intubation.">Tracheal rapid ultrasound exam (T.R.U.E.) for confirming endotracheal tube placement during emergency intubation.</a> Resuscitation. 82 (10), 1279-1284 (2011).</li><li>Sotoodehnia, M., Rafiemanesh, H., Mirfazaelian, H., Safaie, A., Baratloo, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrasonography+indicators+for+predicting+difficult+intubation:+A+systematic+review+and+meta-analysis.">Ultrasonography indicators for predicting difficult intubation: A systematic review and meta-analysis.</a> BMC Emergency Medicine. 21 (1), 76 (2021).</li><li>Prasad, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparison+of+sonography+and+computed+tomography+as+imaging+tools+for+assessment+of+airway+structures.">Comparison of sonography and computed tomography as imaging tools for assessment of airway structures.</a> Journal of Ultrasound in Medicine. 30 (7), 965-972 (2011).</li><li>Andruszkiewicz, P., Wojtczak, J., Sobczyk, D., Stach, O., Kowalik, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effectiveness+and+validity+of+sonographic+upper+airway+evaluation+to+predict+difficult+laryngoscopy.">Effectiveness and validity of sonographic upper airway evaluation to predict difficult laryngoscopy.</a> Journal of Ultrasound in Medicine. 35 (10), 2243-2252 (2016).</li><li>Adhikari, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pilot+study+to+determine+the+utility+of+point-of-care+ultrasound+in+assessing+difficult+laryngoscopy.">Pilot study to determine the utility of point-of-care ultrasound in assessing difficult laryngoscopy.</a> Academic Emergency Medicine. 18 (7), 754-758 (2011).</li><li>Ezri, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prediction+of+difficult+laryngoscopy+in+obese+patients+by+ultrasound+quantification+of+anterior+neck+soft+tissue.">Prediction of difficult laryngoscopy in obese patients by ultrasound quantification of anterior neck soft tissue.</a> Anaesthesia. 58 (11), 1111-1114 (2003).</li><li>Yadav, N. K., Rudingwa, P., Mishra, S. K., Pannerselvam, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrasound+measurement+of+anterior+neck+soft+tissue+and+tongue+thickness+to+predict+difficult+laryngoscopy+-+An+observational+analytical+study.">Ultrasound measurement of anterior neck soft tissue and tongue thickness to predict difficult laryngoscopy - An observational analytical study.</a> Indian Journal of Anaesthesia. 63 (8), 629-634 (2019).</li><li>Martinez-Garcia, A., Guerrero-Orriach, J. L., Pino-Galvez, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrasonography+for+predicting+difficult+laryngoscopy.+Getting+closer.">Ultrasonography for predicting difficult laryngoscopy. Getting closer.</a> Journal of Clinical Monitoring and Computing. 35 (2), 269-277 (2020).</li><li>Carsetti, A., Sorbello, M., Adrario, E., Donati, A., Falcetta, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Airway+ultrasound+as+predictor+of+difficult+direct+laryngoscopy:+A+systematic+review+and+meta-analysis.">Airway ultrasound as predictor of difficult direct laryngoscopy: A systematic review and meta-analysis.</a> Anesthesia and Analgesia. 134 (4), 740-750 (2022).</li><li>Petrisor, C., Szabo, R., Constantinescu, C., Prie, A., Hagau, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrasound-based+assessment+of+hyomental+distances+in+neutral,+ramped,+and+maximum+hyperextended+positions,+and+derived+ratios,+for+the+prediction+of+difficult+airway+in+the+obese+population:+A+pilot+diagnostic+accuracy+study.">Ultrasound-based assessment of hyomental distances in neutral, ramped, and maximum hyperextended positions, and derived ratios, for the prediction of difficult airway in the obese population: A pilot diagnostic accuracy study.</a> Anaesthesiology Intensive Therapy. 50 (2), 110-116 (2018).</li><li>Reddy, P. B., Punetha, P., Chalam, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrasonography+-+A+viable+tool+for+airway+assessment.">Ultrasonography - A viable tool for airway assessment.</a> Indian Journal of Anaesthesia. 60 (11), 807-813 (2016).</li><li>Wu, J., Dong, J., Ding, Y., Zheng, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+anterior+neck+soft+tissue+quantifications+by+ultrasound+in+predicting+difficult+laryngoscopy.">Role of anterior neck soft tissue quantifications by ultrasound in predicting difficult laryngoscopy.</a> Medical Science Monitor. 20, 2343-2350 (2014).</li><li>Pinto, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Predicting+difficult+laryngoscopy+using+ultrasound+measurement+of+the+distance+from+skin+to+the+epiglottis.">Predicting difficult laryngoscopy using ultrasound measurement of the distance from skin to the epiglottis.</a> Journal of Critical Care. 33, 26-31 (2016).</li><li>Falcetta, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+two+neck+ultrasound+measurements+as+predictors+of+difficult+direct+laryngoscopy:+A+prospective+observational+study.">Evaluation of two neck ultrasound measurements as predictors of difficult direct laryngoscopy: A prospective observational study.</a> European Journal of Anaesthesiology. 35 (8), 605-612 (2018).</li><li>Chalumeau-Lemoine, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Results+of+short-term+training+na&#239;ve+physicians+in+focused+general+ultrasonography+in+an+intensive-care+unit.">Results of short-term training na&#239;ve physicians in focused general ultrasonography in an intensive-care unit.</a> Intensive Care Medicine. 35 (10), 1767-1771 (2009).</li></ol>

The author has nothing to disclose.

Ultrasound of the airway is an effective methodology to examine the airway. The goal is to incorporate airway examination into daily practice to give additive value to the standard pre-anesthetic assessment of the airway before the induction of anesthesia.
It is best to start the scanning protocol from the submandibular space with the transducer positioned along the long axis of the body - the sagittal plane. From there, the transducer is turned in the transverse position along the midline and...

Airway management is a crucial part of a patient&#39;s perioperative care and is an essential skill for an anesthesiologist. Failure to secure a proper airway can result in unplanned intensive care admissions and complications, prolonged hospital stays, and an increased risk of brain damage and death. The American Society of Anesthesiologists (ASA) 2022 difficult airway task force updated the definition of a difficult airway to include the following: difficult mask ventilation, a difficult laryngoscopy view, a high number of intubation attempts, the use of advanced airway adjuncts, and difficult extubation or ventilation1. The visual assessment of the airway before intubation includes looking for, evaluating, and allocating a Mallampati score, observing for signs of obstruction, and assessing the neck mobility. This is commonly known as the LEMON method. Additional assessments include radiographic, oropharyngeal, or external anatomic airway structure assessments and the upper lip bite test2.&#160;No method is without limitations as a predictor of significant intubation difficulty. These many quality assessments may explain why the incidence of difficult airways varies from 5% to 22% and the positive predictive value (PPV) is low. A recent meta-analysis showed a low prevalence of difficult intubation in patients with a Mallampati score of III or IV, making the Mallampatti scoring system less sensitive and specific than measured ultrasound parameters3. Images of the airway provided on ultrasound are comparable to radiography, rendering it an appealing alternative. Ultrasound of the airway has been gaining momentum as an adjunct in airway management since point-of-care ultrasound protocols were introduced and shown to be supported by clinical data based on identifying endotracheal tube placement in trauma patients4. Ultrasound provides the clinician with a dynamic anatomical assessment, which is impossible with clinical examination alone.
Studies indicate the added value of specific ultrasound parameters in determining a difficult laryngoscopy visualization. The feasibility of point-of-care ultrasound (POCUS) for airway management in the perioperative setting is still an area of great interest. Ultrasound reliably images all the structures visualized by CT, and infrahyoid airway structures agree well with the parameters measured by CT5. Various ultrasound measurements at different levels of the neck have been studied. The following measurements correlate with difficult direct laryngoscopy: (1) the hyomental distance (HMD); (2) the thyrohyoid membrane (THM); (3) the distance from the skin to the epiglottis (DSE); (4) the distance from the skin to the hyoid bone (SHB); and (5) the distance from the skin to the vocal cords (SVC). This method is suitable for general populations and specific populations, such as those with obesity. A full stomach, rapid sequence intubation, gross visual anatomical abnormalities, and restricted neck mobility from different causes preclude using ultrasound to assess the airway.
This narrative review discusses the significant ultrasound parameters in the POCUS of the airway and supplies training suggestions that can be used in everyday practice. Ultrasound is simple, portable, easy, and has a short learning curve.
Sound above a frequency of 20 MHz is called ultrasound, and medical imaging uses 2-15 MHz. Ultrasound waves are transmitted and received by an ultrasound transducer, commonly called an ultrasound probe. The resistance of the ultrasound wave traveling through tissue is called the acoustic impedance. Ultrasound waves reflect from the tissue-air interface back to the transducer, and different tissues have different acoustic impedances. Bone gives a strong echo, meaning it is referred to as being hyperechoic and appears white. In addition, bone absorbs the ultrasound waves, and nothing passes beyond it. This phenomenon is described as acoustic shadowing. Airway structures that contain cartilage create a small echo; they are described as hypoechoic structures and appear dark on the ultrasound image. As calcifications develop with aging, these structures appear more echogenic5.&#160;A more heterogenic appearance is seen with muscle and connective tissue. Glandular tissue appears brighter, meaning this tissue is hyperechoic. It is essential to understand the air-tissue border concept. The ultrasound waves do not travel through the air but return to the transducer, creating a strong reflection. The returning echo signal is a dispersion artifact - a reverberation causing multiple white lines. The ultrasound beam at the air-mucosa interface creates a bright white line. Denser tissue appears brighter on the screen, and the structures beyond cannot be observed. Clinically, only the tissue from the skin to the anterior luminal surface of solid tissue is visualized. The posterior wall of the pharynx and larynx cannot be visualized. Acoustic shadowing reflects the ultrasound beams returning to the probe6.
The ultrasound transducers include a curved low-frequency (C5-1 MHz) transducer, a high-frequency linear array (L12-4 MHz), (L12-5) MHz, or&#160;(L13-6 MHz) transducer. The airway structures are superficial within 2-3 cm from the skin but are deeper in obese patients due to the increased anterior neck fat tissue. The curved low-frequency C5-1 MHz transducer displays a broader field of view for a better submandibular view. If only one transducer is available, then the high-frequency linear array performs all ultrasound examinations relevant to the airway assessment. The transducer must have complete contact with the skin. A generous amount of conductive gel is needed to maintain the skin contact. In males, it is challenging to prevent air from being trapped between the skin and the transducer due to the prominent thyroid cartilage. In this instance, minimal caudal and cranial adjustments can be used to optimize the image.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Gel-Lubricant jelly</td>
			<td>MediChoice</td>
			<td>13143 gram, LUB Sterile</td>
			<td>Bacteriostatic,water soluble-alcohol free.</td>
		</tr>
		<tr>
			<td>Philips SPARQ Point of Care System</td>
			<td>Philips</td>
			<td>Transducer L12-4 MHz</td>
			<td>Broadband linear. 128elements. 38.4 mm.</td>
		</tr>
	</tbody>
</table>

point-of-care ultrasound: a review of ultrasound parameters for predicting difficult airways

Airway management remains a crucial part of perioperative care. The conventional approach to assessing potentially difficult airways emphasizes the LEMON method, which looks for and evaluates the Mallampati classification, signs of obstruction, and neck mobility. Clinical findings help predict a higher likelihood of difficult tracheal intubation, but no clinical result reliably excludes difficult intubation. Ultrasound as an adjunct to clinical examination can provide the clinician with a dynamic anatomical airway assessment, which is impossible with clinical examination alone. In the hands of anesthesiologists, ultrasound is becoming more popular in the perioperative period. This method is particularly applicable for identifying proper endotracheal tube positioning in specific patient populations, such as those who are morbidly obese and patients with head and neck cancer or trauma. The focus is on identifying the normal anatomy, correctly positioning the endotracheal tube, and refining the parameters that predict difficult intubation. Several ultrasound measurements are clinical indicators of difficult direct laryngoscopy in the literature. A meta-analysis revealed that the distance from the skin to the epiglottis (DSE) is most associated with a difficult laryngoscopy. An ultrasound of the airway could be applied in routine practice as an adjunct to the clinical examination. A full stomach, rapid sequence intubation, gross visual anatomical abnormalities, and restricted neck flexibility prevent using ultrasound to assess the airway. The airway evaluation is performed with a linear array transducer of 12-4 MHz, with the patient in the supine position, with no pillow, and with the head and neck in a neutral position. The central axis of the neck is where the ultrasound parameters are measured. These image acquisitions guide the standard ultrasound examination of the airway.

This paper aims to provide significant ultrasound parameters that are predictive of a difficult laryngoscopy. To date, 30 studies have analyzed several different ultrasound parameters. Two meta-analyses have identified the five most studied parameters that significantly differ between easy and difficult direct laryngoscopy views and have higher sensitivity and specificity than the classic Mallampatti classification12. This narrative review follows the scanning protocols from the studies shown in <...

Watch this Scientific Journal Video about Point-of-Care Ultrasound: A Review of Ultrasound Parameters for Predicting Difficult Airways at JoVE.com

Point-of-Care Ultrasound: A Review of Ultrasound Parameters for Predicting Difficult Airways

A point-of-care ultrasound (POCUS) is a simple, non-invasive, and portable tool that enables dynamic airway assessment. Several studies have attempted to determine the role of ultrasound parameters as an adjunct to clinical examination in predicting difficult laryngoscopies.

Airway management remains a crucial part of perioperative care. The conventional approach to assessing potentially difficult airways emphasizes the LEMON ...

The ultrasound image acquisition can guide the standard ultrasound assessment of the airway. Ultrasound can provide the clinician with a dynamic anatomical airway assessment, which is not possible with clinical examination alone. The technique is simple and one can practice it on oneself and colleagues.It is possible to achieve competency after about 20 exams. Begin by asking the patient to lie down in a supine position without a pillow. To ensure standardization and best measurements, ask the patient to maintain the head and neck in a neutral position.Ask the patient to rest their tongue on the lower incisors. For consistency, the tongue should remain in the same position throughout the ultrasound examination. Once the patient is positioned correctly, apply a gel medium on the transducer to ensure there is no air between the skin and the transducer.Place the transducer transversely on the anterior neck of the patient with minimal pressure, while preserving skin contact. Then place the transducer midline on the central axis in the transverse position. And beginning from the submandibular space with slow fine movements, move the transducer cordally.For a submandibular image, place the transducer longitudinally in the submental space along the body's central axis. Click on freeze, followed by clicking on measure, then measure the distance from the outer border of the mentum to the hyoid bone. As the value of the distance in centimeters pops up on the screen, click on acquire.Rotate the transducer in the transverse position and place it over the central axis of the neck. Manipulate the transducer cordally with fine slow movements for visualizing the structures of interest. To visualize the thyroid hyoid membrane or THM, palpate the thyroid cartilage and the hyoid bone, and place the transducer in between the transverse position, while ensuring it stays in the central axis of the neck.Sequentially, click on freeze and measure before measuring the distance from the skin to the anterior border of the epiglottis in the center. As the distance in centimeters pops up on the screen, click on acquire. Then move the transducer one centimeter to the right and as demonstrated previously, repeat the measurement.Once the distance value appears on the screen, acquire the data. Next, move the transducer one centimeter to the left of the center and repeat the process of acquiring the measurement. Average the three measurements to obtain the THM.Keep the transducer in the same position and stay in the next central axis to view the hypoechoic curvilinear epiglottis as a dark space. Click on freeze, followed by clicking on measure. Then measure the distance from the skin to the center of the bright white line.As the value of the distance in centimeters pops up on the screen, click on acquire. Move the probe one centimeter left of the midline and acquire the measurement again. Then move the transducer one centimeter to the right of the midline to acquire the measurement for the third time.Average the three measurements to obtain the distance from the skin to the epiglottis or DSC. Angle the transducer tail about 20 degrees down. Palpate the hyoid bone and place the transducer directly over the hyoid bone while keeping the probe in the central axis of the neck.Sequentially, click on freeze and measure. Measure the distance from the skin to the center of the hyoid bone, seen as a bright echogenic line, curved upside down above the hypoechoic shadow and acquire the data. Move the probe one centimeter lateral to the midline on the left to acquire one more measurement.For the third measurement, move the transducer one centimeter to the right of the midline and average the three measurements to obtain the distance from the skin to the hyoid bone or SHB. To measure the distance from the skin to the vocal cords or SVC, place the transducer transversely over the thyroid cartilage while staying in the central axis of the neck. Click on freeze followed by clicking on measure.Then measure the distance from the skin to the upper border of the right vocal cord and acquire the data. Repeat the same measurement on the left vocal cord and average the two measurements to obtain the SVC. In 30 studies, several different ultrasound parameters predictive of a difficult laryngoscopy were analyzed.Two meta-analyses identified the five most studied parameters that significantly differed between easy and difficult direct laryngoscopy views. In the neutral position, an HMD value of 3.4 to 4.5 centimeters was associated with difficult direct laryngoscopy. The parameter had a sensitivity and a specificity of 100%and 71.4%respectively, and was predictive in general and obese populations.A TMH value higher than 2.8 centimeters predicted a difficult laryngoscopy. This parameter had a sensitivity of 64.7%and a specificity of 77.1%A meta-analysis found DSE as the parameter correlating the most with difficult direct laryngoscopy. The average DSE value greater than 2 to 2.5 centimeters had a positive predictive value of about 30%to 50%while the negative predictive value of the parameter ranged from 95%to 97%An SHB greater than 1.28 centimeters correlated with difficult direct laryngoscopy.The parameter had a sensitivity and specificity of 85.7%and 85.1%respectively. In difficult direct laryngoscopies, SVC measurements from about 0.9 to 1.3 centimeters were reported. Maintaining the head in the neutral position and resting the tongue on the lower incisors is important.The transducer must rest on the central axis of the neck and should be moved slowly. Ultrasound can be incorporated into daily practice as an adjunct to the clinical examination of the airway.

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1.1K Views.  Weill Cornell Medical Center (WCMC). The ultrasound image acquisition can guide the standard ultrasound assessment of the airway. Ultrasound can provide the clinician with a dynamic anatomical airway assessment, which is not possible with clinical examination alone. The technique is simple and one can practice it on oneself and colleagues.It is possible to achieve competency after about 20 exams. Begin by asking the patient to lie down in a supine position without a pillow. To ensure standardization and best measurements,...