POINT-OF-CARE ULTRASONOGRAPHY AS AN AIRWAY ASSESSMENT TOOL By Ryan Harte A thesis submitted to the School of Radiologic Sciences in collaboration with a research agenda team In partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN RADIOLOGIC SCIENCES (MSRS) WEBER STATE UNIVERSITY Ogden, Utah December 15, 2023 1 THE WEBER STATE UNIVERSITY GRADUATE SCHOOL SUPERVISORY COMMITTEE APPROVAL of a thesis submitted by Ryan Harte This thesis has been read by each member of the following supervisory committee and by a majority vote found to be satisfactory. ______________________________ Dr. Tanya Nolan, EdD Chair, School of Radiologic Sciences ______________________________ Dr. Laurie Coburn, EdD Director of MSRS RA ______________________________ Dr. Robert Walker, PhD Director of MSRS ______________________________ Christopher Steelman, MS Director of MSRS Cardiac Specialist 2 Abstract Background This case report discusses a patient who presented with hoarseness, dysphagia, and respiratory distress. Although bedside airway examinations were performed, there were no indications that the patient would present with airway difficulties; however, imaging studies revealed a large laryngeal mass which was compromising the patient’s airway. While the patient awaited transfer to a tertiary facility, his impending respiratory failure led to emergency intubation with preparation for potential emergency tracheostomy. Discussion Traditional bedside airway assessments are often not reliable indicators of difficult airways and leave clinicians to rely on previous imaging studies for additional information. Although these studies provide further information regarding a patient’s airway, they often are unobtainable during emergencies and contribute to increased radiation exposure. Ultrasound assessment of the upper airway provides more dynamic information than traditional clinical examination methods and can help guide airway management before, during, and after airway manipulation. Conclusion Although some bedside clinical examinations are useful in predicting difficult airways, studies have shown that a combination of tests or more specific and sensitive tests would decrease the number of unanticipated airway difficulties. Because upper airway ultrasound is an emerging field of study, there is still need for larger studies with a focus on determining which upper airway ultrasound assessments provide the best clinical outcomes. 3 Introduction Clinicians use bedside airway exams to assess anatomic landmarks prior to airway manipulation.1 The information gathered from these exams provides clues helpful in predicting difficult mask ventilation, laryngoscopy, and intubation. 1-3 The most common tests used prior to airway manipulation include the Mallampati or modified Mallampati test, the upper lip bite test (ULBT), the inter-incisor distance (IID), the thyromental distance (TMD), and the sternomental distance (SMD).1,3 Although the American Society of Anesthesiologists (ASA) recommends performing a pre-operative airway evaluation, they do not specify which assessment tests sufficiently evaluate airway anatomy, thus leaving clinicians to decide which tests provide the most valuable information.2 The most commonly used screening tool, the Mallampati or modified Mallampati test, helps predict difficult airways by analyzing visibility in the oropharynx relative to tongue size. 4,5 The patient is asked to sit upright, open their mouth as wide as they can, and stick out their tongue, without phonating.5 The original Mallampati test differs from the modified Mallampati in that the grade scale was changed from a three-grade to a four-grade scale.4 The score given relays information about which structures can be seen.4,5 For example, a Mallampati I indicates that the examiner can visualize the tonsillar pillars, uvula, soft palate, and hard palate whereas a Mallampati IV signifies visualization of only the hard palate. 5 Difficult intubation is usually predicted when the Mallampati score is III or more. 4,5 Although this is the most commonly used exam, the Mallampati only gives one piece of information regarding a person’s airway. The upper lip bite test (ULBT) and inter-incisor distance (IID) are tests that assess the patient’s incisors and temporomandibular joint (TMJ) mobility to predict difficult laryngoscopy and intubation.6-8 To perform the ULBT, the patient is asked to extend the lower incisors as far 4 as possible past their upper incisors.5,6,8 Inability to do this is considered predictive of difficult laryngoscopy.5,6,8 To measure the IID, the patient is asked to open their mouth as wide as they can so that the clinician can visually estimate the distance between upper and lower incisors.5-7 During this visual assessment, the clinician can also assess the characteristics of the upper incisors.5-7 An IID less than 3 cm is used as a positive predictor of difficult airway because inadequate mouth opening complicates laryngoscope insertion and glottic view.5-7 Prominent upper incisors also suggest difficult laryngoscopy because they impede laryngoscope manipulation necessary for direct visualization of the glottic opening. 5 Both the ULBT and IID evaluate TMJ mobility to predict whether laryngoscopy will be difficult since the jaw has to be opened and thrust anteriorly to facilitate a direct view. 3,5-8 Although these tests provide useful information regarding mandibular mobility, the size of the mandible itself also plays an important role in laryngoscopic visualization. During direct laryngoscopy, the size of the mandible affects glottic view because the tongue is displaced into the submandibular space, while the jaw is lifted anteriorly. 3,5 If the mandible is small, the tongue may not be adequately displaced due to a diminished submandibular space, thus causing difficulty in obtaining laryngoscopic visualization. 3,5 The thyromental distance (TMD) is a measure of the distance from the thyroid notch to the lower mental border.5 In order to measure the TMD, the patient is asked to look up at the ceiling , with the neck fully extended and mouth closed, while the observer visually estimates the distance between these two anatomic landmarks.5 If the TMD is estimated to be less than 6.5 cm, or roughly 3 fingerbreadths, the patient is considered a higher risk of difficult airway. 5 The sternomental distance (SMD) is another visual evaluation that is often assessed along with the TMD since both exams are carried out in the fully extended neck position. 5,7 This exam 5 is important because during direct laryngoscopy, alignment of the oral, pharyngeal, and laryngeal axes through cervical flexion and atlantooccipital extension provides optimal view of the glottic opening.5 Measuring the SMD helps the examiner determine whether the patient’s head and neck mobility will allow for this ideal positioning. 5 To evaluate the SMD, the examiner estimates whether the distance from the suprasternal notch to the mentum is greater than 12.5 cm. A SMD of less than 12.5 cm is indicative of difficult laryngoscopy and intubation. 5,7 Because each airway assessment tool provides information relative to specific aspects of laryngoscopy and intubation, understanding the information provided during each airway assessment allows clinicians to decide which exams to carry out prior to airway manipulation. Clinicians rely on these airway evaluations because they are quick, easy to perform at bedside, and allow for preparation of obvious difficulties. 3,5 For these reasons, a combination of airway assessments is often utilized to increase the likelihood of accurately predicting airway difficulty.2,3 Literature Review While traditional airway assessment techniques do provide useful information in predicting difficult airways, there remains a suboptimal number of unexpectedly difficult airways due to the low specificity and sensitivity of these exams. 1,3 These unexpectedly difficult airways dramatically increase the risk of unsuccessful airway management and the associated increased morbidity and mortality.1,2 Interestingly, researchers in Denmark found that when difficult intubation was predicted using subjective bedside exams, only 25% of the cases were actually difficult.2 They also found that 3,154 of the 3,391 difficult intubations encountered during their study were unexpected despite prior screening. 2 This is complicated by the fact that endotracheal intubations are often emergent in nature. 9 A 2016 survey of emergency medical care reported 6 that nearly 350,000 intubations occur in the emergency department each year in the United States.9 This data brings into question which bedside exams most accurately and consistently prepare clinicians for airway difficulties. Although it remains one of the most frequently used airway exams, the modified Mallampati test (MMT) has shown limited value in predicting difficult laryngoscopy. 3,4 In a study aimed at determining the accuracy of the MMT in predicting difficult laryngoscopy, researchers found that this test failed to detect 35.4% of patients with difficult intubations. 4 In this study of 1,518 patients screened pre-operatively using the MMT, researchers determined that MMT had a 64.6% sensitivity, 82.4% specificity (p < 0.0001), a negative predictive value of 98.6 %, and a positive predictive value of 10.7% (p< 0.0001). 4 These findings indicate that the MMT is more useful in predicting easy intubations than difficult intubations. 4 Researchers further concluded that the MMT is weakened because the score may vary based on observer and patient position.4 Another systematic review of 133 studies on airway exams conducted by Roth et al., reported that the MMT showed the highest sensitivity (0.40-0.61) for detecting difficult intubation.3 However, they concluded that the MMT was still a poor screening test since out of every 11 patients, 5 patients who would be difficult intubations would be missed. 3 The lack of accurate prediction and reliability in screening necessitates other airway assessments. In a prospective blinded study, Khan and his colleagues found that the ULBT demonstrate higher accuracy and specificity than the modified Mallampati test (p<.001). 8 A systematic review conducted by Faramarzi et al., assessed the accuracy, sensitivity, and specificity of the ULBT in predicting difficult laryngoscopy and intubation. 8 Researchers found that of the 27 studies included in the review, the accuracy and specificity of the ULBT was greater than 85% in 24 studies and the sensitivity was greater than 70% in eleven studies.8 7 According to their review, the ULBT is useful in identifying those patients who will not have a difficult airway but will still miss approximately 30% of patients who do have difficult airways due to the moderate sensitivity of the ULBT. 8 Another systematic review comparing the diagnostic accuracy of bedside airway exams by Roth and his colleagues included 133 studies involving 844,206 patients and demonstrated similar results. 3 Their findings indicated that the ULBT demonstrated the highest sensitivity, at 67%, of the seven bedside airway exams used to identify difficult laryngoscopy.3 In another study comparing the assessment of the IID to the SMD in patients undergoing head and neck surgery, researchers concluded that the IID had a high specificity at 77% (p<0.007) whereas the specificity of the SMD was only 51%. 7 Their findings, however, demonstrated struggles similar to those found in other airway exams in that the positive predictive value of the IID and SMD was 38% and 10% while the negative predictive value was 88% and 74% respectively. 7 Studies which included the TMD provided similar results. Roth and his colleagues further demonstrated in their study that the TMD has lower sensitivity in detecting difficult intubation than the MMT (p<0.001). 3 They reported one study of 53,041 patients which included 77 difficult mask ventilation cases, and reported that the sensitivity and specificity of the TMD was 0.13 and 0.94, respectively. 3 These findings also signify the need for additional airway exams since they demonstrate the tests’ ability to predict easy airways rather than difficult airways. Several studies have pointed to the fact that, when used alone, there is no single bedside test that can accurately identify all patients with difficult airways.3 Clinicians can increase predictive accuracy by performing a multifactorial assessment of several parameters, but it can be impractical and time-consuming to attempt to perform a large number of airway assessments prior to airway manipulation.1,3 Because many airway evaluations provide subjective results that 8 vary from one examiner to the next, there is an apparent need for development of objective tests which decrease interobserver variability and increase the accuracy of airway predictions. 1,3 In emergency situations, complications with airway management can be largely avoided through the use of point-of-care ultrasound (POCUS) assessment. 9,10 Ultrasound assessment of the upper airway provides more information than traditional clinical examination methods and can be used before, during, and after intubation. 1,9,11-14 POCUS is useful in identifying a difficult airway prior to sedation or an intubation attempt, in confirming endotracheal tube location and depth, and in preemptively identifying important landmarks should there be a need for emergency cricothyroidotomy.1,9-14 Although traditional airway assessments are used to predict difficult laryngoscopy, the incidence of unanticipated difficult laryngoscopy remains. In one pilot study of sublingual ultrasound in 100 patients, researchers found that the sensitivity and specificity of predicting difficult laryngoscopy using sublingual ultrasound were 73% and 97% respectively, which was much higher than traditional airway assessment methods. 15 In a different prospective, doubleblinded study of 484 patients, researchers found that the ultrasound measurements of temporomandibular joint mobility had more predictive accuracy in assessing difficult laryngoscopy than other indirect assessors like the ULBT, IID, TMD, and MMT.16 They also found that the ultrasound measurements could be used independently to predict airway difficulty.16 One single-blinded, observational study used two ultrasound measurements of the neck to predict difficult laryngoscopy. 17 The study found that an average distance from the skin to epiglottis at the level of the thyrohyoid membrane of 2.54 cm was highly predictive of difficult laryngoscopy.17 The results demonstrated 94% sensitivity in females versus 86% sensitivity in males while the specificity was 83% to 92% in females to males respectively. 17 9 These studies prove promising in finding a solution to the problem of unreliable predictive airway assessments. 10 Case Description A 66-year-old male presented to the emergency room (ER) with symptoms of throat pain and dysphagia for two weeks, and shortness of breath. He had no significant medical history with the exception of being a 40-pack-year smoker and heavy alcohol drinker. During his ER visit, he had a CT scan of his neck, which revealed mucosal soft tissue thickening at the level of the glottis. The patient was referred to the radiology department for an esophagram. The examination revealed a laryngeal mass with frank aspiration followed by bronchospasm. After the study, a general surgeon was consulted for endoscopic placement of a feeding tube; however, the surgeon felt that due to the risk of tumor avulsion or hemorrhage, the patient was a better candidate for open placement of a gastrostomy tube and anesthesia providers were consulted. Bedside examinations performed by the anesthesiologist revealed adequate head and neck range of motion and normal scoring on all examinations including the MMT, ULBT, IID, TMD, and the SMD. However, prior imaging studies presented considerable safety concerns for the anesthesia providers about airway protection and intubation difficulty. Because there were limited resources available at the facility, no significant change in the patient’s respiratory status, and concerns over airway protection under anesthesia, the decision was made to transfer the patient to a tertiary facility for definitive treatment of periglottic/laryngeal mass. However, while awaiting transfer, the patient developed an altered mental status with respiratory failure and required assisted ventilation with a bag-valve-mask. Since the patient was stable but requiring airway protection and support, the decision was made to transfer the patient to the post-anesthesia care unit (PACU) for controlled intubation with a surgeon present for emergency tracheostomy if needed. Because the patient was not cooperative, awake fiberoptic intubation was not an option, though it would have been safer. With continuous vital sign monitoring in place, the patient was 11 induced with intravenous administration of Etomidate 16 mg. The initial attempt with a video laryngoscope only revealed a view of a large laryngeal mass surrounding the glottis and shifting the vocal cords. The endotracheal tube (ETT) was unable to be passed through the vocal cords. A second attempt with assistance from a second anesthesia provider was made using a fiberoptic bronchoscope and a video laryngoscope. Using the video laryngoscope, the bronchoscope was guided through what appeared to be vocal cords. Once the fiberoptic view confirmed that the bronchoscope was in the trachea, the ETT was passed over the scope and secured. ETT position was also confirmed with positive bilateral breath sounds, positive end-tidal CO2, and a chest xray. The patient was then transferred to the intensive care unit where he awaited transfer to a tertiary facility. 12 Discussion/Conclusion Ultrasound assessment of the upper airway provides more information than traditional clinical examination methods and can aid in preemptively identifying important landmarks in emergency situations.1,9-17 The patient in this study is a good example of the inability of traditional airway exams to identify truly difficult airways because his bedside examinations revealed no alarming findings, no obvious deformities, and no abnormal range of motion in his head and neck. In their study of the usage of upper airway ultrasound, Adi et al, reported on a similar patient who presented with worsening shortness of breath, hoarseness, and no abnormal physical findings on examination.11 The patient was also uncooperative and unstable, but had no prior imaging studies.11 The physician utilized upper airway ultrasound and found a large laryngeal mass which prompted emergency tracheostomy and prevented further detioration. 11 Unlike the patient in the aforementioned study, the patient described in this case report had previous imaging studies which identified the airway hazard prior to airway manipulation; however, given his symptoms, his respiratory collapse may have been avoided through prompt investigation using UAUS. In a case reported by Iqhbal et al, upper airway ultrasound was used to guide emergency airway management in a patient who presented with hoarseness, stridor, and respiratory distress.18 Bedside examination revealed no abnormal physical findings in the head, neck, or chest.18 Due to the patient’s declining respiratory status, physicians performed a quick, bedside airway ultrasound which revealed a mass located near the cricoid cartilage in the upper airway. 18 This abnormal anatomic structure precluded the patient from having an emergency cricothyroidotomy if traditional intubation techniques were unsuccessful. 18 Therefore, the airway ultrasound helped guide the decision to preform emergency tracheostomy in a patient with impending respiratory failure.18 In a separate study by Adi et al, they reported on the correlation 13 between upper airway ultrasound findings and CT scans in four patients with suspected laryngeal trauma.19 In each case, a focused upper airway ultrasound was performed and the findings prompted immediate airway intervention.19 After the airway was successfully secured, the patients’ CT scans confirmed the diagnosis made from the focused ultrasound assessment of the upper airway with 100% accuracy.19 In these studies, Adi et al, reported that the UAUS expedited the intervention process by providing rapid and accurate information at the bedside. 19 Conclusion Although some bedside clinical examinations are useful in predicting difficult airways, studies have shown that a combination of tests or more specific and sensitive tests would decrease the number of unanticipated airway difficulties. 1-19 Many of the studies regarding the use of UAUS have investigated the accuracy in identification of oropharyngeal and subglottic structures and the correlation between ultrasound measurements and the Cormack-Lehane scores.9-17 In these studies, visualization of the hyoid bone, measurement of the pre-epiglottic space, hyomental distance, anterior neck thickness and tongue size have proven to be successful predictors of difficult laryngoscopy.9-17 Although current literature has demonstrated the benefits of upper airway ultrasound, there is still need for larger studies with a focus on determining which upper airway ultrasound assessments provide the best clinical outcomes. 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