2 August 2019 No. 15

Making Airwaves

Upper Airway Ultrasonography

Sunthurie Pillay

Moderator: Belinda Kusel

School of Clinical Medicine Discipline of Anaesthesiology and Critical Care

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CONTENTS

Introduction ................................................................................................................... 3

The growing role of airway ultrasonography .............................................................. 4

Getting the right sound system ................................................................................... 5

ORIENTATION OF TRANSDUCER IN NECK ............................................................. 5

Basic anatomy and sonoanatomy of the upper airway .............................................. 6

Clinical Application ....................................................................................................... 9

Prediction of the difficult intubation ........................................................................ 9

Localization of the Trachea ..................................................................................... 10

Prediction of endotracheal tube and Double Lumen Tube size ........................... 11

Confirmation of endotracheal tube placement ...................................................... 12

Localization of the cricothyroid membrane ........................................................... 14

Ultrasound guided Percutaneous Dilatational tracheostomy .............................. 15

Prandial status and risk of aspiration .................................................................... 16

Other potential uses ................................................................................................ 17

Limitations ................................................................................................................... 19

The Future of Airway Ultrasound ............................................................................... 20

CONCLUSION .............................................................................................................. 21

REFERENCES .............................................................................................................. 22

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Introduction

A Brief History of Ultrasound

Interest in ultrasound (US) dates back to 1794 when then physiologist, zoologist and

Bishop of Pavia, Lazarro Spallanzani, thought to examine the navigational techniques of

bats (1). He blinded them and found that they were as capable as unblinded bats in their

ability to fly and avoid obstacles. Supplementary to this examination, Charles Jurine

plugged the ears of bats with wax and noted that they lost their control of navigation,

concluding that receiving the sound stimulus was important. The bats needed to hear in

order to “see” and pilot their course this would later be termed echolocation. These

discoveries would unintentionally shape the future of ultrasound.

Fast forward to 1822, where Daniel Colloden discovered the speed of sound under water

using an underwater bell and in 1842 Christian Andreas Doppler described the doppler

effect predicting the velocity of the emitter or observer of a wave due to change in

frequency.

1880 was the year in which the Piezoelectric effect (the conversion of electric energy to

mechanical and sound energy) was discovered by Pierre and Jacques Curie, and the

reverse piezioelectric effect was discovered the following year.

In the 19th Century the invention of sonars helped detect icebergs preceding a ships

course and it was discovered that the frequency of ultrasound waves were higher than

those in the human hearing range.

It was in 1942 that Dr Karl Dussik thought to apply ultrasound medically and while placing

a probe on the skull attempted to detect brain tumours. In 1949 Howry and Holmes were

pioneers in the use of B-mode in ultrasound for breast tumour detection. In 1965 Krause

and Soldner invented real-time processes allowing for dynamic imaging. Duplex, endo-

and 3D sonography were discovered in the following decades and the process of

discovery continues even today.

Airway ultrasonography is a relatively recent application of the modality but a seemingly

natural progression of the use of this non-invasive, mobile, quick and valuable bed side

tool.

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The growing role of airway ultrasonography

Point of care ultrasound (POCUS) is an increasingly used examination as our familiarity

with ultrasound grows. Point of care refers to bringing the diagnostic tool to the patient’s

bedside to assist with assessment and management as opposed to moving the patient to

a radiological facility. It does not require immobility or sedation (2). This can be compared

to performing a bed side chest x-ray, without having to adjust the patient’s position or

exposing them to harmful radiation. The anaesthesia, critical care and emergency

medicine fields have embraced POCUS as they often deal with ill patients who need

emergent evaluation and intervention. These patients may be too sick to mobilize, or time

does not allow this due to the urgency of proposed treatment and potential effects on

outcome (3). Airway mismanagement remains an important contributor to anaesthesia

related morbidity and mortality (4). Airway ultrasonography has the potential to assist us

in the assessment of the difficult airway, exclude oesophageal intubation and guide front

of neck airway access in elective and emergency situations (3). Looking at the accuracy

of measures by comparing them to CT scan images, ultrasound imaging and measures

of the infrahyoid region correlate well (5). Although the airways consist of upper and lower

areas, this booklet will focus on upper airway sonography. Most of the sonographic

images in the text to follow is from an excellent article by Kristensen et al highlighting the

clinical application of airway sonography (6). The interest in upper airway ultrasound has

been growing in the last two decades and as its use is increasingly adopted, further

studies will assist in ongoing validation of this tool for various applications.

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Getting the right sound system

Sound is a disturbance propagating through a material (7). Each sound is characterized

by its frequency and intensity. Frequency is measured in Hertz (Hz) and describes the

number of oscillations per second. Human hearing perceives sound wave frequencies

below 20kHz. Ultrasound is defined as any sound above this frequency and medical

ultrasound is used above the frequency of 2MHz. The nature of the material in which the

sound propagates determines its velocity.

The linear transducer is best for visualizing the superficial airway structures (within 5cm

from skin) and does this by emitting medium to high frequency (5-14 MHz) sound waves

(6). High frequency allows for better resolution images with better lateral 2-point

discrimination at the cost of depth of penetration. For deeper structures such as the

submandibular and subglottic regions the curved low-frequency transducer (5 MHz) is

most suitable, allowing a wider field of view. This probe will offer a lower resolution and

deeper penetration.

Once the probe has been selected, image optimization must still occur considering

optimal probe position, gain, depth and sector selection. The aim is to keep the desired

structure in the centre of the displayed image and use the minimum depth and sector

width required to increase the frame rate, resolution and therefore image quality.

Due to its wave-like properties reflection, refraction, scatter, absorption and transmission

of sound occur as it passes through soft tissue structures, allowing characterization of the

shape and internal architecture of that structure in addition to those behind it. It is

important to be familiar with artefacts and know the difference between these and organic

structures. The artefacts themselves can be very useful. The image is built from the

reflected sound signals (8). Reflection of sound is marked at interfaces between tissues

of different acoustic impedance such as between air and tissue.

When positioning the patient for ultrasound airway examination, patients should be placed in supine sniffing position with a pillow under the occiput to achieve optimum head extension and neck flexion (8).

ORIENTATION OF TRANSDUCER IN NECK

Sagittal view (longitudinally in the midline)

Transverse view (transversely across the anterior surface of the neck)

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Basic anatomy and sonoanatomy of the upper airway

Illustration A: Sagittal section through the upper airways

Knowledge of the upper airway anatomy is a prerequisite to performing upper airway

ultrasonography. The following structures, which are relevant to airway management, can

be examined with US: the mouth and tongue, the hyoid bone, epiglottis, the larynx, the

cricoid cartilage, tracheal cartilages, the oesophagus and the thyroid gland (3). Illustration

A shows a basic sagittal view of the upper airways. Of importance to anaesthetists is the

fact that the mouth and oropharynx is a shared aerodigestive tract, and knowledge of the

anatomy guides our methods of securing airway access.

Starting proximally with the first sonographic image, Figure 1 shows the of the floor of the

mouth and the tongue. Acoustic shadows can be seen behind the mentum of the mandible

anteriorly and hyoid bone posteriorly. The curved orange line signifies the mucosal-air

interface, the grey area to the left of the orange line is all artefact.

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Fig. 2

Illustration B: Anterior view of the larynx Illustration C: Superior view of the glottic opening

Cartilage does permit good penetration of ultrasound waves allowing definition of the

thyroid and cricoid cartilages which have distinctive shapes compared to the tracheal

rings. Calcification of the thyroid and cricoid cartilage (3), can make visualization of the

cords harder with increasing age, whereas the epiglottis remains hypoechoic. The vocal

cords are best seen in the transverse plane through the thyroid cartilage as a window (as

viewed in figure 2). The thyroid cartilage appears as a thick upside-down V shape (yellow

in figure 2). The vocal cords appear hypoechoic (darker) but are medially outlined by the

hyperechoic (lighter) vocal ligaments (blue in fig 2). Figure 3 is taken by moving the probe

caudally from the position used to obtain the image in Fig 2. This image shows the ovoid

or sideways C-shape of the cricoid cartilage in transverse section compared to the v

shape of the thyroid cartilage.

Fig. 3: Transverse section through The cricoid cartilage

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In the sagittal plane, the cricoid cartilage appears as a hypoechoic oval bump or hump

(purple in Fig. 4). This is important to identify as mentioned later in the booklet when

looking at the cricothyroid membrane (orange) for emergency airway access, which lies

between the cricoid cartilage and the thyroid cartilage (green). The tracheal cartilages are

also hypo echoic and appear as a “string of beads” or “string of pearls” in this plane. The

hyperechoic mucosal air interface leads to artefact inferior to this interface.

In the transverse plane, the tracheal rings appear as a thinner, wider inverted U (blue

figure 5) compared to the cricoid cartilage. The tracheal ring is hypoechoic with the air

mucosal interface appearing as a hyperechoic line with reverberation artefact below this.

The oesophagus (yellow in figure 5) is seen at the level of the first and second tracheal

cartilage, located posterior to the left thyroid nodule. Visible peristaltic movement can be

seen inside the esophageal lumen by asking the patient to swallow. In some instances,

the oesophagus is located posterior to the trachea – in which case one will be unable to

identify it due to the shadow cast from the trachea (9).

During procedures such as elective front of neck access, the thyroid gland and isthmus

is important to identify prior to airway instrumentation to reduce potential damage. Figure

6 shows the thyroid gland and isthmus with the oesophagus posterior to the left lobule

(8).

Fig. 6: Transverse view of neck just above the

suprasternal notch at the level of thyroid gland(Th) showing the Esophagus (arrow) and trachea (T).

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Clinical Application

Prediction of the difficult intubation

Evaluation of the airway is of utmost importance for safe anaesthetic practice, yet in some

instances clinical examination has yielded variable results, leading to the unanticipated

difficult airway despite normal clinical examination. To bolster these clinical examination

measures, the application of airway ultrasonography may show promise. This option may

also be useful in a patient who cannot obey commands to assess the airway by routine

examination for example in sedated, trauma or paediatric patients.

Various authors have proposed different measures. Wojtczak suggested a hyomental

distance ratio of < 1.1 could predict grade 3 or 4 Cormack-Lehane view of the vocal cords

on direct laryngoscopy in obese patients (10). The ratio is made by dividing the measures

taken between the mentum and the hyoid bone with the neck in the neutral position and

in full extension (Fig 7).

Fig. 7

Adhikari et al. demonstrated that anterior neck thickness at the level of the hyoid bone

and thyrohyoid membrane (more than 2.8 cm) is a predictor for difficult laryngoscopy (11).

Wu et al also found anterior neck thickness at these levels to predict a difficult intubation

and found the measures slightly superior to stand alone clinical measures such as

thyromental distance or Mallampati score (12). In contrast, Komatsu et al. found

sonographic measures failed to predict difficult laryngoscopy in obese patients (13).

Inability to identify the hyoid bone has been associated with difficult laryngoscopy in a

study by Hui and Tsui (14). Further large-scale studies are required before any

recommendations can be made.

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Fig. 8

Localization of the Trachea

Upon airway assessment, external palpation of the trachea can assist in concluding

whether it is deviated from its usually central position above the sternal notch. In a patient

without neck pathology this may be a simple assessment, but accurate localization of the

trachea is challenging when there is distortion of neck anatomy such as the case post

irradiation or neck surgery, patients with short thick necks or some thoracic pathology (6).

X-rays may not always be helpful in this situation and one would rely on CT scan

preferably, but for real time assessment, the ultrasound can be a vital aid. One looks for

the trachea by placing the linear probe in the transverse plane in the midline of the neck

just above the sternal notch and scans cranially to view it at different levels looking for the

tracheal rings as described earlier in Figure 5. Figure 8 below demonstrates a clinical

situation in which the trachea is deviated away from the midline and palpation was not

possible.

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Prediction of endotracheal tube and Double Lumen Tube size

There is good correlation between subglottic transverse diameter measured by

ultrasound and the outer ETT diameter in the paediatric population (15,16). Compared to

currently used age-based and height-based formula, Shibasaki et al. found that

ultrasound is superior in estimating ETT size for both cuffed and uncuffed tubes (15). The

measurements were taken at the lower edge of the cricoid cartilage during ventilation and

it was found that age and height-based formula can only predict about a third of cuffed

ETT size and 60 % of uncuffed tube size compared to ultrasonography (98 and 96 %,

respectively). In a more recent study however, Mahran et al. found formulae and

ultrasound to be equally effective in calculating the correct size of uncuffed ETT (17).

Regarding Double-Lumen Tubes (DLTs) one is particularly concerned about avoiding

trauma to the airways and misplacement of the tube on movement which can interfere

with the surgical field and oxygenation. Appropriate choice of tube size can potentially

reduce these complications (6). CT scan measures to determine the size of trachea have

been used to guide DLT size and is an accurate method. The table below lists the DLT

sizes that correlated with different tracheal widths as measured by ultrasound in a study

by Sustic et al, which were comparable to CT scan measures (18). In an emergency, an

ultrasound measurement might be favorable compared to obtaining a CT scan, due to

previously mentioned advantages of POCUS.

Ultrasound measurement: Tracheal Width (mm)

Double Lumen Tube size prediction (Fr)

≥15.9 32

≥17.4 35

≥18.3 37

≥19.3 39 ≥21.2 41

Table 1: Tracheal width measures with proposed DLT size of choice

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Fig. 9: Sonographic image of

the trachea and oesophagus

(with Tube indicated). The

image depicts the presence of

an ETT in the lumen of the

oesophagus

Confirmation of endotracheal tube placement

There are various methods currently in practice to confirm ETT placement within the

trachea. Capnography is currently the gold standard for confirmation of ETT placement

in the airway. Direct observation of the ETT passing between the vocal cords is another

method, but may not always be possible especially when laryngoscopy is difficult (18).

The use of ultrasound detects correct ETT insertion indirectly by excluding oesophageal

intubation. If the ETT is inserted in the oesophagus some call this the “double trachea” or

“double tract sign” sign as appears as if two tracheas are alongside each other as

depicted in Fig. 9.

Accidental oesophageal intubation can lead to disastrous complications, the ultimate of which is death. Using dynamic ultrasound and real time imaging at the time of intubation, oesophageal intubation can be identified prior to insufflation of the stomach. This is useful in teaching environments and noisy environments without capnography or where capnography may not be reliable (e.g. cardiac arrest) (19). Chou et al. demonstrated that the use of Tracheal Rapid Ultrasound Exam (TRUE) can be used in emergency situations as confirmation of ETT placement can be performed within 16 seconds (20). The situation in which this technique is not appropriate is in patients whose oesophagus is located directly posterior to the trachea due to masking of the oesophagus by the acoustic shadow cast by the trachea(3).

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Depth of ETT

After confirming that the ETT is within the trachea, the next important step is to confirm

that it is not in one of the mainstem bronchi. Sitzwohl et al. found that auscultation and

chest rise during clinical assessment failed to detect up to 55 % of endobronchial

intubations (21). Brunel and Ramsingh et. al also mentioned the shortcomings of physical

examination and found several cases within their study population who had had

endobronchial intubations despite equal breath sounds auscultated bilaterally (22,23).

Endobronchial insertion can be identified as lung sliding being present on one side of the

lung field (the side of endobronchial intubation) and no lung sliding or only lung pulse on

the other. The tube must then be withdrawn until lung sliding is observed bilaterally(23).

This requires the knowledge of lower airway ultrasonography. Tessaro et al. suggested

filling the ETT cuff with saline and performing airway sonography can accurately and

rapidly distinguish between correct endotracheal versus endobronchial tracheal tube

positions in children (24). Using an ultrasound to correctly identify the position of the ETT

is useful not just at time of intubation but also for monitoring daily movements without the

need for repeated radiation exposure such as in the critical care setting with prolonged

ventilation and the potential for tube displacement and resultant impaired ventilation (25).

The pregnant population would also benefit from less radiation exposure.

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Fig. 10

Localization of the cricothyroid membrane

An important rescue strategy for managing a difficult airway is gaining infraglottic airway

access by cricothyroidotomy. The traditional landmark technique correctly identifies the

cricothyroid membrane in 30 % of cases (26). This leaves large room for improvement

and there are now ultrasound guided techniques that allow for rapid, repeatable

identification of the cricothyroid membrane. The suggested timing for this image

acquisition is before any type of induction or awake tracheostomy with the added safety

of having localized the cricothyroid membrane should the initial plan fail, and emergent

airway access becomes necessary. The first method for localizing the cricothyroid

membrane, known as the “String of Pearls” (SOP) technique (3) is described as in figure

10 using the linear probe and performed in the sagittal plane.

The SOP technique has been well described and is suggested as the first method to use.

The TACA or Thyroid-Airline-Cricoid-Airline technique is done in the transverse plane.

The thyroid cartilage is identified (knowing the characteristic shape), then move the probe

caudally to identify the cricothyroid membrane which will be identified by the air-mucosal

interface as a hyperechoic line, then move the probe further caudally to see the cricoid

cartilage, then move the probe back cranially over the confirmed cricothyroid membrane

and mark this position (3).

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Ultrasound guided Percutaneous Dilatational tracheostomy

Ultrasound guided percutaneous dilatational tracheostomy (PDT) allows real-time

localization of the anterior trachea, it’s individual cartilaginous rings above the sternal

notch as well as important surrounding structures (7). Ultrasound can be used to guide

most of the procedure or just initially to locate the appropriate intercartilagenous space.

The benefit of visual guidance is the ability to choose the appropriate space, avoid

structures such as blood vessels and thyroid tissue and prevent further advancement of

the needle once within the tracheal lumen, by measuring the distance from skin to lumen,

to prevent damage to the posterior tracheal wall. This helps reduce potential

complications like tissue injury, stenosis, fistula and hemorrhage (7). In cadaver models,

Siddiqui et al. showed that injuries to the airway were three times lower in the ultrasound

guided group even in cadavers with distorted neck anatomy when compared digital

palpation by non-experienced ultrasound users, although it took longer to complete the

procedure (196 vs 110 s) (27). One of the causes of death following PDT is uncontrolled

hemorrhage. In such cases, autopsies have shown that the tracheostomy level was more

caudal than intended, eroding maor vessels including the innominate vein and the arch

of the aorta (28). As many as one in four patients require a change in PDT puncture site

after ultrasound assessment (29). The Traditional landmArk versus ultRasound Guided

Evaluation Trial (TARGET) Study (30) and Dinh et al. (31) found that real-time ultrasound

guidance improves the success rate of the first PDT attempt and puncture accuracy

compared to traditional anatomical landmark. The benefit over bronchoscope guided PDT

is that a bronchoscope may occlude the ETT lumen and result in hypercapnia, whereas

ultrasound Doppler-guided PDT does not.

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Prandial status and risk of aspiration

There are some emergency situations where the patient is unable to convey their prandial

status prior to emergency surgery (e.g. for traumatic brain injury with lowered level of

consciousness) or in the elective setting where patients may have reduced gastric

emptying despite having fasted the recommended amount of time. In such instances

ultrasonography of the stomach may assist in evaluating the risk of aspiration and

whether further fasting, promotility drugs or other measures of security to prevent

aspiration in the emergency setting are needed, like securing the airway with an ETT

rather than supraglottic airway.

At present ultrasound looking at gastric content can rule-in high risk for aspiration but

when certain features are absent this does not preclude an aspiration risk (5).

The correct positioning for the patient is in the right lateral decubitus position (highest

sensitivity) or in the seated position. The low frequency abdominal probe is placed in the

sagittal plane in the epigastrium and the antrum of the stomach is found just posterior to

the liver. An empty antrum is signified by visualizing only the muscle layers (low risk for

aspiration), liquid content appears hypoechoic (and upon measuring < 300mls confers a

low risk of aspiration, and >300 mls high risk), and thick fluids or solid content appears as

a mixture of solid and gas which appears like a “frosted glass” image (which always

signifies high risk) (5).

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Other potential uses

OSA

Obstructive sleep apnea (OSA) is a risk factor for peri operative morbidity such as peri-

operative airway obstruction and respiratory depression. Ultrasound measurement of the

width of the tongue base and lateral pharyngeal walls has found that larger dimensions

correlate with the severity of sleep-related breathing disorders (32).

Detection of subglottic stenosis

Ultrasonography of the airway looking at subglottic diameter was shown to correlate well

with MRI measure at the same level (33). This could potentially be used to assist with

revealing the presence of subglottic stenosis in a patient with stridor and assist with an

airway management plan and ETT size.

Prediction of successful extubation

Air-column width (the width of air passed through the vocal cords as determined by US in

transverse plane over the thyroid cartilage) in ventilated patients was found to be

significantly narrower in patients with post extubation stridor as compared to those who

did not experience stridor (34). Sutherasan et al. looked at patients with and without post-

extubation stridor and suggested a cutoff value of 1.6 mm (below which there is increased

risk for stridor) (35).

Diaphragmatic displacements, once again requiring lower airway ultrasonography skills,

are thought to reflect the strength and endurance of respiratory muscle function. The more

significant the diaphragmatic displacement, the more preserved the respiratory muscle

function and greater chances of being able to wean off a ventilator. The results of variable

trials have been inconclusive, and no cut offs can be recommended at present (36).

Airway related nerve blocks

Awake fiberoptic intubation requires a compliant patient a well anaesthetized airway. The

superior laryngeal nerve may be blocked under ultrasound guidance, which is especially

useful when landmarks are difficult to identify. The greater horn of the hyoid bone and the

superior laryngeal artery are identified, and the local analgesic was injected in between

(37). A high frequency (8-15MHz) hockey stick probe may be used to identify the nerve

itself, and although difficult, it has been described(37).

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Assessment of vocal cord movement for thyroid and parathyroid surgery

During certain surgical procedures within the neck, such as thyroid and parathyroid surgery, there is a risk of nerve damage and resultant ipsilateral or bilateral vocal cord paralysis. Ultrasonography looking at vocal cord movement can assess the function of the superior laryngeal nerve or recurrent laryngeal nerve, with absence of movement on phonation or coughing implying damage (3). The visualization of cord movement is affected by sex and aging as older male patients will have calcified thyroid cartilages, affecting the acoustic window.

Confirmation of gastric tube placement

At present the confirmation of gastric tube placement usually requires a chest X-ray,

which has a 100% sensitivity to detect weighted-tip nasogastric tubes within the stomach.

Abdominal ultrasonography performed in the ICU had a high sensitivity for detecting

correct gastric tube placement (97%) as well as shorter time to acquisition than chest xray

(24 vs 180 minutes) (38).

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Limitations

Ultrasound will always be operator dependent and reproducibility of findings is an

essential part of US training. Sound has some innate limitations that were discussed in

the earlier chapters, and misinterpretation of artefact or the inability to see past echo

reflective interfaces make its use challenging. Ultrasound use may be limited further due

to factors such as patient habitus (i.e. post radiotherapy and marked inability for pattern

recognition). Therefore, in some cases it still may be necessary to replace or supplement

ultrasonography with other imaging modalities. The role of airway sonography is to

answer a specific question, this is unlike application of cardiac ultrasound where the aim

would be to get 4 or 5 main FATE views with a set of differentials to exclude in your mind.

With airway ultrasonography one must have a specific question one wishes to answer:

where is the cricothyroid membrane? Is the ETT in the trachea or oesophagus? Is the

patient at high risk of aspiration? The process is meant to take minimal amounts of time

and should not delay definitive imaging when ultrasound images are ambiguous or delay

emergent treatment when images are not obtainable to anatomical distortion.

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The Future of Airway Ultrasound

Many airway ultrasound courses are available online from training centres such as the

USABCD. This ability to rapidly disseminate information will lead to more awareness of

the modality, its advantages and short comings. With regards to technology, three-

dimensional and pocket-sized devices are likely to move the boundaries for both the

quality and the availability of ultrasonographic imaging of the airway. Systems

incorporating smartphones are also making sonography easier to access and reducing

costs.

As described in the section on Other Uses, there are so many applications of airway

sonography waiting to be validated. Case studies are also becoming available such as

an ultrasound guided intubation by Fiadjoe et al (39). Real-time ultrasonography was

used to direct the insertion of the endotracheal tube during intubation without

performing laryngoscopy in a patient of 14 months old who failed traditional laryngoscopy.

They located the tube in the pharynx by ultrasound and assessed its relationship to the

glottis opening. They modified the trajectory of insertion of the tube to place it through the

glottis opening. These and other new trials are revealing exciting new results, however

these must be interpreted with the knowledge of potential limitations. With time, practice

and improved technology everyday use of ultrasound to assist with airway management

may become the new norm.

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CONCLUSION

Airway management is a routine part of anaesthetic practice. These skills are equally

important in the critical care, emergency and pre-hospital settings. Ultrasound has many

advantages for imaging the airway—it is safe, quick, repeatable, portable, widely

available and gives real-time dynamic images relevant for several aspects of

management of the airway. While it is not meant to replace clinical acumen, its serves to

add to a growing body of knowledge that promotes patient safety and better outcomes.

There is a learning curve associated with its use, but many studies have shown that

teaching these skills does not take copious amounts of time, relative to the benefits

derived. The table below provides a summary of the indications for airway

ultrasonography that are related to the strength of evidence available thus far (3).

While confirmation of tracheal intubation and identification of the cricothyroid membrane

have by far been the most promising and valid recommendations for use, there are

growing bodies of evidence looking at the potential use of ultrasound related to the many

facets of airway management.

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