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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
Page 2 of 24
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
Page 3 of 24
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.
Page 4 of 24
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.
Page 5 of 24
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)
Page 6 of 24
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.
Page 7 of 24
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
Page 8 of 24
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).
Page 9 of 24
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.
Page 10 of 24
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.
Page 11 of 24
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
Page 12 of 24
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).
Page 13 of 24
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.
Page 14 of 24
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).
Page 15 of 24
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.
Page 16 of 24
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).
Page 17 of 24
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).
Page 18 of 24
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).
Page 19 of 24
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.
Page 20 of 24
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.
Page 21 of 24
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.
Page 22 of 24
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