2. • success rate of real emergency airway access – 36%
• inability to identify the cricothyroid membrane –
main contributor
• identifying the cricothyroid membrane clinically in
the obese has success rates of 0-39%
• After some training, sonographic identification of the
CTM is close to 100%
3. • a structured training programme lasting ∼1 h, leads
to a clinically useful skill level
• significant retention of skills exists after 6 months
• ultrasound guided marking of the cricothyroid
membrane is unaffected by changing neck positions
• Two techniques recommended…the transverse/TACA
and the longitudinal/string of pearls technique
4. • Authors recommendations…
• Identify the CTM before commencing any airway
management
• The mean time to mark the CTM was 24 sec with the
TACA method and 37 seconds with the Longitudinal
method
• Identify the CTM clinically and if any doubt exists,
then sonographic identification should be
performed!
5. Our Structured Training
Program
• Airway anatomy using ultrasound
• Longitudinal – String of Pearls method
• Transverse – TACA method
• Examples
• Practical session
• Ultrasound for confirmation of ETT placement
97. What about real time needle guidance
STEP 1
• Explore the airway in transverse
• Identify key features - TACA technique
STEP 2
• Find the cricoid cartilage and angle cranially
98.
99.
100. What about real time needle guidance
STEP 1
• Explore the airway in transverse
• Identify key features
STEP 2
• Find the cricoid cartilage and angle cranially
STEP 3
• Use an out of plane technique
• Watch the tip of the needle
103. Our Structured Training
Program
• Airway anatomy using ultrasound
• Longitudinal – String of Pearls method
• Transverse – TACA method
• Examples
• Practical session
• Ultrasound for confirmation of ETT placement
This narrative review summarizes the current evidence for application of airway ultrasonography for identification of the cricothyroid membrane compared with the clinical techniques. They identified the best-documented techniques for bedside use, their success rates, and the necessary training for airway-ultrasound-naïve clinicians
Success rate of real emergency airway access performed by anaesthetists is low, with only 9 of 25 (36%) attempts being successful. An inability to identify the cricothyroid membrane is an important contributor to this high failure rate, because misplacement is the most common complication when attempting cricothyrotomy
Identifying the cricothyroid membrane with traditional modalities of inspection and palpation is notoriously low, especially in obese patients, for whom reported success rates vary between 0 and 39%.
A 1h structured lesson that consisted of e-learning, a lecture, and hands-on training resulted in clinically useful 84–90% success in morbidly obese females (100% with at least one of two techniques applied)
The results from the published literature, we can draw the following conclusions:
(i) the identification of the cricothyroid membrane by clinical measures (inspection and palpation) alone is insufficient in a high fraction of patients, especially the obese;
(ii) ultrasonography improves the accuracy of identification of the cricothyroid membrane, with a success rate very close to 100% once the clinicians have gained some experience;
(iii) after a structured training programme lasting ∼1 h, it is possible to attain a clinically useful skill level;
(iv) the ultrasound guided marking of the cricothyroid membrane is unaffected by changing neck positions (e.g. markings made in the extendedneck position before head manipulation to intubate the trachea accurately identify the cricothyroid membrane also after the intubation attempt when the head and neck are repositioned in extension); and
(v) after learning ultrasound-guided techniques, significant retention of skills exists after 6 months
A 1h structured lesson that consisted of e-learning, a lecture, and hands-on training resulted in clinically useful 84–90% success in morbidly obese females (100% with at least one of two techniques applied)
Before initiating airway management, the potential ease or difficulty of performing cricothyrotomy and tracheostomy should be evaluated, and an attempt should be made to identify the cricothyroid membrane.
The pre-anaesthetic identification of potentially difficult or even impossible cricothyroid membrane access may direct the clinician towards a more conservative approach, such as awake intubation or awake elective tracheostomy under local anaesthesia
Identify the cricothyroid membrane before commencing any airway management, instead of waiting until an emergency airway crisis situation arises.
The cricothyroid membrane should be identified in all patients before induction of anaesthesia and in all patients with airway compromise if time allows. The initial approach is through inspection and palpation and if this also fails or any doubt exists, then ultrasonographic identification should be performed
So.. We will go through…
Airway anatomy in Longitudinal and Transverse using Ultrasound
Explaining the two techniques recommended to identify and mark the Cricothyroid membrane
Going through some examples of more challenging patients as we do that
Having a hands on practical session
If there is time going through the use of Ultrasound while intubating
The relevant airway anatomy..
The Hyoid bone
The Thyrohyoid membrane
The Thyroid cartilage with superior and inferior horns, the thyroid notch superiorly, the laryngeal prominence
The Cricothyroid membrane.. with the inferior horns of the thyroid cartilage extending caudally
The Cricoid cartilage
The Cricotracheal ligament and the tracheal rings
This is the part we will focus on today.. The Thyroid cartilage, Cricothyroid membrane, Cricoid cartilage and tracheal rings
Going through the muscles/strapmuscles…..Anterior to the cricothyroid joint.. The cricothyroid muscles
Covered by the Sternothyroid muscles
Which in turn is covered by the Sternohyoid muscles
The Thyroid cartilage has various forms and there is slight anatomical variation between patients.. which will then influence the surface and sonoanatomy of the CTM slightly… we will see examples of this later
This is a Panoramic view of the Airway and Neck in transverse.. a bit of revision..
Bloodvessels/Fluid appears anechoic/black.. Veins are compressible and Arteries not
So we identify the Internal jugular vein and Carotid artery
Glandular tissue or structures are homogenous and mildly to strongly hyperechoic.. More echogenic than surrounding muscles etc
Muscles appear more hypoechoic and striated with hyperechoic strands… here we see the strapmuscles we just discussed.. Sternothyroid and Sternohyoid… and the sternocleidomastoid muscles
The thyroid gland
The Oesophagus.. is normally situated posteriorly and slightly to the left of the trachea. More easily identifiable if imaging slightly from the left and asking the patient to swallow. It has a bowel signature .
The Trachea appears as a horseshoe shaped structure in the middle of the screen with the dirty shadowing extending to the bottom of the screen
At the soft tissue/air interface .. Air strongly reflects the Ultrasound beam and a hyperechoic white line appears with dirty grey shadowing behind it.
Artefacts… like reverberation artefact are visualised that create multiple parallel white lines on the screen. This will be better demonstrated on the non panoramic view
Visualization of structures such as the posterior pharynx, posterior commissure and post wall of the trachea is thus prevented by intraluminal air.
Trachea and air/tissue interface
Air.. always causes dirty shadowing behind it.. obscuring the view behind
Due to a great impendance difference btw soft tissue and bone .. Bone also appears hyperechoic/white ..the US beam is absorbed.. And you get dark clean shadowing behind it
The vertebral body and the longus coli muscles just above
You can easily measure the diameter of the airway..
This is a Longitudinal scan panoramic view of the airway.
Cartilaginous structures such as the thyroid cartilage, the cricoid cartilage and the tracheal rings appear homogenously hypoechoic or dark..
Both thyroid and cricoid cartilages show variable and progressive calcification through life… starting in the 2-3rd decade
Muscles and connective tissue are also hypoechoic but as mentioned have a more striated heterogenous appearance when compared to cartilage
On this LS – you can clearly see the hypoechoic tracheal rings … called the string of pearls.
The largest and most anterior pearl is the cricoid cartilage ..
The string is the hyperechoic tissue /air interface with the reverberation artefact underneath that..
Then identify the characteristic shape of the thyroid cartilage.
Between the cricoid and the thyroid cartilage lies the cricothyroid membrane… a bright hyperechoic white line between the thyroid cartilage and the cricoid cartilage
The skin surface
The Cartiligenous structures : string of pearls, cricoid and thyroid cartilage which will appear in yellow
The cricothyroid membrane between the cricoid and thyroid cartilages … will appear in orange
The string.. The white hyperechoic line ..the tissue/air interface just underneath the tracheal rings.. Will appear in blue
And lastly…the reverberation artefact or dirty shadowing below the tissue/air interface
You can then easily measure the cricothyroid membrane and in particular the depth
So moving on to the two techniques… and starting with the longitudinal technique
Performing the longitudinal technique - the ‘string of pearls’ technique – 37 seconds
The sternal bone is palpated, and the ultrasound transducer is placed transversely on the patient’s anterior neck cephalad to the suprasternal notch to see the trachea (horse shoe shaped dark structure with a posterior white line; Fig. 2).
The transducer is rotated into a longitudinal position showing the trachea in a longitudinal position. A number of dark (hypoechoic) rings will be seen anterior to the white hyperechoic line (air–tissue border), akin to a ‘string of pearls’. Identify the string of pearls.The dark hypoechoic ‘pearls’ are the anterior part of the tracheal rings.
The transducer is kept longitudinally in the midline and slid cephalad until the cricoid cartilage comes into view (seen as a larger, more elongated and anteriorly placed dark ‘pearl’ compared with the tracheal rings). Further cephalad, the distal part of the thyroid cartilage can also be seen.
Whilst still holding the ultrasound transducer with the right hand, the left hand is used to slide a needle (as a marker, for its ability to cast a shadow in the ultrasound image) between the transducer and the patient’s skin until the needle’s shadow is seen midway between the caudal border of the thyroid cartilage and the cephalad border of the cricoid cartilage.
Now the transducer is removed; the needle marks the centre of the cricothyroid membrane in the transverse plane, and this can be marked on the skin with a pen.
The following Images were taken off a real patient and present the reality a bit more…Slightly off center Trans shot.. We see the homogenous slightly hyperechoic thyroid isthmus anterior to the airline or air/tissue interface of the Trachea
From the skin.. Connective tissue and muscle.. Then slicing through the thyroid isthmus .. Then we get down to the string of pearls… hypoechoic pearls on the white hyperechoic airline ( air/tissue interface). Posterior to the airline.. We see the dirty shadowing and reverberation artefact and some mirror image artefact
We then slide the transducer cephalad..
And a bit more..
Until we identify the cricoid cartilage… it’s the largest, most anterior and slightly elongated pearl.. And you often see a mirror image below the string
Once you have identified the cricoid cartilage .. Its easy.. The cricothyroid membrane will be just cephalad to it.. A bright echogenic line and the lower part of the thyroid cartilage can be easily appreciated
So if we put all of that into a clip…we start in trans and identify the trachea in the middle of our screen.. We rotate the probe into longitudinal section and identify the string of pearls….. We then slide the probe up and identify the largest most anterior pearl..the cricoid.. Then the cricothyroid membrane and then the thyroid cart
After that we mark it.. How?
Slide the drawing up needle in underneath the probe.
It causes a shadow/reverberation artefact to the bottom of the screen or shadowing depending on the needle.
Ensure the artefact passes through the cricothyroid membrane..
Remove the probe and mark the CTM where your needle is.
Why choose water – artefacts much more obvious, no other soft tissue interference
Drawing up needle or paperclip
These apply to many areas of ultrasound
Here we are using water to demonstrate the reverberation artefact… very well visualised with water
Describe how the reverberation artefact moves from the cricoid to the thyroid cartilage
So… identify the cricothyroid memebrane.. ensure the reverberation artefact passes through it… remove the transducer and mark the CTM where the needle is.
Patient post Thyroid surgery with swollen neck ... Identification of the CTM prior to any airway management. Unable to identify the CTM clinically..
STEP 1
Find the trachea in transverse
Look for an air filled tube…. Horse shoe shaped trachea
STEP 2
Rotate the probe to longitudinal and slide up
Rotate into longitudinal section.. identify the string of pearls and slide up the probe to identify the cricoid… the biggest, most anterior pearl
Identify the string of pearls.. Slide up the probe and identify the largest , most anterior pearls the cricoid cartilage
Identify the thyroid cartilage and between the two lies the CTM. Measure the depth! In this case .. due to swelling its almost 2cm deep
Slide a drawing up needle under the probe to mark the CTM… then remove the probe and mark the skin.
We are now going to move on and examine the anatomy in transverse
The transducer is placed transversely on the anterior neck at the estimated level of the thyroid cartilage
identify the hyperechoic triangular shaped structure …the thyroid cartilage…
The superior edge of the thyroid cartilage.. has a really steep slope!
Resembling a very steep volcano
Stratovolcanoes
http://ete.cet.edu/gcc/?/volcanoes_types/
The slope of the volcano or the thyroid cartilage gradually becomes less steep..as we move the probe caudally
The slope gradually decreases and the top of the cartilage gradually becomes more rounded
And more rounded
The slope gradually decreases and the top of the cartilage gradually becomes more rounded
Until its almost a plateau… and you see the beginning of the cricothyroid membrane .. And then the beginning of a caldera or crater forming
Until .. You see the beginning of the cricothyroid membrane appearing… the airline or air/tissue interface of the cricothyroid membrane… all dependent on the anatomy of the patient
You then see the airline or air/tissue interface of the cricothyroid membrane appearing bordered on either side by the strap muscles
The cricothyroid membrane or caldera.. or crater…
Cricothyroid membrane …shown in blue
Looking like a caldera out volcanic crater
With the strap muscles forming the lateral borders of the cricothyroid membrane
If we keep on scanning inferiorly in transverse we then get to the cricoid cartilage
the cricoid cartilage
The cricoid cartilage… dark hypoechoic C shaped structure
And then the tracheal rings..
The tracheal rings… which are also hypoechoic but much thinner then the more anterior thicker and larger cricoid cartilage
The false vocal cords or vestibular folds lay parallel and cephalad to the true cords, are more hyperechoic in appearance and remain relatively immobile during phonation.
The true vocal cords appear as two triangular hypoechoic structures (the vocalis muscles), outlined medially by the hyperechoic vocal ligaments and are observed to oscillate and move toward the midline during phonation
In a study on 229 participants with ages ranging from 2 months to 81 years the true and false cords were visible in all female participants. In
males, the visibility was 100% below the age of 18 and gradually decreased to < 40% of males aged 60 or more.
Performing the transverse technique - the ‘TACA’ technique stands for: Thyroid cartilage–Airline– Cricoid cartilage–Airline – mean of 27s
(i) The transducer is placed transversely on the anterior neck at the estimated level of the thyroid cartilage, and the transducer is moved until the thyroid cartilage is identified as a hyperechoic triangular structure (Fig. 1).
(ii) The transducer is then moved caudally until the cricothyroid membrane is identified; this is recognizable as a hyperechoic white line resulting from the echo of the air–tissue border of the mucosal lining on the inside of the cricothyroid membrane, often with parallel white lines (reverberation artefacts) below.
(iii) The transducer is then moved further caudally until the cricoid cartilage is identified (a ‘black lying C’ with a white lining).
(iv) Finally, the transducer is moved slightly back cephalad until the centre of the cricothyroid membrane is identified.
(v) The location of the cricothyroid membrane can be marked both transversely and sagittally on the skin with a pen. By identifying the highly characteristic shapes of both the thyroid and the cricoid cartilages, both the cephalad and caudal borders of the cricothyroid membrane can be identified.
(i) The transducer is placed transversely on the anterior neck at the estimated level of the thyroid cartilage, and the hyperechoic triangular structure of the thyroid cartilage is identified… the transducer is then slowly moved down.. And the decreasing slope of the thyroid cartilage is noted until the airline of the CTM is identified.
Airline or Air tissue interface of the CTM is identified.. Bright hyperechoic line with reverberation artefact below it.
The probe is moved caudally until the cricoid cartilage is identified.. Dark hypoechoic lying C shaped Cartilage
The probe is then moved back in a cephalad direction and the middle of the CTM is identified and marked!
Place the tansducer transversely over the thyroid cartilage…
Identify T the thyroid cartilage… slide the transducer down and identify.. A – the airline of the CTM .. Slide the transducer further caudally and identify C - the cricoid cartilage and then angle up and identify A – the Airline
This is an example of a slightly more challenging patient…
The TACA/transverse technique is normally the better one to use here as the longitudinal technique can be much more difficult in the obese
The transverse or TACA method is much easier in the short thick neck! Here is a very short clip!
At times a prescan reveals anatomical variants or pathology that is really good to be aware of!
Sometimes we gain additional information to assist in management of the patient…Scanned in transverse from inferior to superior. Very large aberrant course ..? Brachiocephalic artery .. ??ask
Could put additional examples in here!
This is a Trauma case with direct trauma to the neck.. An example how a prescan can alter your management..
Can anyone identify the pathology?
Scanning through using the TACA method… we identify the thyroid cartilage.. Note the oedema and air anterior to the cartilage
The Airline of the CTM.. Anatomy slightly more difficult to recognise due to overlying oedema and swelling. Note the strap muscles not quiet as clear. Depth of the ctm .. Now 2 cm
The cricoid
The CTM – well visualised in long.. Note the aie above the thyroid cartilage and oedema anterior to the CTM
So what we have been advocating is doing a prescan.. prior to any airway procedure.. Especially those deemed to be difficult. If contemplating realtime needle guidance…like placing a cannula prophylactically.. We recommend the TACA technique and out of plane approach
To end off…. The CTM in long…– string of pearls technique
And in trans… The transverse/TACA technique
So.. We have gone through…
Airway anatomy in Longitudinal and Transverse using Ultrasound
Explaining the two techniques recommended to identify and mark the Cricothyroid membrane
Going through some examples of more challenging patients as we do that
Having a hands on practical session
If there is time going through the use of Ulrtrasound while intubating
