Januari 04, 2017
hi, my name is keith greenland. i'm a fellow of the australian and new zealand college of anaesthetists and also a fellow of the hong kong college of anaesthesiologists. i received an md from the university of queensland in april 2011 on a thesis based on my new approach to diffficult airway management. this film clip is one of a series that i've produced based on the work i've been doing over the last seven years this particular lecture is titledreinventing our approach to direct
laryngoscopy. it takes a number of concepts that have beenpreviously described in other film clips and puts it together in an overview of how i've approached airway management. the two concepts i would like to cover in this lecture is first of all, the model for direct laryngoscopy and tracheal intubation and the two-curve theory.
firstly, the model for direct laryngoscopy was the actual foundation for the lecture i gave on airway assessment. this is an important model for understanding airway configuration and has a direct impact on the new concept which i'll be talkingabout which is the two-curve theory. but let's just revise what we know about the model here we have a patient, a diagram of a patient with the
pillow underneath the head and extension of the upper cervical, so wehave the sniffing position the head and neck positioning is a critical phase and revolves around the cervical spine this is the sniffing position, but anaesthetists also have to have to understand the principles of for instance the neutral position no pillow
vertical gaze, as in manual in-line neck stabilisation equally they should understand even positioning outside their own specialty for instance, ent surgeons will have no pillow and a shoulder bolster underneath the shoulder when they are performing microlaryngoscopy in a suspension laryngoscope using a suspension laryngoscope, so one needsto understand
all aspects of head and neck positioning and a concept or theory that covers all these airway configurations in different head and neck positions iscritical to a fundamental understanding of airway management. let's just look at, in the sniffingposition first of all, we have flexion of the lower cervical and extension of the upper cervical
as i said this revolves around the posterior column or the cervical spine once we have the patient positioned then we open the mouth, put the laryngoscope along the floor of the mouth and pull up on the mandible and submandibular tissues, the tip of the blade will sit in the vallecula
and pull up on the hyoid producing tension on the hyo-epiglottic ligament and lifts the epiglottis. this really revolves around the dynamic phase and the anterior column, the mandibule and submandibular tissues finally there is the middle column the airway passage itself, which has
it's own intrinsic problems for instance foreign bodies, perilaryngeal tumours, epiglottitis or have been, may also be influenced byabnormalities of the anterior and posterior column this is another format for the model, the anterior, middle and posterior columns the mandible and sumandibular tissues the airway configuration and the cervical spine
but lets for instance just start with the posterior column, the static phase the cervical spine itself there are abnormalities, as i said, manual in-line neck stabilisation ankylosing spondylitis where there is an impact on the the difficulty of laryngoscopy due to the cervical spine abnormality we stand at the top of the bed this is our traditional approach to direct laryngoscopy
the important aspect of for instance thesniffing position is the extension of the upper cervical this is because we stand at the top of the bed if you look at ankylosing spondylitisfor instance patients have that condition flexion of the lower cervical and even to some degree, flexion of the upper thoracic but it's the lack of the extension of the occipito-atlanto-axial complex that leads to difficulties. so its the extension of this
upper cervical that's critical. the extension occurs mainly at the between the occiput and c1, butthere is some extension between c1 and c2 and so what governs this is often the gapbetween the occiput and c1 spine and to some degree the c1 - c2 gap this covers whether the patient is in thesniffing position for anesthesia or hyperextension for suspension laryngoscopy.
the alignment of the axes and the position of the head and neck was actually taught as the "three axis alignment" theory the oral axis, the pharyngeal axis and the laryngeal axis. these diagrams have been taken from miller in 2005 but similar diagrams appear in justabout every airway review article or book for anaesthesia and emergency medicine and icu.
the top diagram looks at theneutral position and then going down to the lower diagram with the sniffing position where the axes start to line up. these diagrams are a reflection of the diagrams fromthe original article in the 1940s by bannister and macbeth they
took soft tissue x-rays and projected axes onto a diagram that they drew from the soft tissue x-rays so in this case, they had the axes of the larynx, pharynx and mouth. we can see in the top diagram theneutral position no pillow, vertical gaze there is not much of alignment but as we go to the sniffing positionhead lift and extension of the head back we have complete alignment, especially witha laryngoscope in place.
now the three axis alignment theory ispart and parcel of just about every airway textbook the problem occurred though, when adnet came out with a study in 2001 in anaesthesiology and took mris and drew in the axes and found that there was very littlealignment of the axes. in the top diagram the neutral position, in the bottom diagram the sniffing position there is actually very little
in the way of alignment if you look at the neutral position between bannister and macbeth, and adnet there is good correlation with thediagram but the sniffing position shows there is a major problem withthe theory and in fact if you look down from, in theadnet column, from the neutral position to the sniffing position there'svery little change in the alignment of those axes. this is even more so if you look at thediagrams from miller
or other diagrams in textbooks where the pharyngeal axis is markedly different from what occursin real life. so is this unreasonable? probably not. you got to remember that these axes are justsimply proposed by two workers in 1944. there is no anatomical boundary here, these are just simply concept axes.
so where does the pharyngeal, laryngealand mouth axis actually fall? this is quite a debatable point. so the fact that they can be drawn indifferent positions obviously leads to the controversy we have so what i would suggest is that wejust forget about straight lines and look at what the airway configuration truly is and really it is curves.
this is an mri of myself in the neutralposition, no pillow vertical gaze and we have the oropharyngeal curve going around up to the glottis and down to the trachea. what i would suggest is that we break this into two. the primary curve, which is the oropharyngeal curve and the secondary curve the pharyngo-glotto-tracheal curve the point of inflection, where thesecurves change
is probably around about the base of the epiglottis so what we have here if we put in aproposed line of sight is a grade three intubation, this often occurs with manual in-line stabilisation. this is because the vestibule that is the area above the glottis to the tip of the epiglottis
is the axis is facing, is running upwards so we got the glottis above the epiglottis this "axis to the vestibule" is really almost the same as the "tangent to the point of inflection", that is the point between the primary and secondary curve. this is why for instance we need external laryngeal pressure
to drop the glottis down to swing the axis, the green arrow to run downwards so we have a line of sight. it starts to line up with the line of vision let's look at what happens when we dohead lift. if we take the curve from the last diagram put it down and see how this changes
what happens is that the secondary curvestarts to flatten the primary curve remains the same. this is just with head lift. when we go to head lift there is also now,because we have flattening of the secondary curve, flattening of the "vestibule axis" or the flattening of the "tangent to the point of inflection" and we start now getting a grade one or grade two intubation. i might say that is an mri
scanner and the amount head lift here is fairly limited. there was about seven centimeters inthis case with myself but in fact with a decent size pillowone would expect in fact that flattening would be even more of the secondary curve and the green arrow would be pointing downwards so more in line with the line of vision so that's just head lift what happens with
the sniffing position that is headlift and now we're extending the head back again we take the airway curve from the neutral position put in on to the diagram and see what changes now we've got flattening of the secondary curve as well as flattening of the primary curve, so in summary extension causes flattening of theprimary curve alone headlift
causes flattening of the secondary curve now we need a laryngoscope in to the mouth to flatten the primary curve completely to get successful laryngoscopy. our vestibule axis somewhat horizontal and if there was more head left, probablydownsloping so we are now looking at a grade one or grade two intubation, with laryngscopy
for completeness let's just look at the extension position, this is the position where ent surgeons do suspension laryngoscopy, that is no pillow often a shoulder bolster and extension only. what would we predict? because there is no head lift the secondary curve should remain the same because there is marked extension of thehead and neck
on the upper cervical you get flattening of theprimary curve and this is exactly what happens. we have really no effect on thesecondary curve and flattening of the primary curve. our line of sight now, i might say, becuase of the lack of head lift is now flat or flatter that's why ent surgeons sit down when they're performing suspension laryngoscopy.
anaesthetists stand because of the head left and the rotation of the head we need to stand to get a line of vision. but going back to the ent surgeons with suspension laryngoscopy we've got flattening ofthe primary curve alone no effect on the secondary curve
an upsloping vestibule axis and ofcourse we need external laryngeal pressure, this is almost mandatory for suspension laryngoscopy, that they requiresomeone to push down on the neck to rotate that green axis downwards. now what happens with airwayconfiguration in different patients is also critical. what we were talking about before was just the normal now we have to also look at the abnormal; whether it's retrognathia,
short neck, increased submandibular tissues. let's for instance look at a condition common, very common now, obesity here we have a woman with one pillow. this is now the "ramp position" theposition recommended for obese patients this was proposed by collins and where we're looking at the external meatus level with the sternal
notch. this often requires two pillows underneath the head and one underneath the shoulders. why does it require that? if you just put two pillows underneath the head we have a confounding issue. if we just put two pillows underneath the head we have now adequate head lift but we have now, probably, a fixed flexiondeformity, one could say.
the head rotates forwards so the third pillow, or the third bolsterunderneath the shoulders is an important part of the ramp position to provide extension of the head and neck backwards. now the external meatus level with the sternalnotch are simply just secondary markers to understand the process of airway configuration and head neck position
one has to look at what these secondary markers truly indicate if we take a look at for instance theneutral position and we look at the external meatus here and go down to the midline it projects down to the clivus. is not really directly related to theairway but it is just behind the nasopharynx
the nasopharynx is now below the glottis and the sternal notch. if we look at the sniffing position, here we have the external meatus projects down
to the clivus, the bony buttress behind the sphenoid this again obviously is behind the nasopharynx, but now the nasopharynx is above the glottis and the sternal notch. this red arrow is reminiscent ofthe green arrow the "vestibule axis". now this is in non obese
patients, these mris but what we're talking about here isthe external meatus the clivus, the nasopharynx, the glottis and the sternal notch, all will not change with obesity they will have the same relationship. so we now have an idea of what thesniffing position really is about the external meatus level with the sternal notch are secondary markers indicating
or the vestibule axis being downsloping. let's have a look at the anterior column as i said the anterior column is the submandibular tissues as well as the mandible issues really revolve around a number ofproblems commonly there is a problem with lack of volumeof this space retrognathia for instance
lack of compliance of the tissues for instance radiotherapy the submandibular tissues or ludwig's angina or problems with the actual the column itself being fixed and that will be often tmj dysfunction that would befor instance ankylosis of the tmj or a fracture through the tmj fromtrauma but the first two are the most common
volume and compliance let's have a look at volume there is an absolute reduction in volumethat occurs this is what we're talking about this is what we are drawing forward an inverted triangular pyramid tmj to tmj to the incisor and the apex of this inverted triangular pyramid is the hyoid
this is what we need to draw forward with our laryngoscope to get a line of vision over the axillary teeth to the glottis so when we're assessing this we need to look at the incisor to hyoid distance, but this is very hard to assess at the bed side
but what we can assess is the thyromental distance which fortunately correlates reasonably well with the incisor to hyoid there's the tmj to incisor which correlates well with the mandibular length as in retrognathia and the tmj to tmj whichcorrelates well with the narrowness of the palate so if we look at two aspects, first of all is there is theabsolute and relative, which i will mention in
a moment the short mandible this is the component where there is a lack of volume there is the short thyromental distance or short incisor-hyoid distance this often correlates with a retrognathia as well poor development of the mandible
which still causes a lack of volume and finally narrowness of the palate lack of room for a laryngoscope and tube to get a view and just simply lack ofvolume there to move things out of the way there is what i call relative reduction in volume first of all this often due to bucked teeth why is bucked teeth a problem?
well, bucked teeth are not just related to the front two incisors often the full front incisor, the secondary incisor and canines are the problem when we put a laryngoscope in and lift up the mandible the laryngoscope blade often comes close tothe front two incisors but our line of vision is not over those incisors butoften over the canines, or the second secondary incisors but these are often all
protruding in patients with bucked teeth what happens here is that the mandibleis a normal size but we need to pull that mandible and submandibular tissues further forward than normal to get a line of sight so that causes the problem any abnormal
prominent teeth will give us a problem with simply a line of sight over that area so in a way they are acting like a retrognathic patient the corrollary of that is no teeth that is to say, that when you have no teeth,you don't have to pull the mandible and submandibular tissues forward as much and you get a better chance of getting a view. this is an important concept becausereally in the end
patients often have a variety of problemsthat may lead to a difficult airway. some degree of restricted neck movement,some degree of retrognathia, some degree of poor compliance with the submandibular tissues for instance. if you had no upper maxillary teeth then this mitigates a lot of theproblems that may be occuring, and makes laryngoscopy easy. second aspect of relative retrognathia
is just simply the large tongue, macroglossiaof acromegalics which can be difficult from many aspects but anyone in the normal population can have a large tongue. this is just simply a larger bulk thatdoesn't mean that compliance is an issue or the volume is an issue, absolute volume's an issue it's just a bulky tongue to get out of the way. let's just look at the compliance, reduced compliance now.
this gentleman had a biopsy of histongue and then he had a reactionary hemorrhage later and now he has a tongue that'snon-compliant, this is now becoming what was a very easy intubation is now a very difficult so the volume is all right but the tissues are non-compliant they dont move when you lift up as i've said, radiotherapy to the submandibular tissues
ludwig's angina these sort of conditions lead to poorcompliance now the middle column the middle column is a much more difficult area to assess and to visualise these conditions, for instance, the foreign body on the right hand side and epiglottitis is on the left
are just typical of intrinsic issues of the middle column there is no disruption of the airway, it is distorted and this can be quite a problem to both assess and manage. so what we're looking at here is really
three columns the cervical spine and the impact that has on the airway configuration the anterior column retrognathia large tongues, poor compliance of the submandibular tissues, for instance and the middle column so the anterior and posterior columns can impact on the
middle column but the middle column with having foreign bodies, epiglottitis, perilaryngeal tumours, can have its ownintrinsic problems. so the whole concept or airway management has to rest on a firm foundation of what i feel two important themes, first of all, the columns and second of all, the two-curve theory
so then when we have presented with patient who is difficult we need a diagnosis after all difficult airway is a manifestation of a cause, an etiology our airway management has to be tailored to that particular cause. in the end we need a close relationship,a close understanding of these two
very important concepts if we're gonna successfully managedifficult airway. the idea often is that we approach difficult airwayfrom the equipment point of view, that we are looking at airway management and looking for a device that's thepanacea of all difficult airways this is a flawed approach
airway management like every aspect of medicine should start with a diagnosis andlead to a treatment. you don't look for a treatment whichwill solve all your problems, when the cause of the problems are so varied. so we need to have an airway concept that is universal
and adapts to all aspects andincorporates all airway devices so what we're looking at here is a new approach from the ground up. as einstein said "we cannot solve ourproblems with the same thinking we used when we created them."
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