A new approach to airway assessment-"Line of Sight" and more. Recommendations of the Task Force of Airway Management Foundation (AMF).

Assessment of airway is recommended by every airway guideline to ensure safe airway management. Numerous unifactorial and multifactorial tests have been used for airway assessment over the years. However, there is none that can identify all the difficult airways. The reasons for the inadequacy of these methods of airway assessment might be their dependence on difficult to remember and apply mnemonics and scores, inability to identify all the variations from the "normal", and their lack of stress on evaluating the non-patient factors. Airway Management Foundation (AMF) experts and members have been using a different approach, the AMF Approach, to overcome these problems inherent to most available models of airway assessment. This approach suggests a three-step model of airway assessment. The airway manager first makes the assessment of the patient through focused history, focused general examination, and focused airway assessment using the AMF "line of sight" method. The AMF "line of sight" method is a non-mnemonic, non-score-based method of airway assessment wherein the airway manager examines the airway along the line of sight as it moves over the airway and notes down all the variations from the normal. Assessment of non-patient factors follows next and finally there is assimilation of all the information to help identify the available, difficult, and impossible areas of the airway management. The AMF approach is not merely intubation centric but also focuses on all other methods of securing airway and maintaining oxygenation. Airway assessment in the presence of contagion like COVID-19 is also discussed. Copyright:

Introduction

A thorough assessment of the airway is recommended by every airway guideline as the first step towards safe airway management.[12345] Although, the definitions of the difficult airway are retrospective in nature,[1] the airway assessment is proposed so that the airway manager can identify the potentially difficult airway and make necessary preparations to deal with the difficulty. However, most of the guidelines and thus airway assessment methods are mainly intubation centric. Some of the guidelines include questions that need to be answered at the end of airway assessment[13] but almost none suggests any particular way to collate all these answers so as to make the assimilation simple.

Numerous ways of conducting airway assessment have been proposed that include many unifactorial and multifactorial tests and scores.[6789101112] An approach based on assessing multiple airway features in an eleven-point table that follows the “line of sight” during conventional oral laryngoscopy is described in the American Society of Anesthesiologists (ASA) guidelines.[113] Compared to any single test, multifactorial tests and a combination of multiple unifactorial tests alter both the sensitivity and specificity of detecting difficult airway, but the outcomes are variable.[14] However, none of the airway assessment methods can ensure detection of all difficult airway situations. Even a comprehensive, detailed airway assessment that prompts the operators to look at multiple airway risk factors and document the likely areas of difficulty did not result in a better prediction of the difficult airway when compared with the “regular” airway assessment.[15]

There is a need for a user-friendly and intuitive airway assessment model that allows quick and uniform assessment of multiple factors so as to identify most of the difficult airways. If an airway assessment tool could highlight the area(s) of difficulty and their probable amenability to optimization within the available resources, it would become even more wholesome.

Based on these needs, Airway Management Foundation (AMF) proposes a new approach to airway assessment, the AMF Approach. This approach offers a step ahead of the currently prevalent methods as it prompts the airway manager to view any difficult airway in the light of not only the patient factors but also the non-patient factors. It is not merely intubation centric but also focuses on all other methods of securing the airway and maintaining oxygenation. It promotes the thought process that supraglottic airway devices (SADs) are not merely rescue devices but first-line airway management devices as well. It replaces extubation with emergence; thereby further promoting the thought process that general anesthesia (GA) can be conducted successfully without intubation as well. The model is based on an organized “line of sight” method [Appendix I] and assessment cut-offs that are based on the known predictors [Appendix II] and added cut-offs keeping the newer devices and techniques in mind. The assessment findings categorize the areas of airway management as available, difficult, and impossible; difficult being optimizable as against impossible that is not optimizable. Optimizability is dependent on the available resources at the time when airway management is contemplated. The approach thus guides the airway manager in planning the airway management strategies. Finally, the AMF approach promotes the concept of over-diagnosing airway problems and making arrangements for them, rather than missing them and getting caught unawares. An outline of what is known and what is needed in airway assessment, and what makes the AMF approach unique is depicted in Table 1.

Table 1

Outline of what is known and what is needed in airway assessment, and what AMF approach offers

What is known

Most airway guidelines recommend thorough airway assessment before airway management to identify areas of difficulty.

Most guidelines and airway assessment methods are mainly intubation centric.

Numerous unifactorial and multifactorial tests and scores are described for airway assessment.

The ASA guidelines recommend eleven points along the “line of sight” to assess for difficult intubation.

The sensitivity and specificity of detecting difficult airway are different with different tests and their combinations.

None of the airway assessment methods can ensure detection of all difficult airway situations.

What is needed

An airway assessment model that allows the identification of most of the difficult airways.

An assessment tool that also identifies the possibility of optimization of the areas of difficulty.

What does the AMF Approach offer

It prompts the assessment of patient factors and nonpatient factors.

It focuses on all the methods of securing the airway and maintaining oxygenation and consequently floats the concept of emergence in place of extubation.

It uses the AMF “line of sight” method of focused airway assessment having modified cut-offs keeping the new devices and techniques in mind.

It introduces the concept of difficult and impossible areas of airway management; difficult being optimizable as against impossible that is not optimizable.

The approach guides the airway manager to plan airway management strategies.

It stresses on over-diagnosing airway problems and making arrangements accordingly.

The AMF Approach

The AMF approach offers a unique roadmap to the airway manager to collect, tabulate, and process the information obtained during airway assessment. Since most airway assessment models only identify areas of difficulty in airway management, the AMF approach shall guide the airway manager about the management options for assessed difficulties simultaneously through its three-step approach:

Assessment of Patient

Assessment of Non-Patient Factors

Assimilation of All Assessments

Step I. Assessment of Patient

The AMF approach involves a simple and quick method to identify all the predictors of the problematic airway [Appendix II] that are present in a patient so that the likely areas of difficulty in airway management [Figure 1] can be pinpointed. It may be worth clarifying here that difficult intubation is a situation wherein laryngeal inlet is visible (i.e., laryngoscopy accomplished) yet an endotracheal tube will not pass or pass with considerable difficulty, into the trachea.

Figure 1

Likely areas of difficulty during airway management

The assessment of the patient consists of mainly three steps. The fourth step of airway ultrasonography (USG) or imaging—although useful—may not be always needed [Figure 2]:

Figure 2

Components of Assessment of Patient; Clockwise from Top Left. (GPEgeneral physical examination; USG-ultrasonography; AMF-Airway management foundation).

Focused History: history focused on detecting conditions that can have effect on airway management (diabetes mellitus, ankylosing spondylitis, rheumatoid arthritis, etc.).

Focused general physical examination (GPE): general examination focused to detect findings that can impact airway management, including considerations because of the specific patient condition (pregnancy/labor, obesity, age, etc.).

Focused Airway Examination using the AMF “Line of Sight” (LOS) Method: this approach recommends looking at multiple features along the line of sight moving systematically along the airway from parts of face and mouth to the neck.

Airway USG or other Imaging – only when needed.

The findings of all the steps of the Assessment of Patients are tabulated as shown in Table 2.

Table 2

Suggested Method of Assessment of Patient, Including the AMF “Line of Sight” (LOS) Method for Focused Airway Examination. (References in Appendix II)

Focused History	Variation	Area of Possible difficulty
Mental status, Hearing/speech, Level of apprehension, Consent	Mentally challenged, Hearing/speech impaired, Apprehensive, Refusal	Consent and Cooperation
Snoring	Present	MV
Previous Airway Event	Present	As per the event
Known supra-glottic/glottic/sub-glottic obstruction	Present	MV, SAD, Intubation
Neck irradiation	Present	MV, Lx
Tobacco/Gutka Chewer	Present	SAD, Lx
Cervical spine trauma/surgery	Present	Lx
Diabetes, Ankylosing spondylitis, Rheumatoid arthritis	Present	MV, Lx
Focused General Examination	Variation	Area of Possible Difficulty
Age	> 45 years; >55 years	SAD; MV
Gender	Male	SAD; MV
BMI (Obesity)	BMI >30 kg/m2	MV; Lx; Surgical access
Gait	Stiff	Lx
Voice	Hoarse	MV; SAD; Intubation
	Hyponasality	MV; Nasal intubation
Pregnancy	Advanced pregnancy	Lx; Intubation
	Active labor
Prayer sign	Positive	Lx
Focused Airway Examination: Line of Sight (LOS) method	Variation	Area of Possible difficulty
Nose	Deformed, Narrow nares/nasal passage, Blocked nostril(s)	Nasal Intubation
	Bilateral blocked nostrils	MV
Malar Region, Cheeks	Deformed, Masses, Flowing beard	MV
Mouth	Deformed	MV
	Microstomia	SAD, Lx
Teeth	Edentulous	MV
	Missing, bucked, loose irregular, overbite, removable false denture	Lx
	IIG <3 cm	Lx
	IIG <2 cm	SAD
Oral Cavity	MMP >2	MV, Lx
	High arched, narrow, or cleft palate	SAD, Lx
	Space occupying masses	MV, SAD, Lx
Lower Jaw	Receding, prognathic	Lx
	Injury, Mass	MV
Lower jaw subluxation	ULBT Class 3 or ULCT Class >II/III	MV, Lx
Mandibular space	TMD <6.5 cm	MV, SAD, Lx
	Poor compliance, scarring	MV, Lx
Neck swelling, deformity, gross tracheal deviation	Present	Intubation, Surgical access
Cricothyroid membrane	Impalpable	Surgical access
Neck Length	SMD <12.5 cm	Lx, Surgical access
Neck Circumference	>40 cm (F)/>42 cm (M)	Lx, MV
Head-Neck ROM	<90°	MV, Lx, Surgical access

Airway USG or other Imaging - These are indicated only in cases where the Assessment of Patient by the above method suggests the possible involvement of area(s) that could not be accessed/visualized through the clinical assessment alone. However, some airway managers use USG routinely during some airway assessments, e.g., while planning for extubation or to mark the cricothyroid membrane before planned or emergency front of neck access. BMI-body mass index; MV-mask ventilation; SAD-supraglottic airway device; Intubn-intubation; Lx-laryngoscopy; IIG-inter-incisor gap; ULBT-upper lip bite test; ULCT-upper lip catch test; MMP-modified Mallampati class; TMD-thyromental distance; SMD-sternomental distance

STEP-II. Assessment of Non-Patient Factors

After tabulating the patient factors, the AMF Approach prompts the airway manager to focus his attention on non-patient factors that may have a significant effect on airway management. Assessment of non-patient factors consists of the assessment of resources, surgical requirements, and airway manager's mindset:

Resources – Assessment of resources is crucial to plan airway management in any location. This consists of:

Assessment of manpower – Manpower not only means extra hands but also people with more knowledge and skills.

Assessment of fallback capabilities – Fallback capabilities mean availability of ICU or higher referral center if needed.

Assessment of available equipment including paraoxygenation equipment.

Equipment – a lot of optimization is dependent on the equipment that is available [Table 3].

Table 3

The AMF Suggested Method of Assimilation of Assessments to Aid Airway Management Planning

Areas	Available, Difficult or Impossible?		Optimization needed for Difficult (some examples)
Cooperation	A/D/I		Attendants/Medication*
Mask ventilation	A/D/I		OPA, NPA, Case specific†
SAD placement	A/D/I		2nd generation SAD, Preshaped SADs, Laryngoscope, Bougie‡
Laryngoscopy	A/D/I		OELM, other blades (e.g., McCoy blade), Videolaryngoscope, Fiberscope, Case specific§
Intubation	A/D/I		Stylet, Bougie, Magill forceps, Cuff inflation,[19] Case specific║
Front of neck access	A/D/I		Bandage removal, Scar incision, Ultrasound-guided
Emergence	A/D/I		Fully awake, Bailey’s maneuver,[20] AEC¶
Resources				Available?
Equipment				Yes/No
Knowledge and Skills				Yes/No
Extra hand				Yes/No
Paraoxygenation**				Yes/No
Fall back capabilities††				Yes/No
Surgical requirement				Possible?
Special patient position		Yes/No		Yes/No
Airway shared		Yes/No		Yes/No
Airway manager’s mindset				Possible?
Is intubation MUST?		Yes/No		Yes/No
Can SAD be the definitive airway device?		Yes/No		Yes/No

* - Attendant is allowed inside the operation theater to comfort the patient (for children or patients with a handicap (mentally or physically challenged); very small (¼ to ½ of the usual) dose of anxiolytic may be considered. †e.g., cling film for beard, gauze pieces to puff out cheeks, ramping for obese, etc., OPA-oropharyngeal airway, NPA-nasopharyngeal airway. ‡Bougie-guided introduction requires gentle pharyngoscopy as well.[21]. § - e.g., gauze pack for missing incisors or cleft palate, ramping for obese, etc., OELM-optimum external laryngeal manipulation. ║e.g., gauze pack for missing incisors or cleft palate. ¶In addition to these optimization options that suggest that the airway device will be removed on the table itself, the airway manager can either defer the removal of the airway device till the airway and patient have stabilized or perform tracheostomy before removal of the airway device. AEC - airway exchange catheter. **e.g., Nasal prong, Auxiliary O2 flow, High flow nasal cannula (HFNC)/ Transnasal humidified rapid insufflation ventilatory exchange (THRIVE). Please remember that paraoxygenation may be difficult or impossible in the presence of blocked bilateral nasal passages, while attempting nasal intubation in the presence of large oral swelling and in the presence of large laryngeal or tracheal swelling/foreign body. ††e.g., ICU or a higher referral center

Paraoxygenation is the broad term used by AMF for various methods of providing O2 during the attempts to secure the airway. It includes (but is not limited to) – (a) use of nasal prongs with O2 flows up to 10–15 Lpm [attached to either common gas outlet (of older anesthesia workstations) or to auxiliary O2 outlet of newer ones], also called nasal oxygenation during efforts of securing a tube (NODESAT)[216], (b) high-flow nasal cannula (HFNC)[17], or (c) transnasal humidified rapid insufflation ventilatory exchange (THRIVE).[18]

Surgical Requirements – Airway management is best tailored to meet the surgical requirements, if safely possible. Changes in airway management plan may be necessitated by patient positioning, sharing of the airway with the surgeon, surgical technique (e.g., robotic surgery, laser surgery), etc.

Airway manager's mindset – Some airway situations can be managed in more than one ways, and the final method of management is guided by the mindset of the airway manager in charge. The same is true regarding the decision to continue with an SAD after it has been used to secure the airway in an emergency of intubation failure.

STEP III. Assimilation of All Assessments

The third step of the AMF Approach is the assimilation of the findings of the assessment of the patient and those of the assessment of non-patient factors. AMF proposes to conduct this process of assimilation through a standardized method as shown in Table 3.

Once the boxes in Table 3 are filled, the airway manager is lead to clear-cut available (A), difficult (D), and impossible (I) areas of airway management, viewed in the light of not only the airway assessment findings but also those of assessment of available resources, surgical requirements, and airway manager's mindset.

An area or component of airway management is considered “impossible” when it is, or is likely to be, not optimizable within the available resources.

On the other hand, a component of airway management is labeled as “difficult” if it is considered optimizable within the available resources. The optimization skills and techniques are well known, but the important ones are included in Table 3 to make the AMF Approach and the recommendations more useful and complete.

The possibility of maintaining oxygenation during the process of airway access forms an important component of assimilation and decision-making.

This final step of assimilation paves way for a safe airway management plan for the patient and in the situation in question. Three points need to be made here: (i) with the patient's safety being the top priority, even slight doubt about the optimizability of any component should be enough to label it “impossible” and; (ii) same findings in assessment may be called “difficult” under some circumstances and “impossible” under other circumstances (depending upon available resources) or vice-versa; and finally, (iii) the AMF assimilation process promotes the concept that if used properly, SADs should be considered as definitive airway devices in many more cases than at present.

Using the AMF Approach

Let us apply the AMF Approach in a test case. A healthy 20-yr-boy with post-traumatic bilateral temporomandibular joint (TMJ) ankylosis is posted for bilateral TMJ release. There is no significant history other than a fall on the chin 5 years ago followed by gradually increasing difficulty in mouth opening. His assessment is shown in Table 4.

Table 4

Assessment of the Test Patient

Focused History	Variation	Area of Possible Difficulty
Snoring	Present	MV
Focused General Examination	Variation	Area of Possible Difficulty
All factors	None	None
Focused Airway Examination: Line of Sight (LOS) Method	Variation	Area of Possible Difficulty
Nose	None*	None*
Malar Region, Cheeks	None	None
Mouth	None	None
Teeth	IIG=0.4 cm*	SAD, Lx*
Oral Cavity	Can’t be assessed*	No comments*
Lower Jaw	Receding*	MV, Lx*
Lower jaw subluxation	ULBT Class 3*	MV, Lx*
Mandibular space	None	None
Neck swelling, deformity, tracheal deviation	None	None
Cricothyroid membrane	None	None
Neck Length, Circumference, ROM	None	None

*Features relevant to this case

As far as non-patient factors are concerned, the patient is in a tertiary care center with all the resources. The surgical team is fine with both oral and nasal routes but will keep the face turned to one side for the initial half and then turn it to the other side. Let us now tick the boxes of the assimilation table for this patient as shown in Table 5.

Table 5

Assimilation of Assessments of the Test Patient

Areas	Available/Difficult/Impossible		Optimization needed
Cooperation	Available		None
Mask ventilation	Difficult		Head tilt, NPA
SAD placement	Impossible		None
Laryngoscopy	Difficult (direct laryngoscopy impossible but nasal fiberscope-guided laryngoscopy possible)		Flexible fiberscope guidance
Intubation	Available		As needed during fiberscopy; Blind nasal (±Et CO2 guidance, Cuff inflation technique)
Front of neck access	Available		None
Emergence	Available		None
Resources				Available?
Equipment (Flexible fiberscope)				Yes
Knowledge and Skills				Yes
Extra hand				Yes
Paraoxygenation				Yes
Fall back capabilities				Yes
Surgical requirement				Possible?
Special patient position		Yes		Yes
Airway shared		No		-
Airway manager’s mindset				Possible?
Is intubation MUST?		Yes		Yes
Can SAD be the definitive airway device?		No		No

The airway manager now has a clear picture of all the factors (patient and nonpatient) to help him make airway management plan(s). If the same patient was in a center that did not have equipments and/or skills for flexible fiberscopy or if the patient was an uncooperative child, then the assimilation table would have looked different, leading to different management strategies.

Likely Outcome of AMF Approach

These AMF recommendations for Airway Assessment, through the described AMF Approach, have the potential to make airway assessment all-inclusive yet simple to remember and apply in day-to-day practice. If practiced and conducted regularly, the whole process takes less than 5 min. It is not claimed that using the method of assessment put forward in these recommendations will recognize and successfully resolve all problematic airways. However, the three-step AMF Approach is much more holistic than any available model.

The assessment and tabulation of Patient Factors [Table 2] suggested in these recommendations lead to the likely problematic areas. The non-mnemonic, non-scoring-based “line of sight” (LOS) method of focused airway assessment [Appendix I] makes assessment of the patient very easy to use because it is fully focused to find the predictors of difficulty [Appendix II] as these appear in the line of sight of the airway manager [Tables 2 and 4]. The next step of rating of the problematic areas detected during the patient assessment as ”available”, “difficult”, or ”impossible” in the light of all non-patient factors [Tables 3 and 5] provides a unique perspective to the airway manager to conduct much safer airway management than he would do otherwise. This is because while ticking the boxes in Table 3, the airway manager is compelled to think of optimization options available around him and arrange these before embarking on airway management [Table 5]. The usefulness of AMF Approach has been tested and approved by many AMF experts and members over the past nearly 10 years.

And finally, in the time of COVID-19 pandemic, a thought process needs to be nurtured wherein the airway manager is prepared to conduct airway assessment in a patient who is a potential carrier of a contagious infection that is spread by aerosol. This has been taken care of in Appendix IA, which suggests a modification of the AMF Approach under these circumstances.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.