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Table of Contents
REVIEW ARTICLE
Year : 2020  |  Volume : 36  |  Issue : 3  |  Page : 303-315

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


1 Department of Anesthesiology and Intensive Care, Maulana Azad Medical College and Lok Nayak Hospital, New Delhi, India
2 Department of Anesthesiology and Intensive Care, Lok Nayak Hospital, New Delhi, India
3 Department of Anesthesiology and Intensive Care, Baba Saheb Ambedkar Medical College and Hospital, New Delhi, India
4 Department of Anesthesiology and Intensive Care, ABVIMS and Dr. RML Hospital, New Delhi, India
5 Department of Anesthesiology and Intensive Care, PGIMS, Rohtak, Haryana, India
6 Department of Anesthesiology and Intensive Care, PGI, Chandigarh, India

Date of Submission09-May-2020
Date of Acceptance19-Jun-2020
Date of Web Publication15-Sep-2020

Correspondence Address:
Dr. Rakesh Kumar
C.334 Saraswati Vihar, Delhi - 110 034
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/joacp.JOACP_236_20

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  Abstract 


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.

Keywords: Airway assessment, airway management, COVID-19, line of sight, mnemonic, pandemic, paraoxygenation


How to cite this article:
Kumar R, Kumar S, Misra A, Kumar NG, Gupta A, Kumar P, Jain D. A new approach to airway assessment— “Line of Sight” and more. Recommendations of the Task Force of Airway Management Foundation (AMF). J Anaesthesiol Clin Pharmacol 2020;36:303-15

How to cite this URL:
Kumar R, Kumar S, Misra A, Kumar NG, Gupta A, Kumar P, Jain D. A new approach to airway assessment— “Line of Sight” and more. Recommendations of the Task Force of Airway Management Foundation (AMF). J Anaesthesiol Clin Pharmacol [serial online] 2020 [cited 2020 Oct 24];36:303-15. Available from: https://www.joacp.org/text.asp?2020/36/3/303/295106




  Introduction Top


A thorough assessment of the airway is recommended by every airway guideline as the first step towards safe airway management.[1],[2],[3],[4],[5] 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[1],[3] 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.[6],[7],[8],[9],[10],[11],[12] 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.[1],[13]

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 [Additional file 1]] and assessment cut-offs that are based on the known predictors [Appendix II [Additional file 2]] 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

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  The AMF Approach Top


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:

  1. Assessment of Patient
  2. Assessment of Non-Patient Factors
  3. 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

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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).

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  • 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)

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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].
    • 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)[2],[16], (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.
Table 3: The AMF Suggested Method of Assimilation of Assessments to Aid Airway Management Planning

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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 Top


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

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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

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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 Top


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 [Table 2] and [Table 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 [Table 3] and [Table 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 [Additional file 3], which suggests a modification of the AMF Approach under these circumstances.

Acknowledgement

  • Our gratitude to Dr. Raminder Sehgal for being a part of the first attempt at simplification of airway assessment nearly 17 years ago.
  • Special thanks to AMF instructors who have been using, teaching, and enriching the AMF Approach for a long time (in alphabetical order): Dr. Akhil Agarwal, Dr. Anju Grewal, Dr. Bhavna Saxena, Dr. Kavita R Sharma, Dr. Manoj Bhardwaj, Dr. Manpreet Singh, Dr. Munisha Agarwal, Dr. Nishkarsh Gupta, Dr. Ranju Singh, and Dr. SD Sharma.
  • Thanks to a large pool of AMF instructors from various institutions from all over India for their constant support and feedback. Some noteworthy among these being (in alphabetical order): ABVIMS & Dr. RML Hospital Delhi, AIIMS Delhi, AIIMS Patna, ASCCMS Jammu, BSA Medical College & Hospital Delhi, DMCH Ludhiana, ESIC Hospital & PGIMSR Delhi, GMCH Amritsar, GMCH Chandigarh, Hindu Rao Hospital Delhi, LHMC Delhi, MAMC & Lok Nayak Hospital Delhi, Medanta Hospital Gurugram, PGI Chandigarh, PGIMS Rohtak, VMMC & Safdarjung Hospital Delhi, SGRD Medical College & Hospital Amritsar, Sir Ganga Ram Hospital Delhi, SPS Hospital Ludhiana, UCMS & GTB Hospital Delhi.
  • Thanks to All AMF members for their valuable inputs from time to time.


Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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