Evaluation of Functional Dimensions of Macintosh Laryngoscope Blade During Direct Laryngoscopy in Patients With Normal Mouth Opening
Evaluation of Functional Dimensions of Macintosh Laryngoscope Blade During Direct Laryngoscopy in Patients With Normal Mouth Opening
Direct laryngoscopy and intubation is an essential initial aspect of airway access during
 general anesthesia. To perform the procedure effectively, it requires adequate mouth opening,
 head and neck movement, and a normal temporo-mandibular joint mobility. Any issue with the
 above three results in a compromised upper airway at the outset and the condition is known as
 anticipated difficult airway, i.e. an airway that is difficult to access with conventional
 laryngoscopy and intubation methods. To overcome the difficulty, either one has to resort to
 newer advanced technique and equipment or the available conventional technique needs to be
 refined and modified to suit the requirement. While the former requires extraordinary
 expertise and finances, an option difficult to achieve in developing countries; the latter
 warrants focused interest to develop alternative approach with the same set of equipments.

 Since submucous fibrosis and the associated restricted mouth opening have taken the
 proposition of an epidemic owing to widespread use of betel nut and tobacco; these patients,
 when requiring surgery, are difficult candidates for GA and airway control. The fact that,
 when they arrive as pre-surgical candidates, they have variable degree of mouth opening
 restriction, which if approached with a strategy, may be amenable to conventional control of
 airway. If investigators paint all the patients with mouth restriction as difficult airway,
 it will result in uncalled surgical, economic, health system and psychological burden.
 Therefore, it is prudent to undertake research relating to refinement of airway access
 techniques with the easily available, cheap and user- friendly equipment (conventional
 laryngoscope), such that a proportion of above stated burden can be reduced.

 In view of the above, investigators plan to undertake a study to enhance our working
 knowledge with a conventional laryngoscope (Macintosh) to facilitate ways to control the
 airway difficulty secondary to mouth opening restriction. Investigators believe that the
 prospective knowledge thus generated would help us identify whether there is a feasibility of
 conventional airway management or an alternative advanced access technique is needed in the
 first place. This will prevent undue cancellations, delayed surgeries, and patient morbidity.
Upper airway access is one of the essential components of general anaesthesia, and more often
 than not, it is gained by direct laryngoscopy followed by tracheal intubation. While direct
 laryngoscopy depends on laryngoscope blade design and the anesthetists' skill set, the ease
 of tracheal intubation is influenced by the line-of-view to the glottis gained by the
 laryngoscopy maneuver. In patients with normal mouth opening (≥4.0 cm), the act of
 conventional airway access is not difficult given that the neck extension and the TMJ joint
 mobility is within normal limits. Conversely, it becomes difficult in patients who have mouth
 opening restriction, and hence they are adjudicated as 'anticipated difficult airway' (ADA).
 The ADA, attracts several issues that, not uncommonly, converges on to time inefficiency,
 heightened equipment cost, operator anxiety, and unfortunately, patient morbidity. There are
 many causes of restricted mouth opening, defined technically as reduced inter-incisor
 distance (IID) including trauma, TMJ movement limitation, intra/extra-oral pathology
 resulting in pain, or the most common pathology in the Indian subcontinent, oral submucosal
 fibrosis (SMF). While the pathology itself is a forerunner of oral mitosis, it is the
 associated restricted mouth opening component that put conventional airway access efforts of
 the anaesthesiologist in spot, and consequently, a whole, sometimes unnecessary rigmarole has
 to be activated under the heading of 'advanced approach to ADA'.

 Oral submucous fibrosis (SMF) is a well-recognized, potentially malignant progressive
 condition afflicting the oral cavity that is characterised by a reduced mouth opening. The
 reduction in mouth opening occurs due a vertical reorientation of collagen fibrils that are
 normally haphazardly arranged. Of the currently available multiple classifications to
 identify disease stage/severity, the functional classification based on the inter-incisor
 distance (IID) seems to be most relevant.

 IID forms an important component of airway examination and a value of less than 3-cm is
 suggestive of difficulty in airway management. However, despite the above, SMF is largely
 unrecognized as a cause of airway difficulty, and even when recognized, no set protocol is
 available to ensure (as far as possible) a favourable outcome in terms of least morbidity to
 the patient, and stress to the anaesthesiology team in question.

 Need Assessment for the Study Generally, in a tertiary level centre, with all facilities at
 hand, cases with a reduced IID are normally tackled using a fiberoptic bronchoscope guided
 tracheal intubation. However, in India, the burden of this disease lies to a great extent in
 rural/suburban settings where access to a fiberoptic bronchoscope is unlikely. As a result
 these cases are referred to 'higher' centres for management. This imposes undue burden
 (logistics/ financial) onto patients and their families. Hence, there is a great need for
 anaesthesiologists working at the primary/secondary level healthcare set up to get oriented
 to this problem and be able to manage it with conventional options (direct laryngoscopy &
 intubation) available to them.

 Scientific Contention Direct laryngoscopy remains the foremost among the various techniques
 available to access the upper airway and the Macintosh blade has been the most preferred
 blade type. In order to improve direct laryngoscopy, many modifications of blade design have
 been tested/ compared with the Macintosh blade, but apparently, the clarity as to which
 laryngoscope blade is most suited for a given airway remains low. For the majority of
 practicing anaesthesiologists, the availability of different laryngoscope designs has only
 increased the hit-and-trial option for laryngoscopy.

 Since the time it was first introduced, the Macintosh blade (size 1, 2, 3, 4, and 5) has
 weathered many newer laryngoscope blade designs and stood by our side with consistent/optimal
 performance. Per se, from a technical standpoint, although shaped the same, various sizes of
 the Macintosh blade are not exactly similar, the discrepancy becomes obvious when comparing
 sizes 1, 2 with 3 & 4. Unfortunately, investigators are still unclear as to how design
 characteristics and the various sizes of the Macintosh blade impact the process of direct
 laryngoscopy. Generally, the selection of laryngoscope blade (type and sizes) is largely a
 function of individual experience and preferences. The absence of predefined parameters for
 the selection of the most appropriate laryngoscope blade for a given airway remains
 arbitrary. Apparently, an anaesthesiologist will be able to intubate an adult trachea with
 any of the laryngoscope blade, however, blade type and size selection assumes significance in
 the presence of a difficult airway.

 The three factors which influence successful direct laryngoscopy performance are:

 i) The ability to place the laryngoscope blade tip in vallecular recess and engage the hyoid
 bone. This requires an adequate length of the blade to be introduced orally to reach the
 vallecula (transition space between base of the tongue and the epiglottis) position.

 ii) The ability to displace the tongue aside for clear view to the glottic-epiglottic region
 iii) Achieving a clear line-of-sight to the glottis-opening. To ensure that the tip of the
 laryngoscope blade engages the hyoid by placement in the vallecula, an adequate blade length
 must be inserted into the oral cavity. Normally, this is easily achieved. However, when faced
 with a situation involving reduced mouth opening/inter-incisor distance (e.g.as in case of
 SMF), the length of blade that can be inserted into the oral cavity (functional length)
 becomes a function of the width of the blade's flange at the incisor point. Thus the size of
 the flange, corresponding to the width of the blade that must be accommodated in the oral
 cavity assumes particular significance in patients with reduced inter-incisor gap. Typically,
 for the Macintosh blade's curved design confers different length to its flange's glossal
 (concave) and the palatal (convex) surface, the functional width of its flange increases from
 the tip towards the heel [Figure]. Based on the degree of mouth opening restriction and the
 available IID (in cm), during preoperative evaluation, one can predict and plan how long a
 Macintosh blade length will be required and what size of the blade would suffice to be placed
 orally through the available IID.

 Hypothesis Development Marks et al, utilized an x-ray based method to devise a method to
 evaluate laryngoscope blade design during active laryngoscopy procedure. Technically, they
 found that Macintosh sizes 3 and 4 have a more refined blade design that provides greater
 degree of forward space enhancement (FSE, allows greater mandibular space for the tongue to
 be moved into) than other conventional blades (Miller, Soper, etc.). This FSE-effect gets
 further magnified with increase in functional length of the blade (the length of the blade
 inside the oral cavity during active laryngoscopy).

 Their elaborate work addressed the performance of the laryngoscope blade (size, type)
 selection in a theoretical setting. The information gleaned from their assessment offered
 valuable suggestions on optimal blade position during direct laryngoscopy and included:

 i) Mandibular space 'encroachment/enhancement' with the use of different blade types/sizes,
 and ii) 'Line-of-vision' (view to the glottis) versus 'mandibular space restriction' (space
 for tongue displacement during laryngoscopy).

 However, still, the clinical feasibility of knowledge thus gained from performance assessment
 facilitated by x-ray/fluoroscopy is difficult to translate into routine clinical practice.

 As the investigator prepares to take the conventional direct laryngoscopy process into
 difficult airway situations where the primary difficulty is due to reduced mouth opening,
 there is a need to convert theoretical knowledge into clinical suggestions. Investigators
 thus contend that unless they get accustomed with greater clarity on the use of routine
 equipments, and analyse their practical feasibility in difficult situations, the element of
 randomness and subjectivity will continue to be a setback.
Inclusion Criteria:

 1. Consenting adults

 2. Both gender

 3. Age: 20-65 years

 4. Normal preoperative upper airway evaluation and without the presence of anticipated
 airway access difficulty

 5. Patients scheduled for surgery under general anaesthesia with airway control by direct
 laryngoscopy and tracheal intubation

 Exclusion Criteria:

 1. Patient refusal

 2. Anticipated airway access difficulty

 3. Edentulous patients

 4. Patients with dental problem (missing tooth, overlap, cosmetic treatment)

 5. Vulnerable Patients: High risk situation, major surgery, extremes of age, obstetric
 patients

 6. Previously difficult airway