Efficacy of Cormack Lehane grading for intubation difficulty with three different videolaryngoscopes in comparison with macintosh laryngoscope: A Prospective randomised controlled trial

Introduction

Difficult and failed intubations are the leading cause of anesthesia related morbidity and mortality among all others¹. There are many strategies developed to assess and manage difficult intubations but still many difficul tintubation scenarios are encountered only at induction. Multiple types of indirect laryngoscopes have come into vogue and they play a major role in difficult airway algorithm^{2, 3}.

Videolaryngoscope is an indirect laryngoscope that shows non-line sight view of the larynx. All have an intense light source and fibreoptic camera built in a laryngoscope blade. Direct laryngoscopy requires alignment of oral, pharyngeal and laryngeal axis whereas indirect videolaryngoscopes require only pharyngeal and laryngeal axis to be aligned for view of glottis.

Several studies have shown that videolaryngoscopes improve the visualisation of glottic aperture in terms of better Cormack lehane⁴ grade. While one gets a better view with these equipments there is sometimes problem associated with negotiation of endotracheal tube. This is because there is no line of sight and therefore no space through which to pass the ETT. This problem is multitude in VDLs without guiding channel as it is difficult to visualise the ETT within the minimal field of vision available. Using malleable stylet to angle the ETT to the curvature of laryngoscopic blade helps in nonchanneled VDLs. Channeled VDLs are primarily dependent of manuevering the scope to appropriately negotiate the ETT into the glottis.

Extrapolating cormack lehane⁵ classification to VDLs is not applicable as glottic visualisation may not always equate to successful intubation in them. Insertion and advancement of ETT may fail despite clear video assisted visualisation. Furthermore intubation using VDLs tend to be slower due to lack of experience, difficulty with tube advancement and division of operators attention in two domains.

Intubation difficulty scores (IDSs) are typically used to indicate the difficulties of intubations with different laryngoscopes^{6, 7, 8} , although it remains controversial whether the IDS is suitable for the evaluation of indirect laryngoscopes⁹ . The optimisation manuevers to be applied for different  indirect laryngoscopes are different and hence cannot be utilised in common.

This study was therefore designed to evaluate the use of cormack lehane grading and intubation difficulty scores for assessment of intubation difficulty in three different videolaryngoscopes in comparison with direct laryngoscope.

Hypothesis: Cormack lehane grading is different with different videolaryngoscopes and is not efficient to assess the difficulty in intubation with videolaryngoscopes

The C-MAC (Karl Storz Endoscopy, Tuttlingen, Germany) is an indirect VDL that comprises of standard Macintosh blade attached to a video unit. A potential advantage of this non channelled scope is that it can be used both as direct as wellas indirect laryngoscope. The profiency of the device is also easy to acquire than other VDLs because of its usual scope design.

Airtraq (Prodol Meditec SA, Vizcaya, Spain) consists of series of lenses and an exaggerated curvature and provides high quality wide angle view of the larynx without alignment of any axis. It has a side channel for placement of endotracheal tube to facilitate an easier and faster intubation. Though it is channeled there is still possibility of passing ETT which require correcting manuevers like excess lifting or rotational movement. Despite these issues airtraq has been proven successful in multiple situations of difficult airway.

MacGrath (Aircraft Medical, Edinburgh, UK) is fully portable VDL which has disposable blade fitted over a steelcamera support with an LCD screen fitted on the top of the handle. Thelength of the blade can be adjusted to suit the patient size and use of stylet is recommended for intubations.

Methodology:

Study design: Prospective, Randomised, controlled Single centered Cross sectional study

Study Location: Nizam’s Institute of Medical Sciences, Hyderabad. Tertiary care hospital deemed University.

Study population: (Sample size) A total of 360 patients (with 90 in each group) will be enrolled.There are no studies comparing cormack lehane grading with videolaryngoscopes. A priori analysis had indicated a sample size of 90 patients in each group to provide 90% power and a 5% level of significance with effect size of 0.2.

Study Groups: Group A- Airtraq

                        Group C – C- MAC

                        Group MG – McGrath

                        Group M – MacIntosh

Study Criteria:

            Inclusion: ASA Physical status – I, II and III

                        Age: 18- 70

                        Elective surgery

                        General Anesthesia

            Exclusion: Pregnancy

                        Pediatric cases

                        Emergency

                        Anticipated rapid desaturation

                        Mouth opening less than 3 cm

Procedures under spontaneous ventilation

Study Procedure:

After obtaining institutional ethics committee approval patients will be recruited for the study and informed consent will be obtained. Preoperative assessment and premedication will be based on the institutional protocol. On the day of surgery, patients will be connected to monitors like eelctrocardiogram, pulse oximetry and non invasive blood pressure monitors. An intravenous cannula will be secured and connected to fluid. Patients will be premedicated and induced as per the wish of the intubating anesthesiologist. Mask ventilation will be checked and graded accordingly before muscle relaxant. At the end of three minutes, the assigned laryngoscope as per randomisation is inserted in the oral cavity. The Cormack lehane grading is announced by the intubator followed by intubation. Closed circuit will be connectedto the endotracheal tube and the tube postionwillbe confirmed by end tidal carbondioxide trace and auscultation. Anesthesia is maintained as per the institutional protocol in the intraoperative period.

Parameters studied:

Airway parameters: Mouth opening

            Mentohyoid distance

            Thyromental distance

            Sternomental distance

            Neck circumference

            Neck movements

            Intraoral pathologies

            Pathologies in neck

Airway management:

            Mask ventilation grading: grade 1-Ventilated by mask

                        Grade 2- Ventilated by mask with oralairway / adjuvant

                        Grade 3- Difficult ( Inadequate/unstable/ Requiring 2 people)

                        Grade 4- Unable to mask ventilate

            Type of equipment used for intubation

            Time taken for Laryngoscopy- Time frominsertion of blade between teeth until the anesthesiologist had obtained the best possible view of the glottis

            Time taken for intubation- Time from best visualisation of glottis to ETT placement through the vocal cords as evidenced by visual confirmation.

            Cormack Lehane grade-

            Intubation Difficulty Score –

            Use of Stillet/ Bouggie-

            Total number of passes of the ETT in the direction of cords

            Position of glottis where the ETT hitches whenit is unable to pass the ETT

            Any change in the scope used,If so why?

Intubation Grading: depending on the manuevers used which are Laryngeal pressure, Bouggie / Stillet, Changes in head or scope position to bring glottic aperture to the centre of the field.

            Grade 1- No manuevers

            Grade 2- 1 manuever

            Grade 3- 2 Manuevers

            Grade 4- 3 Manuevers

Complications:

            Desaturation to less than 90%

            Trauma / Bleeding in the airway

Esophageal intubation

Failed attempt- a) If anesthesiologist felt it clinically appropriate to abandon test laryngoscope and use an alternative device

            b) Trachea was not intubated in three attempts with selected laryngoscope

The ease of intubation was measured by asking every student to evaluate the ease of his intubation attempt for each device using a linear scale (0 = easy, 10 = difficult).

Statistical analysis:

The data will be recorded and statistically analysed using SPSS software version 17.

References:

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