Endotracheal intubation is a potentially lifesaving procedure used in various routine clinical and emergency situations like trauma to the airway, head injury, facio-maxillary trauma. These patients are considered to have cervical spine injury until proven otherwise. Special care has to be taken during intubation procedure by immobilizing the cervical spine with a collar or by manual-in-line-stabilization (MILS). Difficulty with laryngoscopy and intubation arising from multiple attempts or excessive movement of neck for alignment of oro-pharyngeal-laryngeal axes may cause serious complications by injuring the vital centers located in the cervical spinal cord.

Various devices to intubate such patients have been used e.g. various supraglottic airways (1), fiberoptic bronchoscope (2), lighted stylets (3), conventional laryngoscopes or videolaryngoscopes (VLS) (4). Videolaryngoscopes have the advantage of containing miniature video cameras that provide indirect glottic view without requiring oral, pharyngeal and laryngeal axes alignment. McGrath^® and GlideScope^® are two commonly used VLS. McGrath^® is fully portable having an LCD display attached to its handle, whereas GlideScope^® has a separate viewing screen.

Lacunae in the existing knowledge

Extensive search of literature revealed that there are a few case reports or case series mentioning the successful use of McGrath^® videolaryngoscope in simulated difficult airway scenarios or cervical spine immobilization (5, 6). GildeScope^® has also proven to be useful in severe cervical spondylolisthesis (7). Recently a simulation study in manikins on the comparative evaluation of different VLS, including MVL and GlideScope^®  in trapped car accident victims (8) and immobilized cervical spine (9) have been published. However, there are no randomized controlled trials on ease of intubation, time to intubate and success rate of intubation using these VLS in patients with immobilized cervical spine.

Therefore, the present study is designed to evaluate and compare the performance of McGrath^® and GlideScope^® videolaryngoscopes with the gold standard Macintosh laryngoscope in adults with normal cervical spine undergoing elective surgeries requiring intubation of trachea and whose neck has been immobilized with the help of cervical collar. The primary outcome measure to define performance of the laryngoscope will be success rate of intubation in the first attempt. The secondary outcome measures would be time taken for successful intubation, number of attempts, glottic view according to Percentage of Glottic Opening (POGO) score (10, 11), Cormack and Lehane (C&L) score (12), difficulty in laryngoscopy and difficulty in intubation, requirement of release of neck collar and complications, if any.

AIMS AND OBJECTIVES

Aim:

To evaluate the performance of McGrath^® videolaryngoscope, GlideScope^®  laryngoscope and compare these with conventional Macintosh laryngoscope for endotracheal intubation after applying cervical collar to simulate a cervical spine injury scenario in adult patients with normal cervical spine who are about to undergo surgery requiring general anaesthesia with tracheal intubation.

Objectives:

To study and compare the following parameters using McGrath^® videolaryngoscope, GlideScope^® laryngoscope and Macintosh laryngoscope:-

·         Success rate of intubation in the first attempt

• Time for successful intubation
• Glottic view according to POGO score and C&L grading
• Number of intubation attempts
• Difficulty in laryngoscopy
• Difficulty in intubation
• Requirement of release of neck collar
• Complications, if any

MATERIALS AND METHODS

The proposed study will be conducted in Department of Anaesthesiology and Critical Care, University College of Medical Sciences & Guru Teg Bahadur Hospital, Delhi after obtaining approval from the institutional ethics committee.

Study Design:

This prospective randomized, single blind controlled trial will be undertaken after taking written informed consent from all the participating subjects.

Patient Selection:

A total of 60 patients of either sex posted for elective surgical procedures requiring general anaesthesia with tracheal intubation will be studied.

Inclusion criteria

-        Age between 18-60 years.

-        ASA physical status I-II.

Exclusion criteria

-        Patients who do not give consent to participate in the trial

-        Cervical spine disorders

-        Patients requiring surgeries of oral cavity, larynx, pharynx and neck.

Randomization and Group Allocation:

The patients will be randomly allocated to one of the three groups by using a computer generated random number table. The groups will be allocated depending on the laryngoscope selected for use.  Size of the blade and the ETT will be chosen as per standard guidelines and patient profile.

Procedure:

A written informed consent for participation in the study will be taken. Preoperative evaluation of patients will be done as per standard protocol. Airway assessment will be done and Mallampati class, thyromental distance, inter incisor gap and any restriction in flexion and extension movements of the neck will be noted. Patients will be kept nil per orally overnight before surgery, as per usual practice. Tablets Alprazolam 0.25 mg and Ranitidine 150 mg will be administered in the night before and morning of surgery with a few sips of water.

In the operating room, lead II electrocardiography, pulse oximetry and non-invasive oscillometric blood pressure monitoring will be started. Cervical collar will be applied on the patients just prior to induction of anaesthesia. General anaesthesia will be induced using morphine 0.1 mg/kg i.v. and propofol 2.0-2.5 mg/kg i.v. After ensuring successful bag mask ventilation, vecuronium 0.1 mg/kg i.v. will be administered to facilitate laryngoscopy and placement of the ETT. Capnography will be instituted after induction of anaesthesia. Laryngoscopy and intubation will be attempted under full muscle relaxation. Patients will be ventilated with 33% O₂ in N₂O and isoflurane.

All patients will be placed with head in the neutral position. Laryngoscopy will be performed by anaesthesiologists proficient in using the laryngoscope selected for a particular group taking care not to extend the cervical spine. Proficiency in using a particular type of laryngoscope shall be said to be acquired after the anaesthesiologist has performed at least 25 intubations with that particular laryngoscope. 

The laryngoscopic view will be graded according to the POGO score (10, 11) and Cormack and Lehane grading (12).

POGO score (10, 11)

The percentage of glottic opening (POGO) score represents the portion of the glottis visualized. It is defined anteriorly by the anterior commisure and posteriorly by the inter-arytenoid notch. The score ranges from 0% when none of the glottis is seen to 100% when the entire glottis including the anterior commisure is seen.

Figure 1: The percentage of glottic opening (POGO) score for representation of the portion of glottis visualized.

Cormack and Lehane Grading system (12)

Four laryngoscopic grades are described in Cormack and Lehane Grading system.

Grade I: Most of the glottis is visible.

Grade II: Only the posterior extremity of the glottis is visible.

Grade III: Only the epiglottis is seen.

Grade IV: Epiglottis is not seen.

Intubation will be attempted using an appropriately sized styletted ETT. Correct placement of ETT will be confirmed by auscultation and appearance of ETCO₂. Time to successful intubation will be recorded and ETT will be fixed after confirming equal air entry in bilateral lung fields.

Difficulty in both laryngoscopy and intubation will be rated according to the grades defined as below:

Difficulty in Laryngoscopy

If laryngoscopy is found to be difficult, increased anterior force with laryngoscope or change of blade to one size higher can be used to facilitate laryngoscopy.  A bougie can also be used as an intubating aid, if required.

Laryngoscopy difficulty score:-

Grade I: Easy Laryngoscopy without any maneuver

Grade II: Laryngoscopy requiring an increased anterior force

Grade III: Change of laryngoscope blade to one size higher

Grade IV: Change of laryngoscope blade used with an increased anterior force

Difficulty in Intubation

Difficulty in intubation will be defined by Intubation difficulty score, as follows:-

Grade I: Intubation easy

Grade II: Intubation possible with change of blade size or increased anterior force

Grade III: Requirement of Bougie for intubation

Grade IV: Requirement of release of neck collar

In case, intubation requires release of neck collar i.e., Grade IV, it will be considered as failure to intubate with the particular laryngoscope for this study purpose.

Anaesthesia will be maintained according to the standard guidelines practiced for all general anaesthesia cases.

Trauma to lips, teeth, structures in oral cavity and larynx or presence of blood on the laryngoscope blade and ETT will be recorded, if noted at the time of laryngoscopy and intubation, and just before extubation.

Number of Intubation attempts

Number of intubation attempts will be noted. If the ETT is withdrawn from oral cavity to be re-inserted, it will be counted as a new attempt. Three attempts will be allowed before the insertion is considered impossible or failed.

Time for successful intubation

Time for successful intubation will be defined as the time from start of laryngoscopy to the confirmation of successful ventilation using EtCO₂ waveform.

Failure to Intubate

When the anaesthesiologist is unable to intubate with neck collar in place and requests the removal of neck collar or there is inability to intubate in three attempts as described above, it would be considered as failure to intubate in the present study.

Other variables

The demographic variables, nature of surgery and duration of surgery will also be recorded in all the patients.

Sample Size Calculation

Considering a success rate of 100% for McGrath^® Videolaryngoscope and 59% for Macintosh laryngoscope according to a previous study in the literature (13), at 90% power and 95% confidence interval a sample of 19 cases in each group is required. Since the success rate for GlideScope^® group is not available, the same number of patients will be included in this group also. So we decided to include 20 subjects in each group.

REFERENCES

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