Introduction

Endotracheal intubation is considered the definitive airway for resuscitation and airway management. The Macintosh laryngoscope(MAC) is the most commonly used device for directly visualizing the structures of the larynx and facilitating tracheal intubation. In recent years, video-laryngoscopes (VL) based on the principles of indirect laryngoscopy have been introduced into clinical practice. When compared with direct laryngoscopy, video laryngoscopy can provide a significantly better view of the larynx, which is useful in situations of difficult tracheal intubation.

Naso-tracheal intubation (NTI) is often required for head and neck surgeries. Direct laryngoscopy moves the larynx upwards and elevates the glottis, which lengthens the distance between the glottic orifice and the posterior pharyngeal wall, thereby making it difficult to guide the nasally introduced tube into the glottis. Thus, it often requires the use of Magill’s forceps to align this ETT tip with the glottic inlet. Direct laryngoscopy with MAC with the use of Magill’s forceps to direct endotracheal tube (ETT) into glottic opening, is time-consuming and may lead to trauma to surrounding structures and damage ETT cuff.

The anterior angulation of the blade and placement of the video camera allow the operator to see structures that would be difficult to see under direct vision. C-MAC VL allows adequate glottic view, without the need for aligning oropharyngeal and laryngeal axes. VL creates a more direct route from the nasopharynx to the trachea, which may lead to easier and quicker nasal intubation. In addition CMAC VL has slim blade profile and edges are inclined, thus reducing the potential contact area of the blade with the upper incisors. Thus, it provides extra space for manipulating the tube during intubation. It magnifies airway view and allows supporting staff to optimise their assistance such as applying adequate external manipulation as necessary.

Previous studies have demonstrated that video laryngoscopes improve laryngeal view and ease intubation difficulty particularly in novices when compared with MAC in the routine orotracheal intubations. It has also been found that time to intubate(TTI) by experienced, as well as novices in case of orotracheal intubations with a VL, is more than that by using MAC. But in case of nasal intubation with VL the time taken by the experienced user is less than that by using MAC. There are no studies on TTI by novices for nasotracheal intubation by VLs.

Aim

The aim of this study is to compare the efficacy of the CMAC videolaryngoscope –C-blade with the Macintosh laryngoscope for nasotracheal intubation by novices in patients undergoing head and neck cancer surgeries. The primary objective is to compare the time taken for intubation using the two devices. Secondary objectives are to compare success rates for intubation and difficulty level during intubation in the two groups of patients.

Inclusion Criteria

1.     ASA  grade I/II

2.     Age group between 18-60 years

3.     Mallampatti grade I and II

4.     Patients needing nasotracheal intubation for elective head and neck surgeries

Exclusion criteria

1.     Refusal of consent

2.     Patients having risk factors for gastric aspiration

3.     Patients with previously documented difficult tracheal intubation

4.     Patients who had undergone previous head and neck surgery

5.     Emergency surgical procedure

6.     Patients with an anticipated difficult airway. Criteria for difficult airway are as follows: (2 or more)

a) Thyromental distance less than 6 cm  b) Mallampatti classification III or IV c) Inter-incisor distance less than 4 cm.  d) Jaw subluxation 0 or -1  e) Neck extension less than 90 degrees  f) Radiotherapy to head or neck region g) Limited tongue protrusion  h) Obesity – BMI more than 35  i) Buck teeth / missing incisors

Materials and Methods

Study is designed as a parallel arm, randomised controlled trial, comparing C MAC videolaryngoscope( C blade) with Macintosh direct laryngoscope.

Patient selection: Patients requiring a nasal endotracheal tube for head and neck surgeries at Tata Memorial Hospital and ACTREC will be enrolled in the study. All patients fulfilling the inclusion criteria and after obtaining informed written consent, on the day prior to surgery, will be included in the study. Patients will be randomized on the morning of surgery to either the control group (intubation using standard Macintosh blade) or intervention group (intubation using C blade of CMAC videolarygoscope) by a computer-generated block randomisation using opaque sealed envelopes. The patients will remain blinded about their intubation technique.

Randomisation will be executed in a 1:1 ratio control group( intubation using standard Macintosh blade) using permuted block randomisation (PBR) with variable block length. Anaesthesiologist will be randomly selected using simple random sampling without replacement. For 20 anaesthesiologist, 20 subjects will be randomly assigned to any of the arm using PBR after that next 20 patients will be assigned to opposite arm for same 20 anaesthesiologists.

Sample size: A pilot study showed that the mean time to intubation in novices using the Macintosh laryngoscope was 100 seconds with a standard deviation of 30 seconds. To detect a decrease in intubation time by 20 seconds using the McGrath videolaryngoscope, at 2-side 5% level of significance and 80% power, we would need to study 20 pairs of intubations. We have 20 first-year MD Anaesthesiology students each year; we plan to collect paired data for intubation using each device from each student.

Providers: The laryngoscopy would be performed by novices; these residents who had recently commenced training in anaesthesia. They will be performing under the supervision of the operation theatre consultant anesthesiologist. This is the standard of care in a teaching institute where students are trained to use both the devices under the guidance of the consultant anaesthesiologist. We have defined novices for the study - Those residents who have had done a minimum number of 5 oral intubations using the Macintosh blade and 5 oral intubations using the CMAC c blade and also less than 5 nasal intubations with either device will be considered as novices. Intubation using standard Macintosh blade and CMAC VL will be in consecutive patients by the novices.  Both the study team and anaesthesia team will remain blinded until the patient enters the operating room at which time the randomisation envelope will be opened.

Conduct of anaesthesia: Monitoring, induction, and maintenance of anaesthesia will be standardized in both the groups. In the operating room, patients will receive standard monitoring with cardioscope, pulse oximetry and non-invasive blood pressure. Nostrils are prepared by instilling 0.1% xylometazoline drops and 2% lignocaine jelly. After pre-oxygenation with 100% oxygen for three minutes, induction of anaesthesia is carried out using Inj. Fentanyl 2 microgram per kilogram and Inj. Propofol titrated to loss of response to verbal command. After confirming ability to mask ventilate, Inj. Vecuronium 0.1 milligram per kilogram is given and mask ventilation continued. The adequacy of neuromuscular blockade before intubation will be measured before intubation, using a peripheral nerve stimulator.

Intubation will be attempted 30 seconds after the disappearance of any response to train-of-four stimulation. The patients would be provided with supplemental oxygen using nasal cannula with flow at 8L/min from the beginning of intubation till the endotracheal tube is inserted into the trachea. Laryngoscopy will be attempted with blade size according to actual body weight.  Body weight equal to or less than 70 kg will be intubated with size 3 Macintosh blade whereas those above 70 kg by size 4 Macintosh blade. While in case of the CMAC VL the type C blade of size 3 will be used for body weight equal to or less than 70 kg and size 4 for body weight above 70 kg.

A maximum of two intubation attempts with the study device is permitted. Removal and re-insertion of the laryngoscope into the mouth will be considered as an attempt. Mask ventilation will be provided whenever the attending consultant anesthesiologist deemed it necessary. All outcomes will be recorded by an independent observer(research nurse) in the respective operation theatre, who is not a part of the study.

Outcome measures:
Primary outcome: The primary outcome is the time to intubation. This is defined as the time from gripping the laryngoscope until registration of three waves of expired CO2. TTI will be measured in seconds using a stopwatch. In case of repeated attempts, the stopwatch will continue to run until successful endotracheal intubation is confirmed.

Secondary outcomes included:

1.     Rate of successful intubation: Successful intubation will be defined as successful placement of the tube in the trachea within three attempts. Inability to intubate within three attempts is considered as a failed intubation, after which choice of further intubation techniques and devices will be  at the discretion of the attending consultant anaesthesiologist.

2.     Number of attempts needed for successful intubation

3.     Need for use of optimisation manoeuvres (BURP)

4.     The Cormack and Lehane grade at laryngoscopy

5.     Percentage of difficult intubations in each group: The difficulty of intubation will be graded as per the Intubation Difficulty Score (IDS) proposed by Adnet and a score of 5 and above would suggest moderate to major difficulty.

6.     The occurrence of complications (visible trauma to lip or oral mucosa or blood on the laryngoscope).

Statistics:

Data obtained will be analysed by t-test, chi-square test and Fisher exact test wherever applicable. Categorical variables will be expressed as Number of patients and percentage of patients and compared across the 2 groups using Pearson’s Chi-Square test for Independence of Attributes.

Continuous variables will be expressed as Mean ± Standard Deviation and compared across the 2 groups using unpaired t-test if the data follows normal distribution and Mann-Whitney U test if the data does not follow normal distribution. The statistical software SPSS version 20 will be used for the analysis. An alpha level of 5% will be taken, i.e. if any p-value is less than 0.05 it will be considered as significant.