Comparison of laryngeal mask airway CTrach™ and Airtraq^® videolaryngoscopes as conduits for endotracheal intubation in patients with simulated limitation of cervical spine movements by manual in-line stabilization

Abstract

Background and Aims:

Laryngeal mask airway (LMA) CTrach™ and Airtraq^® videolaryngoscopes are useful for endotracheal intubation in patients with limited cervical spine movements and other predicted difficult airways. We aimed to compare LMA CTrach™ and Airtraq^® videolaryngoscopes as conduits for endotracheal intubation in patients with simulated limitation of cervical spine movements by manual in-line stabilization (MILS).

Material and Methods:

This was a prospective, randomized study including 50 patients undergoing elective surgeries under general anesthesia. Patients were assigned to undergo intubation using Airtraq^® (n = 25) or LMA CTrach™ (n = 25) by an experienced anesthesiologist, while MILS was provided. Laryngoscopy and intubation were compared in terms of time taken to obtain optimal laryngeal view, successful intubation, total time, percentage of glottis opening (POGO) score, maneuvers required for optimal laryngeal view and alignment of endotracheal tube, and number of attempts and complications. An integrated score was calculated to classify the attempt as good, restricted, or poor.

Results:

Time taken to obtain optimal laryngeal view, successful intubation, and total time in both groups were comparable. POGO score >50% was seen in 25 and 21 patients in Groups A and C. Seventy-six percent and ninety-six percent in Groups A and C, respectively, had a good integrated score; 6% and 1% had restricted score; none had a poor score; and the difference between them was statistically significant (P = 0.042).

Conclusions:

LMA CTrach™ and Airtraq^® are similar with respect to time taken for obtaining optimal laryngeal view, successful intubation, and total time when used for intubation in patients with simulated limitation of cervical spine movements.

Introduction

Conventional intubation requires sniffing position for the alignment of the oral, pharyngeal, and laryngeal axes to achieve a direct line of vision from the mouth to the vocal cords. This involves flexion of the lower cervical spine, extension of the upper cervical spine, and the atlanto-occipital joint.[1,2] Although conventional intubation with a direct laryngoscope offers fastest and easiest way of securing airway in normal patients, it may not be the same in patients requiring cervical spine immobilization where direct laryngoscopy with manual in-line stabilization (MILS) is performed.[3,4,5] This technique offers a difficulty for intubation because of limitation of cervical spine movements.[6,7,8] Introduction of video-assisted intubation has made handling of anticipated and unanticipated difficult airways easier and hence has found a role in the current American Society of Anesthesiologists (ASA) difficult airway algorithm.[9,10] Airtraq^® videolaryngoscope and laryngeal mask airway (LMA) CTrach™ are two such devices that provide preformed channels to ease the passage of the endotracheal tube (ETT) into the trachea. Applications of Airtraq^® include anticipated difficult laryngoscopy, rescue device following failed direct laryngoscopy, airway management of morbidly obese patients, polytrauma patients with suspected cervical spine injury requiring immobilization, patients with limited mouth opening, and for fiberscope teaching.[11,12,13,14] LMA CTrach™ has been used in morbidly obese patients and patients with anticipated difficult airways and simulated difficult airways.[15,16,17,18] Although these devices provide excellent glottic views in difficult airway situations such as cervical immobilization, one limitation is the inability to pass the ETT into the larynx through the preformed channels with a tendency to migrate posteriorly into the esophagus.[19] Previous studies have shown that Airtraq^® when compared to LMA CTrach™ takes lesser time to achieve optimal laryngeal view as well as intubation.[14] We felt that this could probably be attributed to the fact that an additional step of check ventilation is done when CTrach™ is used, before attaching the monitor to the device. Finally, as these two devices are commonly preferred in our institution to intubate patients with cervical immobilization, we wanted to compare their performance as conduits for endotracheal intubation. Thus, our primary objective was to compare the LMA CTrach™ and Airtraq^® with respect to time taken to obtain an optimum laryngeal view, successful endotracheal intubation, and total time in patients with simulated limitation of cervical spine movements by MILS. The secondary objectives included grading of laryngeal view before and after manipulation, additional maneuvers required to optimize the view, maneuvers required to aid endotracheal intubation, and number of intubation attempts and complications.

Material and Methods

After obtaining approval from Institutional Ethics Committee, this prospective and randomized study was commenced with 50 consenting patients who were undergoing elective surgical procedures requiring general anesthesia with endotracheal intubation. Patients aged between 18 and 60 years belonging to the ASA physical status I and II were included in this study. Those undergoing emergency surgeries, with high risk of aspiration, limited mouth opening (<2 finger breadth), oral or maxillofacial pathology, known cardiorespiratory diseases, and body mass index (BMI) >35 kg/m² were excluded from this study. Patients were randomized into two groups using computer-generated random sequence. In Group A, endotracheal intubation was done under Airtraq^® visualization and in Group C, CTrach™ was used. Group allocation was concealed using sealed envelopes which were opened by the anesthesiologist who performed endotracheal intubation. There were two observers: Observer 1 performed the preoperative evaluation, performed the MILS, and recorded the observations. Observer 2 was an anesthesiologist, who was experienced with the use of Airtraq^® and CTrach™ and performed all the intubations. Experience being defined as having used both devices in >20 patients before commencing the study. On the day of surgery, all patients were monitored with electrocardiogram Lead II, noninvasive blood pressure, pulse oximeter, and capnograph. General anesthesia was induced with propofol 2–2.5 mg/kg, and fentanyl 2 μg/kg. Muscle relaxation was achieved with vecuronium 0.1 mg/kg and patients were ventilated with 2% isoflurane in 100% oxygen. After 3 min, check laryngoscopy was done with an appropriate-sized Macintosh laryngoscope blade by observer 2 and those patients with Cormack and Lehane Grade 4 were excluded from the study. Now, with the head in neutral position, cervical spine immobilization was achieved using MILS by observer 1. Standing to the left of the patient and facing him/her, both mastoid processes were grasped by the thumb and the occiput was cupped in the hands. While avoiding axial traction, forces equal and opposite to those created by the anesthesiologist who was intubating was applied so as to prevent or minimize the head and neck movement. A stopwatch was placed next to the patient's head and immediately started and required timings were noted. Endotracheal intubation was performed by observer 2 with continued MILS as per group allocation.

In Group A, preloaded Airtraq^® of size 3 for females with a 7.0 mm ETT and size 4 for males with 8.0 mm ETT inserted in the preformed channel was used after attaching the adaptor for remote wireless imaging. The blade was passed into the mouth in the midline over the center of the tongue until the tip reached the vallecula, and the epiglottis was lifted to get the glottis in the center of the view on the remote wireless monitor. Glottic view was graded using percentage of glottis opening (POGO) scale[20] from 0 to 100%. If the view was poor, that is, <25%, maneuvers such as inclusion of epiglottis with the Airtraq^® blade, rotation, or angulation were performed and the best grade obtained after manipulation was noted. This was considered the optimal glottic view. The preloaded ETT was passed into the trachea under vision and correct placement was confirmed by the passage of black line into the glottic opening. In Group C, a preloaded CTrach™ of size 3 for small adult (30–50 kg) with 7.0 mm ETT and size 4 for normal adult (50–70 kg) with 8.0 mm ETT was used. The device was inserted using one-handed rotational technique and cuff was inflated with air to achieve a “just airtight seal” or to a maximum pressure of 60 cm H₂O (maximum air volumes: size 3 = 20 ml; size 4 = 30 ml). Viewer was attached to the connector and glottic view was graded using POGO scale. If the view was poor, i.e., <25%, maneuvers such as Chandy's maneuver[21] and up-down movement were performed and the best grade obtained was noted again after manipulation and considered the optimal glottic view. The ETT was then passed into the trachea under vision.

Time taken to obtain optimal laryngeal view was recorded as time from the insertion of the device in the mouth beyond incisor to obtaining optimal glottic view on the respective video monitors. Time taken for successful intubation was recorded as time from exit of the ETT from the tip of the device to the confirmation of successful placement by the passage of the black line into the glottic opening. Total time was a sum of the above two parameters. In both groups, an attempt was considered failed if intubation remained unsuccessful or saturation dropped below 95% or if time exceeded 120 s. If an intubation attempt failed, the patient was mask ventilated with 100% oxygen and isoflurane 1.5–2%, and the second attempt with the same device was allowed with continued MILS. If this also failed, conventional intubation was performed. Complications such as the presence of soft-tissue trauma or dental trauma, blood on the device introduced or ETT on removal indicating lower airway trauma, and sore throat at 12 h were recorded. Based on the previously recorded parameters, an integrated score was calculated to summarize the secondary objectives [Table 1]. Intubating conditions were graded based on the total score as poor for a score of 5–6, restricted for a score of 7–8, and good for a score of 9–10.

Table 1.

Integrated score parameters

Based on the results obtained from a pilot study on 10 patients, five in each group, the mean and standard deviation in Group A and Group C were 51.6 ± 19.9 s and 33.9 ± 8.17 s, respectively. The sample size was determined to be 25 to detect a difference of 30 s in total time allowing for an alpha error on 0.05 and power of 80%. Continuous, quantitative data with normal distribution such as age, weight, and BMI were analyzed using independent t-test. Chi-square test was used to analyze gender, ASA physical status, ease of insertion, POGO scoring, maneuvers required for optimal laryngeal view and to align the ETT, number of attempts taken, complications, and to calculate integrated score. Mann–Whitney U-test was used to analyze quantitative data with nonnormal distribution such as time for optimal laryngeal view, successful intubation, and total time. SPSS version 20.0. Armonk, NY: IBM Corp was used to compute the above-mentioned statistics.

Results

The age, gender, ASA physical status, weight, height, and BMI in both the groups were comparable [Table 2]. There was an equal distribution of Cormack and Lehane Grades 1, 2, and 3 and no patients with Grade 4 on check laryngoscopy.

Table 2.

Demographic data

The median time for optimal laryngeal view, time for successful intubation, and total time were comparable between the two groups [Table 3]. POGO score was statistically significant in favor of Group C [Table 3]. In Group A, three patients required external laryngeal manipulation and one patient needed inclusion of epiglottis with the blade to optimize laryngeal view. Only one patient in Group C required additional Chandy's maneuver for optimization of the laryngeal view. To align the ETT, one patient required rotation of the tube and four required external manipulations in Group A. While in comparison, the maneuvers required in Group C were rotation of the tube in two and external laryngeal manipulations in five patients, respectively. Most of the patients in both groups were intubated in the first attempt. In terms of complications, one patient in Group A had blood on the videolaryngoscope and also sore throat postoperatively, whereas another patient in this group had complained of postoperative sore throat only. One patient in Group C had blood on the tip of the ETT seen during extubation. The overall integrated score was statistically significant in favor of Group C [Table 3].

Table 3.

Laryngoscopy and intubation characteristics

Discussion

In our study, we found that one of our primary outcomes of time taken for optimal laryngeal view was more in Group A as compared to Group C, which was contrary to previous study by Arslan et al.[15] We felt that the additional step of check ventilation, which is done when CTrach™ is used contributes significantly to the time taken to obtain a laryngeal view. We thus eliminated the check ventilation, as we wanted to compare the devices for their property to behave as conduits for endotracheal intubation. Accordingly, this additional time got reduced in Group C and made these devices comparable. The results achieved with reference to total time were in concordance with the study conducted by Arslan et al., although the difference was much higher in their study.[15]

In a study conducted by Liu et al., view of the larynx with LMA CTrach™ was found to be difficult as compared to the direct laryngoscopy.[22] In our study, we found out that the best possible laryngeal view using POGO score was better (>50%) with LMA CTrach™ as compared to Airtraq^® (P = 0.037). All the patients in LMA CTrach™ group had a POGO score of >50% and only one patient required Chandy's maneuver to improve the score. In the Airtraq^® group, initial POGO score of <25% was seen in four patients and application of additional maneuvers improved POGO score for two patients while the remaining two patients continued to have a POGO score of <50%. Because the CTrach™ shape is based on magnetic resonance imaging of the human airway that enables a close fit with the oropharynx and optimal alignment with the laryngeal inlet, especially after cuff inflation, the views were good. To some extent, the similarity of the CTrach™ to the regularly used proseal LMA could also have contributed to easy insertion and better placement of the device and hence better views.

Patients in both the groups were successfully intubated in the first attempt in most of the cases which is in consensus with previous studies conducted by Maharaj et al. and Swadia et al., where patients were intubated in the first attempt in a comparison of Airtraq^® and direct laryngoscopy with Macintosh blade and CTrach™ and Macintosh blade, respectively.[15,23,24] Even Bilgin and Bozkurt studied the LMA CTrach™ in patients undergoing MILS and demonstrated a higher rate of successful tracheal intubation on the first attempt when compared with the intubating LMA and McCoy laryngoscope.[25]

To summarize our secondary objectives, we used an integrated score and found that it was significantly better in the LMA CTrach™ group as compared to the Airtraq^® group. Restricted score was seen in the Airtraq^® group mainly due to the combination of poorer glottic views requiring external manipulations, maneuvers to align the ETT, and complications in the form of blood on ETT or sore throat. To some extent this could be attributed to the fact that previous studies with Airtraq^® have shown that the bulk of this device sometimes causes external trauma contributing to lower score as seen in our study.[26] Another contributing factor being migration of ETT posteriorly into the esophagus requiring external manipulation to guide the ETT from the preformed channel of Airtraq^® into the trachea. And finally, the combination of more than one factor in the same patient has made the score less in this group.

There are a few limitations of this study. We could not blind the observers who performed the laryngoscopy and provided MILS. Furthermore, the intubations were performed on patients with normal anatomy of the cervical spine with MILS in situ. Extrapolating the findings to patients with instability of the cervical spine will need further evaluation in that specific cohort of patients. Finally, our integrated score is not a standard validated score. However, as it gives an overall summation of our secondary objectives, we proceeded to apply it for this study.

Conclusions

LMA CTrach™ and Airtraq^® are similar with respect to time taken for obtaining optimal laryngeal view, successful intubation, and total time when used for intubation in patients with simulated limitation of cervical spine movements.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.