Comparison of GlideScope video laryngoscope with Macintosh laryngoscope in adult patients undergoing elective surgical procedures

Abstract

Background:

GlideScope (GS) is a video laryngoscope that allows a real-time view of the glottis and endotracheal intubation. It provides a better view of the larynx without the need for alignment of the airway axes.

Aim:

This prospective randomized comparative study is designed to compare the intubation time, hemodynamic response, and complications associated with intubation using a GS or Macintosh laryngoscope (ML) in adult subjects undergoing elective surgical procedures.

Materials and Methods:

Sixty American Society of Anesthesiologists physical status 1–2 patients were included in this prospective randomized comparative study. Patients were randomized to be intubated using either a GS or an ML. The primary outcome measure was the intubation time. The secondary outcome measures were the hemodynamic response to intubation and the incidence of mucosal injury.

Statistical Analysis:

Mean and standard deviation were calculated for different parameters under the study. The observed results were analyzed using Student's t-test for quantitative data and Z-test of proportions. P<0.05 was considered statistically significant.

Results:

Intubation time was longer in GS group (45.7033 ± 11.649 s) as compared to ML (27.773 ± 5.122 s) P< 0.0001 with 95% confidence interval (95% CI) −13.2794 to −22.5806. GS provided better Cormack and Lehane laryngoscopic view (P = 0.0016 for grade 1 view) with 95% CI −0.1389 to −0.5951. GS group exhibited more laryngoscopic response than ML group with more increase in blood pressure and heart rate, but the difference was not statistically significant. More cases of mucosal trauma were documented in GS group.

Conclusion:

Use of GS to facilitate intubation led to better glottic view but took a longer time to achieve endotracheal intubation. GS was associated with more hemodynamic response to intubation and mucosal injury in comparison with an ML.

INTRODUCTION

Video laryngoscopes are indirect laryngoscopes that do not provide a line of sight visualization of the larynx. GlideScope (GS) is one such video laryngoscope developed by John Pacey, a Canadian surgeon.[1] It has a high-resolution camera and light source embedded within the laryngoscope blade, which is bent through 60° at the midline and is available in four different sizes.[1,2] A view of the patient's larynx is projected onto an external liquid crystal display screen mounted on a separate stand. The camera situated at the distal tip of the GS provides an improved view of the glottis without the need for anterior displacement of the lower jaw.[3,4]

Despite a better glottic view displayed by the GS as compared to the conventional Macintosh laryngoscope (ML), there is a problem in manipulation of the endotracheal tube (ETT) into the larynx as the angle through which the ETT has to turn to enter the larynx is more acute than with the conventional laryngoscope and there is reported incidence of airway trauma with the GS.[1,5] To overcome this problem, GS is sold with a malleable stylet angled 60° at the tip. This enables the user to position the ETT anterior enough, to insert into the trachea.

Various studies[2,3] compared intubation using a GS with other laryngoscopes which show that GS provides a better glottic view when compared to ML. Our study was intended to determine if this improved glottic view translates into shorter intubation time and better hemodynamics. The primary outcome measure was the intubation time. The secondary outcome measures were the hemodynamic response to intubation and the incidence of mucosal injury. The aim of our study was to compare the intubation times, hemodynamic response to intubation, and complications associated with the use of GS and ML. We hypothesize that intubation with a GL is associated with longer intubation times and more hemodynamic response than with the conventional ML.

MATERIALS AND METHODS

After obtaining Institutional Ethical Committee (NRI Academy of Sciences) approval and written informed consent, 60 adult American Society of Anesthesiologists physical class 1–2 patients aged 18–65 years of either sex, posted for surgeries under general anesthesia between July 2015 and September 2015 were included in this prospective randomized comparative study. Patients with known coronary artery disease, airway pathology, and patients who needed rapid sequence intubation were excluded from this study. Patients were randomly allocated to two groups GS (Portable GVS^®, Verathan Medical, Canada) or group ML of 30 each. The allocation sequence was generated by a random number table and group allocation was concealed in sealed opaque envelopes, which were not opened until patient consent had been obtained. The sample size was calculated using a pilot study. All the intubations were performed by anesthesiology resident undergoing training, who have done a minimum of 50 intubations using Macintosh blade and 10 intubations using GS. For obvious reasons, it was not possible to blind the residents performing the intubation to the intubation device used by them.

Following placement of standard monitors and intravenous access, all the patients were preoxygenated with 100% oxygen for 3 min and received glycopyrrolate 5 μg/kg. Anesthesia was induced with 0.02 mg/kg midazolam, 1 μg/kg fentanyl, and titrated doses of propofol until the loss of verbal contact. Vecuronium bromide in a dose of 0.1 mg/kg was administered to facilitate endotracheal intubation and anesthetic depth was maintained with mask ventilation using 1% sevoflurane in oxygen until tracheal intubation. Endotracheal intubation was attempted 5 min after the administration of neuromuscular blocker using a cuffed ETT of internal diameter 7 mm for females and 8 mm for males. A “J” shaped stylet bent through 60° was inserted into the ETT to facilitate intubation in GS group. The parameters documented during the study were the time to achieve endotracheal intubation (intubation time) and Cormack and Lehane laryngoscopic grade(CL). Requirement of external laryngeal pressure to facilitate glottic visualisation and the number of attempts required to secure the endotracheal tube were also recorded. Intubation time was the time from introduction of the laryngoscope blade into the mouth to the visual appearance of ETCO₂ trace the following intubation. Postinduction and immediate postintubation and 3 min postintubation noninvasive blood pressures and heart rates were recorded. The presence of blood on the laryngoscope tip to detect the presence of mucosal injury and the incidence of sore throat after extubation were documented. Intubation was stopped and bag and mask ventilation commenced, if laryngoscopy exceeded 120 s, or if the oxygen saturation dropped to below 90%, or if the handle of the laryngoscope was removed out of the mouth to facilitate proper insertion. Patients were mask ventilated for 1 min with 1% sevoflurane in oxygen between the attempts if more than one intubation attempt was required. After successful intubation, the cuff of the ETT was inflated with air to a pressure of 20 mm Hg using a manometer. Anesthesia was maintained with 1% sevoflurane in 50% oxygen and 50% nitrous oxide thereafter. After 3 min of data collection, subsequent anesthesia management was according to the discretion of the anesthetist.

Statistical analysis

MedCalc statistical software (Trial version 13.3) was used to analyze the data. The demographic data analysis, such as differences in average age, and weight between the control and transversus abdominis plane block groups, was tested with an unpaired two-tailed Student's t-test. The difference between two independent samples was tested. Summary statistics, mean, and standard deviation were calculated for different parameters under the study. Data were statistically described as frequency (number of cases) when appropriate. The observed results were analyzed using Student's t-test for quantitative data or Z-test of proportions. P <0.05 was considered statistically significant. The power of the study was calculated using the difference between the mean intubation times between the two groups. To attain a 99% power of the study, with an assumption of α error of 0.05, the sample size was calculated to be 19 patients in each group.

RESULTS

A total of 61 patients were included in the study. One patient was excluded from the study due to failed intubation after three attempts with GS and he was intubated with ML using a gum elastic bougie. The study population was divided into two groups ML and group GS with 30 patients in each group. Both the groups had comparable demographic variables [Table 1]. Sixteen patients in GL group and 19 patients in ML group had Mallampati class 1 airway score. Eleven patients in GS group and eight patients in ML group had Mallampati class 2 airway score. Three patients in GS group and two patients in ML group had Mallampati class 3 airway score. No patient in GL group had a Mallampati class 4 airway score in contrast to one patient from ML group [Table 1]. The mean intubation time was significantly less in group ML (27.773 ± 5.122 s) when compared to group GS (45.7033 ± 11.649 s) with a P < 0.0001, 95% confidence interval (95% CI) −13.2794 to −22.5806 [Table 2]. Patients in group GS had a higher rise in mean systolic, diastolic, mean arterial pressures, and heart rates immediately, and 3 min after intubation but the difference was statistically insignificant. Whereas the mean postinduction blood pressure was more in ML group though the difference was not statistically different, indicating that GS intubation led to an increased rise in blood pressure and heart rate [Tables 3 and 4]. Significantly more patients in group GS had grade 1 CL laryngoscopic view (27 patients) as compared to group ML (16 patients) P = −0.0016 (95% CI −0.1389 to −0.5951). Two patients from GS group and 10 patients from ML had grade 2, CL glottic view. Only one patient from GS group hah grade 3, CL glottic view against four patients in ML group [Table 5]. Requirement of external laryngeal pressure to facilitate endotracheal intubation was significantly more in group ML (12 patients) as compared to group GS (four patients) (P = −0.0195), 95% CI 0.4907–0.0433 [Table 5]. Four patients in group GS required the second attempt to facilitate glottic visualization and intubation, whereas all the patients in group ML were intubated at the first attempt. No patient from either group required more than 120 s for laryngoscopy nor had a drop in oxygen saturation below 90% requiring mask ventilation. Four patients in group GS exhibited blood stain at laryngoscope tip and no patient in group ML had this complication. More patients in group GS (eight patients) had a postoperative sore throat as compared to group ML (10 patients) but the difference was not statistically significant P = −0.5746 (95% CI 0.1648 to −0.2988) [Table 5].

Table 1.

Demographic data in ML and GS groups

Table 2.

Intubation time with ML and GS

Table 3.

Hemodynamic variables (SBP, DBP in mm Hg) in ML and GS groups

Table 4.

Hemodynamic variables (MAP in mm Hg, HR in beats/min) in ML and GS groups

Table 5.

Conditions for intubation and mucosal trauma with ML and GS

DISCUSSION

Our study demonstrated that a longer time was required for endotracheal intubation using a GS when compared to ML (primary outcome measure) which could be due to the time required to negotiate the ETT through the vocal cords, even though the GS provided a better glottic view. The exaggerated curvature of the GS blade with enhanced optics, offers the advantage of being able to “look around the corner,” allowing better view of the glottis without having to align oral, pharyngeal and laryngeal axes. Improved glottic view with GS does not necessarily translate to shorter intubation time, as it does not provide line of sight view of the glottis, in contrast to a direct laryngoscopy. More number of patients in ML required the application of external laryngeal pressure to facilitate glottic visualization, but waste intubated in a shorter time. Proper positioning of the GS took more number of attempts and required removal and repositioning in more number of patients when compared to ML group. Hemodynamic response to layngoscopy and intubation was more in GS group though the difference was not statistically significant (secondary outcome measure). Mucosal injury was more in GS group than the ML group.

Our study results were comparable to results of previous studies that reported improved glottic visualization and better CL view with GS when compared to ML.[2,6] Even when a grade 1 or 2 CL laryngoscopic view is obtained with the GS, intubation may not be possible in the first attempt.[1] Trauma to the oral structures is reported to be high with GS. This emphasizes the need for constant visual assessment of the tip of the ETT under direct vision during the initial oropharyngeal insertion, as well as during subsequent advancement of the tube.[1] Our study showed that GS do not possess an added advantage over an ML for endotracheal intubation in patients with uncomplicated airways when intubations were performed by trained residents. However, better glottic visualization provided by GS might aid in difficult intubation scenarios and may prove useful in intubations performed by minimally trained medical and paramedical professionals. This directs the need for further studies in such subsets.

Various studies by experienced and novice users, in patients with normal and difficult airways, in adult and pediatric patients have compared GS with direct laryngoscopy.[7,8,9] Because of a short learning curve and enhanced user satisfaction and in minimally trained interns and paramedics, who do not routinely perform endotracheal intubations, GS is supposed to be useful in medical and paramedical training in emergency departments.[3,9]

In a randomized clinical trial by Sun et al., the majority of patients showed improvement in the CL grade (P < 0.001) obtained with the GS, when compared with ML. The mean time to intubate was 30 s in the direct laryngoscope group and 46 s in the GS group. The time to intubate for CL grade 3 was similar in both groups, being 47 s for the direct laryngoscope group and 50 s for the GS group, respectively.[2] A study by Solimana et al. compared GS with ML in 100 adult patients undergoing cardiac surgery and found a higher catecholamine levels after the use of GS. They also demonstrated a longer intubation time, more intubation response, and mucosal trauma in GS group.[10] The difference in the hemodynamic response to intubation was statistically significant between the GS and ML groups in contrast to our study where though the two groups varied in the hemodynamic response to intubation with more increase in blood pressure and heart rate in GS group, the variation was not statistically different. GS was found to be useful in patients with anticipated difficult intubation with restricted cervical spine mobility.[8,11,12] Bathory et al. evaluated tracheal intubation in patients having their cervical spine immobilized by a semi-rigid collar and head tapped to the trolley and concluded that GS gives a better CL laryngoscopic glottic view compared to ML and a high intubation success rate without clinically relevant injuries.[11] A randomized clinical trial by Malik et al. showed that GS and Airway Scope laryngoscopes required more time but reduced intubation difficulty and improved glottic view over the ML when used in patients undergoing cervical spine immobilization.[12]

Ibinson et al. compared GS with a direct laryngoscope using a propensity score-matched analysis and had a greater first-attempt success rate with a GS than a Direct laryngoscopy (Macintosh or Miller blade). GL was found to be 99% successful for intubation after the initial failure of direct laryngoscopy, however at the expense of a higher rate of minor mucosal injury. The intubations were performed by anesthesiologists, nurses, or trainees.[6] The competency of the intubating person might have affected the results. This could be due to the fact that direct laryngoscopy generally requires a steeper learning curve and a longer duration to master the technique as compared with the GL. In a propensity score-matched analysis of data by Choi et al. from a multicenter emergency department airway registry, the overall first-attempt intubation success and failure rates did not significantly differ between GL and ML in the emergency department setting.[13] GS intubation was compared to various other laryngoscopes. In a study by Aqil, when comparing GS to a fiberoptic bronchoscope, time to achieve successful intubation was more in fiberoptic bronchoscope group while the GS group required external laryngeal manipulation in more number of cases to facilitate endotracheal intubation. They also reported more hemodynamic response in GS group which could be due to external laryngeal manipulation, despite an excellent CL glottic view in GS group.[14] In a mannequin study by Nasim et al., GS and Pentax Airway Scope possessed advantages over the conventional ML when used by Advanced Paramedics in normal and simulated difficult intubation scenarios.[3] In a meta-analysis of randomized controlled trials in cervical spine immobilization by Suppan et al. among ML, Airtraq, Airway Scope, C-Mac, GS, and McGrath devices only Airtraq was associated with a statistically significant reduction in both the rate of intubation failures at the first attempt and in the time to successful intubation.[15]

The limitations of the study were, for obvious reasons it was not possible to blind the person performing the endotracheal intubation to the intubation device being used. All the intubations were not done by the same person who could lead to bias, but all the postgraduates who participated in the study were equally trained to perform endotracheal intubation. Certain measurements such as laryngoscopic grade are subjective and a cross over study would be more ideal as each patient varies in the degree of intubation difficulty.

CONCLUSION

Though GL provided a better laryngoscopic view, it took a longer time to negotiate the ETT in to the larynx and thus resulted in longer intubation time, more laryngoscopic response and more mucosal trauma compared to ML. Further studies in a larger subset of patients with variable degrees of anticipated intubation difficulty comparing GS with other intubation devices are required to demonstrate the clinical utility of GS.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest