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PATIENT SAFETY

A Comparison of GlideScope® Videolaryngoscopy to Direct Laryngoscopy for Nasotracheal Intubation

From the Department of Anesthesia and Perioperative Medicine, University of Western Ontario, London, Ontario, Canada.

Address correspondence to Dr. Philip M. Jones, Department of Anesthesia and Perioperative Medicine, London Health Sciences Centre—University Hospital, London, Ontario, Canada N6A 5A5. Address e-mail to philip.jones{at}lhsc.on.ca.

Abstract

BACKGROUND: In this study, we compared the effectiveness of direct laryngoscopy (DL) and the GlideScope® videolaryngoscope (GVL) for nasotracheal intubation, as judged by the time to intubation (TTI—the primary outcome) and the ease of intubation.

METHODS: Seventy patients requiring nasotracheal intubation for elective surgery were randomly allocated to intubation with the GVL or DL. TTI was assessed by a blinded observer. Operators were blinded until the start of laryngoscopy. A Visual Analog Scale assessed the ease of intubation. The number of intubation attempts, number of failures, glottic grades, amount of bleeding, usage of Magill forceps, and the severity of postoperative sore throat were recorded.

RESULTS: The median TTI was 23.2 s faster with the GVL (43.5 s, interquartile range [IQR]: 39.8–67.3) than with DL (66.7 s, IQR: 53.8–89.9), P = 0.0023. Nasotracheal intubation was easier with the GVL than with DL (Visual Analog Scale 10 mm, IQR: 5.5–18, vs 20 mm, IQR: 10–32, P = 0.0041). The incidence of postoperative moderate or severe sore throat was significantly reduced in the GVL group (9% vs 34%, P = 0.018). Glottic exposure was significantly better with the GVL. Magill forceps were not used in the GVL group, but were used 49% of the time in the DL group, P < 0.0001. The incidence and severity of bleeding were similar between groups.

CONCLUSIONS: Compared with DL, the GVL has superior performance characteristics when used for nasotracheal intubation and demonstrates an important reduction of postoperative sore throat. The GVL has a clear role in routine nasotracheal intubation.

The GlideScope® videolaryngoscope (GVL—Verathon Medical Inc., Bothell, WA) has an established role in routine orotracheal intubation.1–3 In the context of nasotracheal intubation, the GVL has been shown to be superior to direct laryngoscopy (DL) when used by novices in airway management,4 and in a prospective observational trial, the GVL has demonstrated a high intubation success rate.5 However, no study has compared DL with GVL for nasotracheal intubation in a prospective, blinded, randomized, clinical trial. This study was performed to ascertain whether DL is superior to the GVL for nasotracheal intubation, as judged by the time to intubation (TTI) and the ease of intubation.

METHODS

This trial was registered at www.clinicaltrials.gov (NCT00400972). After obtaining local research ethics board approval, patients were screened for enrollment in the trial. Patients were eligible for inclusion if they were at least 18-yr-old and scheduled for elective dental or maxillofacial surgery requiring nasotracheal intubation. Patients were excluded if they had a known difficult airway, required rapid sequence induction, or if the attending anesthesiologist considered use of the GVL to be contraindicated. The study was conducted at the three teaching hospitals in London, Ontario, Canada. One location had the second generation (color) GVL (GlideScope Large, Verathon Medical Inc.), whereas the other sites had the first generation GVL. To ensure that the operators in the study were familiar with the GVL, anesthesiologists and anesthesiology residents had to have performed at least 10 GVL intubations (oral or nasal) to participate in the trial. An operator was arbitrarily defined as being experienced if they had successfully performed 10 GVL-assisted nasotracheal intubations before the study commenced. Written informed consent was obtained from all patients and operators. The null hypothesis was that there would be no difference in TTI between the groups.

Patients were randomly assigned to either DL or GVL using computer-generated codes enclosed within opaque envelopes that were opened by a study assistant just before laryngoscopy took place. The nares of the patient were vasoconstricted with 0.1% xylometazoline hydrochloride spray (three drops on each side). The nasotracheal tube (NTT—Portex Polar Preformed Nasal RAE, Hythe, Kent, UK; Fig. 1) was warmed and lubricated with sterile water-soluble lubricant before use, and the attending anesthesiologist chose the NTT size before the randomization envelope was opened.

View larger version (112K): [in this window] [in a new window]   Figure 1. The nasotracheal tube used in the study (Portex Polar Preformed Nasal RAE, Hythe, Kent, UK).

Patient demographics and Mallampati score6 were recorded preoperatively by the attending anesthesiologist. Both the DL and the GVL were present in the operating room to ensure blinding of the operator. Appropriate monitoring for each patient was applied, and administration of oxygen was performed to an end-tidal oxygen concentration of 80%. Induction and maintenance of anesthesia was not standardized. All patients had a nondepolarizing muscle relaxant administered, but the drug and dose were at the discretion of the attending anesthesiologist. After induction, the patient's lungs were ventilated with 100% oxygen until the operator deemed it appropriate to start the process of intubation. The device to which the patient had been randomized was then given to the operator by a study assistant, unblinding the operator. Laryngoscopy was performed, the patient was nasotracheally intubated and the lungs ventilated via the NTT. If the operator removed the laryngoscope from the mouth, this was counted as an additional attempt at intubation. Operators were permitted to use external laryngeal manipulation or change the position of the patient's head to improve the glottic view or to facilitate intubation. Ventilation by mask was permitted between attempts if necessary.

The TTI was chosen as the primary outcome because it represents an objective global assessment of all of the factors necessary to intubate the trachea, including device insertion, glottic exposure, advancement of the NTT to the correct location, and device removal. In addition, the TTI can be easily measured with a clear end-point by a blinded observer. The TTI started at the end of the period of bag-mask ventilation (at the moment when the mask was removed from the patient's face), and ended when end-tidal CO₂ of at least 30 mm Hg was seen on the monitor. The blinded observer watched the patient until timing was started and then turned so that only the anesthesia monitor was visible. At no point did the observer see the laryngoscope used (the Macintosh laryngoscope was activated before induction, regardless of patient group assignment, so that the sound created by opening the laryngoscope for use would not unblind the timer). If the intubation attempt took longer than 150 s, it was deemed a failure and the patient was intubated using a different modality. Failed intubations were included in the analysis (recorded as a TTI of 150 s). Prespecified secondary outcomes included ease of intubation (as recorded by the operator immediately after intubation on a 100 mm visual analog scale), the number of failures, the number of attempts made, the amount of bleeding that occurred, and whether or not Magill forceps were used. The operator recorded the ease of visualization of the glottic structures based on the classification described by Cormack and Lehane.7 The TTI was not divulged to the operator until after the data collection sheet had been completed. Two min after the intubation, the blinded observer suctioned the oropharynx three times in a back-and-forth sweeping motion using a Yankauer suction catheter, and qualitatively graded the amount of blood present in the suction tubing as none, trace, moderate, or copious. On the first postoperative day, the patient was asked about the presence of a postoperative sore throat and, if present, was asked to qualitatively grade its worst state as mild, moderate, or severe. The question posed to the patient regarding sore throat was asked with strict adherence to a prespecified script on the data collection sheet. Postoperative moderate or severe sore throat was specified a priori as a secondary outcome.

Sample size calculation was based on parametric analysis even though nonparametric analysis was planned for the outcomes in the study.8 A between-group difference of 10 s in TTI was considered clinically significant. The standard deviation (sd) of TTI was estimated from two studies investigating GVL-assisted nasotracheal intubation that demonstrated sds of 13 s4 and 11.5 s.5 A conservative sd estimate of 14 s for TTI was used with standard type I and type II error rates ( = 0.05, β = 0.20). The calculated sample size was 31 per group; a total sample size of 70 patients was selected.

TTI and ease of intubation were assessed using the Mann–Whitney test. Categorical data were analyzed using Fisher's exact test. Data are shown as median and interquartile range (IQR) unless otherwise noted. No corrections for multiple comparisons were made.9 Data were analyzed using GraphPad Prism software, version 4.0c for Macintosh. Results were considered statistically significant when P < 0.05.

RESULTS

Seventy patients were recruited. One patient in the GVL group was withdrawn from analysis after randomization due to a timing malfunction, which resulted in no data for TTI for that patient. Baseline demographics were similar between study groups (Table 1). A heterogeneous group of operators was recruited, with the majority of operators being inexperienced with the technique of GVL-assisted nasotracheal intubation.

The mean TTI was 23.2 s faster in patients nasotracheally intubated with the GVL (43.5 s, IQR: 39.8–67.3) compared with DL (66.7 s, IQR: 53.8– 89.9), P = 0.0023. To assess the temporal component of the success of intubation, a Kaplan–Meier plot was constructed (Fig. 2).

View larger version (15K): [in this window] [in a new window]   Figure 2. Kaplan–Meier plot demonstrating the success of nasotracheal intubation as a function of time.

The ease of intubation Visual Analog Scale demonstrated that operators found the GVL significantly easier for nasotracheal intubation compared to DL (Fig. 3).

View larger version (15K): [in this window] [in a new window]   Figure 3. Ease of intubation by operators as measured on a 100 mm Visual Analog Scale (VAS). The markings on the data collection form filled out by the operators was marked "easy" (at 0 mm) and "difficult" (at 100 mm). Bars and text indicate median VAS and the interquartile range.

The rate of a moderate or severe sore throat postoperatively was much lower in the GVL group compared to the DL group (9% vs 34%, P = 0.018), and glottic exposure was significantly better in the GVL group (Table 2). Magill forceps were not necessary for any GVL patient, but were required for approximately half of the DL group, P < 0.0001. The severity of bleeding and the number of intubation failures were not different between groups.

DISCUSSION

In a group of heterogeneous operators and patients, using the GVL for nasotracheal intubation results in a median time to intubation that is 23.2 s faster than with DL. Nasotracheal intubation using the GVL was also found to be easier for the anesthesiologist and resulted in significantly better glottic exposure. An absolute risk reduction of 25% in the incidence of postoperative moderate or severe sore throat was demonstrated, meaning that for every four patients nasotracheally intubated with the GVL instead of DL, one moderate or severe postoperative sore throat could be prevented.

The Kaplan–Meier plot showing the percentage of patients intubated as time progressed demonstrates the superiority of the GVL at all time points. At 50 s, only 14% of patients in the DL group were intubated, whereas 59% of patients were already intubated in the GVL group.

Two patients in the DL group failed to be intubated within 150 s. The first patient exhibited a grade three glottic view and could not be intubated with DL. Since the GVL was prepared as part of the trial protocol, it was used for intubation, and the patient was intubated easily with a grade 1 glottic view. In the second patient, despite good glottic exposure, the NTT could not be adequately aligned with the glottis, even with the use of Magill forceps. The patient ultimately had the surgery performed with an orotracheal tube, which was inserted easily.

The measurement of TTI was started as the mask was removed from the patient's face to preserve blinding of the timer. The TTI was stopped when end- tidal CO₂ was observed on the anesthesia monitor (as opposed to when the endotracheal tube cuff was inflated) to provide a clinically meaningful variable (apneic time) and to provide the most objective end-point possible. It is likely that extra time included at the beginning of the intubation (between removing the mask and starting laryngoscopy) and at the end of intubation (from placing the NTT until visualizing end-tidal CO₂) would be, on average, similar between the groups. Therefore, the time benefit realized when using the GVL for nasotracheal intubation is likely because of an advantage occurring during the actual laryngoscopy and intubation.

There are several advantages when using the GVL for nasotracheal intubation that could explain the lower TTI. Better glottic exposure has been demonstrated, allowing the operator to more quickly visualize the target to which the NTT is being directed. In addition, Magill forceps were not used when using the GVL, reducing the amount of time necessary for insertion of the Magill forceps, manipulation of the NTT tip, and removal of the Magill forceps. Finally, it seems likely that the GVL distorts the anterior airway anatomy less than when using DL, because it is not necessary to align the tracheal, pharyngeal, and oral axes when using the GVL, in contrast to DL. Reduced airway distortion could potentially create a more direct route from the nasopharynx to the trachea, necessitating less NTT manipulation and, consequently, a shorter TTI.

Even though Magill forceps were not used in the GVL group, it was observed that operators commonly used a combination of rotating the NTT between their fingertips, slight rotation of the patient's head, and/or flexion of the patient's neck to align the tip of the NTT with the glottis. Once the tip of the NTT was between the vocal cords, it was often helpful for the operator to reduce the distraction of the anterior neck tissues by lowering the GVL, advancing the tube into the trachea, and then lifting the GVL back up to ensure the NTT was still between the vocal cords.

The marked reduction in postoperative moderate or severe sore throat may be due to several factors. Avoiding the usage of Magill forceps may avoid direct pharyngeal mucosal trauma. In addition, it may be that less anterior pressure is exerted on the anterior airway structures (including the tongue) when performing GVL when compared with DL, and this lack of pressure could be linked to reduced sore throat. Finally, since the TTI of the GVL group was shorter, the GVL contact time with the oropharynx was less than with DL, and it is possible that reduced duration of contact of any laryngoscope with pharyngeal mucosa may be associated with a reduction in sore throat.

Operators were aware that they were participating in a clinical trial and that the intubation was being timed. This could unto itself lead to better clinical performance (the Hawthorne effect).10 However, it is expected that any improvement would likely be equally distributed between the groups, minimizing the impact of this effect. The potential for preexisting bias by an individual for or against DL or the GVL could conceivably have an impact on the results of this trial. Since it is impossible to blind an anesthesiologist as to the instrument being used for intubation, this trial endeavored to minimize any systematic bias by maintaining blinding of all study personnel until the last possible moment, and the person assessing the outcomes of the trial was fully blinded until all data had been collected.

Although no distinction was made in this study between bleeding from the nasopharynx (which could only be attributable to the NTT) versus the oropharynx (attributable to the laryngoscope used, the NTT, and/or Magill forceps usage), randomization should result in an equal proportion of patients in each group experiencing bleeding from the nasopharynx. Therefore, the overall amount of bleeding should remain a valid indicator of the relative amount of trauma incurred by each intubating technique. In addition, NTT size was determined by the attending anesthesiologist before knowing the allocation of the study patient to reduce the potential for systematic bias. As in every randomized clinical trial, it is possible that randomization did not adequately balance operator experience, factors that influence time to intubation, or factors contributing to nasopharyngeal bleeding.

In conclusion, when compared with DL, nasotracheal intubation with the GVL results in a faster, easier intubation that is associated with a clinically significant reduction in postoperative moderate or severe sore throat. The GVL has a clear role in routine nasotracheal intubation.

ACKNOWLEDGMENTS

We thank our anesthesia colleagues, the respiratory therapists who assisted us with data collection, and the oral surgeons whose patients were involved in the trial.

Footnotes

Accepted for publication January 28, 2008.

Reprints will not be available from the author.

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