Abstract

Nasotracheal intubation (NTI) is usually required in patients undergoing maxillofacial surgery. Though video-scopes have been demonstrated to perform well in oral endotracheal intubation, limited information is available concerning NTI. The aim of the study is to compare the efficiency of video-scopes and the traditional direct laryngoscopy in NTI. One hundred and eight patients scheduled for elective oro-maxillofacial surgery under nasotracheal intubation general anesthesia were randomly allocated into one of 3 groups of GlideScope, Pentax AirWay Scope, or Macintosh laryngoscope respectively. The primary outcome measures were total intubation time and each separate time interval (time A: for placement for the nasotracheal tube from selected nostril to oropharynx; time B: for use of devices to view the glottic opening; time C: for advancing nasotracheal tube from oropharynx into trachea and removing the scope from the oral cavity). The secondary outcomes were measurement of scores of modified naso-intubation difficulty scale (MNIDS) and attempts at intubation.

Results

Mean total intubation time and time C interval were taken with GlideScope (33.1 s and 9.7 s), Pentax (38.4 s and 12.9 s), and Macintosh (42.2 s and 14.9 s) respectively. There was a significant difference among the groups (total time, P = 0.03; time C, P = 0.02). The median score of MNIDS was significantly lower using GlideScope or Pentax compared with using Macintosh in NTI (P = 0.037) and difficult intubation grading by MNIDS presented as easier in the GlideScope group than in the Macintosh group (0.016). Using GlideScope, intubation was successful at the first attempt in 80% patients whereas only 65% and 72.5% with the Pentax and Macintosh (P = 0.02).

Conclusion

As compared with the Macintosh laryngoscope, the GlideScope video laryngoscope fac

Keywords

Nasotracheal intubation (NTI); GlideScope; Pentax airway scope; Macintosh laryngoscope;

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1. Introduction

Nasotracheal intubation (NTI) is commonly practiced in patients undergoing oro-maxillofacial surgery to provide a secure airway and good operation field. Using Macintosh laryngoscope (ML) to facilitate NTI is a conventional direct laryngoscope technique. However, new video laryngoscope devices allowing viewing indirectly through video display equipped with the blade tip camera such as GlideScope (Verathon, Bothell, WA, USA) and the Pentax Airway Scope (Pentax AWS; Pentax, Tokyo, Japan) for intubation have been demonstrated to improve intraoral field exposure and increase efficiency in glottic visualization for both normal and difficult airway management.^1–5

The GlideScope, with a fixed steep 60-degree angulation blade, often needs to use a GLiderite^® rigid stylet to enable a quick endotracheal intubation.³ However, it is not allowable to use this rigid stylet while the double-curve endotracheal tube is passing through the nasal cavity. Using Pentax AWS to assist oro-tracheal intubation, the blade should be attached, endotracheal tube lubricated, and loaded into the tube channel aside the blade. The blade is then placed beneath the epiglottis to visualize the glottis.⁶ However, the designed blade is not recommended for double-curve endotracheal tube placement also, due to the indirect laryngoscopy only requiring alignment of the pharyngeal and laryngeal axes.^1,7 Both devices have been reported to be more effective than the Macintosh laryngoscope for orotracheal intubation.^1,4,8–12 However, there is limited information concerning the efficiency of indirect laryngoscopy in double-curve nasotracheal intubation.^7,13 The purpose of this randomized, single-blinded study was to evaluate the efficiency of the two video laryngoscopes: the GlideScope and the Pentax AWS, vis-à-vis the Macintosh laryngoscope for elective NTI in patients undergoing oro-maxillofacial surgery.

2. Methods

After approval from the local Institutional Review Board (IRB No. KMUH-IRB-990188) and approval for clinical trial investigation (NCT02448277), written informed consent was obtained from each patient enrolled. A total of 108 patients classified as American Society of Anesthesiologist physical status I or II, aged 20–65 years, who were undergoing elective oro-maxillofacial surgery were included in the study. Patients with a limited mouth opening of less than 3 cm, a history of documented difficult tracheal intubation, cervical spine instability, chronic suppurative sinusitis, and contraindications to NTI were excluded.

All patients received pre-anesthesia airway evaluation before entering the operation room, and their inter-incisor distance, thyromental distance and Mallampati classification were measured and recorded. The patients were allocated randomly into three groups as follows: 108 index cards were placed in 108 envelopes, and 36 cards were marked with the code for each airway device including GlideScope, Pentax AWS and direct Macintosh laryngoscopes in the randomized, clinical, controlled study. Code A represented GlideScope, code B represented Pentax AWS, and code C represented Macintosh laryngoscope. Each patient selected an envelope after entering the operation room for airway device.

All patients were blinded to the chosen device. Nasotracheal intubations were performed by an experienced anesthesiologist using GlideScope^® video-laryngoscope (Verathon Inc., Bothell, WA, USA), Pentax Airway Scope (AWS; Pentax Corporation, Tokyo, Japan) or Macintosh laryngoscope. Each patient was asked to fast for at least 8 h and was given no premedication prior to surgery. On arrival at the operating room (OR), patients were monitored with heart rate (HR), lead II electrocardiography (ECG), and noninvasive blood pressure (BP). The selected nostril was sprayed with 6% cocaine by an intranasal mucosal atomization device (Wolfe Troy Medical, Inc. Salt Lake City, Utah, USA). Anesthesia was induced with fentanyl 2 mcg/kg, thiamylal 5 mg/kg, and cis-atracurium 0.2 mg/kg to facilitate NTI. Patients were manually ventilated with 60% oxygen for three minutes following loss-of-eyelash reflex. A 22-gauge catheter was inserted into the radial artery following loss of consciousness for continuous blood pressure measurement. Propofol 1 mg/kg was given prior to intubation to blunt intubation-related hemodynamic responses. A preformed double-curved endotracheal tube of high-volume low-pressure cuff with Murphy eye tip (Unomedical Sdn. PharmaPlast, Kedah, Malaysia) was used in all patients (7 mm ID for men and 6.5 mm ID for women). Inhaled sevoflurane was administered to maintain end-tidal concentration at 2.5–3.5% and end-tidal CO2 (ETCO2) concentration within the range of 35–40 mmHg.

An independent nurse anesthetist recorded all data in each one of these trials. The primary outcomes were evaluated by total intubation time and each time interval (time A: placement of the nasotracheal tube from selected nostril to oropharynx; time B: use of devices to view the glottic opening; time C: nasotracheal tube advanced from oropharynx into trachea and removal of the scope form oral cavity). The secondary outcomes were scores of modified naso-intubation difficulty scale (MNIDS) developed by Adnet and colleagues and attempts of intubation.¹⁴ The MNIDS scored intubation conditions were assessed as follows: N1, additional intubation attempts; N2, number of supplementary operators, directly but not assisted; N3, alternative intubation techniques such as change of head position or cuff inflation intervention; N4, glottic exposure grading as Cormack–Lehane minus 1; N5, lifting force; N6, glottic exposure with BURP maneuver; N7, vocal cords position.¹⁵ The MNIDS scores were categorized as easy (0), minor difficulty (0 ≤ scores ≤ 5), major difficulty (5 < scores). Hemodynamic responses (heart rate and mean arterial pressure changes) were measured at each time point of cocaine spray, peri-intubation period, and NTI-related side-effects were also compared. Other parameters assessed in relation to anesthesia included: nasal bleeding, inflated cuff, backward upward rightward pressure (BURP) maneuver and postoperative adverse events (sore throat, hoarseness, dysphagia).

In this study, the expected difference of mean total intubation time between groups was 10 s and of the common within group deviation was 12 s. At least 33 patients were needed in each group with set power of 0.8 and significance level of 0.05. We enrolled patients' number to 36 in each group to allow for unexpected patient withdrawal and attrition. Group differences in intubation-related time taken were compared by ANOVA followed by Scheffe test of multiple post hoc analyses. Numerical variables are given as mean or unexpected patient withdrawal and attrition. Group differences in intubation-related time taken were compared by ANOVA followed by Scheffe test of mu the χ2 test. SPSS 17.0 software (SPSS Inc., Chicago, IL, USA) was used for all statistical analyses. A P value < 0.05 was considered statistically significant.

3. Results

The demographic data (age, body mass index, and gender difference) and airway data (inter-incisor width, thyromental distance, and Mallampati classification) are shown in Tables 1 and 2. There was no significant difference between the three groups. Three patients in the Pentax group were excluded from this study as one suffered from acute URI attack, one failed to have the tube inserted through the nasal cavity, and one patient exhibited limited mouth opening even after induction agents were given (Fig. 1).

The mean total and each separate time C spent were calculated as 32.9 s and 9.9 s in the GlideScope group, 38.4 s and 12.9 s in the Pentax group, and 42.7 s and 8.5 s in the Macintosh group respectively (Table 3). Both total intubation time and time C interval in the GlideScope group were shorter than the Macintosh group (both P < 0.05); there was no significant difference in intubation time spent between GlideScope and Pentax groups.

The median score of MNIDS was 0 in GlideScope and Pentax groups and 2 in the Macintosh group (P = 0.037). The difficulty of intubation grading in the GlideScope group was not seen in the Macintosh group (P = 0.016) (Table 4). More patients in the Macintosh group required the BURP maneuver to assist intubation than did patients in GlideScope and Pentax groups (Table 5). There were no statistical differences between the groups on intubation attempts, incidence of nasal bleeding, use of cuff inflation technique to assist intubation, perioperative hemodynamic responses to intubation, and post-OP side effects (Tables 6 and 7).

4. Discussions

In this study, using GlideScope for nasotracheal intubation provided shorter mean total intubation time and time C time interval taken than in using the Macintosh laryngoscope. Using video-laryngoscope for either GlideScope or Pentax AWS virtually needed no BURP maneuver to view the glottis clearly as compared with traditional laryngoscope. In addition, the median score of MNIDS was zero as using video-laryngoscope as compared with a score of two in the Macintosh laryngoscope and intubation difficulty grading was easier in the GlideScope group than in the Macintosh group. Therefore, we demonstrated that the GlideScope is a feasible tool for nasotracheal intubation as compared with the Macintosh.

Many clinical reports have evaluated the efficiency of airway devices by using first-attempt intubation successful rate as a parameter.^9,16 Nevertheless, patients in normal airway were not able to present any difference between the video-laryngoscope and traditional laryngoscope in this study. However, we demonstrated that using the GlideScope enabled shortened mean total intubation time spent for nasotracheal intubation as compared with the Macintosh laryngoscope. The main results suggested that the reduced intubation time with the GlideScope mainly resulted from reduced time interval to advance the tube tip from the oropharynx into the trachea. Though the median score of MNIDS was reduced with video laryngoscopes, the airway devices showed no benefit of time-saving to obtain the glottic view in patients with normal airway. This is in accordance with other studies where the GlideScope and Pentax WAS reduced the grading of intubation difficulty and the GlideScope saved intubation time when compared with the Macintosh laryngoscope.^5,17

Several studies have reported that the Pentax AWS is an effective device for both orotracheal and nasotracheal intubation.^5,8,11,16,18 In a meta-analysis for orotracheal intubation, Hoshijima et al.¹¹ reported that the Pentax AWS achieved a better glottis view than the Macintosh laryngoscope, but there was no significant difference in success rate and intubation time and adverse events. Ono et al.¹⁶ reported that using Pentax AWS for NTI was 100% successful with an 86.4% success rate at first attempt. However, 10 patients were categorized into moderate difficulty scale (IDS > 5) and 37 patients need cuff inflation technique to assist tube placement respectively. Large tongue and higher Cormack grade may impinge smoothly nasotracheal intubation. In our results, the Pentax AWS also achieved a 69.7% success rate at first attempt. However, we place the Pentax AWS blade beneath the epiglottis initially and withdrawal from the epiglottis was slow if required. The technique to use the tool of Pentax AWS is different from Ono et al. in that the blade top was in a fixed position either in vallecula or under the epiglottis. This is why the Pentax group patients in our study needed no third attempt at nasotracheal intubation. However, it posits that the use of the Pentax AWS by a novice intubator may lead to a situation where unsuccessful nasotracheal intubation might occur even under a clear glottis view. A possible explanation might be that the Pentax AWS blade is 18 mm thick and its lower tube channel located at the glottic opening might impede nasotracheal tube advancement and the tip of the endotracheal tube may therefore fail to advance through obstruction by arytenoid cartilages.¹⁹

The GlideScope was demonstrated as an effective device for nasotracheal intubation in this study. However, Puchner et al.¹⁷ showed that using the GlideScope for nasotracheal intubation reduced the score of modified intubation difficulty scale and improved the glottis view but did not save time as compared with using the Macintosh laryngoscope. Although there is different outcome between that report and our results, in tracing the context, they included 20 patients in each group and 6 anesthesiologists to execute intubation; however, 36 patients in each group were included and 2 anesthesiologists were used for intubation in our study. In addition, Xu et al.⁷ using the GlideScope in patients of ankylosing spondylitis presented shorter nasotracheal intubation time than by using the Macintosh laryngoscope. Therefore, further investigations are warranted to clarify the issue of using the GlideScope to save intubation time. The GlideScope for nasotracheal intubation revealed an 81% successful rate at the first attempt²⁰ that was in line with our result (82.1%). Therefore, the GlideScope reduced the MNIDS scores and reduced intubation attempts as compared with the Macintosh laryngoscope. Interestingly, we found that the GlideScope was superior to the Pentax AWS in intubation time, intubation difficulty and success rate; however, determining the exact mechanisms warrants further investigation.

We conclude that the GlideScope facilitated NTI by saving total intubation time, reduced intubation difficulty demonstrated by zero median score of MNIDS, and non-use of the BURP maneuver as compared with the Macintosh laryngoscope. In this study, we demonstrated that GlideScope was a better device as compared with the Macintosh laryngoscope for normal airway patients undergoing oro-maxillofacial surgery with NTI.