Review Article. Pentax Airway Scope â vs Macintosh laryngoscope for tracheal intubation in adult patients: a systematic review and metaanalysis*

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1 Review Article doi: /anae Pentax Airway Scope â vs Macintosh laryngoscope for tracheal intubation in adult patients: a systematic review and metaanalysis* H. Hoshijima, 1 N. Kuratani, 2 Y. Hirabayashi, 3 R. Takeuchi, 4 T. Shiga 5 and E. Masaki 6 1 Assistant Professor, 6 Professor and Chairman, Division of Dento-Oral Anaesthesiology, Tohoku University Graduate School of Dentistry, Miyagi, Japan 2 Chief, Department of Anaesthesia, Saitama Children s Medical Center, Saitama, Japan 3 Professor, Department of Anaesthesia, International University of Health and Welfare Hospital, Tochigi, Japan 4 Assistant Professor, Department of Anaesthesia, Saitama Medical University Hospital, Saitama, Japan 5 Professor, Department of Anaesthesia, Kaken Hospital, International University of Health and Welfare, Chiba, Japan Summary The Pentax Airway Scope â is a single-use optical videolaryngoscope designed to assist with difficult tracheal intubation. We systematically reviewed the efficacy of the Pentax Airway Scope with that of a conventional laryngoscope for tracheal intubation in adults with normal and difficult airways. We included 17 randomised controlled trials with a total of 1801 participants. We used the DerSimonian and Laird random-effects model to calculate pooled relative risk or weighted mean differences. The relative risk (95% CI) of a Cormack Lehane grade-1 laryngeal view was 2.40 ( ) with the Pentax Airway Scope compared with the Macintosh laryngoscope, p < We found no other differences between the two laryngoscopes. Despite a superior laryngeal view, the Pentax Airway Scope provides little clinical benefit over the conventional laryngoscope.... Correspondence to: H. Hoshijima hhoshi@dent.tohoku.ac.jp *Presented in part at the annual meeting of the American Society of Anesthesiologists, Washington, DC, USA; October Accepted: 2 April 2014 Introduction The Pentax Airway Scope â (Pentax AWS â, S-100; Pentax, Tokyo, Japan) was developed as a single-use optical videolaryngoscope for anticipated difficult tracheal intubation. It has a transparent blade (Intlock), a charge-coupled device camera and a liquid crystal display (LCD) monitor. The blade was designed to guide the tracheal tube into the glottis, permit sufficient space to observe laryngeal structures, and protect the camera unit from contamination. The Pentax AWS is adjusted according to the mark on the LCD that indicates the glottic position, and the tracheal tube is passed through the Intlock into the trachea [1, 2]. Whether the Pentax AWS is better than a Macintosh laryngoscope for adults is uncertain. There have been anecdotal reports of successful tracheal intubation with the Pentax AWS in patients after failed intubation with a Macintosh laryngoscope [3]. One study reported faster, more frequently successful tracheal intubations with the Pentax AWS than the Macintosh 2014 The Association of Anaesthetists of Great Britain and Ireland 911

2 Hoshijima et al. Pentax AWS vs Macintosh laryngoscope for tracheal intubation laryngoscope [4]. The Pentax AWS provides a better view of the glottis than the Macintosh laryngoscope [5 10]. On the other hand, intubation time was shorter with the Macintosh laryngoscope in patients undergoing cervical spine surgery [11] with equivalent laryngeal views [11, 12]. The rate of oral or pharyngeal injury may be higher with the Macintosh laryngoscope than with the Pentax AWS [12], or it may be similar [6 9, 13 15]. In a previous meta-analysis, we compared channelled videolaryngoscopes (the Pentax AWS and Airtraq â ) with the Macintosh laryngoscope for manikins Articles initially identified up to January 2014 (n = 364) Studies excluded: (n = 312) Did not use a Pentax AWS (n = 187) Case reports (n = 99) Not a RCT (n = 26) Trials meeting inclusion criteria (n = 52) Comparison with unrelated laryngoscopes (n = 7) Studies of paediatric patients (n = 4) Lateral position studies (n = 3) Studies included in the meta-analysis (n = 16) Manikin studies (n = 22) Figure 1 Meta-analysis flow chart. AWS, airway scope; RCT, randomised controlled trial. and patients [16, 17]. The channelled videolaryngoscopes had higher intubation rates and shorter intubation times than the Macintosh laryngoscope, but we did not assess laryngeal view or the rates of oral and pharyngeal injury. Therefore, we performed this systematic review and meta-analysis to compare the efficacy of the Pentax AWS with that of the Macintosh laryngoscope for tracheal intubation in adults. We hypothesised that the Pentax AWS would be equal or superior to the Macintosh laryngoscope in adult patients in a clinical setting. Methods We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guideline [18]. We searched to January 2014 MEDLINE, Embase and the Cochrane Central Register of Controlled Trials. We used both individually and in combination: Airway Scope ; Pentax AWS ; Macintosh laryngoscope. We also searched the references from the studies and reviews we retrieved. We did not impose any language restrictions. We included prospective randomised controlled trials (RCTs) of the Pentax AWS vs Macintosh laryngoscope for adult oral or nasal tracheal intubation. We excluded duplicate publications. Two authors (HH and RT) independently assessed each article for inclusion and extracted data using the same Table 1 Characteristics of assessed studies. Author year [Reference] Patients (AWS/Mac) ASA status 45 (22/23) 1 2 Obstructive sleep apnoea Hirabayashi et al [25] 39 (19/20) N/A Normal, nasotracheal Suzuki et al.2012 [24] 60 (30/30) 1 2 Normal, nasotracheal, Indirect elevation of epiglottis 60 (30/30) 1 2 Normal, nasotracheal, Direct elevation of epiglottis Arima et al [20] 109 (56/53) N/A Prehospital setting Abdallah et al [15] 99 (50/49) 2 4 Morbid obesity 36 (18/18) 1 2 MILS 100 (50/50) 1 2 Normal 200 (100/100) 1 3 Normal Nishikawa et al [14] 40 (20/20) 1 2 Normal 50(25/25) 1 3 Difficult airway 60 (30/30) 1 3 MILS Hirabayashi & Seo 2009 [4] 502 (264/256) N/A Normal 60 (30/30) 1 3 MILS Enomoto et al [5] 203 (99/104) 1 2 MILS Komatsu et al [13] 96 (48/48) 1 3 MILS Maruyama et al [11] 24 (12/12) 1 2 Normal Notes AWS, pentax AWS; Mac, macintosh laryngoscope; MILS, manual in-line neck stabilization; N/A, not available The Association of Anaesthetists of Great Britain and Ireland

3 Hoshijima et al. Pentax AWS vs Macintosh laryngoscope for tracheal intubation Anaesthesia 2014, 69, data collection form, with disagreements resolved through discussion. We recorded: intubation rate on first attempt; intubation time; Cormack Lehane classification (grade 1 vs grade 2); and rates of oral or pharyngeal injury. We analysed the interactions of these outcomes with the anticipated difficulty of intubation. Anticipated difficult airways were: morbidly obese participants [15]; participants with immobilised cervical spines [5 7, 10, 13]; participants with obstructive sleep apnoea [19]; predicted difficult intubations (thyromental distance < 6 cm, Mallampati classification 3 4 or inter-incisor distance < 4 cm) [8]; during chest compression [20]. We estimated risks of bias in the following methodological domains: sequence generation; allocation concealment; blinding of participants, personnel and outcome assessors; incomplete outcome data; selective outcome reporting; and other potential threats to validity [21]. We contacted authors to resolve data discrepancies. We similarly retrieved and analysed manikin studies for comparison. Statistical analysis was performed in Comprehensive Meta-analysis version (Biostat, Englewood, NJ, USA). We combined data from RCTs with DerSimonian and Laird random-effects models: relative risk with 95% CI for categorical variables; weighted mean difference with 95% CI for continuous variables. We considered p values < 0.05 statistically significant. We assessed heterogeneity with the Cochrane Q statistic and the I 2 statistic, which indicates the percentage of variability due to heterogeneity rather than to sampling error [22]. We did not pool results when the p value for heterogeneity was < 0.10 or the I 2 value exceeded 50%. We assessed funnel plot asymmetry with Begg s test [23]. Results We included 17 comparisons in 16 RCTs (Fig. 1, Table 1), with 1801 participants [4 15, 18, 19, 20, 24, 25]. The difficulty of intubation was anticipated as normal in eight RCTs and difficult in nine RCTs. The risks of bias are summarised in Fig. 2. There was no funnel plot asymmetry: Kendall correlation coefficient 14.0, p = There was no difference between laryngoscopes in rate of intubation on first attempt or intubation time (Figs 3 and 4). The Pentax AWS was twice as likely as the Macintosh laryngoscope to provide a good glottic Hirabayashi et al [25] Arima et al [20] Abdallah et al [15] Nishikawa et al [14] Hirabayashi & Seo 2009 [4] Enomoto et al [5] Komatsu et al [13] Maruyama et al [11] Figure 2 Risks of bias in the included studies. Green circles, red circles and yellow circles indicate low risk of bias, high risk of bias and unclear risk of bias, respectively. view (Fig. 5). There was no difference in the rates of oral or pharyngeal injury (Fig. 6). There was no interaction between anticipated intubation difficulty and normal airway in all outcomes except the glottis view, p = We included 22 manikin studies (42 trials) [26 47]. The Pentax AWS was more effective than the Macintosh laryngoscope for all outcomes except the rate of audible dental clicks or significant dental compression (equivalent to oral or pharyngeal injury in human studies, Table 2) The Association of Anaesthetists of Great Britain and Ireland 913

4 Hoshijima et al. Pentax AWS vs Macintosh laryngoscope for tracheal intubation Enomoto et al [5] Abdallah et al [15] Arima et al [20] Komatsu et al [13] Hirabayashi & Seo 2009 [4] Hirabayashi et al [25] Nishikawa et al [14] Maruyama et al [11] Figure 3 Forest plot of the rate of tracheal intubation using the Pentax Airway Scope (AWS) compared with the Macintosh laryngoscope. The centre of each square represents the relative risk for individual trials, and the corresponding horizontal line represents the 95% CI. The diamonds represent the pooled results. Discussion The results of our meta-analysis suggest that the Pentax AWS offers a superior glottis view compared with the Macintosh laryngoscope, but showed no differences in other outcomes, such as intubation rate, intubation time and rate of oral or pharyngeal injury. These results suggest that the Pentax AWS provides little clinical benefit for tracheal intubation over the conventional Macintosh laryngoscope. There are two possible explanations for this. First, tracheal intubation is possible in many cases even without a full view of the glottis. In a previous study of tracheal intubation using the Macintosh laryngoscope, most laryngoscopists succeeded in tracheal intubation of Cormack Lehane grade-2 cases [48], which we defined as poor glottic view. Second, tracheal intubation using the Pentax AWS may not be possible when a clear view of the glottis is obtained. Tracheal intubation with the Pentax AWS fails in 1 4% attempts when the tip of the tracheal tube hits the arytenoids, despite a clear view of the glottis [49, 50]. Although the Pentax AWS was designed for difficult intubation, no significant benefit was associated with its use in patients with difficult airways when compared with use of the conventional Macintosh laryngoscope [16]. A possible reason for this finding was that most RCTs (16 of 17) studied experienced laryngoscopists, who might have been capable of achieving successful tracheal intubation with the Macintosh laryngoscope, even in patients with difficult airways. In our previous meta-analysis, we performed a subgroup analysis to investigate the influence of the characteristics of laryngoscopists (novice and experienced). The intubation time with the Pentax AWS was faster than that with the Macintosh laryngoscope in novice laryngoscopists [16]. Only one of 17 RCTs in the present meta-analysis studied novice laryngoscopists, compared with eight of 18 RCTs in the previous meta-analysis, which might be one factor associated with the lack of superiority of the Pentax AWS. Another explanation might be lack of statistical power: our previous metaanalysis analysed more airway intubations due to the pooling of data from 13 manikin studies. In manikin The Association of Anaesthetists of Great Britain and Ireland

5 Hoshijima et al. Pentax AWS vs Macintosh laryngoscope for tracheal intubation Anaesthesia 2014, 69, Arima et al [20] Abdallah et al [15] Enomoto et al [5] Komatsu et al [13] Maruyama et al [11] Hirabayashi & Seo 2009 [4] Nishikawa et al [14] Hirabayashi et al [25] Figure 4 Forest plot of intubation time for tracheal intubation using the Pentax Airway Scope (AWS) compared with the Macintosh laryngoscope. The centre of each square represents the weighted mean difference for individual trials, and the corresponding horizontal line represents the 95% CI. The diamonds represent the pooled results. Enomoto et al [5] Maruyama et al [11] Figure 5 Forest plot of glottis view with the Pentax Airway Scope (AWS) compared with the Macintosh laryngoscope, Cormack Lehane grade 1 vs other grades. The centre of each square represents the relative risks for individual trials, and the corresponding horizontal line represents the 95% CI. The diamonds represent the pooled results. studies, the rate and time for tracheal intubation were higher and shorter, respectively, with the Pentax AWS than with the Macintosh only if the simulated airway was difficult, but not if it was easy [41]: nine of 13 manikin RCTs in our previous meta-analysis simulated difficult airways, possibly accounting for the superiority 2014 The Association of Anaesthetists of Great Britain and Ireland 915

6 Hoshijima et al. Pentax AWS vs Macintosh laryngoscope for tracheal intubation Abdallah et al [15] Komatsu et al [13] Nishikawa et al [14] Figure 6 Forest plot of the rate of oral or pharyngeal injury after tracheal intubation with the Pentax Airway Scope (AWS) compared with the Macintosh laryngoscope. The centre of each square represents the relative risk for individual trials, and the corresponding horizontal line represents the 95% CI. The diamonds represent the pooled results. Table 2 Differences in efficacy between the Pentax Airway Scope and the Macintosh laryngoscope in manikin trials. Binomial outcomes are reported as relative risk and the continuous outcome as weighted mean difference. Outcome RCTs Effect (95% CI) p value I 2 statistic Intubation rate ( ) < Intubation time; s ( 9.91 to 16.5) < Glottis view ( ) Injury ( ) < RCTs, randomised controlled trials. of the Pentax AWS over the Macintosh [16]. In clinical studies of anticipated difficult intubations, many of the tracheal intubations proved easy. Several reports have suggested that the Pentax AWS is an effective device for intubating the tracheas of patients with difficult airways. Iguchi et al. [51] reported successful tracheal intubation using the Pentax AWS in a patient with Treacher Collins syndrome, Cormack and Lehane grade 4, after several unsuccessful intubation attempts with the Macintosh laryngoscope. Jeyadoss et al. [52] reported successful tracheal intubation with the Pentax AWS in a patient with a massive thyroid tumour and tracheal compression after failed intubation with a fibrotic bronchoscope. If the RCTs we analysed had included such extreme cases, the Pentax AWS might have proven superior to the Macintosh laryngoscope in difficult airway patients. The RCTs included in our study had a number of important limitations: they could not blind the laryngoscopist to patient or laryngoscope characteristics, and there was clinical heterogeneity, including laryngoscopists with different levels of familiarity and skill with the Pentax AWS and different definitions of failure of intubation. In conclusion, the Pentax AWS offered a superior glottic view compared with the Macintosh laryngoscope, which was not associated with a higher intubation rate or shorter intubation time. In the general adult population, the Pentax AWS appears to provide little clinical advantage for tracheal intubation. Competing interests No external funding and no competing interests declared The Association of Anaesthetists of Great Britain and Ireland

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