Bougies as an aid for endotracheal intubation with the Airway Scope: bench and manikin comparison studies

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1 Tkenk et l. BMC Anesthesiology (2017) 17:133 DOI /s RESEARCH ARTICLE Open Access Bougies s n id for endotrchel intubtion with the Airwy Scope: bench nd mnikin comprison studies Ichiro Tkenk 1*, Kzuyoshi Aoym 2, Tmo Iwgki 1 nd Yukri Tkenk 1 Abstrct Bckground: When encountering difficult irwy with n Airwy Scope (AWS) bougie cn be inserted into the endotrchel tube in the AWS chnnel. The ngulted tip of the bougie cn be guided towrd the glottis by rotting it. We tested the ese of rotting bougies (Venn reusble, Boussignc, Portex single-use, nd Frov) in n endotrchel tube when plced in the AWS chnnel. Methods: Bench study: Seven nesthesiologists inserted ech of the four types of bougies into 7.0 mm endotrchel tube in n AWS chnnel nd rotted the bougie end (side of bougie operted by hnd) clockwise or counterclockwise to n ngle of in 45 increments. The rottion ngle of the bougie tip (trchel side) ws mesured for ech bougie nd the degree of force required to rotte them ws exmined. Mnikin study: Using the sme four bougies, the sme seven nesthesiologists ttempted to intubte mnikin tht simulted difficult irwy. Success rte nd time required for successful intubtion were compred between the four bougies. Results: Bench study: The difference in the rottion ngle between the bougie tip nd end ws significntly lrger with Portex single-use nd Frov bougies thn with Venn reusble nd Boussignc bougies (P < 0.01). The rottion ngles of the tips of Venn reusble, Boussignc, Portex single-use, nd Frov bougies were 145 /123 (clockwise / counterclockwise), 92 /108, 46 /56, nd 39 /51, respectively, when their ends were rotted to n ngle of 180. Venn reusble nd Boussignc bougies could be rotted in the endotrchel tube by cliniclly cceptble rottionl force. Mnikin study: TimestointubtionwithVennreusble[25(SD,5)s]ndBoussignc bougies [35 (6) s] were significntly shorter thn with Portex single-use [61 (17) s] nd Frov bougies [69 (22) s] (P < 0.01). There were no significnt differences in success rte between the four bougies. Conclusions: Venn reusble nd Boussignc bougies re useful id for intubtion with n AWS. Portex single-use nd Frov bougies seem to be less suitble for this technique. Different bougies my be of vrying utility when used with n AWS or irwy device with n endotrchel tube chnnel. Keywords: Endotrchel intubtion Videolryngoscopy Bougie Bckground The Airwy Scope (AWS, HOYA-Pentx, Tokyo, Jpn) belongs to the fmily of chnneled videolryngoscopes with built-in monitor, like the Airtrq (Prodol Meditec S.A., Vizcy, Spin) or the King Vision videolryngoscope (Ambu Inc., Bllerup, Denmrk). The blde is designed to mtch the ntomy of the upper irwy nd * Correspondence: dd6xj6rx7@yhoo.co.jp 1 Deprtment of Anesthesi, Kyushu Rosi Hospitl, 1-1 Sonekit, Kokurminmi, Kitkyushu , Jpn Full list of uthor informtion is vilble t the end of the rticle provides n excellent view of the glottis, even in ptients with difficult irwys [1, 2]. During ttempts t endotrchel intubtion with n AWS, the curvture of n endotrchel tube nd n endotrchel tube guiding chnnel of the AWS blde determines the direction in which the tube dvnces. This direction is thus fixed, which is displyed on the AWS monitor screen s trget symbol. The trget symbol is ligned with the glottis to chieve insertion of the tube into the trche [1, 3]. Filure to lign the trget symbol with the glottis prevents insertion of n endotrchel tube into the trche, mking intubtion The Author(s) Open Access This rticle is distributed under the terms of the Cretive Commons Attribution 4.0 Interntionl License ( which permits unrestricted use, distribution, nd reproduction in ny medium, provided you give pproprite credit to the originl uthor(s) nd the source, provide link to the Cretive Commons license, nd indicte if chnges were mde. The Cretive Commons Public Domin Dediction wiver ( pplies to the dt mde vilble in this rticle, unless otherwise stted.

2 Tkenk et l. BMC Anesthesiology (2017) 17:133 Pge 2 of 7 with n AWS difficult. Moreover, direct lift of the epiglottis with the blde tip is necessry for successful intubtion with n AWS. Filure to chieve this cn result in the dvncing tube impinging on the epiglottis [4 6]. Becuse thin ngulted tip cn esily be mnipulted in desired direction, smll bougie with n ngulted tip cn fcilitte precise insertion, even into smll trget [6 9]. Such bougie cn be pssed through the nrrow curved lumen of the endotrchel tube tht is plced into the AWS chnnel nd cn be dvnced into the glottis nd trche, even when the trget symbol cnnot be ligned with the glottis or the epiglottis cnnot be lifted directly with the tip of the AWS blde [4 6]. When using bougie s n id to intubtion with n AWS, the lryngoscopist often ttempts to guide its ngulted tip towrd the glottis by rotting its end tht is closest to the irwy dptor of the endotrchel tube. However, rottion of the bougie within the tube my result in twisting of its shft, preventing full trnsmission of the rottionl force pplied t its end to the ngulted tip. To the best of our knowledge, no published studies hve exmined which bougies cn be freely nd esily rotted in the lumen of the endotrchel tube set in the curved blde of n AWS. We therefore exmined the ese or difficulty of rotting four commercilly vilble bougies within the endotrchel tube inserted into n AWS chnnel nd the efficcy of these bougies in difficult intubtion simultion mnikin. Methods Bench study Seven nesthesiologists with t lest 5 yers experience prticipted in this study s follows (Fig. 1). They exmined four commercilly vilble bougies: Venn reusble trchel tube introducers (Smiths Medicl, Keene, NH, USA), Boussignc bougies (Vygon, Ecouen, Frnce), Portex single-use bougies (Smiths Medicl, Keene, NH, USA), nd Frov intubting ctheters (Cook Medicl, Bjeverskov, Denmrk) (Tble 1). The order of testing of the bougies nd the direction of rottion were rndomly ssigned by seled envelope technique. A 7.0 mm internl dimeter stndrd endotrchel tube (Smiths Medicl, Tokyo, Jpn) ws inserted into the endotrchel tube guiding chnnel of n AWS blde (Intlock-TL, HOYA-Pentx, Tokyo, Jpn) nd the tip of the endotrchel tube ws locted beside the scope window of the AWS blde [3]. The tip of the AWS blde ws set 15 mm from the circulr protrctor tht ws stnding verticlly on tble. The inferior corner of the ngulted tip of ech bougie ws mrked. After the bougie hd been thoroughly lubricted with 8% lidocine spry, it ws inserted into the endotrchel tube with its ngulted tip, which ws locted 5 mm beyond the blde tip, being directed towrds 12 o clock. The mrk indicting the inferior corner of the ngulted tip of the bougie ws then ligned with the center of the circulr protrctor on the monitor screen of the AWS. The power switch of the AWS ws turned off nd the bougie tip (trchel side) ws conceled with the hood. The bougie end (side of bougie operted by hnd) ws then rotted clockwise or counterclockwise to n ngle of in 45 increments s mesured by nother circulr protrctor tht ws set on the irwy dptor of the endotrchel tube. The furthest the bougie tip reched fter mximl rottion ws mrked on the circulr protrctor. The degree of force required to rotte the bougie ws subjectively clssified s esy, moderte, difficult, nd impossible for ech bougie. The bougie ws then exchnged in ccordnce with predetermined sequence nd the rottion ngles of its tip were mesured in the sme fshion. Assistnts, who were blinded to the purpose of the study nd the type of bougie, clculted the rottion ngles on the circulr protrctor. Mnikin study A mnikin ws used to simulte difficult irwy. In this mnikin the epiglottis could not be lifted directly with the AWS blde [6]. The sme seven nesthesiologists ttempted to intubte the mnikin s trche using the sme four bougies. An AirSim mnikin (TruCcorp, Belfst, Northern Irelnd) ws utilized, its tongue being inflted with 75 ml of ir, which provided the Cormck nd Lehne grde 3 view with Mcintosh lryngoscope. The order of testing of the bougies ws rndomly ssigned by seled envelope technique. A 7.0 mm internl dimeter stndrd endotrchel tube ws inserted into the AWS chnnel. After the bougie hd been thoroughly lubricted with 8% lidocine spry, it ws inserted into the tube with its ngulted tip directed towrds 12 o clock. The mnikin ws plced supine without pillow on flt tble. Next, the nesthesiologist inserted n AWS blde into its mouth until its tip ws positioned in the vllecul. After the glottis hd been fully exposed, the lryngoscopic view chieved ws ssessed using Cormck nd Lehne clssifiction. The nesthesiologist then ttempted to guide the bougie tip towrd the glottis by rottion, inserted the bougie into the trche, nd dvnced the endotrchel tube over it. An ssistnt mesured time to intubtion, which ws defined s the time from insertion of the AWS blde between the teeth to the endotrchel tube cuff pssing through the vocl cords. Pssge of the cuff ws confirmed on the monitor screen of the AWS. The ttempt ws deemed filure if the intubtion ttempt took longer thn 120 s or the endotrchel tube ws inserted into the esophgus. The bougies were exchnged in ccordnce with predetermined sequence nd the nesthesiologists were ttempting intubtion with ech of them in the sme fshion. The lryngoscopic grde, time required for successful intubtion, nd success or filure of intubtion were recorded.

3 Tkenk et l. BMC Anesthesiology (2017) 17:133 Pge 3 of 7 Bougie end (side of bougie operted by hnd) Airwy Scope Protrctor (bougie end) 15mm 5mm Airwy dptor 7mmID Endotrchel Tube Protrctor (bougie tip) Blde (Intlock- TL) Inferior corner of ngulted tip (mrk) Bougie tip (trchel side) Bougie end (side of bougie operted by hnd) b Protrctor (bougie end) Hood Protrctor (bougie tip) Bougie tip (trchel side) Fig. 1 Experimentl protocol for the bench study. According to the instruction mnul [3], 7.0 mm internl dimeter stndrd endotrchel tube is inserted into the guiding chnnel of n Airwy Scope blde, the tip of which is set 15 mm from the circulr protrctor tht stnds verticlly on tble (). The nesthesiologist mrks the inferior corner of the ngulted tip of the bougie then, with the ngulted tip directed towrds 12 o clock, inserts the bougie into the tube, loctes the tip 5 mm beyond the blde tip, nd ligns the mrk with the center of the protrctor on the monitor screen of the AWS (). The power switch of the Airwy Scope is turned off. The nesthesiologist then rottes the bougie end (side of bougie operted by hnd) clockwise or counterclockwise to n ngle of in 45 increments while looking t the protrctor tht is set on the irwy dptor of the endotrchel tube (b). The bougie tip (trchel side) is not visible becuse of the hood (b). The ngle of the bougie tip creted by rotting its end is mesured. α: rottion ngle of the bougie tip Tble 1 Relevnt chrcteristics of the four commercilly vilble bougies tested Bougie Length (cm) Dimeter (Fr) Angulted tip Construction mteril Product Venn reusble cm / 35 inner: polyester outer: resin Smiths Medicl Boussignc cm / 40 polyether block mide Vygon Portex single-use cm / 35 polyvinyl chloride Smiths Medicl Frov cm / 30 polyethylene Cook Medicl

4 Tkenk et l. BMC Anesthesiology (2017) 17:133 Pge 4 of 7 Sttisticl nlysis To evlute the performnce of ech bougie s n id to endotrchel intubtion with n AWS, the differences in rottion ngle between its end nd tip, which were the primry endpoint, were clculted. A preliminry study hd estblished tht the difference in rottion ngle ws 129 with SD of 13 when Portex single-use bougie end ws rotted clockwise to n ngle of 180 (unpublished dt presented t the 63th Annul Meeting of the Jpnese Society of the Anesthesiologists, Fukuok, 26 My, 2016). With 20% bsolute chnge defined s cliniclly importnt chnge [10], it ws clculted tht minimum smple size of six ws required to detect such chnge with α = 0.05 nd β = 0.2. Significnt differences were tested for by one-wy ANOVA with Bonferroni post hoc correction for multiple comprisons. Rottion of the bougie by n esy or moderte degree of force ws considered cliniclly cceptble nd Fisher s exct probbility test ws used for comprison. Differences in the Cormck-Lehne lryngoscopic grde nd success rte were nlyzed by Kruskl-Wllis test nd the chi-squre test, respectively. A p vlue <0.05 ws considered to denote significnce. Sttisticl nlysis ws crried out using SttView 5.0 (SAS Institute, Cry, NC, USA). Results Bench study Difference in rottion ngle between the bougie tip nd end (Fig. 2) Figure 2 shows the rottion ngles of the tip of ech bougie creted by rotting its end. The differences in the rottion ngle between the bougie tip nd end were significntly lrger with Portex single-use nd Frov bougies thn with Venn reusble nd Boussignc bougies (P < 0.01). The rottion ngles of the tips of Venn reusble, Boussignc, Portex single-use, nd Frov bougies were 145 /123 (clockwise / counterclockwise), 92 /108, 46 /56, nd 39 /51, respectively, when their ends were rotted clockwise or counterclockwise to n ngle of 180. Venn reusble nd Boussignc bougies could be rotted in n endotrchel tube plced into n AWS chnnel, the former chieving superior vlues. At ll ngles tht we mesured, the rottion chieved t the tips of Portex single-use nd Frov bougies ws less thn onethird of tht pplied t their ends. Degree of force required to rotte the bougie (Tble 2) All seven nesthesiologists could rotte Venn reusble nd Boussignc bougies by pplying esy or moderte rottionl force to their ends; however, rottion of Portex single-use nd Frov bougies ws difficult or impossible. Venn reusble nd Boussignc bougies could be rotted esier thn Portex single-use nd Frov bougies (P <0.01). Mnikin study Time required for successful intubtion (Tble 3) Men times required for successful intubtion with Venn reusble, Boussignc, Portex single-use, nd Frov bougies were 25 (SD, 5) s, 35 (6) s, 61 (17) s, nd 69 (22) s, respectively. Intubtion times were significntly shorter with Venn reusble nd Boussignc bougies thn with Portex single-use nd Frov bougies (P < 0.01) despite no significnt differences in Cormck-Lehne lryngoscopic grde between the four bougies. Rottion ngle of the bougie tip (degree) Venn reusble Boussignc Portex single-use Frov Idel line 90 Counterclockwise 45 Clockwise Rottion ngle of the bougie end (degree) Fig. 2 Men (SD) of rottion ngle of the tip of ech bougie creted by rotting its end. Idel line (dotted line) denotes complete trnsmission of the rottionl force t the bougie end long the shft to its tip. The difference between the idel line nd ech colored line is tht in rottion ngle between its end nd tip. P < 0.01 vs Venn reusble. b P < 0.01 vs Boussignc bougie

5 Tkenk et l. BMC Anesthesiology (2017) 17:133 Pge 5 of 7 Tble 2 Degree of force required to rotte the bougie tips s clssified by ech nesthesiologist Degree of force for rottion Bougie Venn reusble Boussignc Portex single-use Frov Esy Moderte Difficult Impossible Esy or moderte is considered cliniclly cceptble P < 0.01 vs Venn reusble b P < 0.01 vs Boussignc Number of successful intubtions (Tble 3) All seven nesthesiologists chieved endotrchel intubtion with Venn reusble nd Boussignc bougies but 2 nd 3 of them filed to chieve with Portex single-use nd Frov bougies, respectively. There ws no significnt difference in success rte between the four bougies. Discussion Bench study demonstrted tht Venn reusble nd Boussignc bougies could be rotted without difficulty in the lumens of endotrchel tubes plced into the chnnel of n AWS. However, the rottion chieved t the tips of Portex single-use nd Frov bougies ws less thn onethird of tht pplied t their ends becuse their shfts twisted, preventing full trnsmission of the rottionl force pplied t their ends to their tips. Lryngoscopists must rotte the bougies with one hnd only becuse they hve to hold the AWS in the other hnd. Thus, bougies tht require ppliction of excessive force to chieve free rottion of the bougie tip in the endotrchel tube re not useful ids to intubtion with n AWS. Of the four bougies tht we studied, only Venn reusble nd Boussignc bougies could be esily rotted in the lumens of the endotrchel tubes by pplying n esy or moderte degree of rottionl force, which we considered cliniclly cceptble, to their ends; thus these bougies were cliniclly useful ids to intubtion with n AWS. In contrst, rottion of the ends of Portex single-use nd Frov bougies to 180, which required excessive force, chieved less thn 56 rottion of their tips. In the scenrio of difficult intubtion with n AWS tht we simulted, four steps were required to chieve insertion of bougie into the trche: 1) directing the ngulted tip towrds 6 o clock by rottion; 2) positioning it behind the epiglottis; 3) chnging the direction of the tip from 6 o clock to 12 o clock; nd 4) dvncing the bougie through the vocl cords while keeping close to the lryngel surfce of the epiglottis. The nesthesiologists were ble to insert Venn reusble nd Boussignc bougies into the trche without difficulty becuse their tips rotted esily. In contrst, even when the nesthesiologists used considerble rottionl force to rotte the ends of Portex single-use nd Frov bougies, their tips did not rotte freely nd could not be guided in the desired direction. Thus, it ws often difficult for the nesthesiologists to plce the bougies tips behind the epiglottis, which prolonged time required for the intubtion ttempt nd mde chievement of endotrchel intubtion difficult. These findings supported the results of the bench study. We therefore recommend using Venn reusble or Boussignc bougie, prticulrly in ptients whose trche re difficult to intubte with n AWS. Even when n excellent view of the glottis hs been chieved, it is sometimes difficult to insert n endotrchel tube long the ntomicl curve-shped blde of videolryngoscope cross the vocl cords [4 6, 11 15]. This is common difficulty in endotrchel intubtion using videolryngoscopes [11]. Previous studies hve suggested tht bougies cn effectively ddress this problem [1, 4 6, 11 15]. For exmple, bougies re reportedly useful for ssisting intubtion with n Airtrq [14, 15]. We believe Tble 3 Lryngoscopic view, success rte, nd time required for successful intubtion with n Airwy Scope nd bougie in mnikin Bougie Venn reusble Boussignc Portex single-use Frov Lryngoscopic view (grde1/2/3) 6/1/0 7/0/0 7/0/0 7/0/0 Success rte 7/7 7/7 5/7 4/7 Time required for successful intubtion (second) 25(5) 35(6) 61(17),b 69(22),b Vlues for time to intubtion re men (SD) P < 0.01 vs Venn reusble b P < 0.01 vs Boussignc

6 Tkenk et l. BMC Anesthesiology (2017) 17:133 Pge 6 of 7 tht our findings re pplicble to ddressing difficult intubtion using the fmily of chnneled videolryngoscopes with ntomiclly-shped blde nd guiding chnnel tht is designed to direct the endotrchel tube towrd the glottis. Severl fctors contribute to rotting bougie in the lumen of n endotrchel tube; these comprise the construction mteril, size, curvture, structure of the inner surfce of the endotrchel tube, lubriction, nd the construction mteril of the bougie. In this study, the endotrchel tube nd lubricnt were identicl in ll tests. We believe tht the construction mteril of the bougie my influence its rottion in the endotrchel tube. The four bougies tested were constructed with different polymers (Tble 1), which hd different torsion strength properties. The polymers of Portex single-use nd Frov bougies might tend to twist ginst the friction tht occurred during rottion in the nrrow curved lumen of the tube, compred with those of Venn reusble nd Boussignc bougies. We consider tht the difference in their properties is possible explntion for difficult rottion. Further studies re needed. Airwy trum cn occur during intubtion with bougie s result of ggressive plcement of the bougie or rilroding the endotrchel tube over it. However, this compliction hs been reported even when the bougie hs been dvnced without resistnce nd the tube esily rilroded over it [16]. Moreover, there hve been some cses of displcement of the epiglottis nd its prolpse into the trche beside the endotrchel tube during ttempts of intubtion with n AWS [17]. Anesthesiologists should be wre of these possible complictions of intubtion with bougie nd/or n AWS, nd be mindful to mnipulte the bougie nd endotrchel tube gently nd crefully during intubtion ttempts. If n injury of the lrynx nd trche is suspected, it should be identified directly or with fiberscope. Study limittions Our experimentl design hs some potentil limittions. It ws impossible to blind the nesthesiologists to the bougie being used, potentilly bising mesurement of the rottion ngle of the bougie tip. In ddition, the seven nesthesiologists who did the bench study were the sme s the ones who did the mnikin study, which might cuse potentil for bis in the results of the mnikin study. Regrding mesuring the ngle of rottion of the bougies tips, we postulted tht they rotted round the corner of the ngulted tip tht hd been mrked. However, when bougie end ws rotted, its tip did not lwys drw perfect circle becuse the center sometimes moved, potentilly introducing bis in mesuring the ngle of rottion. When using bougie s n id to intubtion with n AWS, precise rottion of the bougie tip my be unnecessry becuse it is visible on the monitor screen. Ese of mnipultion of the tip in desired direction should be more importnt thn precise rottion. In the bench study, it ws clerly esier to rotte Venn reusble nd Boussignc bougies thn Portex single-use nd Frov bougies. Moreover, in the mnikin study, in which the epiglottis could not be directly lifted with the tip of the AWS blde, the 180 rottion of the bougie tip tht ws required for successful intubtion ws often difficult to chieve with Portex single-use bougies nd Frov intubting ctheters. Thus, we believe tht these bises were of minor importnce. We used n AirSim mnikin in this study. A preliminry ssessment of the bility of vrious commercilly vilble mnikins to simulte scenrio of difficult intubtion with n AWS, which differs from tht with conventionl lryngoscope, resulted in us choosing n AirSim mnikin s the most suitble for our purposes. Notbly, this ws bench nd mnikin study imed t compring four bougies, the findings my not ccurtely indicte how ech bougie performs in humns. Becuse our study ws designed for scenrio of difficult intubtion with n AWS, we used reltively smll size endotrchel tube. Further studies using lrger endotrchel tubes re therefore needed. Bougies re designed s ids to endotrchel intubtion with conventionl lryngoscope rther thn devices for rotting in the nrrow curved lumens of the endotrchel tubes [6 8]. Thus, the results of this study do not reflect the performnce of these bougies when used for their originl purposes. Conclusions We hve demonstrted by both bench nd mnikin studies tht the four bougies tht we studied re not equivlent in terms of their rottion in the lumens of endotrchel tubes plced into the chnnel of n AWS. Of the four bougies investigted, we found tht Venn reusble trchel tube introducers nd Boussignc bougies re useful ids to intubtion with n AWS. Portex single-use bougies nd Frov intubting ctheters seem to be less suitble for this technique. Different bougies my be of vrying utility when used with n AWS or irwy device with n endotrchel tube chnnel. We recommend confirming tht the bougie to be used does rotte esily within the endotrchel tube plced into the chnnel of n AWS before using it. Abbrevitions ANOVA: Anlysis of vrince; AWS: Airwy Scope; s: second; SD: Stndrd devition Acknowledgements Not pplicble.

7 Tkenk et l. BMC Anesthesiology (2017) 17:133 Pge 7 of 7 Funding We received no specific funding for this work. Avilbility of dt nd mterils The dtsets generted nd nlyzed during the current study re vilble from the corresponding uthor on resonble request. Authors contributions IT conceived, designed, performed the experiments, nlyzed the dt, nd drfted the mnuscript. KA performed the experiments nd nlyzed the dt. TI performed the experiments nd contributed mterils nd nlysis tools. YT performed the experiments nd contributed mterils nd nlysis tools. All uthors red nd pproved the finl mnuscript. 13. Btuwitge B, McDonld A, Nishikw K, et l. Comprison between bougies nd stylets for simulted trchel intubtion with the C-MAC D- blde videolryngoscope. Eur J Anesthesiol. 2015;32: Dont N, Villevieille T, Msson Y, Vuthier A, Rousseu JM, Pelletier C. In cse of difficult intubtion with the Airtrq : the gum elstic bougie my ssist. Ann Fr Anesth Renim. 2011;30: Mtsuym K, Shibt M, Fujink W, Tktori M, Td K. Effectiveness of gum elstic bougie for trchel intubtion with Airtrq opticl lryngoscope. Msui. 2012;61: Shin M, Anglde D, Buchberger M, Jnkowski A, Albldejo P, Ferretti GR. Cse reports: itrogenic bronchil rupture following the use of endotrchel tube introducers. Cn J Anesth. 2012;59: Suzuki A, Ktsumi N, Hond T, et l. Displcement of the epiglottis during intubtion with the Pentx-AWS Airwy Scope. J Anesth. 2010;24: Ethics pprovl nd consent to prticipte The need for ethicl pprovl ws wived by the Institutionl Ethicl Committee becuse no ptients were involved in this study. Informed consent to prticipte in the study ws obtined from ll prticipnts. Consent for publiction Not pplicble. Competing interests The uthors declre tht they hve no competing interests. Publisher s Note Springer Nture remins neutrl with regrd to jurisdictionl clims in published mps nd institutionl ffilitions. Author detils 1 Deprtment of Anesthesi, Kyushu Rosi Hospitl, 1-1 Sonekit, Kokurminmi, Kitkyushu , Jpn. 2 Deprtment of Anesthesi, Kitkyushu Generl Hospitl, 1-1 Higshijono, Kokurkit, Kitkyushu , Jpn. Received: 6 Februry 2017 Accepted: 25 September 2017 References 1. Asi T, Liu EH, Mtsumoto S, et l. Use of the Pentx-AWS in 293 ptients with difficult irwys. Anesthesiology. 2009;110: Hely DW, Mties O, Hovord D, Kheterpl SA. systemtic review of the role of videolryngoscopy in successful orotrchel intubtion. BMC Anesthesiol. 2012;12: PENTAX-AWS. AWS-S100 instruction mnul. Tokyo, Jpn: Pentx-HOYA Corportion; Tkenk I, Aoym K, Iwgki T, Tkenk Y, Kdoy T. Approch combining the irwy scope nd the bougie for minimizing movement of the cervicl spine during endotrchel intubtion. Anesthesiology. 2009;110: Tkenk I, Aoym K, Kinoshit Y, et l. Combintion of Airwy Scope nd bougie for full-stomch ptient with difficult intubtion cused by unnticipted ntomicl fctors nd cricoid pressure. J Clin Anesth. 2009;21: Seto A, Tkenk I, Aoym K, et l. Efficcy of bougie in difficult intubtion with the Airwy Scope cused by inbility to lift the epiglottis directly. Msui. 2010;59: Mcintosh RR. An id to orl intubtion. Br Med J. 1949;1: Noln JP, Willims WE. An evlution of gum elstic bougie. Intubtion times nd incidence of sore throt. Anesthesi. 1992;47: Ltto IP, Stcey M, Mecklenburgh J, Vughn RS. Survey of the use of the gum elstic bougie in clinicl prctice. Anesthesi. 2002;57: Minmi T, Tkenk I, Aoym K, et l. Comprison of the bility of torque control blockers to rotte with tht of conventionl bronchil blockers: mnikin study. Msui. 2017;66: Frerk C, Mitchell VS, McNrry AF, et l. Difficult Airwy Society intubtion guidelines working group. Difficult Airwy Society 2015 guidelines for mngement of unnticipted difficult intubtion in dults. Br J Anesth. 2015;115: Asi T. Videolryngoscopes: do they truly hve roles in difficult irwys? (Editoril). Anesthesiology. 2012;116: Submit your next mnuscript to BioMed Centrl nd we will help you t every step: We ccept pre-submission inquiries Our selector tool helps you to find the most relevnt journl We provide round the clock customer support Convenient online submission Thorough peer review Inclusion in PubMed nd ll mjor indexing services Mximum visibility for your reserch Submit your mnuscript t