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A randomized controlled comparison of
non-channeled king vision, McGrath MAC
video laryngoscope and Macintosh direct
laryngoscope for nasotracheal intubation in
patients with predicted difficult intubations
Haozhen Zhu, Jinxing Liu, Lulu Suo, Chi Zhou, Yu Sun
*
and Hong Jiang
*
Abstract
Background: King Vision and McGrath MAC video laryngoscopes (VLs) are increasingly used. The purpose of this
study was to evaluate the performance of nasotracheal intubation in patients with predicted difficult intubations
using non-channeled King Vision VL, McGrath MAC VL or Macintosh laryngoscope by experienced intubators.
Methods: Ninety nine ASA I or II adult patients, scheduled for oral maxillofacial surgeries with El-Ganzouri risk index
1–7 were enrolled. Patients were randomly allocated to intubate with one of three laryngoscopes (non-channeled
King Vision, McGrath MAC and Macintosh). The intubators were experienced with more than 100 successful
nasotracheal intubations using each device. The primary outcome was intubation time. The secondary outcomes
included first success rate, time required for viewing the glottis, Cormack-Lehane grade of glottis view, the number
of assist maneuvers, hemodynamic responses, the subjective evaluating of sensations of performances and
associated complications.
Results: The intubation time of King Vision and McGrath group was comparable (37.6 ± 7.3 s vs. 35.4 ± 8.8 s) and
both were shorter than Macintosh group (46.8 ± 10.4 s, p< 0.001). Both King Vision and McGrath groups had a 100%
first attempt success rate, significantly higher than Macintosh group (85%, p< 0.05). The laryngoscopy time was
comparable between King Vision and McGrath group (16.7 ± 5.5 s vs. 15.6 ± 6.3 s) and was shorter than Macintosh
group (22.8 ± 7.2 s, p< 0.05) also. Compared with Macintosh laryngoscope, Glottis view was obviously improved
when exposed with either non-channeled King Vision or McGrath MAC VL (p< 0.001), and assist maneuvers
required were reduced (p< 0.001). The maximum fluctuations of MAP were significantly attenuated in VL groups
(47.7 ± 12.5 mmHg and 45.1 ± 10.3 mmHg vs. 54.9 ± 10.2 mmHg, p< 0.05 and p< 0.01). Most device insertions were
graded as excellent in McGrath group, followed by Macintosh and King Vision group (p= 0.0014). The tube
advancements were easier in VLs compared with the Macintosh laryngoscope (p< 0.001). Sore throat was found
more frequent in Macintosh group compared with King Vision group (p< 0.05).
Conclusions: Non-channeled King Vision and McGrath MAC VLs were comparable and both devices facilitated
nasotracheal intubation in managing predicted difficult intubations compared with Macintosh laryngoscope.
Trial registration: ClinicalTrials registration number NCT03126344. Registered on April 24, 2017.
Keywords: Airway management - video laryngoscopes - Nasotracheal intubation
© The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver
(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
* Correspondence: dr_sunyu@163.com;dr_jianghong@163.com
Department of Anesthesiology, Shanghai Ninth People’s Hospital Affiliated to
Shanghai Jiao Tong University School of Medicine, 639 Zhizaoju Road,
Shanghai 200011, China
Zhu et al. BMC Anesthesiology (2019) 19:166
https://doi.org/10.1186/s12871-019-0838-z
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
Introduction
The video laryngoscope (VL) has been well established
as an approach in airway management for patients with
difficult direct laryngoscopy [1–5]. However, most of the
literatures focused on their usage for oral intubation.
Nasotracheal intubation (NTI), often required for oral
and maxillofacial operation, may be complicated by
causing injuries to the nasal passage and sinusitis [6]. In
addition, a superior laryngoscopy does not guarantee a
successful advancement of the tube into the trachea and
external manipulation of the larynx, a Magill forceps,
change in head position or partial inflation of cuff is re-
quired [6–9].
The success of a VL assisted intubation depends on
multiple factors, such as blade design (acute angled or
Macintosh like; channeled or non-channeled); quality of
the image on the monitor, as well as the experience of
the intubator [5,10]. Recently, the McGrath MAC VL
(Fig. 1a) (Aircraft Medical, Edinburgh, UK) has been
widely used. It has a battery powered handle, on the top
of which is an adjustable liquid crystal display monitor.
It has an angulated single-use blade without a guiding
channel. It was reported to facilitate routine NTIs in
normal patients compared with Macintosh laryngoscope
[11,12]. The King Vision VL (Fig. 1b) (Ambu Inc.,
Denmark) is also a portable device with similar design
with McGrath MAC VL. King Vision VL is relative
newer and cheaper. Different from McGrath, its monitor
is fixed to the handle. It has a channel integrated to the
blade to facilitate tube guidance into the trachea though,
channeled King Vision VL required longer time and pro-
vided lower success rates on first attempt for oral intub-
ation in normal airway compared to McGrath MAC VL
[13]. It is argued that channeled devices are often bulky
and can be difficult to use in patients with limited
mouth opening [2,13,14]. However, the King Vision VL
is also available with standard non-channeled blade for
NTI. Recent study also found time for tracheal intub-
ation could be shortened by using a non-channeled
blade [15]. In addition, the King Vision VL is reported
that can provide a better vision condition which may be
beneficial to NTI.
A recent systematic review comparing VL versus DL
for NTI showed that VL is particularly beneficial for pa-
tients with difficult airways [16]. However, only two ran-
domized controlled trials (Airtriq and C-MAC versus
Macintosh) were enrolled [7,17]. It remains unclear
whether non-channeled King Vision or McGrath MAC
VL, compared with conventional laryngoscope, provide
shorter intubation time and a higher first success rate
for NTI when used by experienced provider in manage-
ment of predicted difficult intubation. It is also unclear
whether non-channeled King Vision VL is superior to
McGrath MAC VL when used for NTI. We therefore
performed this randomized, controlled trial to fill the
gap. Our hypothesis was that the non-channeled King
Vision and McGrath MAC VL were comparable, and
both video devices were superior to Macintosh laryngo-
scope in terms of shorter intubation time and higher
first success rate.
Methods
Ethics approval and consent to participate
This trial was approved by IRB (2017–308-T228) from
Shanghai Ninth People’s Hospital Affiliated to Shanghai
Jiao Tong University School of Medicine, and registered
at clinicaltrials.gov (NCT03126344). Written consents to
participate were obtained from all participants after en-
rollment. Our study was adhered to the applicable
Fig. 1 The video laryngoscopes evaluated in our study. A: non-channeled King Vision video laryngoscope. B: McGrath MAC video laryngoscope
Zhu et al. BMC Anesthesiology (2019) 19:166 Page 2 of 9
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Consolidated Standards of Reporting Trials (CONSORT)
guidelines.
Subjects
Consecutive patients, between 18 and 60 years old with
American Society of Anesthesiologists (ASA) classifica-
tion of I or II, and requiring NTI for elective oral and
maxillofacial surgery, were screened in the Preoperative
Evaluation Unit of our institute. Prediction of difficult
intubation is graded by El-Ganzouri multivariate risk
index (EGRI) based on seven parameters (body weight,
modified Mallampati class, mouth opening, thyromental
distance, neck movement, prognathism, and history of
difficult airway) [17,18] (Additional file 1). Patients were
enrolled if EGRI score 1–7[17]. In cases where an awake
NTI was planned [i.e. EGRI score > 7, history of reflux
or diagnosed oesophageal disease, severe obstructive
sleep apnea (OSA) and morbid obesity (body mass index
> 40 kg/m
2
)] were excluded from the study.
Method of anesthesia
The study was designed as a single blind, three parallel
arms, randomized controlled trial comparing NTIs using
non-channeled King Vision VL, McGrath MAC VL and
Macintosh DL in adults with predictors of difficult air-
ways. The size 3 blades were used in both King Vision
and McGrath group. The standard Macintosh blade (size
3 for female; size 4 for male) was used as control.
Patients were asked which nostril was clearer. If both
sides were equal and the surgeon had no objection, the
right nostril was chosen [19]. Patients were randomly
assigned to King Vision group, McGrath group or Mac-
intosh group via a computer generated randomization
table. All NTIs were performed by attending anesthesiol-
ogists experienced with more than 100 successful NTIs
with each device.
No premedication was administered. Lactated Ringer’s
solution infusion was started intravenously to deal with
the fluid loss from the overnight fast after entering the
operating theatre. A standard preparation was then per-
formed, including heart rate (HR), lead II ECG, SpO
2
(pulse oximetry), and end expiratory carbon dioxide. A
Bispectral (BIS) index sensor was attached to the pa-
tient’s forehead in conjunction with the BIS Monitor.
Cannulation of right radial artery was performed under
local anesthesia for invasive blood pressure monitoring.
All patients were preoxygenated by a facemask in the
position of neutral. Prior to anesthesia induction, the nasal
mucosa was well prepared with 1% tetracaine hydrochlor-
ide jelly for 2 min and five drops of ephedrine hydrochlor-
ide nitrofurazone (containing approximately 2 mg
ephedrine) in all patients. Baseline hemodynamic data
were recorded by an investigator after a stabilization
period of 10 min.
The nasotracheal tube used was reinforced endo-
tracheal tube (ETT, Safety-Flex with Murphy Eye, oral/
nasal, Athlone, Ireland; ID 6.5 mm in female and ID 7.0
mm in male patients) and was well lubricated with 1%
tetracaine hydrochloride jelly. Dosing of induction medi-
cations was given at the discretion of the attending anes-
thesiologists. Induction agents included midazolam
(0.02 mg/kg), propofol (1.5~2 mg/kg) and fentanyl (2 μg/
kg). Upon loss of consciousness and jaw relaxation,
manual ventilation was tested. If manual ventilation was
available, cissatracurium besilate (0.15 mg/kg) was ad-
ministrated and post induction values were recorded 3
min after induction. Unsuccessful manual ventilation led
to study exclusion.
The anesthesiologist tried to intubate when the Train
of Four (TOF) count reached zero and BIS value de-
creased to 50. NTI was performed in a standard manner.
First, a preformed ETT was inserted into the nostril and
advanced to the posterior nasopharyngeal wall. Second,
a laryngoscope blade was introduced into the mouth to
expose the glottis. If it’s necessary, the BURP maneuver
(backward, upward, right-sided pressure) on the thyroid
cartilage was attempted to obtain good glottis visibility
[20]. And ultimately, the ETT was inserted into the tra-
chea with the aid of Magill’s forceps, head flexion, or
cuff inflation if necessary.
The primary outcome was the intubation time, defined
as the interval between opening the mouth and the time
when three consecutive end-tidal CO
2
waves were ap-
peared on the monitor. Since the time required for SpO
2
to decrease during apnea was about 150 s [21], we de-
fined a failure as the intubation time took longer than
150 s [22], SpO
2
less than 92% or oesophagus intubation.
The patient was mask ventilated after a failed attempt.
In VL groups, the intubator should try the other video
device for the second attempt. In Macintosh group, the
patient’s airway was managed using either non-
channeled King Vision or McGrath MAC VL at the dis-
cretion of the intubator. If the second attempt was still
unsuccessful, the fiberoptic bronchoscope (FOB) was ap-
plied. If intubation is not possible with FOB, the patient
was awakened.
Secondary outcome measures included time to expose
the glottis (laryngoscopy time) and the view of glottis
opening valued by Cormack-Lehane grade. A Cormack-
Lehane grade IV was defined as laryngoscopy failure. A
blinded investigator also recorded the hemodynamic
changes (MAP, HR) during the procedure of NTI. The
maximum values of invasive MAP were recorded. After
successful intubation, the subjective sensation of the
intubator (ease of device insertion, quality of view on
display and ease of tube advancement) was graded as ex-
cellent, good, fair and poor. Other intubation parameters
included incidences of bleeding or dental injury, number
Zhu et al. BMC Anesthesiology (2019) 19:166 Page 3 of 9
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of assist maneuvers (use of BURP maneuver, Magill’s
forceps, or cuff inflation). Twenty four hours after the
procedure, a nurse anesthetist blinded to group assign-
ment recorded the severity of sore throat and
hoarseness.
Statistical analysis
Our sample size estimation was based on previous stud-
ies [11,23], in which the standard deviations (SD) of in-
tubation time were estimated as 8 and 13.7 s. To detect
a intergroup difference of 10 s in intubation time with α
of 0.05 and βof 0.8, we estimated that 30 patients would
be enough for each group. To compensate for patients
dropping out during the study, additional patients (10%)
were added. The final sample size of 33 patients was in
each group.
Mean (SD) or Median (IQR [range]) was used to de-
scribe the parametric data. The number (percentage)
was used to describe nonparametric data. Statistical ana-
lyses were performed with Prism 5.0 for Windows
(GraphPad Software, Inc., La Jolla, California, USA). Bin-
ary data for three groups were analyzed using chi-square
test and each two groups were compared with chi-
square segmentation method or Fisher’s exact test as ap-
propriate. One-way analysis of variance (ANOVA) with
post-hoc Bonferroni’s Multiple Comparison test was
used to analyze parameter data for changes within
groups. The Kruskal-Wallis ANOVA with post-hoc
Dunn’s test was used to analyze ordinal data. A pvalue
less than 0.05 was considered as significant.
Results
In total, 99 patients were enrolled in this study between
June 2017 and January 2018(Fig. 2). The distribution of
the patient characteristics and difficult intubation pre-
dictors were well balanced between three groups
(Table 1). Five patients in Macintosh group were intu-
bated successfully with VLs (two patients with King Vi-
sion and three patients with McGrath VL) after failed
intubation attempt. All failures were due to poor glottis
exposure and esophagus intubation. These patients were
excluded from follow-up data analysis as these outcomes
were not controlled.
Regarding the primary outcome measure intubation
time, King Vision and McGrath groups were comparable
(37.6 ± 7.3 s vs. 35.4 ± 8.8 s) and both were significantly
shorter than Macintosh group (46.8 ± 10.4 s, p< 0.001,
Table 2).
Regarding the secondary outcomes, both King Vision
and McGrath groups had a 100% first attempt success
rate, significantly higher than Macintosh group (85%, p<
0.05, Table 2). The laryngoscopy time was comparable
Fig. 2 Consort flow chart
Zhu et al. BMC Anesthesiology (2019) 19:166 Page 4 of 9
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between King Vision and McGrath groups (16.7 ± 5.5 s vs.
15.6 ± 6.3 s) and were significantly shorter than Macintosh
group (22.8 ± 7.2 s, p< 0.05, Table 2), also. Glottis view
was obviously improved when exposed with either non-
channeled King Vision or McGrath MAC VL: the percent-
age of Cormack-Lehane grade I or II was 100% in VLs
groups and 48% in Macintosh group, respectively (p=
0.0004, Table 2). The number of assist maneuvers re-
quired was 5, 4 and 18 in King Vision, McGrath and Mac-
intosh group, respectively (p< 0.0001, Table 2). The SpO
2
did not differ between groups.
Changes in hemodynamic responses during anesthesia
induction and intubation were demonstrated in Fig. 3.
Briefly, both MAP and HR decreased significantly in
each group after anesthesia induction. Then glottis ex-
posure with each laryngoscope and following ETT place-
ment caused significantly increase in MAP and HR.
Finally, MAP and HR descended slowly 1, 3, 5 min after
successful intubation. Notably, the maximum fluctua-
tions of MAP (MAP
max
−MAP
post-induction
) in King Vi-
sion and McGrath groups were comparable and both
were significantly attenuated compared with Macintosh
group (47.7 ± 12.5 mmHg and 45.1 ± 10.3 mmHg vs.
54.9 ± 10.2 mmHg, p< 0.05 and p< 0.01 respectively,
Table 2).
Results of the subjective sensations between devices
were listed in Table 3. Most device insertions were graded
as excellent in McGrath group (91%), followed by Macin-
tosh (82%) and King Vision group (54%) (p= 0.0014).
Quality of view on display did not differ between King Vi-
sion and McGrath groups. The ease of tube advancement
was comparable between King Vision and McGrath
groups, and both were much better than Macintosh group
(p< 0.001). There were no cases of desaturation and den-
tal injury during NTIs. Sore throat was found more fre-
quent in Macintosh group compared with King Vision
group (p< 0.01). Occurrence of bleeding and hoarseness
seemed more frequent in Macintosh group, but failed to
show significance. These symptoms were minor and
ceased spontaneously without intervention.
Discussion
Although many studies about indirect laryngoscopes
were carried out, only two randomized controlled trial,
to our knowledge, have compared the VLs (Airtraq and
C MAC respectively) with Macintosh laryngoscope in
Table 1 Patient characteristics and difficult intubation profiles
King Vision
n=33
McGrath
n=33
Macintosh
n=33
pvalue
Men (%) 15 (45%) 19 (58%) 16 (48%) NS
Age; years 38 (12) 36 (11) 40 (11) NS
BMI; Kg·m
−2
22 (3) 22 (3) 22 (3) NS
ASA class I/II (%) 11/22 (33/67%) 15/18 (45/55%) 13/20 (40/60%) NS
Neck movement < 80° (%) 2 (6%) 1 (3%) 1 (3%) NS
Mallampati III or IV (%) 30 (91%) 31 (94%) 30 (91%) NS
Interincisor gap < 3 cm (%) 9 (27%) 10 (30%) 8 (27%) NS
Thyromental distance < 6 cm (%) 8 (27%) 9 (27%) 11 (33%) NS
Ability to prognath (%) 30 (91%) 28 (85%) 29 (88%) NS
EGRI scores 3 (2,4.5) 3 (2.5,4) 3 (2,4) NS
Data presented as mean (SD), median (IQR [range]) or number of patients (percentage). BMI: Body Mass Index. ASA class: American Society of Anesthesiologists
classification. EGRI: El-Ganzouri risk index. NS: not significant
Table 2 Intubation profiles
King Vision
n=33
McGrath
n=33
Macintosh
n=33
pvalue
Intubation time (sec)
1
37.6 (7.3) *** 35.4 (8.8) *** 46.8 (10.4) < 0.0001
First success of intubation (%) 33 (100%) * 33 (100%) * 28 (85%) 0.0017
Laryngoscopy time (sec)
1
16.7 (5.5) * 15.6 (6.3) * 22.8 (7.2) 0.0002
C-L grade I/II/III/IV 29/4/0/0 *** 27/6/0/0 *** 6/10/12/5 < 0.0001
C-L grade I and II (%) 33 (100%) *** 33 (100%) *** 16 (48%) 0.0004
Assist maneuvers (%)
1
5 (15%) *** 4 (12%) *** 18 (64%) < 0.0001
Difference between MAP
maximum
and MAP
post-induction
(mmHg)
1
47.7 (12.5)* 45.1 (10.3)** 54.9 (10.2) 0.0030
Data presented as mean (SD) or number (percentage). C-L: Cormack and Lehane. MAP: mean arterial pressure. NS: not significant. Assist maneuvers: use of the
BURP maneuver, Magill’s forceps or cuff inflation.
1
: n = 28 in Macintosh group. *p< 0.05; **p< 0.01; ***p< 0.001 compared with Macintosh group
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Fig. 3 Changes in hemodynamic responses during anesthesia induction and intubation. Up: Heart Rate. Down: MAP. MAP: mean arterial pressure
Table 3 Sensations of performances and any complications
King Vision n= 33 McGrath
n=33
Macintosh
n=28
pvalue
Ease of device insertion (excellent/good/fair/poor) 18/13/2/0 # (54/40/6/0%) 30/3/0/0 (91/9/0/0%) 23/5/0/0 (82/18/0/0%) 0.0014
Quality of view on display (excellent/good/fair/poor) 33/0/0/0 (100/0/0/0%) 32/1/0/0 (97/3/0/0%) / NS
Ease of tube advancement (excellent/good/fair/poor) 28/5/0/0 *** (85/15/0/0%) 29/4/0/0 *** (88/12/0/0%) 13/10/4/1 (46/36/14/4%) 0.0001
Desaturation (%) 0 (0) 0 (0) 0 (0) NS
Bleeding (%) 1 (3%) 0 (0) 4 (14%) 0.0357
Dental injury (%) 0 (0) 0 (0) 0 (0) NS
Sore throat (%) 3 (11%) ** 8 (24%) 12 (43%) 0.0093
Hoarseness (%) 2 (6%) 1 (3%) 5 (18%) 0.969
Data presented as number (percentage). NS: not significant. #p< 0.05 compared with McGrath group. *p< 0.05; **p< 0.01; ***p<0.001 compared with
Macintosh group
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patients showing predictors of difficult nasal intubation
[7,17]. King Vison and McGrath MAC VLs are relative
newer and are also well worth studying. We provided
the first study about the non-channeled King Vision and
McGrath MAC VLs for NTIs in predicted difficult
patients.
Our main result was that the time to successful NTI
with both VLs was significantly faster than with Macin-
tosh DL. The intubation time mainly comprises two
parts: time to view the vocal cords and time required for
tube passage through glottis. Firstly, we confirmed both
non-channeled King Vision and McGrath MAC VL sig-
nificantly shortened the laryngoscopy time in predicted
difficult patients, which was certainly a reason for a
shortened intubation time. The result showed less asso-
ciation between predictors of difficult intubations and
glottis exposure using non-channeled King Vision or
McGrath MAC VL than using Macintosh DL. Secondly,
laryngoscopy with non-channeled King Vision or
McGrath MAC caused less anterior elevation of the lar-
ynx than invasive direct laryngoscopy because airway
axes alignment was not needed. This might provide a
more direct route from nasopharynx to glottis and
therefore ease advancing the tube into the trachea. In
current study, we confirmed it was easier to advance the
ETT through the glottis, accordingly less frequency of
assist maneuvers was required in VL groups. Thirdly,
when doing oral intubation with VLs, we often bend the
styletted tracheal tube to a greater degree (‘hockey stick’
like) to follow the curvature of the video blade, which al-
ways hinder stylet removal and increase intubation time
[24,25]. However, stylet was not required for NTI in
our study. So use of VLs also saved time required for
tube advancement by decreasing the frequency of add-
itional assist maneuvers and stylet removal [7,11,24].
We noticed the laryngoscopy time was longer in King
Vision group compared with McGrath group. Alvis
et al., in a recent comparison with McGrath, suggested
that it was difficult when inserting the channeled blade
of King Vision VL into the mouth [13]. Here we found it
also more difficult when introducing the non-channeled
King Vision blade compared with McGrath blade. The
blade of King Vision is longer and more acute angled.
We agree with the author who claimed a specific angle
to the patient’s chest was required when insertion King
Vision ‘L’shaped blade [13]. On the contrary, the blade
design of the McGrath VL is similar to the classic Mac-
intosh DL. This provides the intubator with a familiar
laryngoscopy experience. The channeled blade of King
Vision may decrease the oral cavity for tube adjustment
and advancement during oral intubation [2,13]. During
NTI, however, no such difficulty was observed when ad-
vancing the trachea tube with non-channeled King Vi-
sion VL. This was in contrast to oral intubation [13].
Although the intubation time was a little bit longer in
King Vision group, the clinical relevant is debatable be-
cause SpO2 was not different between King Vision and
McGrath VL.
The predictors of difficult airways used in our study
are reliable [26]. To compare difficult intubation levels,
EGRI was used in our study [17,18]. It is reported that
EGRI > 7 were more suitable for awake fiberoptic intub-
ation [27]. Therefore, only patients with EGRI score 1–7
were included in our study. Although the variation of
enrollment was big, the EGRI scores were similar be-
tween groups. In addition, the distributions of risk factor
were also comparable. The proportion of Cormark-
Lehane grade III and IV in Macintosh group suggested
patients enrolled were predicted difficult intubations.
The 15% failure rate of Macintosh DL seem quite high
though, the success rate of Macintosh DL (85%) was
similar to what has been described previously [3,17].
Both non-channeled King Vision and McGrath
MAC VLs improved the Cormack-Lehane grade sig-
nificantly which was the main superiority of VLs. St
Mont et al. demonstrated first attempt success rate of
NTI by Airtraq was 94% in predicted difficult airway
[7]. Hazarika H et al. reported a 98% first attempt
success rate of NTI by C-MAC D-Blade VL for diffi-
cult nasal intubation [17]. Here, we demonstrated the
success rate of first attempt of NTI was 100% in non-
channeled King Vision and McGrath groups. The ‘you
see that you fail’situations of King Vision reported
previously [2,14]didnotoccurinpresentstudy.This
could be explained by the fact that its ‘L’shape blade
conformed to the upper airway well though; it always
hindered oral ETT advancement. While during NTI,
the shape and size of the non-channeled King Vision
blade has little influence on the tube advancement
and oral cavity allowed for nasotracheal tube adjust-
ment is big enough. Therefore, these results clearly
demonstrate that both non-channeled King Vision
and McGrath MAC VLs are good choices for NTIs.
All failed Macintosh assisted NTIs were because of
the poor glottis view, even with the help of assist ma-
neuvers. These patients were eventually easily intu-
bated on the first attempt with either non-channeled
King Vision or McGrath MAC VLs. We believe that
both of them can serve as a promising backup alter-
nativeforfailedNTIusingMacintoshDL.However,
VLs are not the Holy Grail [28]. Actually, VLs will
fail under certain conditions; the total success range
was 37–98% in literature [2]. Although our results
seem to suggest a 100% success rate of VLs intub-
ation, our result should be interpreted with caution
due to small sample size. Also, the results of this
studymaynotbeapplicabletoothertypesofpa-
tients, such as severe OSA or morbid obesity. The
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NTIs in our study were done by experienced attend-
ing anesthesiologists. Hence, there may generalize bias
in experience.
To avoid missing any hemodynamic response, invasive
blood pressure was used in current study. In addition,
the maximum fluctuation of MAP was chosen to reflect
the hemodynamic change. This could partially explain
why our data were different from previous study [17].
During NTI, stimulations of the nasopharyngeal struc-
tures, oropharyngeal structures and trachea induced by
laryngoscopy or ETT advancement are three main stages
of hemodynamic changes [29]. To optimizing glottis ex-
posure in difficult laryngoscopy patients, enhanced up-
ward lifting force of Macintosh blade was required [30].
The laryngeal prominence was excessively compressed
and the oropharynx structure was therefore distorted. In
such circumstance, assist maneuvers were often used to
help the ETT through the glottis in the Macintosh
group. However, the VLs allow to view glottis from the
monitor, intubate tube using less maneuvers and poten-
tially less force which minimized stimuli applied to the
oropharyngeal structures during intubation [31]. Our
data strongly demonstrated that the non-channeled King
Vision and McGrath MAC VLs might provide clinical
advantages in attenuating the hemodynamic changes to
potential difficult NTI patients.
Most participants felt McGrath blade insertions were
easiest. That was because of its slim design as we dis-
cussed before. McGrath MAC was lightest and more
portable than the others. The monitor could be adjusted
to an optimized angle for intubation. Although it was
claimed that the King Vision VL could provide a better
vision condition, we did not see the difference. Quality
of view on display did not differ between King Vision
and McGrath VLs. Reducing the usage of assist maneu-
vers, fewer demanding of the physical workload and
lower anterior pressure exerted on the soft structures
could be linked to reduced sore throat and hoarseness
occurrences in both VL groups. The King Vision group
had the fewest cases of sore throat. We guessed the
length and angle of the King Vision non-channeled blade
might be more beneficial to exposure of glottis com-
pared with Macintosh like blade, and accordingly less
workload was required. However, oral surgical proce-
dures might confound these results since they tend to
cause similar symptoms, and further study is required.
Some limitations of our study should be considered
carefully. First, neither the intubator nor the independ-
ent observer could be blinded from the groups. How-
ever, we have minimized adverse effects by defining
robust outcome measures. Second, if we compared both
Cormark-Lehane and POGO scores, our results should
be more convincing. Third, our results might be biased
by the variable experience of the intubator with different
laryngoscope. It is believed that intubation with VL re-
quire a complex hand-eye-coordination competencies
which grow with a learning curve [32]. On the other
hand, it was suggested that novices could translate direct
laryngoscopy technique to video laryngoscopy if it is
similar to classic Macintosh laryngoscope [33]. There-
fore, the results might not necessarily be obtained by
novice users. Finally, the participants included did not
represent genuine difficult airways. We believe it ethic-
ally questionable to test a new intubation device on
genuine difficult airway patients. Therefore, further stud-
ies may be carried out to clarify these issues.
Conclusion
In summary, we observed that NTIs with non-channeled
King Vision and McGrath VLs in the setting of predicted
difficult intubations resulted in shorter intubation time,
higher first success rate, better qualities of glottis view,
attenuated hemodynamic responses, and fewer inci-
dences of side effect compared with Macintosh DL.
These data provided evidence that NTI using King Vi-
sion and McGrath were comparable, and both devices
were superior to Macintosh DL in managing the difficult
intubations.
Additional files
Additional file 1: El-Ganzouri risk index. (DOC 44 kb)
Abbreviations
ASA: America Society of Anesthesiologists; BMI: Body Mass Index; DL: Direct
laryngoscope;; EGRI: El-Ganzouri risk index; HR: Heart rate; MAP: Mean arterial
pressure; NTI: Nasotracheal intubation; VL: Video larynogoscope
Acknowledgements
We would like to thank all the participants in this study for their willing
cooperation.
Authors’contributions
YS and HJ contributed to the study design, study coordination, and writing
of the manuscript. HZ, LS, JL and CZ contributed to the data collection. HZ
and YS contributed to the data analysis. All authors approved the final
version of the manuscript.
Funding
The publication was funded as part of Shanghai Health System (grant no.
2016ZB0203–01). The funding body played no roles in the design of the
study and collection, analysis, and interpretation of data and in writing the
manuscript.
Availability of data and materials
The datasets of current study are available from the corresponding author
on reasonable request.
Ethics approval and consent to participate
This trial was approved by IRB (2017–308-T228) from Shanghai Ninth
People’s Hospital Affiliated to Shanghai Jiao Tong University School of
Medicine, and registered at clinicaltrials.gov (NCT03126344). Written consents
to participate were obtained from all participants after enrollment.
Consent for publication
Not applicable.
Zhu et al. BMC Anesthesiology (2019) 19:166 Page 8 of 9
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
Competing interests
The authors declare that they have no competing interests.
Received: 4 March 2019 Accepted: 21 August 2019
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