Incidence and predictors of difficult nasotracheal intubation with airway scope

Abstract

The airway scope (AWS) improves views of the larynx during orotracheal intubation. However, the role of the AWS in routine nasotracheal intubation has not been studied adequately.
One hundred and three patients undergoing dental and maxillofacial surgery that required general anesthesia and nasotracheal intubation were enrolled. The study was approved by our Institution Review Board, and written informed consent was obtained from all patients. We evaluated the success rate of AWS intubation and the incidence of difficult nasotracheal intubation using a modified intubation difficulty scale (IDS) to examine preoperative characteristics and intubation profiles. Categories were difficult intubation (IDS ≥5), mildly difficult (IDS = 1-4), and intubation without difficulty (IDS = 0). We also assessed the incidence of the use of Magill forceps or cuff inflation (the cuff of endotracheal tube is inflated with 10-15 ml air) to guide the endotracheal tube into the glottis.
AWS nasotracheal intubation was 100 % successful. The cuff inflation technique was used in 37 patients. Neither Magill forceps nor other devices were needed for any patient during AWS use. The incidence of difficult nasotracheal intubation was 10 % (n = 10). Of the patients, 61 % (n = 63) had mildly difficult intubation and 29 % (n = 30) had no difficulty. Patients with difficult intubation were more likely to be male and to have a larger tongue and a higher Cormack grade than in the other two groups. Complications, involving minor soft tissue injury, were observed in only 1 patient (1 %).
The AWS achieves a high success rate for nasotracheal intubation with cuff inflation in patients undergoing dental and maxillofacial surgery.

Full text

ORIGINAL ARTICLE
Incidence and predictors of difficult nasotracheal intubation
with airway scope
Koyu Ono
•
Tomoko Goto
•
Daishi Nakai
•
Shuhei Ueki
•
Seiichiro Takenaka
•
Tomomi Moriya
Received: 5 February 2013 / Accepted: 17 December 2013 / Published online: 17 January 2014
Ó The Author(s) 2014. This article is published with open access at Springerlink.com
Abstract
Purpose The airway scope (AWS) improves views of the
larynx during orotracheal intubation. However, the role of
the AWS in routine nasotracheal intubation has not been
studied adequately.
Methods One hundred and three patients undergoing
dental and maxillofacial surgery that required general
anesthesia and nasotracheal intubation were enrolled. The
study was approved by our Institution Review Board, and
written informed consent was obtained from all patients.
We evaluated the success rate of AWS intubation and the
incidence of difficult nasotracheal intubation using a
modified intubation difficulty scale (IDS) to examine pre-
operative characteristics and intubation profiles. Categories
were difficult intubation (IDS C5), mildly difficult
(IDS = 1–4), and intubation without difficulty (IDS = 0).
We also assessed the incidence of the use of Magill forceps
or cuff inflation (the cuff of endotracheal tube is inflated
with 10–15 ml air) to guide the endotracheal tube into the
glottis.
Results AWS nasotracheal intubation was 100 % suc-
cessful. The cuff inflation technique was used in 37
patients. Neither Magill forceps nor other devices were
needed for any patient during AWS use. The incidence of
difficult nasotracheal intubation was 10 % (n = 10). Of the
patients, 61 % (n = 63) had mildly difficult intubation and
29 % (n = 30) had no difficulty. Patients with difficult
intubation were more likely to be male and to have a larger
tongue and a higher Cormack grade than in the other two
groups. Complications, involving minor soft tissue injury,
were observed in only 1 patient (1 %).
Conclusion The AWS achieves a high success rate for
nasotracheal intubation with cuff inflation in patients
undergoing dental and maxillofacial surgery.
Keywords Airway scope  Video laryngoscope  Difficult
nasotracheal intubation
Introduction
Nasotracheal intubation usually is accomplished using
direct laryngoscopes such as the Machintosh or McCoy.
Although direct laryngoscopes provide a sightline view of
the airway during nasotracheal intubation, the patient’s
neck must be extended and Magill forceps are needed to
guide the endotracheal tube into the glottis. The Airway
Scope (AWS; Hoya, Tokyo, Japan), a video laryngoscope
designed for oral tracheal intubation, has proven useful for
patients with difficult airways [1, 2], such as restricted neck
movement [3–5]. Another recent study also demonstrated
that the AWS offers better intubation conditions than a
Macintosh laryngoscope during nasotracheal intubation
[6]. Nevertheless, inserting an endotracheal tube with AWS
may occasionally fail, despite good visualization of the
glottis [7]. In addition, nasotracheal intubation sometimes
is needed to guide the tip of endotracheal tube into the
glottis with use of Magill forceps or cuff inflation tech-
nique. Reports on a small number of patients found the cuff
inflation technique useful for guiding the tip of nasotrac-
heal tube into the glottis under AWS or Airtraq [8, 9].
K. Ono (&)  D. Nakai  S. Ueki  S. Takenaka  T. Moriya
Departments of Dentistry and Maxillofacial Surgery,
Itoh Dento-Maxillofacial Hospital, 4-14 Kokaihonmachi,
Kumamoto 860-0851, Japan
e-mail: hoku4koyu3@yahoo.co.jp
T. Goto
Departments of Anesthesiology, Itoh Dento-Maxillofacial
Hospital, Kumamoto, Japan
123
J Anesth (2014) 28:650–654
DOI 10.1007/s00540-013-1778-2

However, the role of AWS in nasotracheal intubation with
guidance with either Magill forceps or cuff inflation has not
been studied adequately. We assessed the success rate of
AWS intubation and the incidence of difficult nasotracheal
intubation in patients who underwent dental and maxillo-
facial surgery. We also analyzed the predictors for difficult
intubation and the role of cuff inflation technique on
guiding the endotracheal tube to the glottis during naso-
tracheal intubation by AWS.
Methods
Study population
The Institutional Research Ethics Committee of Itoh Den-
to-Maxillofacial Hospital approved the study protocol, and
written informed consent was obtained from each patient.
A total of 103 patients (aged 16 years and older) under-
going elective dental maxillofacial surgery were enrolled
between December 2011 and April 2012. Exclusion criteria
were ASA physical status III–IV, age \16 years, and
limited mouth opening (\3 cm). Data of patient charac-
teristics and preanesthetic risk were evaluated by a single
attending anesthesiologist. Parameters and common pre-
dictors of difficult intubation included age, gender, body
mass index (BMI), snoring, sleep apnea syndrome (history
of diagnosed, treated, or episode of apnea), mandibular
retrusion (posterior displacement of the mandibula),
restricted neck movement (limited extension, limited flex-
ion), large tongue (disproportionately large size occupying
oropharyngeal space with teeth press marks on the lateral
borders of the tongue), Mallampati grade, and upper lip
bite. The upper lip bite test class was graded according the
following criteria: class I, lower incisors can bite the upper
lip above the vermilion line; class II, lower incisors can
bite the upper lip below the vermilion line; and class III,
lower incisors cannot bite the upper lip [10].
Patient management
AWS was performed by five dental anesthesiology resi-
dents with more than 3 months of experience and were
supervised by one attending anesthesiologist. When the
patients arrived in the operating room, they were monitored
by electrocardiogram, noninvasive blood pressure, pulse
oximetry, and capnometry (20, 30, 40, 50, 60 s step-up
alarm of apnea set available). Each patient’s head was
positioned on a dental chair support to achieve a neutral
position. After oxygen was administered for at least 3 min
with a face mask, anesthesia was induced with IV fentanyl
100 lg, propofol 2 mg/kg, and sevoflurane. Appropriate
neuromuscular blockade was achieved with rocuronium
0.6 mg/kg before airway manipulation.
Procedural scores for intubation difficulty were evalu-
ated during tracheal intubation, as well as the modified
Cormack–Lehane grade [11], position of the AWS top
blade in vallecula or epiglottis, number of attempts,
dependent need for external manipulation or cuff inflation
technique, Magill forceps, a gum elastic bougie, or a
bronchofiber. When the tip of the endotracheal tube was
withdrawn into the laryngopharynx, the cuff of the tube
was sequentially inflated with 10–15 ml air (cuff inflation
technique) until guiding the glottis and then was deflated
after the tip of the tube entered into laryngeal inlet. The
trachea was intubated with a Parker Flex-Tip endotracheal
tube (Parker Medical, Ranch, CO, USA) or Ivory nasal
tube (Smith Medical, Hythe, UK). The anesthesiologist
assigned to the case chose the internal diameter size of
the endotracheal tube based on the patient’s characteris-
tics and surgical procedure. If surgery was expected to be
longer than 2 h, a softer Ivory nasal tube was selected to
prevent nasal injury. A failed intubation was defined as an
attempt that required more than 30 s. When nasal intu-
bation failed, the endotracheal tube was connected to an
anesthetic circuit and the lungs were manually ventilated
with the patient’s mouth occluded by hand. All compli-
cations of hypoxia [oxygen saturation measured by pulse
oximetry (SpO
2
) \90 %] during nasotracheal intubation,
and dental, pharyngeal, tracheal, or laryngeal injury were
recorded.
Intubation difficulty sale
Difficulty of intubation was assessed according to the
modified intubation difficulty scale (IDS) developed by
Adnet et al. [12] on the basis of seven variables: N1,
number of additional intubation attempts; N2, number of
additional operators; N3, number of alternative intubation
techniques used such as bronchofiber; N4, AWS view as
defined by modified Cormack and Lehane (0 = grade 1,
the vocal cords were completely visible; 1 = grade 2a,
partial view of the vocal cords; 2 = grade 2b, only the
arytenoids and epiglottis seen; 3 = grade 3, only the epi-
glottis visible); N5, lifting force required during AWS
(0 = normal, 1 = increased); N6, need to apply external
laryngeal pressure to improve glottis (0 = not applied,
1 = external laryngeal pressure was used); and N7, aid
technique in intubation (0 = not applied, 1 = lifting head,
2 = use of cuff inflation, 3 = use of Magill forceps or gum
elastic bougie). The IDS score was the sum of N1 through
N7. We defined three groups of patients according to the
IDS values: not difficult (IDS score = 0), mildly difficult
(IDS score = 1–4), and difficult (IDS score C5).
J Anesth (2014) 28:650–654 651
123

Statistical analysis
Data are reported as mean (± SD) and incidences (both
absolute and percentage). One-way analysis of variance
was used to compare data for parametric data between
groups. When statistical significance was found, post hoc
comparisons were made by Bonferroni’s method. The chi-
square statistic test or Fisher’s exact test with Bonferroni
correction for multiple comparisons was used to compare
all nonparametric data between groups. A P value \0.05
was considered significant.
Results
Nasotracheal intubation using the AWS was successful in
all 103 patients. Tracheal intubation was judged easy in 30
patients (29 %), mildly difficult in 63 patients (61 %), and
difficult in 10 patients (10 %). Preoperative and other
characteristics for all patients are summarized in Table 1.
More patients with difficult intubation were male and had
large tongues and a higher Cormack grade than the other
two groups. There were no statistically significant differ-
ences for other variables among the three groups. There
were no incidences of hypoxia during intubation in any
group.
The number of nasotracheal intubation attempts and
optimization maneuvers required were significantly higher
in patients with difficult intubation compared with the other
two groups (Table 2). Cuff inflation was needed to guide
the endotracheal tube to the visualized glottis in 28 (44 %)
patients of the mildly difficult group and to 9 (90 %)
patients of the difficult group. No Magill forceps or other
devices were needed for any patient. Complications were
noted in only 1 patient (1 %), that involving minor soft
tissue injury. Before surgery began, the surgeon checked
the oral cavity for bleeding and found a submucosal
hematoma of the left palatal arch in a 32-year-old man
undergoing sagittal split ramus osteotomy. After confirm-
ing that there was no bleeding from the soft palate, the
endotracheal tube was removed. No major complications,
such as dental, pharyngeal, tracheal, or laryngeal injury
were found.
Table 1 Patient characteristics and preoperative intubation conditions
Not difficult (n = 30) Mildly difficult (n = 63) Difficult (n = 10) P value
Age, years (mean ± standard deviation) 35 ± 15.5 32 ± 14.2 355 ± 15.8 0.665
Gender (male/female) 4/26 24/39 6/4
a
0.029
Height (m) 1.6 ± 0.06 1.6 ± 0.08 1.7 ± 0.09
a
0.006
Weight (kg) 53.1 ± 9.4 56.4 ± 10.7 61.7 ± 13.0 0.771
Body mass index (kg/m
2
) 20.9 ± 2.80 21.2 ± 2.68 21.7 ± 2.64 0.706
Snoring (%) 7 (23.3) 18 (28.6) 4 (40) 0.825
Sleep apnea syndrome (%) 1 (3.3) 1 (1.6) 2 (2) 0.150
Mandibular retrusion (%) 3 (10) 5 (7.9) 1 (10) 0.913
Restricted neck movement (%) 0 (0) 0 (0) 1 (10) 0.395
Large tongue (%) 1 (3.3) 9 (14.3) 5 (50)
b
0.008
Mallampati grade I/II/III/IV 20/10/0/0 42/18/3/0 8/2/0/0 0.944
Upper lip bite I/II/III 30/0/0 60/3/0 9/1/0 0.935
a
Significantly different from ‘‘not difficult’’ by post hoc analysis
b
Significantly different from ‘‘not difficult’’ and ‘‘mildly difficult’’ by post hoc analysis
Table 2 Intubation profiles for nasotracheal intubation difficulty
Not
difficult
(n = 30)
Mildly
difficult
(n = 63)
Difficult
(n = 10)
P value
Modified Cormack–
Lehane grade (I/IIa/
IIb/III)
30/0/0/0 50/13/0/0 4/5/1/0
a
0.038
Number of attempts (1/
2/3)
30/0/0 58/4/1 1/7/2 \0.001
Additional management
of intubation (none/
lifting head/cuff
inflation/Magill’s
forceps)
30/0/0/0 5/30/28/0 0/1/9/0 \0.001
Lifting force 0 7 9 \0.001
External laryngeal
manipulation
06 9\0.001
Tracheal tube (Ivory
tube/Parker tube)
16/14 32/31 7/3 0.721
Position of AWS top
(Vallecula/Epiglottis)
9/21 13/50 2/8 0.754
AWS airway scope
a
Significantly different from ‘‘not difficult’’ by post hoc analysis
652 J Anesth (2014) 28:650–654
123

Discussion
Our results have shown that the AWS achieved a high rate
of success for nasotracheal intubation with cuff inflation in
patients who underwent dental and maxillofacial surgery.
Males and those with large tongues and higher Cormack
grade were more common among the patients with difficult
nasotracheal intubation.
Previous studies have demonstrated that the AWS
reduces the difficulty of tracheal intubation in restricted
cervical patients and in a manikin with tongue edema [3, 4,
13]. On the other hand, our study demonstrated that the
AWS increased the need for additional attempts and opti-
mization maneuvers in men and patients with large ton-
gues. In this study, failed intubation was defined as
procedures longer than 30 s in which the accumulated
number of intubation attempts has increased. A large ton-
gue may make inserting INTLOCK (single-use blade) of
the AWS along the palate to be difficult. Abdallah et al.
[14] reported that a narrowed oropharyngeal space in obese
patients might impede manipulation of the relatively bulky
INTLOCK of the AWS. In addition, male gender and
snoring are risk factors for obstructive sleep apnea [15, 16].
Although snoring was not a risk factor for difficult nasal
intubation in this study, further work is needed on whether
the AWS improves the grade of glottis views in patients
with obstructive sleep apnea syndrome.
Magill forceps sometimes are needed to guide the tip of
the endotracheal tube into the glottis during nasotracheal
intubation. Several studies have reported that cuff inflation
or a gum elastic bougie is useful to guide the tip of tube
located posterior toward the glottis [8, 9, 17]. We used cuff
inflation in 37 patients. Cuff inflation is a simple and useful
way to correct the position of the endotracheal tube tip
during nasotracheal intubation by the AWS. Although we
did not use the gum elastic bougie in this study, this device
may be required in patients when cuff inflation fails. In our
institution, the AWS has reduced the use of bronchofiber-
guide intubation and changed our airway management of
nasotracheal intubation in patients undergoing dental and
maxillofacial surgery.
Complications involved one male patient with minor
submucosal hematoma of his palatal arch. He had a large
tongue and required two intubation attempts. His large
tongue may have disturbed the insertion of the INTLOCK
of the AWS along the palate. The AWS blade may be too
large for the patient with a narrow oropharyngeal space.
Ogino et al. [18] reported on a small female patient who
developed distinct airway edema after palatal laceration
caused by inserting the AWS. Generally, we use a single
size for the INTLOCK component of the AWS. Recently,
smaller sizes of the INTLOCK component have been
released as thin types for adults, children, and infants.
Because of the relatively bulky blade, the AWS should be
inserted carefully along the palate in patients with narrow
oropharyngeal space such as caused by a large tongue.
Our study has some limitations. First, it was performed
in a single institution. Thus, our institutional standards or
patients might have biased the results. Second, we modified
the definition of difficult intubation to be an IDS score of 5
or more, which often differs between institutions.
In conclusions, the AWS achieved a high rate of success
for nasotracheal intubation with cuff inflation in patients
undergoing dental and maxillofacial surgery. A minor
complication, minor soft tissue injury, was noted in one
patient. There were no major complications. The AWS
should be inserted carefully along the palate in patients
with oropharyngeal spaces made narrow by a large tongue
or other anatomic factors.
Acknowledgments The authors thank Dr. Jon Moon for his edito-
rial assistance.
Open Access This article is distributed under the terms of the
Creative Commons Attribution License which permits any use, dis-
tribution, and reproduction in any medium, provided the original
author(s) and the source are credited.
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