Keywords Airtraq laryngoscope - McCoy laryngoscope - duration of intubation - hemodynamic response
Introduction
Cervical spine injury occurs in 1 to 4% of all major trauma victims.[1 ] However, these injuries are often associated with significant morbidity and mortality,
largely as a result of accompanying spinal cord injuries.[2 ] Although very little can be done about the initial injury to the spinal cord, utmost
care should be taken to prevent secondary insults, particularly with regard to appropriate
spinal immobilization during airway management.[2 ]
[3 ] During any airway intervention in such patients, maintenance of head in a midline
neutral position is essential to avoid potentially catastrophic neurological sequelae.[2 ]
[4 ]
Direct laryngoscopy requires flexion of the cervical spine and atlanto-occipital extension,
which helps in alignment of the oral, pharyngeal and laryngeal axes, thus creating
a direct line of vision from the mouth to the vocal cords. However, this may be hazardous
in cervical spine injury patient.
In patients with cervical spine immobility or instability, intubation requires two
contradicting objectives: sufficient laryngeal exposure and least cervical movement.
To restrict the cervical spine movements in such case, a rigid cervical collar is
applied, which reduces mouth opening, thus hindering tracheal intubation with the
standard laryngoscope.[5 ] Besides this, cervical collar lifts up the chin and moves the larynx anteriorly,
further adding to the difficult intubation.[6 ] The anterior portion of the collar can be removed to facilitate tracheal intubation.
However, this jeopardizes the safety of cervical spine. Manual inline stabilization
that is recommended for cervical spine immobilization also impairs the glottic visualization.[7 ]
Even with a cervical collar in situ, there are various airway devices such as lighted stylet, intubating laryngeal mask
airway (LMA), and Macintosh laryngoscope which have been shown to augment the easy
placement of endotracheal tube with minimal cervical movement.[8 ]
[9 ] It has been suggested that fiber optic intubation is the most reliable method of
intubation in patients with cervical injury.[10 ] But it may not be widely available everywhere and its use requires good skill and
practice.
Traditionally, McCoy laryngoscope is used when the cervical spine movement is not
desired, as it provides better glottic view by elevating epiglottis with the movement
of hinged tip. Airtraq is an optical laryngoscope that uses magnifying wide-angle
mirrors, a light emitting diode light source, and a tracheal tube guide channel, to
facilitate rapid visualization and passage of an endotracheal tube. First, it permits
visualization of the glottis without alignment of the oral and pharyngeal axes and
second allows intubation without hyperextension of neck. Both McCoy and Airtraq have
shown to be effective in managing airway in difficult airway situations as well as
in simulated patients with a cervical collar.[11 ]
The present study aimed to compare the orotracheal intubation guided by Airtraq and
McCoy laryngoscope in the presence of rigid cervical collar simulating cervical spine
immobilization in patients undergoing surgery.
Materials and Methods
This hospital based-randomized interventional study was conducted between February
2016 and November 2016, after approval from institutional ethics committee and research
review board. A total of 60 adult patients of American Society of Anesthesiologist
(ASA) physical status I and II of both genders aged 20 to 50 years, who were scheduled
for elective surgery requiring general anesthesia and intubation were included in
two groups (intubation guided by either Airtraq or McCoy laryngoscope) consisting
of 30 patients each. The sample size was decided on the basis of 95% confidence interval
and 80% power to verify the expected difference of 10.03 ± 14 seconds in mean intubation
time with Airtraq (28.73 seconds) and McCoy (39.11 seconds) laryngoscope. Written
informed consent was taken from all the patients.
Exclusion criteria included patient's refusal to participate, anticipated difficult
intubation (Mallampatti grade 4, thyromental distance <6 cm, sternomental distance
< 12 cm, mentohyoid distance <5 cm, and/or neck circumference > 42 cm), patients with
risk of pulmonary aspiration of gastric contents, pregnant patients, morbid obesity,
history of cervical spine pathology, airway distortion or trauma.
Randomization was done by computer-generated random number table, and the random numbers
were kept in sequentially numbered opaque envelopes. The envelope was opened and the
patient was allocated to one of the two groups, according to the technique to be used
for intubation. Patients included in group A (n = 30) were intubated with Airtraq laryngoscope while those in Group B (n = 30) were intubated with McCoy laryngoscope.
On arrival in the operation theater, fasting status, consent, and preanesthetic check-ups
were checked. Rigid cervical collar was applied. Baseline parameters (heart rate [HR],
systolic blood pressure [SBP], diastolic blood pressure [DBP], and mean arterial pressure
[MAP]) were recorded. Two intravenous lines with 18 G cannula were secured. Ringer
lactate drip was started. Premedication with Inj. glycopyrrolate (0.005 mg/kg IV)
+ Inj. midazolam (0.05 mg/kg) + Inj. fentanyl citrate (2 µg/kg IV) + Inj. xylocard
(1–1.5 mg/kg) was given along with preoxygenation for 3 minutes before inducing anesthesia.
Hemodynamic parameters (HR, SBP, DBP, and MAP) were recorded again just before induction.
Induction of anesthesia was done using Inj. propofol (2 mg/kg), followed by Inj. rocuronium
(0.9 mg/kg IV). Parameters (HR, SBP, DBP, and MAP) were recorded just after induction.
Intubation was done after 90 seconds of rocuronium injection with endotracheal tube
(8.0 mm ID in males and 7.5 mm ID in females) either by Airtraq laryngoscope or by
McCoy laryngoscope, depending on randomization. Position of the tube was checked by
auscultation and confirmed by end tidal carbon dioxide (EtCO2 ) tracings. Parameters (HR, SBP, DBP, and MAP) were recorded again, just after intubation
and then 1, 3, and 5 minutes after intubation.
In each case, intubation time was noted, which was defined as the time taken from
removal of face mask for intubation to removal of the laryngoscope and connection
of anesthesia circuit to the endotracheal tube. Intubation was said to have failed
if the introduction of the intubating device was not possible, or more than three
attempts were required, or intubation time was more than 120 seconds. Modified intubation
difficulty score (IDS) described by Adnet et al, using the seven parameters (number
of operators, number of attempts, number of additional techniques, Cormack–Lehane
view, lifting force, laryngeal pressure, and vocal cord position) for intubation with
Airtraq and McCoy laryngoscope was noted ([Table 1 ]).[12 ] Difficulty in insertion of laryngoscope was graded by the intubating anesthesiologist
as per Likert's scale i.e., 2 (very difficult to insert) to +2 (very easy to insert).
Airway-related complications in the form of injury to lips, teeth, mucosal injury,
laryngospasm, bronchospasm, postoperative stridor, and sore throat were also noted.
Table 1
Modified intubation difficulty score (IDS)
McCoy laryngoscope
Airtraq
Abbreviation: IDS, intubation difficulty score.
N1
No. of intubation attempts > 1
No. of intubation attempts > 1
N2
The number of operators > 1
The number of operators > 1
N3
No. of alternative intubation techniques used Hinge used: 1; Bougie used: 2; others
(Magill forceps, etc.): 3
No. of alternative intubation techniques used Bougie used: 1; others (Magill forceps,
etc.): 2
N4
Glottic exposure (Cormack–Lehane: grade:–1, N4 = 0)
Glottic exposure (Cormack–Lehane: grade–1, N4 = 0)
N5
Lifting force required during laryngoscopy normal: 0; increased: 1
Lifting force required during laryngoscopy normal: 0; increased or change in position
of Airtraq required: 1
N6
Necessity for external laryngeal pressure no: 0; yes: 1
Necessity for external laryngeal pressure no: 0; yes: 1
N7
Position of the vocal cords at intubation abduction/not visualized: 0; adduction:
1
Position of the vocal cords at intubation abduction/not visualized: 0; adduction:
1
Statistical analysis was performed by using SPSS Statistics version 22.0.0 (SPSS Inc.,
Chicago, Illinois, United States). Categorical variables (gender, ASA grade, and Mallampati
grade) were presented as frequency, percentage and proportions and intergroup comparison
of these variables was done using Chi-square test. Continuous variables, such as age,
weight, airway parameters, duration of intubation, and hemodynamic parameters (HR,
SBP, DBP, and MAP) were presented as mean ± standard deviation. Intergroup comparison
of continuous variables was done by unpaired t -test. Statistically significant level for the analyses was set as p < 0.05.
Results
A total of 60 patients were enrolled in the study with 30 patients in each group.
The demographic data and baseline airway characteristics amongst both the groups are
summarized in [Table 2 ]. Both the groups were comparable with regard to age, weight, gender distribution,
ASA grade distribution, Mallampati grade distribution, and distribution of airway
parameters (thyromental distance, sternomental distance, mentohyoid distance, and
neck circumference; [Table 2 ]).
Table 2
Demographic data and airway characteristics of the patients
Characteristic
Group A (Airtraq)
Group B (McCoy)
p -Value
Age (Y)
41.23 ± 13.22
38.27 ± 7.362
0.287
Sex (male/female)
16/14
18/12
0.609
Weight (kg)
62.5 ± 8.35
63.53 ± 7.86
0.623
ASA grade (1/2)
18/12
16/14
0.609
Mallampati grade (1/2/3)
17/10/3
19/8/3
0.706
Thyromental distance (cm)
7.6 ± 0.77
7.85 ± 0.69
0.185
Mentohyoid distance (cm)
4.92 ± 0.63
5.25 ± 0.99
0.122
Sternomental distance (cm)
17.06 ± 0.89
17.34 ± 2.80
0.613
Neck circumference (cm)
34.30 ± 2.06
35.16 ± 2.81
0.183
Inter incisors gap (cm)
4.4 ± 0.38
4.41 ± 0.366
0.917
The mean time for intubation was 25.2 ± 5.11 seconds in Group A (Airtraq) and 27.3
± 4.47 seconds in Group B (McCoy) and the difference was not statistically significant
(p = 0.14; [Fig. 1 ]). The mean intubation difficulty score was significantly lower in Group A (Airtraq)
when compared with that in Group B (McCoy, p = 0.001; [Table 3 ]). There was statistically significant difference in the difficulty in insertion
of laryngoscope between two groups suggesting that McCoy laryngoscope was difficult
to insert as compared with Airtraq laryngoscope (p = 0.04; [Table 4 ]).
Fig. 1 Comparison of time taken for intubation (in seconds) between Airtraq and McCoy laryngoscopy.
Table 3
Comparison of intubation difficulty score between Group A (Airtraq) and Group B (McCoy)
Parameters
Group A (Airtraq)
Group B (McCoy)
IDS
Mean
SD
No. of patients
Mean
SD
No. of patients
p -Value
Abbreviations: IDS, intubation difficulty score; SD, standard deviation.
N1
0
0
0
0.1
0.3
3
0.019
N2
0
0
0
0
0
0
1
N3
0
0
0
0.1
0.3
3
0.019
N4
0
0
0
0.17
0.37
6
0.009
N5
0.06
0.25
2
0
0
0
0.15
N6
0.03
0.18
1
0.2
0.43
6
0.02
N7
0
0
0
0
0
0
1
Total
0.1
0.30
0.53
0.62
0.001
Table 4
Comparison of difficulty in insertion of laryngoscope between Group A (Airtraq) and
Group B (McCoy)
Variables
Group A (Airtraq)
Group B (McCoy)
p -Value
Very difficult (–2)
1
0
0.004
Slightly difficult (–1)
3
9
Not difficult (0)
2
10
Easy (+1)
19
10
Very easy (+2)
4
1
The mean baseline hemodynamic variables (HR, SBP, DBP and MAP) were comparable in
both the groups. In intergroup comparison, the increase in mean heart rate (just after
intubation and 1 minute after intubation) in Group B (McCoy) was statistically significant
as compared with that in Group A (Airtraq; p = 0.03, 0.02, respectively). After induction, mean SBP decreased in both the groups,
but it increased to above postinduction values after intubation. The increase in SBP
just after intubation and at 1-minute time point in Group B (McCoy) was statistically
significant in contrast to that in Group A (Airtraq; p = 0.01, 0.002, respectively). Similarly, the mean DBP decreased in both the groups
after induction, but it increased after intubation and remained above postinduction
values at all time points. There was statistically significant difference in increase
in DBP in Group B (McCoy) as compared with that in Group A (Airtraq) just after intubation
and 1 minute after intubation time point (p = 0.02, 0.04, respectively). In both the groups, average MAP decreased after induction,
which then increased after intubation and remained above the baseline values. The
difference between the increase in MAP in Group B (McCoy) was statistically significant
as compared with that in Group A (Airtraq) just after intubation and at 1-minute time
point after intubation (p = 0.02, 0.03, respectively). This is illustrated in [Fig. 2 ].
Fig. 2 (A –D ) Comparison of changes in hemodynamic parameters at different time points before
and after intubation with Airtraq and McCoy laryngoscope.
There was no difference in the incidence of complications in the two groups ([Table 5 ]).
Table 5
Comparison of airway complications amongst the two groups
Variables
Group A (Airtraq)
Group B (McCoy)
p -Value
Lip injury
1 (0.03%)
1 (0.03%)
0.82
Sore throat
2 (0.06%)
3 (0.1%)
Nil
27 (99%)
26 (98.7%)
Discussion
Management of the airway is an important skill and responsibility for anesthesiologists.
Failure of securing and managing an airway can lead to disastrous outcomes.
Effective management of an airway in cases of cervical spine injury is one of the
major challenges faced by anesthesiologists. It necessitates cautious patient positioning,[13 ] difficult intubation cart, presence of a skilled anesthesiologist, and a trained
assistant for providing cervical spine immobilization. In patients with instability
of cervical spine, immobilization of spine is necessary. Injury to the spinal cord
has been reported during endotracheal intubation of such patients where immobilization
of cervical spine is not implemented.[11 ] Immobilization of spine results in difficulty in intubation. Use of cervical collar
in situ or maneuver such as manual in line stabilization (MILS) for immobilization
of cervical spine has been shown to reduce the necessary glottis exposure.[14 ] Reduced inter incisor gap and immobility of cervical spine contributes to a large
number of cases with grades 3 and 4 laryngoscopic views during conventional laryngoscopy
with the use of a rigid cervical collar, tape, and sandbags.[15 ]
Several devices have been developed to overcome these issues, particularly in patients
at risk of cervical spine injury. A variety of work has been done to study the laryngoscopic
view, ease of intubation, hemodynamic changes during laryngoscopy, and intubation
and associated complications in patients with cervical collar in situ.[12 ]
The Airtraq video-laryngoscope has been designed to facilitate intubation in normal
and anticipated difficult cases. It does so, because of its blade with exaggerated
curvature and an internal arrangement of optical components which facilitates a better
view of the glottis and reduces the number of airway optimization maneuvers required.
In patients with immobilized cervical spine, Airtraq has been shown to have advantages
over direct laryngoscopy, which is difficult or not recommended.[16 ]
[17 ]
[18 ] Advantages of Airtraq over McCoy laryngoscope mentioned in literature include less
time for intubation, better intubation difficulty score, limited movements at the
cervical spine, and ease of intubation in patients with normal airways.[11 ]
[19 ]
Our study aimed to evaluate the relative efficacy of Airtraq laryngoscope and McCoy
laryngoscope when used by an experienced anesthesiologist in the clinical setting
of simulation of cervical immobilization using rigid cervical collar, in terms of
time taken for intubation as the primary outcome of the study. Shorter the time taken
for intubation less would be the hypoxia and its deleterious effects on body's hemodynamics.
Turkstra et al reported 66% lesser movement at occiput—C1, C2 to C5 and C5 to thoracic
segments with Airtraq than that during Macintosh laryngoscopy.[19 ] Also, higher success rate of intubation have been reported with Airtraq in patients
with cervical immobilization with collar by Koh et al.
[20 ] Arslan et al evaluated the effectiveness of the Airtraq as compared with LMA CTrach
devise in patients with simulated cervical spine injury after application of a rigid
cervical collar. They found that Airtraq shortened the tracheal intubation time and
reduced the mucosal damage when compared with the CTrach.[21 ]
In contrast to the previous studies, the present study showed that there was no significant
difference in the time taken for intubation with Airtraq as compared with McCoy laryngoscope.
Though the time taken for intubation was less in Airtraq than McCoy, the difference
was not statistically significant (p = 0.142). The time for intubation was slightly longer than usual, in both the groups,
which could have been attributed by the presence of cervical collar. The time taken
for intubation also depends on the skill of the anesthesiologist, thus explaining
the variability in duration of intubation in various studies evaluating McCoy[15 ]
[22 ]
[23 ] and Airtraq laryngoscope. Haidry et al[24 ] found an intubation time of 22.8 ± 4.1 seconds with McCoy laryngoscope, Komatsu
et al[25 ] noted that the time taken for intubation with McCoy was 40 ± 14 seconds and Joseph
et al[26 ] observed intubation time of 22.9 seconds with McCoy. Maruyama et al[27 ] found 23 ± 5 seconds as time taken for intubation with McCoy laryngoscope. Durga
et al[11 ] reported 33.27 ± 13.25 seconds of time to intubation with McCoy and 28.95 ± 18.53
seconds with Airtraq and concluded that there was not any significant difference between
the time taken for intubation between the two devices, which is in corroboration with
our results. In contrast, study by Aliet al[28 ] showed that the time taken for intubation was significantly less with Airtraq laryngoscope
than the McCoy. In the present study, we demonstrated that the time taken for intubation
is almost the same with Airtraq and McCoy laryngoscope suggesting that no device is
superior to another in terms of preventing hypoxia in emergent situations.
Intubation difficulty score was found to be significantly lower in Group A (Airtraq)
as compared with Group B (McCoy). Also, Group A (Airtraq) required lesser intubation
attempts, no change of position, better Cormack–Lehane grading, no lifting force,
and less external laryngeal pressure as compared with McCoy group which was statistically
significant. Similar findings were noted by Durga et al[11 ] who in their study concluded that intubation attempts, number of operators, alternative
techniques for intubation, lifting force, and external laryngeal pressure required
were higher in patients of McCoy group as compared with that of Airtraq group.
Difficulty in intubation despite good glottic visualization is a problem reported
with most video laryngoscopes.[29 ] Difficulty in insertion of laryngoscope is a parameter, we recorded as per Likert's
scale i.e., −2 which was very difficult to insert Airtraq or McCoy laryngoscope to
+2 which was very easy to insert. There was significant difficulty in inserting McCoy
as compared with Airtraq.
Comparison of mean values of heart rate, SBP, DBP and MAP at different time points
showed that these hemodynamic parameters were lower and more stable in Group A (Airtraq)
than in Group B (McCoy) with significant differences at post intubation time point
and 1 minute after intubation.
According to the study conducted by McCoy et al,[30 ]
[31 ] use of McCoy laryngoscope reduces the force required for better laryngoscopy by
lifting epiglottis and ultimately reducing stress response to laryngoscopy. Nishiyama
et al[29 ] and Tewari et al[32 ] compared McCoy and Macintosh blades and showed that use of McCoy blade resulted
in lesser change in HR and BP. On the other side, some studies (Han et al,
[33 ] Román et al,
[34 ] and Shimoda et al[35 ]) did not find any significant difference in the circulatory response between McCoy
blade and Macintosh blade. This finding could be attributed to the fact that the Airtraq
provides a view of the glottis without aligning the oral, pharyngeal, and tracheal
axes and therefore requires less force to be applied during laryngoscopy, while using
a cervical collar in situ which did not allow alignment of the three airway axes and
lead to more lifting force and more manipulations with McCoy laryngoscope, to get
a glottic view.
No major complication was noted in any of the group, except lip injury and sore throat,
which were statistically not significant. However, Durga et al[11 ] demonstrated significantly less airway trauma with Airtraq compared with McCoy laryngoscope.
Our study has few limitations. First, blinding of the anesthesiologist to the device
being used was not possible, leading to a potential bias. Second, some of the measurements
in the study are subjective. Another limitation is that the intubation was performed
by an experienced anesthesiologist and hence the results seen may differ in the hands
of less experienced anesthesiologists.
Conclusion
We conclude that although, with Airtraq laryngoscope, intubation can be performed
more swiftly in emergency situations requiring cervical immobilization, which is of
utmost priority to avoid further neurological injury, the time taken for intubation
is similar to that of McCoy. This suggests that there is no device which can be labeled
as superior over another in terms of preventing hypoxia.
