Abstract
Background:
The most commonly used devices for direct visualization of the larynx and tracheal intubation are Macintosh and McCoy laryngoscopes. C-MAC video laryngoscope, based on the principles of indirect laryngoscopy, has been introduced into clinical practice in recent years. Video laryngoscope may be useful in difficult tracheal intubation situations.
Aim:
We aimed at comparing the McCoy and C-MAC video laryngoscope with conventional Macintosh laryngoscope for hemodynamic responses of orotracheal intubation among adults receiving general anesthesia for elective surgeries.
Settings and Design:
This was a hospital-based randomized, double-blind, comparison, done between June 2015 and October 2016 after permission of institutional ethical committee.
Materials and Methods:
One hundred and fifty patients with normal airways undergoing elective general anesthesia were randomly allocated to undergo intubation using either Macintosh (Group A), McCoy (Group B), or C-MAC video laryngoscope (Group C). Hemodynamic changes associated with intubation were recorded immediately before and after laryngoscopy and intubation, every minute for 5 min and at 10 min after intubation by an independent observer. The time taken to perform endotracheal intubation and Cormack and Lehane score were also noted in all three groups.
Statistical Analysis:
Data were compiled, and statistical analysis was performed using SPSS 17.0 version.
Results:
Hemodynamic response after intubation was least in Group B (McCoy) as compared to Group A (Macintosh) and Group C (C-Mac) (P = 0.001). Ninety-two percentage patients were in Cormack and Lehane score Class I in Group C in comparison to 52% in Group A and 48% in Group B (P = 0.000). Time for intubation taken in Group A, Group B, and Group C was 15.53 ± 1.53 min, 18.65 ± 0.44 min, and 22.82 ± 1.323 min, respectively (P = 0.000).
Conclusion:
The McCoy laryngoscope provided better attenuation of hemodynamic responses to laryngoscopy and intubation than the Macintosh and C-Mac video laryngoscope whereas more appearance of Cormack and Lehane score Class I was seen with the C-MAC video laryngoscope. Furthermore, the time taken to perform endotracheal intubation was the longest with the C-MAC video laryngoscope.
Keywords: Attenuation, C-MAC laryngoscope, Macintosh laryngoscope, McCoy laryngoscope, tracheal intubation
INTRODUCTION
Laryngoscopy and tracheal intubation are known to evoke the stress responses, in the form of tachycardia, systemic hypertension, arrhythmias,[1] and increased intracranial pressure exposing the patient to unwanted risk.[2] These responses are more marked in treated and untreated hypertensive patients.[3]
It has been observed that amount of forces exerted during laryngoscopy is the key determinant for mechanical stimulation of supraglottic region and stretch receptors present in the respiratory tract, while endotracheal intubation and cuff inflation contributing little additional stimulation. Thus, use of different types of laryngoscope blades can help decreasing these responses.
The Macintosh laryngoscope (MCL) has been the “gold standard” device for direct laryngoscopy and tracheal intubation since its invention by Foregger and Foregger in 1940s.[4] The McCoy's or Corazelli, London, McCoy laryngoscope is also used for direct laryngoscopy and tracheal intubation.
The C-MAC is an indirect laryngoscope having advantage of abandoning the need to align the optical axis in the pharynx and mouth to visualize the entrance of the larynx and improves laryngeal view.[5]
In past few years, different studies have been conducted successfully to compare Macintosh and McCoy laryngoscopes and Macintosh and video laryngoscopes to assess hemodynamic response to laryngoscopy and intubation; but, few studies have compared these three laryngoscopes together. Hence, our study involves the comparison of Macintosh, McCoy, and C-MAC video laryngoscope to evaluate stress response during intubation.
MATERIALS AND METHODS
The present study was conducted in a prospective and randomized manner at our institute, from June 2015 to October 2016, in 150 adult patients after being approved by institutional ethics committee. A written informed consent was obtained from all patients.
Inclusion criteria
Patients scheduled for elective surgery
Age between 25 and 60 years of both the sexes
Patients with the American Society of Anesthesiologists (ASA) physical status Classes I and II.
Exclusion criteria
Patients with thyromental distance <6 cm
Mallampati Grade ≥ III
Body mass index (BMI) more than 30
Patients with the ASA physical status Classes ≥ III
Pregnant women.
Due to the nature of the study, true blinding was not possible; however, sealed envelope technique was used for group allocation and persons recording observations was unconnected to the study. All the patients in three groups were successfully intubated. The study population was randomly assigned into three groups, namely:
Group A – Laryngoscopy with Macintosh blade number 3 or 4
Group B – Laryngoscopy with McCoy blade
Group C – Laryngoscopy with C-MAC video blade number 3 or 4.
Laryngoscopy and intubations were performed by an anesthesiologist who was familiar and trained with intubation using Macintosh, McCoy, and C-MAC laryngoscope.
All the patients were given tablet alprazolam 0.25 mg and tablet ranitidine 150 mg orally at night and were kept nil orally for at least 6 h before surgery. All the patients were given – midazolam 1 mg, ondansetron 4 mg, and morphine 0.1 mg/kg intravenously (IV) 15 min before induction. After preoxygenation with 100% oxygen for 3 min, induction was done with propofol (1%) 2 mg/kg, IV and muscle relaxation was achieved with IV atracurium 0.5 mg/kg. After 3 min of controlled ventilation, laryngoscopy was performed with Macintosh, McCoy, and C-MAC Video laryngoscope (according to group allocation) in sniffing position and vocal cord visualization was done using Cormack and Lehane's grading and endotracheal tube was passed through vocal cords under vision. No external pressure was applied in any patient. Failure to intubation was defined as failure after three attempts.
Systolic blood pressure, diastolic blood pressure, mean arterial pressure, pulse rate, SpO2, and electrocardiogram were recorded before induction (preinduction), immediately before (preintubation) and after laryngoscopy and intubation (T0), every minute for 5 min following tracheal intubation, and at 10 min after intubation by an independent observer. Significant hemodynamic response such as heart rate and blood pressure with 20% change from baseline (BL) was also recorded. Any arrhythmia and other complications during intubation such as local injuries, bleeding, laryngospasm, and regurgitation were noted. The time taken to intubation was measured from the time the instrument is inserted in mouth to confirmation by capnography. It was noted using a stopwatch.
Statistical analysis
After completion of the study, all the observations were systematically collected. Statistical test used to draw conclusion were, Chi-square test, one-way ANOVA with post hoc Tukey honestly significant difference. Analysis was done using SPSS 17.0 version (SPSS version 17.0. CHICAGO: SPSS Inc. for Window program).
RESULTS
Demographic data were comparable in all three groups in respect to age, gender, BMI, ASA grade, and MPG grade (P = 0.08) [Table 1]. Induction technique and dosages of drugs were same in all the groups.
Table 1.
Distribution of patients in different groups
| Group A (n=50) | Group B (n=50) | Group C (n=50) | |
|---|---|---|---|
| Age (year) | 33.05±5.12 | 36.23±3.14 | 34.11±4.22 |
| BMI, mean±SD | 22.71±2.73 | 23.63±2.09 | 23.31±2.57 |
| Gender | |||
| Female/male | 28/22 | 30/20 | 27/23 |
| ASA grade | |||
| I/II | 26/24 | 26/24 | 26/24 |
| MPG | |||
| I/II | 23/27 | 24/26 | 23/27 |
Values are expressed in n. SD=Standard deviation, ASA=American Society of Anesthesiologists, MPG=Mallampati grade, BMI=Body mass index
On studying each group separately, in Group A (Macintosh), there was a statistically significant increase in heart rate from BL values for up to 2 min (T2) after intubation whereas systolic blood pressure, diastolic blood pressure, and mean blood pressure were significantly raised up to 1-min (T1) postintubation.
In Group B (McCoy), there was a statistically significant increase in all of the study parameters from BL, only up to 1-min postintubation.
In Group C (C-MAC), there was a statistically significant increase in all of the study parameters from BL, up to 5-min postintubation.
On intergroup comparison, the rise in the heart rate compared to BL values was 6.26% in Group B, 14.12% in Group A, and 19.45% in Group C. The difference in heart rate between Group A and Group B remained statistically significant up to 2 min postoperatively. The heart rate response between Group B and Group C was statistically significant up to 5 min postoperatively. No statistically significant changes in heart rate appeared between Group A and Group C [Table 2].
Table 2.
Comparison of changes in heart rate
| Time interval (min) | Mean±SD | A-B | A-C | B-C | ||
|---|---|---|---|---|---|---|
| Group A | Group B | Group C | ||||
| Preinduction (baseline) | 88.84±8.00 | 87.16±10.76 | 86.08±9.31 | 0.647 | 0.311 | 0.835 |
| Preintubation | 82.48±8.04 | 82.36±10.74 | 81.20±9.43 | 0.998 | 0.778 | 0.814 |
| T0 | 101.36±8.35 | 92.56±11.19 | 102.60±9.74 | <0.001 | 0.804 | <0.001 |
| T1 | 95.36±7.69 | 90.76±11.19 | 97.04±9.51 | 0.002 | 0.655 | <0.001 |
| T2 | 92.20±7.39 | 86.08±10.74 | 93.64±8.94 | 0.003 | 0.711 | 0.000 |
| T3 | 89.80±8.02 | 85.04±10.81 | 91.28±8.52 | 0.06 | 0.701 | 0.003 |
| T4 | 87.76±8.10 | 83.68±11.04 | 89.64±8.37 | 0.74 | 0.569 | 0.005 |
| T5 | 86.08±8.25 | 82.08±11.13 | 89.12±8.65 | 0.089 | 0.527 | 0.005 |
| T10 | 83.96±8.51 | 80.88±12.12 | 80.00±9.43 | 0.285 | 0.865 | 0.108 |
P<0.05 is significant, P<0.001 is highly significant. SD=Standard deviation
Attenuation of the rise in systolic blood pressure is statistically significant in Group B. A rise of only 5.18% compared to BL values was observed in Group B (McCoy) when compared with 12.20% in Group A (Macintosh) and 13.40% in Group C (C-MAC) (P > 0.05). Systolic blood pressure, diastolic blood pressure, and mean blood pressure were returned to close to basal values earlier in Group A and Group B (1 min) then in the Group C (5 min) [Table 3].
Table 3.
Comparison of changes in systolic blood pressure
| Time interval (min) | Mean±SD | A-B | A-C | B-C | ||
|---|---|---|---|---|---|---|
| Group A | Group B | Group C | ||||
| Preinduction (baseline) | 127.72±6.68 | 128.04±9.94 | 127.76±7.15 | 0.979 | 1.000 | 0.983 |
| Preintubation | 121.52±7.45 | 121.88±11.36 | 121.28±7.00 | 0.998 | 0.778 | 0.814 |
| T0 | 143.16±5.14 | 134.64±10.17 | 144.72±6.24 | 0.000 | 0.553 | 0.000 |
| T1 | 134.20±5.78 | 129.96±9.88 | 138.60±6.10 | 0.015 | 0.011 | 0.000 |
| T2 | 128.52±6.09 | 127.76±9.76 | 134.92±5.90 | 0.867 | 0.061 | 0.000 |
| T3 | 124.24±7.32 | 126.56±9.64 | 132.52±5.89 | 0.298 | 0.072 | 0.001 |
| T4 | 121.28±8.15 | 125.40±9.48 | 131.16±5.99 | 0.060 | 0.061 | 0.001 |
| T5 | 119.52±7.55 | 123.64±11.77 | 129.92±6.12 | 0.054 | 0.055 | 0.001 |
| T10 | 116.04±6.25 | 119.20±10.15 | 124.84±6.16 | 0.107 | 0.062 | 0.061 |
P<0.05 is significant, P<0.001 is highly significant. SD=Standard deviation
Suppression of maximum rise in diastolic blood pressure was also seen in Group B which was statistically significant. The minimum rise in the diastolic blood pressure compared to BL was only 6.88% in Group B (McCoy) compared to 14.55% in Group C (C-MAC) and 13.66% in Group A (Macintosh) [Table 4].
Table 4.
Comparison of changes in diastolic blood pressure
| Time interval (min) | Mean±SD | Group A-B | Group A-C | Group B-C | ||
|---|---|---|---|---|---|---|
| Group A | Group B | Group C | ||||
| Preinduction | 82.64±9.51 | 81.40±7.91 | 82.68±6.62 | 0.725 | 1.000 | 0.710 |
| Preintubation | 77.56±9.66 | 76.52±7.10 | 76.72±5.85 | 0.778 | 0.849 | 0.991 |
| T0 | 93.52±8.33 | 86.92±7.92 | 94.52±6.98 | 0.000 | 0.796 | 0.000 |
| T1 | 86.56±8.13 | 82.68±7.55 | 89.88±6.66 | 0.028 | 0.071 | 0.000 |
| T2 | 82.56±8.36 | 80.76±7.09 | 87.32±6.34 | 0.437 | 0.150 | 0.000 |
| T3 | 80.12±8.40 | 79.84±7.38 | 85.48±6.23 | 0.980 | 0.130 | 0.001 |
| T4 | 76.60±8.65 | 78.56±7.48 | 84.20±6.26 | 0.397 | 0.070 | 0.001 |
| T5 | 75.52±8.74 | 77.20±8.26 | 83.16±6.37 | 0.535 | 0.230 | 0.001 |
| T10 | 72.88±7.94 | 73.60±6.97 | 79.36±6.18 | 0.867 | 0.870 | 0.071 |
P<0.05 is significant, P<0.001 is highly significant. SD=Standard deviation
Similarly, mean arterial pressure was increased 6.12% in Group B, 12.94% in Group A, and 14.01% in Group C compared to BL values [Table 5]. The effect of laryngoscopy and intubation on hemodynamic profiles remained for shortest duration in Group B (McCoy) and for longest duration in Group C (C-MAC).
Table 5.
Comparison of changes in mean blood pressure
| Time interval (min) | Mean±SD | A-B | A-C | B-C | ||
|---|---|---|---|---|---|---|
| Group A | Group B | Group C | ||||
| Preinduction | 97.66±7.87 | 96.94±7.94 | 97.70±6.10 | 0.877 | 1.000 | 0.863 |
| Preintubation | 92.21±8.21 | 91.64±7.94 | 91.57±5.74 | 0.920 | 0.902 | 0.000 |
| T0 | 110.06±6.63 | 102.82±7.97 | 111.25±6.02 | 0.000 | 0.668 | 0.000 |
| T1 | 102.44±6.49 | 98.44±7.62 | 106.12±5.71 | 0.009 | 0.18 | 0.000 |
| T2 | 97.88±6.94 | 96.42±7.26 | 103.18±5.45 | 0.515 | 0.616 | 0.000 |
| T3 | 94.82±7.40 | 95.41±7.35 | 101.17±5.32 | 0.902 | 0.832 | 0.000 |
| T4 | 91.49±7.89 | 94.17±7.40 | 99.85±5.36 | 0.136 | 0.767 | 0.000 |
| T5 | 90.18±7.76 | 92.68±8.68 | 98.74±5.51 | 0.218 | 0.321 | 0.000 |
| T10 | 87.26±6.85 | 88.80±6.89 | 94.52±5.50 | 0.462 | 0.435 | 0.634 |
P<0.05 is significant, P<0.001 is highly significant. SD=Standard deviation
Ninety-two percentage patients were in Class I (Cormack and Lehane score) in Group C in comparison to 52% in Group A and 48% in Group B (P = 0.000) [Table 6].
Table 6.
Comparison of Cormack and Lehane grade
| CL grade | Group A (n=50) | Group B (n=50) | Group C (n=50) | Overall grading |
|---|---|---|---|---|
| I | 26 (52.0) | 24 (48.0) | 46 (92.0) | 96 (64.0) |
| II | 24 (48.0) | 26 (52.0) | 4 (8.0) | 54 (36.0) |
Values are expressed in n and percentage. P=0.000; highly significant. CL=Cormack and Lehane
Time for intubation taken in Group A, Group B, and Group C was 15.53 ± 1.53 min, 18.64 ± 0.44 min, and 22.82 ± 1.323 min, respectively, which was statistically significant in-between the groups (P > 0.05) [Figure 1].
Figure 1.
Comparison of time for intubation
Spo2 changes at postintubation in all three groups were nonsignificant. There was no incidence of failed intubation in either of the group. No incidence of cyanosis, laryngospasm, arrhythmia, regurgitation, local injury, and bleeding was found in all three groups.
DISCUSSION
Obtunding the hemodynamic responses during laryngoscopy and intubation remains a major concern for the anesthesiologists. Deep anesthesia, topical anesthesia, opioids, calcium channel blockers, beta blockers, and laryngeal mask airway have been tried with varying success.[6,7,8]
In our study, we found that our primary outcome of hemodynamic responses to laryngoscopy and intubation was least in Group B (McCoy) as compared to Group A (Macintosh) and Group C (C-MAC), which was contrary to previous study by Buhari and Selvaraj.[9] This can be attributed to differences in inclusion criteria, as they studied only ASA 1 patients and found no statistically significant increase of hemodynamic parameters at any time interval while using MCL compared to McCoy and C-MAC laryngoscopes. Han et al. also did not find any statistically significant difference between Macintosh and McCoy laryngoscopes in terms of hemodynamic responses after laryngoscopy and intubation. It could be due to use of fentanyl in their study.[10]
Previous studies had shown that hemodynamic responses to laryngoscopy and intubation were less with McCoy laryngoscope compared with different types of laryngoscopes used in their studies.[1,11,12] It may be due to function of the McCoy blade through a lever attached to its proximal end and decreases the force on glossoepiglottic fold.
The C-MAC has higher hemodynamic response to intubation compared to McCoy laryngoscope while no statistically significant differences were seen between Macintosh and C-MAC laryngoscopes. Similarly, Sarkilar et al. did not find any significant change in terms of hemodynamic response to intubation between Macintosh and C-MAC laryngoscopes.[13]
There was a statistically significant reduction of the Cormack–Lehane score in our study while using the C-MAC video laryngoscope. Similar results were found with use of another video laryngoscope called Airtraq in different studies.[14,15,16] Hence, the Cormack–Lehane score may be applied to predict the outcome of both direct and indirect laryngoscopy.
Similar to our study, previous authors also observed longer intubation time with video laryngoscope compared to MCL.[4,17]
In our study, longer duration of intubation was found in C-MAC group compared to Macintosh and McCoy group. The experience of a person who performed the laryngoscopy and inclusion criteria of studies are the influencing factors to determine intubation time.
There were some limitations with regard to our study. First, we could not blind the anesthetist to the laryngoscope being used. Second, results of the study may be differed in the hands of inexperienced or less experienced anesthetist. Third, the Cormack–Lehane score was initially validated for use with direct laryngoscopy whereas we used this score for indirect laryngoscopy. Finally, more studies are required to determine advantages of C-MAC over other devices.
CONCLUSION
McCoy laryngoscope provides better attenuation of hemodynamic responses to laryngoscopy and intubation as compared to MCL and C-MAC laryngoscope. However, C-MAC laryngoscope can be used in cases of predicted difficult intubation because of the better laryngoscopic view despite maximum time taken for intubation.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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