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ORIGINAL ARTICLE
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First-pass success rate and number of attempts required for intubation in anticipated difficult airway: Comparison between Macintosh and channeled King Vision video laryngoscopes


1 Department of Anaesthesia and Critical Care, GMC, Srinagar, Jammu and Kashmir, India
2 Department of Anaesthesiology and Critical Care, All India Institute of Medical Sciences, Vijaypur, Jammu, Jammu and Kashmir, India
3 Department of Anaesthesiology and Critical Care, Acharya Shri Chander College of Medical Sciences and Hospital, Jammu, Jammu and Kashmir, India

Date of Submission10-Apr-2022
Date of Decision24-Aug-2022
Date of Acceptance30-Aug-2022
Date of Web Publication31-Oct-2022

Correspondence Address:
Sunana Gupta,
Additional Professor, Department of Anaesthesia and Critical Care, All India Institute of Medical Sciences, Vijaypur Jammu, Jammu and Kashmir
India
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/aer.aer_68_22

   Abstract 

Background and Aims: Video laryngoscopy has been shown to improvise Cormack–Lehane grading and rate of successful tracheal intubation and is now incorporated in most of the difficult airway guidelines. Since there is scarce literature regarding the use of channeled blade of King Vision video laryngoscope (KVVL) in anticipated difficult intubation, we planned to undertake this randomized control trial to assess the performance of channeled blade of KVVL and Macintosh laryngoscope in patients with anticipated difficult intubation. Design and Setting: This prospective randomized study was conducted in a tertiary care hospital. Materials and Methods: Patients fulfilling the inclusion criteria were randomly assigned equally to the KVVL group or Macintosh group. The primary outcome of the study was intubation success in the first attempt and number of attempts required for intubation, and the secondary outcomes were Cormack–Lehane grading and time required to intubate in both the groups. Results: The first-pass success of intubation was 88.6% in the KVVL group and 76.5% in the Macintosh group (P = 0.035). The second attempt of intubation was required in 11.4% and 20.6% of patients in the KVVL and Macintosh groups, respectively. Cormack Lehane Grade I was achieved in 100% of patients of the KVVL group as compared to 29.4% of patients in the Macintosh group. Moreover, the difference was statistically significant (P = 0.035). The mean duration of intubation was prolonged in the KVVL group as compared to the Macintosh group, and the difference was statistically significant (P = 0.04). Conclusion: The channeled blade of KVVL had a higher first-pass success rate and required fewer attempts to intubate when used in patients with anticipated difficult intubation. Further, the KVVL was found to be significantly better than the Macintosh laryngoscope in terms of Cormack–Lehane grading, but the time taken to intubate the trachea was more in the KVVL group.

Keywords: Anticipated difficult intubation, channeled blade, King Vision video laryngoscope, Macintosh laryngoscope



How to cite this URL:
Raja R, Gupta S, Mehta N, Attal P. First-pass success rate and number of attempts required for intubation in anticipated difficult airway: Comparison between Macintosh and channeled King Vision video laryngoscopes. Anesth Essays Res [Epub ahead of print] [cited 2022 Dec 4]. Available from: https://www.aeronline.org/preprintarticle.asp?id=360089


   Introduction Top


Managing a patient of anticipated difficult airway is always a challenge for the anesthesiologist. The incidence of difficulties during intubation is 1%–8.5%, whereas failed intubation occurs in 0.1%–0.3% of cases. Hypoxia occurring during management of difficult airway can contribute significantly to perioperative morbidity and mortality.[1]

Video laryngoscopes have characteristics of both rigid laryngoscopes and fiber-optic bronchoscopes. Video laryngoscope was introduced in clinical practice in 2001, and since then, they have transformed the management of difficult airway. Video laryngoscopes provide a better glottis view and do not require alignment of the oral, pharyngeal, and tracheal axes. This is mainly of advantage in patients with unfavorable anatomy for direct laryngoscopy. Most of the difficult airway guidelines have laid stress on the role of video laryngoscopes in the management of both anticipated and unanticipated airways.[2],[3]

King Vision video laryngoscope (KVVL) is a portable, battery-operated, rigid video laryngoscope having a screen fixed to the handle and removable blades. The channeled blade has a channel for guiding the endotracheal tube (ETT) and is hyperangulated. Several studies have reported that KVVL provides better glottis view and higher intubation success as compared to conventional Macintosh or other video laryngoscopes.[4],[5] Published literature regarding the use of KVVL in difficult airway is limited to simulated difficult airway, nasotracheal intubation, case reports, or obese patients,[6],[7],[8],[9] but we could not find any study of its use in anticipated difficult intubation in elective patients. Regarding the use of channeled blades, there are conflicting results as few authors have found them to be bulky[7] and difficult to use, whereas others have reported that it allows faster intubation.[10] It remains unclear whether the channeled blade of KVVL is beneficial in patients with anticipated difficult airway.

We, therefore, performed this randomized prospective controlled trial, and our primary outcome was success in the first attempt of intubation and number of attempts required while intubating with channeled blade of KVVL and Macintosh laryngoscope in patients with anticipated difficult intubation. The secondary objective was to compare Cormack–Lehane grading and duration of intubation in both the groups.


   Materials and Methods Top


Institute ethics committee approval (ASCOMS/IEC/RP&T/2019/350) was taken, and the study was registered in the Clinical Trials Registry of India (CTRI/2020/04/024897). The study was conducted between June 2020 and May 2021. Written informed consent was obtained from each patient to participate in this study, and the study was conducted adhering to the principles of the Declaration of Helsinki.

Study design

This was a prospective, randomized, single-center, controlled trial.

Study population

Patients scheduled for elective surgeries under general anesthesia were included.

Sample size

The sample size of the study was calculated by G*Power software using two proportion comparison formulas under inequality category. For calculating the sample size, we took p1 90% and p2 60% with a proportionate difference of 30%. The level of significance was 5% with a power of 80% and an allocation ratio (N2/N1) of 1. The final calculated sample size was 72 with each group comprising 36 patients.

Patients who filled the inclusion criteria were allocated into two study groups randomly according to a computer-generated table of randomization, each group comprising 36 patients:

  • Group 1 (n = 36): Patients in this group were intubated using the channeled blade of KVVL
  • Group 2 (n = 36): Patients in this group were intubated using Macintosh laryngoscope


Inclusion criteria

Patients of either sex with American Society of Anesthesiologists physical status (ASA PS) Class I and II and any one or more of the followings were included in the study:

  1. Mallampatti Grade III and IV
  2. A thyromental distance <6 cm with neck in full extension
  3. Neck circumference >40 cm for males and 38 cm for females, measured at the level of the cricoid cartilage
  4. Interincisior gap <3 cm
  5. Body mass index >35 kg.m−2
  6. Limited head-and-neck extension.


Exclusion criteria

  1. Patient refusal
  2. Age <20 years or >70 years
  3. ASA PS Class > II
  4. Patients without criteria for predicted difficult airway.


Standard anesthesia plan was followed in all the patients.

After arrival in the preoperative room, an intravenous catheter was secured and the patients were then shifted to the operation theater and continuous standard monitoring was started using continuous electrocardiography (lead II), SpO2, noninvasive blood pressure, and EtCO2. All patients were preoxygenated for at least 3 min, and induction was done by fentanyl 1.5 μg.kg−1 intravenously (i.v.), propofol 2 mg.kg−1 i.v., and neuromuscular blockade achieved with succinylcholine 1 mg.kg−1 i.v. All intubations were performed by senior anesthesiologists who had an experience of doing at least 100 intubations using video laryngoscope.

The following parameters were recorded:

  1. Cormack Lehane Grading


    • Grade I: visualization of entire vocal cords
    • Grade II: visualization of posterior part of the laryngeal aperture
    • Grade III: visualization of epiglottis only
    • Grade IV: no glottic structures seen.


  2. Duration of intubation was defined as time interval between placements of ETT between the dental arches to the first deflection on capnograph
  3. Success rate of intubation in the first attempt was noted
  4. Number of attempts required to intubate were recorded.


An attempt was defined as the time from introduction of laryngoscope into the oral cavity until its removal.

Failure to intubate

Patients who required more than three attempts or more than 2 min to intubate were excluded from the statistical analysis. They were managed according to difficult airway algorithm 2015.

Statistical analysis

Data were collected, coded, and entered in MS Excel 2010. Data were analyzed using OpenEpi version 3.01. Qualitative variables were represented using percentages and proportions, and for quantitative variables, mean and standard deviation were calculated. The tests of significance applied were independent t-test to calculate the difference between the mean of two quantitative variables. Chi-square test and Fisher's exact test were used to access the association between categorical variables. P < 0.05 was considered statistically significant.


   Results Top


The distribution of the demographic parameters and difficult intubation criteria were comparable between the two groups, as shown in [Table 1]. This study was adhered to CONSORT guidelines (http://www. consort-statement.org) [Figure 1].
Figure 1: Consort flowchart

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Table 1: Patient characteristics and difficult intubation profiles

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Intubation was successful in the first attempt in 31 (88.6%) patients in the KVVL group and 26 (76.5%) patients in the Macintosh group. There was a statistically significant difference between the KVVL and Macintosh groups (P = 0.035) [Table 2].
Table 2: Success rate of intubation in the first attempt

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Intubation was successful in the second attempt in 7 (20.6%) patients in the Macintosh group and 4 (11.4%) patients in the KVVL group. Intubation was successful in the third attempt in 1 (2.9%) patient in the Macintosh group and 0 (0.0%) patient in the KVVL group. There was a statistically significant difference between the KVVL and Macintosh groups (P = 0.035) [Figure 2].
Figure 2: Histogram showing number of attempts at intubation

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The mean duration of intubation in the KVVL group was 12.03 ± 3.63 s and in the Macintosh group was 10.41 ± 2.75 s. A significant difference was observed between the King Vision and Macintosh groups (P = 0.04) [Figure 3].
Figure 3: Histogram showing mean duration of intubation (in seconds)

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Cormack–Lehane Grade I (full view of vocal cords) was seen in all 35 (100%) patients of the King Vision group and 10 (29.4%) of the Macintosh group. Grade II (partial view of vocal cords) was seen in 10 (29.4%) of the Macintosh group. Furthermore, Grade III was seen in 9 (26.5%) patients in the Macintosh group. Grade IV (neither the epiglottis nor glottis seen) was seen in 5 (14.7%) in the Macintosh group [Figure 4]. There was a statistically significant difference between the two groups (P = 0.001).
Figure 4: Histogram showing distribution of patients according to Cormack and Lehane Grade

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Intubation was unsuccessful in one patient of the KVVL group and two patients of the Macintosh group, and these patients were excluded from the statistical analysis [Table 3].
Table 3: Failure to intubate

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   Discussion Top


The skill of video laryngoscopy is being increasingly used for managing both normal and difficult airways. The role of the different types and designs of video laryngoscopes in difficult airway is being evaluated. Video laryngoscopy has been adopted as a first option in intubating morbidly obese or in other obese patients with anticipated difficult intubation.[6]

In our study, the first-pass success of intubation was 88.6% in the KVVL group and 76.5% in the Macintosh group. The difference between the two groups was statistically significant (P = 0.035). The importance of first-pass success rate of intubation has been emphasized in difficult away society guidelines.[11] The first-pass success of intubation has been associated with a relatively small incidence of adverse effects, and an increase in number of attempts leads to increase in adverse attempts[12] Aziz et al. in their study concluded that acute angled video laryngoscopes were very helpful in anticipated difficult laryngoscopy and intubation success in these patients was improved by video laryngoscopy.[13]

Regarding the number of attempts required to intubate, the KVVL group performed better as compared to the Macintosh group (P = 0.035). The guidelines laid down by the Difficult Airway Society 2015 have emphasized the importance of intubating in the first attempt and in case of failure to limit the number and durations of further laryngoscopy attempts. In case of failure of direct laryngoscopy, alternative techniques are more helpful as further attempts with the same technique have nearly an 80% failure rate.[14] Video laryngoscopy is associated with a high rescue intubation success rate and is more commonly used than other rescue techniques. Pieters et al. in their study were of the opinion that video laryngoscope should become the standard of care for managing difficult airway and may be initial approach to every intubation.[15]

In the present study, Cormack and Lehane Grade (CLG) 1 was achieved in 100% of patients in the KVVL group and 29.4% of patients in the Macintosh group, and the difference was statistically significant. This could be because of the fact that video laryngoscope has camera at the tip of the blade which eliminates the need of aligning the laryngeal, pharyngeal, and oral axes.[4] We have chosen acute-angled channeled blade which might have resulted in CLG I in all the patients of the KVVL group as has been documented by Kelly and Cook who reported that extra-curved video laryngoscope blades increase the chance of seeing round the corner in difficult airway scenarios.[16] The mean duration of intubation was significantly high in the KVVL group as compared to the Macintosh group (P = 0.04). Similar results of increased duration of intubation with video laryngoscope have been found in some other studies also.[4] In spite of achieving CLG I in all patients of the KVVL group, it took a longer time to intubate these patients and 11.4% of the patients required a second attempt also to intubate. Lafferty et al. have reported that “gaining a view of the vocal cords is the easy part” when using video laryngoscope it is easy to achieve a good glottis view, but it requires proper training, regular practice, and the use of device-specific adjuncts to ensure that this improved view results into successful intubation.[17] Sahajanandal et al. have described in their study that channeled blade of KVVL took a longer time due to difficulty in introducing blade in patients' mouth and they overcome this problem by introducing the blade first and then connecting the handle.[8] Few researchers are of the opinion that a specific angle to the patient's chest was required when inserting King Vision L-shaped blade.[7],[18] We introduced the tip of the blade by keeping it parallel to patients' chest and then manipulating it once it enters patients' mouth.

We were not able to intubate one patient in the KVVL group and two patients in the Macintosh group with the assigned laryngoscopes, and these patients were excluded from the analysis. Video laryngoscopy is a complex skill and requires extensive and regular practice. Furthermore, the skill of direct laryngoscopy is altogether different than video laryngoscopy which requires good hand–eye coordination and being skilled in direct laryngoscopy does not equate to skill with video laryngoscope. The same applies to different types of video laryngoscopes available with each requiring skill attained by practice.[15]

There are few limitations of our study. First, all tracheal intubations were performed by an anesthesiologist performing video laryngoscopy for two years and in a controlled environment, so the results cannot be generalized to novices and for intubations outside the operation theater. Second, since video laryngoscopy is altogether a different skill as compared to direct laryngoscopy, the criteria of anticipated difficult video laryngoscopy may differ from that of difficult direct laryngoscopy. Further studies may be required to find out the same. Third, we have not compared the nonchanneled blade to channeled blade of KVVL.


   Conclusion Top


The use of channeled blade of KVVL resulted in high first-pass success rate and fewer attempts required to intubate in patients with anticipated difficult airway as compared to Macintosh laryngoscope. Further, the use of KVVL resulted in improved Cormack Lehane grading but prolonged the time required to intubate.

Short Key Messages:

  1. Use of King Vision Video Laryngocsope resulted in high first pass success rate in anticipated difficult intubations
  2. Number of attempts required to intubate were less with the use of KVVL
  3. Cormack and Lehane grading was also improved with the use of KVVL.


Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

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Crosby ET, Cooper RM, Douglas MJ, Doyle DJ, Hung OR, Labrecque P, et al. The unanticipated difficult airway with recommendations for management. Can J Anaesth 1998;45:757-56.  Back to cited text no. 1
    
2.
Frerk C, Mitchell VS, McNarry AF, Mendonca C, Bhagrath R, Patel A, et al. Difficult airway society 2015 guidelines for management of unanticipated difficult intubation in adults. Br J Anaesth 2015;115:827-48.  Back to cited text no. 2
    
3.
Myatra SN, Shah A, Kundra P, Patwa A, Ramkumar V, Divatia JV, et al. All india difficult airway association 2016 guidelines for the management of unanticipated difficult tracheal intubation in adults. Indian J Anaesth 2016;60:885-98.  Back to cited text no. 3
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Avula RR, Vemuri NN, Tallapragada R. A prospective crossover study evaluating the efficacy of king vision video laryngoscope in patients requiring general anesthesia with endotracheal intubation. Anesth Essays Res 2019;13:36-9.  Back to cited text no. 4
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Kleine-Brueggeney M, Greif R, Schoettker P, Savoldelli GL, Nabecker S, Theiler LG. Evaluation of six videolaryngoscopes in 720 patients with a simulated difficult airway: A multicentre randomized controlled trial. Br J Anaesth 2016;116:670-9.  Back to cited text no. 6
    
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Sahajanandan R, Dhanyee AS, Gautam AK. A comparison of King vision video laryngoscope with CMAC D-blade in obese patients with anticipated difficult airway in tertiary hospital in India – Randomized control study. J Anaesthesiol Clin Pharmacol 2019;35:363-7.  Back to cited text no. 8
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13.
Aziz MF, Abrons RO, Cattano D, Bayman EO, Swanson DE, Hagberg CA, et al. First-attempt intubation success of video laryngoscopy in patients with anticipated difficult direct laryngoscopy: A multicenter randomized controlled trial comparing the C-MAC D-blade versus the glidescope in a mixed provider and diverse patient population. Anesth Analg 2016;122:740-50.  Back to cited text no. 13
    
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