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Table of Contents
Year : 2020  |  Volume : 4  |  Issue : 2  |  Page : 46-48

The predictive value of skin-to-epiglottis distance to assess difficult intubation in patients who undergo surgery under general anesthesia

Department of Anesthesiology, Faculty of Medicine, Sanglah General Hospital, Udayana University, Denpasar-Balinese, Indonesia

Date of Submission02-Feb-2020
Date of Decision02-Mar-2020
Date of Acceptance13-Mar-2020
Date of Web Publication11-May-2020

Correspondence Address:
Dr. Tjokorda Gde Agung Senapathi
Department of Anesthesiology, Faculty of Medicine, Sanglah General Hospital, Udayana University, Jl- Diponegoro, Denpasar 80114, Balinese
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/BJOA.BJOA_7_20

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Background: Intubation is crucial in the management of anesthesia because it is related to the maintenance of oxygenation and ventilation during general anesthesia. Clinical markers for predicting difficult airway have limitations, including requiring coordination with patients. The use of ultrasonography (USG) to measure the distance of the skin to epiglottis is expected to estimate the difficulty level of intubation. Patients and Methods: This was a cross-sectional study of 128 patients who underwent surgery under general anesthesia. We examined the skin-to-epiglottis distance using US prior to surgery. We then assessed the Cormack–Lehane scores during direct laryngoscopy for intubation. The unpaired t-test was used to assess differences in the skin-to-epiglottis distance between patients with easy intubation (Cormack–Lehane I and IIa) and difficult intubation (Cormack–Lehane IIb, III, and IV). Results: The cutoff value of skin-to-epiglottis distance between easy and difficult intubation was 26.05 mm. The sensitivity and specificity of this method to predict difficult airway were 69.4% and 93.5%, respectively. The positive and negative predictive values were 80.6% and 88.7%, respectively. Conclusion: The skin-to-epiglottis distance of >26.05 is a risk factor for difficult intubation.

Keywords: Airway, Cormack–Lehane classification, sensitivity, specificity

How to cite this article:
Agung Senapathi TG, Wiryana M, Aryabiantara I W, Ryalino C, Roostati RL. The predictive value of skin-to-epiglottis distance to assess difficult intubation in patients who undergo surgery under general anesthesia. Bali J Anaesthesiol 2020;4:46-8

How to cite this URL:
Agung Senapathi TG, Wiryana M, Aryabiantara I W, Ryalino C, Roostati RL. The predictive value of skin-to-epiglottis distance to assess difficult intubation in patients who undergo surgery under general anesthesia. Bali J Anaesthesiol [serial online] 2020 [cited 2023 Mar 22];4:46-8. Available from: https://www.bjoaonline.com/text.asp?2020/4/2/46/284185

  Introduction Top

Laryngoscopy and intubation are crucial in the management of perioperative anesthesia. Intubation has several complications that occur during laryngoscopy, insertion of the endotracheal tube (ET), and extubation. Cook etal.[1] representing the 4th National Audit Project of the Royal College of Anesthetist and Difficult Airway Society reported that 168 cases (6%) out of 2803 patients in the UK who underwent general anesthesia experienced complications related to intubation.

Problems related to the airway not only include complications related to intubation but also the possibility of difficult airways. The difficult airway is a challenge for the anesthesiologist, especially if ventilation is difficult when conventional laryngoscopy is planned. In 2013, the American Society of Anesthesiologists (ASA) defined difficult intubation as an increase in the amount of time and frequency of direct laryngoscopy experiments required for intubation, or the need for special techniques or tools for intubation.[2] Koh et al.[3] reported that 5.8% of 951 patients who underwent elective surgery without a previous history of difficult intubation had Intubation Difficulty Scale scores >5. They also reported that 16.2% of the patients showed Cormack–Lehane scores >3. Another study reported that in 17,292 patients, it was difficult to intubate in 805 patients (4.7%) and 11 patients (0.1%) failed to intubate.[4]

The existence of a problematic airway causes morbidity and mortality rates to increase. A study in Japan showed that in ASA 1 physical status patients, there were 10/1000,000 cases of death, with 40% of them related to difficult airway problems.[5] Thus, the assessment of the airway to avoid complications and failure during intubation is crucial. Anesthesiologists have used many clinical markers and predictive modalities to predict various sensitivities and specificities of difficult airway. A number of these modalities have benefits, but most require the cooperation of patients, making it difficult for patients who are not so cooperative and those who are unconscious, thus limiting its predictive value.

The use of ultrasonography (USG) in the field of anesthesia, especially for diagnostic preoperative airway assessment, is expected to bring more benefits to predict the possibility of a difficult airway. Previous studies have examined the use of US as a predictor of difficult airways with mixed results.[6],[7],[8] The goal of this study was to assess the validity of skin-to-epiglottis distance measured using US in assessing difficult airway in patients who undergo surgery under general anesthesia.

  Patients and Methods Top

This is a cross-sectional study conducted by collecting the data from 128 adult patients who underwent surgery under general anesthesia using an ET. The study was approved by the Committee of Ethical Research of Udayana University/Sanglah General Hospital.

We examined the skin-to-epiglottis distance of the patients using US during the preoperative visit, which is conducted no more than 24 h before the surgery. During direct laryngoscopy at the time of surgery, we noted the Cormack–Lehane scores[9] for each patient. The Cormack–Lehane score is a classification frequently used to designate the laryngeal view through direct laryngoscopy. It was first published in 1984 and has become the gold standard for airway classification both in airway-related research and in daily clinical practice.

We used the Statistical Package for the Social Sciences (IBM Corp. Released 2016. IBM SPSS Statistics for Windows, Version 24.0. Armonk, NY, USA) 24.0 software for data analysis. Kolmogorov–Smirnov and Shapiro–Wilk tests were used for normality tests. Data that were not normally distributed were transformed using the SPSS log10 program until normally distributed. We then analyzed the data using the unpaired t-test to test the hypothesis. P < 0.05 was considered statistically significant.

  Results Top

The study patients comprised 56 men (43.8%) and 72 women (56.2%), with their average age being 48 years [Table 1]. The median body mass index (BMI) value was 22.3 (4.9) kg/m[2]. The median value of the cervical perimeter was 37 (6) cm. Of the 128 patients, 106 (82.8%) had Mallampati–Gatt scores 1 and 2, and the remaining patients (22, 17.2%) had Mallampati–Gatt scores 3 and 4. During laryngoscopy intubation, it was easy to intubate in 92 (71.9%) patients (Cormack–Lehane I and IIa scores) and difficult to intubate in 36 (28.1%) patients (Cormack–Lehane IIb, III, and IV scores).
Table 1: Research patients' characteristics

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We used the Kolmogorov–Smirnov test for normality test in the easy-to-intubate group and the Shapiro–Wilk test in the difficult-to-intubate group. We found that the distribution of easy intubation data groups was not normally distributed, so we transformed the data using the SPSS log10 program. Levene's test revealed that the significance value of the data was 0.012, so the data variance was not normal [Table 2]. With a P value for the abnormal data variance of <0.001, we concluded that there was a significant difference between the skin-to-epiglottis distance of the easy intubation group and the difficult intubation group.
Table 2: Levene's test and unpaired t-test of the skin-to-epiglottis distance

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The cutoff value of the receiving operator characteristic curve was 24.15 mm. From this cutoff value, we compiled a 2 × 2 table and found that the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of skin-to-epiglottis distance were 69.4%, 93.5%, 80.6%, and 88.7%, respectively [Table 3].
Table 3: Predictive value of skin-to-epiglottis distance

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  Discussion Top

This study aims to determine whether there are differences in the average skin-to-epiglottis distance between easy and difficult intubation groups. This study used a total population sampling, so it is not specifically differentiated by sex and age.

In this study, the median BMI was 22.3 (4.9) kg/m[2]. Previously, similar studies reported a higher mean of BMI.[7],[8] This may be due to the difference in the mean BMI between the Caucasian and Asian races. Komatsu et al.[10] reported a study of 64 obese patients and concluded that BMI was not correlated with the difficulty level of intubation, but rather, the distribution of body fat in the neck region was affected by ethnicity or race.

In our study, the skin-to-epiglottis distance between the two groups (easily intubated vs. difficult to intubate) was statistically different. Our results correspond well with previously published similar studies. Falcetta etal. and Falcetta etal. reported that the cutoff values for difficult intubation were 25.4 mm[7] and 24.15 mm, respectively.[8] Pinto et al.[11] reported a 27.5 mm cutoff point and Adhikari et al.[12] reported a cutoff point of 28.0 mm.

The use of ultrasound to measure the skin-to-epiglottis distance is expected to reduce the morbidity and mortality due to difficult intubation because the anesthesiologist can detect difficult intubation cases earlier. With the thickening of fat tissue in the preepiglottic space, the visualization of the glottis by direct laryngoscopy blades becomes more difficult, because the curved angle in the airway increases. By detecting this, measures can be taken to prepare the intubation procedure more thoroughly, such as getting a more experienced colleague or having difficult airway tools ready at our side before anesthetizing the patient.

We obtained 69.4% sensitivity and 93.5% specificity in this study, in terms of how good the skin-to-epiglottis distance could predict the difficulty of intubation, with 80.6% PPV and 88.7% NPV. Its high specificity indicated that skin-to-epiglottis distance was reliable to become a screening test for difficult airway.

  Conclusion Top

The skin-to-epiglottis distance of >26.05 is a risk factor for difficult intubation. The skin-to-epiglottis distance has 69.4% sensitivity and 93.5% specificity to predict difficult airway in the Indonesian population.

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Conflicts of interest

There are no conflicts of interest.

  References Top

Cook TM, Woodall N, Frerk C, Fourth National Audit Project. Major complications of airway management in the UK: Results of the fourth national audit project of the royal college of anaesthetists and the difficult airway society. Part 1: Anaesthesia. Br J Anaesth 2011;106:617-31.  Back to cited text no. 1
Apfelbaum JL, Hagberg CA, Caplan RA, Blitt CD, Connis RT, Nickinovich DG,et al. Practice guidelines for management of the difficult airway: an updated report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Anesthesiology. 2013;118:251-70. doi: 10.1097/ALN.0b013e31827773b2.  Back to cited text no. 2
Koh W, Kim H, Kim K, Ro YJ, Yang HS. Encountering unexpected difficult airway: Relationship with the intubation difficulty scale. Korean J Anesthesiol 2016;69:244-9.  Back to cited text no. 3
Zeng Z, Tay WC, Saito T, Thinn KK, Liu EH. Difficult airway management during anesthesia: Areview of the incidence and solutions. Anaesthesiol Crit Care 2018;1:5.  Back to cited text no. 4
Irita K, Kawashima Y, Morita K, Seo N, Iwao Y, Tsuzaki K, et al. Critical events in the operating room among 1,440,776 patients with ASA PS 1 for elective surgery. Masui 2005;54:939-48.  Back to cited text no. 5
Ezri T, Gewürtz G, Sessler DI, Medalion B, Szmuk P, Hagberg C, et al. Prediction of difficult laryngoscopy in obese patients by ultrasound quantification of anterior neck soft tissue. Anaesthesia 2003;58:1111-4.  Back to cited text no. 6
Falcetta S, Cavallo S, Pelaia P, Sorbello M. Ultrasound measurements as predictors of difficult laryngoscopy. Trends Anaesth Crit Care 2017;12:13-8.  Back to cited text no. 7
Falcetta S, Cavallo S, Gabbanelli V, Pelaia P, Sorbello M, Zdravkovic I, et al. Evaluation of two neck ultrasound measurements as predictors of difficult direct laryngoscopy: A prospective observational study. Eur J Anaesth 2018;35:605-12.  Back to cited text no. 8
Krage R, van Rijn C, van Groeningen D, Loer SA, Schwarte LA, Schober P. Cormack-Lehane classification revisited. Br J Anaesth 2010;105:220-7.  Back to cited text no. 9
Komatsu R, Sengupta P, Wadhwa A, Akca O, Sessler DI, et al. Ultrasound quantification of anterior soft tissue thickness fails topredict difficult laryngoscopy in obese patients. Anaesth Intensive Care 2007;35:32-7.  Back to cited text no. 10
Pinto J, Cordeiro L, Pereira C, Gama R, Fernandes HL, Assunção J. Predicting difficult laryngoscopy using ultrasound measurement of distance from skin to epiglottis. J Crit Care 2016;33:26-31.  Back to cited text no. 11
Adhikari S, Zeger W, Schmier C, Crum T, Craven A, Frrokaj I, et al. Pilot study to determine the utility of point-of-care ultrasound in the assessment of difficult laryngoscopy. Acad Emerg Med 2011;18:754-8.  Back to cited text no. 12


  [Table 1], [Table 2], [Table 3]

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