Prediction of difficult endotracheal intubation by different bedside tests: An observational study :Kirti Kamal, Divya Rani, Geeta Ahlawat, Teena Bansal, Bali Journal of Anesthesiology

ORIGINAL ARTICLE
Year : 2023 | Volume : 7 | Issue : 1 | Page : 8--12

Prediction of difficult endotracheal intubation by different bedside tests: An observational study

Kirti Kamal, Divya Rani, Geeta Ahlawat, Teena Bansal
Department of Anaesthesiology and Critical Care, Pt. B. D. Sharma PGIMS, Rohtak, Haryana, India

Correspondence Address:
Divya Rani
c-602, Shri Durga CGHS Society, Dwarka Sector 11, New Delhi 110075
India

Abstract

Background: An incidence of difficult intubation in elective surgery is 1.5%–8%. Multiple attempts during tracheal intubation can cause airway injuries bleeding, brain hypoxia, and even cardiac arrest. Unanticipated failure and inability to secure difficult airway can lead to “cannot ventilate, cannot intubate” condition. Preoperative assessment and bedside tests play a vital role in predicting and stratifying risk of difficult intubation. This study was done to determine the incidence of difficult intubation and diagnostic accuracy of different bedside tests for predicting intubation difficulty in patients without airway pathology scheduled for elective surgery under general anesthesia. Materials and Methods: Two hundred patients, aged 20–50 years, American Society of Anaesthesiologists I and II, without airway pathology undergoing elective surgery were evaluated preoperatively using simple bedside tests such as Mallampati grading (MPG), interincisor gap (IIG), thyromental distance (TMD), sternomental distance, upper lip bite test, neck circumference, and atlantooccipital extension to predict difficult intubation. Statistical confirmation was done using Pearson’s chi-square test and univariate and multivariate logistic regression. Results: In our study, the incidence of difficult intubation was observed as 6%. High sensitivity for predicting difficult intubation was seen with IIG > TMD > MPG, and high specificity among the relevant bedside tests was seen with TMD > MPG > IIG. Tests with high positive predictive value were TMD > MPG, whereas high negative predictive value was seen with IIG > TMD >MPG. Conclusion: IIG, TMD, and MPG can be used to predict difficult intubation in patients without airway pathology.

How to cite this article:
Kamal K, Rani D, Ahlawat G, Bansal T. Prediction of difficult endotracheal intubation by different bedside tests: An observational study.Bali J Anaesthesiol 2023;7:8-12

How to cite this URL:
Kamal K, Rani D, Ahlawat G, Bansal T. Prediction of difficult endotracheal intubation by different bedside tests: An observational study. Bali J Anaesthesiol [serial online] 2023 [cited 2023 Mar 22 ];7:8-12
Available from: https://www.bjoaonline.com/text.asp?2023/7/1/8/371175

Full Text

Introduction

Endotracheal intubation is considered to be the “gold standard” for airway management during the administration of general anesthesia and in critical care setting. An incidence of difficult intubation in patients scheduled for elective surgery under general anesthesia has been reported as 1.5%–8%.[1] The American Society of Anaesthesiologists (ASA) Task Force defined difficult endotracheal intubation when proper insertion of the tracheal tube with conventional laryngoscopy requires more than three attempts or more than 10 min.[2] Multiple attempts during tracheal intubation under direct laryngoscopy to secure the airway can cause traumatic injuries in airway, edema, bleeding, brain hypoxia, and even cardiac arrest. Difficult airway in itself is a combination of many factors such as difficult mask ventilation, difficult laryngoscopy, and difficult intubation. Unanticipated failure and inability to secure difficult airway can lead to “cannot ventilate, cannot intubate” condition.[3] Hence, it is important for an anesthesiologist to achieve the patent airway as soon as possible and maintain it for easy gas exchange. Preoperative assessment plays an extra role in predicting and managing patients with difficult airway. Many clinical methods have been used for airway assessment, which includes bedside tests, radiographs, ultrasound, computed tomography, magnetic resonance imaging, and nasendoscopy.[4] The bedside tests are Mallampati grading (MPG), interincisor gap (IIG), thyromental distance (TMD), sternomental distance (SMD), upper lip bite test (ULBT), neck circumference (NC), and atlantooccipital extension (AOE). These measurements are widely used in isolation or in combination for predicting difficult endotracheal intubation.[5]

These bedside tests play a vital role during preoperative examination to stratify risk and identify the patients with potential difficult intubation to avoid complications.[6] Although many such studies have been conducted in western population comparing few airway parameters, not many studies have been done in Indian population and with the use of such a wide range of airway parameters. Hence, this study was designed to predict the incidence of difficult intubation in Indian population and to determine the diagnostic accuracy of different bedside tests for predicting intubation difficulty in patients without airway pathology scheduled for elective surgery under general anesthesia.

Materials and Methods

This prospective, randomized double-blinded study was conducted in a tertiary care hospital and medical college over a period of 1 year after approval from institutional ethical committee (no. IEC/Th/18/Anst24), Clinical Trial Registry India registration, and the procedures were conducted in accordance with the Helsinki Declaration 2013. The purpose and protocol of the study were explained, and informed written consent was obtained from all the patients included in the study. A total of 200 patients, aged 20–50 years, of either sex, belonging to ASA physical status I and II requiring endotracheal intubation, were scheduled for elective surgery under general anesthesia. Patients with upper airway pathology, neck mass, cervical spine injury, edentulous/loose or missing teeth, pregnancy, intraoral mass or tumor, temporomandibular joint ankylosis, facial and tongue anomalies, history of obstructive sleep apnea, and body mass index (BMI) ≥ 35 kg/m2 were excluded from this study. The sample size for our study was calculated from the results of a similar study conducted on the incidence of difficult intubation in Indian population.[7]

All the patients were subjected to detailed history and complete physical and systemic examination before the surgery. Patients’ age, height, and weight were recorded, and BMI was calculated. In our study, the parameters used as screening tests to evaluate difficulty of the airway were MPG, IIG, TMD, SMD, ULBT, NC, and AOE. Upon arrival for preanesthetic checkup, the airway of study population was assessed using these parameters.

MPG was observed with patients in the sitting position with the head in a neutral position.[8],[9] Patients were asked to open the mouth and protrude the tongue without phonation, which was then graded. IIG was measured as the interincisor distance with maximum mouth opening using Vernier’s caliper.[10],[11] TMD was obtained as the straight distance from the tip of thyroid cartilage to the tip of inside the mentum with neck fully extended and mouth closed, using a measuring tape.[11],[12] SMD was measured as the straight distance from the upper border of the manubrium to the tip of mentum with neck fully extended and mouth closed using a measuring tape.[13],[14] ULBT was performed by asking the patient to bite the upper lip using mandibular teeth as far as possible for predicting difficult endotracheal intubation by testing the range and freedom of mandibular movement and the architecture of the teeth.[15] NC was measured at the level of thyroid cartilage using a measuring tape.[11] AOE was assessed in the sitting position with spine supported by chair; goniometer is placed over the external auditory meatus with proximal arm of goniometer perpendicular to ground and distal arm of goniometer parallel to maxillary teeth with head in the neutral position and mouth closed. Then the patient was asked to extend the head completely; this angle was measured using goniometer.[16],[17] MPG III and IV, IIG < 4 cm, TMD < 6.5 cm and SMD < 12.5 cm, ULBT class III, NC ≥ 37.5 cm, and AOE < 35° represented as predictors of difficult intubation.

The measurements and grading of airway parameters used in our study as bedside tests were correlated with intubation difficulty sum score (IDS score), where IDS score ≥ 5 was considered as the marker of difficult intubation.[18] The IDS score is sum of seven variables N1–N7 with one score each: N1 = number of additional intubation attempts, N2 = number of additional persons directly attempting (not assisting) intubation, N3 = number of alternative intubation techniques used, e.g., changing from oral to blind nasotracheal intubation or from a curved to a straight blade of laryngoscope during intubation, and N4 = glottis exposure as defined by Cormack and Lehane grading.[19] N5 = lifting force applied during laryngoscopy, N5= 0: inconsiderable lifting force applied, N5= 1: considerable lifting force applied, N6 = need to apply external laryngeal pressure to improve glottis exposure, N6 = 0: no external pressure applied, N6 = 1: considerable external pressure applied. Applying Sellick’s manoeuvre does not alter the score, N7 = position of the vocal cords at intubation, N7= 0: abducted or not visible, N7= 1: adducted.

In the operating room, routine monitors were attached and vitals were recorded. Intravenous cannula was secured, a standardized general anesthesia technique was conducted, and endotracheal intubation was done by an experienced consultant anesthetists (>5 years’ experience) who was unaware of the airway measurements. Further anesthetic management was done as per the case and surgical requirement. After the completion of surgery, residual neuromuscular block was reversed and extubated when the patient was fully awake. Patients were then transferred to postanesthesia care unit.

Continuous variables were presented as mean ± Standard Deviation. Categorical variables were expressed as frequencies and percentages. Relationship between two categorical variables was determined using Pearson’s chi-square test or the chi-square test. Descriptive statistics was analyzed with SPSS software (IBM Corp. Released 2013, IBM SPSS Statistics for Windows, Version 22.0, Armonk, NY: IBM Corp.). To identify potential factors associated with various bedside tests for predicting difficult intubation in patients without airway pathology, univariate analyses were performed. Multivariate logistic regression model was used to identify independent risk factors for various bedside tests. P values < 0.05 were considered to be statistically significant.

Results

The data of 200 patients were analyzed, among which 114 patients (57%) were males and 86 patients (43%) were females. The tests used to conduct our study were Pearson’s chi-square test and logistic regression with a confidence level of 95%. Among the study population, statistically significant (P ≤ 0.001) patients to predict difficult intubation included nine patients with MPG III and IV, 12 patients were observed with IIG < 4 cm, 10 patients were noted with TMD < 6.5 cm, one patient was noted with SMD < 12.5 cm, 13 patients had ULBT class III, and none of the patients were observed with NC > 37.50 cm and AOE < 35° [Table 1]. Among the study population of 200 patients, 12 patients were noted with IDS score ≥ 5 as the predictor of difficult intubation [Figure 1]. Therefore, we found the overall incidence of difficult intubation of 6% in patients without airway pathology. The highest sensitivity for predicting difficult intubation was observed with IIG > TMD > MPG, and high specificity among the relevant bedside tests was seen with TMD > MPG > IIG. Tests with the highest positive predictive value (PPV) was seen with TMD > MPG, whereas the highest negative predictive value (NPV) was seen with IIG > TMD > MPG [Table 2]. Based on these findings, IIG < 4 cm, TMD < 6.5 cm, and MPG III and IV in combination are considered statistically most significant preoperative bedside predictors of difficult intubation in patients without airway pathology.{Table 1} {Figure 1} {Table 2}

Discussion

During the preanesthetic evaluation, an assessment of the airway is one of the most important factors to predict the difficulty during endotracheal intubation. Several bedside tests such as MPG, IIG, TMD, SMD, NC, and AOE are used in isolation or in combination to anticipate difficult airway.[20] These preoperative bedside tests are simple, effortless, repeatable, noninvasive, and economical.[21] In our observational study, patients without airway pathology requiring endotracheal intubation scheduled for elective surgery were enrolled to identify the diagnostically accurate bedside tests as the predictor of difficult intubation and to determine the incidence of difficult intubation.

The overall incidence of difficult intubation using IDS scale was observed as 6% in patients without airway pathology. We found that TMD, MPG, and IIG are diagnostically more accurate bedside predictors of difficult intubation. The highest sensitivity for predicting difficult intubation was observed with IIG > TMD > MPG, and high specificity among the relevant bedside tests was seen with TMD > MPG > IIG. Tests with the highest PPV was seen with TMD > MPG, whereas the highest NPV was seen with IIG > TMD > MPG. TMD was observed to be the bedside test with high sensitivity, specificity, PPV, and NPV.

Prakash et al. conducted a prospective randomized study in Indian population to assess anatomical and clinical factors for difficult laryngoscopy and intubation.[22] They found an incidence of difficult laryngoscopy and tracheal intubation in Indian population as 9.7% and 4.5%, respectively. They found MPG grade III and IV, IIG ≤ 3.5 cm, and TMD < 6 cm independently correlated with difficult laryngoscopy and intubation comparable to our study. Similar results were also observed by Dhanger et al. who conducted the study to determine the incidence and the diagnostic accuracy of bedside tests to predict difficult intubation in the Indian population.[7] An overall incidence of difficult intubation observed by them was 13%. Receiver operating characteristic curve of 3 or 4 was used for modified Mallampati test (MMT) and >5.62 for NC/TMD ratio for predicting difficult intubation. They concluded that the diagnostic accuracy of NC/TMD and MMT score was better as compared to the various other bedside tests to predict difficult endotracheal intubation in Indian population. Shiga et al. conducted a meta-analysis of bedside screening test performance to predict difficult intubation in apparently normal patients.[23] They found that the overall incidence of difficult intubation was 5.8%. The area under the curve for MPG was 82%, TMD was 64%, and IIG was 72%. They concluded that MPG and TMD when used in combination have greater discriminative power than as independent parameters similar to the results of our study. Panjiar et al. studied comparison of different airway assessment tests to predict difficult laryngoscopy in geriatric patients.[24] The incidence of difficult laryngoscopy found in their study was 25%. The highest sensitivity (80%) and NPV (91.86%) were seen with TMD similar to findings in our study.

Results of our study were different from the results observed by Badheka et al. who compared ULBT and ratio of height to TMD with other airway assessment tests for predicting difficult intubation.[25] They found sensitivity of MPG as 78.99%, IIG as 76.47%, TMD as 70.59%, PPV of IIG as 87.5%, MPG as 85.45%, and TMD as 84%. Unlike our study in which the overall specificity and NPV were more than sensitivity and PPV, they found sensitivity and PPV more than the specificity and NPV of the parameters included in the study.

The differences in the results may be attributed to the difference in regional population, small sample size, demographic parameters, anthropometric parameters, race or ethnicity, anatomical variations, cut off values, and interobserver variations.[7],[22],[23],[24],[25]

Few limitations of our study include a small sample size, so we could not statistically analyze the gender, BMI, and age-related implications of bedside tests to predict difficult intubation. India being a highly populous with diverse regions inhabiting varied ethnic groups with different demographic and anthropometric profiles, these results limited to our study conducted at a single center cannot be generalized for the whole population regarding the best predictor for difficult intubation in patients without airway pathology scheduled for elective surgery under general anesthesia requiring endotracheal intubation. Hence, it is recommended to further conduct multicentric randomized controlled trials using a large sample size. Although, nowadays, ultrasound-guided parameters are used to evaluate the difficult airway, in many developing countries because of limited resources, ultrasound may not be available everywhere and always. Also, the requirement of trained personnel to perform these ultrasound-guided tests is limited. Therefore, the conventional methods of assessing the difficult airway are also of equal importance to predict difficult endotracheal intubation.

Conclusions

In this study, we observed that the incidence of difficult intubation is 6% in patients without airway pathology. Based on the findings of our study, we recommend the use of IIG, TMD, and MPG as an integral part of preanesthetic checkup of patients scheduled for elective surgery under general anesthesia requiring endotracheal intubation.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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