Predicting Difficult Intubation in Surgical Patients Scheduled for General Anaesthesia: A Prospective Study of 435 Patients

Abstract

BACKGROUND: Unanticipated difficult tracheal intubation is a significant source of morbidity and mortality in anaesthetic practice which can be reduced by identification of potential difficult intubation. OBJECTIVE: We aimed the present study to know the incidence of difficult intubation, factors associated with it and the predictive value of various airway predictors in anticipating difficult visualization of larynx and difficult intubation. METHODS: 435 adult patients (>18 year) undergoing general anaesthesia with intubation were examined preoperatively for demographic details (age, sex, weight), dentition, airway pathology and six airway predictors i.e. Inter Incisor Gap (IIG), Modified Mallampatti Grading (MMPG), Upper lip bite test (ULBT), Thyromental distance (TMD), Sternomental distance (SMD) and subluxation of mandible (SLM). All patients were anaesthetized using standard protocol with thiopentone (5mg/kg) and succinylcholine (1.5 mg/kg). On direct laryngoscopy, Cormack Lehane (CL) grading was noted. CL grade I, II was defined as easy visualization of larynx (EVL) and CL grade III, IV as difficult visualization of larynx (DVL). Difficult intubation score (DIS) was calculated as sum of CL grade and number of intubation attempts. DIS of less than or equal to 4 was defined as easy intubation (EI) and DIS > 4 was defined as difficult intubation (DI).Sensitivity, specificity, positive and negative predictive value, positive and negative likelihood ratios(LR) and odd's ratio value for six airway predictor tests was calculated by standard formulae. RESULTS: Incidence of DVL was 12.65% (n=55) and DI was 9.65% (n=42), with no failed intubation. All airway tests had very high negative predictive value (>90%) which implicates they identify easy intubations more precisely. MMPG and ULBT were found as nearly perfect airway predictors for difficult intubation having odds ratio of .7%) respectively, along with very high sensitivity of 92.80% and 85.7% respectively. Presence of ULBT III is the best predictor of difficult intubation (+LR 21.97) and absence of MMPG III, IV is the best predictor of difficult intubation (-LR 0.091). Abnormal dentition and airway pathology also increase the risk of difficult intubation, P<0.001. CONCLUSION: We conclude that ULBT and MMPG are "nearly perfect" airway predictors and should be used routinely during pre-anesthetic visit for screening of difficult intubation.

2022 American Society of Anesthesiologists Practice Guidelines for Management of the Difficult Airway *

“…Observational studies reported comparative findings for facial and jaw features and anatomical measurement for difficult versus nondifficult airway patients as well as sensitivity, specificity, positive predictive, negative predictive, and accuracy values for difficult laryngoscopy and intubation. Findings for facial and jaw features, 7–11,13,14,18,27,33,38–40,42,43,45–47,49,51–54,57,58,64,68,123–159 anatomical measurements, 7–11,13–15,18,22,23,27–30,33,35,37–40,45–47,49,51–54,57,58,60, 64,65,68,70,123–132,134–154,156,158–203 and ultrasound anatomical measurements 69,139,162,170,194,196,203–213 were shown to have very high predictive and comparative variability, with sensitivity, specificity, and significance values ranging from low to very high across all patient measures (Category B2-E evidence). No single characteristic was identified as consistently being more predictive than another, and multivariate measures intended to predict difficult airways were too few and diverse among the studies to determine a common set of predictors.…”

“…Findings for the above patient characteristics were shown to have very high predictive and comparative variability, with sensitivity, specificity, and significance values ranging from low to very high across all patient demographic measures (Category B2-E evidence). 6–70 No single characteristic was identified as consistently being more predictive than another, and multivariate measures intended to predict difficult airways were too few and diverse among the studies to determine a common set of predictors.…”

Comparison of Upper Lip Bite Test with Modified Mallampati Score in Predicting Difficult Intubation

“…The high sensitivity of the test would mean that the test would identify patients with difficult intubation. Asghar Ali et al (10) and Naithani et al (11) had a sensitivity of 87.5% and 92.8% respectively for ULBT. Khan et al (8) had reported a sensitivity of 76.5% for ULBT.…”

Predictors of Difficult Airway Management in Thyroid Surgery: A Five-Year Observational Single-Center Prospective Study

“…Predictors of difficult airway management in thyroid surgery abnormalities have been shown to pose a significant risk factor for DI 26 . Oral anomalies exerted significant influence on the incidence of DI in our study.…”