European Journal of Cardiovascular Medicine

Obesity may be defined as a health condition in which excess of fat deposition occurs and has become a major health challenge. As per World Health Organization (WHO), individual’s whose body mass index (BMI) greater than or equal to 30 kg per square meter of body surface is termed as obese 1. The study done by Misra et al., 73 among Asians, the definition of obesity has been changed to BMI ≥ 25 kg.m-2 for metabolic managements, but it doesn’t effect the acute management of the airway, so we are considering BMI ≥ 30 kg.m-2 for airway assessment of obese patients. Inability to maintain oxygenation among the obese population leads to complications which can account for the 30% of the deaths.2 The ASA (American society of anesthesiologists) closed claim data analysis of adverse respiratory events had found out that one third of death was attributed solely to anaesthesia due to inability to maintain airway.

When anaesthesia malpractice claims were considered, difficult intubation was the second most frequent damaging event.4 most catastrophes have occurred when possible difficult airway was not recognized early.5 the importance of preoperative assessment of airway to reduce anaesthesia related complications has been evaluated over the last century. In view of all above mentioned findings several methods and techniques were developed, Cormack and Lehane scoring system, Mallampati test etc. for predicting intubation difficulty.

Among non-obese and obese individuals, the incidence of difficult laryngoscopy is similar (about 10%). But there are more reports of difficult intubation among obese patients. This can be due to changes in upper airway present among them. There are some clinical predictors which increases the risk of difficult airway in obese patients. Increased neck circumference, Mallampati’s grade III or IV and diagnosis of obstructive sleep apnea syndrome (OSAS) are some of the factors related to difficult intubation.

However, measurement of neck circumference alone may not attribute to the amount of soft tissue at various topographic regions within the neck. Using magnetic resonance imaging (MRI), Horner 6 proposed that among obese patients with OSA’S, more fat was present in areas surrounding the collapsible segments of the pharynx. The study done by Ezri et al. 7 using ultrasonography suggested that difficult airway among obese patients can be predicted by quantifying the neck soft tissue at the level of the vocal cords and suprasternal notch. They further noted that the only measurement that fully distinguishes easy and difficult intubation was the amount of pretracheal soft tissue as quantified by ultrasonography. The above findings point out that why some obese patients are easy to intubate, while others not

Moreover, by review of literature, we found that increased neck circumference had good sensitivity and relatively low specificity as well as decreased thyromental distance had high specificity and low sensitivity for predicting difficult intubation preoperatively. So, the hypothesis was that by taking the ratio between these two above indices a new predictor of difficult intubation with better statistical and clinical outcome can be generated. So, in this dissertation we aspire to explore a preoperative predictor of difficult intubation, named ratio of neck circumference to thyromental distance which needs no special equipment, minimal time for performance and is not uncomfortable to patient. It is a noninvasive test which has got better statistical significance compared to other indices

After approval from the ASRAMS Institutional Ethics Committee, the procedure was clearly explained to patients and informed written consent was obtained. The study was conducted during the period, April 2024- March 2025 at ASRAM General and Super-Specialty Hospital, Eluru, Andhra Pradesh. Validated Intubation difficulty score (IDS score) for each obese patient was assessed intra operatively by the anesthetist who performed intubation. The entire study population were divided into easy and difficult intubation groups based on the IDS score. IDS score greater than or equal to five was considered as difficult intubation. NC/TM distance ratio greater than or equal to five was correlated with IDS score greater than or equal to five. The study assessed the statistical significance of NC/TM distance ratio and difficult intubation by univariate and multivariate logistic regression analysis and its comparison with Mallampati score and neck circumference with respect to sensitivity / specificity/ positive predictive value and negative predictive value. The study also calculated the incidence of difficult intubation among obese patients

A total of 328 obese patients were assessed for our study between September 2014 and March 2015 and among them, 250 patients who underwent endotracheal intubation were recruited for the study after obtaining informed consent. The patients excluded were those who underwent only regional anaesthesia, those who had regional blocks alone, those who had surgery using laryngeal mask airway and not willing to participate for the study. The SPSS software (version 16.0) was used to analyze the data. A total of 250 obese patients who underwent tracheal intubation were divided into two arms, namely easy intubation group (IDS score less than 5) and difficult intubation group (IDS score greater than or equal to 5). There were 52 and 198 patients among easy and difficult intubation groups respectively. The following are the results. 10.1

DEMOGRAPHIC DATA

The baseline data comparing age, gender, weight, height, ASA status, BMI, between easy intubation group and difficult intubation group are tabulated below. Here easy intubation group (IDS <5) is referred as group 1 and difficult intubation group (IDS ≥5) as group 2.

TABLE 1

RESULTS OF PRIMARY OBJECTIVE

TABLE 2

All the obese patients were intubated by anesthetists who had more than three years of clinical experience in anesthesiology. As enumerated in table no 15, the clinical experience of the anesthetists seems comparable between the two groups and around 50 % of anesthetists who intubated study patients had experience between 3- 5 years. The most commonly used material/equipment to aid intubation among obese patients was in order of stylets, ramping and glide scope respectively. Thirty percent of obese patients were intubated with the help of stacking/ramping. The limited use of ramping technique among obese patients was noted in this study which needs to be emphasized among the anesthetists.

The use of indirect laryngoscopes among obese patients was as high as 18 percent and may be due easily availability of the equipment’s in our hospital. Among easy intubation group, most of the intubations were done by first attempt (97 %) and first operator (96.0 %) respectively. More operators and attempts were needed to intubate difficult intubation group. The Cormack and Lehane grading were 3 and 4 in 57.7 % of patients among difficult intubation group and 2 % among easy intubation group. Most of the patients required considerable lifting force and external laryngeal pressure for optimal visualization of vocal cords among difficult intubation group

Among obese patients, NC/TMD ratio can be considered as a better preoperative predictor of difficult intubation and incidence of difficult intubation among them was as high as 20.8 percent

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