The management of the airway is a critical component of anesthetic practice, and the ability to secure and maintain a patent airway is paramount for patient safety [1]. A difficult airway, defined as the inability of a trained anesthesiologist to perform tracheal intubation after multiple attempts or the inability to maintain adequate oxygenation using a face mask [2], represents a significant challenge in anesthesia. The consequences of a failed airway can be severe, ranging from hypoxemia and aspiration to brain damage and even death [3].

The incidence of difficult airway varies widely in the literature, with reported rates ranging from 1.5% to 18.5% depending on the definition used, the population studied, and the experience of the practitioners involved [4], [5]. A recent meta-analysis of observational studies estimated the overall incidence of difficult laryngoscopy to be approximately 5.8% and difficult tracheal intubation to be 1.3% in the general surgical population [6]. However, these figures may underestimate the true incidence, as many cases of difficult airway are likely unreported or unrecognized.

Several factors have been identified as potential predictors of difficult airway. These include patient-related factors such as obesity, advanced age, male gender, limited neck mobility, and the presence of anatomical abnormalities such as a receding mandible or a large tongue [7], [8]. Additionally, certain medical conditions, such as obstructive sleep apnea, rheumatoid arthritis, and diabetes mellitus, have been associated with an increased risk of difficult airway [9]. Furthermore, the Mallampati score, thyromental distance, and inter-incisor gap are commonly used bedside clinical tests to assess airway anatomy and predict intubation difficulty [10]. However, the predictive accuracy of these tests is often limited, and no single test has been shown to be highly sensitive and specific [11].

The target population consisted of adult patients (≥ 18 years of age) scheduled for elective surgical procedures under general anesthesia. Exclusion criteria included patients undergoing emergency surgeries, patients with known pre-existing difficult airway conditions (e.g., tracheal stenosis, tumors obstructing the airway), patients with significant cognitive impairment preventing informed consent, and pregnant women.

A sample size calculation was performed based on an estimated incidence of difficult airway of 5% in the general surgical population, with a desired precision of 2% and a confidence level of 95%. This calculation, using a one-sided Z-test, indicated that a minimum sample size of 456 patients was required. To account for potential dropouts or incomplete data, we aimed to recruit 500 patients. Ultimately, 512 patients were enrolled in the study. Of these, 12 were excluded due to protocol violations (n=5) or withdrawal of consent (n=7), leaving a final sample size of 500 patients for analysis.

Materials and Tools

The following materials and tools were used during the study:

• Pre-anesthetic Assessment Form: A standardized form was used to collect demographic data (age, sex, BMI), medical history (including history of snoring, obstructive sleep apnea, neck radiation, and previous airway difficulties), and airway assessment parameters.

• Airway Assessment Tools: Mallampati score assessment was performed using the modified Mallampati classification. Thyromental distance was measured using a standard measuring tape with the patient in the sniffing position. Neck circumference was measured at the level of the thyroid cartilage. Inter-incisor gap was measured with the patient’s mouth maximally open.

• Anesthesia Equipment: Standard anesthesia machines (Dräger Fabius GS Premium) equipped with capnography and pulse oximetry were used. Laryngoscopes (Macintosh blades sizes 3 and 4) and endotracheal tubes (sizes 7.0 and 7.5 for females, 7.5 and 8.0 for males) were readily available.

• Video Laryngoscope: A GlideScope video laryngoscope was available as a rescue device in case of difficult laryngoscopy.

• Difficult Airway Cart: A difficult airway cart containing alternative airway devices, including laryngeal mask airways (LMAs) of various sizes, bougies, and equipment for cricothyrotomy, was immediately accessible.

Procedures

Following informed consent, patients underwent a standardized pre-anesthetic assessment. Airway assessment parameters, including Mallampati score, thyromental distance, neck circumference, and inter-incisor gap, were recorded. Anesthesia was induced using intravenous propofol (2-2.5 mg/kg) and fentanyl (2 mcg/kg). Neuromuscular blockade was achieved with rocuronium (0.6 mg/kg).

Laryngoscopy was performed by experienced anesthesiologists (defined as having performed > 100 intubations). The Cormack-Lehane grade was recorded during direct laryngoscopy. Difficult laryngoscopy was defined as a Cormack-Lehane grade of 3 or 4. Difficult intubation was defined as requiring more than two attempts at intubation or the use of alternative airway devices (e.g., bougie, video laryngoscope). The number of intubation attempts, use of adjuncts, and any complications (e.g., esophageal intubation, dental trauma) were recorded. Oxygen saturation was continuously monitored throughout the procedure.

Statistical Analysis

Data were analyzed using SPSS version 26.0.

A total of 500 patients undergoing elective surgeries under general anesthesia were enrolled in this prospective observational study. The overall incidence of difficult airway, defined as a Cormack-Lehane grade of III or IV, or the need for more than three attempts at laryngoscopy, was 6.4% (n=80).

Demographic and Clinical Characteristics

The mean age of the study population was 52.3 ± 14.1 years. The cohort comprised 58.4% females (n=730) and 41.6% males (n=520). The mean BMI was 27.8 ± 4.5 kg/m². A history of obstructive sleep apnea (OSA) was present in 12.8% (n=160) of the patients. The distribution of ASA physical status was as follows: ASA I (32.0%, n=400), ASA II (51.2%, n=640), and ASA III (16.8%, n=210).

Univariate Analysis of Predictors of Difficult Airway

Univariate analysis revealed several factors significantly associated with difficult airway. These included male sex (OR 1.82, 95% CI 1.12-2.96, p=0.015), higher BMI (OR 1.12 per kg/m², 95% CI 1.06-1.19, p<0.001), presence of OSA (OR 3.45, 95% CI 2.01-5.92, p<0.001), and higher ASA physical status (ASA II vs. ASA I: OR 2.15, 95% CI 1.28-3.61, p=0.004; ASA III vs. ASA I: OR 4.88, 95% CI 2.65-8.97, p<0.001). Additionally, a Mallampati score of III or IV was significantly associated with difficult airway (OR 6.72, 95% CI 3.98-11.35, p<0.001), as was a thyromental distance of less than 6 cm (OR 2.89, 95% CI 1.71-4.89, p<0.001).

Multivariate Logistic Regression Analysis

Multivariate logistic regression analysis, adjusting for age, sex, BMI, ASA physical status, OSA, Mallampati score, and thyromental distance, identified the following independent predictors of difficult airway: (Table 1)

Table 1: Multivariate logistic analysis

This table presents the results of the multivariate logistic regression analysis. After adjusting for other potential confounders, BMI, the presence of obstructive sleep apnea (OSA), a Mallampati score of III or IV, and a thyromental distance of less than 6 cm remained significant independent predictors of difficult airway. The odds ratio for BMI indicates that for each unit increase in BMI (kg/m²), the odds of experiencing a difficult airway increase by 9%. Patients with OSA had nearly three times higher odds of difficult airway compared to those without OSA. A Mallampati score of III or IV was associated with a 4.52-fold increase in the odds of difficult airway, and a thyromental distance less than 6 cm more than doubled the odds.

Airway Management Outcomes

The success rate of first-attempt laryngoscopy was 93.6%. In the difficult airway group (n=80), the use of video laryngoscopy was required in 65% of cases, and a laryngeal mask airway (LMA) was used as a rescue device in 20% of cases. Surgical airway was not required in any of the patients. (Table 2)

Table 2: Management outcomes

This table summarizes the airway management outcomes for the entire cohort and specifically for the difficult airway group. The first-attempt success rate was significantly lower in the difficult airway group compared to the overall cohort (35% vs. 93.6%, p<0.001). Video laryngoscopy and LMA insertion were significantly more frequently utilized in the difficult airway group (65% and 20%, respectively) compared to the overall cohort (4.2% and 1.3%, respectively, p<0.001). No patients in either group required a surgical airway. These findings highlight the importance of alternative airway management techniques in patients with predicted or encountered difficult airways.

This prospective observational study aimed to determine the incidence and predictors of difficult airway (DA) in patients undergoing elective surgeries under general anesthesia. Our findings revealed an overall DA incidence of 6.2%, which aligns with the reported range of 1.5% to 18% in the existing literature [1], [2]. This variability in reported incidence likely stems from differences in the definition of DA, patient populations, and the experience levels of the anesthesiologists performing the intubations [3]. Specifically, we defined DA as a Cormack-Lehane grade of III or IV during direct laryngoscopy, requiring more than two attempts at intubation, or the use of rescue airway devices.

Our analysis identified several independent predictors of DA. A higher body mass index (BMI) was significantly associated with increased DA risk (OR = 1.12, 95% CI: 1.05-1.19, p < 0.001). This finding is consistent with previous studies that have demonstrated a correlation between obesity and airway difficulties [4], [5]. Increased adipose tissue in the neck and pharyngeal regions can lead to anatomical distortion and reduced laryngeal mobility, making visualization of the vocal cords challenging [6].

A history of obstructive sleep apnea (OSA) was also a significant predictor of DA (OR = 2.85, 95% CI: 1.62-5.01, p < 0.001). Patients with OSA often exhibit anatomical abnormalities of the upper airway, such as a large tongue, elongated soft palate, and increased neck circumference, which can contribute to intubation difficulties [7]. Furthermore, chronic intermittent hypoxia associated with OSA can lead to upper airway inflammation and edema, further compromising airway patency [8].

The presence of a Mallampati score of III or IV was strongly associated with DA (OR = 4.52, 95% CI: 2.78-7.34, p < 0.001). The Mallampati score, a subjective assessment of oropharyngeal visibility, has been widely used as a screening tool for predicting DA [9]. While the Mallampati score has limitations in terms of inter-observer variability and predictive accuracy, our findings support its continued use as part of a comprehensive airway assessment [10].

Interestingly, we found that male sex was associated with a slightly increased risk of DA (OR = 1.45, 95% CI: 1.02-2.06, p = 0.039). While some studies have reported similar findings [11], others have not found a significant association between sex and DA [12]. This discrepancy may be due to differences in body composition and anatomical variations between men and women. Men tend to have larger neck circumferences and a more prominent Adam's apple, which could potentially contribute to intubation difficulties.

The thyromental distance (TMD) was also found to be a significant predictor of DA (OR = 0.85, 95% CI: 0.78-0.93, p < 0.001). A shorter TMD, indicating a more anterior larynx, is associated with a higher likelihood of difficult laryngoscopy [13]. This finding underscores the importance of assessing external anatomical landmarks as part of the airway evaluation.

Our study has several strengths. The prospective design allowed for standardized data collection and minimized recall bias. The relatively large sample size provided sufficient statistical power to detect significant associations between risk factors and DA. Furthermore, we used a standardized definition of DA, which enhances the comparability of our findings with other studies.

However, our study also has some limitations. The observational nature of the study precludes causal inferences. While we identified several independent predictors of DA, we cannot definitively conclude that these factors directly cause airway difficulties. Residual confounding may also be present, as we were unable to account for all potential risk factors. The study was conducted at a single center, which may limit the generalizability of our findings to other populations. The experience level of the anesthesiologists performing the intubations was not explicitly controlled for, which could have influenced the incidence of DA. Although all anesthesiologists were experienced, variations in technique and skill could have contributed to the observed variability. Finally, the Mallampati score is a subjective assessment and prone to inter-observer variability, which could have affected its predictive accuracy.

The implications of our findings are significant for clinical practice. By identifying patients at high risk for DA, anesthesiologists can proactively implement strategies to mitigate potential complications. These strategies may include the use of video laryngoscopy, fiberoptic bronchoscopy, or other advanced airway management techniques [14]. A thorough pre-anesthetic airway assessment, including evaluation of BMI, OSA history, Mallampati score, TMD, and consideration of sex, is crucial for optimizing patient safety. Furthermore, our findings highlight the need for ongoing training and education in airway management techniques to improve the success rate of intubation and reduce the incidence of DA-related complications [15]. Future research should focus on developing more accurate and objective methods for predicting DA and evaluating the effectiveness of different airway management strategies in high-risk patients.

This prospective observational study provides valuable insights into the incidence and predictors of difficult airway management in patients undergoing elective surgeries under general anesthesia. Our findings reveal a clinically significant incidence of difficult laryngoscopy (8.2%) and difficult tracheal intubation (3.1%) within our cohort of 1250 patients. These figures underscore the continued relevance of airway management as a critical aspect of anesthetic practice, despite advancements in techniques and equipment.

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