European Journal of Cardiovascular Medicine

Airway management is a vital part of anaesthetic practice as failure to secure the airway effectively can lead to severe complications, including hypoxia, aspiration and even mortality in extreme cases.¹ Predicting a difficult airway prior to anaesthesia induction is essential for ensuring patient safety and improving outcomes. While clinical predictors such as the Modified Mallampati classification, thyromental distance, neck mobility and inter-incisor distance are commonly used during preoperative airway assessment. These tests often fall short in sensitivity and specificity. This can lead to unanticipated difficult laryngoscopy (DL) even in patients initially considered to have an easy airway.^2,3 Advanced imaging techniques like magnetic resonance imaging (MRI) and computed tomography (CT) offer high-resolution anatomical details but are impractical for routine use due to cost, limited accessibility, radiation exposure (in the case of CT) and lack of portability.³ In contrast the ultrasonography has emerged as a practical, bedside-friendly, non-invasive and cost-effective tool for evaluating airway anatomy. It allows dynamic visualization of the anterior neck soft tissues and provides objective measurements that may enhance airway prediction accuracy. Several studies have suggested that ultrasonographic (US) evaluation can offer more reliable and quantifiable data compared to traditional methods.^4,5 In this study seven ultrasonographic parameters were assessed to predict difficult laryngoscopy in adult patients undergoing elective oncologic surgery. These parameters included tongue width, cross-sectional area (CSA) of the tongue, CSA of the floor of the mouth and mento-hyoid distance (MHD) using a curvilinear probe, while skin-to-hyoid (SH) distance, skin-to-epiglottis (SE) distance and anteroposterior thickness of the geniohyoid muscle were measured with a linear probe. The primary aim of this study was to examine the association between these preoperative ultrasonographic airway measurements and laryngoscopic view (LSW) and to compare their predictive accuracy with conventional clinical predictors such as the Modified Mallampati classification and neck circumference. The research hypothesis was that ultrasonographic measurements particularly SE and SH distances would offer higher sensitivity and specificity in predicting DL. The study also hypothesized that integrating ultrasonographic parameters into standard preoperative assessment protocols could improve the detection of potentially difficult airways. Aiding in a better planning and patient safety especially in oncological surgical setting.

Study Setup and Design this prospective observational study was carried out at Oncology Institute between September 2022 and June 2024. It included 123 adult patients diagnosed with cancer and scheduled for elective surgeries under general anesthesia. The study was approved by the Institutional Ethics Committee and written informed consent was obtained from each participant prior to enrollment. To reduce bias and maintain objectivity the study was designed to include a blinding component. The anaesthesiologist responsible for preoperative ultrasonographic airway evaluation was different from the one performing direct laryngoscopy and intubation. The anaesthesiologist performing the laryngoscopy was unaware of the ultrasound results, ensuring a blinded assessment of the laryngoscopic view. The sample size was calculated using ROC-based estimation considering an anticipated incidence of 10–15% for difficult laryngoscopy in the cancer population. With a confidence level of 95% and a power of 80%, a minimum of 120 patients was required. To strengthen the analysis and account for potential dropouts, 123 patients were ultimately recruited.

Inclusion Criteria

Eligible patients were aged between 18 and 60 years and were classified as American Society of Anaesthesiologists (ASA) physical status I or II. Both male and female patients were included.

Exclusion Criteria

Exclusion criteria involved patients with known difficult airways, including those with maxillofacial deformities, congenital anomalies, limited neck movement due to cervical spine pathology or previous surgeries. Severely obese individuals with a body mass index (BMI) greater than 40 kg/m² and those with limited mouth opening (<3 cm) were excluded. Patients undergoing emergency procedures were also excluded due to the inability to perform preoperative assessment in such settings.

Methods                               

Preoperative evaluation was performed a day prior to surgery and included both clinical and ultrasonographic assessments. Clinical airway assessment consisted of the Modified Mallampati classification, mouth opening measured as inter-incisor distance and neck circumference. Ultrasonographic evaluation was conducted using both a 6-13 MHz linear probe and a 2-5 MHz curvilinear probe with the patient lying supine, head in a neutral position and mouth closed with the tongue resting on the floor of the mouth. The skin-to-epiglottis (SE) distance was measured through the thyrohyoid membrane, appearing as a dark curvilinear structure. The skin-to-hyoid (SH) distance was recorded as the vertical distance from the skin surface to the hyperechoic hyoid bone. Anteroposterior thickness of the geniohyoid muscle was recorded in the transverse plane. Cross-sectional areas of the tongue and mentohyoid distance were captured in the midsagittal plane and cross sectional area of floor of mouth and tongue width were measured in transverse view. On the day of surgery standard monitoring including electrocardiogram (ECG), non-invasive blood pressure and pulse oximetry was recorded. Anaesthesia induction was with preoxygenation using 100% oxygen for three minutes followed with intravenous midazolam (1 mg) and fentanyl (2 mcg/kg) for sedation and analgesia. Intravenous propofol (2 mg/kg) was used for induction and neuromuscular relaxation was achieved using intravenous succinylcholine (1 mg/kg). Succinylcholine was chosen as it has rapid onset and short duration of action making it especially suitable in scenarios where difficult intubation was unanticipated. In the event of a failed intubation attempt the drugs short duration allows for a quick return of spontaneous respiration making it preferable over longer acting neuromuscular blockers. Direct laryngoscopy was performed using an appropriately sized Macintosh curved blade by an experienced anaesthesiologist. The laryngoscopic view was graded using the Cormack-Lehane system- Grades I and II were categorized as easy laryngoscopy while Grades III and IV were considered difficult. For patients in whom DL was encountered, a structured management approach based on the Difficult Airway Society (DAS) guidelines was implemented. A second attempt was made with improved positioning or an alternate blade. If unsuccessful a bougie-assisted intubation was performed. In persistent cases video laryngoscopy was used as a rescue technique. If intubation remained unsuccessful and ventilation became compromised, supraglottic airway devices were employed and emergency cricothyroidotomy was considered as the final resort.

Statistical Analysis

All statistical analyses were performed using SPSS version 22.0 and R software version 3.2.2. A p-value of less than 0.05 was considered statistically significant. Continuous variables were analysed using the Student’s t-test and Levene’s test to assess variance homogeneity. Categorical data were compared using the Chi-square test, Receiver operating characteristic (ROC) curve analysis was used to evaluate the predictive performance of both clinical and ultrasonographic parameters. The area under the curve (AUC) with 95% confidence intervals was calculated for each parameter to assess its predictive strength for difficult laryngoscopy.

Table 1: Comparison of Clinical Variables Based on Laryngoscopic View

There was no statistically significant difference in age, weight or height between patients with easy and difficult laryngoscopy (p > 0.05). BMI however was significantly higher in the difficult laryngoscopy group (25.6 ± 4.22 vs. 22.65 ± 3.06, p < 0.001) indicating a strong correlation between increased BMI and airway difficulty. ​

Table 2: Modified Mallampati Grades and Laryngosocopic view in the study population

The Modified Mallampati classification showed that the majority of patients (71.5%) were categorized as Grade 2. In terms of laryngoscopic view, 87.8% of patients had an easy laryngoscopy, whereas 12.2% experienced difficult laryngoscopy highlighting a notable proportion of patients with challenging airway management.

Table 3: Association Between Modified Mallampati Classification and Laryngoscopic view

A significant correlation was observed between the Modified Mallampati classification and the laryngoscopic view. Among patients with easy Mallampati grades, 94.05% had easy laryngoscopy, while only 5.9% encountered difficulty. Among patients with difficult Mallampati grades, 40.9% experienced difficult laryngoscopy demonstrating a higher Mallampati grade is strongly associated with an increased risk of airway difficulty.

Table 4: Comparison of Intubation Time and Number of Attempts Based on Laryngoscopic View

Patients with difficult laryngoscopy had a significantly longer intubation time compared to those with easy laryngoscopy (25.53 ± 4.09 sec vs. 21.42 ± 4.06 sec, p ≤ 0.001). The majority (80%) of difficult laryngoscopy cases required 20–30 seconds for intubation with 13.3% taking more than 30 seconds. Additionally, 33.3% of difficult laryngoscopy patients needed multiple attempts whereas 96.3% of easy laryngoscopy cases were intubated on the first attempt has the strong association between airway difficulty and prolonged intubation.

  Table 5: ROC Curve Analysis of Sonographic and Clinical Parameters for Predicting Difficult Laryngoscopic View

The skin-to-epiglottis distance was the most accurate predictor of difficult laryngoscopy, with 100% sensitivity and 84.26% specificity (AUROC: 0.971, p < 0.001). The cross-sectional area of the tongue also showed a strong predictive value (AUROC: 0.863, p < 0.001). Other significant predictors included skin-to-hyoid distance (AUROC: 0.771, p < 0.001) and width of the tongue (AUROC: 0.759, p = 0.005). Neck circumference, mento hyoid distance and geniohyoid thickness demonstrated poor predictive ability with AUROC values close to 0.5. ​

This prospective observational study examined how preoperative clinical and ultrasonographic (US) airway assessments correlate with laryngoscopic view (LSW) in patients with cancer undergoing elective surgery. The findings emphasize the growing role of ultrasonography as a dependable, non-invasive tool for predicting difficult laryngoscopy (DL), especially when used alongside well-established clinical parameters like the Modified Mallampati Score (MMS).

Grade 3 MMS was associated with 60% of DL cases in our study. Several patients with Grade 2 MMS also experienced difficult laryngoscopy highlighting a limitation in the sensitivity of this tool. This shortfall has been echoed in existing literature where MMS sensitivity ranges from 53% to 60% and specificity ranges from 80% to 89% making it insufficient when used alone to anticipate DL.⁶^,⁷ These observations are consistent with the meta-analysis conducted by Lundstrøm et al. which concluded that the Mallampati score by itself is not a reliable standalone predictor and should be supplemented with additional clinical or imaging methods. ⁸

Among the clinical variables assessed body mass index (BMI) emerged as a significant factor. Patients with DL had a noticeably higher BMI (25.6 ± 4.22 kg/m²) compared to those with an easy laryngoscopy (22.65 ± 3.06 kg/m²), with the difference being statistically significant (p < 0.001). This supports the hypothesis that increased soft tissue in the anterior neck commonly seen in patients with higher BMI may obscure glottic structures and make intubation more challenging. These findings align with previous studies that associate increased BMI with difficult airway scenarios. ⁹ Parameters like height, weight and age did not differ significantly between the easy and difficult laryngoscopy groups, echoing earlier findings that suggest these are weak or inconsistent predictors of DL. ¹⁰^-¹²

The real strength of this study lies in the evaluation of ultrasonographic parameter which proved to be more accurate than clinical predictors. Of all the ultrasound-based measures the skin-to-epiglottis (SE) distance was the most reliable indicator showing an impressive AUROC of 0.971, with 100% sensitivity and 84.26% specificity. A shorter SE distance corresponded with easier laryngoscopy presumably due to reduced anterior neck soft tissue. This result supports previous meta-analyses reporting pooled sensitivity and specificity values of 80% and 70% respectively for SE distance.⁶ Similarly, the skin-to-hyoid (SH) distance also showed predictive strength (AUROC 0.771, p < 0.001) reaffirming the advantage of ultrasound in evaluating airway anatomy.

In addition to SE and SH distances, tongue width and cross-sectional area (CSA) were also significant indicators of DL with AUROCs of 0.759 and 0.863 respectively. These findings show the influence of tongue volume and shape in determining laryngoscopic view. Supporting these past studies have noted that tongue thickness exceeding 6 cm is associated with DL with sensitivity and specificity as high as 75% and 94%, respectively. ¹³^,¹⁴ On the other hand variables like mentohyoid distance (MHD) and neck circumference showed low predictive value (AUROC ~0.5) suggesting limited usefulness when used in isolation. ¹⁵

Our findings also demonstrated that patients with difficult laryngoscopy had longer intubation times and more frequent failed attempts. The mean time to intubation in the DL group was significantly higher (25.53 ± 4.09 seconds) compared to the easy group (21.42 ± 4.06 seconds, p ≤ 0.001). A 33.3% of DL cases required two attempts whereas only 3.7% in the easy group needed more than one attempt. These observations stress the clinical importance of accurate preoperative identification of difficult airways to reduce the likelihood of complications such as hypoxia, airway trauma or cardiovascular instability during intubation.

ROC curve analysis added further weight to the predictive superiority of ultrasound over traditional methods. Both SE distance and tongue CSA demonstrated better sensitivity and AUROC values compared to MMS reinforcing the need for a multimodal assessment approach. The SH distance showed higher sensitivity (100%) than SE (75%) but SE had better specificity (89.77%). These patterns are in line with findings by Bhagavan et al. who also emphasized the complementary nature of SE and SH in airway evaluation. ¹⁶

Several other studies from the literature lend support to our findings. Adhikari et al. found that anterior neck thickness greater than 2.8 cm at the hyoid or thyrohyoid level was a better predictor of DL than visualization of the vocal cords.¹⁷ Similarly Alessandri et al. observed that the skin-to-hyoid distance had a strong association with both difficult mask ventilation and DL.¹⁸ A separate meta-analysis identified hyomental distance in the neutral position as a consistently reliable indicator, with an AUROC greater than 0.85.¹⁹ Komatsu et al. noted that ultrasound-based airway measurements were less reliable in obese patients indicating that findings in this subgroup should be interpreted cautiously.²⁰ Shiga et al. suggested that the combination of MMS with thyromental distance improves the prediction of DL more than either parameter alone.²¹ In another related study Parameshwari et al. assessed SE, SH, tongue volume and floor-of-mouth thickness and reported that SE had the highest sensitivity (75%) and negative predictive value, albeit with moderate specificity (63.6%).¹⁵

More recently a large-scale meta-analysis by Fulkerson et al. and Carsetti et al. further validated the diagnostic strength of ultrasonographic airway assessment reporting AUROC values of 0.87 or higher for SE and SH distances.^6,²² These studies lend additional credibility to our results and support the routine incorporation of sonographic evaluation in airway planning.

One of the key strengths of this study is its focus on an oncological patient population which has often been underrepresented in airway prediction research. The findings show that ultrasonographic parameters, particularly SE and SH distances retain high diagnostic accuracy in this group as well. This extends the clinical utility of ultrasound to the preoperative care of oncology patients. By directly comparing clinical and sonographic predictors using ROC analysis, this study provides a robust comparative framework for future research.

Despite these strengths, the study has a few limitations. Being a single-center study with a relatively small sample size, the findings may not be universally generalizable. All ultrasound assessments were performed by a single anesthesiologist, which may introduce operator-related variability and limit reproducibility. Also, the study did not include thyromental distance a commonly used and validated predictor which may limit the applicability of our predictive model when compared to multimodal scoring systems.

A larger multicenter studies involving diverse patient populations are needed to validate these findings and enhance their external applicability. There is also a need to standardize ultrasonographic airway assessment protocols including training modules and reproducibility metrics across operators. Combining sonographic parameters with established clinical tools like thyromental distance and neck mobility could result in more comprehensive and reliable predictive models. The integration of artificial intelligence and machine learning into ultrasound analysis presents an exciting opportunity to develop real-time, automated airway risk stratification tools.

this study shows that using ultrasound to assess the airway especially by measuring the skin-to-epiglottis and skin-to-hyoid distances is more accurate than traditional clinical methods in predicting difficult laryngoscopy in cancer patients. Among all the parameters we studied the skin-to-epiglottis distance and tongue cross-sectional area gave the most reliable results. Clinical tools like the Modified Mallampati Score were less effective on their own. Including ultrasound in routine preoperative checks can help doctors better identify patients who might face airway challenges allowing for safer and more informed planning in those undergoing cancer surgery.

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