Ultrasound vs Clinical Parameters for Difficult Airway Prediction in Obesity

Comparison of Airway Ultrasonography and Conventional Difficult Airway Parameters for Predicting Difficult Airway in Obese Patients: A Prospective Observational Study

Obesity is associated with anatomical changes in the upper airway that increase the risk of difficult laryngoscopy and difficult mask ventilation during anesthesia. Conventional airway assessment parameters such as Mallampati score, neck circumference, and STOP-BANG scale are widely used but have limited predictive accuracy in obese patients. Airway ultrasonography has emerged as a promising non-invasive tool for difficult airway prediction; however, ultrasonographic criteria have not yet been standardized.

This prospective observational study aims to evaluate the utility of airway ultrasonography in predicting difficult airway in adult obese patients (BMI >30 kg/m²) scheduled for elective surgery under general anesthesia. Ultrasonographic measurements will include the distance from skin to hyoid bone (DSHB) at the level of the hyoid bone, the anterior neck soft tissue thickness at the thyrohyoid membrane level, and the hyomental distance ratio (HMDR). These parameters will be compared with conventional airway assessment tools and correlated with intraoperative Cormack-Lehane laryngoscopy grade and Han Scale mask ventilation score to determine their predictive value for difficult airway.

Study Overview

• Status: Not yet recruiting
• Conditions: Difficult Airway; Difficult Airway Intubation; Difficult Mask Ventilation; Obesity (BMI > 35)
• Intervention / Treatment: Diagnostic test: Airway Ultrasonography

Detailed Description

Airway management is a critical component of clinical anesthesia. A difficult airway is defined as a situation in which a conventionally trained anesthesiologist experiences difficulty with mask ventilation, laryngoscopy, supraglottic airway ventilation, tracheal intubation, extubation, or invasive airway management. Unanticipated difficult laryngoscopy and difficult mask ventilation can lead to catastrophic outcomes. The incidence of difficult laryngoscopy and intubation is estimated at 1.5-13%, and approximately 28% of anesthesia-related deaths are attributable to failed mask ventilation or intubation.

Obesity (BMI ≥30 kg/m²) is associated with significant anatomical alterations in the upper airway and head and neck region. Accumulation of adipose tissue in the pharynx and hypopharynx narrows the airway lumen. A larger tongue is more difficult to displace into the submental space during laryngoscopy. Enlarged tonsils further reduce oropharyngeal space. Fat deposition in the neck, shoulders, and back complicates optimal patient positioning for laryngoscopy. Excessive soft tissue around the face and cheeks impairs effective mask seal and ventilation.

With advances in portable ultrasound technology, airway ultrasonography has become an increasingly utilized clinical tool for preoperative airway assessment. However, ultrasonographic criteria for predicting difficult airway have not yet been standardized.

Study Protocol:

Adult obese patients (BMI >30 kg/m², aged 18-65 years, ASA I-III) scheduled for elective surgery requiring orotracheal intubation under general anesthesia will be enrolled. Prior to the operating room, the following conventional airway parameters will be assessed: neck circumference, Mallampati score, and STOP-BANG scale. Airway ultrasonographic measurements will be performed preoperatively and will include:

Distance from skin to hyoid bone (DSHB) at the transverse view of the hyoid bone level Anterior neck soft tissue thickness at the thyrohyoid membrane level Hyomental distance ratio (HMDR): ratio of hyomental distance in extension (HMDe) to hyomental distance in neutral position (HMDn)

Upon arrival to the operating room, standard monitoring will be applied including electrocardiogram (ECG), non-invasive blood pressure, peripheral oxygen saturation (SpO2), body temperature, and bispectral index (BIS). Following monitoring and preoxygenation (2 minutes with 100% oxygen via face mask), standard anesthesia induction will be performed with intravenous propofol 2 mg/kg, fentanyl 2 mcg/kg, and rocuronium 0.6 mg/kg. After adequate neuromuscular blockade, orotracheal intubation will be performed.

Mask ventilation difficulty will be graded using the Han Scale during the mask ventilation phase. Laryngoscopy difficulty will be graded using the Cormack-Lehane classification at the time of intubation.

Mechanical ventilation will be maintained in volume control mode with tidal volume of 6-8 ml/kg, targeting end-tidal CO2 (EtCO2) of 35-40 mmHg. Anesthesia maintenance will be provided with 1.5-2% sevoflurane in 50% O2/air at 2 L/min and intravenous remifentanil infusion at 0.05-0.5 mcg/kg/min, targeting BIS 40-60. Normothermia will be maintained with an active forced-air warming device throughout the procedure.

Twenty minutes before the end of surgery, standard postoperative analgesia and prophylaxis will be administered: paracetamol 1 g, tramadol 1 mg/kg, and ondansetron 4 mg intravenously. Heart rate, blood pressure, EtCO2, and SpO2 will be documented every 30 minutes intraoperatively.

At the end of surgery, anesthetic agents will be discontinued. Sugammadex 2 mg/kg IV will be administered for reversal of neuromuscular blockade upon return of spontaneous respiratory effort. Patients with adequate respiratory effort and BIS ≥85 will be extubated and transferred to the post-anesthesia care unit (PACU) when conscious, with recovered muscle strength and hemodynamic stability. Standard monitoring will continue in the PACU prior to ward transfer.

Primary Outcome: Preoperative ultrasonographic assessment of anterior neck using DSHB and HMDR parameters and their correlation with intraoperative Cormack-Lehane grade.

Secondary Outcome: Determination of whether DSHB and HMDR can predict difficult airway in adult obese patients when correlated with Cormack-Lehane laryngoscopy grade and Han Scale mask ventilation score.

• Study Type: Observational
• Enrollment (Estimated): 70

Contacts and Locations

• Study Contact: Name: Emin Mert Koyutürk, MD; Phone Number: +905362403394; Email: mertkytrk@gmail.com

Study Locations

• Turkey (Türkiye)
  • Istanbul, Turkey (Türkiye)
    • Fatih Sultan Mehmet Training and Research Hospital
    • Contact: cansu ofluoglu, md; Phone Number: +905358640564; Email: cansuakin.iu@gmail.com

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

• Sampling Method: Non-Probability Sample

Study Population

Adult obese patients (BMI >30 kg/m², aged 18-65 years, ASA I-III) scheduled for elective surgery requiring orotracheal intubation under general anesthesia at Fatih Sultan Mehmet Training and Research Hospital, Istanbul, Turkey.

Description

Inclusion Criteria:

• Age 18-65 years
• BMI >30 kg/m2
• ASA physical status I, II, or III
• Scheduled for elective surgery requiring orotracheal intubation under general anesthesia
• Written informed consent obtained

Exclusion Criteria:

• Emergency surgery
• History of previous head and neck surgery or radiotherapy
• Known or anticipated difficult airway (history of difficult intubation)
• Presence of cervical spine pathology or limited neck mobility
• Presence of oropharyngeal or laryngeal pathology
• Pregnancy
• Patients with tracheostomy
• Refusal to participate

Study Plan

How is the study designed?

Number of groups / cohorts

1

Cohorts and Interventions

Group / Cohort

Intervention / Treatment

Obese Patients Undergoing General Anesthesia; Adult obese patients (BMI >30 kg/m², aged 18-65 years, ASA I-III) scheduled for elective surgery requiring orotracheal intubation under general anesthesia. Preoperative airway assessment will include conventional parameters (Mallampati score, neck circumference, STOP-BANG scale) and airway ultrasonographic measurements (distance from skin to hyoid bone [DSHB] and hyomental distance ratio [HMDR]). Standard anesthesia induction will be performed with propofol 2 mg/kg, fentanyl 2 mcg/kg, and rocuronium 0.6 mg/kg. Mask ventilation difficulty will be graded using the Han Scale and laryngoscopy difficulty using the Cormack-Lehane classification. Anesthesia will be maintained with sevoflurane and remifentanil infusion targeting BIS 40-60.

Diagnostic test: Airway Ultrasonography; Preoperative airway ultrasonography will be performed by a trained anesthesiologist using a linear ultrasound probe with the patient in the supine position and head in neutral position. The following measurements will be obtained: (1) minimum distance from skin to hyoid bone (DSHB) at the transverse view of the hyoid bone level, (2) anterior neck soft tissue thickness at the thyrohyoid membrane level, and (3) hyomental distance ratio (HMDR), calculated as the ratio of hyomental distance in full extension (HMDe) to hyomental distance in neutral position (HMDn). These ultrasonographic parameters will be correlated with intraoperative Cormack-Lehane laryngoscopy grade and Han Scale mask ventilation score to assess their predictive value for difficult airway in obese patients.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Correlation of Ultrasonographic Airway Parameters (DSHB and HMDR) with Cormack-Lehane Laryngoscopy Grade	Preoperative ultrasonographic measurements including the minimum distance from skin to hyoid bone (DSHB) at the hyoid bone level and the hyomental distance ratio (HMDR, calculated as hyomental distance in full extension divided by hyomental distance in neutral position) will be correlated with the intraoperative Cormack-Lehane laryngoscopy grade. Cormack-Lehane grades III and IV will be defined as difficult laryngoscopy. The diagnostic accuracy of DSHB and HMDR in predicting difficult laryngoscopy will be assessed using ROC curve analysis.	Perioperative/Periprocedural

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Predictive Value of Conventional Airway Parameters for Difficult Laryngoscopy	Conventional preoperative airway assessment parameters including Mallampati score, neck circumference, and STOP-BANG scale will be correlated with intraoperative Cormack-Lehane laryngoscopy grade. Cormack-Lehane grades III and IV will be defined as difficult laryngoscopy. The diagnostic accuracy of each conventional parameter will be assessed using ROC curve analysis and compared with ultrasonographic parameters.	Perioperative/Periprocedural
Predictive Value of Ultrasonographic and Conventional Airway Parameters for Difficult Mask Ventilation	Preoperative ultrasonographic measurements (DSHB and HMDR) and conventional airway parameters (Mallampati score, neck circumference, STOP-BANG scale) will be correlated with intraoperative mask ventilation difficulty graded using the Han Scale. Han Scale grades III and IV will be defined as difficult mask ventilation. Diagnostic accuracy of each parameter will be assessed using ROC curve analysis.	Perioperative/Periprocedural

Collaborators and Investigators

• Sponsor: Fatih Sultan Mehmet Training and Research Hospital

Study record dates

Study Major Dates

• Study Start (Estimated): April 10, 2026
• Primary Completion (Estimated): October 10, 2026
• Study Completion (Estimated): November 1, 2026

Study Registration Dates

• First Submitted: March 27, 2026
• First Submitted That Met QC Criteria: April 9, 2026
• First Posted (Actual): April 14, 2026

Study Record Updates

• Last Update Posted (Actual): April 14, 2026
• Last Update Submitted That Met QC Criteria: April 9, 2026
• Last Verified: April 1, 2026

More Information

Terms related to this study

• Keywords: Neck circumference; General anesthesia; Mallampati score; Obese patients; Difficult airway prediction; Orotracheal intubation; Airway ultrasonography; Cormack-Lehane classification; Han Scale; Hyomental distance ratio; Distance from skin to hyoid bone; STOP-BANG scale
• Additional Relevant MeSH Terms: Nutrition Disorders; Overnutrition; Body Weight; Overweight; Pathological Conditions, Signs and Symptoms; Nutritional and Metabolic Diseases; Signs and Symptoms; Obesity
• Other Study ID Numbers: FSMAİRWAY

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No