Anatomic Features of the Neck and Preoperative Tests as Predictive Markers of Difficult Laryngoscopy

Study Overview
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Brief Summary
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In this prospective, open cohort study the diagnostic value of tests based on neck anatomy in predicting difficult laryngoscopy was assessed. The anatomic features of the neck measured were head extension, mouth opening, upper lip bite, Mallampati class, thyromental distance, sternomental distance, ratio of height to thyromental, neck circumference, thyrosternal distance, hyomental distance at full head extension (FHE) and at neutral position (NP), ratio of neck circumference to thyromental distance and ratio of hyomental distance FHE to hyomental distance NP.

Detailed Description
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Difficult airway assessment is based on various anatomic parameters of upper airway, much of it being concentrated on oral cavity and the pharyngeal structures. The diagnostic value of tests based on neck anatomy in predicting difficult laryngoscopy was assessed in this study . The sample consisted of adult patients scheduled to receive general anaesthesia. Anatomic features of the neck were measured pre-operatively. The anatomic features of the neck measured were thyromental distance, sternomental distance, ratio of height to thyromental, neck circumference, thyrosternal distance, hyomental distance at full head extension (FHE) and at neutral position (NP), ratio of neck circumference to thyromental distance and ratio of hyomental distance FHE to hyomental distance NP. The commonly used predictive tests head extension, mouth opening, upper lip bite test and Mallampati class were also measured. The laryngoscopic view was classified according to the Cormack-Lehane Grade (1-4). Difficult laryngoscopy was defined as Cormack-Lehane Grade 3 or 4. Years of experience of the anaesthesiologists were recorded, as well as the number of tries needed to intubate the patient. The optimal cut-off points for each predictive tests were identified by using receiver operating characteristic analysis. Sensitivity, specificity and positive predictive value and negative predictive value (NPV) were calculated for each test. Multivariate analysis with logistic regression, including all variables, was used to create a predictive model. Comparisons between genders were also performed to explore possible differences in diagnostic value and cut-off points. Finally, the years of experience of the clinician and the number of tries needed to intubate the patient were compared to assess risk of bias.

Official Title
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Anatomic Features of the Neck and Preoperative Tests as Predictive Markers of Difficult Direct Laryngoscopy

Conditions
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Airway Management, Predictive Value of Tests

Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Adult patients BMI less than 35 kg/m2 No known neck or airway pathology Scheduled for surgical procedures under general anaesthesia with tracheal intubation Exclusion Criteria: Age less than 18 years BMI higher than 35 kg/m2 Obvious airway malformations Need for rapid sequence induction/intubation under cricoid pressure Awake intubation Cervical spine pathology requiring specific manipulation Obstetric cases

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Difficult laryngoscopy classification using Cormack-Lehane Grade | Assessment of difficult laryngoscopy at the time of the airway management procedure. Classified as Grade I - visualization of entire laryngeal aperture, grade II - visualization of only posterior commissure of laryngeal aperture, grade III - visualization of only epiglottis, grade IV - visualization of just the soft palate. | immediate | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Thyromental distance measured in cm with a measuring tape | The distance from the mentum to the thyroid notch while the patient's neck is fully extended and the mouth closed | immediate | 
| Sternomental distance measured in cm with a measuring tape | The distance from the suprasternal notch to the mentum while the patient's neck is fully extended and the mouth closed | immediate | 
| Ratio of height to thyromental distance | Calculated ratio of the height in cm to the aforementioned thyromental distance | immediate | 
| Thyrosternal distance calculated in cm | Calculated from the subtraction: sternomental (cm) minus thyromental (cm) | immediate | 
| Neck circumference measured in cm with a measuring tape | Measurement at the level of the cricoid cartilage while the patient's neck is in neutral position | immediate | 
| Ratio of neck circumference to thyromental distance | Calculated ratio of the neck circumference to the aforementioned thyromental distance | immediate | 
| Hyomental distance at full head extension (FHE) measured in cm with a measuring tape | The distance from the mentum to the hyoid bone while the patient's neck is fully extended and the mouth closed | immediate | 
| Hyomental distance at neutral position (NP) measured in cm with a measuring tape | The distance from the mentum to the hyoid bone while the patient's neck is in neutral position and the mouth closed | immediate | 
| Ratio of hyomental distance at FHE to hyomental distance at NP | Calculated ratio of the aforementioned variables | immediate | 
| Mallampati class | Classified as class I - soft palate, fauces, uvula, and pillars seen, class II - soft palate, fauces, and uvula seen, class III - soft palate and base of uvula seen and class IV - soft palate not visible. | immediate | 
| Mouth opening measured in cm with a measuring tape | The distance between the upper and lower incisors with the mouth fully open | immediate | 
| Upper lip bite test | Classified as class I - lower incisors can bite the upper lip above the vermilion line, class II - lower incisors can bite the upper lip below the vermilion line and class III - lower incisors cannot bite the upper lip. | immediate | 
| Head extension measured in degrees with goniometer | The patient was asked to hold head erect, facing directly to the front, then asked to extend the head maximally and the examiner estimated the angle traversed by the occlusal surface of upper teeth using a goniometer. | immediate | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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difficult laryngoscopy, neck circumference, sternomental distance, thyromental distance, hyomental distance, thyrosternal distance