Airway management is extremely important for providing safe anesthesia. Endotracheal intubation, on the other hand, is the most important step in airway management, especially since it requires rapid and successful execution. Inadequate airway management; is associated with complications that require high-level care and cost, such as death, brain damage, increased need for intensive care, prolonged recovery period, and emergency tracheostomy. 15-25% of anesthesia-related deaths are associated with airway management. 17% of settled cases against anesthesiologists are composed of airway-related events (often difficult intubation, inadequate oxygenation/ventilation, and pulmonary aspiration).

An important point in ensuring airway patency is preoperative evaluation. Difficulties arising from anatomical features can be revealed by careful evaluation of mouth opening, the structure of tongue and palate, thyromental distance (TMM), sternomental distance (SMM), mobility of cervical vertebrae, jaw occlusion, and necessary precautions can be taken.

The most commonly used tests to determine the degree of difficulty of intubation are the modified Mallampati test, the thyromental distance, the upper lip bite test, the inter incisor space, and the sternomental distance. Recent studies are trying to confirm the sensitivity and specificity of existing tests. However, there is no test with 100% specificity and sensitivity in predicting difficult laryngoscopy and intubation.

In this prospective observational study, two new parameters "mandibular profile angle" and "mandibular mental angle" will be evaluated with the Cormack-Lehane Score during laryngoscopy as a predictor of difficult laryngoscopy. Modified Mallampati test, neck circumference, thyromental distance, sternomental distance, and many other tests have been used for predicting difficult intubation however, none of them are able to predict "difficult intubation" exactly. "mandibular profile angle" and "mandibular mental angle" may provide new horizons for predicting difficult intubation. These two measurements will be compared with the Cormack-Lehane score during laryngoscopy for sensitivity, specificity, and positive or negative predictive values. As well as the Cormack-Lehane Score, we will be comparing these angle measurements' predictive values with the other specified predictive tests such as Modified Mallampati test, neck circumference, thyromental distance, sternomental distance.

Having received informed consent, 1000 ASA I-III patients aged between 18-80, who will be operated under general anesthesia, will be included in this prospective observational study. The number of patients is determined according to the numbers in previous studies, but will be finalized as 90% power and 5% error as a result of the power analysis after the prior study.

Before the anesthesia induction the Modified Mallampati test, neck circumference, thyromental distance, sternomental distance will be measured as well as "mandibular profile angle" and "mandibular mental angle". "Mandibular profile angle" is defined as; The angle between the mentum of the mandibula and the lateral tips of the mandibula where the profiler ends. "Mandibular mental angle" is defined as; the angle between the mentum of the mandibula and the two ends of the mandibular arch.

After induction of anesthesia, the difficulty of laryngoscopy will be determined by Cormack-Lehane Score by a senior anesthesiologist.

Having received the measurements, tests for sensitivity and specificity, and negative/positive predictive values for difficult intubation will be processed.

Inclusion Criteria:

• General Anesthesia
• ASA I,II,III

Exclusion Criteria:

• Patients with upper respiratory tract tumors
• history of surgery, burns and trauma to the upper respiratory tract
• congenital head-neck anomaly,
• giant goiter, and
• pregnancy

All patients who will operated under general anesthesia by endotracheal intubation

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