Ultrasound has become an essential tool for the daily work of any doctor, but in certain specialties such as Anaesthesiology, its use has greatly increased the safety offered to patients throughout the perioperative period, either to perform nerve blocks, for vascular access, intraoperative hemodynamic management or any other use that allows increasing quality of care.

The management of the upper airway and the diagnosis of pathological conditions are essential skills for any doctor especially for Anaesthesiologist, ER physician, or Intensive Care physician. Because an inadequate airway management continues to be an important contributor to patient mortality and morbidity, any tool that can improve it should be considered as an addition to conventional clinical evaluation.

Unfortunately, most of the clinical parameters that should allow us to assess a potential difficult airway, do not always lead us to an adequate prediction, that is why US(Ultrasound) is use as an emerging tool in many fields, is also gathering strength in this search for a definitive predictor parameter.

Ultrasound has many obvious advantages (safe,fast, repeatable, portable, widely available and gives dynamic images in real time).

Sonographic studies are operator-dependent and although the identification of basic structures could be acquired with only a few hours of training, but more complex studies require a learning curve of months or even years. The high frequency linear probe (5-14 MHz) is probably the most suitable for the airway because images are of superficial structures (within 0-5 cm below the skin surface).

The growing academic interest in the use of US to look for predictors of difficult airway is centred mainly on measurements at the level of pretracheal tissues.

But the greatest limitation of these studies is the disparity of the fat distribution that exists between different ethnic groups and and sexes, and the lack of standardization method in patient´s intubation conditions.

So, the investigator propose to assess different ultrasound windows at the level of pretracheal tissues such as independent predictors of Difficult Airway.

Inclusion Criteria:

• Patients (male or female) ASA I-III, aged between 18 and 90 years, undergoing scheduled surgery requiring orotracheal intubation. The signature of the informed consent is required authorizing its inclusion in the study.

Exclusion Criteria:

• Obesity class II defined as a BMI greater than 35.
• Pregnant.
• Cervical tumors, goiter or patients who have required radiotherapy at the cervical level
• Abnormalities that condition anatomy alterations such as facial / cervical fractures.
• Maxillofacial abnormalities
• People who cannot give their consent.

Patients undergoing scheduled surgery requiring orotracheal intubation.