This study will aim to test the accuracy of the ultrasonography measurement of the epiphyseal diameter of the distal radius in the prediction of the size of the cuffed and uncuffed ETT that best fits in children (1-6 years old) in comparison with the traditional age-based formulas.

Various formulas are used to predict the inner diameter (ID) of the ETT tube whether uncuffed or cuffed based on weight, age, height, and finger size. The accuracy of these formulas is questionable. These formulas depend on the child's demographic characteristics assuming that he/she has normal growth and development and cannot be applied to children with altered growth and development. Moreover, these formulas predict the ID of the ETT ignoring the tube thickness and the OD of the selected tube.

ultrasound has recently been identified as an accurate alternative to these formulas. The US-measured epiphyseal diameter of the distal radius is a method that has been recently introduced as a surrogate for the tracheal diameter. The issue is that the size of the airway can be considered a reflection of the body's growth, assuming that the growth rates of the cartilage all over the body are closely related to each other. Therefore, the measurement of the growth of the bony cartilage of the hand can be considered a surrogate marker of the tracheal diameter.9 The extent to which ultrasonography by this method can succeed in predicting the optimal pediatric ETT size remains under investigation.

Inclusion Criteria:

• Weight: 10-30 kg.
• Age: 1-6 years.
• Sex: both males and females.
• ASA physical status: I-II.
• Operation: elective surgery in which airway management with an endotracheal tube is needed.

Exclusion Criteria:

• Upper airway malformations.
• Upper airway surgery.
• Active respiratory illness (cough, fever, rhinorrhea) on the day of anesthesia,
• Anticipated difficult airway.

Children aged 1-6 years of both sexes undergoing surgical procedures in which an endotracheal tube is needed.