The Effect of Anthropometric Measurements on Block Success, Performance Time , and Ultrasound Visibility Score.

Anthropometric measurements will be performed using a standard tape measure while the patient is in the supine position with the neck in a neutral and fully extended position. Neck circumference measured at the level of the cricoid cartilage, sternomental distance (the distance between the manubrium sterni and the mentum), and thyromental distance (the distance between the thyroid cartilage and the mentum) will be measured and recorded. Additionally, the ratio of neck circumference to thyromental distance will be calculated and added to the data.

Block Performance and Technical Data Observational data will be collected while the interscalene nerve block, which is routinely performed for upper extremity surgeries at our center, is administered under standard conditions. The moment the ultrasound probe touches the skin will be defined as the "block onset time," and the moment the block needle is withdrawn from the skin will be defined as the "block completion time." The difference between these two time points will be recorded as the "total performance time." If the number of needle insertions into the skin (number of punctures) is more than one, it will be specified. Under ultrasound guidance, brachial plexus depth (the distance between the skin and the C5 spinal nerve root, in cm) will be measured. The active ingredient and volume (mL) of the administered local anesthetic drug will be recorded in the data form.

Image Quality and Clinical Evaluation Ultrasound screen images obtained during the procedure will later be shown to 5 anesthesiology and reanimation specialists specified in the study plan, and they will be scored between 1 and 5 in terms of the clarity of anatomical structures.

At 5, 10, and 20 minutes following the block performance:

Sensory Block: evaluated in the C5 and C6 dermatome areas, Motor Block: evaluated via elbow flexion, Vital Signs: SpO\_2 measured by peripheral pulse oximetry and heart rate (beats/minute) values will be monitored and recorded.

Success Criteria and Follow-up At the end of the 20th minute, block success will be evaluated by assessing whether the level of anesthesia required for surgery has been achieved. In cases where the block is insufficient, fails, or conversion to general anesthesia is required for any other reason, the reasons will be noted in detail.

Potential side effects and complications that may develop after the procedure (e.g., Horner's syndrome, hoarseness, dyspnea, vascular puncture, local anesthetic systemic toxicity \[LAST\]) will be monitored up to the 6th postoperative hour. In addition, the study will be completed by recording the total narcotic analgesic consumption in the first 24 hours, the patient satisfaction score at the 6th postoperative hour (scored from 0 to 10), and the Visual Analog Scale (VAS) score (scored from 0 to 10).

The obtained data will be analyzed using the SPSS software with appropriate statistical methods (correlation analysis, regression, etc.) to determine the relationship between anthropometric measurements, duration, and success.