This prospective, randomized controlled clinical trial aims to evaluate the effect of lateral neck cold application for vagal nerve stimulation on pain perception during peripheral venous cannulation in obese patients. Venous cannulation is a routine but painful procedure, especially in individuals with a body mass index (BMI) greater than 30, who often have heightened pain sensitivity due to chronic inflammation.

Participants will be randomly assigned to one of two groups:

Group 1 (Cold Application Group): A cold marble stone (0-4°C) will be applied to the lateral neck region (over the sternocleidomastoid muscle) for 5 seconds immediately before venous cannulation.

Group 2 (Control Group): Standard venous cannulation will be performed without any prior intervention.

Pain intensity will be assessed using the Visual Analog Scale (VAS) immediately after cannulation. Hemodynamic parameters (heart rate, blood pressure, oxygen saturation, respiratory rate) will be recorded before and after the procedure.

The primary outcome is the difference in VAS scores between the two groups. Secondary outcomes include changes in hemodynamic parameters. The study will enroll 150 participants over approximately two months following ethics approval.

Inclusion Criteria:

• Adults aged 18-72 years
• physical status I-III
• Scheduled for elective surgery
• Body Mass Index (BMI) > 30 kg/m²
• Provided written informed consent

Exclusion Criteria:

• Emergency surgical cases
• Oncologic surgery
• Pregnant patients
• History of hand dorsum surgery or scarring
• Psoriasis or other local skin lesions/infections at cannulation site
• Peripheral vascular disease
• Chronic analgesic, opioid, steroid, or gabapentinoid use
• Substance abuse history
• Peripheral neuropathy
• Previous or ongoing oncologic treatment
• Severe mental retardation or communication impairment preventing cooperation