Infraclavicular brachial plexus block in hand and forearm surgery has the advantages of high success rate and low risk of complications and is useful in providing long-lasting and effective postoperative analgesia in these patients. In response to hypoxemia at high altitude, increased blood viscosity, decreased carbon monoxide diffusion capacity, increased cerebral arterial blood flow, decreased blood volume and decreased cardiac output occur. At high altitude, the serum level of local anesthetics may increase due to an increase in their ionized fraction and a decrease in their clearance. In this respect, the pharmacodynamic and pharmacokinetic properties of peripheral nerve blocks may be altered when performed at high altitude. The primary objective of this prospective study was to test the hypothesis that postoperative pain scores are higher in patients undergoing infraclavicular nerve block at high altitude than in patients at low altitude.

This multicenter prospective randomized study will be initiated after approval of the Ethics Committee of Health ScienceUniversity Diyarbakir Gazi Yasargil Training and Research Hospital. Patients will be recruited simultaneously in 3 hospitals, Hatay Training and Research Hospital, Hatay, Turkey (100 m above sea level);Health Science Health Science University Diyarbakir Gazi Yasargil Training and Research Hospital, Diyarbakir, Turkey (675 m above sea level) and Health Science University Van Regional and Training Research Hospital, Van, Turkey (1726 m above sea level).

Infraclavicular brachial plexus blocks (coracoid approach) will be performed by administering a local anesthetic mixture of 1.5 mg/kg lidocaine 2% + 1 mg/kg bupivacaine 0.5% at the 6 o'clock position of the axillary artery under US guidance.

Group V (1726 meter altitude): In the application of infraclavicular brachial plexus blocks (coracoid approach); 1.5mg/kg dose of bupivacaine and 1mg/kg lidocaine mixture will be applied around the axillary artery in the 6 o'clock position under US guidance.

• The block will be applied only once, approximately 15-20 minutes before surgery.
• All patients will undergo electrocardiographic monitoring, oxygen saturation monitoring with pulse oximetry and blood pressure measurement with automatic pneumatic manometer before the application.
• Intravenous 1mg midazolam and 50 mcg fentanyl will be administered to all patients for premedication before the procedure.
• The amount of medication to be given to all patients will be prepared as 1.5mg/kg bupivacaine and 1mg/kg lidocaine.
• The prepared drug will be administered around the axillary artery at the appropriate anatomical location determined under ultrasound guidance.
• Ultrasound device will be used as a supportive device during the application.
• The application will be performed by an anesthesiologist with at least 5 years of experience.
• mode of delivery will be provided face to face and individually
• The administration will be only once, 20-30 minutes before the surgical procedure, with a dose adjustment of 1.5mg/kg bupivacaine and 1mg/kg lidocaine per kilogram of weight.
• The application will be made in the preoperative preparation room in the operating room of the hospital where the surgery will be performed.
• The local anesthetic dose to be used in the application will be calculated according to the weight of the patient. local anesthetics will be prepared by another anesthesiologist in the preoperative preparation room just before the application.
• In the postoperative period, if the pain intensity (VAS) is <4, 100 mg paracetamol will be administered intravenously, if VAS = 4, 100 mg tramadol will be administered intravenously

Group D (675 meter altitude): In the application of infraclavicular brachial plexus blocks (coracoid approach); 1.5 mg/kg dose of bupivacaine and 1mg/kg lidocaine mixture will be applied around the axillary artery in the 6 o'clock position under US guidance.

• The block will be applied only once, approximately 15-20 minutes before surgery.
• All patients will undergo electrocardiographic monitoring, oxygen saturation monitoring with pulse oximetry and blood pressure measurement with automatic pneumatic manometer before the application.
• Intravenous 1mg midazolam and 50 mcg fentanyl will be administered to all patients for premedication before the procedure.
• The amount of medication to be given to all patients will be prepared as 1.5 mg/kg bupivacaine and 1mg/kg lidocaine.
• The prepared drug will be administered around the axillary artery at the appropriate anatomical location determined under ultrasound guidance.
• Ultrasound device will be used as a supportive device during the application.
• The application will be performed by an anesthesiologist with at least 5 years of experience.
• mode of delivery will be provided face to face and individually
• The administration will be only once, 20-30 minutes before the surgical procedure, with a dose adjustment of 1.5 mg/kg bupivacaine and 1mg/kg lidocaine per kilogram of weight.
• The application will be made in the preoperative preparation room in the operating room of the hospital where the surgery will be performed.
• The local anesthetic dose to be used in the application will be calculated according to the weight of the patient. local anesthetics will be prepared by another anesthesiologist in the preoperative preparation room just before the application.
• In the postoperative period, if the pain intensity (VAS) is <4, 100 mg paracetamol will be administered intravenously, if VAS = 4, 100 mg tramadol will be administered intravenously

Comparator / control treatment Group H (100 meter altitude): In the application of infraclavicular brachial plexus blocks (coracoid approach); 1.5 mg/kg dose of bupivacaine and 1mg/kg lidocaine mixture will be applied around the axillary artery in the 6 o'clock position under US guidance.

• The block will be applied only once, approximately 15-20 minutes before surgery.
• All patients will undergo electrocardiographic monitoring, oxygen saturation monitoring with pulse oximetry and blood pressure measurement with automatic pneumatic manometer before the application.
• Intravenous 1mg midazolam and 50 mcg fentanyl will be administered to all patients for premedication before the procedure.
• The amount of medication to be given to all patients will be prepared as 1.5 mg/kg bupivacaine and 1 mg/kg lidocaine.
• The prepared drug will be administered around the axillary artery at the appropriate anatomical location determined under ultrasound guidance.
• Ultrasound device will be used as a supportive device during the application.
• The application will be performed by an anesthesiologist with at least 5 years of experience.
• mode of delivery will be provided face to face and individually
• The administration will be only once, 20-30 minutes before the surgical procedure, with a dose adjustment of 1.5 mg/kg bupivacaine and 1mg/kg lidocaine per kilogram of weight.
• The application will be made in the preoperative preparation room in the operating room of the hospital where the surgery will be performed.
• The local anesthetic dose to be used in the application will be calculated according to the weight of the patient. local anesthetics will be prepared by another anesthesiologist in the preoperative preparation room just before the application.
• In the postoperative period, if the pain intensity (VAS) is <4, 100 mg paracetamol will be administered intravenously, if VAS = 4, 100 mg tramadol will be administered intravenously

Inclusion Criteria:

• Between 18-55 years old
• Body mass index between 20 and 25
• Patients with American Society of Anesthesiologists classification (ASA) physical status I or II

Exclusion Criteria:

• Patients aged younger than 18 and older than 55 years
• American Society of Anesthesiologists classification (ASA) ≥ III
• Body mass index (BMI) >35
• Known history of allergy to local anesthetics preoperative chronic pain and therefore long-term analgesic use
• In case of coagulopathy
• Have a condition that constitutes a contraindication for the application of the block (local infection, sepsis, local anesthetic medicine allergy; severe neurological, muscular or psychiatric disease, coagulation disorders)
• With marked cognitive impairment
• Patients who did not want to participate in the study.