The goal of this observational study is to evaluate the relationship between preoperative cardiopulmonary performance indicators and preoxygenation efficiency along with oxygen reserve depletion in patients scheduled for elective surgery under general anesthesia. The main questions it aims to answer are:

What is the relationship between Hand Grip Strength (HGS) and the time taken for end-tidal oxygen (EtO_2) to reach 90% during preoxygenation? What is the relationship between the 6-Minute Walk Test (6MWT) distance and the Oxygen Reserve Index (ORI) depletion time during the apnea period?

Participants will be asked to perform the following tasks during their preoperative and intraoperative care:

Complete a 6-Minute Walk Test (6MWT) to determine preoperative functional capacity.

Perform a Hand Grip Strength (HGS) test using a calibrated hand dynamometer to measure muscle strength.

Undergo standardized preoxygenation with 100% oxygen via a tight-fitting face mask in the operating room while end-tidal oxygen (EtO_2) and Oxygen Reserve Index (ORI) levels are continuously monitored.

Inclusion Criteria:

Patients aged >18 years ASA physical status I-III Scheduled for elective surgery under general anesthesia Voluntary written informed consent to participate in the study

Exclusion Criteria:

Severe COPD (Chronic Obstructive Pulmonary Disease) or restrictive lung disease NYHA Class III-IV Heart Failure Neuromuscular diseases Upper extremity pathologies affecting hand function (preventing HGS measurement) Orthopedic or neurological conditions preventing the 6-minute walk test (6MWT) Emergency surgeries

Patients scheduled for elective surgery at Ankara Bilkent City Hospital, Department of Anesthesiology and Reanimation, who will undergo preoxygenation before anesthesia induction.