This prospective observational study aims to evaluate whether non-invasive hemodynamic parameters, including the plethysmographic variability index (PVI) and perfusion index (PI), can predict post-induction hypotension in patients undergoing diagnostic direct laryngoscopy under general anesthesia. Patients aged 18-75 years with ASA physical status I-III scheduled for elective direct laryngoscopy will be included. PVI and PI values will be recorded before anesthesia induction and in the early post-induction period. The relationship between these indices and the decrease in mean arterial pressure after induction will be analyzed to determine their predictive value for hypotension.

Post-induction hypotension is a common hemodynamic complication during the early phase of general anesthesia and may lead to adverse perioperative outcomes, particularly in patients with limited physiological reserve. Early identification of patients at risk for hypotension may allow clinicians to implement preventive strategies and optimize perioperative hemodynamic management. Recently, non-invasive perfusion-related parameters derived from pulse oximetry have gained attention as potential indicators of intravascular volume status and cardiovascular responsiveness.

The plethysmographic variability index (PVI) is a dynamic parameter reflecting respiratory variations in the perfusion index and is considered a non-invasive surrogate marker of fluid responsiveness. The perfusion index (PI), which represents the ratio of pulsatile to non-pulsatile blood flow in peripheral tissues, provides information about peripheral perfusion and vascular tone. These indices are continuously and non-invasively obtained using pulse oximetry and may offer clinically useful information regarding hemodynamic status during anesthesia induction.

Direct laryngoscopy performed under general anesthesia may be associated with significant hemodynamic fluctuations during both the induction phase and airway manipulation. Identifying reliable non-invasive predictors of blood pressure reduction during this period may improve intraoperative monitoring and facilitate early intervention.

Inclusion Criteria:

• Scheduled to undergo elective direct laryngoscopy under general anesthesia Body mass index (BMI) between 18 and 40 kg/m² ASA physical status classification I-III Provision of written informed consent after being informed about the study

Exclusion Criteria:

• Severe arrhythmias Advanced heart failure Severe valvular heart disease Preoperative shock or hemodynamic instability requirement for continuous vasopressor or inotropic infusion Significant peripheral vascular disease affecting peripheral circulation

The study population will consist of adult patients aged 18-75 years with ASA physical status I-III who are scheduled to undergo elective diagnostic direct laryngoscopy under general anesthesia at the Department of Anesthesiology and Reanimation and the Department of Otorhinolaryngology of Gaziantep University Faculty of Medicine Hospital. Patients meeting the eligibility criteria and providing written informed consent will be consecutively enrolled. The study will include patients undergoing routine perioperative monitoring, and non-invasive hemodynamic parameters such as plethysmographic variability index (PVI) and perfusion index (PI) will be recorded during the peri-induction period.