Is Permissive Hypotension Truly Harmless? Early Biomarker Evidence of Subclinical Kidney Injury in Rhinologic Surgery

This study aims to investigate the effects of permissive hypotension, which is routinely used in rhinologic surgeries such as rhinoplasty, septoplasty, and functional endoscopic sinus surgery (FESS), on renal function. Although permissive hypotension has been widely practiced to improve surgical field visibility and reduce intraoperative blood loss, its specific definition is not standardized in the literature. In most studies, maintaining mean arterial pressure (MAP) within the range of 50-65 mmHg is considered permissive hypotension. MAP values below 60 mmHg have been associated with increased risk of cardiac and renal complications. However, in otherwise healthy patients, such episodes are frequently tolerated without clinically apparent renal dysfunction. The kidneys have a strong compensatory reserve capacity, and early tubular injury may not be detected by conventional renal function tests such as serum creatinine. Therefore, the use of more sensitive biomarkers is necessary to detect potential subclinical injury. In this prospective observational study, serum NGAL and cystatin C levels will be measured from routine preoperative and postoperative (12-24 hours) blood samples obtained from adult patients undergoing rhinologic procedures. A ≥25% increase in these biomarkers from baseline will be considered indicative of subclinical acute kidney injury. Additionally, intraoperative hemodynamic data will be monitored, and the duration of MAP \

Inclusion Criteria: * Adults aged 18-65 years * Scheduled for elective rhinologic surgery (rhinoplasty, septoplasty, or functional endoscopic sinus surgery) * ASA physical status I-II * Able to provide written informed consent * Undergoing controlled hypotension anesthesia as part of routine clinical management Exclusion Criteria: * Known chronic kidney disease (baseline creatinine above normal range or documented CKD) * Uncontrolled hypertension or uncontrolled diabetes mellitus * Contraindications to controlled hypotensive anesthesia * Pregnant or breastfeeding women * History of major cardiovascular disease affecting renal perfusion (e.g., severe heart failure) * Use of nephrotoxic medications preoperatively that may interfere with renal biomarker interpretation * Perioperative complications requiring deviation from routine anesthetic management (e.g., major bleeding or hemodynamic instability)