Anesthesia Drug Response Index in Obese Patients Using Perfusion Index + BIS: A Novel Composite Model

Abstract

Background: Obese patients undergoing general anesthesia are vulnerable to post-induction hypotension because obesity alters anesthetic drug distribution, autonomic tone, vascular reserve, and cardiopulmonary compensation. Bispectral index (BIS) and perfusion index (PI) are usually interpreted separately, although induction response involves simultaneous hypnotic, vascular, and hemodynamic changes. Objective: To determine whether peri-induction changes in BIS and PI, individually and as part of a composite Anesthesia Drug Response Index (ADRI), are associated with post-induction hypotension in obese adults undergoing elective surgery under general anesthesia. Methods: This prospective cohort study included 128 obese adult patients with BMI ≥30 kg/m². BIS, PI, MAP, and heart rate were recorded at baseline and during the first ten minutes after induction. Post-induction hypotension was defined as MAP reduction ≥20% from baseline, MAP <65 mmHg, or vasopressor requirement. Predictive performance of BIS fall, PI rise, baseline PI, and ADRI was evaluated using ROC analysis. Results: Post-induction hypotension occurred in 39 patients (30.5%). Hypotensive patients had higher BMI, more ASA III status, more hypertension, lower baseline MAP, and higher baseline PI. ADRI showed the strongest internal discrimination, with sensitivity 84.6%, specificity 80.9%, and AUC 0.86 at a cut-off score ≥7. Conclusion: Combined BIS and PI response assessment may improve early peri-induction risk classification in obese surgical patients. ADRI demonstrated promising internal discrimination but requires external validation before clinical implementation.