Postoperative hypotension in the post-anesthesia care unit (PACU) is common and linked to adverse outcomes. The Hypotension Prediction Index (HPI) predicts hypotensive events intraoperatively, but its PACU application is unexplored. This study aims to investigate the effectiveness of HPI-guided monitoring in preventing PACU hypotension.

Study Design This prospective, randomized, controlled, single-center trial will be conducted in the PACU of a tertiary care hospital. The study aims to evaluate the effectiveness of HPI in preventing postoperative hypotension. All procedures follow institutional protocols, and the trial is designed to reduce bias through randomization and stratification.

Study Population Eligible patients are adults (≥ 19 years) undergoing elective surgery under general anesthesia, with arterial catheters in place and an expected PACU stay of ≥ 30 minutes. Exclusion criteria include immediate postoperative ICU admission, use of vasopressors during anesthesia emergence, ASA physical status V, or contraindications to arterial monitoring. These criteria ensure a focus on patients suitable for PACU monitoring with arterial lines. The study population is representative of high-risk surgical patients requiring advanced hemodynamic monitoring.

Intervention Patients will be randomized 1:1 to the HPI group, which receives continuous HPI monitoring (Edwards Lifesciences HemoSphere platform, Irvine, CA, USA) with interventions such as fluid boluses or vasopressors if HPI is ≥ 85 per protocol, or to the control group, which receives standard PACU monitoring including non-invasive blood pressure, heart rate, and oxygen saturation. The interventions in the HPI group follow institutional guidelines to ensure consistency, while the control group receives routine PACU monitoring practices. Randomization will be used in a computer-generated sequence, stratified by ASA class (I-II vs. III-IV) to balance risk profiles.

Outcomes The primary outcome is the incidence of hypotension (mean arterial pressure [MAP] < 65 mmHg for more than 1 minute) during the PACU stay. Secondary outcomes include time to the first hypotensive episode, total duration of hypotension, vasopressor and fluid administration (frequency and dose), PACU stay duration, and postoperative complications such as nausea and acute kidney injury. Acute kidney injury (AKI) in the PACU was defined using the Kidney Disease: Improving Global Outcomes (KDIGO) criteria, specifically as an increase in serum creatinine by ≥ 0.3 mg/dL within 48 hours of surgery or an increase to ≥1.5 times baseline within 7 days, assess via blood samples collect during or immediately after the PACU stay. Urine output criteria are not used due to the short PACU duration and inconsistent catheterization. These outcomes are selected to evaluate both the effectiveness and impact of the HPI on clinical management. Complications are monitored to assess safety and secondary effects.

Inclusion Criteria:

• Age ≥ 19 years
• Undergoing elective surgery under general anesthesia
• Presence of intra-arterial catheter at the end of surgery
• Expected PACU stay of ≥ 30 minutes
• Provided written informed consent

Exclusion Criteria:

• Immediate postoperative ICU admission
• Use of vasopressors during emergence from anesthesia
• ASA physical status classification of V
• Known contraindications to arterial line placement
• Participation in another interventional study within 30 days

No masking; open-label study due to the nature of real-time hemodynamic monitoring intervention.