Comparing Two Different Norepinephrine Infusion Rates for Prophylaxis Against Spinal-induced Hypotension in Elderly

Overview

Hip surgery in the elderly is commonly performed under spinal anesthesia, which is associated with a lower risk of postoperative complications. However, this population is highly susceptible to postspinal hypotension-occurring in up to 69% of cases-which can compromise organ perfusion and increase the risk of organ failure and mortality. Vasodilation-induced hypotension is typically managed with vasopressors, and norepinephrine, with both α- and weak β-agonist activity, has recently been introduced as a prophylactic agent in this setting. Prior research demonstrated that a norepinephrine infusion at 0.1 mcg/kg/min effectively prevented hypotension in elderly patients undergoing hip arthroplasty, but only one dose was tested. Given findings from obstetric studies suggesting lower effective doses, the current study aims to determine whether a lower infusion rate (0.07 mcg/kg/min) is non-inferior to the higher dose in maintaining intraoperative blood pressure. Identifying the optimal dose is important for minimizing drug exposure while ensuring hemodynamic stability.

Baseline preoperative blood pressure will be recorded in the supine position as average of 3 reading with difference less than 5 mmHg in the mean arterial pressure. Inferior vena cava collapsibility will be used to assess the patient's intravascular volume status. After induction of spinal anesthesia, patients will receive the vasopressor infusion according to the previous randomization All drug preparations will be done by a research assistant who will be responsible for opening the envelope and group assignment with no further involvement in the study. Any episode of hypotension (defined as mean arterial pressure (MAP) \< 70% of the baseline or MAP\<65mmHg) will be managed by 5 mcg norepinephrine. If bradycardia (defined as heart rate less than 50 bpm) with hypotension occurred, it will be manged with 9 mg ephedrine. If bradycardia occurred with hypertension (MAP increase 20% over the baseline) and persisted for more than one reading, the vasopressor infusion will be stopped. If hypertension occurred (defined as increased mean arterial pressure by \> 20% of the baseline reading), vasopressor infusion will be decreased by 50%. If hypertension persisted 2 minutes after reduction of the infusion, the vasopressor infusion will be stopped. The vasopressor will be returned to 50% of the starting dose if there was further decline in blood pressure. The infusion will continue for 45 minutes after spinal anesthesia.