Phenylephrine versus Norepinephrine Infusion in the Prevention of Spinal Anesthesia-Associated Hypotension during Total Knee Replacement Procedures: A Randomized Controlled Trial

Background: Spinal anesthesia (SA), commonly used in total knee replacement (TKR), is frequently associated with spinal anesthesia-induced hypotension (SAIH). Vasopressors such as phenylephrine (PE) and norepinephrine (NE) are administered to manage this effect. This trial aimed to compare PE and NE infusions for preventing SAIH during TKR, assessing cardiovascular stability and adverse outcomes.Methods: This randomized, double-blind controlled trial included 135 patients aged 50–75 years undergoing elective TKR under SA. They were assigned into three equal groups: the PE Group received 0.1 μg/kg/min PE, Group NE received 0.05μg/kg/min NE, and C (control group) received 0.9% saline (0.01mL/kg/min). The primary outcome was the incidence of SAIH, while secondary outcomes included hemodynamic parameters and adverse events. Results: The incidence of hypotension was significantly lower in both vasopressor groups (PE: 6.67%; NE: 8.89%) versus control (51.11%, P<0.001), with similar rates between the NE and the PE (P=1). NE maintained intermediate heart rate (HR) values between PE and control throughout surgery (P<0.05). NE produced superior hemodynamic stability, with significantly higher blood pressures than both PE and control (5-95 min) and greater mean arterial pressure (MAP) than control (5-115 min) and PE (5-85 min). NE also demonstrated better cardiac performance, with consistently higher stroke volume (SV), cardiac output (CO) than PE, while PE showed reduced SV (20-100 min) and CO (10-120 min) versus control (P<0.05). Adverse event incidences were similar across groups.Conclusions: Both phenylephrine and norepinephrine effectively prevent spinal anesthesia-hypotension during TKR. Norepinephrine offers greater cardiovascular stability without increasing adverse events.