Hypotension from spinal anesthesia in patients aged greater than 80 years is due to a decrease in systemic vascular resistance

Study ObjectivesTo determine the exact mechanism underlying spinal anesthesia-induced hypotension in the elderly patient.DesignRetrospective case-control study.SettingOperating room (OR) in a general hospital.MeasurementsRecords from 60 consecutive patients over 80 years of age, who underwent hip fracture repair (intramedullary nail or compression hip screw) during spinal anesthesia were studied. After injection of isobaric 0.5% bupivacaine in the L3-L4 intervertebral space in the lateral decubitus position, patients were turned supine. Acetate Ringer’s solution (300 mL) was infused over 30 minutes after subarachnoid puncture. A decrease in systolic arterial pressure to less than 100 mmHg was treated with an intravenous injection of 5 mg ephedrine. The hypotension group (n=18) comprised patients who required ephedrine during the 30 minutes after the puncture, and the nonhypotension group (n=42) consisted of patients who maintained stable arterial pressure with crystalloid infusion only.MeasurementsCardiac output (CO) and stroke volume variation (SVV) every 20 seconds using the Vigileo-FloTrac system continuously from arrival in the operating room (OR) to 30 minutes after the subarachnoid puncture were recorded. Serial changes in systemic vascular resistance (SVR), CO, and SVV from baseline after puncture were compared between the two groups.Main ResultsThe decrease in SVR over 20 minutes after the puncture was significantly greater in the hypotension group than the nonhypotension group (P = 0.047). Cardiac output was stable in the two groups. Stroke volume variation in the first 10 minutes after the puncture increased to similar levels in the two groups, then decreased gradually to baseline. No significant differences were noted in circulatory parameters on arrival at the OR.ConclusionsA decrease in SVR, not CO, is the main mechanism of hypotension seen during spinal anesthesia in elderly patients.