Effect of Intravenous Ondansetron on Hemodynamics after Spinal Anesthesia in Patients undergoing Total Knee Replacement

Abstract

Hypotension following spinal anesthesia is a common physiological complication. It was defined as a decrease of mean arterial blood pressure of more than 20%. Among the mechanisms causing hypotension during spinal anesthesia is sympatholysis inducing a decrease in systemic vascular resistance as well as the Bezold-Jarisch reflex. The latter becomes activated by decreased venous return to the right heart, triggering receptors in the cardiac wall, leading to vasodilation, bradycardia and hypotension. Among the receptors involved are chemoreceptors responding to 5-hydroxytryptamine3 (5-HT3, serotonin). Nausea and vomiting are well recognized complications of spinal anaesthesia and are seen more commonly when the sympathetic blockade extends to above the tenth thoracic segment. The causes of this unpleasant complication include reduction in cerebral blood Row due to arterial hypotension, increased gastrointestinal peristalsis due to preganglionic sympathetic blockade. Shivering is involuntary, oscillatory muscular activity, it is a physiological thermoregulatory response to cold. Under spinal anaesthesia, shivering occurs as a response to lowering of core body temperature and decrease in blood supply to the upper body.