Prospective Observational Study to Compare Hemodynamic Alterations in Severe Aortic Stenosis and Severe Mitral Regurgitation After High Spinal Anesthesia in Patients Undergoing Aortic Valve and Mitral Valve Replacement Surgery

Spinal anesthesia (SA) involves injecting local anesthetic into the intrathecal space. Since it was first described, understanding of the physiology and pharmacology of drugs acting within the subarachnoid space has improved. Physiological changes observed following SA are believed to be attributed to their blockade of peripheral and cardiac sympathetic fibers. The changes in cardiac output (CO) observed following SA were originally thought to be explained by the 'pre-load reduction' theory that describes a decrease in CO resulting from reduced venous return leading to arterial hypotension. However, this theory was questioned due to failed attempts to avoid SA induced hypotension by three preventative techniques: preloading with crystalloids or colloids, lower limb compression, and lateral tilt maneuvers (1). Additional studies and subsequent data led to further questioning of the pre-load reduction theory and supported a shift to an 'after-load reduction' theory. This proposes that hypotension following SA is a result of sympathetic blockade causing arterial dilatation (1,2). With this knowledge, it has traditionally been taught to avoid SA in severe aortic stenosis (AS) for risk of decreased coronary perfusion, while SA has been considered safe, or even beneficial in those with severe mitral regurgitation (MR). However, there is a paucity of real time evidence to help support these claims. Furthermore, individuals with experience in performing SA in patients with severe AS and/or MR have questioned the hemodynamic effects that are traditionally described (3).

With advancements in echocardiographic techniques, point of care ultrasound has emerged in critical care to become the standard for evaluating hemodynamic changes observed in hemodynamic instability or cardiovascular collapse (4). This provides an opportunity to assess CO, and its associated parameters including venous return, preload, afterload, and contractility, in real time. With this tool, one can compare the hemodynamic changes in patients with AS or MR before and after high SA given for their cardiac surgery for valve replacements or repair (AVR or MVR).

Hypothesis and Study Objectives:

This study may provide real time information to support or challenge traditional understanding of the hemodynamic changes seen following SA in those with severe AS or severe MR. Since, hemodynamic stability is goal in all patients after any type of anesthesia, the primary objective is to compare requirement of vasopressors, inotropes, and inodilators required to maintain desired hemodynamic goals (Mean arterial pressure 65-100 mmHg and HR 50-100/min) and to observe and compare hemodynamics alteration by using echocardiographic parameters of venous return, cardiac index (CI), preload, afterload, and cardiac contractility using myocardial performance index (Tei index) (5) before and after high SA in patients having predominant severe AS or MR. Furthermore, subgroup analysis will be conducted to compare hemodynamic parameters and medication requirements to meet target hemodynamic goals among patients with preserved and reduced left ventricular systolic function (for AS reduced LVEF < 50 %, for MR reduced LVEF < 60%).

Methodology: