Arterial Stiffness and General Anesthesia Induced Hypotension in Patients on Angiotensin-converting Enzyme Inhibitors

Induction of general anesthesia to the patient could be a challenging period of anesthesia management. Due to autonomic system suppression, hemodynamic fluctuation, such as hypotension or hypertension, is commonly seen during this period. Furthermore, it has been observed that a fraction of patients who develop hypotension may be refractory to vasoactive medications to attempt to restore the systemic arterial blood pressure back to an acceptable level. Previous studies have shown that patients chronically taking angiotensin converting enzyme (ACE) inhibitors have a higher incidence of developing hypotension under general anesthesia as well as being refractory to adrenergic vasoconstrictor medications given to help restore systemic blood pressure. Interestingly, not all patients taking ACE inhibitors have shown the described hemodynamic response after induction of general anesthesia. Therefore, investigators are attempting to identify what changes in vascular physiology in those patients may contribute to acute refractory systemic hypotension. Specifically, investigators wish to explore whether differences in baseline levels of arterial stiffness potentially contribute to this phenomenon. Arterial applanation tonometry is a non-invasive technique that has been shown to reliably provide indices of arterial stiffness. In the proposed project, applanation tonometry will be performed on the right carotid and femoral arteries to assess carotid-femoral pulse wave velocity, a surrogate for aortic stiffness. (SphygmoCor system, AtCor Medical, Sydney, Australia) The measurement will be obtained before induction of general anesthesia in the pre-surgical area. During induction of general anesthesia with standard induction agents, brachial blood pressure will be measured by a cuff every minute up to 10 minutes after tracheal intubation. A hypotensive response to anesthesia will be defined by a systolic arterial blood pressure below 90mmHg upon induction. Hypotensive patients th