Arterial Stiffness as a Predictor of Refractory Hypotension After Induction of General Anesthesia in Patients Chronically Treated With Angiotensin-converting Enzyme Inhibitors

Background: Induction of anesthesia consists with administration of anesthetics followed by endotracheal intubation. During the induction of anesthesia moderate hemodynamic disturbances (either systemic arterial hyper- or hypo-tension) are common due to concurrent autonomic nervous system suppression and from the stress response from endotracheal intubation. Previous studies demonstrate that patients chronically treated with angiotensin converting enzyme (ACE)-inhibitors have higher incidence of developing hypotension after induction of general anesthesia, which typically, can be restored with small doses of adrenergic drugs such as phenylephrine (100 to 200 mcg) to acceptable blood pressure levels. However, some patients that develop hypotension may be refractory to those medications, which in turn poses a significant challenge in controlling the hemodynamics of patients. The consequence of the severe hypotension could be canceled surgery, ischemic stroke, myocardial infarction or even death.

Interestingly, this refractory systemic hypotension does not occur in all anesthetized patients prescribed ACE inhibitors. Notably, easily treatable systemic arterial hypotension after induction of general anesthesia is not a clinical problem. Critical issue arises only if the patient under general anesthesia does not respond to therapeutic doses of adrenergic agonists. Therefore, identifying patients who will demonstrate refractory hypotension after the induction of general anesthesia is a novel idea and has significant clinical implications for peri-operative blood pressure control by anesthesiologists.

Thus, the overall goals of the proposed research will be to use preoperative non-invasive measures of vascular stiffness to predict which patients might be at risk for severe hypotension that is refractory to adrenergic vasoconstrictor medications following induction of general anesthesia in patients chronically treated with angiotensin-converting enzyme inhibitors.

Method/Design: The study will be human subject non-randomized observational study. This study will be conducted at day of surgery administration area and main operation room at University of Iowa Hospitals and clinics. Arterial stiffness will be measured at day of surgery administration area prior to the surgery.

Carotid-Femoral Pulse Wave Velocity (Aortic Stiffness). Carotid-femoral pulse wave velocity (cfPWV) will be determined by applanation tonometry using the Sphygmocor system by sequentially recording ECG-gated carotid and femoral artery waveforms. Pulse wave signals will be recorded by tonometers positioned at the base of the right common carotid artery and over the right femoral artery. The time (t) between the feet of simultaneously recorded waves will be determined as the mean of 10 consecutive cardiac cycles. PWV is calculated by the system software from the distance between measurement points (D) and the measured time delay (t) as follows: cfPWV = D/Δt (m/s) where D is distance in meters and t is the time interval in seconds.