Noncardiac surgery: widening the gap in pulse pressure.

Over 72 million Americans have hypertension (HTN) with three quarters of hypertensive individuals being older than 50 years. Furthermore, almost one third of adults presenting for noncardiac surgery and two thirds presenting for coronary bypass surgery report a preexisting history of HTN. Worldwide, HTN may affect as many as 1 billion people and be responsible for 7.1 million deaths per year. In the ambulatory setting, the clinical consequences of chronic HTN have been well characterized as being highly associated with coronary heart disease, stroke, renal failure, retinopathy, peripheral vascular disease, and most important, mortality and poor quality of life. Contrasting this to the perioperative setting, our understanding of the contribution of severely elevated systolic or diastolic blood pressure (BP) to perioperative outcomes had been hindered by data that were several decades old, by studies with design and methodology flaws, and by underappreciating the importance of evaluating perioperitative HTN according to subtypes, microvascular and macrovascular. Such distinction is critical because the underlying etiology, pathophysiology, demographic, and therapeutic options can differ extensively for each subtype. Also of relevance and poorly studied are the vascular biologic effects arising from surgery/anesthesia-mediated sympathoadrenal, endocrine, hematologic, and inflammatory responses. Several years ago, we and others began investigating the influences of preexisting HTN according to subtypes on major postoperative vascular events after coronary artery bypass graft surgery. Specifically, components of BP (systolic, diastolic, and mean) as well as categories of high BP (Fig. 1) defined by the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC 7) were analyzed as risk predictors. The first report found an independent and stronger association between isolated systolic HTN in comparison with isolated diastolic HTN and major adverse cardiac events (MACE). These data have been followed by several publications finding that elevated pulse pressure (PP), more than systolic or diastolic BP, is a significant and an independent predictor of stroke, MACE, renal failure, and shortand long-term mortality. These reports were principally derived from analysis of patients undergoing cardiac surgery. Both isolated systolic HTN and widened PP are indices of larger vessel “stiffness,” a pathophysiologic characteristic that strongly influences the rate of pressure wave propagation within the arterial tree. As the left ventricle ejects, the resultant systolic pressure generated is dependent on the stroke volume and the compliance of the larger arterial vessels. Arterial compliance, in turn, relates to the change in volume (stroke volume) and the ensuing change in pressure (PP). With aging comes increased vascular stiffness (i.e., reduced compliance), causing both the forward propagated and reflected arterial waves within the arterial tree to travel much more rapidly than in a “nonstiff” arterial tree, resulting in early return of the retrograde waves to the central aorta during late systole as opposed to early diastole. Generally, this repetitive pulsatile stress imposed onto vascular walls is related to progressive breakdown of the elastic elements and many other mechanisms that enable vascular “cushioning. ” The ensuing remodeling changes result in medial necrosis, vascular stiffening, and resistance, as well as endothelial dysfunction and disruption of atherosclerotic plaques, which potentiate both local and distal thrombotic events. In this issue of Anesthesia & Analgesia, 2 reports have evaluated whether there is a relationship between PP and adverse outcomes after noncardiac peripheral vascular surgery. Both studies share common features in that the designs are retrospective and descriptive and neither study found statistically significant P values in researching for an association between PP and fatal and nonfatal events after peripheral vascular surgery. Why do these findings from patients undergoing peripheral vascular surgery differ from prior reports that demonstrate a strong association between preexisting PP and postoperative adverse outcomes in the setting of cardiac surgery? To begin, let’s examine the study design and questions asked by these 2 reports. The study by Asopa et al. included 412 patients who underwent vascular a World Health Organization [WHO]. 2002. Available at: http://www.who. int/whr/2010/whr10_en. pdf. Accessed XX xx, 20xx.