Aortic Clamp Hypertension Is Avoidable

To the Editor: When we provide general anesthesia for abdominal aortic surgery, must we expect a "significant increase in mean arterial pressure" occasioned by aortic clamping [1]? Is hypertension truly "the most dramatic and consistent component in hemodynamic response to aortic cross-clamping" [1]? Gelman et al.'s recent canine subjects maintained a central venous pressure of 3 mm Hg during anesthesia and while suprarenal aortic cross-clamping provoked a 30% increase in arterial blood pressure [1]. Clinically attainable general anesthesia can block adrenergic and cardiovascular responses to skin incision [2] and, as seen in daily practice, to aortic manipulations. However, such an anesthetic, of a 2-MAC (minimum alveolar anesthetic concentration) magnitude [2], requires a replete intravascular volume for stable hemodynamics to be maintained. Another series of aortic surgery patients who did not experience significant changes of mean arterial pressure upon aortic cross-clamping [3] perhaps fared thusly because they could better accommodate a MAC BAR (minimal alveolar concentration to block adrenergic response, equaling 2.05-MAC) [2] anesthetic; their baseline central venous pressure was 11 mm Hg [3]. In essence, a more generous intravascular volume allows MAC BAR anesthesia, which begets unaltered blood pressure during aortic clamping, as witnessed in clinical practice and in print [3,4]. Daniel B. Gould, MD Department of Anesthesiology, St. Louis Regional Medical Center, St. Louis, MO 63112