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Infrarenal aortic clamp hypertension is exacerbated by baroreceptor blockade
J S Giglia1, G B Zelenock, L G D'Alecy
1Department of Surgery, University of Michigan Medical School, Ann Arbor, Michigan 48109, USA.
Insights
Aortic clamping during surgery can cause hypertension by blocking compensatory reflexes. This effect is worsened by combined alpha and beta adrenergic blockade, highlighting its role in cardiovascular complications.
Area of Science:
- Cardiovascular Physiology
- Surgical Anesthesia
- Adrenergic Pharmacology
Background:
- Aortic clamp-induced hypertension is a known risk factor for cardiovascular complications after infrarenal aortic surgery.
- Understanding the underlying physiological mechanisms is crucial for mitigating these risks.
Purpose of the Study:
- To investigate the physiological mechanisms responsible for hypertension induced by aortic clamping.
- To determine the role of adrenergic blockade in clamp-induced hypertension.
Main Methods:
- Measurements of mean arterial pressure (MAP), cardiac output, heart rate, and left ventricular pressure were taken in anesthetized dogs.
- Dogs received varying levels of adrenergic blockade: alpha, beta, combined alpha and beta, or no blockade.
- The infrarenal aorta was clamped after ligating collateral vessels.
Main Results:
- MAP increased immediately after aortic clamping in all groups.
- The magnitude of MAP increase was directly related to the extent of adrenergic blockade.
- Combined alpha and beta blockade resulted in the most significant increase in MAP (16.7 +/- 1.3 mm Hg).
Conclusions:
- Acute intraoperative hypertension during infrarenal aortic clamping is attributed to the blunting of baroreceptor reflex mechanisms.
- Adrenergic blockade, particularly combined alpha and beta blockade, exacerbates clamp-induced hypertension.
- These findings underscore the importance of managing blood pressure during aortic procedures.
Abstract:
Aortic clamp-induced hypertension has long been implicated in the cardiovascular mortality and morbidity following infrarenal aortic operations. We studied the physiologic mechanisms leading to clamp-induced hypertension. Mean arterial pressure (MAP), cardiac output, heart rate, and left ventricular pressure were measured in alpha-chloralose-anesthetized dogs. Animals received alpha, beta, both alpha and beta, or no adrenergic blockade (n = 3, 4, 12 and 7, respectively). The infrarenal aorta was clamped following ligation of the infrarenal collateral vessels (lumbar, circumflex iliac, and tail arteries). Statistical analysis used paired t tests within groups, and ANOVA and unpaired t tests between groups, with Bonferroni's correction as indicated. Following placement of the clamp, MAP increased immediately in all groups, with magnitude of the increase related to the extent of adrenergic blockade. MAP increased 5.6 +/- 0.8 mm Hg with no blockade (P = 0.0005), 6.7 +/- 0.8 mm Hg with alpha blockade (P = 0.0153), 15 +/- 3.1 mm Hg with beta blockade (P = 0.0163), and 16.7 +/- 1.3 mm Hg with combined alpha and beta blockade (P < 0.0001). The increase in MAP immediately following infrarenal aortic clamping was most pronounced with combined alpha and beta blockade. We suggest that acute intraoperative hypertension associated with infrarenal aortic clamping is caused by the attenuation of compensatory baroreceptor reflex mechanisms.