Abstract
Hypotension is a common occurrence, especially in anesthetized patients and in critical patients suffering from hypovolemia due to shock and sepsis. Hypotension can also occur in normovolemic animals, anesthetized or conscious, under conditions of vasodilation or decreased cardiac function. The main consequence of hypotension is decreased organ perfusion and tissue injury/dysfunction. In the human literature there is no consensus on what is the threshold value for hypotension, and ranges from < 80 to < 100 mmHg for systolic blood pressure and from < 50 to < 70 mmHg for mean arterial blood pressure have been referenced for intraoperative hypotension. In veterinary medicine, similar values are referenced, despite marked differences in normal arterial blood pressure between species and with respect to humans. Therapeutic intervention involves fluid therapy to normalize volemia and use of sympathomimetics to enhance cardiac function and regulate peripheral vascular resistance. Despite these therapeutic measures, there is a subset of patients that are seemingly refractory and exhibit persistent hypotension. This review covers the physiological aspects that govern arterial blood pressure control and blood flow to tissues/organs, the pathophysiological mechanisms involved in hypotension and refractory hypotension, and therapeutic considerations and expectations that include proper interpretation of cardiovascular parameters, fluid recommendations and therapy rates, use of sympathomimetics and vasopressors, and newer approaches derived from the human literature.
Highlights
What Is Hypotension?In simple terms, hypotension is a lower than normal arterial blood pressure
An example of short-term control are changes that occur during exercise in all or most of the factors, to increase arterial blood pressure and cardiac output to meet tissue demands, but the increase in cardiac output exceeds that of arterial blood pressure because local muscle activity results in a decrease in vascular resistance to improve blood flow while veins and small arterioles of other tissues exhibit a decrease in vascular compliance to improve venous return [20]
Long-term control of cardiac output and arterial blood pressure is the result of adaptation of baroreceptors within hours to days to changes in circulating volume and arterial blood pressure, of the instauration of higher vascular resistance that results in higher arterial blood pressure and minimal changes in cardiac output, and of an active participation of the kidney that responds to the increase in arterial blood pressure with endocrine and electrolyte mechanisms to control pressure and volume by increasing urinary output [20]
Summary
Similar values are referenced, despite marked differences in normal arterial blood pressure between species and with respect to humans. Therapeutic intervention involves fluid therapy to normalize volemia and use of sympathomimetics to enhance cardiac function and regulate peripheral vascular resistance. Despite these therapeutic measures, there is a subset of patients that are seemingly refractory and exhibit persistent hypotension. This review covers the physiological aspects that govern arterial blood pressure control and blood flow to tissues/organs, the pathophysiological mechanisms involved in hypotension and refractory hypotension, and therapeutic considerations and expectations that include proper interpretation of cardiovascular parameters, fluid recommendations and therapy rates, use of sympathomimetics and vasopressors, and newer approaches derived from the human literature
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