• Neural and humoral mechanisms keep the blood pressure fairly constant over a broad range of pressures. However, below a critical value (e.g. 50-60 mmHg for the brain), blood flow and oxygen delivery become dependent on perfusion pressures.
• The term hypotension describes a decrease in blood pressure which threatens organ perfusion and, eventually, oxygen delivery to the peripheral tissues.
• Decreased tissue oxygen availability may be followed by ischemia, cell death, and organ failure. It may also lead to 'priming' of sublethal injured cells, with release of second messengers and the possible consequence of a generalized inflammatory state following reperfusion of injured tissue with therapy.
• Consequences of hypotension for the 'vital' organ systems include cerebral and myocardial ischemia, particularly in the presence of coronary artery or cerebrovascular disease.
• While the final pathway of multiple organ failure complicating hypotension is rather uniform, the hemodynamic profile varies and is related to the underlying disease process.
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