Permissive hypotension

Permissive hypotension or hypotensive resuscitation is the use of restrictive fluid therapy, specifically in the trauma patient, that increases systemic blood pressure without reaching normotension (normal blood pressures). The goal blood pressure for these patients is a mean arterial pressure of 40-50mmHg or a systolic blood pressure less than or equal to 80. This goes along with certain clinical criteria. Following traumatic injury some patients experience hypotension (low blood pressure) that is usually due to blood loss (hemorrhage) but can be due to other causes as well (for example, blood leaking around an abdominal aortic aneurysms). In the past, physicians were very aggressive with fluid resuscitation (giving fluids such as normal saline or lactated Ringer's through the vein) to try to bring the blood pressure to normal values. Recent studies have found that there is some benefit to allowing specific patients to experience some degree of hypotension in certain settings. This concept does not exclude therapy by means of i.v. fluid, inotropes or vasopressors, the only restriction is to avoid completely normalizing blood pressure in a context where blood loss may be enhanced. When a person starts to bleed (big or small) the body starts a natural coagulation process that eventually stops the bleed. Issues with fluid resuscitation without control of bleeding is thought to be secondary to dislodgement of the thrombus (blood clot) that is helping to control further bleeding. Thrombus dislodgement was found to occur at a systolic pressure greater than 80mm Hg. In addition, fluid resuscitation will dilute coagulation factors that help form and stabilize a clot, hence making it harder for the body to use its natural mechanisms to stop the bleeding. These factors are aggravated by hypothermia (if fluids are administered without being warmed first it will cause body temperature to drop).

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