Reversing Acidosis
There currently exist no convincing data supporting the administration of bicarbonate or tris-hydroxymethyl aminomethane (THAM) to directly reverse metabolic acidosis in trauma patients, even when the pH is less than 7.2. Correction of the metabolic acidosis in the trauma patient is better achieved through aggressive blood and blood product resuscitation and vasopressor support until surgical control of hemorrhage is achieved, shock is reversed, and end-organ perfusion is restored. If direct reversal of severe acidosis is still sought, THAM has a slight advantage over bicarbonate in patients with hypernatremia or concomitant respiratory acidosis, as it does not involve excessive administration of sodium or the by-production of CO2 (18). Several endpoints of resuscitation need to be set a priori and followed diligently as vital signs alone are poor indicators of end-organ perfusion. Base deficit and lactate levels are reliable perfusion indices worth trending as markers of the adequacy of resuscitation; the initial levels at the time of presentation, as well as their clearance from plasma within the first few hours of resuscitation, correlate with mortality in trauma patients (19, 20).
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Permissive Hypotension
Definition
Permissive hypotension is one of the central components of DCR. Permissive hypotension is the strategic decision to delay the initiation of fluid resuscitation and limit the volume of resuscitation fluids/blood products administered to the bleeding trauma patient by targeting a lower than normal blood pressure, usually a systolic blood pressure of 80–90 mmHg or a mean arterial pressure (MAP) of 50 mmHg.
Rationale
The theories behind permissive hypotension suggest that a lower target blood pressure (and thus a lower volume of resuscitation fluid) will improve patient outcomes by (1) decreasing the incidence and severity of dilutional coagulopathy and (2) avoiding the hypothetical “pop the clot” effect, which occurs when the fresh and unstable clot sealing a vascular laceration is dislodged when the intravascular pressure increases. A third potential advantage of restricting the volume of resuscitative fluids relates to the amelioration of the inflammatory cascade, which is exacerbated in response to exogenous fluids administration.