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Describe compensatory mechanisms that take place in response to blood loss.
When blood loss occurs during surgery, there is loss of intravascular volume and reduction in oxygen-carrying capacity because of the loss of Hb.
As intravascular volume decreases, compensatory vasoconstriction and tachycardia occur in an attempt to preserve CO. Continuing volume loss results in decreased CO, causing a reduction in oxygen delivery to tissues. Restoration of intravascular volume by infusion of either colloid solution in a 1:1 ratio to blood loss or crystalloid solution in a 3:1 ratio allows normalization of CO and maintenance of hemodynamic stability.
Several mechanisms are available to respond to the loss of oxygen-carrying capacity. First, with restoration of intravascular volume CO may actually increase, maintain-ing or even increasing oxygen delivery. Second, at the tissue level, oxygen extraction may increase. Normal mixed venous oxygen saturation is approximately 75%. This indi-cates that only 25% of available oxygen is being extracted. Therefore, a substantial reserve of oxygen is available to the tissues, which can be used simply by increasing the amount extracted.
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