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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