Effect of blood loss on vascular responsiveness in pedicled groin flaps in a rat model

Using the clamping method (closing and opening the flap feeding artery) and continuous laser Doppler flowmetry, the effects of blood withdrawals on flap blood flow and on active and passive mechanisms regulating it were investigated in 12 Sprague-Dawley rats. Measurements were made during stable normovolemic conditions, during hypovolemia (after 3 ml/kg and after 6 ml/kg blood withdrawal), and after retransfusion of the shed blood. The continuous blood flow responses during and after the clamping procedure were analyzed. After clamp release, the increase in blood flow, duration of overshoot, and peak flow of overshoot were significantly greater (the level of significance was set equal to 0.05) in the registrations performed after blood withdrawals than before them. The post-ischemic response curves indicating significantly increased flap hyperemia during reperfusion in the registrations after blood withdrawals may be associated with decreased vascular resistance in the flap. Thus, the authors conclude that a short-term decrease in blood pressure caused by blood loss may prepare the flap microcirculation for tolerating more ischemia.