Platelet sequestration in lung with hemorrhagic shock and reinfusion in dogs

We compared red blood cell (RBC) and platelet transit through the pulmonary vascular bed under control conditions (n = 8) and during hemorrhagic shock (n = 8) in anesthetized spontaneously breathing dogs, using a modification of the indicator-dilutor technique. Platelets and RBCs from each animal were labeled with 51Cr and 99mTc, respectively, and were rapidly injected into the right atrium while blood was sampled from the ascending aorta. The mean transit time (MTT), volume of distribution, and percent recovery for RBCs and platelets were calculated, as was the percent extraction of platelets. We found 1) the the difference between RBC and platelet MTT increased (p less than 0.01), 2) that the percent extraction of platelets increased (p less than 0.001), and 3) that the percent recovery of platelets fell (p less than 0.01) during the shock period. These values all returned to control levels after reinfusion of the shed blood. The relationship between a transient reduction in blood flow and platelet extraction was then studied in a third group of dogs (n = 5) where inflation of a balloon in the inferior vena cava was used to reduce cardiac output (CO). These studies showed that platelet extraction was inversely related to CO. We conclude that the increased platelet sequestration seen in the lung during hemorrhagic shock is primarily related to decreased blood flow.