Platelet sequestration in lung with hemorrhagic shock and reinfusion in dogs

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Abstract
Red blood cell (RBC) and platelet transit through the pulmonary vascular bed were compared 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 RBC 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 RBC and platelets were calculated, as was the percent extraction of platelets. The difference between RBC and platelet MTT increased (P < 0.01). The percent extraction of platelets increased (P < 0.001). The percent recovery of platelets fell (P < 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 studied in a 3rd group of dogs (n = 5) where inflation of a balloon in the inferior vena cava was used to reduce cardiac output (CO). Platelet extraction was inversely related to CO. The increased platelet sequestration seen in the lung during hemorrhagic shock apparently is primarily related to decreased blood flow.