Role of the hematocrit in a rabbit model of arterial thrombosis and bleeding

Background: A decrease in hematocrit lengthens bleeding time, The authors s tudied the role of hematocrit variations in an experimental model of arteri al thrombosis and bleeding. Methods: The Felts model was used in 24 rabbits. After anesthesia was induc ed and common monitors were positioned, the right common carotid artery was exposed and a 60% stenosis was induced. A compression injury of the artery was then produced, which triggered a series of cyclic episodes of thrombos is and clot lysis (cyclic flow reductions [CFRs]). After counting the numbe r of CFRs that occurred in 20 min (CFR1), the animals were assigned randoml y to one of three groups (n = 8 in each group): control, hemodilution with rabbit homologous platelet-rich plasma, and hemodilution n with gelatin sol ution and then reinfusion of the shed blood. The effect of hemodilution wit h replacement by platelet-rich plasma or by colloid was observed by recordi ng the number of CFRs during another 20-min period (CFR2), A third period o f observation (CFR3) followed shed blood reinfusion in the gelatin, solutio n group. Ear immersion bleeding time was recorded after each CFR period. Results: In the two experimental groups, the decrease in hematocrit (from 3 6 +/- 3% to 23 +/- 2% and from 38 +/- 3% to 23 +/- 2%, respectively; mean /- SD) abolished CFRs (from a median of 4 to 0 and 7 to 0, respectively) an d significantly lengthened bleeding time (from 76 +/- 24 s to 114 +/- 36 s and from 84 +/- 37 s to 127 +/- 29 s, respectively). Blood reinfusion in th e group that received the gelatin solution caused CFR to reappear (CFR3 = 4 ), Conclusions: Decreases in hematocrit reduced the cyclic arterial thrombosis rate and increased the bleeding time in the rabbits in this study, Hematoc rit normalization caused thrombosis to reappear.