Effect of polycythemia on vascular volume in the newborn dog.

The effect of polycythemia [hematocrit (Hct) 64-80] on blood volume (BV) was studied in 27 unanesthetized, splenectomized newborn dogs (age 6-14 days, postsplenectomy 5-13 days). Normovolemic polycythemia (N) was induced in nine pups by exchange transfusion with 75 ml/kg of adult, packed (to Hct 95) red blood cells (RBC). Hypervolemic polycythemia (H) was induced in 11 pups by transfusion of RBC (50 ml/kg). Seven pups received exchange transfusion with 75 ml/kg of whole blood and served as controls (C). Red cell volume (RCV, 51CrRBC) and plasma volume (PV, 125I-fibrinogen and Evans blue) were measured prior to and at 1, 2, and 4 h after transfusion, before the pups received fluid orally. The pups were fed 8 ml X kg-1 X h-1 after 4 h, and measurements were repeated at 8 and 24 h. BV fell in C prior to 4 h by 10 +/- 4% (SD) (P less than 0.01) and then rose to initial levels. BV rose in the N pups by 17 +/- 9 (P less than 0.01), 14 +/- 5 (P less than 0.01), 9 +/- 10 (P less than 0.1), 17 +/- 9 (P less than 0.01), and 31 +/- 17% (P less than 0.01) at 1, 2, 4, 8, and 24 h post transfusion. BV rose in the H pups by 41 +/- 8, 35 +/- 10, 23 +/- 11, 27 +/- 6, and 43 +/- 9% (all P less than 0.01). Thus newborn dogs with induced N or H equilibrate rapidly to a BV significantly higher than C levels.(ABSTRACT TRUNCATED AT 250 WORDS)