Effects of the spleen, epinephrine, and splenectomy on determination of blood volume in cats.

Blood volume (BV), RBC mass, plasma protein (PP), and PCV were determined in (i) awake, nonsplenectomized (NSPX) cats before and after splenic contraction was induced by IV administration of epinephrine, (ii) in pentobarbital-anesthetized, NSPX cats before and after splenic contraction was induced by epinephrine and splenectomy, and (iii) in awake, splenectomized (SPX) cats before and after epinephrine was administered. Blood volume, absolute RBC mass in the spleen could not be determined accurately in awake or anesthetized, NSPX cats. Accurate BV and RBC mass determinations could only be obtained in cats without the spleen; mean BV and RBC mass of awake or anesthetized, SPX cats were 4.1% and 1.4% or body weight, respectively. The spleen was a dynamic sequestering organ for feline erythrocytes (RBC). Epinephrine (0.1 ml of 1:1,000) given IV resulted in the observed contraction of the spleen within 2 minutes. Relaxation of the spleen with RBC uptake began 3 minutes after epinephrine was given and it proceeded at a rate of approximately 0.93% of circulating PCV/min. At 20 minutes after epinephrine was given, a steady state of PCV occurred, and 20% of the maximum circulating PCV observed after the administration of epinephrine was stored within the spleen. At 60 minutes after epinephrine was given to awake, SPX cats, intravascular fluid influx of 4 ml/kg resulted in a decrease of PCV and PP. At 3 hours after splenectomy was done, intravascular fluid efflux resulted in hemoconcentration--a calculated fluid deficit of 2.5 ml/kg/hr occurring during the 3 hours after surgical removal of the spleen.