Objective: To investigate the effect of i.v. administration of fluids on the furosemide-induced reduction in right atrial pressure (RAP) and relative change in blood volume (BV) of splenectomized mares.
Animals: 5 splenectomized mares.
Procedure: RAP was measured by use of a micromanometer placed in the right atrium. Jugular venous blood was collected for measurement of hematocrit, plasma total protein concentration, and hemoglobin concentration. Right atrial pressure was recorded and blood samples were collected immediately before furosemide (1 mg/kg of body weight, i.v.) administration, then every 15 minutes for 240 minutes. Beginning 120 minutes after furosemide administration, polyionic fluids (lactated Ringer's solution) were administered (2 L q 15 min) for 120 minutes.
Results: Furosemide induced a significant (P < 0.05) decrease in mean RAP (7.6 +/- 1.5 and 3.2 +/- 1.2 mm of Hg before and 15 minutes after furosemide administration, respectively), and BV (8.4 +/- 1.1 % by 15 minutes). Polyionic fluid administration restored RAP and BV. The volume of polyionic fluids administered (32 +/- 2 ml/kg) was not significantly different from the volume of urine produced (38 +/- 7.8 mg/kg). Difference was not apparent in the relation between change in BV and RAP before or after fluid administration.
Conclusions: The effect of furosemide on RAP of horses is mediated in large part by furosemide-induced reduction in BV. However, an effect of furosemide on venous compliance cannot be excluded as contributing to the reduction in RAP.