Relationship of intravenous administration of Ringer's lactate solution to pulmonary edema in halothane-anesthetized cats
Authors: Bjorling D. E. , Rawlings C. A. 
Published: February 2025

Three days before experimentation was started, thoracotomies were performed on 24 cats to allow implantation of catheters in the aorta, main pulmonary artery, and left atrium. The susceptibility of halothane-anesthetized cats to pulmonary edema due to iv administration of crystalloid fluids was tested by infusing Ringer's lactate solution (rls) in 3 groups of 8 cats at the following dose rates; 11 ml/kg/hr; 90 ml/kg/hr; and 225 ml/kg/hr. Ringer's lactate solution (90 ml/kg/hr) was given to a 4th group of 8 cats in which thoracotomies were not done before experimentation. Cardiovascular hemodynamics, total lung compliance, arterial blood gas tensions and acid-base balance, pcv, plasma total solids concentration, and plasma colloid osmotic pressure were measured and recorded before fluid administration and at various times during fluid administration. Respiratory rate, rectal temperature, and clinical observations also were recorded. After 60 minutes of fluid administration, the lungs were harvested, radiographed, weighed, and homogenized for determination of extravascular lung water (elw). Control measurements of elw were obtained from a 5th group of 8 cats which were not given (iv) fluids.

Cats given 225 ml of rls/kg over the course of an hour developed ascites and occulonasal discharge and had fluid present in their tracheas. There were no changes in respiratory rate or heart rate in any group. Rectal temperature was significantly decreased at 60 minutes (termination) in cats given 225 ml of rls/kg. The rate of fluid administration did not affect total lung compliance or arterial blood gas values, except for a decrease in arterial PO2 after the 225 ml/kg dose was given. Central venous pressure was increased between 15 minutes and termination in cats given the 225 ml/kg dose. Left atrial pressure and pulmonary arterial pressure were significantly increased from 30 minutes until termination in this group. Cardiac index was greater at termination than at base line in cats given 225 ml of rls/kg/hr. However, there were no differences among all groups when cardiac indices at termination were compared. Packed cell volume, plasma total solids concentration, and plasma colloid osmotic pressure were significantly decreased at termination in cats given the 90 and 225 ml/kg/hr doses. The elw at termination of cats given the 225 ml/kg dose was significantly greater than that of other groups. The elw was not related to mean left atrial pressure at termination, but did vary in a negative linear regression with plasma total solid values and plasma colloid osmotic pressure. A positive linear relationship was seen between elw and the left atrial pressure-plasma colloid osmotic pressure differential at termination.

The results of this study indicate that the susceptibility of cats to the development of pulmonary edema is similar to that of other animals. In the absence of cardiopulmonary disease, rls may safely be given to cats at a rate of 90 ml/kg/hr. Since they are small animals, smaller total quantities are tolerated.