The influence of crystalloid type on acid–base and electrolyte status of cats with urethral obstruction

Objective: To compare the effect of a balanced isotonic crystalloid solution with that of 0.9% sodium chloride on the acid–base and electrolyte status of cats with urethral obstruction.
Design: Randomized prospective clinical trial.
Setting: Academic veterinary emergency room.
Animals: Sixty-eight cats with naturally occurring urethral obstruction.
Interventions: Cats were randomized to receive either a balanced isotonic crystalloid solution (Normosol-R, n =39) or 0.9% sodium chloride ( n =29) for fluid therapy. Baseline venous blood gas and blood electrolyte values were obtained at the time of admission and at intervals during the course of therapy.
Measurements and main results: Baseline values were similar between groups. Cats receiving Normosol-R had a significantly higher blood pH at 12 hours, a significantly greater increase in blood pH from baseline at 6 and 12 hours, as well as a significantly higher blood bicarbonate concentration at 12 hours and a significantly greater increase in blood bicarbonate from baseline at 6 and 12 hours. Conversely, the increase in blood chloride from baseline was significantly higher at 2, 6, and 12 hours in cats receiving 0.9% sodium chloride. There were no significant differences in the rate of decline of blood potassium from baseline between groups. Subgroup analysis of hyperkalemic cats (K⁺>6.0 mmol/L) and acidemic cats (pH<7.3) yielded similar findings.
Conclusions: While both crystalloid solutions appear safe and effective for fluid therapy in cats with urethral obstruction, the use of a balanced electrolyte solution may allow more rapid correction of blood acid–base status within the first 12 hours of fluid therapy. The use of a potassium-containing balanced electrolyte solution does not appear to affect the rate of normalization of blood potassium in treated cats with urethral obstruction.