Acid–base and electrolyte balance following administration of three crystalloid solutions in dogs undergoing elective orthopaedic surgery

To compare acid–base balance and incidence of hyperchloraemic metabolic acidosis following administration of three crystalloid solutions to dogs undergoing anaesthesia for orthopaedic surgery. Prospective, randomised, clinical study. Sixty dogs. During a non–standardised anaesthetic, 0.9% saline (S), Hartmann's solution (H) or a polyionic glucose–free maintenance solution (M) was administered IV at 10 mL kg−1 hour−1. Venous blood pH, PCO2, PCV, total protein, urea, sodium, potassium and chloride concentrations were measured at induction of anaesthesia (T0) and after 2 hours of fluid therapy (T2). Base excess (BE), bicarbonate, corrected chloride concentration (corrCl), osmolality, change in plasma volume (PV) and strong ion gap (SIG) were calculated. Changes in variables within groups (1–sample Student's t–test/Wilcoxon signed rank test) and between groups (1–way anova/Kruskal–Wallis) were assessed. Data are presented as median (interquartile range). Significance was set at p < 0.05. No significant differences existed between groups for pH, PCO2, PCV, total protein, urea, potassium, corrCl, PV and SIG. Potassium significantly increased in all groups. Significant differences existed between groups S and M for BE, sodium, chloride, bicarbonate and osmolality, and between groups H and M for sodium and osmolality. Chloride concentration significantly changed from 116 (114–117) to 117 (116–119) mmol L−1 in group S, 116 (115–118) to 115 (113–117) mmol L−1 in group H and 116 (115–118) to 114 (113–118) mmol L−1 in group M. In groups H and M, sodium and osmolality decreased, and BE and bicarbonate concentration increased significantly. Plasma volume increased by 28 (14–44)%, 25 (5–40)% and 24 (13–33)% in groups S, H and M, respectively. Hyperchloraemic metabolic acidosis did not develop after intraoperative 0.9% saline, Hartmann's solution or maintenance solution at 10 mL kg−1 hour−1 for 2 hours in dogs undergoing elective orthopaedic surgery. Bicarbonate and BE increased after Hartmann's and maintenance solutions. Increases in potassium concentration were unexplained.