Effects of fluid therapy on total protein and its influence on calculated unmeasured anions in the anesthetized dog

Objective – To determine the effects of IV lactated Ringer's solution at a rate of 10 mL/kg/h in anesthetized dogs on total protein (TP) measurement and calculation of unmeasured anions (UAs) using 2 quantitative methods of acid‐base status determination, strong ion gap, and modified base deficit. Design – Prospective clinical study. Animals – Forty‐three dogs, anesthetic health status I or II according to the American Society of Anesthesiologists, undergoing surgery under general anesthesia. Interventions – Arterial blood analyses for gas tensions, acid‐base balance, electrolytes, lactate, hemoglobin (Hb), PCV, and TP were performed under general anesthesia immediately after induction and again after administration of approximately 10 mL/kg of lactated Ringer's solution (given over 1 h). UAs were determined using strong ion gap and modified base deficit. Measurements and Main Results – Fluid replacement for 1 hour decreased TP, Hb, and PCV by 8%, 7.8%, and 8.6%, respectively. The degree of decrease in TP did not impact the calculation of UAs by quantitative methods when the prefluid administration TP value was used instead of the postfluid TP value in the calculation. Comparison of the two methods showed a low correlation (r≤0.68) and marked differences in the precision (1.96 SD). Conclusions: The degree of decrease in TP after 1 hour of fluid replacement at approximately 10 mL/kg does not affect determination of UAs when prefluid TP is used within that time period.