The Pleth Variability Index as a Guide to Fluid Therapy in Dogs Undergoing General Anesthesia: A Preliminary Study

The aim of this prospective, randomized clinical trial was to evaluate the use of the pleth variability index (PVi) to guide the rate of intraoperative fluid therapy compared to a traditional fixed-fluid-rate approach in ASA 1-2 dogs undergoing surgery. Twenty-seven dogs met the inclusion criteria and were randomly assigned to the conventional fluid management group (CFM, n = 12) or the PVi-guided group (PVi, n = 15). The CFM group received a fixed rate of 5 mL kg^-1 h^-1 of crystalloid solution, while in the PVi group the rate was continuously adjusted based on the PVi: PVi < 14% = 3 mL kg^-1 h^-1; 14% ≤ PVi ≥ 20% = 10 mL kg^-1 h^-1; and PVi > 20% = 15 mL kg^-1 h^-1. Hypotension (MAP < 65 mmHg) in the CFM was treated with a maximum of two fluid boluses (5 mL kg^-1 in 10 min) and in the case of no response, dobutamine (1-3 mcg kg^-1 min^-1) was administered. In the PVi group, the treatment of hypotension was similar, except when the PVi > 14%, when dobutamine was started directly. Total fluid volume was significantly lower in the PVI group (0.056 ± 0.027 mL kg^-1 min^-1) compared to the CFM group (0.132 ± 0.115 mL kg^-1 min^-1), and the incidence of hypotension was lower (p = 0.023) in the PVi group (0%) compared to the CFM group (41%). The mean arterial pressure (MAP) was significantly higher in the PVi group during surgery. Dobutamine was never administered in either group. Preliminary data suggest that the PVi may be considered as a potential target to guide fluid therapy in dogs; larger studies are needed, especially in cases of cardiovascular instability.