Ionized magnesium role in anesthetized and hospitalized dogs and cats

Magnesium is the second most abundant intracellular cation and it plays a vital role in the body. In recent years, interest in magnesium has growth, however, veterinary studies have predominantly focused on total magnesium, even though ionized fraction represents the biologically active form. The widespread availability of blood gas analyzers has allowed quicker measurement of ionized magnesium, improving the diagnosis of dysmagnesemia, a common condition in both human and veterinary patients that is often underdiagnosed. This PhD project includes three studies regarding ionized magnesium in dogs and cats. The first study was retrospective and established a reference range for ionized magnesium in 45 healthy cats, resulting in 0.61-1.11 mmol/L. Moreover, the incidence of dysmagnesemia in hospitalized dogs and cats was evaluated, enrolling 430 dogs and 310 cats. Canine patients presented a high incidence of hypomagnesemia (35.5%), not associated with increased mortality, whereas in cats, despite hypermagnesemia had a low incidence (8%), it was associated with increased mortality. In dogs, hypomagnesemia was more common in neurological (51%), neoplastic (50%), and endocrine (42%) pathologies. In cats, instead, hypermagnesemia showed a higher incidence in endocrine (28.6%), systemic (13.6%), and urinary (12.9%) pathologies. Neither in dogs nor in cats, dysmagnesemia was associated with longer hospitalization or with changes in systolic arterial pressure or mean arterial pressure. The second study elaborated a reference range for ionized magnesium on 120 healthy dogs, which resulted 0.44-1.01 mmol/L. Furthermore, it evaluated the impact of intraoperative fluid therapy on 65 dogs. After premedication, Lactated Ringer administration started at a rate of 3 mL/kg/h IV. Venous blood gas analyses were conducted after 1 hour of fluid therapy (T1) and 1 hour after fluid discontinuation (T2). Despite Lactated Ringer solution lacks of magnesium, an increase in calcium, magnesium, and potassium was observed, likely due to the effect of fluid therapy, as well as to the mild acidosis developed during anesthesia and the active warming during recovery. Moreover, a decrease in BUN, creatinine, lactate, hematocrit, and hemoglobin were observed, probably due to the preserved tissue perfusion and to the diluting effect of fluid therapy. The third study compared the effectiveness of three different magnesium supplementation treatments in hospitalized hypomagnesemic dogs. Sixty dogs were enrolled and divided into three groups of 20 each. The RES group received Rehydration Electrolyte Solution III at 3 mL/kg/h IV for 3 hours and blood gas analyses were performed at the end of infusion (T3), 2 hours (T5), and 24 hours (T24) post-infusion. The MgHUM group received oral human magnesium supplementation at 1-2 mEq/kg, while the MgVET group received oral veterinary supplementation according to manufacturer guidelines. For these two groups, blood gas analyses were performed 3 hours (T3), 5 hours (T5), and 24 hours (T24) after the administration. Fluid therapy with Rehydration Electrolyte Solution III showed to be effective in the management of hypomagnesemia. If oral supplementation is preferred, the human product UltraMag® has proven to be a valid alternative thanks to its particular formulation in a sucrosomial form.