Prevalence and prognostic importance of hypomagnesemia and hypocalcemia in horses that have colic surgery

Objective-To determine the prevalence of hypomagnesemia and hypocalcemia in horses with surgical colic. Animals-35 horses with surgically managed colic. Procedure-Serum concentrations of total magnesium (tMg(2+)) and calcium (tCa(2+)), as well as ionized magnesium (iMg(2+)) and calcium (iCa(2+)) were analyzed before surgery and 1, 3, 5, and 7 days following surgery. A lead-II ECG and pertinent clinical data were also obtained at each time. Results-Preoperative serum tMg(2+) and iMg(2+) concentrations were below the reference range in 6 (17%) and 19 (54%) horses, respectively. Serum concentrations of tCa(2+) and iCa(2+) were less than the reference range in 20 (57%) and 30 (86%) horses before surgery. Horses with strangulating lesions of the gastrointestinal tract had significantly lower preoperative serum concentrations of iMg(2+) and iCa(2+), as well as a higher heart rate than horses with nonstrangulating lesions. Horses that developed postoperative ileus had significantly lower serum concentrations of iMg(2+) after surgery. Serum concentrations of magnesium and calcium (total and ionized) correlated significantly with the PR, QRS, QT, and corrected QT (QTc) intervals. Horses that were euthanatized at the time of surgery (n = 7) had significantly lower preoperative serum concentrations of iMg(2+), compared with horses that survived. Neither serum magnesium nor calcium concentrations were predictors of hospitalization time or survival. Conclusions and Clinical Relevance-Hypomagnesemia and hypocalcemia were common during the perioperative period, particularly in horses with strangulating intestinal lesions and ileus. Serum concentrations of tMg(2+) and tCa(2+) were less sensitive than iMg(2+) and iCa(2+) in detecting horses with hypomagnesemia and hypocalcemia.