Electrolyte disorders in horses with colic. Part 1: potassium and magnesium

Abstract

Electrolyte disorders are common in horses with acute abdominal disease, and are a significant cause of morbidity. They are especially prevalent in horses treated surgically for colic, and may be present before, during and after surgery. In one study, 54% of horses admitted for surgical colic had preoperative serum ionised magnesium concentrations below the reference range and 86% subnormal serum ionised calcium concentrations (Garcia-Lopez et al. 2001). Electrolyte abnormalities are particularly prevalent in horses with strangulating obstructions of the intestine. These horses have lower preoperative serum concentrations of ionised magnesium and calcium than horses with nonstrangulating lesions (Dart et al. 1992; Garcia-Lopez et al. 2001). Horses with decreased preoperative ionised magnesium were also more likely to be subjected to euthanasia during surgery. The role of electrolyte derangements in contributing to adverse clinical events in horses with colic is still being investigated. The association between cardiac electrical disorders and blood calcium, magnesium and potassium concentrations is well established in the horse (Harrington 1974; Glazier et al. 1979, 1982; Reef 1999) (Fig 1). Derangements in blood electrolyte concentration might also be associated with a longer hospital stay. Martin et al. (1994) reported that dogs with low serum magnesium concentrations were hospitalised for twice as long as those with a normal serum magnesium concentration. Conversely, Garcia-Lopez et al. (2001) did not find any correlation between serum ionised magnesium or calcium concentrations and length of hospitalisation, incidence of complications or survival in horses treated surgically for colic. The association between serum concentrations of potassium, calcium and magnesium with post operative ileus is still unknown in the horse. Dart et al. (1992) speculated that decreased serum calcium concentrations might contribute to ileus. Garcia-Lopez et al. (2001) found lower serum concentrations of ionised magnesium and calcium in horses that developed post operative ileus, than in those that did not. These decreased electrolyte concentrations may be due to decreased intake and increased loss of electrolytes in gastric reflux. It is now possible to measure electrolytes using ‘patientside’ portable analysers. The introduction of these cartridgebased systems has enabled results to be obtained quickly and easily when laboratory techniques are unavailable (Grosenbaugh et al. 1998). Different sensors are available to measure different combinations of electrolytes, blood biochemistry, PCV and blood gas tensions. The price of these hand-held devices is rapidly decreasing and they are now affordable for many private practices. The normal range for any electrolyte may vary to some degree between analysers. Therefore, horse specific normal ranges should be obtained from the manufacturers, if possible. In Part 1, we discuss the importance of potassium and magnesium and Part 2 covers calcium, sodium, chloride and phosphorus.