Changes in the SID Actual and SID Effective Values in the Course of Respiratory Acidosis in Horses With Symptomatic Severe Equine Asthma-An Experimental Study.

Equine asthma syndrome is an allergic, inflammatory airway disease that usually affects older horses. Respiratory acidosis is an acid-base imbalance caused by alveolar hypoventilation. The acid-base balance may be assessed using the Henderson-Hasselbalch equation as well as the Stewart model. The authors hypothesized that systemic respiratory acidosis changes the ionic concentrations affecting water dissociation. The study group included 16 Warmblood, mixed breed horses of both sexes with a history of severe equine asthma, and 10 healthy horses were used as controls. Arterial and venous blood were collected from all the horses. The pH, pO ₂ , and pCO ₂ and HCO _3- were assessed in the arterial blood. Na, K, Cl, albumin, and P _inorganic (P _i ) were assessed in the venous blood. The obtained results were used to calculate the anion gap (AG), modified AG, actual strong ion difference (SID _a ), weak non-volatile acids, and effective strong ion difference (SID _e ) values for all the horses. A systemic, compensatory respiratory acidosis was diagnosed in the study group. The concentration of Na in the blood serum in the study group was significantly higher, whereas the concentration of Cl was significantly lower than the values in the control group. The SID _a and SID _e values calculated in the horses from the study group were significantly higher than those in the control group. Significantly higher SID _a and SID _e values confirm the presence of ionic changes that affect water dissociation in the course of respiratory acidosis in horses. The SID _a and SID _e values may be useful in the diagnosis and treatment of respiratory acidosis in horses, which warrant further investigation.
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