Changes in blood gases and electrolytes of horses given varying doses of sodium bicarbonate

Eight Quarter Horse mares, ranging in age from 5-15 years were used in a 4-week Latin-Square design experiment in which pairs of horses were given 0, 333, 666, or 1000 mg/Kg body weight of sodium bicarbonate (NaHCO₃) via nasogastric tube once weekly. Blood samples were drawn immediately before nasogastric intubation and then in one-hour increments for eight hours and once again at twenty-six hours after intubation. Blood pH, HCO₃^-, PCO₂, and PO₂ and the serum electrolytes, Na⁺, K⁺, Cl^- and Ca⁺⁺ were determined. Each treatment with NaHCO₃ produced an increase (p<.01) in pH and HCO₃^- within two hours post-intubation, and an increase (p<.01) in PCO₂ within four hours. Peak mean values for pH, HCO₃^-, and PCO₂ were reached between four and six hours after intubation for all NaHCO₃ treatments and remained elevated through eight hours after intubation. Serum Na⁺ was elevated (p<.01) and serum K⁺ and Cl^- were reduced (p<.01) following NaHCO₃ administration. All blood gas and serum electrolyte changes were found to return to near baseline levels by 26 hours after intubation. The fact that peak mean pH and HCO₃^- values were not reached until up to four hours after NaHCO₃ administration is important to consider when developing regulations for pre-race blood gas testing.