Ionic composition of gastric reflux and small intestinal fluid in horses: implications for fluid replacement

Small intestinal (SI) distension and gastric reflux (GR) are common in horses with mechanical and functional ileus. Removal of GR results in fluid/ion losses.

1) Determine the capacity of healthy SI; 2) measure ion concentrations in normal SI fluid, GR, or fluid from SI undergoing resection. The authors hypothesized that Na⁺ and Cl^- concentrations would be lower and higher, respectively, in GR as compared to SI fluid from healthy horses, while there would be little difference in K⁺ concentration.

Observational study: two to 15 meters of SI from 15 horses were distended with water to 6-7 cm in diameter. Volume drained was measured to determine capacity. Ion concentrations were measured in SI fluid from healthy horses (n=10), GR (n=11), and strangulated bowel (n=2).

Normal SI had a fluid capacity of 2.8 ± 0.6 L/m. Na⁺, K⁺, and Cl^- concentrations were 100 ± 6, 22 ± 5, and 66 ± 30 mmol/L, respectively, in normal SI fluid; 77 ± 16, 16 ± 11, and 96 ± 25 mmol/L, respectively, in GR; and 116 ± 11, 12 ± 5, and 43 ± 27 mmol/L, respectively, in fluid from strangulated SI. Concentrations of Na⁺ were lower (P<0.01) and Cl^- greater (P<0.03) in GR than in normal SI fluid or fluid from strangulated SI, while all fluid K⁺ concentrations were 3-5-fold greater than serum K⁺ concentration.

These data can be used to estimate water and ion losses that occur with SI disorders to implement appropriate fluid therapy plans.