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

Background: 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.

Aims/objectives: 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.

Methods: 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).

Results: 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.

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