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

Ionic composition and fluid capacity of the small intestine and gastric reflux in horses were studied to better understand fluid and electrolyte losses during small intestinal disorders, aiming to improve fluid replacement therapy.

Objective of the Study

• Determine the fluid capacity of the healthy small intestine (SI) in horses.
• Measure and compare ion concentrations (sodium, potassium, chloride) in normal small intestinal fluid, gastric reflux (GR), and fluid from strangulated small intestine (SI) in horses.
• Test the hypothesis that sodium (Na) would be lower and chloride (Cl) would be higher in gastric reflux compared to normal SI fluid, with potassium (K) concentrations remaining similar.

Background

• Small intestinal distension and gastric reflux commonly occur in horses suffering from ileus caused by mechanical blockage or functional issues.
• Removal of gastric reflux leads to significant fluid and electrolyte losses, which necessitates effective fluid replacement therapy.

Methods

• Healthy small intestine segments (ranging from 2 to 15 meters) from 15 horses were experimentally distended with water until a diameter of 6-7 cm was reached.
• Volume of fluid drained was measured to estimate the fluid capacity per meter of small intestine.
• Samples of fluid were collected from three groups:
  • Normal small intestinal fluid (10 horses).
  • Gastric reflux fluid (11 horses) typically associated with ileus or obstruction.
  • Fluid from strangulated bowel (2 horses) to represent pathological small intestinal conditions.
• Ion concentrations of sodium (Na), potassium (K), and chloride (Cl) were analyzed in collected fluids.

Key Findings

• Normal small intestine fluid capacity was found to be approximately 2.8 ± 0.6 liters per meter of intestine length.
• Ion concentrations varied among normal SI fluid, gastric reflux, and strangulated SI fluid:
  • Normal SI fluid: Na = 100 ± 6 mmol/L, K = 22 ± 5 mmol/L, Cl = 66 ± 30 mmol/L.
  • Gastric reflux (GR): Na = 77 ± 16 mmol/L (significantly lower), K = 16 ± 11 mmol/L, Cl = 96 ± 25 mmol/L (significantly higher).
  • Strangulated SI fluid: Na = 116 ± 11 mmol/L, K = 12 ± 5 mmol/L, Cl = 43 ± 27 mmol/L.
• Potassium concentrations in all fluid samples were 3 to 5 times higher than typical serum potassium levels, indicating high K content in intestinal fluids.
• Statistical analysis showed significant differences (P<0.01 for Na and P<0.03 for Cl) in GR fluid compared to normal and strangulated SI fluids.

Interpretation and Implications

• The lower sodium and higher chloride concentrations in gastric reflux fluid relative to normal small intestinal fluid suggest that electrolyte composition of gastric reflux differs and this affects fluid and electrolyte balance in affected horses.
• High potassium concentrations in all intestinal fluids imply that losses of potassium during fluid removal or gastric reflux are substantial and should be considered during fluid therapy.
• Quantification of both fluid volume capacity and ionic composition is essential to accurately estimate water and ion losses in horses with small intestinal disorders.
• These results provide a basis for formulating fluid replacement protocols tailored to the specific electrolyte losses seen in gastric reflux and small intestinal diseases in horses.
• Effective fluid therapy based on this data could improve clinical outcomes by more precisely correcting dehydration and electrolyte imbalances.

Conclusions

• This study provides valuable reference data on small intestinal fluid capacity and ionic composition of intestinal fluids and gastric reflux in horses.
• Understanding these parameters assists veterinarians in estimating the extent of fluid and electrolyte losses during intestinal diseases, guiding better fluid replacement strategies.
• Future clinical fluid therapy can be optimized by considering the lower sodium, higher chloride, and elevated potassium concentrations occurring in gastric reflux fluid during small intestinal dysfunction.