Why are hypertonic fluids used in short bowel syndrome?

Hypertonic Fluids in Short Bowel Syndrome Management

Hypertonic fluids should be limited in short bowel syndrome (SBS) patients, particularly those with high-output jejunostomies, as they exacerbate fluid losses and worsen dehydration by causing stomal losses of water and sodium. 1

Fluid Management Principles in SBS

Pathophysiology of Fluid Losses

• Patients with SBS without a colon may be "net secretors," losing more water and sodium from their stoma than they take in orally, especially those with <100 cm of residual jejunum 1
• Daily jejunostomy output can exceed 4 L in severe cases, leading to significant dehydration and electrolyte imbalances 1
• Jejunostomy effluent contains approximately 90-100 mmol/L of sodium, making sodium depletion a major concern 1, 2

Types of Fluids to Avoid

• Hypotonic fluids (water, tea, coffee, alcohol) should be restricted as they cause large stomal sodium losses 1
• Hypertonic fluids (fruit juices, sodas, commercial sip feeds) should be limited as they can cause stomal losses of both water and sodium 1
• A common misconception is that patients should drink large quantities of water, which actually increases ostomy output and creates a vicious cycle of fluid and electrolyte disturbances 1

Recommended Fluid Management Approach

Oral Rehydration Solutions (ORS)

• Use glucose-electrolyte oral rehydration solutions with sodium concentration of at least 90-100 mmol/L to enhance absorption and reduce secretion 1
• The World Health Organization (WHO) cholera solution (sodium 90 mmol/L) is commonly recommended, often without the potassium chloride component 1
• Patients should sip these solutions throughout the day in small quantities rather than consuming large volumes at once 1
• Commercial ORS products differ from sports drinks by having higher sodium content and lower sugar content 1

Fluid Restriction Protocol

• Total oral hypotonic fluid intake should be restricted to less than 500 ml daily 1
• Patients with marginally high stoma outputs (1-1.5 L) often benefit from oral fluid restriction (<1 L/day) combined with added dietary salt 1
• Monitor urine output (target at least 800-1000 ml/day) and random urine sodium (target >20 mmol/L) to ensure adequate hydration 1

Parenteral Support When Needed

• Intravenous normal saline (2-4 L/day) may be required for initial rehydration in patients with high-output stomas 1
• Parenteral fluids without macronutrients may be needed if stool output consistently exceeds fluid intake 1
• During hot weather, patients on overnight parenteral nutrition may require additional intravenous fluids during the day to prevent dehydration 1
• Patients with less than 100 cm of jejunum typically require parenteral saline, and those with less than 75 cm usually need parenteral nutrition and saline long-term 1

Monitoring and Adjustments

• Monitor changes in weight, laboratory results, stool/ostomy output, urine output, and complaints of thirst 1
• To correct hypokalaemia, first correct sodium/water depletion and normalize serum magnesium 1
• Hypomagnesaemia is common and is treated by correcting sodium depletion, providing magnesium supplements, and occasionally with oral 1-alpha hydroxycholecalciferol 1

Common Pitfalls to Avoid

• Administering too much intravenous fluid, which can readily cause edema due to high circulating aldosterone levels 1
• Encouraging patients to drink hypotonic solutions to quench thirst, which paradoxically increases sodium losses 1
• Failing to recognize that patients with SBS and a preserved colon have different fluid management needs than those with jejunostomies 1
• Overlooking the need for sodium restriction in patients with end-jejunostomies who are "net secretors" 1

By implementing these fluid management strategies, clinicians can help reduce morbidity, improve quality of life, and potentially reduce parenteral support requirements in patients with short bowel syndrome 3.