The Purpose and Uniqueness of St Mark's Solution
St Mark's solution is a specialized oral rehydration solution (ORS) developed at St Mark's Hospital in London to meet the specific needs of patients with high-output stomas, intestinal fistulas, or short bowel syndrome. For these individuals, standard oral rehydration solutions are often unsuitable due to their electrolyte composition. The intestinal malabsorption in these conditions necessitates a solution with a specific sodium-to-glucose ratio to maximize fluid and electrolyte absorption.
A central feature of St Mark's solution is its potassium-free formula, which is critical for patients at risk of hyperkalemia (high blood potassium). Standard World Health Organization (WHO) oral rehydration solutions, and many commercial ORS products, contain potassium, which can be dangerous for this patient group. The formulation is designed to be isotonic, meaning it has a solute concentration similar to blood, which promotes more efficient absorption of salt and water. The typical ingredients include:
- Glucose powder
- Sodium chloride (table salt)
- Sodium bicarbonate (baking soda)
These ingredients are dissolved in a specific volume of water to provide a high-sodium, potassium-free electrolyte mix that helps counteract the significant fluid and sodium losses common with high-output stomas.
Equivalent and Alternative Oral Rehydration Solutions
For those who cannot access or tolerate St Mark's solution, several alternatives exist, though they must be used under medical supervision to ensure they meet the specific needs of the patient. The primary goal of any equivalent is to replicate a high-sodium, potassium-free profile when necessary. It is important to note that while some equivalents can be made at home, commercial options often provide more consistent and accurate measurements.
Alternative Homemade Solutions
One common alternative is the UHB (University Hospitals Bristol) solution, which is considered equally effective as St Mark's but has a slightly different taste. The key difference lies in its bicarbonate source:
- UHB Solution: Replaces sodium bicarbonate with sodium citrate. Sodium citrate is sometimes preferred for its less bitter taste, which can improve patient compliance. The ingredients typically include glucose powder, sodium chloride, and sodium citrate.
Additionally, simpler homemade recipes exist for general rehydration, though they lack the specialized profile of St Mark's solution. The World Health Organization (WHO) provides a basic oral rehydration salts recipe for general use in emergency situations, but it does contain potassium. For patients who require a potassium-free solution, these basic versions are not suitable.
Commercial Oral Rehydration Products
Commercial rehydration tablets or powders, such as Dioralyte or O.R.S Hydration Tablets, can sometimes serve as an alternative, but only with careful modification and medical guidance.
Caution: These products generally contain potassium and a lower concentration of sodium than St Mark's solution. To approximate a higher sodium concentration, they may be used in a more concentrated mixture (e.g., using more sachets or tablets in a given volume of water). However, this approach is not suitable for patients who must avoid potassium, as it significantly increases the potassium intake. It is imperative to discuss this with a healthcare professional before attempting any modification of commercial products.
Unsuitable Alternatives: The Danger of Sports Drinks
Sports drinks are frequently mistaken for suitable rehydration solutions but are explicitly discouraged for clinical rehydration needs. They have a high sugar content and a low sodium concentration, making them inefficient for rehydration in patients with malabsorption issues. Drinking large amounts of low-sodium fluids can actually worsen dehydration by drawing more sodium and water out of the body and into the gut.
Comparison of Oral Rehydration Solutions
| Feature | St Mark's Solution | Standard WHO ORS | Modified Commercial ORS | Sports Drinks (e.g., Gatorade) |
|---|---|---|---|---|
| Sodium Content | High | Medium | Variable, often lower than St Mark's | Low |
| Potassium Content | Potassium-free | Contains potassium | Contains potassium | Low to trace amounts |
| Bicarbonate Source | Sodium Bicarbonate or Sodium Citrate | Sodium Citrate | Variable | N/A (often buffered with phosphates) |
| Primary Use | High stoma/fistula output, short bowel syndrome | General diarrhea management, severe dehydration | General dehydration, if potassium isn't a concern | Replenishing fluids post-exercise, not clinical use |
| Availability | Not commercially available; prepared at home or in hospital pharmacy | Packets or pre-mixed solution | Readily available at pharmacies and supermarkets | Readily available in stores |
Considerations for Creating an Equivalent
If creating a homemade equivalent under medical guidance, precision is key. A few important points to remember:
- Use Proper Measuring Tools: Always use standard metric measuring tools (e.g., measuring spoons and cups) to ensure the correct concentration.
- Use Accurate Ingredients: Use glucose powder (dextrose), not table sugar (sucrose), as glucose is more efficiently absorbed in the specific mechanism targeted by ORS. Ensure sodium bicarbonate or sodium citrate (for UHB) is fresh and of appropriate grade.
- Discard After 24 Hours: Homemade ORS should be made fresh daily and any unused solution discarded after 24 hours to prevent bacterial growth.
- Improve Palatability: The high salt content can be unpalatable. Chilling the solution, freezing it into a slushy, or adding a small amount of sugar-free cordial can help, but avoid additions that would alter the electrolyte balance.
Conclusion
While no single product is a perfect, universal equivalent for St Mark's solution, viable alternatives exist for patients under the right clinical guidance. Homemade versions, such as the UHB solution, offer a nearly identical electrolyte profile with a potentially milder taste. Commercial ORS products may require significant modification and are not suitable for all patients due to their potassium content. The most important takeaway is that specialized clinical conditions require specialized nutritional approaches. Patients must consult with their doctor or dietitian to determine the most appropriate and safe rehydration strategy. Understanding the specific components and purpose of St Mark's solution is the first step toward finding a safe and effective approach for managing complex hydration needs.
