Definition: Oral Rehydration Therapy (ORT) is the administration of fluid by mouth to prevent or correct dehydration resulting from fluid losses, primarily diarrhea.
Basis of ORT: Relies on the physiological principle of coupled transport of sodium and glucose in the intestinal epithelium (enterocytes).
Significance: Termed “the most important medical advance of the 20th century,” significantly reducing global infant mortality from diarrheal diseases.
PHYSIOLOGY AND MECHANISM OF ACTION
SGLT-1 Cotransporter: Sodium-Glucose Luminal Transporter-1 (SGLT-1) on the apical membrane of mature enterocytes in the villi.
Mechanism: Transports one molecule of glucose and two ions of sodium intracellularly. This process is functionally independent of cAMP levels and remains intact even during enterotoxin-induced secretory diarrhea (e.g., Cholera).
Osmotic Gradient: The intracellular accumulation of Na+ and glucose creates an osmotic gradient, driving the passive absorption of water and electrolytes through paracellular pathways (solvent drag).
Optimal Ratio: The system operates optimally when the molar ratio of glucose to sodium is approximately 1:1 to 1.4:1.
TYPES OF ORS: EVOLUTION AND COMPOSITION
1. Conventional ORS (Standard WHO ORS - 1975)
Background: Formulated primarily to treat severe dehydrating diarrhea like cholera.
Composition (mmol/L):
Sodium: 90
Potassium: 20
Chloride: 80
Base (Citrate): 10
Glucose: 111
Total Osmolarity: 311 mOsm/L
Advantages: Highly effective in preventing mortality in cholera; simple, inexpensive.
Limitations/Drawbacks:
Hyperosmolarity: Slightly hyperosmolar relative to plasma (280-295 mOsm/L).
Osmotic Diarrhea Risk: In non-cholera diarrhea (e.g., Rotavirus), where stool Na+ loss is lower (30-40 mEq/L), unabsorbed glucose and sodium create an intraluminal osmotic penalty, leading to transient worsening of diarrhea.
Clinical Outcomes: Did not reduce stool volume, duration of diarrhea, or the incidence of vomiting, leading to poor compliance and parental dissatisfaction.
Hypernatremia Risk: Increased risk of hypernatremic dehydration in infants with viral gastroenteritis.
2. WHO Reduced Osmolarity ORS (Current Standard - 2002)
Background: Developed to address the hyperosmolarity of conventional ORS while maintaining the optimal Na:Glucose cotransport ratio.
Composition (mmol/L or mEq/L):
Sodium: 75
Potassium: 20
Chloride: 65
Base (Citrate): 10
Glucose: 75
Total Osmolarity: 245 mOsm/L
Advantages (Proven by robust RCTs and Meta-analyses):
Reduces stool output by ~20%.
Reduces incidence of vomiting by ~30%.
Reduces the need for unscheduled IV fluid therapy by ~33%.
Decreases the risk of hypernatremia.
Equally effective as standard ORS in cholera in adults and children.
Recommendation: Currently the single universal ORS recommended by WHO and UNICEF for all ages and all types of diarrheal diseases.
3. Super ORS (Polymer-Based and Amino Acid-Based ORS)
Concept: Designed to increase the delivery of cotransport substrates (glucose/amino acids) without increasing the osmolar load.
A. Polymer-Based ORS (e.g., Rice-based ORS):
Formulation: Replaces 20g/L of glucose with 50g/L of precooked rice powder (or wheat, maize, sorghum).
Mechanism: Starch macromolecules are slowly digested by amylase at the brush border, gradually releasing glucose. This ensures continuous substrate for SGLT-1 without spiking intraluminal osmolarity. Also provides more calories.
Efficacy in Cholera: Significantly superior to conventional ORS in reducing stool volume (by ~30-50%) and duration.
Efficacy in Non-Cholera (Viral) Diarrhea: No significant advantage over WHO reduced osmolarity ORS in non-cholera diarrhea. Hence, not routinely recommended over the 245 mOsm/L formulation globally.
B. Amino Acid-Based ORS:
Formulation: Addition of specific amino acids (Glycine, L-Alanine, Glutamine).
Mechanism: Utilizes distinct, separate amino acid-sodium cotransporters in the gut, working additively with SGLT-1.
Status: Marginal clinical benefit; high cost and lack of stability limit widespread use.
C. Zinc-Fortified ORS: Adding Zinc (to achieve 10-20 mg/day) directly to the ORS packet to ensure compliance with diarrhea treatment guidelines.
4. ReSoMal (Rehydration Solution for Malnutrition)
Background: Specially formulated for children with Severe Acute Malnutrition (SAM) who have altered body composition (total body sodium is high, but intracellular potassium and magnesium are severely depleted).
Plan A (No Dehydration): Used for prevention. Home-based fluids or ORS. Dose: <2 yrs (50-100 ml post-stool), 2-10 yrs (100-200 ml post-stool), >10 yrs (as much as desired).
Plan B (Some/Mild-Moderate Dehydration): ORS is the definitive treatment. Administered at 75 ml/kg over 4 hours. Reassess after 4 hours.
Outcome: Treats 90-95% of acute diarrhea cases without the need for IV fluids.
2. Cholera
Rice-based ORS is highly efficacious and considered the ideal oral fluid for cholera, rapidly replacing massive secretory losses.
Reduced osmolarity ORS is fully sanctioned and effective.
3. Severe Acute Malnutrition (SAM) with Dehydration
Standard ORS is contraindicated in SAM due to the risk of sodium toxicity and heart failure.
Protocol: Use ReSoMal. 5 ml/kg every 30 minutes for the first 2 hours, then 5-10 ml/kg/hr for the next 4-10 hours, alternating with therapeutic feeding (F-75).
4. Short Bowel Syndrome (SBS) / High Stoma Outputs
Reduced osmolarity ORS may lead to net sodium loss in SBS because the shortened jejunum requires a higher sodium concentration gradient for absorption.
Management: Often require customized, hypernatremic ORS (Sodium 90-120 mEq/L) to prevent chronic sodium depletion and failure to thrive. Standard WHO ORS (1975) is sometimes utilized here.
5. Dengue Fever
Role: Crucial during the febrile and critical (plasma leakage) phases.
Application: WHO guidelines advocate aggressive oral rehydration with ORS or fruit juices to maintain intravascular volume, prevent progression to Dengue Shock Syndrome (DSS), and minimize the requirement for IV crystalloids.
6. Burns
In mild to moderate pediatric burns (TBSA < 10-15%), ORS is highly effective for initial resuscitation and fluid maintenance, especially in resource-limited settings where IV access is delayed.
LIMITATIONS AND CONTRAINDICATIONS TO ORT
Absolute Contraindications: Severe dehydration with impending/actual hemodynamic shock (requires immediate IV fluids - Plan C), paralytic ileus, mechanical bowel obstruction, intestinal perforation.
Relative Contraindications (Indications to switch to IV):
Intractable, continuous vomiting (failure of ORT).
High stool output (> 10 ml/kg/hr) outstripping oral intake capacity.
