Types of Dehydration
Dehydration is classified into three main types based on serum sodium concentration and osmolality: isotonic (isonatremic), hypertonic (hypernatremic), and hypotonic (hyponatremic) dehydration. 1
Hypertonic (Hypernatremic) Dehydration
- This occurs when water loss exceeds sodium loss, resulting in elevated serum sodium and hyperosmolality 1
- Develops from defects in two major homeostatic mechanisms: thirst sensation and arginine vasopressin (AVP) release 1
- Causes depletion of both intracellular and extracellular fluid compartments 1
- Clinical signs include dry mucous membranes, tachycardia, and weakness 2
- In Liddle syndrome patients, hypernatremia can occur as a manifestation of the disease itself 3, though this is less common than hypokalemia
Hypotonic (Hyponatremic) Dehydration
- Results when sodium loss exceeds water loss, leading to reduced serum sodium and hyposmolality 1
- Can occur in salt depletion states, edematous conditions, and syndrome of inappropriate antidiuretic hormone secretion (SIADH) 1
- Differential diagnosis requires careful assessment of extracellular fluid volume and urine sodium concentration 1
- Treatment depends on the underlying pathophysiology: isotonic saline for salt depletion versus water restriction for mild cases in cirrhosis 1
- Severe symptomatic hyponatremia requires hypertonic saline therapy, sometimes with intravenous furosemide 1
Isotonic (Isonatremic) Dehydration
- Proportional loss of water and sodium, maintaining normal serum sodium levels 1
- Most common type in acute gastroenteritis with diarrhea and vomiting 4, 5
- Treatment involves isotonic crystalloid solutions such as Lactated Ringer's solution or normal saline 4
Special Considerations in Liddle Syndrome
- Liddle syndrome typically presents with volume expansion rather than dehydration due to excessive sodium reabsorption 6, 3
- However, dehydration with hypokalemia can be an initial manifestation, particularly in infancy 7
- The paradox occurs because while total body sodium is increased, patients may present with dehydration symptoms during acute illness or before diagnosis 7
- Persistent hypernatremia and hypokalemia in Liddle syndrome reflect the underlying pathophysiology of excessive epithelial sodium channel activity 3
Clinical Pitfall to Avoid
Do not assume Liddle syndrome patients cannot develop dehydration—while the disease causes sodium retention and volume expansion, acute illnesses or inadequate fluid intake can still lead to dehydration states, particularly hypertonic dehydration given the tendency toward hypernatremia 7, 3