Dehydration is a condition that occurs when the body loses more fluids than it takes in. The body needs a certain amount of fluids to function properly, and when it doesn’t have enough, it can lead to dehydration. It can result from various causes such as excessive sweating, vomiting, diarrhoea, fever or insufficient fluid intake.
Symptoms of dehydration can vary depending on the severity of the dehydration, but some common symptoms include:
SYMPTOMS
- Thirst
- Dry mouth
- Fatigue
- Dark yellow urine
- Dry skin
- Dizziness or lightheadedness
- Confusion
- Rapid heartbeat or breathing
Pathophysiology
Dehydration is a complex physiological process that involves multiple mechanisms at the cellular and systemic levels. These include:
Fluid Loss and Water Homeostasis
- Dehydration occurs when there is an imbalance between fluid intake and fluid loss. Fluid loss can result from sweating, respiratory water loss, urinary water loss or gastrointestinal fluid losses (vomiting, diarrhoea).
- Water homeostasis is regulated by various mechanisms, including the renin-angiotensin-aldosterone system (RAAS), vasopressin (antidiuretic hormone, ADH), and the thirst mechanism.
- RAAS activation leads to increased renal sodium and water reabsorption to preserve fluid volume.
- ADH release from the posterior pituitary promotes water reabsorption in the kidneys to maintain water balance.
- Thirst sensation is stimulated when there is increased plasma osmolality, leading to the desire to drink and restore fluid levels.
Cellular Response to Dehydration
- At the cellular level, dehydration triggers a series of adaptive responses to maintain cellular integrity and function.
- Cellular water loss leads to an increase in intracellular solute concentrations, causing cell shrinkage.
- Cells respond by activating osmolyte transporters and intracellular osmolyte synthesis to counterbalance the increased osmolality and restore cell volume.
- Aquaporins, specialised water channels in cell membranes, play a crucial role in regulating water movement in response to osmotic imbalances.
Electrolyte Imbalance
- Dehydration disrupts the balance of electrolytes in the body, leading to potential electrolyte imbalances.
- Sodium is a key electrolyte affected by dehydration. As fluid is lost, sodium concentration in the extracellular fluid increases, potentially causing hypernatraemia.
- Potassium, chloride and other electrolytes can also be affected, leading to imbalances that can impact cellular function and homeostasis.
Systemic Effects of Dehydration
- Decreased blood volume and blood pressure: Fluid loss reduces circulating blood volume, leading to reduced venous return and cardiac output, resulting in decreased blood pressure.
- Impaired tissue perfusion: Reduced blood flow and oxygen delivery to tissues can lead to cellular hypoxia and impaired organ function.
- Renal effects: Dehydration activates the RAAS and ADH systems to conserve water, leading to concentrated urine and reduced urine output. This can affect renal function and potentially contribute to the development of acute kidney injury (AKI).
Severe Dehydration
Severe dehydration can be life-threatening and requires immediate medical attention. Symptoms of severe dehydration include:
- Not urinating or very dark yellow urine
- Sunken eyes
- Dry, cool skin
- Rapid heartbeat or breathing
- Delirium or unconsciousness
Dehydration can be treated by drinking fluids, and in severe cases, may require the use of intravenous fluids. It’s important to note that once dehydration occurs it’s crucial to replenish not only the water but also the electrolytes lost.
It is also important to prevent dehydration by drinking enough fluids throughout the day, especially when it’s hot or you are physically active. Infants, young children, elderly, and those with chronic illness are particularly at risk for dehydration and should be closely monitored.