6.3 Disorders of fluid balance and drinking behavior

Fluid balance disorders can seriously mess with your body's hydration levels. From diabetes insipidus causing excessive peeing to SIADH making you retain too much water, these conditions can wreak havoc on your thirst and drinking behaviors.

Understanding these disorders is crucial for grasping how our bodies regulate fluids. Whether it's dealing with dehydration or overhydration, knowing the causes, symptoms, and treatments helps us appreciate the delicate balance our bodies maintain when it comes to thirst and drinking.

Fluid balance disorders

Diabetes Insipidus and SIADH

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• Diabetes insipidus (DI) causes excessive urine production due to insufficient antidiuretic hormone (ADH) or kidney resistance to ADH
  • Central DI results from inadequate ADH production in the hypothalamus
  • Nephrogenic DI occurs when kidneys fail to respond to ADH
• Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) results from excessive ADH release, leading to water retention and hyponatremia
• DI symptoms include polyuria, polydipsia, and dehydration
• SIADH symptoms manifest as nausea, headache, confusion, and in severe cases, seizures or coma
• DI causes stem from head trauma, tumors, or genetic factors
• SIADH triggers include certain medications (SSRIs, carbamazepine), cancers (lung, pancreatic), or central nervous system disorders (meningitis, encephalitis)
• Diagnosis involves assessing urine osmolality, serum sodium levels, and conducting water deprivation tests or ADH stimulation tests
  • Urine osmolality in DI typically low (< 300 mOsm/kg)
  • Serum sodium in SIADH usually low (< 135 mEq/L)

Other Fluid Balance Disorders

• Hypernatremia results from excessive water loss or inadequate water intake
  • Causes include severe diarrhea, excessive sweating, or limited access to water
  • Symptoms include thirst, confusion, muscle twitching, and seizures
• Hyponatremia occurs when sodium levels in the blood are abnormally low
  • Can result from conditions like heart failure, cirrhosis, or excessive water intake
  • Symptoms range from nausea and headache to seizures and coma in severe cases
• Edema involves excessive fluid accumulation in body tissues
  • Can be localized (peripheral edema) or generalized (anasarca)
  • Causes include heart failure, kidney disease, or liver cirrhosis

Factors in excessive drinking

Physiological Causes of Polydipsia

• Polydipsia manifests as excessive or abnormal thirst leading to increased fluid intake, often exceeding 3 liters per day in adults
• Diabetes mellitus contributes to polydipsia through increased blood glucose levels and subsequent osmotic diuresis
• Diabetes insipidus leads to polydipsia due to the inability to concentrate urine, resulting in excessive water loss
• Certain medications cause dry mouth (xerostomia) or increased urination, prompting excessive fluid intake
  • Anticholinergics (atropine, scopolamine)
  • Diuretics (furosemide, hydrochlorothiazide)
• Chronic alcohol use promotes polydipsia through its diuretic effects and impact on ADH secretion
  • Alcohol inhibits ADH release, leading to increased urine production and thirst

Psychological Factors in Excessive Drinking

• Psychogenic polydipsia associates with mental disorders, potentially resulting from a malfunctioning thirst mechanism in the hypothalamus
• Anxiety disorders and obsessive-compulsive behaviors can lead to compulsive water drinking as a coping mechanism or ritualistic behavior
• Schizophrenia strongly correlates with polydipsia, possibly due to altered dopamine signaling affecting thirst perception and water regulation
  • Up to 20% of chronic schizophrenia patients exhibit polydipsia
• The brain's reward system may play a role in excessive drinking behavior
  • Some individuals experience a pleasurable sensation from drinking large quantities of water
  • This reinforcement can lead to habitual overconsumption

Consequences of dehydration vs overhydration

Chronic Dehydration Effects

• Decreased cognitive function impairs attention, memory, and decision-making abilities
• Impaired physical performance reduces endurance, strength, and coordination
• Increased risk of kidney stones and urinary tract infections due to concentrated urine
• Electrolyte imbalances, particularly hyponatremia and hyperkalemia, lead to cardiac arrhythmias and muscle weakness
• Exacerbation of chronic conditions such as hypertension and diabetes
• Increased risk of heat-related illnesses (heat exhaustion, heat stroke)
• Disrupted hormonal balance affects ADH and aldosterone levels, which regulate fluid homeostasis

Overhydration Consequences

• Water intoxication results in hyponatremia, causing cerebral edema, seizures, and in severe cases, death
  • Serum sodium levels below 120 mEq/L can be life-threatening
• Increased intracranial pressure potentially causes headaches, confusion, and altered mental status
• Strain on the cardiovascular system leads to increased blood volume and potential heart failure in susceptible individuals
• Disruption of the body's hormonal balance affects ADH and aldosterone levels
• Gastrointestinal discomfort, including nausea and vomiting
• Muscle cramps and weakness due to electrolyte imbalances
• In extreme cases, can lead to hypothermia due to dilution of electrolytes involved in temperature regulation

Managing fluid balance disorders

Treatment Strategies for Specific Disorders

• Diabetes insipidus management involves hormone replacement therapy with desmopressin (DDAVP) for central DI
  • Nephrogenic DI treatment focuses on addressing underlying causes and may include thiazide diuretics
• SIADH treatment includes fluid restriction, salt supplementation, and in some cases, vasopressin receptor antagonists (tolvaptan)
  • Fluid restriction typically limits intake to 800-1000 mL/day
• Psychogenic polydipsia treatment involves behavioral interventions and cognitive-behavioral therapy
  • In some cases, antipsychotic medications address underlying mental health conditions
• Fluid intake monitoring and regulation are crucial in managing polydipsia
  • Often involves a multidisciplinary approach with mental health professionals and nephrologists
  • May include setting fluid intake limits and scheduled voiding

General Management Approaches

• Electrolyte replacement and careful fluid management are essential in treating both dehydration and overhydration
  • Close monitoring of serum sodium levels guides treatment
• Education on proper hydration practices and recognition of thirst cues prevents and manages fluid balance disorders
  • Teaching patients to monitor urine color as an indicator of hydration status
• In severe cases of fluid imbalance, hospitalization may be necessary
  • Intravenous fluid administration for dehydration
  • Dialysis to correct severe electrolyte abnormalities
• Lifestyle modifications can help manage fluid balance
  • Reducing caffeine and alcohol intake
  • Adjusting diet to include appropriate sodium and potassium levels
• Regular follow-up and monitoring ensure long-term management of fluid balance disorders
  • May include periodic blood tests and urine analysis