clinical dehydration

Etiology

• combined Na+ & H2O depletion
  • extra-renal losses
    • gastrointestinal
      • vomiting
      • diarrhea
      • gastrointestinal suction
      • fistula
    • abdominal sequestration
      • peritonitis
      • rapid accumulation of ascites
    • skin
      • sweating
      • burns
  • renal losses
    • renal disease
      • diuretic phase of acute renal failure
      • post-obstructive diuresis
      • chronic renal failure
      • salt-wasting renal tubular disease
    • diuretic excess
    • osmotic diuresis
      • diabetic glycosuria
      • urea
    • mineralocorticoid deficiency
      • Addison's disease
      • hypoaldosteronism
• isolated H2O depletion
  • extrarenal
    • skin (insensible losses)
    • lungs
  • renal
    • diabetes insipidus (central & nephrogenic)
  • hypothalamic dysfunction

Pathology

• diminished glomerular filtration (pre-renal azotemia)

Clinical manifestations

• diminished skin turgor
• dry mucous membranes
• resting supine tachycardia
• orthostatic hypotension
• supine hypotension with more severe dehydration
• lethargy, weakness & confusion, especially in the elderly
• oliguria
• dizziness (GRS9)
• dehydration & delirium is common in the elderly

Laboratory

• hematocrit may be increased
• serum protein may be increased
• serum Na+ may be increased or decreased
• serum creatinine & urea nitrogen are generally increased (pre-renal azotemia)
• BUN/creatinine ratio generally > 20
• urinary Na+
  • < 10 mmol/L with extra-renal losses
  • > 20 mmol/L with renal or adrenal disorders (until Na+ depletion becomes severe)

Complications

• dehydration associated with acute renal failure demonstrated by rising serum creatinine may be associated with diminished clearance of renally cleared drugs
  • elevated gabapentin levels due to diminished clearance may manifest as dizziness

Management

• modest dehydration may be corrected by oral fluids in patients without gastrointestinal disorders
• intravenous fluids
  • normal saline (0.85%) is generally fluid of choice
  • 2-3 liters is generally adequate for moderate dehydration
  • larger volumes may be required for severe dehydration
• correct electrolyte disturbances
• (hypodermoclysis) subcutaneous infusion of fluid
  • up to 1500 mL of fluid (i.e. saline) may be infused daily into subcutaneous tissue (i.e. thigh, abdominal wall, thorax or back)

More general terms

• hypovolemia (extracellular volume depletion)

Additional terms

• clinical hydration
• hypernatremia
• hyponatremia
• lack of water