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Questions and Answers
What is the normal total body water (TBW) for men?
What is the normal total body water (TBW) for men?
What is the major cation in the extracellular fluid (ECF)?
What is the major cation in the extracellular fluid (ECF)?
The normal osmolality of body fluids ranges from _____ mOsm/kg water.
The normal osmolality of body fluids ranges from _____ mOsm/kg water.
285-295
What does hyponatremia indicate?
What does hyponatremia indicate?
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Hyponatremia is only a concern for elderly patients.
Hyponatremia is only a concern for elderly patients.
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What is a common complication due to rapid correction of hyponatremia?
What is a common complication due to rapid correction of hyponatremia?
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Match the following fluid and electrolyte disorders with their corresponding definitions:
Match the following fluid and electrolyte disorders with their corresponding definitions:
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What is the essential criterion for diagnosing SIADH?
What is the essential criterion for diagnosing SIADH?
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A plasma sodium concentration of less than _____ mEq/L indicates hyponatremia.
A plasma sodium concentration of less than _____ mEq/L indicates hyponatremia.
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Study Notes
Composition of Fluid Compartments & Total Body Water
- Average fluid composition in the body is 55% - 60%.
- Total Body Water (TBW) percentages by demographic:
- Men: 60% of body weight
- Women: 55% of body weight
- Pediatrics: 70% of body weight
- Geriatrics: 50% of body weight
Distribution of Water
- Major cation in intracellular fluid (ICF): potassium (K).
- Major cation in extracellular fluid (ECF): sodium (Na).
- Sodium-potassium pump regulates cation concentration difference between ICF and ECF.
- Hypothalamus controls TBW and sodium management.
- Osmoreceptors stimulate ADH secretion from the posterior pituitary gland.
- ADH increases water reabsorption by upregulating AQP2 channels in renal collecting ducts.
Plasma Osmolality
- Defined as the number of osmoles per kilogram of water (mOsm/kg).
- Normal osmolality of body fluids: 285-295 mOsm/kg.
- Glucose conversion from mg/dL to mmol/L requires division by 18.
Introduction to Sodium and Water Disorders
- Hyponatremia: low plasma sodium concentration (< 135 mEq/L).
- Hypernatremia: high plasma sodium concentration, resulting from too much sodium or too little water.
- Dysvolemia: sodium disorder; dysnatremia: water/tonicity disorder.
- Hypovolemia: sodium deficit (dehydration); hypervolemia: sodium excess.
Hyponatremia Overview
- Common, especially among the elderly (15-20% inpatient, 7-11% outpatient).
- Associated risks: cognitive decline, falls, fractures, gait instability, mortality, kidney stones.
- Management complications can arise from hyponatremia itself or from rapid correction attempts.
Classification of Hyponatremia
- Mild: serum sodium between 130 and 135 mmol/L.
- Moderate: serum sodium between 125 and 129 mmol/L.
- Severe: profound drops leading to significant clinical manifestations.
SIADH (Syndrome of Inappropriate Antidiuretic Hormone Secretion)
- Characterized by hypoosmolar hyponatremia (plasma osmolality < 100 mOsm/kg).
- Essential criteria include:
- Urinary sodium > 30 mmol/L with normal dietary intake.
- Absence of pituitary, thyroid, adrenal, or renal insufficiency.
- Lack of diuretic use.
- Supplemental criteria include:
- Low serum uric acid and normal serum urea/creatinine levels.
- Failure to correct hyponatremia with saline infusion, improvement through fluid restriction.
Pseudo-hyperkalemia
- Defined as an artificially elevated plasma potassium concentration due to cellular movement.
- Contributing factors:
- Prolonged tourniquet use or repeated fist clenching causing acidosis.
- Delay in processing blood samples leading to hemolysis and potassium leakage.
- Leukocytosis and thrombocytosis can also affect test results.
- Importance of evaluating renal function and reviewing medication lists.
Renal Function Assessment
- Estimations using MDRD equation, Cockcroft-Gault equation, and 24-hour creatinine clearance.
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Description
This quiz covers the composition of fluid compartments, total body water, and its distribution in the human body according to age and gender.
