Fluid And Electrolyte Balance Flashcards
What is renal hypovolaemia?
A condition characterized by low blood volume in the renal system.
It can lead to decreased renal perfusion and impaired kidney function.
What is osmotic diuresis?
Diuresis caused by the presence of substances in the renal tubules that inhibit water reabsorption, which can be endogenous (like glucose and urea) or exogenous (like mannitol).
It leads to increased urine output.
Name two types of pharmacologic diuretics.
- Thiazide diuretics
- Loop diuretics
These are used to promote diuresis in various medical conditions.
What is hypokalaemia?
A condition where plasma potassium levels are less than 3.5 mmol/L.
It can result from redistribution of potassium or true potassium deficits.
List some symptoms of hyperkalemia.
- Mental confusion
- Weakness
- Tingling
- Flaccid paralysis of extremities
- Weakness of respiratory muscles
Severe hyperkalemia can lead to cardiac arrest.
What are the consequences of disturbance in potassium homeostasis?
Serious consequences include muscle weakness, irritability, and paralysis.
Hypokalemia is particularly dangerous when plasma K+ concentrations drop below 3.0 mmol/L.
What is the reference interval for plasma potassium?
3.5-5.5 mmol/L.
Only 1.5% to 2% of total body potassium is present in the extracellular fluid.
What causes central diabetes insipidus?
Decreased or absent ADH secretion due to causes like head trauma, hypophysectomy, or pituitary tumors.
This condition leads to excessive urination and thirst.
How is nephrogenic diabetes insipidus caused?
Renal resistance to ADH due to drugs (like lithium), sickle cell anemia, or Sjögren syndrome.
It results in dilute urine and hypernatremia.
What is hypervolemic hypernatremia?
A condition where there is a net gain of water and sodium, with sodium gain exceeding water gain.
It is often seen in patients receiving hypertonic saline.
What is the significance of urine Na+ concentration in diagnostic evaluation of hypovolaemia?
Urine Na+ concentration is often >20 mM in renal causes of hypovolemia, indicating renal loss of sodium.
A lower concentration suggests non-renal causes.
What is the primary cause of hyperkalemia?
Hyperkalemia can result from redistribution, increased intake, or increased retention of potassium.
Preanalytical conditions can also cause pseudohyperkalemia.
True or False: Hypernatremia is always hyperosmolar.
True.
Hypernatremia occurs when plasma Na+ levels exceed 150 mmol/L.
What are the criteria for diagnosing SIADH?
- Decreased serum osmolality (< 275 mmol/L)
- Increased urine osmolality (> 100 mOsm/Kg)
- Increased urine sodium (>20 mmol/L)
- No other cause for hyponatremia
This helps differentiate SIADH from other conditions.
What is the management goal for hypovolemia?
To replace fluid loss and ongoing losses with appropriate fluid, and correct electrolyte and acid-base disorders.
Normal saline is often the resuscitation fluid of choice.
What indicates renal losses of potassium in a hypokalemic setting?
Urine excretion exceeding 25 to 30 mmol/L.
This suggests that kidneys are the primary source of potassium loss.
What is the typical urine osmolality in non-renal causes of hypovolemia?
> 450 mOsm/kg.
This indicates a strong renal response to conserve sodium and water.
What are some causes of redistribution hyperkalemia?
- Acidosis
- Tissue hypoxia
- Insulin deficiency
- Massive intravascular hemolysis
- Severe burns
- Violent muscular activity
- Tumor lysis syndrome
These conditions cause potassium to shift from intracellular to extracellular fluid.
What are common symptoms of hypovolemia?
Fatigue, weakness, thirst, postural dizziness, oliguria, confusion
Symptoms of hypovolemia are nonspecific.
What physical examination findings indicate hypovolemia in adults?
Decreased jugular venous pressure (JVP), orthostatic tachycardia, orthostatic hypotension
Orthostatic tachycardia is an increase of >15–20 beats/min upon standing.
What causes excessive renal water excretion leading to hypovolemia?
Decreased circulating vasopressin, renal resistance to AVP
This occurs in central and nephrogenic diabetes insipidus.
Define hyponatremia.
A plasma Na+ concentration <135 mM
Reference interval for Na+ is 135-145 mM.
What is a common cause of hyponatremia in hospitalized patients?
Increase in circulating AVP and/or increased renal sensitivity to AVP combined with free water intake
Hyponatremia occurs in up to 22% of hospitalized patients.
What are the clinical manifestations of hyponatremia?
Nausea, generalized weakness, mental confusion
Symptoms are due to changes in osmolality.
What are the categories of hyponatremia?
Hypo-osmotic, Isosmotic (pseudohyponatremia), Hyperosmotic
Measurement of plasma osmolality is important in assessing hyponatremia.
What defines pseudohyponatremia?
Serum sodium <135 mmol/L with normal serum osmolality (280 to 300 mOsm/kg)
It is an artifact from blood sample processing.
What are common causes of normal volume hyponatremia?
Syndrome of inappropriate ADH (SIADH), primary polydipsia, hypothyroidism
These conditions lead to normal volume status despite low sodium.
What causes dilutional hyponatremia?
Excess water retention, often detected as edema
Seen in advanced renal failure, congestive heart failure, hepatic cirrhosis, nephrotic syndrome.
What is the renal loss of Na+ associated with?
Salt wasting nephropathies, osmotic diuresis, use of diuretics, adrenal insufficiency
Renal loss is likely if urine Na+ is elevated (>20 mmol/L).
What indicates extrarenal loss of Na+?
Low urine Na+ (<10 mmol/L) and fractional excretion of sodium <1
Extrarenal loss can occur from GI fluid loss or skin loss.
What is hypo-osmotic hyponatremia characterized by?
Low plasma sodium with accompanying low plasma osmolality
It may be depletional or dilutional with varying volume status.
What causes hyperosmotic hyponatremia?
Increased quantities of other solutes in the ECF
Seen in hyperglycemia, mannitol infusion, and uremia.
What are non-renal causes of hypovolemia?
Fluid loss from gastrointestinal tract, skin, respiratory system
Accumulations can also occur in specific tissue compartments.
How does plasma chloride concentration relate to sodium concentration?
Cl− concentrations generally follow those of Na+
Useful in the differential diagnosis of acid-base disturbances.
What is the formula for calculating plasma osmolality?
2({Na} + {K}) + ({Glucose} + {Urea})
This calculation is essential for understanding plasma osmolality.
What is osmolality?
Estimation of osmolar concentration of plasma expressed as mOsm/kg
Normal osmolality of extracellular fluid is 280-295 mOsm/kg.
What is fluid homeostasis?
Mechanisms to maintain total body water and salt content constant
Achieved through glomerular filtration and renal excretion.
What factors determine fluid movement between compartments?
Colloid osmotic pressure, capillary hydrostatic pressure
Movement is influenced by Starling forces.
What is the role of vasopressin in fluid balance?
Regulates water retention to maintain plasma osmolality between 285-295 mOsm/kg
It is crucial for maintaining water balance.
What is osmolality?
Osmolality is the concentration of a solution expressed as the total number of solute particles per kilogram.
Osmolality is typically measured in clinical laboratories using an osmometer.
What is the normal osmolality range of extracellular fluid?
280-295 mOsmol/kg.
What are the mechanisms that ensure water balance in the body?
- Vasopressin secretion
- Water ingestion
- Renal water transport
What is the function of vasopressin (AVP)?
AVP acts on renal V2-type receptors in the thick ascending limb of Henle and principal cells of the collecting duct, stimulating water absorption.
What major factors control sodium balance?
- Renal blood flow
- Aldosterone
What is the role of aldosterone?
Aldosterone is a mineralocorticoid hormone that promotes sodium retention and the loss of potassium and hydrogen ions at the distal renal tubule.
What does hypovolaemia refer to?
A state of combined salt and water loss leading to contraction of the extracellular fluid volume (ECFV).
What are the causes of decreased serum osmolality?
- Syndrome of inappropriate ADH secretion (SIADH)
- Overhydration
- Hyponatraemia
- Adrenocortical insufficiency
- Sodium loss (diuretic or low-salt diet)
What is the difference between osmolality and osmolarity?
Osmolality is the concentration of solute particles per kilogram of solvent, while osmolarity refers to particles of solute per liter of solution.
What is the formula for calculating osmolarity?
Calculated osmolarity = 2(Na+) + 2(K+) + Glucose + Urea (all in mmol/L).
What is a normal osmotic gap?
Less than 10-15 mOsmol/kg.
What condition is characterized by hyposecretion of ADH?
Diabetes insipidus.
What stimulates the secretion of antidiuretic hormone (ADH)?
Increased osmolality in the blood.
What effect does a low serum osmolality have on ADH release?
It suppresses the release of ADH, leading to decreased water reabsorption.
What is the significance of the osmotic gap?
It indicates the presence of other osmotically active solutes not accounted for in calculated osmolality.
What is the calculated osmolarity formula excluding potassium?
Calculated osmolarity = 2(Na+) + Glucose + Urea (all in mmol/L).
True or False: Osmolarity has largely replaced osmolality in clinical discussions.
False.
