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Flashcards in Electrolytes Deck (52)
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Where is sodium found?

55% in plasma and other extracellular fluid
40% in bone as sodium hydroxyapatite
2-5% in organs and cells


Which electrolyte is the most abundant within ECF?

Sodium - 90% of the extracellular cations


What is sodiums role within ECF?

Maintaining plasma and extracellular fluid volume.


What is the role of ADH in the prevention of water depletion and hyperosmolaority?

Renal concentration and water retention - acts to fight water depletion and hyperosmolarity.
Thirst centre in the posterior pituatary release ADH - acts to conserve water and therefore dilutes sodium.


What is tonicity?

The ability of a solution to change the shape or tone of a cell by changing the volume of internal water.


Define osmosis

The movement of water molecules from an area of high concentration to and area of low concentration through a partially permeable membrane. It is a passive process


What effect does hypertonic solutions have on cells?

Water will move from the intracellular space and into the extracellular space as there is a higher water content within the cell, meaning that the cell with shrink/shrivel in size


What effect dow hypotonic solutions have on cells?

Water will move from the extracellular space into the intracellular space through osmosis leading to the cell swelling in size and potentially rupturing.


What effect dose dietary sodium have on the kidneys and intestines?

When dietary sodium is high, less is absorbed through the GI tract and renal excretion increases, the opposite occurs with low sodium intake.


What causes hypovolemic hyponatremia?

Water and sodium levels both decrease in the extracellular fluid - sodium loss is greater.
Non-renal losses - losses of fluid - D&V, fistulas, gastric suctioning, CF, burns and wounds
Renal losses - osmotic diuresis, salt loosing nephritis, adrenal insufficency, diuretic use.


What is hypervolemic hyponatremia?

As sodium is a concentration, the concentration of water is greater than that of the sodium - the extracelluar fluid is more dilute.
Heart failure, nephroitic syndrome, excessive administration of hypotonic IV fluids


What is euvolemic hyponatremia?

Difficult to diagnose
increase in total body water however the sodium concentration remains constant.
glucocorticoid therapy - impaired renal function
Hypothyroidism - thyroid hormones increase renal blood flow


What is the significant risk of severe hyponatremia?

Cerebral oedema


What are the signs and symptoms of hyponatremia

Many patients are asymptommatic
Need to distingusish between acute vs chronic onset

GI - ?Nausea and vomiting
Neuro - headache, lethargy, reversible ataxia, psychosis, seizures, cerebral oedema, raised ICP


Management options of hypovolemic hyponatremia?

Isotonic saline administration


Management of hypervolemic hyponatremia

fluid restriction and diuretic use to decrease the water content of the extracelluar space


Management of euvolemic hyponatremia

fluid restriction to less than 1l/day


When does Hypovolemic hypernatreamia occur?

?Excessive sweating, vomiting, diarrhoea, diuretics or renal disease


When does hypervolemic hypernatremia occur?

Both water and sodium levels have increase - relatively rare.
Iatrogenic in nature due excessive administration of hypertonic saline or sodium bicarbonate.
Sometimes hyperaldosteronism


When does euvolemic hypernatremia occur?

loss in total body water however the sodium levels remain constant.
Elevated temperature, impaired thirst response, prolonged tachypnoea, diabetes insipidus


What are the signs and symptoms of hypernatremia?

Restlessness, lethargy, irritability
Disorientation, confusion
Stupor, coma, seizures death
Laboured breathing
muscle twitching, spasticity hyperreflexia
nausea vomiting intense thirst


Treatment options for euvolemic hypernatremia

Where the water loss exceeds sodium losses
5% Dextrose


Treatment options for hypovolemic hypernatremia

Isotonic saline until hypotension resolves then 0.45% Saline or 5% Dextrose


Treatment options for hypervolemic hypernatremia

The goal is to remove excess sodium - diuretics with 5% dextrose, if renal impairment is present then dialysis may be required.


What is the predominant intracellular cation?

Potassium - 98% intracellular
less than 2% is extracellular
the concentration of 3.5 to 5.5


What role does potassium play in the ECF/ICF?

The ratio between ICF and ECF determines the resting membrane potential of both nerve cells and muscle cells.


What causes hypokalemia?

Redistribution of K into cells - B2 agonists, phosphodiesterase inhibitors, exogenous insulin
Renal and extrarenal losses


What are the symptoms of hypokalemia?

Often asymptomatic
Generalised weakness, some ascending paralysis, cardiac arrhythmias may be present


Treatment options for hypokalemia

Identify the source
Replace potassium, orally - Sando-K
Peripherally as infusion - max 40mmols/,litre
Centrally much more concentrated


What could cause a false-positive hyperkalemia?

a release of intracellular potassium during phlebotomy or storage of the blood sample