Electrolytes Flashcards
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
SIADH
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
Causes of Hyperkalemia
Excessive intake - supplements or stored blood
Decreased excretion - renal failure, K sparing diuretics, ACE inhibitors
Translocation from ICF to ECF, acidosis, hyperglycaemia, rhabdomyolysis, adrenal insufficency, b2 blockers
Symptoms of hyperkalemia
Often asymptommatic
generalised weakness, paralysis and cardiac arrhythmias
What are the cardiovascular symptoms of hyperkalaemia
Arrhythmias, heart block, delayed conduction, ventricular standstill, Significant ECG
Neuromusclar symptoms of hyperkalemia
parathesisa, weakness, respiratory insufficiency
How does salbutamol reduce K
Binds to B2 receptors, stimulates cAMP, stimulates sodium/potassium pumps
increases movement of plasma potassium ecf to icf
Describe how insulin and dextrose lowers extracellular potassium
As iinsulin acts by movinng glucose from the extracellular space and into cells, the sodium potassium pumps are activated and therefore moves potassium into the cells.
Doesnt reduce the amount of potassium in the body but it does reduce extracellular potassium.
Give 50mls of 50% glucose with 10 units of actrapid.
What is the role of calcium in the treatment of hyperkalemia?
Calcium does not directly have any effect on potassium levels. Used for myocardial protection
You give calcium chloride or calcium gluconate over 10 to 30 minutes.
What treatment option is avaliable for refractory hyperkalemia
Haemodialysis and CRRT.
Actively removes potassium from the extracellular compartment.
Can cause a rapid fall within the first hour of treatment.
What is the chief anion in ECF
Chloride ion
Moves in and out of the cells with sodium and potassium
What constitutes the cointrol of chloride ions
Intake of chloride
Excretion of chloride
Renal reabsoprtion
What relationship does chloride and bicarbonate have?
When chloride ions increase, bicarbonate decreases, when chloride ions decease, bicarbonate increases
What causes hypochloremia
Reduced intake
Excesssive losses - prolonge vomiting, diarrhoea, NG Suctioning
Medications - bicarbonate, corticosteriods, laxatives and diuretics
What causes hyperchloremia
Increased intake - IV Fluids
Secondary to metabloic acidosis
Some medication - ammonium chloride, acetazolamide
What is the role of bicarbonate within homeostasis
acts as a buffer to changes in pH, excreted and reabsorbed to maintain a constant pH
High levels of Bicarbonate occur in
vomiting, dehydration, blood transfusions, overuse of medications that contain bicarb as well as chronic resp acidosis.
Low levels of Bicarbonate occur in
Hyperventilation, aspirin and alcohol overuse. diarrhoea, severe malnutrition, severe burns, shock, liver and kidney disease, uncontrolled diabetes
Where is magnesium found within the body
50-60% found in bone
only 1% extracellular
the rest is found intracellular space.
What is the main role of Magnesium within the body
Enzyme activity, the use of ATP, replication and trasncription of DNA, metabolism of carboghydrates, stabilisation of membrane potentials and nerve conduction
What causes imbalances in magnesium within the body?
Reduced intake - unbalanced diet, depleted foods, dieting
Impaired absoprtion - GI disturbances,
Increased excretion - alcoholism, laxative use, diuretics
What other electrolytes disturbances can occur following hypomagnesia
Hypomagnesaemia (due to it leading to hypokalaemia and hypocalcaemia) can cause potentially fatal complications (eg, ventricular arrhythmia, coronary artery vasospasm, cardiac arrest).
What are the common early symptoms of hypomagnesia
neuromuscular and neuropsychiatric disturbances - tremor, fasciculations, tetany, Chvostek and Trousseau signs, and convulsions.
What are some of the symptoms of Hypermagnesemia
2 to 3 mmol/L — nausea, flushing, headache, lethargy, drowsiness, and diminished deep tendon reflexes.
3 to 5 mmol/L — somnolence, hypocalcaemia, absent deep tendon reflexes, hypotension, bradycardia, and ECG changes.
Above 5 mmol/L) — muscle paralysis, respiratory paralysis, complete heart block, and cardiac arrest. In most cases, respiratory failure precedes cardiac collapse.
