Electrolyte Imbalances Flashcards
What is hypokalaemia defined as?
Potassium <3.5mmol/l.
This is the most common electrolyte disturbance in hospitalised patients due to diuretic therapy.
What are the most common causes of hypokalaemia?
- Diuretic therapy
- Acute illness
- GI losses.
Increased lossess of potassium can be from the urinary tract (diuretic therapy, mineralocorticoid excess - Cushings, aldosterone excess - heart failure, renal artery stenosis
Poor intake due to eating disorders.
Potassium shifting to intracellular compartment (insulin therapy, salbutamol therapy - salbutamol nebules can be used to treat hyperkalaemia).
What are the clinical features of hypokalaemia?
Often asymptomatic.
Weakness.
Intestinal ileus.
ECG changes - T wave flattening and U waves + tachyarrhythmia.
Polyuria (loss of concentrating ability of kidneys)
Severe muscle weakness and flaccid paralysis - when severe: <2mmol/L
What is the intitial treatment for the correction of severe hypokalaemia in patients who cannot swallow?
Potassium chloride with sodium chloride for when sufficient potassium cannot be taken by mouth.
In what patients may compensation for potassium loss be especially necessary?
- Patients taking digoxin or anti-arrhythmic drugs, where potassium depletion may induce arrhythmias;
- Patients whom secondary hyperaldosteronism has occured: renal artery stenosis, cirrhosis of the liver, the nephrotic syndrome, and severe heart failure.
- Patients with excessive losses of potassium in the faeces, e.g. chronic diarrhoea associated with intestinal malabsorption or laxative abuse.
What is recommended for the prevention of hypokalaemia due to diuretics such as furosemide or the thiazides when they are given to eliminate oedema?
The use of potassium-sparing diuretics.
spironolactone, amiloride, and triamterene.
Epithelial sodium channel blockers: amiloride, triamterene.
Aldosterone antagonists:
Spironolactone, eplerenone.
ACEi and ARB are not classically considered to be potassium-sparing diuretics despite a decrease in aldosterone release, which causes potassium-sparing like effects.
Why must smaller doses of potassium salts for the treatment of hypokalaemia (and prevention of it) be used in the elderly?
The elderly are more likely to have some degree of renal insufficiency and so smaller doses are required to reduce the risk of hyperkaleamia.
Why can potassium-sparing diuretics be preferable to the use of potassium salts?
They cause nausea and vomiting and poor compliance is a major limitation to their effectiveness.
What is acute severe hyperkalaemia defined as?
plasma-potassium concentration above 6.5mmol/litre or in the presence of ECG changes
How is acute severe hyperkalaemia (>6.5mmol/l) treated?
Calcium gluconate 10% by slow intravenous injection, titrated and adjusted to ECG improvement, to temporarily protect against myocardial excitability.
An intravenous injection of soluble insulin (5-10units) with 50mL glucose 50% given over 5-15 minutes has what effect on serum-potassium?
Reduces it, this can be repeated if necessary or a continuous infusion instituted.
Salbutamol, by nebulisation or slow intravenous infusion has what effect on serum plasma potassium levels?
Reduces it, unlicensed use, should be used with caution in patients with cardiovascular disease.
When would ion-exchange resins be used to remove excess potassium?
Only in mild to moderate hyperkalaemia when there are no ECG changes.
When would sodium bicarbonate be used by mouth?
For chronic acidic states such as uraemic acidosis or renal tubular acidosis. The dose for correction of metabolic acidosis is not predictable and the response must be assessed. For severe metabolic acidosis, sodium bicarbonate can be given intravenously.
Sodium supplements can have what unintended side effects?
Increased blood pressure, fluid retention, pulmonary oedema. Hypokalaemia may also be exacerbated.
When hyperchloraemic acidosis is associated with potassium deficiency, as in some renal tubular and GI disorders, it may be appropriate to give oral what?
Potassium bicarbonate but acute or severe deficiency should be managed by IV therapy.
Isotonic solutions may be infused safely into a peripheral vein. Solutions more concentrated than plasma, e.g. __% glucose, are best given through what?
20% glucose, an indwelling catheter positioned in a large vein.
Sodium depletion can occur from conditions (not drug induced) such as? [4]
Gastro-enteritits,
Diabetic ketoacidosis,
Ileus,
Ascities
Chronic hyponatraemia rising from inappropriate secretion of antidiuretic hormone should ideally be corrected by what?
Fluid restriction. However, if sodium chloride is required for acute or chronic hyponatraemia, regardless of the cause, the deficit should be corrected slowly to avoid the risk of osmotic demyelination syndrome and the rise in plasma-sodium concentration should not exceed 10mmol/litre in 24 hours. In severe hyponatraemia, sodium chloride 1.8% may be used cautiously.
Why would Hartmann’s solution (compound sodium lactate) be used instead of isotonic sodium chloride solution during or after surgery, or in the initial management of the injured or wounded?
Reduced risk of hyperchloraemic acidosis.
Why should initial potassium replacement therapy not involve glucose infusions?
Because glucose may cause a further decrease in the plasma-potassium concentration.
Sodium bicarbonate is used to control severe metabolic acidosis, which is defined as a pH value of what?
pH <7.1
Mild metabolic acidosis associated with volume depletion should first be managed by what? and why?
Appropriate fluid replacement because acidosis usually resolves as tissue and renal perfusion are restored.
Why is sodium lactate IV infusion no longer used in metabolic acidosis?
Becase of the risk of producing lactic acidosis, particularly in seriously ill patients with poor tissue perfusion or impaired hepatic function.
What antibiotics and antifungals have the potential to causes hypokalaemia?
Ampicillin, high-dose penicillins. Azoles. Amphotericin B Echinocandins. Gentamicin.
What drugs can cause hypokalaemia in overdose?
Verapamil
and
Quetiapine
What are the clinical features of hyperkalaemia?
When present, can be: Muscle weakness and fatigue. Frank muscle paralysis. Shortness of breath. Palpitations or sometimes chest pain. .
The most common causes of hyperkalaemia are due to what?
Decreased renal potassium excretion caused by: renal failure, potassium sparing diuretics, ACEi, ARBs and NSAIDs.
What is hypernatraemia defined as?
serum sodium levels of more than 145mmol/l (severe symptoms typically only occur when levels are above 160mmol/L)
What are normal serum sodium levels?
135-145mmol/L
