Electrolyte Disorders Flashcards
Hyponatraemia (<135mmol/L) can be caused by:
Hypervolaemia (due to excess water) - HF, LF, RF, Hypoalbuminaemia
Normovolaemia - Hypothyroid, SIADH, Addison’s
Hypovolaemia (due to salt loss) -
Renal losses - Hyperglycaemia, Diuretics, Adrenal insufficiency
Extra-Renal - D+V, burns, pancreatitis, haemorrhage
ADH is activated when the body is thirsty via osmoreceptors in the hypothalamus. It’s function is to:
Increase water reabsorption from the renal collecting ducts. Released by the Posterior Pituitary.
How do you differentiate between Na+ renal loss and Na+ extra-renal loss?
Measure urinary sodium - Renal loss > 20mmol/L
Hypervolaemic hyponatraemia is most commonly caused by:
Excessive infusion of 5% Glucose (iatrogenic)
Symptoms of hypervolaemic hyponatrameia:
Cerebral Oedema - headache, convulsions, coma
What is central pontine myelinolysis?
Over-rapid correction of sodium concentration, resulting in quadriparesis, respiratory arrest, seizures due to demyelination most commonly in the pons, but can also occur in basal ganglia, internal capsule, cortex. Diagnosed via MRI.
What are Tolvaptan / Conivaptan?
Vasopressin V2 receptor antagonists, work on the collecting duct
What are the most common causes of hypernatraemia ?
Reduced water intake
Water loss in excess of Sodium
What are the features of hypernatraemia?
Non-Specific - nausea, vomitting, fever, confusion
How do you treat hypernatraemia?
Give water or IV dextrose 5% to try and correct levels over 48h
How do you treat low potassium? (<3.5mmol/L)
KCL supplements / slow infusion if DKA/ Do ECG monitoring
What causes increased redistribution of K+ into cells, causing hypokalaemia?
Increased activity of Na/K/ATPase channel
Alkalosis, B-Agonists or Insulin
What is the function of Aldosterone?
Na+ and K+ regulation, a raised K+ results in Aldosterone activation, resulting in increased secretion of K+ via the distal tubules and collecting ducts
What are the causes of Hyperkalaemia (>5.0 mmol/L)
Reduced excretion - AKI, ACE-is, NSAISs, K+ sparing diuretics, Addisons, Type 4 RTA
Redistribution - DKA, metabolic acidosis, tissue necrosis, digoxin toxicity, suxamethonium
Increased input - KCL, salt substitutes, blood transfusion
What causes hypokalaemia?
Increased renal excretion (>20mmol/L) - Diuretics, corticosteroids, raised aldosterone (LF, HF, Nephrotic syndrome, Cushing’s, Conn’s)
GI losses - vomitting, diarrhoea, ileostomies
Redistribution - Alkalosis, insulin, B-agonists
Reduced intake - Diet, IV fluids inadequate
What are the features of hyperkalaemia?
muscle weakness and paralysis due to impaired neuromuscular transmission
Kussmaul’s breathing - low, deep, sighing inspiration and expiration
ECG changes (indicates emergency) - reduced p wave, widened QRS, tented T wave
How do you treat hyperkalaemia?
Protect the heart - if > 6.5 or ECG changes:
10ml of 10% Calcium Gluconate bolus
Give again in 5mins if ECG changes persist
Redistribute the K+:
Soluble Insulin 10 units in 50ml of 50% dextrose IV over 30mins
Salbutamol nebuliser
Sodium Bicarbonate if severely acidotic (pH < 6.9)
Reduce K+:
Give Resin, it binds to K+
Try dialysis if everything fails
Monitor Glucose (hourly for 6h after insulin infusion) and K+ (2-4h)
What are the features of low magnesium
Similar to hypocalcaemia and hypokalaemia because:
Reduces PTH secretion and leads to PTH resistance
Increases renal excretion of K+
How do you treat low magnesium?
If severe, give MgCl infusion
If less severe, give MgO supplement tablets
What does anion gap indicate?
Acidosis with normal anion gap (6-12mmol/L) means HCL is being retained or Sodium Bicarbonate is being lost
Acidosis with increased gap (>12mmol/L) means the acidosis is due to an exogenous acid - sakicylates, lactate
What are the causes of metabolic acidosis with NORMAL anion gap?
Increased GI loss of HCO - diarhhoea, ileostomy
Increased renal loss of HCO - hyperPTHism, RTA-2, acetazolamide ingestion
Reduced renal H+ loss - RTA-1 and 4
Increased HCl production - increased arginine and lysine catabolism
What are the causes of metabolic acidosis with a RAISED anion gap?
Renal failure (sulphate and phosphate acids)
Ketoacidosis - DKA, starvation, alcohol poisoning
Lactic Acidosis - Shock, LF, severe hypoxia, strenuous exercise
Drug poisoning - salycylates
What type of acidosis does Renal tubular acidosis cause?
Metabolic acidosis with a normal anion gap
