Electrolytes Flashcards
What are some of the causes of hyperkalaemia caused by reduced excretion of potassium?
AKI —> reduced eGFR
Drugs:
- K+ sparing diuretics e.g. amiloride, spironolactone
- ACE inhibitors
- NSAIDs
- ciclosporin
- heparin
Reduced aldosterone
Renal tubular acidosis
Addison’s disease
Metabolic acidosis
Pseudohypoaldosteronism
What are some of the causes of hyperkalaemia caused by increased extraneous load of potassium?
KCl
Diet: salt substitutes
Blood transfusion
What are some of the causes of hyperkalaemia caused by increased release of potassium?
Metabolic acidosis
Diabetic ketoacidosis
Rhabdomyolysis
Drugs:
- succinylcholine
- digoxin
- beta-blockers
- insulin
Vigorous exercise
Haemolysis
What are some of the causes of hyperkalaemia caused by artefacts?
Increased in vitro release from abnormal cells:
- leukaemia
- infectious mononucleosis
- thrombocytosis
Haemolysis in blood bottle
Vigorous fist clenching during phlebotomy
Increased release from muscles
What are some of the causes of renal retention of potassium?
Renal failure:
- acute
- chronic
Tubular secretory failure
- low aldosterone: Addison’s disease, adrenal enzyme defect, hyporeninaemic hypoaldosteronism, NSAIDs, ACE inhibitors, beta-blockers, ciclosporin, heparin
- normal/high aldosterone: pseudohypoaldosteronism, tubulointerstitial disease, amiloride, spironolactone
What are the signs and symptoms of hyperkalaemia?
Muscle weakness
Metabolic acidosis —> Kussmual respiration
Reduced cardiac excitability —> hypotension —> bradycardia —> asystole
What is the ECG appearance in hyperkalaemia?
Tall tented T waves (at least 1/3 of height of preceding R wave)
Reduced P wave and widened QRS complex (>3 squares)
Sine wave pattern (pre-cardiac arrest)
What is the management of severe hyperkalaemia?
ACUTE
- continuous ECG monitoring
- IV access
- protect myocardium: 10ml of 10% calcium gluconate IV over 5min (rpt after 5min)
- drive K+ into cells: 10 units of insulin + 50ml of 50% glucose IV over 10-15min (insulin dextrose)
- +/- correction of severe acidosis by NaHCO3 1.26% infusion
- +/- IV or nebulised salbutamol 0.5mg in 100ml of 5% glucose over 15min
LATER:
- IV furosemide + normal saline (if renal function OK)
- deplete body K+: polystyrene sulfonate resins OR haemodialysis/peritoneal dialysis
What are some of the causes of hypokalaemia caused by increased aldosterone?
Liver failure Heart failure Nephrotic syndrome Cushing's syndrome Conn's syndrome ACTH-producing tumour
What are some of the causes of hypokalaemia caused by redistribution into cells?
Beta-adrenergic stimulation Acute MI Insulin Correction of megaloblastic anaemia Alkalosis Hypokalaemic periodic paralysis (autosomal dominant)
What are some of the causes of hypokalaemia caused by GI losses?
Vomiting Severe diarrhoea Purgative abuse Villous adenoma Ileostomy Uterosigmoidoscopy Fistulae Ileus/intestinal obstruction
What are some of the causes of hypokalaemia caused by renal disease?
Renal tubular acidosis Renal tubular damage Acute leukaemia Nephrotoxicity e.g. amphotericin, aminoglycosides, cytotoxic drugs Release of urinary tract obstruction Bartter's syndrome Liddle's syndrome Gitelman's syndrome
What are some of the causes of hypokalaemia caused by exogenous mineralocorticoid?
Corticosteroids
What are some of the causes of hypokalaemia caused by reduced potassium intake?
IV fluids without K+
What are some of the causes of hypokalaemia caused by increased renal excretion of potassium?
Diuretics:
- thiazides
- loop diuretics
What are the signs and symptoms of hypokalaemia?
Muscle weakness
Symptomatic hyponatraemia
Increased risk of digoxin toxcitiy
What is the management of hypokalaemia?
Depends on the cause:
- increased aldosterone: give spironolactone or other potassium sparing diuretic
- IV fluid replacement: give 20mmol of K+/l
- diuretics/purgatives: withdraw and give PO K+ supplements
What are the causes of hyponatraemia with hypovolaemia?
EXTRA-RENAL
- vomiting
- diarrhoea
- haemorrhage
- burns
- pancreatitis
RENAL
- osmotic diuresis
- severe uraemia
- diuretics
- adrenocortical insufficiency
- tubulo-interstitial renal disease
- unilateral renal artery stenosis
- recovery phase of acute tubular necrosis
What are the causes of hyponatraemia with euvolaemia?
Abnormal ADH release
- vagal neuropathy
- Addison’s
- hypothyroidism
- severe potassium depletion
- SIADH (surgery, intracranial, alveolar, drugs, hormones)
What is the management of hyponatraemia?
Healthy:
- PO electrolyte-glucose mixture
- increase sodium intake with slow sodium 60-80mmol/l/day
Vomiting/sever volume depletion:
- IV fluids + potassium supplements over 24hrs
- correction of acid-base abnormalities
What is the presentation of SIADH?
- confusion
- nausea
- irritability
- fits
- coma
What are the investigations indicated for SIADH?
Diagnosis of exclusion - rule out dilutional hyponatraemia and Addison’s
- ?dilutional hyponatraemia
- euvolaemia
- low plasma osmolality with excessive urine osmolality
- continued urinary sodium excretion above 30mmol/l
- absence of hypokalaemia and hypotension
- normal renal, adrenal, and thyroid function
- no oedema
What is the management of SIADH?
- correct underlying cause
- restrict fluid intake to 500-1l/day
- measure plasma osmolality, serum sodium, and body weight dailt
- can give demeclocycline to inhibit ADH
What is sick cell syndrome?
Leakage of intracellular ions due to reduced Na+/K+ pump action –> hyponatraemia and hypokalaemia
Causes:
- hypoxia
- sepsis
- hypovolaemia
- malnourishment
What are the causes of dilutional hyponatraemia?
Intake of water in excess if kidney’s ability to excrete it with no change in body sodium content
- marathon runners
- excess glucose infusion
- drugs
- psychosis
What is the presentation of hyponatraemic encephalopathy?
- headache, confusion, restlessness, drowsiness, myoclonic jerks, generalised convulsions, coma
- MRI head shows cerebral oedema
- risks = children under 16, premenopausal women, hypoxaemia
What are the investigations in dilutional hyponatraemia?
Plasma urine electrolytes and osmolalities
- plasma sodium, chloride, and urea are LOW –> low serum osmolality
- urine sodium HIGH
- exclude Addison’s (short synacthen), hypothyroidism (TSH, T4), SIADH, drug-induced
What is the management of dilutional hyponatraemia?
- correct underlying cause
- fluid intake restriction to 500-1l per day
- review diuretics
- correct potassium and magnesium deficiencies
- anticipate and prevent overcorrection
What is osmotic demyelination syndrome?
Acute demyelination in the setting of osmotic changes; particularly with rapid increase in extracellular osmolality
Risk factors:
- chronic alcohol use
- cirrhosis
- malnutrition
- hypokalaemia
- pre-existing hypoxaemia
- CNS radiation
- transplant recipients
What are the causes of hyponatraemia with hypervolaemia?
Fluid overload
- heart failure
- liver failure
- oliguric kidney injury
- hypoalbuminaemia
What are pseudo hyponatraemia and artefactual hyponatraemia?
Pseudohyponatraemia = sodium confined to aqueous phase, but concentration expressed in terms of total volume of plasma –> hyponatraemia but plasma osmolality is normal
Artefactual hyponatraemia = blood test taken from limb receiving sodium infusion
What are the causes of hypernatraemia?
Water deficit
- ADH deficiency (pituitary diabetes insipidus)
- iatrogenic: excessive saline, drugs,
- insensitivity to ADH (nephrogenic diabetes insipidus, lithium, ATN)
- insufficient water intake
- excessive water loss
What investigations are indicated in hypernatraemia?
Simultaneous urine and plasma osmolality
- plasma osmolality is HIGH
- urine osmolality < plasma osmolality
- high urine osmolality indicates osmotic diuresis due to unmeasured solute or excessive extrarenal loss of water
Administer desmopressin:
- pituitary diabetes insipidus = increase in urine osmolality
- nephrogenic diabetes insipidus = no change in urine osmolality
What is the management of hypernatraemia?
ADH deficiency –> replace with desmopressin
Withdraw nephrotoxic drugs where possible
Replace water orally or IV
- > 150mmol/l –> 5% glucose/0.45% NaCl
- > 170mmol/l –> 0.9% NaCl over 48hrs
