Electrolyte Imbalance Notes

Electrolyte Imbalances

Hypokalaemia

• Potassium < 3.5mmol/L

• Most common electrolyte disturbance in hospitalized patients due to diuretic therapy

• Can be due to

  • Increased losses

    • Urinary tract (diuretic therapy, mineralocorticoid excess – Cushings, aldosterone excess – heart failure, renal artery stenosis)

    • GI tract (diarrhea, vomiting, laxative abuse)

  • Poor intake (eating disorders)

  • Shift to intracellular compartment (insulin therapy, salbutamol therapy)

Most common causes

• Diuretic therapy

• Acute illness

• GI losses

Clinical features

• Often asymptomatic

• Weakness

• Intestinal ileus

• ECG changes – T wave flattening and U waves + tachyarrhythmia

• Polyuria (loss of concentrating ability of kidney)

• When severe (<2mmol/L)

  • Skeletal muscle weakness and flaccid paralysis

Management

• Treat underlying cause (should be apparent from history/drugs/co-morbidities)

• If potassium is < 2.5mmol/L or <3.0mmol/L in a patient at risk of arrhythmias (e.g post MI) give IV potassium chloride as an infusion not exceeding 20mmol/hr at a concentration not exceeding 40mmol/L as concentrated potassium will damage peripheral veins

• If potassium is between 2.5-3.5mmol/L give oral replacement therapy (unless patient is NBM or vomiting) of 80-120mmol/day in divided doses

Hyperkalaemia

Aetiology

• Renal failure (impaired K+ excretion)

• Reduced mineralocorticoids (Addison’s disease)

• Spironolactone (aldosterone antagonist)

• Potassium-retaining diuretics e.g amiloride

• Cell destruction (rhabdomyalosis, haemolysis, cytotoxic therapy) liberates K+

• Can be an artifact due to haemolysis of blood during venipuncture. Always repeat

Most common causes

• Renal failure

• Drugs in those with borderline or abnormal renal function e.g ACEi, spironolactone

Clinical features

• Usually asymptomatic

• ECG abnormalities (tented T waves, widened QRS, prolonged P-R interval, sine wave appearance)

• Leads to cardiac arrest

Management

• Mild hyperkalaemia (K+ <6.0 mmol/L)

  • Restrict potassium

• Severe hyperkalaemia (K+ >6.5mmol/L or ECG changes)

  • Medical emergency

  • IV calcium gluconate (10ml of 10% over 2 minutes) to stabilize myocardium

  • IV insulin/glucose (50ml 50% glucose and 10units of actrapid insulin)

  • May need potassium-binding resin Calcium resonium or dialysis

Hyponatraemia

Serum sodium <130mmol/L

5% of hospital patients

Excess of extracellular water relative to sodium content of extracellular compartment

Can occur in three circumstances

1. Hypovolaemia

   1. Sodium and water deficit

   2. Renal losses (diuretic therapy, Addisons)

   3. GI loss (diarrhea, vomiting)

   4. Burns, sweating

2. Normovolaemia

   1. No change in body Na+ but increase in water

   2. Inappropriate diuretic therapy

   3. SIADH (syndrome of inappropriate ADH)

3. Hypervolaemia

   1. Increase in body Na+ and water

   2. Renal failure

   3. Cardiac failure, liver failure, nephrotic syndrome

Common causes

• SIADH

• Heart failure

• Inappropriate IV dextrose in post-op patients

• Iatrogenic Addison’s disease (over-rapid cortisol withdrawal or failure to increase steroids in illness)

Management

• Treat underlying pathology

• Determine volume status of patient

• If signs of hypovolaemia present (thirst, tachycardia, hypotension, reduced skin turgor) then give IV sodium chloride

Mild Hyponatraemia

• Treatment may not be necessary

• No evidence that patient’s fluid should be restricted

• Evidence of hypervolaemia (pitting oedema, raised JVP, hypertension) diuretics and water restriction may be necessary

Cautious correction of Na+ is essential to avoid pontine myelinolysis – syndrome of encephalopathy = cranial nerve palsies and quadraplegia

Hypernatraemia

Serum sodium >145mmol

Caused by relative water deficit (defence against it is thirst)

Occurs more commonly in patients unable to increase their water intake

1. Hypovolaemia

   1. Low body Na+ with loss of water exceeding that of Na+

      1. Renal losses (diuretics, osmotic diuresis) Urinary Na+>20mmol/L

      2. Extrarenal loss (sweating, burns, diarrhea) Urinary Na+ <20mmol/L

2. Normovolaemia

   1. Normal body Na+ but water loss

      1. Renal loss (diabetes insipidus, impaired thirst)

      2. Extrarenal loss (resp tract)

3. Hypervolaemia

   1. Increased total body Na+

      1. Sodium gains (hypertonic NaCl, hypertonic dialysis, Cushing’s, hyperaldosteronism) Urinary Na+ >20mmol/L

Common...

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