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Electrolyte Imbalance Notes

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Electrolyte Imbalances HypokalaemiaPotassium < 3.5mmol/L Most common electrolyte disturbance in hospitalized patients due to diuretic therapy
- Can be due to o Increased losses
? Urinary tract (diuretic therapy, mineralocorticoid excess - Cushings, aldosterone excess - heart failure, renal artery stenosis)
? GI tract (diarrhea, vomiting, laxative abuse) o Poor intake (eating disorders) o 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) o Skeletal muscle weakness and flaccid paralysis Management
- Treat underlying cause (should be apparent from history/drugs/comorbidities)
- 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) o Restrict potassium
- Severe hyperkalaemia (K+ >6.5mmol/L or ECG changes) o Medical emergency o IV calcium gluconate (10ml of 10% over 2 minutes) to stabilize myocardium o IV insulin/glucose (50ml 50% glucose and 10units of actrapid insulin) o 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 Urinary Na+
a. Sodium and water deficit
>20mmol/L b. Renal losses (diuretic therapy, Addisons) c. GI loss (diarrhea, vomiting) Urinary Na+
d. Burns, sweating
<20mmol/L 2) Normovolaemia a. No change in body Na+ but increase in water b. Inappropriate diuretic therapy c. SIADH (syndrome of inappropriate ADH) d. 3) Hypervolaemia Urinary Na+
a. Increase in body Na+ and water
>20mmol/L b. Renal failure Urinary Na+ <20mmol/L c. Cardiac failure, liver failure, nephrotic syndrome Common causes
- Heart failure
- Inappropriate IV dextrose in post-op patients
- Iatrogenic Addison's disease (overrapid cortisol withdrawal or failure to increase steroids in illness) Management

Diagnosis Exclusion of adrenal, thyroid, pituitary or renal insufficiency No diuretic usage +
euvolaemia Raised ADH levels =
inappropriate urinary concentration Causes = post-op pain, CNS causes, lung tumour, malignancies, drugs (cyclophosphamide, carbamazepine)

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