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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
- SIADH
- 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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