Test Findings
 

Hypochloraemia

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Overview

  • Hypochloraemia rarely exists on its own, and is usually found in the presence of hyponatraemia (due to salt depletion or dilution) or metabolic alkalosis. Hypochloraemia can also occur in the setting of renal compensation for respiratory acidosis.

Aetiology

    • Causes of Hypochloraemia

    • Salt Loss

    • Extrarenal - vomiting, diarrhoea, 3rd spacing
    • Renal - loop or thiazide diuretic abuse, Addison’s, renal tubular acidosis
    • Dilution

    • Osmotic shift - hyperglycaemia, mannitol
    • Excess water intake - primary polydipsia, beer potomania
    • Antidiuresis - SIADH, hypothyroidism, ACTH deficiency
    • Fluid overload - heart failure, cirrhosis, nephrotic syndrome, renal failure
    • Metabolic Alkalosis

    • GI acid loss - vomiting, NG aspirates, gastric fistula
    • Renal acid loss - diuretics, Cushings, Conns, steroids
    • Systemic bicarbonate excess - massive transfusion, dialysis
    • Compensation for Respiratory Acidosis

    • Hypoventilation - drugs, obstructive sleep apnoea, neuromuscular disorders
    • Dead space ventilation - emphysema

Approach

  • Determine whether the patient is hyponatraemic or has an acid-base abnormality, and then investigate further depending on the result.
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