Occurs in:
To distinguish between compensated primary metabolic alkalosis or respiratory acidosis, and a primary mixed disorder, the clinical picture must be considered. Also, if the HCO3– is greater than 45 mmol/l, it is much more likely to be a mixed disorder.
For example, in a patient on long term thiazide medication for hypertension who presents with an acute exacerbation of COPD:
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It would be easy to be reassured by this patient’s normal pH, but the low potassium and acute presentation of the breathing difficulty should point to this being a more complicated picture. The bicarbonate is unusually high, even for metabolic compensation of a respiratory disorder. The clinical condition of the patient should be treated rather than simply relying on a normal pH.