respiratory acidosis

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This is characterised by a raised PaCO2, a normal or slightly elevated serum bicarbonate, and a low pH.

A respiratory acidosis may be pure, or it may be complicated by a metabolic derangement (i.e. a mixed acidosis). Measurement of the serum bicarbonate permits definitive diagnosis:

  • acute respiratory acidosis:
    • serum bicarbonate increases by 1 mmol/l for each 10 mmHg (or 1.33kPa) increase in PaCO2

  • chronic respiratory acidosis:
    • serum bicarbonate increases by 3.5 mmol/l for every 10 mmHg (or 1.33kPa) increase in PaCO2

  • if the bicarbonate is lower than expected then the condition is likely to be a mixed respiratory acidosis and metabolic acidosis

  • if the bicarbonate is higher than expected then the condition is likely to be a mixed respiratory acidosis and metabolic alkalosis

Last reviewed 10/2018

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