Normal acid-base balance is a normal pH (euphaemia) plus a normal PaCO2 and HCO3. Compensation is normal pH even though the HCO- and PaCo2 are disturbed. Correction is the restoration of normal pH, HCO3 and PaCO2 through correction of the underlying cause. Acidaemia is a low pH whereas acidosis is a high PaCO2 or a low bicarbonate. In the same way, alkalaemia is a high pH whereas alkalosis is a low PaCO2 or high bicarbonate. Acidosis and alkalosis refer to processes that tend to lower or raise pH. Compensatory mechanisms rarely restore the pH to normal. Thus a normal pH in the presence of an abnormal HCO- and PaCO2 immediately suggests a mixed disorder.
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