DISORDERS OF ACID-BASE BALANCE
Plasma pH is normally 7.35-7.45 which represents a H+
concentration of 36-44 mmol/litre. The normal plasma HCo 3 -
concentration is 20 to 30 mmol/litre. The lowest urinary pH is 4.5 units
(with severe metabolic acidosis in presence of normal kidneys) and the
highest urinary pH is 10 units (with severe metabolic alkalosis).
Metabolic Acidosis
Metabolic acidosis can result from the generation or the ingestion
of acid; or from the loss of bicarbonate ions with consequent accumulation
of H+ in the circulation.
This will be compensated for by the increase in ventilation with a
consequent drop in the level of Co 2 and HCo 3 -.
(^) The term acidaemia is sometimes used when compensatory
mechanisms fail to maintain the pH level within the normal range. But in
practice, the term acidosis is usually used whether the pH level is within
the normal range or lower.
Features of metabolic acidosis:
- Low plasma HCo 3 -^ concentration (< 20 mmol/litre).
- Low arterial Co 2 concentration (< 40 mmol/litre).
- Low plasma pH (< 7.35).
Causes of metabolic acidosis: