Arterial pH is normally closely regulated between 7.35 and 7.45
Physiology of pH homeostasis
3 main systems in the body to minimise changes in pH:
- Buffer systems - can minimise any sudden changes in pH by reversibly binding H+
- Phosphate buffer, bicarbonate buffer, protein buffer
- Lungs - rapidly adjust secretion of CO2
- Kidneys - Slowly adjust secretion of H+ in the urine (and reabsorb HCO3)
Acid-base disorders:
Metabolic acidosis
Metabolic alkalosis
Respiratory acidosis
Respiratory alkalosis
In the absence of any significant respiratory disease or hyperventilation, the primary cause is much more likely to be metabolic. However, central hypoventilation (eg, caused by CNS disturbance such as stroke, head injury or brain tumour) causes respiratory acidosis.
Investigations
- ABG/VBG
- U&E - anion gap: A raised anion gap indicates the presence of an organic acid causing the acidosis