Interpretation | blood gas analysis

Step-by-step diagnostics for blood gas analysis (BGA)

(a) pH elevated alkalosis
  normal healthy or compensated disturbance
  reduced acidosis

(b) pCO2 Would this pCO2 level be responsible for this pH value?
  if yes respiratory (or combined) disturbance
  if no and pCO2 is normal no compensation
  if no and pCO2 altered in opposite direction respiratory compensation

(c) BE Would this BE be responsible for this pH value?
  if yes non-respiratory (or combined) disturbance
  if no and BE normal no compensation
  if no and BE altered in opposite direction non-respiratory compensation


respiratory acidosis

(a)     pH lowered → acidosis
(b)     pCO2 elevated. Since CO2 = acid, this pCO2 would cause acidosis → respiratory acidosis
(c)     BE normal → no compensation


Respiratory non-compensated acidosis.

partially compensated respiratory acidosis

(a)     pH reduced → azidosis
(b)     pCO2 elevated → respiratory acidosis
(c)     BE elevated → non-respiratory compensation


Respiratory acidosis, non-respiratory partially compensated.

compensated respiratory acidosis

(a)     pH normal → healthy or complete compensation
(b)     pCO2 elevated → either respiratory acidosis or respiratory compensation of alkalosis
(c)     BE elevated → either non-respiratory alkalosis or non-respiratory compensation of acidosis


In this case, two possible diagnoses may be considered:
    1. compensated respiratory acidosis
    2. compensated non-respiratory alkalosis

The diagnosis may be made based on clinical findings. The patient displayed respiratory insufficiency in association with COPD treated with oxygen therapy, thus:

compensated respiratory acidosis

Non-respiratory alkalosis is also less common than respiratory acidosis and are rarely completely compensated since hypoxia would arise due to hypoventilation and being more damaging than mild alkalosis.