A 56 year old female with history of COPD presents to the emergency department with a 2 day history of fever, increasing breathlessness and purulent phlegm. RR = 26 and oxygen saturation = 85%. An ABG is taken and shows the following:
pH= 7.31
PaO2 = 7 kPa
PaCO2= 7.5 kPa
HCO3= 45 mmol/L
Which type of acid-base abnormality does the ABG show?
Well done, correct.
Answer:
Step 1:The history suggests an infective exacerbation.
Step 2: PaO2 is lower than normal so the patient is hypoxic, they are also hypercapnic suggesting type 2 respiratory failure.
Step 3: pH is lower than normal so the patient is acidotic.
Step 4: PaCO2 is increased.
Step 5: HCO3 is increased.
Putting the information together and using the ROME mnemonic we come to the conclusion that this is a respiratory acidosis. The raised HCO3 shows metabolic compensation however as this takes time to develop, it indicates a long-term compensation for chronic respiratory acidosis. Therefore this is an acute on chronic respiratory acidosis.
