Franz Wiesbauer explains the relationship between pH, HCO3 and pCO2 and a simple rule which will help you decide whether the primary problem is respiratory or metabolic in nature.
Respiratory acidosis = a primary acid-base disorder in which arterial pCO2 rises to an abnormally high level.
A 67 year old gentleman with a BMI of 45 was waiting for his respiratory outpatient clinic appointment. While waiting, he fell asleep. A medical emergency was called because he could not be woken up.