Definition depends on PaO2: Respiratory failure is where PaO 2 <8kPa (normal range PaO 2 is 12 - 13kPa - but depends on age).
Type 1 and Type 2 Respiratory Failure - category depends on PaCO2 (normal range PaO 2 is 12 - 13kPa - but depends on age).

Type 1 respiratory failure

PaCO 2 <6.5kPa (alkalosis – “pink puffer”)
Alveolar hyperventilation to compensate for low PaO 2 – CO2 is lost as it diffuses better. Treat with 60% O2.

type 2 respiratory failure

PaCO 2 >6.5kPa (acidosis – “blue bloater”)
Alveolar hypoventilation as exhaustion occurs and the patient is no longer able to hyperventilate. Treat with 24% O2 (respiratory centre is insensitive to CO2 and respiration is driven by hypoxia – hence high percentage oxygen could remove respiratory drive completely). If treatment fails, intubate and ventilate.

Summary

Type 1

Type 2

PaO 2 <8kPa

PaO 2 <8kPa

PaCO 2 <6.5kPa

PaCO 2 >6.5kPa