Blood gases in blue bloaters

hyperventilation with poor gas exchange

• PIO2 = 20
• PaO2 = 5
• PaCO2 = 8.5
• PIO2 - (PaO2+PaCO2) = 6.5

normal:

• PIO2 = 20
• PaO2 = 13.3 (12-14)
• PaCO2 = 5.3 (5-6)
• PIO2 - (PaO2+PaCO2) = 1.4 (less than 2.5)

In blue bloaters, poor gas exchange leads to prolonged raised PaCO2 which renders the patient's respiratory centre insensitive to hypercapnia. Therefore, these patients rely on hypoxia to stimulate breathing as illustrated here. These patients should be administered oxygen cautiously at only 24% as higher doses may lead to hypoventilation.

Thus, they are often cyanosed - blue - due to hypoxia and an oedematous component gives the bloater part of the name.