Physiological Etiology

1. V/Q mis-match
2. Hypoventilation
   • Can’t breath: COPD, !PE - Pulmonary embolism
   • Won’t breath: !Stroke (CVA) , Intracranial haemorrhage → Issues with Respiratory Control System
3. Increased CO2 production
   • Hyper-metabolic state (Respiratory Acidosis)
   • Overfeeding (after starvation))
   • Drug overdose

Clinical Pearl

• PCO2 respond to Hyperventilation (RR > 30) , but PO2 does not → because HbSat is already high in the well-perfused regions.
• Diffusion problem commonly don’t affect PCO2, but PO2, as CO2 is very diffusible