CO2 transport

• CO2 Balance: 

  • We produce ~ 200 ml of CO2 per min 

  • We excrete ~ 200 ml of CO2 per min 
• CO2 Imbalance: • Producing more CO2 than we excrete / inadequate excretion -->  

  • PaCO2 retention  

  – ↑ number of free H+  

  – ↓ pH  

  – respiratory acidosis 
• Transportation of CO2: 

  • In solution  

  • 7-10% CO2 transported in solution 
  •  Higher than amount O2 in solution 

   
• Transportation of CO2: 

  • Bound to Hb  

  • 20-30% binds to Hb – globin portion 
  • forming carbamino compounds – carboaminohaemoglobin (HbCO2) 

   
• Transportation of CO2: 

  • As a bicarbonate 

  • 60 - 70% CO2 converted to HCO3-  
  • Tissues in this form from tissues to lungs 
  • Conversion in plasma very slow 
  • Conversion in RBC in presence of carbonic anhydrase is rapid 

   
• Clinical Relevance: • Inadequate ventilation ↑CO2  

  • Acute hypoventilation  

  • Post UAS  

  – pain inhibition  

  • Diaphragmatic dysfunction (tidal volumes fall) 

  • Chronic inadequate ventilation  

  – Obstructive conditions (problem breathing out, so there's an increase of co2 in the blood) 

  – V/Q mismatch