Respiratory alkalosis

This is characterised by reduced PaCO2, normal or slightly reduced serum bicarbonate, and a raised pH.

A respiratory alkalosis may be pure or it may be complicated by a metabolic derangement (i.e. a mixed alkalosis). Measurement of the serum bicarbonate permits definitive diagnosis:

• acute respiratory alkalosis:
  • serum bicarbonate decreases by 2 mM for every 10 mmHg (or 1.33kPa) decrease in PaCO2
    
    
• chronic respiratory alkalosis:
  • serum bicarbonate decreases 5 mM for every 10 mmHg decrease in PaCO2
    
    
• if the serum bicarbonate is higher than expected then the condition is likely to be a mixed metabolic alkalosis and respiratory alkalosis
  
  
• if the serum bicarbonate is lower than expected then the condition is likely to be a mixed metabolic acidosis and respiratory alkalosis