If associated with a high 
  
    
      
        
          
            P
            
              
                a
                
                  C
                  
                    O
                    
                      2
                    
                  
                
              
            
          
        
      
    
    {\displaystyle {P_{a_{CO_{2}}}}}
   the high delivery of oxygen to the brain may increase the risk of CNS oxygen toxicity at partial pressures usually considered acceptable.In many people a high 
  
    
      
        
          
            P
            
              
                a
                
                  C
                  
                    O
                    
                      2
                    
                  
                
              
            
          
        
      
    
    {\displaystyle {P_{a_{CO_{2}}}}}
   causes a feeling of shortness of breath, but the lack of this symptom is no guarantee that the other effects are not occurring.
The effects of high 
  
    
      
        
          
            P
            
              
                a
                
                  C
                  
                    O
                    
                      2
                    
                  
                
              
            
          
        
      
    
    {\displaystyle {P_{a_{CO_{2}}}}}
   can take several minutes to hours to resolve once the cause has been removed.