EEG changes denoting minor narcotic effects can be detected for expired gas end tidal partial pressure of carbon dioxide (
  
    
      
        
          
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    {\displaystyle {P_{ET_{CO_{2}}}}}
  ) increase from 40 torrs (0.053 atm) to approximately 50 torrs (0.066 atm).
Vasodilation is another effect, notably in the skin, where feelings of unpleasant heat are reported, and in the brain, where blood flow can increase by 50% at a 
  
    
      
        
          
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    {\displaystyle {P_{ET_{CO_{2}}}}}
   of 50 torrs (0.066 atm), Intracranial pressure may rise, with a throbbing headache.