After 30–90 min, the respiratory center was depressed, and hypotension occurred gradually or suddenly from reduced cardiac output, leading to an apnea and eventually to circulatory arrest. At higher concentrations of CO2, unconsciousness occurred almost instantaneously and respiratory movement ceased in 1 minute. After a few minutes of apnea, circulatory arrest was seen. These findings imply that the cause of death in breathing high concentrations of CO2 is not the hypoxia but the intoxication of carbon dioxide. Treatment
The treatment for acute hypercapnic respiratory failure depends on the underlying cause, but may include medications and mechanical respiratory support. In those without contraindications, non-invasive ventilation (NIV) is often used in preference to invasive mechanical ventilation. In the past, the drug doxapram (a respiratory stimulant), was used for hypercapnia in acute exacerbation of chronic obstructive pulmonary disease but there is little evidence to support its use compared to NIV, and it does not feature in recent professional guidelines.Very severe respiratory failure, in which hypercapnia may also be present, is often treated with extracorporeal membrane oxygenation (ECMO), in which oxygen is added to and carbon dioxide removed directly from the blood.A relatively novel modality is extracorporeal carbon dioxide removal (ECCO2R). This technique removes CO2 from the bloodstream and may reduce the time mechanical ventilation is required for those with AHRF; it requires smaller volumes of blood flow compared to ECMO. Terminology
Hypercapnia is the opposite of hypocapnia, the state of having abnormally reduced levels of carbon dioxide in the blood.
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.