Capnograph Interpretation

Normal Graph

Phase I: At the start of exhalation, anatomical and physiological dead space is
expired, so no CO2Phase II: Exhalation continues, so CO2 rises
Phase III: CO2 plateau
Phase IV: Inspiration








Capnograph in obstructive airway

• Fin-shaped appearance
• Slanting and prolongation of expiratory phase 
• eg. COLD, kinked ETT 

Rebreathing

• Elevated baseline from Zero
• eg. low gas flow

Hyperventilation

• High Resp Rate
• Low EtCO2 

Hypoventilation

• Low Resp Rate
• High EtCO2 

Sudden Fall EtCO2

• Asystole, 
• Hypotension
• Massive Pulmonary Embolism  

Sudden Fall an Rise

Small Air Emboli

Cardiac impulse on EtCO2 

Slanting Capnograph

• Contamination of the expired sample by fresh gas flows 
• Sampling site too near to fresh gas  

Spontaneous Resp Activity

Curare Cleft

• Inadequate muscle relaxation 

Return Of spontaneous resp.

• After Anesthesia