This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardio thoracic surgery  , Subject name: Surgery
Early and reliable indication of air embolisms during anaesthesia can be obtained by continous monitoring of: 
Select and explain. 
A. ECG, B. Blood Pressure, C. End-tidal CO2, D. Oxygen Saturation
C: End-tidal CO2
Answer: C: End-tidal CO2 
Explanation: Capnography: It is the continuous measurement of end tidal CO2 and its waveforms. It works on the principle that infrared light is absorbed by CO2. Useful in diagnosing pulmonary embolism by air, Fat or thrombus (sudden fall in End-tidal CO2 occurs). It may become zero if the embolus is large enough to block pulmonary circulation. Ref:Sabiston 20th edition pgno: 296