This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Unknown
5 year old child going for sitting craniotomy, while positioning in O.T. developed end tidal CO2- Zero mmHg, PO2- 80 mm Hg implies that : 
Select and explain. 
A. Venous air embolism, B. Left lung collapse, C. Endotracheal tube in Oesophagus, D. Endotracheal tube blocked with secretions
A: Venous air embolism
Answer: A: Venous air embolism 
Explanation: Ans. is 'a' i.e. Venous Air embolismThe cranial sinuses have negative air pressure.So, it is possible that if the pt. is in the wrong position while operation, the sinuses may suck some air d/t their negative pressure which can cause a venous embolism.The given value for the gases can occur only in Venous air embolism.