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: Medicine
CO2 level in kPa above which brain stem death is confirmed ? 
Select and explain. 
A. 1, B. 9, C. 5, D. 6.5
D: 6.5
Answer: D: 6.5 
Explanation: Answer- D. 6.5At the end of a period of observation, typically several minutes, aerial Pco2 should be at least > 6.6-8.0 kPa (50-60 mmHg) for the test to be valid.Apnea is confirmed if no respiratory effo has been observed in the presence of a sufficiently elevated Pco2.