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: Anaesthesia
The gas which produces systemic toxicity without causing local irritation is: 
Select and explain. 
A. Ammonium, B. Carbon monoxide, C. Hydrocyanic acid, D. Sulfur dioxide
B: Carbon monoxide
Answer: B: Carbon monoxide 
Explanation: B i.e. Carbon Monoxide Carbon Monoxide Poisoning CO is a colourless, tasteless, non irritant gasQ which is produced due to incomplete combustion of carbon. CO poisoning is defined as > 15 % carboxyhemoglobinQ in blood (normal < 1.5 % in nonsmokers, < 10 % in smokers). Diagnosis is made by cooximetric measurements of blood not by pulse oxymeter. CO has 200 - 300 times the affinity of 02 for hemoglobin. It decreases the affinity of 02 and shifts hemoglobin dissociation curve to right. -Toxicity may be due to smoke inhalation or by degradation of desflurane by CO2 absorbent Lower levels produce systemic toxicity because of binding with cytochrome-c & myoglobin and higher levels produce toxicity due to binding with Hemoglobin leading to tissue hypoxia.