Carbon Monoxide (1)

What is carbon monoxide?

Carbon monoxide is a colourless, odourless tasteless gas, that is by far the most abundant of the criteria pollutants. This deadly gas can kill, and let us first look at a case study.

Case Study:

A male patient, Mr S., presented to the ED having been driven there by his wife after she found him "barely breathing in the garage with his car running." She stated she was at work and came home to find him in his car "very groggy." Mr S. was in a state of respiratory arrest and was intubated shortly after being admitted to the ED and placed on 100% oxygen. His pupils were dilated and very sluggish. He was very lethargic and disoriented. His blood pressure was 166/102 mm Hg, pulse is 102 beats per minute, temperature is 96.4°F, and oxygen saturation is 92% on room air. Breath sounds were diminished, and his respiratory rate was 6 breaths per minute before being intubated. The ED physician obtained a venous blood sample, which revealed the patient's COHb level to be 49%, blood sugar of 185 mg/dL, and total cholesterol level of 260 mg/dL; cardiac enzymes and troponin T were within reference range. His electrocardiogram showed sinus tachycardia with no ST-T wave changes. An arterial blood gas was ordered, and plans were under way to transport Mr S. to a facility where hyperbaric oxygenation (HBO₂) could be provided

As seen, carbon monoxide threatens human health. This is because carbon monoxide has a strong affinity for haemoglobin, Hb, which can be represented by the following equilbrium equation.

Hb(aq) + 4CO(g)  --> Hb(CO)4(aq)

Thus, a person breathing air that contains carbon monoxide converts his/her haemoglobin to Hb(CO)₄, thus reducing the blood’s normal oxygen-carrying capacity. After entering the blood stream through the lungs, carbon monoxide reacts with haemoglobin (Hb) to convert oxyhaemoglobin (O2Hb) to carboxyhaemoglobin (COHb). However, at levels of CO that occur in urban air, there are apparently no detrimental effects on materials or plants, but those levels can adversely affect human
health.

Carbon monoxide, in fact, has a much greater affinity for haemoglobin than does oxygen, so that even small amounts of CO can seriously reduce the amount of oxygen conveyed throughout the body. With this blood stream carrying less oxygen, brain function is affected and heart rate increases in an attempt to
offset the oxygen deficit.