CO affinity to Hb_____ compared to O2 is

(D) >200 times# CARBON MONOXIDE is a common cause of accidental and suicidal poisoning. Its affinity for hemoglobin is 250 times greaterthan that of 02- It therefore binds to hemoglobin and reduces the 02-carrying capacity of blood.> The symptoms of poisoning are due to tissue hypoxia; they progress from headache and fatigue to confusion, syncope, tachycardia, coma, convulsions, shock, respiratory depression, and cardiovascular collapse.> Carboxyhemoglobin levels below 15% rarely produce symptoms; above 40%, symptoms become severe. Treatment includes establishment of an airway, supportive therapy, and administration of 100% O2.> Sulfur dioxide, ozone, and nitrogen dioxide are mucous membrane and respiratory irritants. Methane is a simple asphyxiant.> PATHOPHYSIOLOGYFig: Carbon monoxide shifts the oxygen-haemoglobin saturation curve to the left and changes it to a more hyperbolic shape. Less oxygen is available for the tissues. Shown is the oxygen diffusion gradient difference at 50% saturation> Carbon monoxide has 210 times greater affinity for haemoglobin than oxygen. A small environmental concentration will thus cause toxic levels of carboxyhaemoglobin.> After the carbon monoxide has selectively bound to haemoglobin the oxygen-haemoglobin dissociation curve of the remaining oxyhaemoglobin shifts to the left, reducing oxygen release.> The affinity of carbon monoxide for myoglobin is even greater than for haemoglobin. Bindin g to cardiac myoglobin causes myocardial depression, hypotension and arrhythmias.> Cardiac decompensation results in further tissue hypoxia and is ultimately the cause of death.> Carbon monoxide has a predilection for 'watershed' areas of the brain where there is a meagre blood supply.> Basal ganglia, with their high oxygen consumption, are most often affected. Other commonly affected areas are the cerebral white matter, hippocampus and cerebellum.