Carboxyhaemoglobin dissociation in the cadaver following attempted resuscitation.

A series of 300 cases of fatal carbon-monoxide poisoning showed wide variations in carboxyhaemoglobin saturation. Levels below 50% in 24 subjects under the age of 70 were probably falsely low following attempted resuscitation on the way to hospital. Artificial respiration, especially with oxygen-rich gas, causes dissociation of carboxyhaemoglobin in the lungs of the cadaver while movement of blood into and out of the lungs, with mixing, lowers the saturation levels in the neighbouring large veins. In four cases subclavian blood showed saturation levels much lower than blood from sites further from the lungs. Blood should be taken from the femoral vein to get true readings.