Poor peripheral circulation-poor peripheral circulation leads to false reading due to the lack of haemoglobin in the extremities. the earlobe is more central so retains its blood supply.
cyanide and co will give false readings from any probe due to thier effect on haemoglobin. co binds to haemoglobin to form carboxyhaemoglobin which cannot be distinguished from oxyhaemoglobin by oximetry. oximetry will indicate a higher % arterial saturation of oxygen than is actually present.
oximetry should be applied as soon as possible in an emergency and regularly monitored to ensure early management of hypoxaemia.