I have been doing research on the Disassociation curve and I have a question. With a right shift caused by acidosis or increased HGB levels you get a decreased SPO2 value with the same PA02 pressure. According to my research this is very efficient at the tissue level because it has a looser binding to the 02. Soooo how is this ever a problem? I understand how a left shift would be a problem. But a right shift seems very efficient at the tissue level.
If you really must categorize things into "good" and "bad," a right shift is sorta good for nasty, shocky, hypoxic states because it helps unload that oxygen at the tissues. It also makes it harder to bind the oxygen in the alveoli, but if somebody's breathing effectively -- better yet, if we're breathing for them with high-concentration oxygen, at whatever rate we please -- we can usually deal with that. We'll just breathe more, increasing PaO2 as necessary. As long as the lungs are functioning properly we can usually maintain a nice saturation in the blood, but we CANNOT do anything to unload that oxygen at the tissues. So a left shift would help us oxygenate the blood (but we probably don't need help with that) while making it harder to actually deliver that oxygen to the hungry cells. Bad deal.
That's why right shifts are considered more physiological for most distressed states like shock, sepsis, or just running a 5k. A left shift is great for watching TV (hey, who wants to breathe hard for that?) but not for most emergencies.
Remember that your body likes to be able to both scale up metabolic processes for high demand and also scale them back to conserve energy when demand is low. (Why have a parasympathetic system at all? Wouldn't it be better to be oozing adrenaline from our eyeballs and constantly bouncing off the walls? Well, it might make Thanksgiving dinner a little stressful.)
Obviously this all changes if you're having trouble oxygenating the blood, such as in respiratory emergencies.
