DwayneEMTP Posted January 8, 2007 Posted January 8, 2007 The other night I was watching a series on a group going up Everest. When they were at about 24,000 ft (I think) the Doc (an ER Doc hired for the trip) was taking pulse ox readings from the members of the group. He was showing them to the camera and saying "See that? 65! Man, in the ER we hate anything below a 90, yet up here this is pretty much average" How can that be? I've spent some time in the hospital with sick relatives and if the pulse ox dropped below 90 for a short time, steps were taken. If it dropped below 80 people started to get pretty motivated... Is it just attributed to their acclimation time? I just don't get it, dang it.... Of course, other than the static acceptable numbers I've been exposed to, and hearing here that it has limited value in EMS, I know nothing about it really... Thanks all! Dwayne
fiznat Posted January 9, 2007 Posted January 9, 2007 It seems to me that the low reading is probably coming from two things: First, cellular respiration (in this case referring to the transfer of oxygen and carbon dioxide on and off of the cell) is driven by a pressure (saturation) differential between the air within the lungs and the blood within the capillaries. Oxygen normally diffuses from the air to the blood because the air will have a reletavly high concentration of oxygen compared to the bloodstream. With one concentration high and the other low, oxygen transfers to obtain a balance between the two. The same works for the offloading of CO2, where the air in the lungs normally has a low content and the blood a high content, so CO2 tends to diffuse into the lungs. At high atmospheric pressures, the amount of ambient oxygen is reduced, so you end up with a smaller difference between the concentration of inhaled oxygen in the lungs, and oxygen in the blood. Because the amount of oxygen transferred depends directly on the difference of concentrations between these two areas, LESS oxygen is transferred to the blood-- which results in the decreased O2 saturation the doc was referring to. Second, oxygen saturation monitors depend on an assumption that the person being measured is perfusing blood to the extremity that is being measured. This doesnt necessairly happen in the cold. The body's natural response to cold and stress (both of which I imagine are in abundance up there on the mountian) is to shunt blood inwards towards the core of the body and away from the extremities. If the oxygen saturation was bieng measured on the fingers, it would be no suprise to see that the numbers would be lower simply due to the fact that there is less blood there. Hope this helps!
DwayneEMTP Posted January 9, 2007 Author Posted January 9, 2007 That was great! So it sounds like you're saying the body isn't really dealing with a lower O2 sat level, only it is reported incorrectly due to the redirection of the highest volume of blood? Is that right? Though I certainly appreciate the physiology lesson (truly!) I was most curious about the body operating properly with such a reduced level of oxygen. Wouldn't that cause a break down in the Kreb's cycle (probably making an ass of myself now)? Your explanation makes great sense...thank you for taking the time to answer... By the way, Amazing Blog!! Normally I would rather set my hair on fire than read a blog...I look forward to your entries, I hope you're real proud of it!! Dwayne
EMT/S31 Posted January 9, 2007 Posted January 9, 2007 Pulse Ox readings are used as a crutch for providers that cannot properly evaluate a pt. If their lips are blue I am betting that they are going to need oxygen. Pulse Ox is going out the doors in hospitals too. In acute care settings Co2 output is measured and is a better way of assessing how much oxygen the patient really needs.
fiznat Posted January 9, 2007 Posted January 9, 2007 So it sounds like you're saying the body isn't really dealing with a lower O2 sat level, only it is reported incorrectly due to the redirection of the highest volume of blood? Is that right? No no, the body IS dealing with a lower oxygen saturation - because of the reduced atmospheric O2 as I described first - but also I was saying that I think the redirection of blood may ALSO play a factor as well. Then again I'm not sure of where the saturations were measured anyways, so it may not be a factor at all. The truth is though that these people do in fact have reduced oxygen saturation due to the reduced oxygen in the atmosphere. Though I certainly appreciate the physiology lesson (truly!) I was most curious about the body operating properly with such a reduced level of oxygen. Wouldn't that cause a break down in the Kreb's cycle (probably making an ass of myself now)? Nope you're right. The body does work on lower oxygen saturation, thats a major reason why climbing this high is such a great feat! These people go through the exhaustion of climbing, which is multiplied in intensity by the fact that it is difficult to breathe (and mantain any sort of saturation) up so high. You wouldnt catch me up there, no way! Youre also correct that the under reduced oxygen saturation, the body's production of energy -- ATP -- through the Kreb's cycle is slowed down. The Kreb's cycle is a process of producing energy using oxygen, called aerobic metabolsim. When the body is short on oxygen, it it is unable to use the Kreb's cycle and must use an anaerobic metabolsim (that is, "without oxygen"). The main producer of energy in this case is the process of glycolosis, which is basically the breakdown of sugars in order to produce energy. This method is WAY less efficient (something like 30 times less efficient) at producing ATP compared to the Kreb's cycle, and at the same time an offproduct of the cycle is lactic acid. This is what causes the burning sensation in your muscles when you are exerting yourself completely. Long term produciton of this acid causes problems in and of itself, not to mention the fact that you are producing less energy as well. Like I said, climbing is tough! By the way, Amazing Blog!! Normally I would rather set my hair on fire than read a blog...I look forward to your entries, I hope you're real proud of it!! Thanks man, that means alot!! :oops:
ERDoc Posted January 9, 2007 Posted January 9, 2007 Pulse Ox readings are used as a crutch for providers that cannot properly evaluate a pt. If their lips are blue I am betting that they are going to need oxygen. Pulse Ox is going out the doors in hospitals too. In acute care settings Co2 output is measured and is a better way of assessing how much oxygen the patient really needs. This is wrong in so many ways. If you have let your pt's oxygen level fall so low that they are cyanotic, you have failed them. Pulse ox is also helpful to know how serious the cyanosis really is. If you have a hemoconcentrated pt (ie smoker, COPD etc) they will become cyanotic at a much higher sat than an anemic person will. In order to become cyanotic you need to have 5grams/dl of deoxygenated hemoglobin. In a person with anemia with a hgb of 6, you would need to drop your oxygenated hgb to 1g/dL before you would be cyanotic. This equates with a pulse ox of 16 before they become cyanotic. You had better well know that they are in trouble before they get a sat of 16%. Don't speak for what goes on in hospitals before you have actually managed pts in one. Pulse ox is standard of care. It is used to make clinical judgements all of the time, including in acute care settings. Research your facts before you blindly post.
ERDoc Posted January 9, 2007 Posted January 9, 2007 Dwayne, when you go to altitude there is less O2 in the air, so there will not be as much in the blood. You will initially see a low pulse ox. After a few days, the body will compensate (in most cases) and the pulse ox will return to normal. There is much more going on physiologically, but this is a simple explanation. The partial pressure of atmospheric oxygen is half at the base camp on Everest of what it is at sea level. Emedicine probably has a good article on altitude sickness that might help answer some of your questions.
fiznat Posted January 9, 2007 Posted January 9, 2007 After a few days, the body will compensate (in most cases) and the pulse ox will return to normal. Could you mention a little more about this? How is the compensation achieved? RBC production?
ERDoc Posted January 9, 2007 Posted January 9, 2007 Could you mention a little more about this? How is the compensation achieved? RBC production? Yup, increased RBC production and hyperventillation and increased cardiac output among others.
fiznat Posted January 9, 2007 Posted January 9, 2007 Good havin ya around, Doc. You dont happen to have AIM do ya? I wanted to pick your brain a bit if youve got a sec...
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