relation of O2 to CO2

[6Proz]

After 6 years of developing symptoms, my wife has recently been diagnosed with Primary lateral sclerosis (for her purposes, much like ALS).  Breathing has become a major problem. Pulmonary function test showed marginally okay results (PCO2 of 44, PO2 of 81). Pulse oxygen is usually 94- 96%, but over-night pulse-ox test showed low O2 about 15% of the time.  Pulmonologist, who does not have ALS/PLS patients but talked with ALS clinic, ordered O2 supplementation.  O2 supplementation has not helped much.  She still has trouble breathing, and is always fatigued.  Doctor says she is not close to needing NIPPV because O2 is okay.  I am concerned that she may still retain too much CO2 (her expiratory volume was 86% and residual volume far above predicted).  We are considering buying a home pulse-ox to help gauge her condition, and whether we need to take corrective action.  We have read about CO2 problems with PLS/ALS, but I couldn

[National Jewish]

You are right that the arterial blood gas results are "marginally okay."  At sea level the normal oxygen saturation level is 94% to 96%.  During the night it is normal for this to drop to 92%.  Oxygen saturation (SaO2) can be measured by an oximeter as well as by an arterial blood gas.  At sea level the normal oxygen level is 95 mm Hg to 100 mm Hg.  An arterial blood gas is done to measure the oxygen level (PaO2), since it cannot be measured by an oximeter.  At sea level the normal carbon dioxide level is 35 mm Hg to 45 mm Hg.  Just like with the oxygen level, an arterial blood gas is done to measure the carbon dioxide level (PaCO2), since it cannot be measured by an oximeter.  There is no linear relationship between the oxygen saturation level and the carbon dioxide level.

Your wife

[starion]

You need a specialized, more sophistocated set-up to test CO2 than those of us who have an oximeter for O2.  ONE of these systems are at this website & it costs over $1,300 on this site--there are doubtless other places you could purchase similar equipment at a range of prices.  Oximeters can be purchased for about $300-375 or so at various places on-line.

You should speak with the doctor about what is appropriate for her medical monitoring and needs.  If he believes it is medically NECESSARY for her condition, ask him to prescribe it & submit a pre-authorization request with her insurer so it MAY be at least partially covered.  A FEW patients have been able to get oximeters covered by insurers, but most of our insurers have refused on the grounds that oximeters are only approved for CLINIC use & not personal home use.

http://www.buyemp.com/dept.asp?dept_id=1030104

Good luck!
Aloha,
Starion