sunandsea, sorry I am late in chiming in. I understand your concern and confusion. Pneumonia changes things dramatically. Your original post did not mention pneumonia; I'm assuming your husband was diagnosed a few days later & I'm hoping he is doing better now with the course of antibiotics?
..."pneumonia is a lung infection in which the inflammatory response of the lung tissue results in a build-up of fluid -- pus, basically -- that fills up some of the alveoli. What that means for those alveoli is that they can no longer participate in getting oxygen into your blood... they can't fill up with air because they're already filled up with fluid. So, these alveoli are basically "off-line", and overall this results in a decrease in the lungs' ability to oxygenate the blood."
(https:/
www.quora dot com/What-are-the-effects-of-pneumonia-on-the-respiratory-system)
As both Laurie & Tillie mention, a pulmonologist with ALS experience may decide that low dose, supplemental oxygen may be needed for a short period of time, but this needs to be monitored by arterial blood gas draws (not fun for the patient) and can't be effectively monitored with the finger tip pulse oximeter.
....."Some situations may require administering oxygen, such as pneumonia due to infection or aspiration. If this occurs in patients with respiratory muscle weakness and hypoventilation, then it is important to provide both assisted ventilation and supplemental oxygen, and use ABGs to monitor them". And, ..."If oxygen is being administered, one cannot use noninvasive oximetry to tell whether enough assisted ventilation is being provided; repeated arterial blood gas specimens (ABGs) would be needed".
(http:// gbppa dot org/oxygen.htm)
As I'm sure you know, in ALS it is the delivery system/muscles of inspiration or hypoventilation that is the primary reason the PALS is not getting enough oxygen. Other co-morbidities such as COPD, OSA (obstructive sleep apnea) complicate matters further. Administering oxygen does not provide assistance to the weakening respiratory muscles.
"In hypercapnic respiratory failure due to hypoventilation, the SaO2 falls due to the rise of the CO2. The alveoli in the lungs (tiny gas exchange units) should clear most of the CO2 out with each breath. Instead, with hypoventilation, CO2 accumulates and thus there is decreased room in the alveoli for oxygen. When mechanical ventilation using room air is provided, it lowers the CO2 in the alveoli, corrects the SaO2 and rests the respiratory muscles. The ventilator should be adjusted to achieve a normal SaO2, on room air. If oxygen is being administered, one cannot use noninvasive oximetry to tell whether enough assisted ventilation is being provided; repeated arterial blood gas specimens (ABGs) would be needed." (
http://gbppa dot org/oxygen.htm)
Another consideration is that "room" air is composed of 78% nitrogen, 21% oxygen and 1% trace gases. When the concentration of one gas is increased, it will lower the concentration of others. Nitrogen is also responsible for secretion of a surfactant that prevents collapse of the alveoli with expiration. Oxygen is a drug, and must be treated/monitored as such. O2 therapy provided to a person with ALS is rarely used due to CO2 retention and the delicate balance of nitrogen to oxygen.
I am not a doctor, nor a respiratory therapist; this is just research from the web I thought I would pass on.
Chally, if your reading this as well, what is the elevation where you live? Just wondering if you live at a high elevation? Early on after diagnosis, I almost, inadvertently killed my husband by taking him to the Onizuka Visitor Center @ Mauna Kea (Big Island, HI) which is at 9,200 ft. We were there for night sky observation and access to their telescopes. I did not yet know it, but in addition to early stage ALS respiratory suppression, he was also developing a large pulmonary embolism! I had not yet processed the depth of his respiratory problems. Anyway, high elevations also affect your oxygen saturation levels, which is why I ask (but I also assume your pulmonologist would have factored that in as well?).
