Mom 86yrs bedridden dementia dysphagia and fed with peg tube. had a stroke 6years ago.got mild aspiration pneumonia. on 1liter sats at 91%. is it bad?

Aspiration: Such patients frequently get aspiration pneumonia. The long term prognosis is not good. The short term is not necessarily terrible but if aspiration is repeating then things get worse.

Good for 1 liter: A pao2 of 60 mm/hg is 90% spo2 so your moms pao2 is slightly less, probably 2 liters will get her to 92% which is reasonable. Normal pao2 is 75-100mm/hg. To fully saturate the rbc' you need an oxygen tension between 75 and 100% which in your moms case will not be possible. Plus, giving her too much oxygen may decrease her respiratory drive and cause her to become apneic and retain co2.