My Husband Has Recently Been Diagnosed With Chronic Restrictive Pulmonary

my husband has recently been diagnosed with chronic restrictive pulmonary disease, as well as already having COPD. What should be prescribed for his oxygen level from the concentrator and what range should his oxygenation be. One person told me 89 to 93, yet nurses are SOOO HAPPY to keep him at 99 or 100. I was told that higher levels than 93 could be detrimental. HELP!!! He will be coming home soon.