Is it safe to have two procedures done under anesthesia 37 days apart from each other?

It is perfectly safe as far as anesthesia is concerned. The big unknown is whether you will be in a lot if pain still from your back surgery. You should ask your back doctor what they advise

The risk of complications increases with orthopedic procedures like SI fusion, especially blood clots (DVT)
It is best to do a full rehab after the SI fusion before undergoing another general anesthesia.
Regards
Dr. J

Yes, it is generally safe to have two procedures under anesthesia 37 days apart, provided you’re in good health and your medical team agrees with the timing. The key factors include your overall health, how well you recover from the first procedure, and the specific requirements of each surgery. Both your orthopedic and cosmetic surgeons should coordinate to ensure that your recovery from the first surgery is adequate before proceeding with the second. Always follow your doctors’ advice and ensure you’re fully recovered between procedures.

There isn't much to go on from your description.
Age, past medical history, current medications, height and weight, etc. must all be considered.
Should none of these things be abnormal and your sacro iliac fusion goes smoothly you should be able to proceed.

All the Best,

Dr. J

As long as you're an excellent health, and it's certainly acceptable to undergo to general anesthetics 37 days apart. It doesn't really matter which procedure goes first.