I am pre op, which mcg dosage would you recommend for biotin?

Also, is there anything else I could be taking for hair loss or to prevent hair loss as much as possible post op?

Deficiencies of iron and zinc will result in hair loss...

Anyhow, the majority of post-op people experience some hair loss several months after surgery due to a phase called telogen effluvium.

Surgery, childbirth, and other 'shocks' to the human body may stop the growth of head hair. Hair loss due to telogen effluvium is temporary and the hair usually starts returning by 1 year post-op.

https://patient.info/health/telogen-effluvium

There is no preventing it. It is going to happen. It is going to stop. Your hair is going to come back. Start making peace with that. The hair loss is triggered by many things, including, as the poster above said, the shock to your system. Mine was worst from Month 3 to Month 7. I'm almost a year out and my hair is coming back gangbusters right now.