I too admire your courage at this very challenging time. A gentle reminder: maybe find whatever aspect of the Triple Gem most calms and centres your mind and heart, and decide on it now, so that when the time for 'going in' to the procedure arrives, you are already decided on it, and automatically know what to do.
I can remember when I was in hospital, with internal bleeding (spleen had a rupture). Breathing became painful, and reduced down to what felt like a few centimeters each way (I had a fractured rib). I grounded my mind in that
- the breath that I still had - and kept sending love into my body, visualizing it as light. So for me in that moment, my kammaṭṭhāna
from my ordinary daily practice, became my 'refuge' that got me through that experience with a relatively calm mind. (I got to keep my spleen, btw - it eventually healed.)
But one could choose any
aspect of the three Refuges, I suppose...recollection of the Buddha, of an aspect of the Dhamma that inspires one, or the Sangha (a teacher one has a connection with?), etc. This is just a suggestion of mine based on personal experience, I'm not a professional of any kind! But I offer it as something that helped me thorugh a challenging time, and might
be helpful to you.
In the end, your faith and practice reside in your heart and mind already, and will arise at the right time, I intuit. May you be at peace, sattva! Whatever happens, may the goodness of your faith and practice guide and protect you. I also will await to know the exact time of the op. and you will be in my heart-and-mind especially
at that time.