My little babe Onyx is in critical condition. His urethra is blocked and his potassium levels are at fatal levels. This happened in the last 24 hrs.

Onyx is the goofiest, most laid back little bud. I adopted him from the humane society two years ago. Please help me give Onyx more of a fighting chance! He is hanging on and is a fighter but he is in seriously critical condition. He unfortunately is so laid back that we didn't realize what was happening till 24 hrs in. Any and all help is appreciated and will help him stay in urgent care longer. Thank you in advance!!! Onyx is so special to me.