Pre-operative Considerations:

Please give pimobendan (PO), lasix (PO) and spironolactone (PO) as prescribed the morning of the surgery. I would withhold the benazepril and diphenoxylate until after surgery.

Gabapentin 10mg/kg PO (for sedation)

Anesthetic Plan:

Cerenia 1 mg/kg IV
Buprenorphine 0.02 mg/kg IV

Midazolam/diazepam 0.2 mg/kg IV
-The benzodiazepines will not likely provide enough muscle relaxation to facilitate opening the patient's jaw but they will reduce the amount of induction drug and inhalant require for general anesthesia.
*Reversal – flumazenil 0.02 mg/kg IV

Propofol/Alfaxalone 4 mg/kg IV (to effect)

– After premedication, I would sedate the patient with 1-2 mg/kg of propofol/alfaxalone IV to evaluate how far the jaw will open (if possible) before intubation. This way, the patient will still be spontaneously breathing in case it is very difficult or impossible to intubate the patient and you can either re-evaluate your plan or recover the patient. A common error is to give too much induction drug like propofol or alfaxalone and then the patient becomes apneic and you still can't intubate!

Anesthetic Maintenance:
Isoflurane or Sevoflurane

Fluid Therapy:
2 mls/kg/hr of a balanced crystalloid

Pain Management:
Dental blocks with local anesthetics (lidocaine, bupivicaine or ropivicaine)
Buprenorphine 0.01 mg/kg IV
-I would avoid NSAIDs since the patient is currently on diuretics and ACE inhibitors which may adversely affect the kidneys.
You may consider gabapentin or tramadol orally for pain control.