Hydromorphone 0.05 mg/kg IV or
Fentanyl 5 mcg/kg IV (with constant rate infusion, 3-6 mcg/kg/hr)
Midazolam 0.2 mg/kg IV
Propofol/Alfaxalone 4 mg/kg IV
*Preoxygenate with 100% O2 for 5 minutes before induction.
Maintenance: Isoflurane or sevoflurane with 100% oxygen
Given the history of pulmonary metastatic disease, I would recommend spontaneous ventilation for the duration of the procedure. Mechanical ventilation can be performed however I would utilize a higher respiratory frequency (15 bpm) and lower tidal volume strategy (8 mls/kg), maintaining the peak-inspiratory pressure between 6-8 cmH2O.
A balanced crystalloid may be used for the procedure, however I would limit the fluid rate to 2 mls/kg/hr given the history of heart disease.
Local regional anesthesia:
A ring block at the base of the tail or a coccygeal epidural would be beneficial for pain management with:
Bupivicaine PF 0.5 mg/kg or
Ropivicaine PF 0.5 mg/kg