If it is difficult to place a catheter in this patient, I would administer the following:
Butorphanol 0.2 mg/kg IM or
Buprenorphine 0.02 mg/kg IM
with Alfaxalone 2 mg/kg IM
If the patient is still resistant for catheter placement, you may give another dose of alfaxalone at 1 mg/kg, IM.
In the highly fractious feline patient, I will administer dexmedetomidine 1-2 mcg/kg IM in addition to the above combination. Dexmedetomidine will cause a significant reduction in cardiac output but it is reversible with atipamezole and I personally feel it is still better than stressing the patient with aggressive physical restraint. The opioid/alfaxalone combination is usually adequate for sedation but some cats are just resistant to chemical restraint.
I would recommend pulse oximetry and flow-by oxygen with this patient since it can become apneic with the higher doses of alfaxalone.
For induction, an additional 1-2 mg/kg alfaxalone IV can be used for adequate relaxation of the larynx for intubation.
Maintenance anesthesia can be provided with isoflurane/sevoflurane.
Thank you and Happy Friday!