After "serene and peaceful", you have HE slowly suvvumbs.... which means these two adjectives refer to HE. It could refer to doctors if you change the sentence, for example:
Appearing serene and peaceful as they slowly work on the patient.
Even though the above is a correct sentence, yet the sentence doesn't make any sense, as doctors usually don't appear serene and peaceful during an operation. Just for your reference.
- For Teachers