https://globalsecurityreview.com/nuclear-de-escalation-russi...
As per Russian nuclear doctrine, if Russia is attacked, if it faces an existential threat, it reserves the right to use ... first use nuclear weapons.
My statement is based on what a high ranking indian military official (who has directly trained with Russian strategic forces) has publicly said on this matter - https://youtu.be/pNHUDDqTgdI?t=515 (see at 8m:34s).
"There is a risk of Russia using nuclear weapons. Not against Ukraine, but against the West," said Dmitry Suslov, a member of Russia's Council on Foreign and Defence Policy. "If a single American missile hits Russian military infrastructure inside Russia, we would make an historic jump towards nuclear Armageddon. According to official Russian nuclear doctrine, Russia would launch a strategic nuclear strike against the US and all Nato countries as soon as we witness the launch of Western missiles against our territory, no matter how they are armed. Then the whole planet will die."
Other commenters have hinted at Russia staging a false flag 'dirty bomb' incident, to justify making a nuclear response. That's an alarming thought. But I think it's equally alarming to see how we're being manipulated by the media into accepting some kind of limited nuclear conflict as inevitable and being pre-programmed to accept the "He hit me first!" jutification --especially as [see my other posts on what Putin actually did and didn't say] it seems like the Russian people are being similarly prepared for similar justification.