Dave Majumdar
While a recent RAND Corporation study concluded that Russia could overrun NATO’s member states Estonia, Latvia and Lithuania in the Baltics within sixty hours, the war games did not simulate the use of nuclear weapons. If, however, a war were to breakout between NATO and Russia, nuclear weapons would certainly come into play—especially if the conflict were going poorly for Moscow.
Unlike the Soviet Union, which had a stated “no first use” policy, modern Russia explicitly rejected that pledge in 1993. In fact, as Moscow’s conventional forces continued to atrophy during the economic and social meltdown of the 1990s, Russia developed a doctrine called de-escalation in 2000. Simply put, if Russia were faced with a large-scale attack that could defeat its conventional forces, Moscow might resort to nuclear weapons. In 2010, Russia revised the doctrine somewhat as its conventional forces started to recover from the aftermath of the Soviet collapse—the current version states Moscow would use nuclear weapons in situations “that would put in danger the very existence of the state.”
http://nationalinterest.org/blog/the-buzz/the-brink-when-russia-would-use-tactical-nukes-nato-15281