How would Patriot missiles impact the Ukraine War?

Ukrainian authorities say Russia has launched another major missile attack on energy facilities and infrastructure. Local authorities in the capital Kyiv and and the northeastern city of Kharkiv reported explosions. The latest strikes come as Ukrainian military and civilian leaders warn that the Kremlin is preparing for a new widescale offensive as early as January.
It's been reported that the US is preparing to send Patriot missile systems to Ukraine. Russian officials say that arming Ukraine with Patriot missiles would be regarded as an escalation and would have consequences.