The hosts made three alterations to the side beaten 3-0 in the first leg at Stamford Bridge, with Sidcley, Tamas Kadar and Denys Harmash recalled.
The Blues showed seven changes to the side who drew 1-1 with Wolves at the weekend, with Marcos Alonso, Andreas Christensen, Davide Zappacosta, Ruben Loftus-Cheek, Giroud, Callum Hudson Odoi, and Willian all starting.
And it took the visitors just five minutes to extend their aggregate advantage to four goals, as a corner from Willian was headed on by Loftus-Cheek and Giroud pounced to poke the ball home from six yards out.
Dynamo had the ball in the net with 21 minutes on the clock, but an offside flag cut short the celebrations of Harmash before they had even started.
That was not the case 12 minutes before the interval, as Giroud struck again to make the score 2-0 to Chelsea on the night and 5-0 on aggregate.
Alonso and Loftus-Cheek combined, with the former sending over a cross which Giroud despatched with ease for his eighth goal in the competition this season.
On the stroke of half-time the Blues extended their lead to three on the night as Giroud exchanged passes with Hudson-Odoi, whose cross laid the chance on a plate for Alonso.
Despite being totally out of the tie, Dynamo made a spirited start to the second half, only to concede yet again just before the hour mark.
It was Giroud on target again to complete his hat-trick, with the Frenchman heading home from a Willian free-kick whipped in from the right flank.
A matter of minutes later home keeper Denys Boyko made a superb fingertip save to keep out a 25-yard free-kick from Alonso.
With 12 minutes to play Hudson-Odoi completed the scoring, as he had done in the first leg, racing on to a Giroud throughball to slide the ball past the advancing Boyko and make the final aggregate score 8-0.