Christina:
博迈克 has close to the correct answer. "Shotgun" is actually a form of Advertising Technique. Shotgun Shells, at least in terms of "bird shot" can fire dozens and even hundreds of Lead Pellets.
As a Sales Technique, an equivalent form of advertising your product or business would be like taking a box or several boxes of your business cards to a local Sporting Event like a Football game. Then, every time your team scores a Goal, you jump up with all the happy fans around you, that Throw half a box of your Business cards into the air. That is "Shotgunning".
Also, distributing "flyers" such as a Thousands of Photocopies of your advertisement on Cars, House Doors and so forth, is also a form of "Shotgunning.'
Also, advertising with Newspaper Ads, Radio Ads, TV ads, and BillBoards to get customers, is also a form of "Shotgunning".
So with the Medical Tests and Lab Work, as in:
That means every test in the book, CT, CBC, chem. seven, tux screen, Cristina, you're on labs, George, patient workups, Meredith, get Katie for a CT, she's your responsibility now.
It refers to trying every possible medical test that can be done to get a proper diagnosis of the patient.
.---Warm Regards, Bruce