The method was surprisingly effective, though it was unclear to doctors of the time exactly how it worked. It was theorized that the nicotine in tobacco smoke stimulated cardiovascular activity, or that it warmed the victim, or that it dried the water in their lungs, but nobody's been able to pinpoint it, and those jerks on the ethics board won't green-light our study. So the most reasonable explanation was the element of surprise. Because even when unconscious, the shock of unwittingly getting bellows and a puff of nicotine up the rear is enough for most people's hearts and adrenal glands to start a-pumping.
There was a whole public safety campaign surrounding smoke enemas, which included hanging smoke-blowing kits near popular swimming areas in case someone was in dire need of some lifesaving carcinogenic sodomy. A group of doctors even set up a nonprofit called the Institution for Affording Immediate Relief to Persons Apparently Dead From Drowning, offering cash rewards to anyone who successfully learned how to make buttfog. If you've ever taken a CPR class, do you remember how they taught you to hum "Stayin' Alive" to get the proper rhythm? Well, in the service of public health education, there was also a song about how to air-rim someone, though it was admittedly less catchy.
Eventually, the practice died out -- not because people thought it was bullshit, but because doctors finally figured out that smoking caused cancer. So with the rise of vaping, maybe it's time to bring this technique back into fashion.