>

We use a ketamine/xylazine mix for long-acting anesthesia during mouse brain surgeries in the brain cancer research lab I work in.

"Ketamine ia a noncompetitive, centrally acting, dissociative general anesthetic that provides amnesia, analgesia, and immobility. Ketamine typically is used as an adjunct anesthetic, due to its limited ability to provide adequate skeletal muscle relaxation. When combined with xylazine, the combination is regarded as the agent of choice for rodent injectable anesthesia. The popularity of ketamine–xylazine (KX) is mainly due to its supplemental effects (that is, analgesic properties, muscle relaxation, and sedation)."
"Xylazine (Rompun, Bayer) produces moderate sedation and minimal analgesia in rabbits. It is seldom used as a sole agent but is given in combination with ketamine. The combination causes cardiovascular and respiratory depression, and cardiac arrhythmias are produced at high doses. Xylazine and ketamine have been associated with a high mortality rate (Flecknell et al., 1983)."

Ketamine info source
Xylazine info source
I can attest to the lethality of ketamine/xylazine. We try to titer our doses to be the minimum necessary to keep mice asleep and immobile, but not all mice respond the same, and they develop resistance to ketamine the longer it is used. We sometimes have to "bump" their doses and even small amounts can lead to respiratory and/cardiac failure. Our senior tech has successfully resuscitated several mice by doing mini chest compressions and restored breathing. I've saved two this way. But we still lose between 1-5% of mice due to overdose in our experiments.
I am a doctor, but the Ph.D. kind, not the M.D. kind lol
Picked a few choice paragraphs for info, this isn't the entire article.

More than 40% of street drug samples tested in Rhode Island contained the animal tranquilizer xylazine, according to a new analysis out of Brown University. It’s the latest sign that the drug, which causes sedation and can lead to skin infections and overdoses, is continuing to spread through the illicit drug supply in the United States.
Xylazine, often referred to as "tranq," concerns public health experts because it causes such heavy sedation, which can leave people exposed and vulnerable for long stretches of time. It’s not an opioid, so Naloxone — which can help treat opioid overdoses — doesn’t work to reverse its effects. Xylazine has become increasingly involved in overdose deaths in the U.S.
The drug was common recreationally in Puerto Rico and then started showing up in Philadelphia in the early 2010s, Shover said. For the last decade, it’s been mostly confined to Philadelphia, she noted. Over the past few years, it started appearing in other places — like in Massachusetts and New York City.

Anyone know more about this drug? Curious as to what the draw is considering it's not an opioid, is it something more like Ketamine? I'd have to guess a cheap, accessible drug like that could certainly do some damage, although not sure how many people would go with that over something like heroin/fent. >

When ketamine was being used recreationally in the 90s, kids would tell one another that it caused brain bubbles and all kinds of myths. 
It turned out it was useful for depression and may assist in helping with myelination of damaged neurons. Not only that, but compared to other anesthesia, it's less taxing on the system - it doesn't cause the respiratory changes other anesthetics can or tachycardia, that sort of thing. It's a pretty remarkable thing.
So, assumptions are a difficult thing to really make. I think the brain bubbles myth was such an assumption. I'm not saying this stuff could be good, I'm just saying assumptions and drugs don't always line up.
Ketamine was also used specifically for recreation, not as a cutting agent. 
Xylazine appears to be used specifically as a cutting agent in opiates, so it's probably just a cheap as shit sedative, no one is seeking it out on its own. In animals it's used with ketamine, so it probably adds something ketamine doesn't cover - muscle movement, etc. They're likely not at all comparable. 
Xylazine is a Phenothiazine while Ketamine is classified as a general anesthetic.
I am not a doctor, I just like drug topics.