Hi Jo-In general...
In center they can choose a setting on the machine to warm the blood a bit as it's circulated through the machine. You have to keep in mind that the blood it outside of the body cycling through the machine constantly..so it's very common for people to get the chills during treatment. That's why most centers provide new patients with blankets....and most veteran patients will usually have a bag with at least one more blanket (and a pillow, etc)
On NXStage home hemo, there are a few settings that you can choose to help with the chills...including heating the dialysate (either hanging bags or the pureflow)...to help alleviate the cold/chills.
That being said, people who are more predisposed to getting chills/cold (i.e. poor circulation) will get colder quicker. Also, if someone has a fever while on treatment, they can experience chills as well!
Finally in our Fresenius center (and us at home doing home hemo) wear the white "SMS Versa Gowns" which meet certain criteria for being liquid repellent See here:
http://amdritmed.com/bin/Medicom/public/uploads/catalogs/530762713b848.pdfHope this helps a bit!