Is it permissible for kidney patients who undergo four hours of dialysis to combine the Dhuhr and Asr prayers as a delayed combination (jam‘ ta’kheer), knowing that they experience extreme fatigue during and after the procedure, and is it permissible for them to shorten the prayer?

It is permissible for the sick to combine two prayers according to many scholars. If the time for the first prayer begins before the operation, then it is permissible to combine them by performing them earlier (jama’ taqdim) or later (jama’ ta’khir). If the time for the prayer does not begin until after the operation has started, then it is permissible to combine them by performing them later (jama’ ta’khir). Combining prayers is easier given the severe exhaustion mentioned, and because it is a concession, and Allah loves that His concessions be utilized. Shortening the prayer (qasr) is not permissible because shortening is specific to travel.