My husband had hip replacement revision surgery 8 days ago. last night he complained of frequent urination that kept him up at night. why is this?

Postop diuresis: Two possibilities likely. 1) IV fluids given at time of surgery now being mobilized by kidneys and excreted as urine—excessively sometimes. 2) bladder infection, especially if a catheter used during anesthesia or after—usually associated with itching/burning, cloudiness of urine or bad odor.

Dysuria: Agree with dr linville. Also consider bph/prostatitis from anesthetics and pain meds.