The surgery for an initial biopsy, or evaluative biopsy after treatment, or the installation and removal of a catheter, may have involved general anesthesia - and if there is subsequent surgery as treatment there will certainly be general anesthesia. Such anesthesia profoundly affects the brain in ways that are not yet fully understood, although anesthesia studies are underway. Most side effects of this anesthesia are temporary, but any problems that persist should be reported to your doctors. Probably the most bothersome for anal cancer patients is the likely constipation post-surgery, a result of the anesthesia itself and any pain medication prescribed, as virtually all have constipating effects. Being prepared for the anesthesia experience can help you to relax before and after the surgery.