Why should you not cannulate on the side of a masectomy?

Cannulating on the side of a mastectomy should be avoided because it may increase the risk of lymphedema, a condition characterized by swelling due to lymph fluid buildup. The removal of lymph nodes during the mastectomy can impair lymphatic drainage, making the area more vulnerable to complications. Additionally, there may be a higher risk of infection and discomfort in the affected arm. Therefore, it's generally recommended to use the opposite side for venous access when possible.