There are more risks with this operation due to the fat and its surrounding tissues becoming necrotic (dead tissue). If the fat becomes necrotic from lack of blood supply, the fat tends to turn orange-ish clear and drain from the incision. If the tissue becomes necrotic, that's a whole other ballgame! You must have the tissue removed before a major infection develops, possibly causing gangrene. If anything happens regarding tissue necrosis or compromised vascularity please research Hyperbaric Oxygen Therapy (HBOT) it could save your breasts AND your life. I have a separate section on this.
Even with the ultrasonic technique, patients have been known to receive actual burns from the ultrasonic technique. The fat is actually melted within the body by 'exciting' the fat molecules with high frequency radio waves and is suctioned out. There may be asymmetry, hyper-pigmentation (permanent dark spots) from the bruising. Major blood loss is a factor is some cases. As is hematoma and infection. Unfortunately in most breast reductions, breast feeding will become a memory for any future children. Thankfully there may be newer techniques which may prohibit this type of loss. There is also the risk of loss of blood supply to the treatment area and permanent numbness due to nerve damage.
Another risk of breast reduction is pulmonary Thromboemboli, although not as high of a risk as it is with liposuction-assisted reductions or when liposuction is performed in combination with breast reduction. A thromboebolus is a blood clot and this blood clot can break free and travel to the lungs resulting in pulmonary Thromboemboli. This can put a patient into adult breathing distress and subsequently into cardiac arrest or coma -- leading to the loss of oxygen rich blood to the brain. Pulmonary Thromboemboli can happen within three (3) weeks of the surgery but will most likely show symptoms of shortness of breath and fatigue within the first 72 hours. However, pulmonary Thromboemboli can occur suddenly, without warning. Most patients with P.E. collapse and begin rapid deterioration after attempting to climb a flight of stairs.