In surgery, control of bleeding is achieved with the use of laser or sonic scalpels, minimally invasive surgical techniques, electrosurgery and electrocautery, low central venous pressure anesthesia (for select cases), or suture ligation of vessels.[13] Other methods include the use of blood substitutes, which at present do not carry oxygen but expand the volume of the blood to prevent shock. Blood substitutes which do carry oxygen, such as PolyHeme, are also under development. Many doctors view acute normovolemic hemodilution, a form of storage of a patient's own blood, as a pillar of "bloodless surgery" but the technique is not an option for patients who refuse autologous blood transfusions.