Effects of a 100% perfluorooctylbromide emulsion on ischemia/reperfusion injury following cardioplegia

Clinical potential of nonhemoglobin oxygen therapeutics in cardiac and general surgery

Significant efforts have been made over the past 70 years to find a solution that could substitute for blood. Over the years, the focus has shifted to developing a solution capable of delivering oxygen to the tissues. Fluorocarbons (FC) are highly inert solutions with a high solubility for all gases, making them a prime candidate to become such an oxygen delivery agent. Although clinical research efforts into the use of these agents as substitutes for blood transfusions continue at present, the rapid disappearance of emulsified FCs from the vascular space and accumulation in the liver and spleen may well limit their usefulness as transfusion substitutes. Because of their ability to dissolve significant quantities of oxygen and carbon dioxide, these agents may be more attractive as oxygen delivery agents during periods of local or global organ ischemia, including preservation of organs for transplantation. FCs have also been tested in animal models of cardiopulmonary bypass, and may be efficacious in adsorbing the gases present in air emboli. Recently a second class of oxygen therapeutics (allosteric modifiers) has been developed, and these agents enhance oxygen delivery by shifting the oxygen dissociation curve to the right, thus increasing tissue PO(2). Allosteric modifiers have been shown to effectively shift the p50 of hemoglobin 10mm Hg at clinically relevant dosages, and have been shown (in animal models) to reduce cerebral infarct size following carotid ligation and to improve myocardial performance following myocardial ischemia. Despite significant research efforts, however, none of the solutions under development are currently approved for clinical use by the Food and Drug Administration, with the exception of myocardial contrast imaging agents.

Clinical potential of blood substitutes or oxygen therapeutics during cardiac surgery

Several complications and unforeseen adverse side effects have colluded to keep commercially available blood substitutes or oxygen therapeutic agents tantalizingly "just out of reach." Because the three classes of agents under development have different oxygen-delivery mechanisms and side-effect profiles, each can be expected to have its own unique clinical applications, particularly in the cardiac surgery population. The fact that South Africa recently approved one HBOC for use as a transfusion alternative in patients with chronic anemia indicates that initial clinical use is near for a number of these agents. It is to be hoped that they will be used for several applications rather than just for a "transfusion alternative." Despite some frustrating limitations, all of these agents are antigen and pathogen free, have an acceptable side-effect profile, and have a long shelf life. Increasing volunteer-blood-donor shortages, coupled with increasing blood-transfusion needs, and expanding human immunodeficiency virus and hepatitis B and C epidemics, continue to fuel the demand for further development of these products. Transfusion alternatives will eventually become commercially available--the question is "when," not "if." Equally important, these agents' potential for serving as effective oxygen-delivery agents to ischemic tissues heralds an entirely new field of clinical investigation.

Blood Substitutes in Cardiac Surgery

A safe, inexpensive, noninfectious substitute for red blood cells has long been sought. Despite tremendous advances in blood banking, the logistics of collecting, transporting, and storing human red blood cells contin ues to create infection and shortage problems. The two basic types of blood substitutes currently under devel opment are hemoglobin based and fluorocarbon based. Although they each transport oxygen differently, the basic advantages and limitations are the same. Blood substitute advantages include the unique capacity for room temperature storage, noninfectivity, adequate supply, and low toxicity. Restrictions include limited dosing in the acute period, limited intravascular half-life and, for the fluorocarbons, a requirement for a high PaO2. In addition, there remain questions about the relationship of nitric oxide metabolism to hypertension in hemoglobin solutions. Early clinical and laboratory trials have shown that both types of solutions are effective oxygen-delivery agents, with acceptable side- effect profiles. Clinical trials are currently underway to determine the safety and efficacy of these solutions in patients undergoing cardiopulmonary bypass.