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In this review, we summarize the best available evidence to guide the conduct of adult cardiopulmonary bypass (CPB) to achieve "optimal" perfusion. At the present time, there is considerable controversy relating to appropriate management of physiologic variables during CPB. Low-risk patients tolerate mean arterial blood pressures of 50-60 mm Hg without apparent complications, although limited data suggest that higher-risk patients may benefit from mean arterial blood pressures >70 mm Hg. The optimal hematocrit on CPB has not been defined, with large data-based investigations demonstrating that both severe hemodilution and transfusion of packed red blood cells increase the risk of adverse postoperative outcomes. Oxygen delivery is determined by the pump flow rate and the arterial oxygen content and organ injury may be prevented during more severe hemodilutional anemia by increasing pump flow rates. Furthermore, the optimal temperature during CPB likely varies with physiologic goals, and recent data suggest that aggressive rewarming practices may contribute to neurologic injury. The design of components of the CPB circuit may also influence tissue perfusion and outcomes. Although there are theoretical advantages to centrifugal blood pumps over roller pumps, it has been difficult to demonstrate that the use of centrifugal pumps improves clinical outcomes. Heparin coating of the CPB circuit may attenuate inflammatory and coagulation pathways, but has not been clearly demonstrated to reduce major morbidity and mortality. Similarly, no distinct clinical benefits have been observed when open venous reservoirs have been compared to closed systems. In conclusion, there are currently limited data upon which to confidently make strong recommendations regarding how to conduct optimal CPB. There is a critical need for randomized trials assessing clinically significant outcomes, particularly in high-risk patients.

NONINVASIVE COlHuntsman et al.perfusion imaging using surfactant stabilized microbubbles. (abstr) Circulation 64 (suppl IV): IV-203, 1981 infarctions are not recognizable by standard clinical criteria. ' Current criteria for the clinical evaluation of circulation in myocardial infarction are often timeconsuming, subjective and prone to error. Clinicians are urged to rely on "monitoring of heart rate and rhythm, measurement of systemic and arterial pressure by cuff, obtaining chest roentgenograms to detect heart failure, careful and repeated auscultation of lung fields for pulmonary congestion and edema, measurement of urine flow, examination of the skin and mucous membranes for evidence of the adequacy of perfusion, and arterial sampling of Po2, Pco2, and pH when hypoxemia or metabolic acidosis is suspected."3 Physicians are often reluctant to use invasive CO determinations, except in selected patients, because they cause discomfort and may result in complications.4 I Given the importance of CO assessment, a noninvasive, easily

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Death determined by neurologic criteria, commonly referred to as "brain death," occurs when function of the entire brain ceases, including the brain stem. Diagnostic criteria for brain death are explicit but controversy exists regarding nuances of the evaluation and potential confounders of the examination. Hospitals and ICU teams should carefully consider which clinicians will perform brain death testing and should use standard processes, including checklists to prevent diagnostic errors. Proper diagnosis is essential because misdiagnosis can be catastrophic. Timely, accurate brain death determination and aggressive physiologic support are cornerstones of both good end-of-life care and successful organ donation.

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