Optimal Perfusion During Cardiopulmonary Bypass: An Evidence-Based Approach
Murphy GS, Hessel EA II, Groom RC
Anesth Analg 2009; 108:1394-1417
Comment
This review focuses firstly on the hemodynamic and oxygen delivery variables of cardiopulmonary bypass, and secondly on the major components of the extracorporeal circuit, with the aim of being of assistance to perfusionists, anesthesiologists and surgeons alike to achieve optimal perfusion.
The authors conclude that there is insufficient data and evidence to determine how optimal perfusion can be achieved and that there is a critical need for high quality studies.
They state that since the vast majority of patients survive cardiac surgery with contemporary bypass techniques, it may be more appropriate to identify high-risk patients and concentrate efforts to optimize the techniques for these patients.
Methodologically, the authors have stated that they followed the principles of ACC/AHA process, however, the detail of how this was achieved is difficult to determine. The authors should be congratulated on a comprehensive review of the literature in the areas they have covered.
Guidelines
| Area of review |
Guideline(s) |
|---|---|
| - optimal mean arterial pressure |
- insufficient evidence to determine |
| - safe flow rate on bypass |
- insufficient evidence to determine |
| - hemodilution vs. packed red blood cell transfusion |
- not possible to declare a cause and effect relationship with adverse outcome - not possible to define safe treshold |
| - temperature management |
- no support for one strategy - avoid aggressive rewarming strategies |
| - pulsatile vs. non-pulsatile perfusion |
- uncertainty about effects and methods |
| - alpha stat vs. pH-stat |
- difficult to demonstrate benefit of either technique |
| - open vs. closed venous reservoirs |
- no conclusive evidence - potential benefits with closed reservoirs |
| - cardiotomy suction |
- further studies needed to define impact - potential benefits when avoiding suction |
| - arterial line filters |
- they reduce gaseous and particulate emboli and should be used |
Abstract
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 trans-
fusion 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 hemodi-
lutional anemia by increasing pump flow rates. Furthermore, the optimal tempera-
ture 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, par-
ticularly in high-risk patients.
