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Ann Thorac Surg 2001;72:547
© 2001 The Society of Thoracic Surgeons
a Institute of Immunology and Department of Thoracic and Cardiovascular Surgery, The National Hospital, Oslo, Norway
e-mail: tom.e.mollnes{at}fagmed.uit.no
The aim of perfusion in cardiac surgery is to preserve organ function and hypothermia has been a key ingredient in order to reduce tissue oxygen and nutrient demands. The distribution of blood flow during the induction of hypothermia significantly influences the distribution of temperature change and thus the effectiveness of protection. This article by Slater and associates aims to characterize variations in local blood flow distribution and oxygen delivery during hypothermic cardiopulmonary bypass (CPB) at different flow rates. In contrast to several other reports, the authors have chosen flow-rates that are clinically relevant. The effects of hypothermia per se can, however, not be evaluated since normothermia was not compared. The study confirms previous observations of relatively preserved cerebral blood flow (CBF) compared with other organs and describes a "hierarchy" of regional blood flow among the five organs tested.
Anesthetic and surgical manipulation inevitably interfere with physiologic homeostasis. Although the authors claim that their model simulates a clinical condition, they did not pharmacologically manipulate myocardial function and vascular resistance. Such treatment might have added additional important information with respect to the regional distribution of blood during clinical CPB, particularly if compared with the unmanipulated group studied. The goal of perfusion management during CPB is to provide a balance between supply of nutrients and oxygen and metabolic tissue requirements in an effort to preserve and protect vital organ systems from ischemic damage. This goal is in a clinical situation aided by minimizing tissue demands with the use of hypothermia and controlled anesthesia and by using vasoactive agents, to maintain perfusion parameters that meet the patient’s estimated requirements.
In our opinion, one of the most interesting observations in this study is the fall in CBF combined with a preserved small intestine blood flow when CPB was established. Thus, despite relatively preserved CBF when flow-rate was reduced, the brain already suffered relative to the intestine at 1.9 L/min/m2. This should be considered when interpreting the data presented in Figure 2. Furthermore, we are not convinced that CBF was constant from 1.9 to 1.3 L/min/m2, although the difference was not statistically significant. The line seems to decline and the lack of significance may well be due to the low number of observations, which challenges the reliability of the statistics. Nevertheless, the present study is an interesting contribution to an important field. Hypothermia and protection techniques during perfusion need to be further evaluated in light of these recent findings.
Related Article
Ann. Thorac. Surg. 2001 72: 542-547.
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