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Ann Thorac Surg 2001;72:1331-1335
© 2001 The Society of Thoracic Surgeons

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Original article: cardiovascular

Carbon dioxide management and the cerebral response to hemodilution during hypothermic cardiopulmonary bypass in dogs

^a Department of Anesthesiology, Department of Surgery, Mayo Clinic and Foundation, Rochester, Minnesota, USA
^b Division of Cardiothoracic Surgery, Department of Surgery, Mayo Clinic and Foundation, Rochester, Minnesota, USA

Accepted for publication May 29, 2001.

Address reprint requests to Dr Cook, Mayo Clinic-SMH/MB 2-752, 200 First St SW, Rochester, MN 55905
e-mail: cook.david{at}mayo.edu

Background. Increases in blood flow support oxygen (O₂) delivery with hemodilution. However, with -stat management, the cerebral response to hemodilution is blunted. We tested the hypothesis that carbon dioxide (CO₂) management is a primary determinant of the cerebral blood flow (CBF) response to hemodilution during hypothermic bypass.

Methods. Following Animal Care Committee approval, 15 dogs underwent bypass at 18°C (pH-stat, n = 7 or -stat, n = 8). Measurements were obtained after progressive hemodilution, and cerebral blood flow was determined by sagittal sinus outflow. Arterial pressure was maintained at 60 to 70 mm Hg. The CBF response to hemodilution and cerebral metabolic rate were compared in the two groups of animals.

Results. In both groups, hemodilution increased CBF. At every hematocrit, CBF and O₂ delivery in the pH-stat group exceeded that of -stat group, although O₂ demand did not differ between groups. While absolute CBF in the pH-stat group was greater at every hematocrit, the relative change in CBF from control and the slope of the CBF-Hct relationship did not differ between groups.

Conclusions. pH-stat management is associated with a greater absolute CBF and a greater ratio of cerebral O₂ supply to demand for any degree of hemodilution. However, over the range of hematocrits common in practice, CO₂ management per se does not determine the cerebral response to hemodilution.

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