Effects of pH management during selective antegrade cerebral perfusion on cerebral microcirculation and metabolism: alpha-stat versus pH-stat.
BACKGROUND
Selective cerebral perfusion (SCP) is used for extending the period during which surgical procedures can be safely performed. We sought to determine the direct effects of pH management on cerebral microcirculation and metabolism during SCP.


METHODS
An experimental SCP porcine model was created by selectively allowing cold perfusate only into the bicarotid brachiocephalic trunk during the SCP period. Twenty-four piglets (6 to 8 weeks; mean weight, 26.1 +/- 4.1 kg) underwent 15-minute normothermic cardiopulmonary bypass, 45-minute cooling cardiopulmonary bypass, 60-minute SCP at 25 degrees C, and 45-minute rewarming cardiopulmonary bypass with either alpha-stat or pH-stat perfusion strategy randomly assigned. A cranial window was created over the parietal cortex for visualization of the cerebral vessels with intravital microscopy. Rhodamine-stained leukocytes were observed in cerebral postcapillary venules for adhesion and rolling. Microdialysis analysis was used for determination of brain metabolism.


RESULTS
Brain concentration of lactate was significantly higher in the alpha-stat group at 45 minutes of SCP, and at 15- and 45-minute rewarming intervals (p = 0.03; p = 0.003; and p = 0.05; respectively), reaching borderline statistical significance when assessed throughout the experiment (p = 0.06 for differences between groups). Further, at the end of cooling, the oxygen delivery tended to be higher in the pH-stat group (p = 0.07), whereas at the 30-minute rewarming interval, the oxygen extraction tended to be higher in the alpha-stat group (p = 0.06). There were no statistically significant differences between the groups in leukocyte-endothelial interaction, arterial diameter, or tissue oxygenation.


CONCLUSIONS
The higher concentration of brain lactate and the tendency to higher oxygen extraction levels during rewarming with alpha-stat strategy suggests anaerobic metabolism occurred during SCP. No major differences between pH management strategies in cerebral microcirculation could be shown during SCP.
Dahlbacka
Sebastian
S
Department of Surgery, Clinical Research Center, Oulu University Hospital and University of Oulu, Oulu, Finland. sdahlbac@paju.oulu.fi
Alaoja
Hanna
H
Mäkelä
Jussi
J
Niemelä
Eija
E
Laurila
Päivi
P
Kiviluoma
Kai
K
Honkanen
Anna
A
Ohtonen
Pasi
P
Anttila
Vesa
V
Juvonen
Tatu
T
D000818:Animals; D001921:Brain / Q000378:metabolism*; D002315:Cardiopulmonary Bypass; D002450:Cell Communication; D002560:Cerebrovascular Circulation; D004285:Dogs; D042783:Endothelial Cells / Q000502:physiology; D005260:Female; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000378:metabolism; D007958:Leukocyte Count; D007962:Leukocytes / Q000502:physiology; D017551:Microdialysis; D010100:Oxygen / Q000378:metabolism; D010477:Perfusion / Q000379:methods*
D019344:Lactic Acid; D010100:Oxygen