Optimal blood flow for cooled brain at 20 degrees C.
BACKGROUND
Optimal conditions for deep hypothermic perfusion and protective brain blood flow remain unclear.


METHODS
Dogs (n = 52) underwent 120 minutes of cardiopulmonary bypass at 20 degrees C with perfusion flow rates of 2.5, 5, 10, 20, 40, and 100 mL x kg(-1) x min(-1). We examined the effect of the various flow rates and different perfusion pressures on brain blood flow, metabolism, and intracellular pH.


RESULTS
The brain was ischemic and acidotic when the perfusion flow rate was less than 5 mL kg(-1) x min(-1) and pressure was less than 10 mm Hg. When perfusion pressure was higher than 10 mm Hg, cerebral cortex blood flow was more than 9 mL x 100 g(-1) x min(-1) and intracellular pH, higher than 6.95. The cerebral metabolic rate for oxygen decreased at a flow rate of 2.5 mL x kg(-1) min(-1). The cerebral metabolic ratio of glucose to oxygen and the cerebral vascular resistance were lowest when perfusion pressure was 10 to 30 mm Hg. Full-flow (100 mL x kg(-1) x min(-1)) perfusion caused paradoxical brain acidosis; a flow of 40 mL x kg(-1) x min(-1) provided the best results.


CONCLUSIONS
Both extremely low-flow perfusion and excessive perfusion cause brain acidosis. Low-flow perfusion at a pressure of 20 mm Hg provides cerebral vasorelaxation and aerobic metabolism during operations at 20 degrees C.
Watanabe
T
T
Second Department of Surgery,Yamagata University School of Medicine, Japan.
Oshikiri
N
N
Inui
K
K
Kuraoka
S
S
Minowa
T
T
Hosaka
J
J
Takahashi
T
T
Shimazaki
Y
Y
D000818:Animals; D001783:Blood Flow Velocity; D001921:Brain / Q000378:metabolism; D002315:Cardiopulmonary Bypass; D002540:Cerebral Cortex / Q000098:blood supply; D002560:Cerebrovascular Circulation; D004285:Dogs; D005947:Glucose / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007036:Hypothermia, Induced; D010101:Oxygen Consumption; D014655:Vascular Resistance
D005947:Glucose