Ge. Venn et al., CARDIOPULMONARY BYPASS - PERIOPERATIVE CEREBRAL BLOOD-FLOW AND POSTOPERATIVE COGNITIVE DEFICIT, The Annals of thoracic surgery, 59(5), 1995, pp. 1331-1335
Increased cerebral blood flow occurring during cardiopulmonary bypass
as a result of changes in arterial carbon dioxide tension during acid-
base regulation is thought to increase postoperative cognitive dysfunc
tion. We studied 70 patients undergoing coronary artery bypass procedu
res who were randomized to two different acid-base protocols: pH-stat
or alpha-stat regulation. Cerebral blood flow cerebral blood now veloc
ity, and cerebral oxygen metabolism were measured before bypass, durin
g bypass (hypothermic [28 degrees C] and normothermic phases), and aft
er bypass. Detailed cognitive tests were conducted before operation an
d 6 weeks after operation. During 28 degrees C bypass, cerebral blood
now was significantly (p < 0.05) higher in the pH-stat group than in t
he alpha-stat group (41 +/- 2 versus 24 +/- 2 mL . 100 g(-1). min(-1))
, and cerebral blood now velocity was significantly increased in the p
H-stat group and significantly decreased in the alpha-stat group (152%
+/- 10% versus 78% +/- 7%). Cerebral extraction ratio of oxygen demon
strated a relatively greater disruption of autoregulation in the pH-st
at group than in the alpha-stat group with relative hyperemia of 0.12
+/- 0.02 versus 0.26 +/- 0.03, respectively, during 28 degrees C bypas
s. Using the criterion of deterioration in three or more neuropsycholo
gic tests, a significantly higher proportion of patients in the pH-sta
t group fared less well than in the alpha-stat group (49% +/- 17% vers
us 20% +/- 13%). Patients in the alpha-stat group experienced less dis
ruption of cerebral autoregulation during hypothermic cardiopulmonary
bypass, and this was accompanied by a reduction in postoperative cogni
tive dysfunction.