Bj. Hindman et al., HYPOTHERMIC ACID-BASE MANAGEMENT DOES NOT AFFECT CEREBRAL METABOLIC-RATE FOR OXYGEN AT 27-DEGREES-C - A STUDY DURING CARDIOPULMONARY BYPASSIN RABBITS, Anesthesiology, 79(3), 1993, pp. 580-587
Background. It has been contended that, during cardiopulmonary bypass
at 27-degrees-C, pH-stat management decreases cerebral metabolic rate
for oxygen (CMR(O2)) more than alpha-stat management. In contrast, oth
er studies have not found CMR(O2) to differ between techniques. Using
each animal as its own control, the authors assessed the effect of alp
ha-stat versus pH-stat management on CMR(O2), cerebral blood flow (CBF
), and brain oxygen extraction during cardiopulmonary bypass at 27-deg
rees-C. Methods: Fourteen New Zealand White rabbits, anesthetized with
fentanyl and diazepam, underwent cardiopulmonary bypass at 27-degrees
-C (membrane oxygenator, centrifugal pump, and bifemoral arterial perf
usion). Group 1 animals (n = 7) had alpha-stat management for the init
ial 65-70 min of bypass, and were then changed to pH-stat management f
or the remaining 30 min of bypass. Group 2 animals (n = 7) had pH-stat
management for the initial 65-70 min of bypass, and were then changed
to a-stat management for the remaining 30 min. Measurement of CBF (ra
diolabeled microspheres), CMR(O2) (CBF x brain arterial-venous oxygen
content difference), brain temperature, systemic hemodynamics, and art
erial blood gases were made in each animal under both alpha-stat and p
H-stat conditions.Results. CMR(O2) did not differ between alpha-stat a
nd pH-stat conditions (1.4 +/- 0.3 ml - 100 g-1. min-1; median +/- qua
rtile deviation), and was independent of order of determination. Chang
es in CBF between alpha-stat and pH-stat conditions were associated wi
th proportional opposite changes in cerebral oxygen extraction. Cerebr
al blood flow was significantly greater with pH-stat management than w
ith a-stat management (37 +/- 5 vs. 30 +/- 3 ml . 100 g-1. min-1, resp
ectively). The CBF response to changing Pa(CO2) was significantly grea
ter when going from alpha-stat to pH-stat conditions (group 1) than in
the reverse order (group 2). Conclusions. During cardiopulmonary bypa
ss at 27-degrees-C, hypothermic acid-base management has no measurable
effect on CMR(O2). CMR(O2) was neither extraction limited nor depende
nt on either Pa(CO2), CBF, or hemoglobin oxygen affinity differences b
etween alpha-stat and pH-stat management. Cerebral blood flow response
s to changing CMR(O2) depend on the ''starting'' conditions, with alph
a-stat management appearing to better preserve CBF reactivity than pH-
stat management.