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The Annals of Thoracic Surgery, Vol 41, 525-530, Copyright © 1986 by The Society of Thoracic Surgeons
T Lundar, KF Lindegaard, T Froysaker, A Grip, M Bergman, E Am-Holen and H Nornes
Five patients undergoing extensive cerebral monitoring during
cardiopulmonary bypass (CPB) procedures were subjected to studies on
cerebral CO2 reactivity during nonpulsatile CPB. The cerebral monitoring
included recording of arterial blood pressure (BP), central venous pressure
(CVP), epidural intracranial pressure (EDP), cerebral electrical activity
by a cerebral function monitor (CFM), and middle cerebral artery (MCA) flow
velocity by transcranial Doppler technique. The cerebral perfusion pressure
(CPP) was thus continuously recorded (CPP = BP - EDP). During steady-state
CPB with constant hematocrit, temperature, and arterial carbon dioxide
tension (PaCO2), MCA flow velocity varied with changing CPP in a
pressure-passive manner, indicating that the cerebral autoregulation was
not operative. During moderately hypothermic (28 to 32 degrees C),
nonpulsatile CPB, with steady-state hematocrit, temperature, and pump flow,
we deliberately and rapidly changed PaCO2 for periods of 1 or 2 minutes by
increasing gas flow to the membrane oxygenator, thereby testing the
cerebral CO2 reactivity. Nineteen CO2 reactivity tests, performed at CPP
levels ranging from 17 to 75 mm Hg, disclosed that the cerebral CO2
reactivity decreased with CPP, especially with CPP levels below 35 mm Hg.
In these patients, concomitant changes in CPP during the CO2 reactivity
test could be compensated for by adjusting the observed change in MCA flow
velocity. The corrected CO2 reactivity values obtained in this way ranged
from below 1.0 (observed at CPP levels below 20 mm Hg) to a 3.0 to 4.5% X
mm Hg-1 change in PaCO2 (observed at CPP levels above 35 mm Hg).(ABSTRACT
TRUNCATED AT 250 WORDS)
ARTICLES
Cerebral carbon dioxide reactivity during nonpulsatile cardiopulmonary bypass
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