Effect of differing acid-base regulation on cerebral blood flow autoregulation during cardiopulmonary bypass.
Cerebral dysfunction following cardiopulmonary bypass may be aggravated by altered autoregulation of cerebral blood flow. We have used trans-cranial Doppler to measure middle cerebral artery blood flow velocity during cardiopulmonary bypass managed by either pH-stat or alpha-stat acid-base protocols. Fourteen patients were studied, 7 in each group. During bypass at 28 degrees C, patients underwent incremental alterations in mean arterial pressure from 20-90 mmHg, maintaining systemic perfusion flow at 1.75 L/min per m2. The cerebral extraction ratio of oxygen was measured to indicate matching of cerebral blood flow to demand. The pH-stat group showed a pressure passive cerebral circulation with significant (r = 0.999, P less than 0.05) increase in blood flow velocity with increasing arterial pressure. This also occurred in alpha-stat group during the pressure range of 20-50 mmHg (r = 0.951, P less than 0.05). During the pressure range of 50-90 mmHg in alpha-stat group the change in flow velocity (0.16 cm/sec per mmHg) was significantly (P less than 0.05) less than that in pH-stat group (0.58 cm/second per mmHg). The cerebral extraction ratio of oxygen was less depressed in the alpha-stat group than in the pH-stat group, indicating more appropriate matching of cerebral blood flow and tissue demand. These results suggest that, during alpha-stat managed cardiopulmonary bypass, cerebral blood flow velocity is less subject to wide pressure alteration than pH-stat.
Patel
R L
RL
Department of Cardiothoracic Surgery, The Rayne Institute, St. Thomas' Hospital, London, UK.
Turtle
M R
MR
Chambers
D J
DJ
Venn
G E
GE
D000136:Acid-Base Equilibrium / Q000502:physiology*; D001783:Blood Flow Velocity / Q000502:physiology; D001785:Blood Gas Monitoring, Transcutaneous; D002315:Cardiopulmonary Bypass; D002536:Cerebral Arteries / Q000000981:diagnostic imaging; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative; D014463:Ultrasonography