ALPHA-STAT ACID-BASE REGULATION DURING CARDIOPULMONARY BYPASS IMPROVES NEUROPSYCHOLOGIC OUTCOME IN PATIENTS UNDERGOING CORONARY-ARTERY BYPASS-GRAFTING

Neuropsychologic impairment in patients undergoing cardiopulmonary byp ass may be associated with cerebral blood flow changes arising from di fferent management protocols for carbon dioxide tension during bypass, Seventy patients having coronary artery bypass grafting were randomiz ed to either ps-stat or alpha-stat acid-base management during cardiop ulmonary bypass with a membrane oxygenator. In each patient, cerebral blood flow (xenon 133 clearance), middle cerebral artery blood flow ve locity (transcranial Doppler sonography), and cerebral oxygen metaboli sm (cerebral metabolic rate and cerebral extraction ratio) were measur ed during four phases of the operation: before bypass, during bypass ( at hypothermia and at normothermia), and after bypass. A battery of ne uropsychologic tests were also conducted before and 6 weeks after the operation. During hypothermic (28 degrees C) bypass, cerebral blood fl ow was significantly (p < 0.001) greater in the pH-stat group (41 ml . 100 gm(-1). min(-1); 95% confidence interval 39 to 43 ml . 100 gm(-1) . min(-1)) than in the alpha-stat group (24 ml . 100 gm(-1). min(-1); confidence interval 22 to 26 ml . 100 gm(-1). min(-1)) at constant pre ssure and flow. Arterial carbon dioxide tensions were 41 mm Hg (40 to 41 mm Hg) and 26 mm Hg (25 to 27 mm Hg), respectively; pH was 7.36 (7. 34 to 7.38) and 7.53 (7.51 to 7.55), respectively. Middle cerebral art ery flow velocity was significantly (p < 0.05) reduced in the alpha-st at group to 87% (77% to 96%) of the prebypass value, whereas it was si gnificantly (p < 0.05) increased (152%; 141% to 162%) in the pH-stat g roup. Cerebral extraction ratio for oxygen demonstrated relative cereb ral hyperemia during hypothermic (28 degrees C) bypass in both the pH- stat and alpha-stat groups (0.12 [0.11 to 0.14] and 0.25 [0.22 to 0.28 ], respectively); however, hyperemia was significantly more pronounced in the pH-stat group, indicating greater disruption in cerebral autor egulation. Neuropsychologic impairment criteria of deterioration in re sults of three or more tests revealed that a significantly (Fisher's e xact test, p = 0.02) higher proportion of patients in the pH-stat grou p fared poorly than in the alpha-stat group at 6 weeks (17/35, 48.6% [ 32% to 65.1%], and 7/35, 20% [6.7% to 33.2.2%], respectively). In conc lusion, patients receiving alpha-stat management had less disruption o f cerebral autoregulation during cardiopulmonary bypass, accompanied b y a reduced incidence of postoperative cerebral dysfunction.