Cardiopulmonary bypass time does not affect cerebral blood flow.

BACKGROUND: A time-dependent decline in cerebral blood flow (CBF) has been reported in cardiac surgical patients despite stable pump flows and arterial carbon dioxide tension. Other studies have failed to support these hypothermic cardiopulmonary bypass (CPB) results, showing preservation of CBF during CPB. The purpose of the study was to define the influence of mildly hypothermic CPB duration on CBF. METHODS: Cerebral blood flow was measured using xenon-133 washout and alpha-stat blood gas management during nonpulsatile CPB. Cerebral blood flow measurements were made after the initiation of CPB and near the end of bypass during pump flows of 2.4 L.min-1.m-2. RESULTS: Fifty-two coronary artery bypass patients were studied. The average time between CBF measurements was 54 +/- 20 minutes (mean +/- standard deviation), with a range of 10 to 100 minutes. Temperature and arterial carbon dioxide tension were controlled: after the initiation of CPB, temperature was 35.5 degrees +/- 0.4 degree C and carbon dioxide tension was 37 +/- 2.8 mm Hg; whereas near the end of bypass temperature was 35.6 degrees +/- 0.5 degree C and carbon dioxide tension was 36 +/- 2.3 mm Hg. We found no correlation between CBF and time on CPB (p = 0.47; r = 0.101), in contrast to other studies suggesting that CPB duration may intrinsically affect CBF. CONCLUSIONS: Our experimental results include the following: (1) during mildly hypothermic bypass, CBF does not decrease in relation to time and (2) cerebral flow-metabolism coupling is intact at 35 degrees C.

Effect of perfusion pressure on cerebral blood flow during normothermic cardiopulmonary bypass.

BACKGROUND: We have recently shown that during hypothermic cardiopulmonary bypass (CPB), cerebral autoregulation has a positive slope such that for every 10 mm Hg change in pressure, a 0.86 mL.100 g-1.min-1 change in cerebral blood flow (CBF) is predicted. The purpose of this study was to define the influence of mean arterial blood pressure (MAP) on CBF during normothermic CPB. METHODS AND RESULTS: CBF was measured by use of 133Xe washout and alpha-stat blood gas management during nonpulsatile CPB. CBF measurements were made at a pump flow of 2.4 L.min-1.m-2 at stable normothermia and approximately 15 minutes later after the MAP was increased or decreased > or = 20%. A third data set was recorded after the pressure was returned to the initial value. Forty-five patients were entered into the study. Temperature was held constant. We found a significant effect (P = .016) of change in MAP on change in CBF during normothermic CPB. For a 10 mm Hg increase in MAP, an increase in CBF of 1.78 mL.100 g-1.min-1 is predicted. Along with change in CBF, significant increases in both cerebral metabolic rate and cerebral oxygen delivery were observed. CONCLUSIONS: This information, along with our previous data shows that autoregulation during CPB has a positive slope that is greater with normothermia than hypothermia. Although it is unlikely that these small changes in flow are an important primary effect in the development of hypoperfusion, increased metabolic rate with increased CBF may indicate pressure-dependent collateral flow potentially in regions embolized during CPB.

Cardiovascular effects of intravenous triiodothyronine in patients undergoing coronary artery bypass graft surgery. A randomized, double-blind, placebo- controlled trial. Duke T3 study group.

OBJECTIVE: To test the hypothesis that triiodothyronine (T(3)) administration improves hemodynamic variables and decreases inotropic drug requirements in cardiac surgery patients. DESIGN: Prospective, randomized, double-blind, placebo-controlled trial. SETTING: Tertiary care medical center. PATIENTS: A total of 211 patients undergoing coronary artery surgery at high risk for requiring inotropic drug support. INTERVENTION: At release of aortic cross-clamp, patients were randomized to an intravenous infusion of T(3) (0.8 microg/kg followed by 0.12 microg.kg(-1).h(-1) for 6 hours), dopamine (positive control, 5 microg.kg(-1).min(-1) for 6 hours) or placebo. MAIN OUTCOME MEASURES: Perioperative hemodynamic variables, inotropic support requirements, and serum T(3) concentrations. RESULTS: Mean+/-SEM free T(3) serum concentrations decreased significantly during cardiopulmonary bypass in all groups (from 0.0035+/-0.0001 nmol/L [0.23+/-0.01 ng/dL] to 0.001+/-0.0001 nmol/L [0.7+/- 0.00 ng/dL]; P=.001) and increased to 0.0133+/-0.0004 nmol/L [0.87+/-0.03 ng/dL] (twice normal range; P<.001) following initiation of intravenous T(3). Intravenous T(3) did not change hemodynamic variables or inotropic drug requirements; however, heart rate increased (P<.001), and a trend toward decreased use of inotropic agents was demonstrated in the dopamine group. CONCLUSIONS: Triiodothyronine administration prevents decreases in serum thyroid hormone concentrations associated with cardiopulmonary bypass. Intravenous T(3) does not have dramatic effects on hemodynamic variables in this setting as has been previously suggested. Although mild effects on myocardial performance may exist, we cannot recommend at this time the routine use of intravenous T(3) as an inotropic agent in patients undergoing coronary artery bypass graft surgery.