Effect of alpha-stat vs. pH-stat strategies on cerebral oximetry during moderate hypothermic cardiopulmonary bypass

BACKGROUND AND OBJECTIVES: This study was undertaken to compare the effect of alpha-stat vs. pH-stat strategies for acid-base management on regional cerebral oxygen saturation (RsO2) in patients undergoing moderate hypothermic haemodilution cardiopulmonary bypass (CPB). METHODS: In 14 adult patients undergoing elective coronary artery bypass grafting, an awake RsO2 baseline value was monitored using a cerebral oximeter (INVOS 5100). Cerebral oximetry was then monitored continuously following anaesthesia and during the whole period of CPB. Mean +/- SD of RsO2, CO2, mean arterial pressure and haematocrit were determined before bypass and during the moderate hypothermic phase of the CPB using the alpha-stat followed by pH-stat strategies of acid-base management. Alpha-stat was then maintained throughout the whole period of CPB. RESULTS: The mean baseline RsO2 in the awake patient breathing room air was 59.6 +/- 5.3%. Following anaesthesia and ventilation with 100% oxygen, RsO2 increased up to 75.9 +/- 6.7%. Going on bypass, RsO2 significantly decreased from a pre-bypass value of 75.9 +/- 6.7% to 62.9 +/- 6.3% during the initial phase of alpha-stat strategy. Shifting to pH-stat strategy resulted in a significant increase of RsO2 from 62.9 +/- 6.3% to 72.1 +/- 6.6%. Resuming the alpha-stat strategy resulted in a significant decrease of RsO2 to 62.9 +/- 7.8% which was similar to the RsO2 value during the initial phase of alpha-stat. CONCLUSION: During moderate hypothermic haemodilutional CPB, the RsO2 was significantly higher during the pH-stat than during the alpha-stat strategy. However, the RsO2 during pH-stat management was significantly higher than the baseline RsO2 value in the awake patient breathing room air, denoting luxury cerebral perfusion. In contrast, the RsO2 during alpha-stat was only slightly higher than the baseline RsO2, suggesting that the alpha-stat strategy avoids luxury perfusion, but can maintain adequate cerebral oxygen supply-demand balance during moderate hypothermic haemodilutional CPB.     

Changes in cerebral oxygenation during cold (28 degrees C) and warm (34 degrees C) cardiopulmonary bypass using different blood gas strategies (alpha-stat and pH-stat) in patients undergoing coronary artery bypass graft surgery

BACKGROUND: Impaired cerebral oxygenation, which is reflected by measuring jugular bulb oxygenation, is thought to play an important role in the development of neurological injury after cardiac operations with cardiopulmonary bypass (CPB). The effects of cardiopulmonary temperature and blood gas strategy on cerebral oxygenation are not fully appreciated. METHODS: Sixty patients were randomly allocated into four equal groups (cold alpha-stat, cold pH-stat, warm alpha-stat and warm pH-stat) to compare the effect of these perfusion strategies on cerebral oxygenation monitored by jugular bulb oximetry [jugular bulb oxygen saturation (SjO(2)) and arterial-jugular bulb oxygen content difference (AjDO(2))]. Jugular bulb oxygen saturation and AjDO(2) were measured before CPB, after 5, 20, 40 min on CPB, at start and end of rewarming, 5 min before the end of CPB and 10 min after CPB. Two-way analysis of variance was used to model the lowest SjO(2) and highest AjDO(2) during CPB, with CPB temperature and blood gas management as contributing factors. RESULTS: Significant changes in SjO(2) were only related to the type of blood gas management, with no significant difference between warm and cold CPB patients. In addition, during rewarming, desaturation (SjO(2) 相似文献   

Warming during cardiopulmonary bypass is associated with jugular bulb desaturation.

The objective of this study was to characterize cerebral venous effluent during normothermic nonpulsatile cardiopulmonary bypass. Thirty-one (23%) of 133 patients met desaturation criteria (defined as jugular bulb venous oxygen saturation less than or equal to 50% or jugular bulb venous oxygen tension less than or equal to 25 mm Hg) during normothermic cardiopulmonary bypass (after hypothermic cardiopulmonary bypass at 27 degrees to 28 degrees C). Cerebral blood flow, calculated using xenon 133 clearance methodology, was significantly (p less than 0.005) higher in the saturated group (33.7 +/- 10.3 mL.100 g-1.min-1) than in the desaturated group (26.2 +/- 6.9 mL.100 g-1.min-1), whereas the cerebral metabolic rate for oxygen was significantly lower (p less than 0.005) in the saturated group (1.28 +/- 0.39 mL.100 g-.min-1) than in the desaturated group (1.52 +/- 0.36 mL.100 g-1.min-1) at normothermia. The arteriovenous oxygen difference at normothermia was lower in the saturated group (3.92 +/- 1.12 mL/dL) than in the desaturated group (5.97 +/- 1.05 mL/dL). Neuropsychological testing was performed in 74 of the 133 patients preoperatively and on day 7 postoperatively. There was a general decline in mean scores of all tests postoperatively in both groups with no significant difference between the groups. We conclude that cerebral venous desaturation represents a global imbalance in cerebral oxygen supply-demand that occurs during normothermic cardiopulmonary bypass and may represent transient cerebral ischemia. These episodes, however, are not associated with impared neuropsychological test performance as compared with the performance of patients with no evidence of desaturation.     

Effects of hypothermic and normothermic cardiopulmonary bypass on brain oxygenation.

BACKGROUND: In this study, we assessed the effects of normothermia and hypothermia during cardiopulmonary bypass (CPB) both on internal jugular venous oxygen saturation (SjvO2) and the regional cerebral oxygenation state (rSO2) estimated by near infrared spectroscopy (NIRS). METHODS: Thirty patients scheduled for elective coronary artery bypass graft surgery (CABG) were randomly divided into two groups. Group 1 (n = 15) underwent surgery for normothermic (> 35 degrees C) CPB, and group 2 (n = 15) underwent surgery for hypothermic (30 degrees C) CPB, and alpha-stat regulation was applied. A 4.0-French fiberoptic oximetry oxygen saturation catheter was inserted into the right jugular bulb to continuously monitor the SjvO2 value. To estimate the rSO2 state, a spectrophotometer probe was attached to the mid-forehead. SjvO2 and rSO2 values were then collected simultaneously using a computer. RESULTS: Neither the cerebral desaturation time (duration during SjvO2 value below 50%), nor the ratio of the cerebral desaturation time to the total CPB time significantly differed (normothermic group: 18+/-6 min, 15+/-6%; hypothermic group: 17+/-6 min, 13+/-6%, respectively). The rSO2 value in the normothermic group decreased during the CPB period compared with the pre-CPB period. The rSO2 value in the hypothermic group did not change throughout the perioperative period. CONCLUSIONS: These findings suggest that near infrared spectroscopy might be sensitive enough to detect subtle changes in regional cerebral oxygenation.     

Comparison of pH-state and Alpha-stat Cardiopulmonary Bypass on Cerebral Oxygenation and Blood Flow in Relation to Hypothermic Circulatory Arrest in Piglets

Background: Deep hypothermic circulatory arrest is used in neonatal cardiac surgery. Recent work has suggested improved neurologic recovery after deep hypothermic arrest with pH-stat cardiopulmonary bypass (CPB) compared with alpha-stat CPB. This study examined cortical oxygen saturation (ScO(2)), cortical blood flow (CBF), and cortical physiologic recovery in relation to deep hypothermic arrest with alpha-stat or pH-stat CPB.

Methods: Sixteen piglets were cooled with pH-stat or alpha-stat CPB to 19 [degree sign]C (cortex) and subjected to 60 min of circulatory arrest, followed by CPB reperfusion and rewarming and separation from CPB. Near infrared spectroscopy and laser Doppler flowmetry were used to monitor ScO(2) and CBF. Cortical physiologic recovery was assessed 2 h after the piglets were separated from CPB by cortical adenosine triphosphate concentrations, cortical water content, CBF, and ScO(2).

Results: During CPB cooling, ScO(2) increased more with pH-stat than with alpha-stat bypass (123 +/- 33% vs. 80 +/- 25%); superficial and deep CBF were also greater with pH-stat than with alpha-stat bypass (22 +/- 25% vs. -56 +/- 22%, 3 +/- 19% vs. -29 +/- 28%). During arrest, ScO(2) half-life was greater with pH-stat than with alpha-stat bypass (10 +/- 2 min vs. 7 +/- 2 min), and cortical oxygen consumption lasted longer with pH-stat than with alpha-stat bypass (36 +/- 8 min vs. 25 +/- 8 min). During CPB reperfusion, superficial and deep CBF were less with alpha-stat than with pH-stat bypass (-40 +/- 22% vs. 10 +/- 39%, -38 +/- 28% vs. 5 +/- 28%). After CPB, deep cortical adenosine triphosphate and CBF were less with alpha-stat than with pH-stat bypass (11 +/- 6 pmole/mg vs. 17 +/- 8 pmole/mg, -24 +/- 16% vs. 16 +/- 32%); cortical water content was greater with alpha-stat than with pH-stat bypass (superficial: 82.4 +/- 0.3% vs. 81.8 +/- 1%, deep: 79.1 +/- 2% vs. 78 +/- 1.6%).     

Use of a pH-stat strategy during retrograde cerebral perfusion improves cerebral perfusion and tissue oxygenation

BACKGROUND: Although it is well documented that the use of a pH-stat strategy during hypothermic cardiopulmonary bypass improves cerebral blood flow, an alpha-stat strategy has been almost exclusively used during retrograde cerebral perfusion. We investigated the effects of pH-stat and alpha-stat management on brain tissue blood flow and oxygenation during retrograde cerebral perfusion in a porcine model to determine if the use of a pH-stat strategy during retrograde cerebral perfusion improves brain tissue perfusion. METHODS: Fourteen pigs were managed by an alpha-stat strategy (alpha-stat group, n = 7) or by a pH-stat strategy (pH-stat group, n = 7) during 120 minutes of hypothermic retrograde cerebral perfusion. Retrograde cerebral perfusion was established through the superior vena cava. Brain tissue blood flow and oxygenation were measured continuously with a laser flowmeter and near infrared spectroscopy, respectively. Brain tissue water content was determined at the end of the experiments. RESULTS: During cooling, brain tissue blood flow was significantly higher with use of the pH-stat strategy than with the alpha-stat strategy (86% +/- 10% versus 40% +/- 3% of baseline). During retrograde cerebral perfusion, brain tissue blood flow was also significantly higher (about three times higher) in the pH-stat group than in the alpha-stat group (15% +/- 4% versus 5% +/- 1% of baseline at 60 minutes of retrograde cerebral perfusion). Tissue oxygen saturation appeared to be higher during retrograde cerebral perfusion in the pH-stat group than in the alpha-stat group. Brain tissue blood flow during rewarming remained significantly higher with the use of pH-stat than with the use of alpha-stat. Brain tissue water contents were similar in both groups. CONCLUSIONS: In our pig model, the use of a pH-stat strategy during retrograde cerebral perfusion significantly improves brain tissue perfusion. Therefore, to improve retrograde cerebral blood flow during retrograde cerebral perfusion, it may be preferable to use a pH-stat strategy, rather than an alpha-stat strategy.     

pH-Stat Management Reduces the Cerebral Metabolic Rate for Oxygen during Profound Hypothermia (17 degrees Celsius): A Study during Cardiopulmonary Bypass in Rabbits

Background: Greater cerebral metabolic suppression may increase the brain's tolerance to ischemia. Previous studies examining the magnitude of metabolic suppression afforded by profound hypothermia suggest that the greater arterial carbon dioxide tension of pH-stat management may increase metabolic suppression when compared with alpha-stat management.

Methods: New Zealand White rabbits, anesthetized with fentanyl and diazepam, were maintained during cardiopulmonary bypass (CPB) at a brain temperature of 17 degrees Celsius with alpha-stat (group A, n = 9) or pH-stat (group B, n = 9) management. Measurements of brain temperature, systemic hemodynamics, arterial and cerebral venous blood gases and oxygen content, cerebral blood flow (CBF) (radiolabeled microspheres), and cerebral metabolic rate for oxygen (CMRO2) (Fick) were made in each animal at 65 and 95 min of CPB. To control for arterial pressure and CBF differences between techniques, additional rabbits underwent CPB at 17 degrees Celsius. In group C (alpha-stat, n = 8), arterial pressure was decreased with nitroglycerin to values observed with pH-stat management. In group D (pH-stat, n = 8), arterial pressure was increased with angiotensin II to values observed with alpha-stat management. In groups C and D, CBF and CMRO2 were determined before (65 min of CPB) and after (95 min of CPB) arterial pressure manipulation.

Results: In groups A (alpha-stat) and B (pH-stat), arterial pressure; hemispheric CBF (44 plus/minus 17 vs. 21 plus/minus 4 ml *symbol* 100 g sup -1 *symbol* min sup -1 [median plus/minus quartile deviation]; P = 0.017); and CMRO2 (0.54 plus/minus 0.13 vs. 0.32 plus/minus 0.10 ml Oxygen2 *symbol* 100 g sup -1 *symbol* min sup -1; P = 0.0015) were greater in alpha-stat than in pH-stat animals, respectively. As a result of arterial pressure manipulation, in groups C (alpha-stat) and D (pH-stat) neither arterial pressure (75 plus/minus 2 vs. 78 plus/minus 2 mm Hg) nor hemispheric CBF (40 plus/minus 10 vs. 48 plus/minus 6 ml *symbol* 100 g sup -1 *symbol* min sup -1; P = 0.21) differed between alpha-stat and pH-stat management, respectively. Nevertheless, CMRO2 was greater in alpha-stat than in pH-stat animals (0.71 plus/minus 0.10 vs. 0.45 plus/minus 0.10 ml Oxygen2 *symbol* 100 g sup -1 *symbol* min sup -1, respectively; P = 0.002).     

pH-stat blood gas management provides better cerebral perfusion during deep hypothermic retrograde cerebral perfusion

We performed a retrospective comparative clinical study to evaluate whether pH-stat (n=14) or alpha-stat strategy (n=15) provides better perfusion or oxygen metabolism during hypothermic retrograde cerebral perfusion (RCP). The pH-stat group showed significantly lower superior vena cava (SVC) pressure (21+/-4 versus 27+/-6 mmHg, P<0.0001), apparently lower retrograde cerebral vascular resistance index (7.4+/-2.1 versus 10.1+/-3.8 dynes/s cm(-5) m(-2), P=0.009) but there were no significant differences in RCP flow index, oxygen supply or oxygen extraction between groups. Further studies are necessary to determine which blood gas management is better for RCP, however, pH-stat strategy should be useful in deep hypothermic RCP.     

Temperature monitoring during CPB in infants: does it predict efficient brain cooling?

We examined jugular venous oxygen saturation data in 17 pediatric patients less than 1 year of age undergoing hypothermic cardiopulmonary bypass (CPB). Jugular venous oxygen saturations (JvO2SATS) were measured before bypass and during the active core cooling portion of CPB. The study intervals during CPB included 1 minute after initiation of CPB, at a tympanic membrane temperature of 15 degrees C, and at a rectal temperature of 15 degrees C. During these measurement intervals, there were no significant changes in mean arterial pressure, pump flow rate, arterial oxygen saturation, mixed venous oxygen saturation, carbon dioxide tension, or hematocrit. Six of the 17 patients (29%) demonstrated a significantly lower JvO2SAT (87.1% +/- 6.3% versus 98.1% +/- 0.9%) at a tympanic membrane temperature of 15 degrees C. Patients demonstrating jugular venous desaturation could not be predicted from continuous monitoring of tympanic membrane and rectal temperatures or through on-line measurements of mixed venous oxygen saturation. Low JvO2SAT suggests higher levels of cerebral metabolism and cerebral uptake of oxygen. In the presence of deep hypothermic CPB and stable anesthetic levels, the most likely cause of a low JvO2SAT is inadequate cerebral cooling. We believe JvO2SAT monitoring may be an important adjunct to conventional temperature monitoring in the patient undergoing deep hypothermic CPB or total circulatory arrest.     

Response of cerebral blood flow to phenylephrine infusion during hypothermic cardiopulmonary bypass: influence of PaCO2 management

Twenty-eight adult patients anesthetized with fentanyl, then subjected to hypothermic cardiopulmonary bypass (CPB), were studied to determine the effect of phenylephrine-induced changes in mean arterial pressure (MAP) on cerebral blood flow (CBF). During CPB patients managed at 28 degrees C with either alpha-stat (temperature-uncorrected PaCO2 = 41 +/- 4 mmHg) or pH-stat (temperature-uncorrected PaCO2 = 54 +/- 8 mmHg) PaCO2 for blood gas maintenance received phenylephrine to increase MAP greater than or equal to 25% (group A, n = 10; group B, n = 6). To correct for a spontaneous, time-related decline in CBF observed during CPB, two additional groups of patients undergoing CPB were either managed with the alpha-stat or pH-stat approach, but neither group received phenylephrine and MAP remained unchanged in both groups (group C, n = 6; group D, n = 6). For all patients controlled variables (nasopharyngeal temperature, PaCO2, pump flow, and hematocrit) remained unchanged between measurements. Phenylephrine data were corrected based on the data from groups C and D for the effect of diminishing CBF over time during CPB. In patients in group A CBF was unchanged as MAP rose from 56 +/- 7 to 84 +/- 8 mmHg. In patients in group B CBF increased 41% as MAP rose from 53 +/- 8 to 77 +/- 9 mmHg (P less than 0.001). During hypothermic CPB normocarbia maintained via the alpha-stat approach at a temperature-uncorrected PaCO2 of approximately equal to 40 mmHg preserves cerebral autoregulation; pH-stat management (PaCO2 approximately equal to 57 mmHg uncorrected for temperature, or 40 mmHg when corrected to 28 degrees C) causes cerebrovascular changes (i.e., impaired autoregulation) similar to those changes produced by hypercarbia in awake, normothermic patients.     

Arterial blood gas management in retrograde cerebral perfusion: the importance of carbon dioxide.

OBJECTIVES: Many interventional physiological assessments for retrograde cerebral perfusion (RCP) have been explored. However, the appropriate arterial gas management of carbon dioxide (CO2) remains controversial. The aim of this study is to determine whether alpha-stat or pH-stat could be used for effective brain protection under RCP in terms of cortical cerebral blood flow (CBF), cerebral metabolic rate for oxygen (CMRO2), and distribution of regional cerebral blood flow. METHODS: Fifteen anesthetized dogs (25.1+/-1.1 kg) on cardiopulmonary bypass (CPB) were cooled to 18 degrees C under alpha-stat management and had RCP for 90 min under: (1), alpha-stat; (2), pH-stat; or (3), deep hypothermic (18 degrees C) antegrade CPB (antegrade). RCP flow was regulated for a sagittal sinus pressure of around 25 mmHg. CBF was monitored by a laser tissue flowmeter. Serial analyses of blood gas were made. The regional cerebral blood flow was measured with colored microspheres before discontinuation of RCP. CBF and CMRO2 were evaluated as the percentage of the baseline level (%CBF, %CMRO2). RESULTS: The oxygen content of arterial inflow and oxygen extraction was not significantly different between the RCP groups. The %CBF and %CMRO2 were significantly higher for pH-stat RCP than for alpha-stat RCP. The regional cerebral blood flow, measured with colored microspheres, tended to be higher for pH-stat RCP than for alpha-stat RCP, at every site in the brain. Irrespective of CO2 management, regional differences were not significant among any site in the brain. CONCLUSIONS: CO2 management is crucial for brain protection under deep hypothermic RCP. This study revealed that pH-stat was considered to be better than alpha-stat in terms of CBF and oxygen metabolism in the brain. The regional blood flow distribution was considered to be unchanged irrespective of CO2 management.     

Time course of changes in jugular venous oxygen saturation during hypothermic or normothermic cardiopulmonary bypass in patients with diabetes mellitus

BACKGROUND: Preexisting diabetic mellitus is a risk factor determining postoperative neurological disorders. The present study assesses the effects of normothermic and hypothermic cardiopulmonary bypass (CPB) on jugular venous oxygen saturation (SjvO2)in patients with preexisting diabetic mellitus. METHODS: Sixteen diabetic patients who underwent elective coronary artery bypass grafting surgery were randomly divided into two groups: Group DN (n=8, diabetic patients) underwent normothermic CPB (>35 degrees C), and group DH (n=8, diabetic patients) underwent hypothermic CPB (32 degrees C). Controls were 16 age-matched non-diabetic patients (normothemic group, CN: n=8; hypothemic group, CH: n=8). A 4.0 F fiberoptic oximetry oxygen saturation catheter was inserted into the right jugular bulb to continuously monitor SjvO2 values. Hemodynamic parameters and arterial and jugular venous blood gases were measured seven times. RESULTS: Cerebral desaturation, which was defined as SjvO2 values below 50%, was observed during normothermic CPB in diabetic patients (at the onset of CPB: 46+/-3%, at 20 min after onset of CPB: 49+/-3%, means+/-SD, respectively). No cerebral desaturation occurred in diabetic and control patients during hypothermic CPB. CONCLUSIONS: Patients with preexisting diabetes mellitus experienced cerebral desaturation during normothermic CPB.     

Transcranial Doppler-estimated versus thermodilution-estimated cerebral blood flow during cardiac operations. Influence of temperature and arterial carbon dioxide tension

The ability of the noninvasive continuous transcranial Doppler technique to reflect changes in cerebral blood flow during cardiac operations was evaluated in seven adults. Middle cerebral artery blood flow velocity changes were compared with simultaneous thermodilution measurements of venous blood flow in the ipsilateral internal jugular vein during 11 preset stages of the procedure. Cerebral blood flow was varied by changes in arterial carbon dioxide tension and temperature. High-dose fentanyl-droperidol anesthesia and alpha-stat pH management were employed. To facilitate comparisons between the two methods, the individual awake values of middle cerebral artery flow velocity (45.1 +/- 3.3 cm/sec, mean +/- standard error of the mean) and jugular venous blood flow (382 +/- 37 ml/min) were normalized (100%). Cerebral metabolic rate for oxygen was calculated as the product of jugular arteriovenous oxygen content difference and middle cerebral artery flow velocity or jugular venous blood flow, respectively. The individual correlations between the two flow estimates varied between 0.76 and 0.87 (median 0.83), and the correlation of the combined data from all seven patients was 0.77 (p less than 0.0001). Variations in arterial carbon dioxide tension induced significant changes in the two flow estimates both during normothermia before cardiopulmonary bypass and at deep hypothermia (20 degrees C) during cardiopulmonary bypass. The significant arterial carbon dioxide tension changes had no significant effects either on Doppler- or thermodilution-estimated cerebral metabolic rate for oxygen. Deep hypothermia (20 degrees C) reduced Doppler- and thermodilution-estimated cerebral metabolic rate for oxygen to 22.0% +/- 3.9% and 20.6% +/- 6.9% of the awake levels, respectively. The study supports the validity of using middle cerebral arterial flow velocity changes as an estimate of changes in volume flow through the brain during cardiac operations.     

Comparative analysis of alpha-stat and pH-stat strategies with a membrane oxygenator during deep hypothermic circulatory arrest in young pigs

Using young pigs, this study compared the strategies of alpha-stat and pH-stat during deep hypothermic circulatory arrest (DHCA) for the cooling time of brains during the induction of hypothermia and rewarming time with cardiopulmonary bypass (CPB); the cerebral perfusion rate and metabolism rate, and the ratio of these 2 rates; and the extent of the cerebral edema development after circulatory arrest. Fourteen young pigs were assigned to 1 of 2 strategies of gas management. Cerebral blood flow was measured with a cerebral venous outflow technique. With CPB, core cooling was initiated and continued until the nasopharyngeal temperature fell below 20 degrees C. The flow rate was set at 2,500 ml/min. Once the temperature reached below 20 degrees C, the animals were subjected to DHCA for 40 min. During the cooling period, the acid-base balance was maintained using either alpha-stat or pH-stat strategy. After DHCA, the body was rewarmed to the normal body temperature. The animals then were sacrificed, and we measured the brain water content. The cerebral perfusion and metabolism rates were measured before the onset of CPB, before cooling, before DHCA, 15 min after rewarming, and upon the completion of rewarming. The cooling time was significantly shorter with alpha-stat than with pH-stat strategy while no significant differences were observed in the rewarming time between groups. Also, no significant differences were found in cerebral blood flow volume, metabolic rate, or flow/metabolic rate ratio between groups. In each group, the cerebral blood flow volume, metabolic rate, and flow/metabolic rate ratio showed significant differences in body temperature. Brain water content showed no significant differences between the 2 groups. In summary, this study found no significant differences between alpha-stat and pH-stat strategies, except in the cooling time. The cooling time was rather shorter with the alpha-stat than with the pH-stat strategy.     

Optimal pH strategy for selective cerebral perfusion.

OBJECTIVE: Selective cerebral perfusion (SCP) affords brain protection superior to hypothermic circulatory arrest (HCA) for prolonged aortic arch procedures. Optimal pH strategy for HCA is controversial; for SCP it is unknown. We compared pH strategies during SCP in a survival pig model. METHODS: Twenty juvenile pigs (26+/-2.4 kg), randomized to alpha-stat (n=10) or pH-stat (n=10) management, underwent cooling to 20 degrees C on cardiopulmonary bypass (CPB) followed by 90 min of SCP at 20 degrees C. SCP was conducted with a mean pressure of 50 mmHg and hematocrit of 22.5%. Using fluorescent microspheres and sagittal sinus blood sampling, cerebral blood flow (CBF) and oxygen metabolism (CMRO2) were assessed at the following time points: baseline, after 30 min cooling (20 degrees C), 30 min of SCP, 90 min of SCP, 15 min post-CPB and 2h post-CPB. Visual evoked potentials (VEP) were assessed at baseline and monitored for 2h during recovery. Neurobehavioral recovery (10=normal) was assessed in a blinded fashion for 7 postoperative days. RESULTS: There were no significant differences between the groups at baseline. CBF was significantly higher at the end of cooling, and after 30 and 90 min of SCP in the pH-stat group (P=0.02, 0.007, 0.03). CMRO2 was also higher with pH-stat (P=0.06, 0.04, 0.10). Both groups showed prompt return to values close to baseline after rewarming (P=ns). VEP suggested a trend towards improved recovery in the alpha-stat group at 2h post-CPB, P=0.15. However, there were no significant differences in neurobehavioral score: (alpha-stat versus pH-stat) median values 7 and 7.5 on day 1; 9 and 9 on day 4, and 10 and 10 on day 7. CONCLUSIONS: These data suggest that alpha-stat management for SCP provides more effective metabolic suppression than pH-stat, with lower CBF. Clinically, the better preservation of cerebral autoregulation during alpha-stat perfusion should reduce the risk of embolization.     

Early effects of acid-base management during hypothermia on cerebral infarct volume,edema, and cerebral blood flow in acute focal cerebral ischemia in rats

BACKGROUND: Although the frequency for the use of moderate hypothermia in acute ischemic stroke is increasing, the optimal acid-base management during hypothermia remains unclear. This study investigates the effect of pH- and alpha-stat acid-base management on cerebral blood flow (CBF), infarct volume, and cerebral edema in a model of transient focal cerebral ischemia in rats. METHODS: Twenty Sprague-Dawley rats were subjected to transient middle cerebral artery occlusion (MCAO) for 2 h during normothermic conditions followed by 5 h of reperfusion during hypothermia (33 degrees C). Animals were artificially ventilated with either alpha- (n = 10) or pH-stat management (n = 10). CBF was analyzed 7 h after induction of MCAO by iodo[(14)C]antipyrine autoradiography. Cerebral infarct volume and cerebral edema were measured by high-contrast silver infarct staining (SIS). RESULTS: Compared with the alpha-stat regimen, pH-stat management reduced cerebral infarct volume (98.3 +/- 33.2 mm(3) vs. 53.6 +/- 21.6 mm(3); P > or = 0.05 mean +/- SD) and cerebral edema (10.6 +/- 4.0% vs. 3.1 +/- 2.4%; P > or = 0.05). Global CBF during pH-stat management exceeded that of alpha-stat animals (69.5 +/- 12.3 ml x 100 g(-1) x min(-1) vs. 54.7 +/- 13.3 ml x 100 g(-1) x min; P > or = 0.05). The regional CBF of the ischemic hemisphere was 62.1 +/- 11.2 ml x 100 g(-1) x min(-1) in the pH-stat group versus 48.2 +/- 7.2 ml x 100 g(-1) x min(-1) in the alpha-stat group ( P> or = 0.05). CONCLUSIONS: In the very early reperfusion period (5 h), pH-stat management significantly decreases cerebral infarct volume and edema as compared with alpha-stat during moderate hypothermia, probably by increasing CBF.     

Differences in pH management and pulsatile/nonpulsatile perfusion during cardiopulmonary bypass do not influence renal function.

The renal effects of pulsatile (pulse pressure 18.0 +/- 1.5 mm Hg [mean +/- SEM]) or nonpulsatile perfusion (mean pulse pressure 1.9 +/- 0.4 mm Hg) during either alpha-stat (mean PaCO2 41.2 +/- 0.9 mm Hg measured at 37 degrees C) or pH-stat (mean PaCO2 60.6 +/- 1.7 mm Hg measured at 37 degrees C) pH management of hypothermic cardiopulmonary bypass (CPB) were studied in 100 patients undergoing elective coronary artery bypass surgery. Mean urine output, fractional excretion of sodium and potassium, and renal failure index all increased during the study period; however, there was no difference among the four different CPB management groups. Mean postoperative creatinine and blood urea nitrogen values decreased compared with preoperative values, again without differences among treatment groups. Three patients developed acute renal insufficiency; of these, two had received nonpulsatile perfusion and pH-stat management, and the other had been managed with pulsatile perfusion and pH-stat management. These three patients all had undergone prolonged CPB and required at least two vasoactive drugs and the use of an intraaortic balloon pump to be weaned from CPB. In patients with normal preoperative renal function undergoing hypothermic CPB, neither the mode of perfusion, pulsatile or nonpulsatile, nor the method of pH management, pH-stat or alpha-stat, influences perioperative renal function.     

Comparative effects of propofol versus fentanyl on cerebral oxygenation state during normothermic cardiopulmonary bypass and postoperative cognitive dysfunction

BACKGROUND: The purpose of this study was to examine the comparative effects of propofol and fentanyl on cerebral oxygenation during normothermic cardiopulmonary bypass and postoperative cognitive dysfunction. METHODS: One hundred eighty patients scheduled for elective coronary artery bypass grafting were randomly divided into two groups: propofol group (n = 90) and fentanyl group (n = 90). After induction of anesthesia, a fiberoptic oximetry oxygen saturation catheter was inserted into the right jugular bulb to monitor jugular venous oxygen hemoglobin saturation continuously. Hemodynamic measurements and arterial and jugular venous blood gases were measured at seven time points. All patients underwent a battery of neurologic and neuropsychological tests on the day before the operation and at 6 months after the operation. RESULTS: Cerebral desaturation (defined as a jugular venous oxygen hemoglobin saturation value less than 50%) during cardiopulmonary bypass was more frequent in the fentanyl group than in the propofol group. Cerebral desaturation time (duration when jugular venous oxygen hemoglobin saturation was less than 50%) and the ratio of cerebral desaturation time to total cardiopulmonary bypass time in the fentanyl group differed significantly from those in the propofol group (fentanyl group: 27 +/- 14 minutes, 20% +/- 9%; propofol group: 18 +/- 11 minutes, 14% +/- 7%, respectively, p < 0.05). There was no significant difference in postoperative cognitive dysfunction at 6 months after operation between the two groups (propofol group: 5 of 77, 6%; fentanyl group: 5 of 75, 7%). CONCLUSIONS: Propofol preserved cerebral oxygenation state estimated by jugular venous oxygenation during cardiopulmonary bypass compared with the fentanyl group. However, propofol did not affect postoperative cognitive dysfunction.     

Importance of acid-base strategy in reducing myocardial and whole body oxygen consumption during perfusion hypothermia

During induced hypothermia with cardiopulmonary bypass, acid-base management usually follows one of two strategies: the so-called ectothermic or alpha-stat strategy, in which the pH of the arterial blood increases 0.015 pH units for every degree Celsius decrease in body temperature, or the pH-stat strategy, in which pH remains 7.4 at all temperatures. It has been assumed that oxygen consumption decreases approximately equally during hypothermia with either strategy, although there are biochemical reasons to hypothesize that oxygen consumption would be better maintained with the alpha-stat strategy. We also hypothesized that venous oxygen tension would be lower with the more alkaline alpha-stat strategy than with the pH-stat acid-base strategy, because of the Bohr effect. We tested these hypotheses by placing 10 anesthetized immature domestic pigs on cardiopulmonary bypass. We measured whole body oxygen consumption and myocardial oxygen consumption. Control measurements were made at 37 degrees C. Then the animals were cooled to 27 degrees C and the measurements were repeated. The alpha-stat strategy (pH 7.554 +/- 0.020 at 27 degrees C) was used in five animals and five animals received pH-stat management (pH 7.409 +/- 0.012 at 27 degrees C). Whole body and myocardial oxygen consumption rate decreased in both groups, but more so in the alpha-stat animals than in the pH-stat animals. The unexpectedly high oxygen consumption in the pH-stat animals also resulted in a lower than expected venous oxygen tension. Thus the effect of hypothermia in reducing oxygen consumption was less pronounced with pH-stat acid-base management.     

Influence of pH management on hemodynamics and metabolism in moderate hypothermia.

In moderate hypothermia, three different concepts of pH management have been described to date: pH-stat, alpha-stat, and alkalinity. In our study these pH strategies were compared in adult sheep, with animals serving as their own controls for direct comparability. Hemodynamic parameters, such as mean aortic pressure (from 109 +/- 12 to 72 +/- 23 mm Hg), cardiac output (from 5.55 +/- 1.25 to 4.5 +/- 0.82 L/min), and systemic oxygen consumption (from 3.73 +/- 0.8 to 1.81 +/- 0.4 ml/kg/min), decreased significantly with alpha-stat at 28 degrees C from values for normothermia. No marked or even significant differences were found among the three pH strategies in any value, with the exception of body oxygen consumption. The difference of 2% between pH-stat and alpha-stat, at 0.06 ml oxygen/kg/min, was significant (p < or = 0.05), however of no practical relevance because hypothermia itself caused a decrease of nearly 52%. With regard to myocardial parameters, pH-stat impaired myocardial function compared with both alpha-stat and alkalinity. At nearly identical mean aortic pressures and cardiac outputs, myocardial oxygen consumption reached the highest level in pH-stat (7.65 ml oxygen/100 gm/min; alpha-stat, 6.76 ml oxygen/100 gm/min; p < or = 0.05). Myocardial efficiency thus decreased from 21% (alpha-stat) to 17% (pH-stat). No evident changes in hemodynamic and metabolic values were found for alkalinity vs alpha-stat. The best response to continuously infused epinephrine, however, was found with alkalinity. According to our data there was an impairment of myocardial function without any evident further reduction in body metabolism with pH-stat vs alpha-stat. There were, however, no marked metabolic or hemodynamic differences between alkalinity and alpha-stat, with the exception of a better preservation of sensitivity to adrenergic stimuli with alkalinity.