Apoptotic neuronal death following deep hypothermic circulatory arrest in piglets

BACKGROUND: Deep hypothermic circulatory arrest (DHCA), as used in infant heart surgery, carries a risk of brain injury. In a piglet DHCA model, neocortical neurons appear to undergo apoptotic death. Caspases, cytochrome c, tumor necrosis factor (TNF), and Fas play a role in apoptosis in many ischemic models. This study examined the expression of these factors in a DHCA piglet model. METHODS: Thirty-nine anesthetized piglets were studied. After cardiopulmonary bypass (CPB) cooling of the brain temperature to 19 degrees C, DHCA was induced for 90 min, followed by CPB rewarming. After separation from CPB, piglets were killed at 1, 4, 8, 24, and 72 h and 1 week. Caspase-8 and -3 activity, and concentrations of TNF-alpha, Fas, Fas-ligand, cytochrome c, and adenosine triphosphate (ATP) were measured in the neocortex by enzymatic assay and Western blot analysis. Caspase-8 and -3 activity and cell death were examined histologically. Significance was set at P < 0.05. RESULTS: In neocortex, damaged neurons were not observed in control (no CPB), rarely observed in CPB (no DHCA), and rarely observed in the DHCA 1-h, 4-h, and 1-week reperfusion groups. However, they were seen frequently in the DHCA 8-, 24-, and 72-h reperfusion groups. Although neuronal death was widespread 8-72 h after DHCA, cortical ATP concentrations remained unchanged from control. Both caspase-3 and -8 activities were significantly increased at 8 h after DHCA, and caspase-3 concentration remained elevated for as long as 72 h. Caspase-3 and -8 activity was also observed in damaged neocortical neurons. Cytosolic cytochrome c and Fas were significantly expressed at 1 h and 4 h after DHCA, respectively. Fas-ligand and TNF-alpha were not observed in any group. CONCLUSION: After DHCA, induction of apoptosis in the neocortex occurs within a few hours of reperfusion and continues for several days. Increased Fas, cytochrome c, and caspase concentrations, coupled with normal brain ATP concentrations and apoptotic histologic appearance, are consistent with the occurrence of apoptotic cell death.     

Apoptotic Neuronal Death following Deep Hypothermic Circulatory Arrest in Piglets

Background: Deep hypothermic circulatory arrest (DHCA), as used in infant heart surgery, carries a risk of brain injury. In a piglet DHCA model, neocortical neurons appear to undergo apoptotic death. Caspases, cytochrome c, tumor necrosis factor (TNF), and Fas play a role in apoptosis in many ischemic models. This study examined the expression of these factors in a DHCA piglet model.

Methods: Thirty-nine anesthetized piglets were studied. After cardiopulmonary bypass (CPB) cooling of the brain temperature to 19[degrees]C, DHCA was induced for 90 min, followed by CPB rewarming. After separation from CPB, piglets were killed at 1, 4, 8, 24, and 72 h and 1 week. Caspase-8 and -3 activity, and concentrations of TNF-[alpha], Fas, Fas-ligand, cytochrome c, and adenosine triphosphate (ATP) were measured in the neocortex by enzymatic assay and Western blot analysis. Caspase-8 and -3 activity and cell death were examined histologically. Significance was set at P < 0.05.

Results: In neocortex, damaged neurons were not observed in control (no CPB), rarely observed in CPB (no DHCA), and rarely observed in the DHCA 1-h, 4-h, and 1-week reperfusion groups. However, they were seen frequently in the DHCA 8-, 24-, and 72-h reperfusion groups. Although neuronal death was widespread 8-72 h after DHCA, cortical ATP concentrations remained unchanged from control. Both caspase-3 and -8 activities were significantly increased at 8 h after DHCA, and caspase-3 concentration remained elevated for as long as 72 h. Caspase-3 and -8 activity was also observed in damaged neocortical neurons. Cytosolic cytochrome c and Fas were significantly expressed at 1 h and 4 h after DHCA, respectively. Fas-ligand and TNF-[alpha] were not observed in any group.     

Modified ultrafiltration may not improve neurologic outcome following deep hypothermic circulatory arrest.

OBJECTIVE: Modified ultrafiltration (MUF) improves systolic blood pressure and left ventricular performance, as well as lowering transfusion requirements, after cardiopulmonary bypass (CPB). MUF has also been shown to enhance acute cerebral metabolic recovery after deep hypothermic circulatory arrest (DHCA), but whether this improves neurologic outcome is unknown. METHODS: Sixteen neonatal piglets underwent CPB and 90 min of DHCA. The hematocrit was maintained between 25 and 30%. Alpha-stat blood gas management was used. After separation from CPB, animals were randomized to 15 min of MUF (n = 8) or no intervention (n = 8). Neurologic injury was assessed with behavior scores and histologic examination. Standardized behavior scores were obtained on post-operative days 1, 3, and 6 (0 = no deficit to 95 = brain death). The percentage of injured neurons by hematoxylin and eosin staining and the degree of reactive astrocytosis by glial filbrillary acidic protein (GFAP) immunohistochemistry were assessed to determine histologic scores in the neocortex and hippocampus (0 = no injury to 4 = diffuse injury). RESULTS: There were no statistically significant differences between groups during CPB. After MUF, the hematocrit was significantly higher (40% +/- 5.7 vs. 28% +/- 3.9, P < 0.001). There were no significant differences in behavior scores between groups (p > 0.1). There was resolution of deficits by day 6 in all animals. Neuronal injury was present in 81% (13/16) of the animals with no statistically significant differences between groups in incidence or severity. CONCLUSIONS: Use of MUF after DHCA does not prevent neuronal injury or improve neurologic outcome in this neonatal swine model.     

Regional low-flow perfusion improves neurologic outcome compared with deep hypothermic circulatory arrest in neonatal piglets

BACKGROUND: Regional low-flow perfusion is an alternative to deep hypothermic circulatory arrest, but whether regional low-flow perfusion improves neurologic outcome after deep hypothermic circulatory arrest in neonates remains unknown. We tested neurologic recovery after regional low-flow perfusion compared with deep hypothermic circulatory arrest in a neonatal piglet model. METHODS: Sixteen neonatal piglets underwent cardiopulmonary bypass, were randomized to 90 minutes of deep hypothermic circulatory arrest or regional low-flow perfusion (10 mL.kg(-1).min(-1)) at 18 degrees C, and survived for 1 week. Standardized neurobehavioral scores were obtained on postoperative days 1, 3, and 7 (0 = no deficit to 90 = brain death). Histopathologic scores were determined on the basis of the percentage of injured and apoptotic neurons in the neocortex and hippocampus by hematoxylin and eosin and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick-end labeling (0 = no injury to 4 = diffuse injury). Differences between groups were tested by using the Wilcoxon rank sum test, and results are listed as medians within a range. RESULTS: There were no significant differences between groups during cardiopulmonary bypass. Postoperative neurobehavioral scores were abnormal in 25% (2/8) of the regional low-flow perfusion animals versus 88% (7/8) of controls. Regional low-flow perfusion animals had significantly less neurologic injury compared with controls on postoperative day 1 (0.00 [range, 0-5] vs 12.5 [range, 0-52]; P <.008). There was a trend for less severe injury in the regional low-flow perfusion group (2.0 [range, 1-4] vs 0.0 [range, 0-50]; P =.08) on hematoxylin and eosin. The degree of apoptosis was significantly less in the regional low-flow perfusion group (0.0 [range, 0-1] vs 2.5 [range, 0-4]; P =.03). CONCLUSIONS: Regional low-flow perfusion decreases neuronal injury and improves early postoperative neurologic function after deep hypothermic circulatory arrest in neonatal piglets.     

Large-dose pretreatment with methylprednisolone fails to attenuate neuronal injury after deep hypothermic circulatory arrest in a neonatal piglet model

Conflicting results have been reported with regard to the neuroprotective effects of steroid treatment with cardiopulmonary bypass (CPB) and deep hypothermic circulatory arrest (DHCA). We evaluated the mode and severity of neuronal cell injury in neonatal piglets after prolonged DHCA and the possible neuroprotective effect of systemic pretreatment (>6 h before surgery) with large-dose methylprednisolone (MP). Nineteen neonatal piglets (age, <10 days; weight, 2.1 +/- 0.5 kg) were randomly assigned to 2 groups: 7 animals were pretreated with large-dose systemic MP (30 mg/kg) 24 h before surgery, and 12 animals without pharmacological pretreatment (saline) served as control groups. All animals were connected to full-flow CPB with cooling to 15 degrees C and 120 min of DHCA. After rewarming to 38.5 degrees C with CPB, animals were weaned from CPB and survived 6 h before they were killed, and the brain was prepared for light and electron microscopy, immunohistochemistry, and TUNEL-staining. Quantitative histological studies were performed in hippocampus, cortex, cerebellum, and caudate nucleus. Systemic pretreatment with large-dose MP lead to persistent hyperglycemia but no significant changes of cerebral perfusion. Necrotic and apoptotic neuronal cell death were detected in all analyzed brain regions after 120 min of DHCA. In comparison to the control group, large-dose pretreatment with systemic MP lead to an increase of necrotic neuronal cell death and induced significant neuronal apoptosis in the dentate gyrus of the hippocampus (P = 0.001). In conclusion, systemic pretreatment with large-dose MP fails to attenuate neuronal cell injury after prolonged DHCA and induces regional neuronal apoptosis in the dentate gyrus.     

Desflurane Confers Neurologic Protection for Deep Hypothermic Circulatory Arrest in Newborn Pigs

Background: Cardiopulmonary bypass (CPB) and deep hypothermic circulatory arrest (DHCA), as used for infant heart surgery, carry a risk of ischemic neurologic injury. Volatile anesthetics have neuroprotective properties against both global and focal ischemia at normothermia. The authors examined the hemodynamic and neuroprotective effects of desflurane in a piglet CPB-DHCA model.

Methods: Twenty piglets aged 5-10 days received a desflurane- (6-9% expired) or fentanyl-based anesthetic before and during CPB (before and after DHCA). DHCA lasted 90 min at 19[degrees]C brain. Cardiovascular variables (heart rate, arterial pressure, blood gases, glucose, brain temperature) were monitored. On postoperative day 2, neurologic and histologic outcomes were determined.

Results: Cardiovascular variables before, during, and after CPB were physiologically similar between groups. The desflurane group had better neurologic performance (P = 0.023) and greater postoperative weight gain (P = 0.04) than the fentanyl group. In neocortex, the desflurane group had less tissue damage (P = 0.0015) and fewer dead neurons (P = 0.0015) than the fentanyl group. Hippocampal tissue damage was less in the desflurane group (P = 0.05), but overall, neuronal cell counts in the CA1 sector of the right hippocampus were similar to those in the fentanyl group.     

Desflurane confers neurologic protection for deep hypothermic circulatory arrest in newborn pigs

BACKGROUND: Cardiopulmonary bypass (CPB) and deep hypothermic circulatory arrest (DHCA), as used for infant heart surgery, carry a risk of ischemic neurologic injury. Volatile anesthetics have neuroprotective properties against both global and focal ischemia at normothermia. The authors examined the hemodynamic and neuroprotective effects of desflurane in a piglet CPB-DHCA model. METHODS: Twenty piglets aged 5-10 days received a desflurane- (6-9% expired) or fentanyl-based anesthetic before and during CPB (before and after DHCA). DHCA lasted 90 min at 19 degrees C brain. Cardiovascular variables (heart rate, arterial pressure, blood gases, glucose, brain temperature) were monitored. On postoperative day 2, neurologic and histologic outcomes were determined. RESULTS: Cardiovascular variables before, during, and after CPB were physiologically similar between groups. The desflurane group had better neurologic performance (P = 0.023) and greater postoperative weight gain (P = 0.04) than the fentanyl group. In neocortex, the desflurane group had less tissue damage (P = 0.0015) and fewer dead neurons (P = 0.0015) than the fentanyl group. Hippocampal tissue damage was less in the desflurane group (P = 0.05), but overall, neuronal cell counts in the CA1 sector of the right hippocampus were similar to those in the fentanyl group. CONCLUSIONS: Desflurane-based anesthesia yields hemodynamics during CPB with DHCA that are similar to those with fentanyl-based anesthesia. However, desflurane-based anesthesia improves neurologic and histologic outcomes of CPB-DHCA in comparison with outcomes with fentanyl-based anesthesia.     

Desflurane improves neurologic outcome after low-flow cardiopulmonary bypass in newborn pigs

BACKGROUND: Despite improvements in neonatal heart surgery, neurologic complications continue to occur from low-flow cardiopulmonary bypass (LF-CPB) and deep hypothermic circulatory arrest (DHCA). Desflurane confers neuroprotection against ischemia at normothermia and for DHCA. This study compared neurologic outcome of a desflurane-based with a fentanyl-based anesthetic for LF-CPB. METHODS: Thirty piglets aged 1 week received either fentanyl-droperidol (F/D), desflurane 4.5% (Des4.5), or desflurane 9% (Des9) during surgical preparation and CPB. Arterial blood gases, glucose, heart rate, arterial pressure, brain temperature, and cerebral blood flow (laser Doppler flowmetry) were recorded. After CPB cooling (22 degrees C brain) using pH-stat strategy, LF-CPB was performed for 150 min followed by CPB rewarming, separation from CPB, and extubation. On postoperative day 2, functional and histologic outcomes were assessed. RESULTS: Cardiovascular variables were physiologically similar between groups before, during, and after LF-CPB. Cerebral blood flow during LF-CPB (13% of pre-CPB value) did not differ significantly between the groups. Functional disability was worse in F/D than in Des9 (P = 0.04) but not Des4.5 (P = 0.1). In neocortex, histopathologic damage was greater in F/D than in Des4.5 (P = 0.03) and Des9 (P = 0.009). In hippocampus, damage was worse in F/D than in Des9 (P = 0.01) but not Des4.5 (P = 0.08). The incidences of ventricular fibrillation during LF-CPB were 90, 60, and 10% for F/D, Des4.5 (P = 0.06), and Des9 (P = 0.0002), respectively. CONCLUSIONS: Desflurane improved neurologic outcome following LF-CPB compared with F/D in piglets, indicated by less functional disability and less histologic damage, especially with Des9. Desflurane may have produced cardiac protection, suggested by a lower incidence of ventricular fibrillation.     

Injury pattern of the neonatal brain after hypothermic low-flow cardiopulmonary bypass in a piglet model

Low-flow cardiopulmonary bypass (LF-CPB) is a widely used modality in neonatal heart surgery. While facilitating surgical repair, it poses a risk of neurological injury caused by hypoperfusion. In the present study, we characterize the injury pattern and influencing factors in a piglet hypothermic LF-CPB model. Piglets were anesthetized, tracheally intubated, ventilated, and prepared for CPB. After LF-CPB for 150 min at 22 degrees C (brain) using pH-stat strategy, animals were allowed to survive for 2 or 9 days. Neurological status was assessed daily and magnetic resonance imaging scans were performed. Brains were assessed histologically. Functional neurological impairment was seen in 64%, 30%, and 0% of animals 1, 2, and 9 days after CPB, respectively. All animals showed histological brain damage, predominantly in neocortex and hippocampus, less so in basal ganglia, thalamus, white matter, and cerebellum. Cell death appeared as selective neuronal necrosis in the deeper layers in neocortex and CA1-4 sections in hippocampus. Even in a pH-stat strategy, less neocortical and hippocampal damage correlated with higher arterial partial pressure for carbon dioxide. Less hippocampal damage was associated with higher blood glucose levels. Less functional neurological impairment and basal ganglia damage correlated with higher postoperative hematocrit. IMPLICATIONS: Neuronal injury after hypothermic low-flow cardiopulmonary bypass in a piglet model using pH-stat strategy occurs predominantly in deep neocortex and hippocampus. Factors mitigating injury were higher arterial carbon dioxide, hematocrit, and blood glucose levels.     

Comparison of neurologic outcome after deep hypothermic circulatory arrest with alpha-stat and pH-stat cardiopulmonary bypass in newborn pigs

OBJECTIVE: Deep hypothermic circulatory arrest for neonatal heart surgery poses the risk of brain damage. Several studies suggest that pH-stat management during cardiopulmonary bypass improves neurologic outcome compared with alpha-stat management. This study compared neurologic outcome in a survival piglet model of deep hypothermic circulatory arrest between alpha-stat and pH-stat cardiopulmonary bypass. METHODS: Piglets were randomly assigned to alpha-stat (n = 7) or pH-stat (n = 7) cardiopulmonary bypass, cooled to 19 degrees C brain temperature, and subjected to 90 minutes of deep hypothermic circulatory arrest. After bypass rewarming/reperfusion, they survived 2 days. Neurologic outcome was assessed by neurologic performance (0-95, 0 = no deficit and 95 = brain death) and functional disability scores, as well as histopathology. Arterial pressure, blood gas, glucose, and brain temperature were recorded before, during, and after bypass. RESULTS: All physiologic data during cardiopulmonary bypass were similar between groups (pH-stat vs alpha-stat) except arterial pH (7.06 +/- 0.03 vs 7.43 +/- 0.09, P <.001) and arterial PCO (2) (98 +/- 8 vs 36 +/- 8 mm Hg, P <.001). No differences existed in duration of cardiopulmonary bypass or time to extubation. Performance was better in pH-stat versus alpha-stat management at 24 hours (2 +/- 3 vs 29 +/- 17, P = 0.004) and 48 hours (1 +/- 2 vs 8 +/- 9, P =.1). Also, functional disability was less severe with pH-stat management at 24 hours (P =.002) and 48 hours (P =.053). Neuronal cell damage was less severe with pH-stat versus alpha-stat in the neocortex (4% +/- 2% vs 15% +/- 7%, P <.001) and hippocampal CA1 region (11% +/- 5% vs 33% +/- 25%, P =.04), but not in the hippocampal CA3 region (3% +/- 5% vs 16% +/- 23%, P =.18) or dentate gyrus (1% +/- 1% vs 3% +/- 6%, P =.63). CONCLUSIONS: pH-stat cardiopulmonary bypass management improves neurologic outcome with deep hypothermic circulatory arrest compared with alpha-stat bypass. The mechanism of protection is not related to hemodynamics, hematocrit, glucose, or brain temperature.     

Desflurane Improves Neurologic Outcome after Low-flow Cardiopulmonary Bypass in Newborn Pigs

Background: Despite improvements in neonatal heart surgery, neurologic complications continue to occur from low-flow cardiopulmonary bypass (LF-CPB) and deep hypothermic circulatory arrest (DHCA). Desflurane confers neuroprotection against ischemia at normothermia and for DHCA. This study compared neurologic outcome of a desflurane-based with a fentanyl-based anesthetic for LF-CPB.

Methods: Thirty piglets aged 1 week received either fentanyl-droperidol (F/D), desflurane 4.5% (Des4.5), or desflurane 9% (Des9) during surgical preparation and CPB. Arterial blood gases, glucose, heart rate, arterial pressure, brain temperature, and cerebral blood flow (laser Doppler flowmetry) were recorded. After CPB cooling (22[degrees]C brain) using pH-stat strategy, LF-CPB was performed for 150 min followed by CPB rewarming, separation from CPB, and extubation. On postoperative day 2, functional and histologic outcomes were assessed.

Results: Cardiovascular variables were physiologically similar between groups before, during, and after LF-CPB. Cerebral blood flow during LF-CPB (13% of pre-CPB value) did not differ significantly between the groups. Functional disability was worse in F/D than in Des9 (P = 0.04) but not Des4.5 (P = 0.1). In neocortex, histopathologic damage was greater in F/D than in Des4.5 (P = 0.03) and Des9 (P = 0.009). In hippocampus, damage was worse in F/D than in Des9 (P = 0.01) but not Des4.5 (P = 0.08). The incidences of ventricular fibrillation during LF-CPB were 90, 60, and 10% for F/D, Des4.5 (P = 0.06), and Des9 (P = 0.0002), respectively.     

Cold retrograde cerebral perfusion improves cerebral protection during moderate hypothermic circulatory arrest: A long-term study in a porcine model.

BACKGROUND: Deep hypothermic circulatory arrest is an effective method of cerebral protection, but it is associated with long cardiopulmonary bypass times and coagulation disturbances. Previous studies have shown that retrograde cerebral perfusion can improve neurologic outcomes after prolonged hypothermic circulatory arrest. We tested the hypothesis that deep hypothermic retrograde cerebral perfusion could improve cerebral outcome during moderate hypothermic circulatory arrest. METHODS: Twelve pigs (23-29 kg) were randomly assigned to undergo either retrograde cerebral perfusion (15 degrees C) at 25 degrees C or hypothermic circulatory arrest with the head packed in ice at 25 degrees C for 45 minutes. Flow was adjusted to maintain superior vena cava pressure at 20 mm Hg throughout retrograde cerebral perfusion. Hemodynamic, electrophysiologic, metabolic, and temperature monitoring were carried out until 4 hours after the start of rewarming. Daily behavioral assessment was performed until elective death on day 7. A postmortem histologic analysis of the brain was carried out on all animals. RESULTS: In the retrograde cerebral perfusion group, 5 (83%) of 6 animals survived 7 days compared with 2 (33%) of 6 in the hypothermic circulatory arrest group. Complete behavioral recovery was seen in 4 (67%) animals after retrograde cerebral perfusion but only in 1 (17%) animal after hypothermic circulatory arrest. Postoperative levels of serum lactate were higher, and blood pH was lower in the hypothermic circulatory arrest group. There were no significant hemodynamic differences between the study groups. CONCLUSIONS: Cold hypothermic retrograde cerebral perfusion during moderate hypothermic circulatory arrest seems to improve neurologic outcome compared with moderate hypothermic circulatory arrest with the head packed in ice.     

A novel sialyl Lewis X analog attenuates cerebral injury after deep hypothermic circulatory arrest.

BACKGROUND: The initial step in the inflammatory process, which can be initiated by cardiopulmonary bypass and by ischemia/reperfusion, is mediated by interactions between selectins on endothelial cells and on neutrophils. We studied the effects of selectin blockade using a novel Sialyl Lewis X analog (CY-1503) on recovery after deep hypothermic circulatory arrest in a piglet model. METHODS: Twelve Yorkshire piglets were subjected to cardiopulmonary bypass, 30 minutes of cooling, 100 minutes of circulatory arrest at 15 degrees C, and 40 minutes of rewarming. Five animals received a bolus of 60 mg/kg of CY-1503 and an infusion (3 mg/kg per hour) for 24 hours from reperfusion (group O), and 7 randomly selected control piglets received saline solution (group C). Body weight and total body water content were evaluated 3 hours and 24 hours after reperfusion by a bio-impedance technique. Neurologic recovery of animals was evaluated daily by neurologic deficit score (0 = normal, 500 = brain death) and overall performance categories (1 = normal, 5 = brain death). The brain was fixed in situ on the fourth postoperative day and examined by histologic score (0 = normal, 5+ = necrosis) in a blinded fashion. RESULTS: Two of 7 animals in group C died. The neurologic deficit score was significantly lower in group O than in group C (postoperative day 1, P <.001; postoperative day 2, P =.02). The overall performance category was significantly lower in group O than in group C on postoperative day 2 (P =.01). Percentage total body water after cardiopulmonary bypass was significantly higher in group C than in group O (P =.03). Histologic score tended to be higher in group C than in group O, but this difference did not reach statistical significance (group O = 0.5 +/- 0.7; group C = 1.3 +/- 1.off CONCLUSION: Blockade of selectin adhesion molecules by saturation with a Sialyl Lewisx analog accelerates recovery after 100 minutes of deep hypothermic circulatory arrest in a piglet survival model.     

Myocardial contractility and relaxation after deep hypothermic circulatory arrest in a neonatal piglet model

Cooling before circulatory arrest or ischemic arrest has been reported to influence myocardial performance in isolated neonatal hearts. The aim of the present study was to analyze indices of myocardial contractility and relaxation in an in vivo neonatal model after deep hypothermic circulatory arrest (DHCA). DHCA (18°C; DHCA group; n = 8) or mild hypothermic cardiopulmonary bypass ([MH-CPB] 32°C; MH-CPB group; n = 10) was applied in newborn piglets. After reperfusion (60 and 120 min), left ventricular dP/dt(max) increased in DHCA and MH-CPB, while-dP/dt(max) decreased slightly in DHCA and increased in MH-CPB. Nevertheless, the differences between the two groups did not reach statistical significance. In conclusion, left ventricular contractility remained stable after reperfusion following DHCA, to some degree at the expense of the diastolic function.     

Combination of alpha-stat strategy and hemodilution exacerbates neurologic injury in a survival piglet model with deep hypothermic circulatory arrest

BACKGROUND: The optimal pH strategy and hematocrit during cardiopulmonary bypass with deep hypothermic circulatory arrest (DHCA) remain controversial. We studied the interaction of pH strategy and hematocrit and their combined impact on cerebral oxygenation and neurological outcome in a survival piglet model including monitoring by near-infrared spectroscopy (NIRS). METHODS: Thirty-six piglets (9.2+/-1.1 kg) underwent DHCA under varying conditions with continuous monitoring by NIRS (pH-stat or alpha-stat strategy, hematocrit 20% or 30%, DHCA time 60, 80, or 100 minutes). Neurological recovery was evaluated daily. The brain was fixed in situ on postoperative day 4 and a histological score (HS) for neurological injury was assessed. RESULTS: Oxygenated hemoglobin (HbO2) and total hemoglobin signals detected by NIRS were significantly lower with alpha-stat strategy during cooling (p < 0.001), suggesting insufficient cerebral blood supply and oxygenation. HbO2 declined to a plateau (nadir) during DHCA. Time to nadir was significantly shorter in lower hematocrit groups (p < 0.01). Significantly delayed neurologic recovery was seen with alpha-stat strategy compared with pH-stat (p < 0.05). The alpha-stat group had a worse histological score compared with those assigned to pH-stat (p < 0.001). Neurologic impairment was estimated to be over 10 times more likely for animals randomized to alpha-stat compared with pH-stat strategy (odds ratio = 10.7, 95% confidence interval = 3.8 to 25.2). CONCLUSIONS: Combination of alpha-stat strategy and lower hematocrit exacerbates neurological injury after DHCA. The mechanism of injury is inadequate cerebral oxygenation during cooling and a longer plateau period of minimal O2 extraction during DHCA.     

不同深低温停循环方法对脑组织S-100蛋白表达的影响

目的观察不同深低温停循环方法对脑组织S—100蛋白表达及组织结构的影响。方法将18只实验犬随机分为3组，深低温停循环（deep hypothermic circulatory arrest，DHCA组）组，深低温停循环结合逆行脑灌注（retrograde cerebral perfusion，RCP，DHCA＋RCP组）组，深低温停循环结合顺行性间断脑灌注（intermittent antegrade cerebral perfusion，IACP，DHCA＋IACP组）组。3组犬体外循环开始后将鼻咽温降至18℃，随后停循环90min，开放循环后复温至36℃，随后停机。在停循环前、停循环后45min、90min及开放循环后15min和30min由颈静脉插管留取血液标本进行S-100蛋白含量测定。手术结束时取脑海马组织作透射电子显微镜检查，观察脑组织及神经细胞超微结构的变化。结果3组犬在停循环前颈静脉血S-100蛋白含量差异无统计学意义（P〉0．05），停循环后DHCA组和DHCA＋RCP组S-100蛋白含量较停循环前显著升高（P〈0．01），DHCA＋IACP组S-100蛋白含量停循环前后无显著变化。结论DHCA时间较长时，脑组织会发生缺血缺氧性损伤；RCP对脑组织有一定的保护作用，但易发生脑组织及神经细胞水肿；IACP的脑保护效果较为理想。     

Hypoxemic reperfusion exacerbates the neurological injury sustained during neonatal deep hypothermic circulatory arrest: a model of cyanotic surgical repair.

OBJECTIVE: Deep hypothermic circulatory arrest (DHCA) is frequently used in infants undergoing the Norwood procedure. These infants are necessarily hypoxemic after separation from CPB. Considerable energy has been spent characterizing the physiological and histological consequences of DHCA, but these have largely focused on a normoxemic period of reperfusion. Furthermore, evidence has accumulated to suggest that the cerebral vascular autoregulatory mechanisms are dysfunctional following DHCA. In particular, the vasodilatation that elevates cerebral blood flow (CBF) in response to hypoxemia is absent. This study therefore aimed to investigate whether post-CPB hypoxemia exacerbates brain injury resulting from DHCA. METHODS: Twelve neonatal piglets were subjected to 2h DHCA and then separated from CPB. They were then randomized to either: Group 1, normoxic ventilation (n=5); or Group 2, hypoxemia (n=7), in which the arterial PaO(2) was reduced to 40-50 mmHg for the duration of reperfusion. Following a 20 h period of warm reperfusion, the animals were perfusion fixed and the brain analyzed for histological evidence of injury. Nine additional animals were studied in one of three control groups. RESULTS: All animals survived the protocol. Post-operative parameters - including mean arterial pressure, acid-base status, inotrope requirements and arterial PaCO(2) - were similar. None of the control animals had any evidence of ischemia. Group 1 animals had moderate injury (total score 7.4+/-1.6). In Group 2, three animals sustained irretrievable brain injury evidenced by gross edema and early liquefactive necrosis. The remaining four had severe ischemic histological changes (score 14.5+/-1.6, p<0.03). CONCLUSIONS: Hypoxemic reperfusion after prolonged DHCA results in increased neuronal loss. The use of DHCA for staged palliation may confer disproportionately greater cerebral risk than other patient groups. Alternatively, methods to augment oxygen delivery - such as by ECMO - may be of particular benefit in the early re-perfusion window.     

Deep Brain Hyperthermia While Rewarming from Hypothermic Circulatory Arrest

Abstract   Background: Neurologic injury is a feared and serious long-term complication of cardiopulmonary bypass (CPB) and deep hypothermic circulatory arrest (DHCA). Postoperative hyperthermia was found to enhance postischemic neurologic injury. The use of core temperature as the reference point through CPB assumes parallel changes in brain temperature. We tested the hypothesis that regional and deep brain temperature (DBT) differ during cooling, DHCA, and rewarming. Methods: Neonatal piglets (n = 9) were subject to CPB and cooled to rectal temperature (RT) of 18 °C, 30 minutes of DHCA were initiated, and subsequently the piglets were rewarmed to RT of 36.5 °C and weaned from CPB. Temperature probes were inserted into the DBT targeting the caudate and thalamic nuclei, their position confirmed by pathology. Superficial brain temperature was measured by a temperature probe inserted extradurally. RT, nasopharyngeal (NPT), and tympanic (TT) temperatures were recorded. Results: During cooling the deep brain cooled faster and to lower temperatures compared to RT and TT; NPT reflected DBT accurately. During rewarming DBT was significantly higher than RT and TT. By the end of rewarming the difference between the deep brain and the RT reached statistical significance (30 minutes: 35.1 ± 0.7 vs. 32.3 ± 0.7 p < 0.05, respectively, 40 minutes: 37.5 ± 0.3 vs. 34.7 ± 0.8 p < 0.05, respectively). Conclusion: Deep brain hyperthermia routinely occurs during the last stages of rewarming following DHCA. DBT is accurately reflected by NPT and is directly correlated with inflow temperature. Therefore, during rewarming inflow temperatures should not exceed 36 °C and NPT should be closely monitored.     

Study on cognition disorder and morphologic change of neurons in hippocampus area following traumatic brain injury in rats

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Neuronal Nitric Oxide Synthase Inhibition Reduces Neuronal Apoptosis After Hypothermic Circulatory Arrest

Background. Neurologic injury, including choreoathetosis and learning and memory deficits, occurs after prolonged hypothermic circulatory arrest (HCA). Apoptosis, or programmed cell death, is a possible cause of the neurologic injury seen after HCA. However, the mechanism of apoptosis is unknown. Hypothermic circulatory arrest causes glutamate excitotoxicity, resulting in increased nitric oxide production. We therefore hypothesized that nitric oxide mediates apoptosis. The purpose of this study was to determine if neuronal nitric oxide synthase inhibition reduces neuronal apoptosis in an established canine model of HCA.

Methods. Fourteen male hound dogs (weight, 20 to 27 kg) were placed on closed-chest cardiopulmonary bypass, subjected to 2 hours of HCA at 18°C, rewarmed to normothermia, and sacrificed 8 hours after HCA. Group 1 (n = 7) dogs were treated with the neuronal nitric oxide inhibitor 7-nitroindazole, 25 mg/kg intraperitoneally, before arrest and every 2 hours until sacrifice. Group 2 (n = 7) dogs received vehicle only. The brains were analyzed histopathologically. Apoptosis, identified by hematoxylin-eosin staining, was confirmed by DNA terminal deoxynucleotidyltransferase–mediated dUTP-biotin nick end-labeling assay and electron microscopy. Apoptosis was scored by a blinded neuropathologist from 0 (normal) to 100 (severe injury).

Results. Apoptosis occurred early after HCA in select neuronal populations, including the hippocampus, stria terminalis, neocortex, and entorhinal cortex. Apoptotic neurons showed a characteristic shrunken cytoplasm and nuclear chromatin condensation. 7-Nitroindazole significantly inhibited apoptosis (group 1 versus 2: 19.17 ± 14.39 versus 61.11 ± 5.41; p < .001).

Conclusions. Our results provide evidence that apoptosis is associated with the neurologic injury that occurs after HCA and that nitric oxide mediates the apoptosis that occurs after HCA. Strategies for cerebral protection during HCA may include the inhibition of neuronal nitric oxide synthase.