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.     

Assessing the impact of cerebral injury after cardiac surgery: will determining the mechanism reduce this injury?

Background. Central nervous system dysfunction continues to produce significant morbidity and associated mortality in patients undergoing cardiac surgery. Using a closed-chest canine cardiopulmonary bypass model, dogs underwent 2 h of hypothermic circulatory arrest (HCA) at 18°C, followed by resuscitation and recovery for 3 days. Animals were assessed functionally by a species-specific behavioral scale, histologically for patterns of selective neuronal necrosis, biochemically by analysis of microdialysis effluent, and by receptor autoradiography for N-methyl-D-aspartate (NMDA) glutamate receptor subtype expression.

Results. Using a selective NMDA (glutamate) receptor antagonist (MK801) and an AMPA antagonist (NBQX), glutamate excitotoxicity in the development of HCA-induced brain injury was documented and validated. A microdialysis technique was employed to evaluate the role of nitric oxide (NO) in neuronal cell death. Arginine plus oxygen is converted to NO plus citrulline (CIT) by the action of NO synthase (nNOS). CIT recovery in the cerebrospinal fluid and from canine cortical homogenates increased during HCA and reperfusion. These studies demonstrated that neurotoxicity after HCA involves a significant and early induction of nNOS expression, and neuronal processes leading to widespread augmentation of NO production in the brain.

To further investigate the production of excitatory amino acids in the brain, we hypothesized the following scenario: HCA→ ↑ glutamate, ↑ aspartate, ↑ glycine→ ↑ intracellular Ca²⁺→ ↑ NO + CIT. Using the same animal preparation, we demonstrated that HCA caused increased intracerebral glutamate and aspartate that persists up to 20 h post-HCA. HCA also resulted in CIT (NO) production, causing a continued and delayed neurologic injury. Confirmatory evidence of the role of NO was demonstrated by a further experiment using a specific nNOS inhibitor, 7-nitroindazole. Animals underwent 2 h of HCA, and then were evaluated both physiologically and for NO production. 7-Nitroindazole reduced CIT (NO) production by 58.4 ± 28.3%. In addition, dogs treated with this drug had superior neurologic function compared with untreated HCA controls.

Conclusions. These experiments have documented the role of glutamate excitotoxicity in neurologic injury and have implicated NO as a significant neurotoxin causing necrosis and apoptosis. Continued research into the pathophysiologic mechanisms involved in cerebral injury will eventually yield a safe and reliable neuroprotectant strategy. Specific interventional agents will include glutamate receptor antagonists and specific neuronal NO synthase inhibitors.     

Nitric oxide mediates neurologic injury after hypothermic circulatory arrest

BACKGROUND: Prolonged hypothermic circulatory arrest (HCA) causes neurologic injury. However, the mechanism of this injury is unknown. We hypothesized that HCA causes nitric oxide production to result in neuronal necrosis. This study was undertaken to determine whether the neuronal nitric oxide synthase inhibitor 17477AR reduces necrosis after HCA. METHODS: Thirty-two dogs underwent 2 hours of HCA at 18 degrees C. Nitric oxide synthase catalytic assay and intracerebral microdialysis for nitric oxide production were performed in acute nonsurvival experiments (n = 16). Sixteen animals survived for 72 hours after HCA: Group 1 (n = 9) was treated with 17477AR (Astra Arcus), and group 2 (n = 7) received vehicle only. Animals were scored from 0 (normal) to 500 (coma) for neurologic function and from 0 (normal) to 100 (severe) for neuronal necrosis. RESULTS: Administration of 17477AR reduced nitric oxide production in the striatum by 94% (HCA alone), 3.65+/-2.42 micromol/L; HCA and 17477AR, 0.20+/-0.14 micromol/L citrulline). Dogs treated with 17477AR after HCA had superior neurologic function (62.22+/-29.82 for group 1 versus 141.86+/-61.53 for group 2, p = 0.019) and significantly reduced neuronal necrosis (9.33+/-4.67 for group 1 versus 38.14+/-2.23 for group 2, p<0.00001) compared with untreated HCA dogs. CONCLUSIONS: Our results provide evidence that neuronal nitric oxide synthase mediates neuronal necrosis after HCA and plays a significant role in HCA-induced neurotoxicity. Pharmacologic strategies to inhibit neuronal nitric oxide synthase after the ischemic period of HCA may be clinically beneficial.     

S100beta correlates with neurologic complications after aortic operation using circulatory arrest.

BACKGROUND: Astrocyte protein S100beta is a potential serum marker for neurologic injury. The goals of this study were to determine whether elevated serum S100beta correlates with neurologic complications in patients requiring hypothermic circulatory arrest (HCA) during thoracic aortic repair, and to determine the impact of retrograde cerebral perfusion (RCP) on S100beta release in this setting. METHODS: Thirty-nine consecutive patients underwent thoracic aortic repairs during HCA; RCP was used in 25 patients. Serum S100beta was measured preoperatively, after cardiopulmonary bypass, and 24 hours postoperatively. RESULTS: Neurologic complications occurred in 3 patients (8%). These patients had higher postbypass S100beta levels (7.17 +/- 1.01 microg/L) than those without neurologic complications (3.63 +/- 2.31 microg/L, p = 0.013). Patients with S100beta levels of 6.0 microg/L or more had a higher incidence of neurologic complications (3 of 7, 43%) compared with those who had levels less than 6.0 microg/L (0 of 30, p = 0.005). Retrograde cerebral perfusion did not affect S100beta release. CONCLUSIONS: Serum S100beta levels of 6.0 microg/L or higher after HCA correlates with postoperative neurologic complications. Using serum S100beta as a marker for brain injury, RCP does not provide improved cerebral protection over HCA alone.     

Spinal cord ischemia and reperfusion metabolism: The effect of hypothermia

Purpose: The metabolic and neurologic functional effects of regional hypothermia induced by cold (4° C) heparinized saline perfusion on spinal cord ischemia were evaluated in 35 rabbits.Methods: Spinal cord ischemia was induced for 20 minutes by infrarenal aortic occlusion in anesthetized animals. Regional spinal cord hypothermia was obtained by perfusing the lumbar arteries supplying the spinal cord through an infrarenal aortic catheter. The lumbar spinal cord was "snap frozen" in situ with liquid nitrogen and harvested immediately at the conclusion of the ischemic period or after 24 hours of normothermic reperfusion and neurologic observation. Spinal cord metabolic studies included determination of the energy charge and the intracellular concentrations of adenosine triphosphate, glucose, lactate, glutamate, and aspartate.Results: Postoperative neurologic function was normal in all but one animal treated with hypothermia, while normothermic ischemia resulted in paralysis in all animals ( p = 0.002). Spinal cord temperature during 20 minutes of ischemia and hypothermic perfusion decreased from 37.5° ± 0.43° C to 22.8° ± 0.00° C ( p = 0.0001) compared to a fall in systemic temperature from 38.8 to 36.1 ( p = 0.0001). Hypothermia reduced the decline in energy charge, adenosine triphosphate concentration and glucose concentration during ischemia but had no effect on markedly elevated levels of lactate acid. High-energy phosphates were restored after reperfusion in both normothermic and hypothermic animals and were not predictive of postoperative paraplegia. Intracellular glutamate and aspartate concentrations were unchanged during normothermic ischemia but decreased after reperfusion in all paralyzed animals. Intracellular glutamate and aspartate concentrations increased during hypothermic perfusion and remained elevated after reperfusion in animals with a normal or mildly abnormal neurologic examination result.Conclusions: We conclude that spinal cord hypothermia induced by cold heparinized saline perfusion is a simple technique that prevents paraplegia after 20 minutes of ischemia and preserves intracellular concentrations of important metabolites. (J VASC SURG 1994;19:332-40.)     

S100β correlates with neurologic complications after aortic operation using circulatory arrest

Background. Astrocyte protein S100β is a potential serum marker for neurologic injury. The goals of this study were to determine whether elevated serum S100β correlates with neurologic complications in patients requiring hypothermic circulatory arrest (HCA) during thoracic aortic repair, and to determine the impact of retrograde cerebral perfusion (RCP) on S100β release in this setting.

Methods. Thirty-nine consecutive patients underwent thoracic aortic repairs during HCA; RCP was used in 25 patients. Serum S100β was measured preoperatively, after cardiopulmonary bypass, and 24 hours postoperatively.

Results. Neurologic complications occurred in 3 patients (8%). These patients had higher postbypass S100β levels (7.17 ± 1.01 μg/L) than those without neurologic complications (3.63 ± 2.31 μg/L, p = 0.013). Patients with S100β levels of 6.0 μg/L or more had a higher incidence of neurologic complications (3 of 7, 43%) compared with those who had levels less than 6.0 μg/L (0 of 30, p = 0.005). Retrograde cerebral perfusion did not affect S100β release.

Conclusions. Serum S100β levels of 6.0 μg/L or higher after HCA correlates with postoperative neurologic complications. Using serum S100β as a marker for brain injury, RCP does not provide improved cerebral protection over HCA alone.     

Potential neuroprotective benefits of erythropoietin during experimental hypothermic circulatory arrest

Objective: Recent studies have shown that erythropoietin protects neurons from glutamate toxicity and ischemia. This study was performed to evaluate the potential neuroprotective effect of erythropoietin during experimental hypothermic circulatory arrest. Methods: Twenty pigs were randomized to receive intravenously either 500 IU/kg recombinant human erythropoietin or saline before a 75-minute period of hypothermic circulatory arrest at an intracerebral temperature of 18°C. Results: After the administration of erythropoietin, its concentration in the cerebrospinal fluid increased 4.5-fold 8 hours after the start of rewarming, whereas it did not increase in control animals. The 7-day survival rate was 60% in the erythropoietin group and 70% in the control group (P = 1.0). No significant differences were observed between the study groups in terms of electroencephalography, behavioral score, and histopathologic score. The erythropoietin group had higher vascular resistance and mean arterial pressure values, lower intracerebral concentrations of glutamate and glycerol, higher brain tissue oxygen tension, and lower apoptotic index. Conclusions: Administration of 500 IU/kg erythropoietin intravenously before hypothermic circulatory arrest was followed by an increased erythropoietin concentration in the cerebrospinal fluid. Although previous studies have demonstrated neuroprotective effects of erythropoietin during brain ischemia, the present study, using a chronic porcine model, failed to show any significant benefit after administration of erythropoietin in terms of mortality or brain histopathology. Lower intracerebral concentrations of glutamate and glycerol, higher brain tissue oxygen tension, and lower apoptotic index observed in the erythropoietin group, however, suggest that a distinct neuroprotective effect of erythropoietin might be achieved at different dosages and timing of administration.     

Hypothermic circulatory arrest is not a risk factor for neurologic morbidity in aortic surgery: a propensity score analysis

OBJECTIVE: Hypothermic circulatory arrest has been an important tool in aortic arch surgery, even though its use has recently been discussed controversially. We sought to clarify the role of hypothermic circulatory arrest as a risk factor for mortality and neurologic morbidity in aortic surgery by using a propensity score-matching analysis. METHODS: Five hundred eleven patients (60 +/- 13 years, 349 male patients) who underwent replacement of the ascending aorta with (n = 273) or without (n = 238) arch involvement were analyzed by means of multivariate analysis. Using propensity score matching, we identified comparable patient groups: HCA(+) group and HCA(-) group (n = 110 each). For aortic arch replacement, hypothermic circulatory arrest was used with a mean duration of 14 +/- 9 minutes: 12 +/- 7 minutes or 26 +/- 8 minutes for partial or total arch replacement, respectively. RESULTS: In the entire cohort multivariate analysis identified acute dissection and duration of cardiopulmonary bypass as significant predictors for hospital death. Predictors for stroke were acute dissection, diabetes mellitus, peripheral arterial disease, and concomitant mitral valve surgery, and predictors for temporary neurologic dysfunction were peripheral arterial disease and age. After propensity score matching, the incidence of death (HCA[+]: 0.9% vs HCA[-]: 2.7%), stroke (0% vs 1.8%, respectively), and temporary neurologic dysfunction (15.5% vs 13.6%, respectively) was comparable between the 2 groups. Multivariate analysis identified age, diabetes mellitus, peripheral arterial disease, and concomitant coronary artery bypass grafting as the independent risk factors for temporary neurologic dysfunction. CONCLUSIONS: In a standard clinical setting (hypothermic circulatory arrest of <30 minutes and nasopharyngeal temperature of <20 degrees C), hypothermic circulatory arrest constitutes no significant risk for mortality or neurologic morbidity and thus appears clinically safe. Patient-related risk factors primarily determine clinical outcome.     

Myocyte contractility with caspase inhibition and simulated hyperkalemic cardioplegic arrest

BACKGROUND: Exposure of left ventricular (LV) myocytes to simulated hyperkalemic cardioplegic arrest (HCA) has been demonstrated to perturb ionic homeostasis and adversely affect myocyte contractility on rewarming. Altered ionic homeostasis can cause cytosolic activation of the caspases. While caspases participate in apoptosis, these proteases can degrade myocyte contractile proteins, and thereby alter myocyte contractility. Accordingly, this study tested the hypothesis that caspase inhibition during HCA would attenuate the degree of myocyte contractile dysfunction upon rewarming, independent of a loss in myocyte viability. METHODS: Porcine (n = 8) LV myocytes were isolated and assigned to the following treatment groups: normothermic control: incubation in cell culture media for 2 hours at 37 degrees C; HCA only: incubation for 2 hours in hypothermic HCA solution (4 degrees C, 24 mEq K(+)); or incubation in hypothermic HCA solution supplemented with 10 microM of the caspase inhibitor, z-VAD (z-Val-Ala-Asp-fluoromethyl-ketone, HCA+zVAD). Myocyte viability, assayed as a function of mitochondrial function, was determined to be similar in the normothermic and both HCA groups. RESULTS: The HCA caused a significant reduction in myocyte shortening velocity compared with normothermic control values (41 +/- 6 versus 86 +/- 8 microm/s, p < 0.05). The HCA+zVAD group had significantly improved myocyte shortening velocity compared with the HCA only group (63 +/- 7 microm/s, p < 0.05). CONCLUSIONS: Independent of changes in viability, caspase inhibition attenuated myocyte contractile dysfunction after HCA and rewarming. Thus, caspase activation during HCA contributes, at least in part, to impaired myocyte contractility with rewarming. Supplementation of HCA with caspase inhibitors may provide a means to preserve myocyte contractile function after cardioplegic arrest.     

Involvement of apoptosis in neurological injury after hypothermic circulatory arrest: a new target for therapeutic intervention?

BACKGROUND: This study was undertaken to evaluate the role of apoptosis in neurological injury after hypothermic circulatory arrest (HCA). METHODS: Twenty-one pigs (27 to 31 kg) underwent 90 minutes of HCA at 20 degrees C and were electively sacrificed at 6, 24, 48, and 72 hours, and at 7, 10, and 12 days after HCA, and compared with unoperated controls. In addition, 3 animals that had HCA at 10 degrees C, and 3 treated with cyclosporine A (CsA) in conjunction with HCA at 20 degrees C, were examined 72 hours after HCA. After selective perfusion and cryopreservation, all brains were examined to visualize apoptotic DNA fragmentation and chromatin condensation on the same cryosection of the hippocampus: fluorescent in situ end labeling (ISEL) was combined with staining with a nucleic acid-binding cyanine dye (YOYO). RESULTS: In addition to apoptosis, which was seen at a significantly higher level (p = 0.05) after HCA than in controls, two other characteristic degenerative morphological cell types (not seen in controls) were characterized after HCA. Cell death began 6 hours after HCA and reached its peak at 72 hours, but continued for at least 7 days. Compared with the standard protocol at 20 degrees C, HCA at 10 degrees C and CsA treatment both significantly reduced overall cell death after HCA, but not apoptosis. CONCLUSIONS: The data establish that significant neuronal apoptosis occurs as a consequence of HCA, but at 20 degrees C, other pathways of cell death, probably including necrosis, predominate. Although preliminary results suggest that the neuroprotective effects of lower temperature and of CsA are not a consequence of blockade of apoptotic pathways, inhibition of apoptosis nevertheless seems promising as a strategy to protect the brain from the subtle neurological injury that is associated with prolonged HCA at clinically relevant temperatures.     

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.     

Cerebral Consequences of Hypothermic Circulatory Arrest in Adults

Despite widespread use of hypothermic circulatory arrest (HCA) in aneurysm surgery and for repair of congenital heart defects, there is continued concern about possible adverse cerebral sequelae. The search for ways to improve implementation of HCA has inspired retrospective clinical studies to try to identify risk factors for cerebral injury, and clinical and laboratory investigations to explore the physiology of HCA. At present, risk factors associated with less favorable cerebral outcome after HCA include: prolonged duration of HCA (usually greater than 60 min); advanced patient age; rapid cooling (less than 20 min); hyperglycemia either before HCA or during reperfusion; preoperative cyanosis or lack of adequate hemodilution; evidence of increased oxygen extraction before HCA or during reperfusion; and delayed reappearance of electroencephalogram (EEG) or marked EEG abnormality. Strategies advocated to increase safety of HCA include: pretreatment with barbiturates and steroids; use of alpha-stat pH regulation during cooling and rewarming; intraoperative monitoring of EEG; slow and adequate cooling, including packing of the head in ice; monitoring of jugular venous oxygen content; hemodilution; and avoidance of hyperglycemia. Current investigation focuses on delineating the relationship of cerebral blood flow (CBF) to cerebral oxygen consumption and glucose metabolism during cooling, HCA, rewarming, and later recovery, and identifying changes in acute intraoperative parameters, including the presence of intracerebral enzymes in cerebral spinal fluid, with cerebral outcome as assessed by neurological evaluation, quantitative EEG, and postmortem histology. Clinically, intraoperative monitoring of EEG and measurement of CBF by tracer washout or Doppler flows are contributing to better understanding of the physiology of HCA, and in the laboratory, nuclear magnetic resonance (NMR) spectroscopy has provided valuable insights into the kinetics of intracerebral energy metabolism. Promising strategies for the future include investigation of other pharmacological agents to increase cerebral protection, and use of "cerebroplegia" or intermittent perfusion between intervals of HCA to improve cerebral tolerance for longer durations of HCA.     

Cardiac performance after deep hypothermic circulatory arrest in chronically cyanotic neonatal lambs

OBJECTIVES: It is controversial whether immature cyanotic hearts are more susceptible to ischemic injury than normoxemic hearts. Acutely induced alveolar hypoxic stress before cardiopulmonary bypass has been used as a model of cyanosis and is reported to worsen recovery of immature hearts after subsequent ischemic insult by means of a free radical injury mechanism. Because of concerns about the relevance of acute alveolar repair to the chronic cyanosis encountered clinically, we assessed the effects of chronic cyanosis without alveolar hypoxia, acute alveolar hypoxia, and normoxemia on recovery of cardiac function after deep hypothermic circulatory arrest. METHODS: A chronic cyanosis model was created in 8 lambs by an anastomosis between the pulmonary artery and the left atrium (cyanosis group). Eight lambs underwent sham operation (control). One week later, the animals underwent cardiopulmonary bypass with 90 minutes of deep hypothermic circulatory arrest at 18 degrees C. Another 8 lambs underwent 45 minutes of hypoxic ventilation before bypass, with arterial oxygen tension being maintained at 30 mm Hg (acute hypoxia group). Cardiac index, preload recruitable stroke work, and tau were measured. Malondialdehyde and nitrate-nitrite, nitric oxide metabolites, were also measured in the coronary sinus. Myocardial antioxidant reserve capacity at 2 hours of reperfusion was assessed by measuring lipid peroxidation in left ventricular tissue samples incubated with t-butylhydroperoxide at 37 degrees C. RESULTS: Oxygen tension was 35 +/- 3 mm Hg in the acute hypoxia group versus 93 +/- 7 mm Hg in the control group. In the acute hypoxia group the recovery of cardiac index, preload recruitable stroke work, and tau were significantly worse than that found in both the control and cyanosis groups. Preload recruitable stroke work at 2 hours of reperfusion was slightly but significantly lower in the cyanosis group than in the control group. The postischemic level of nitric oxide metabolites was significantly lower in the acute hypoxia group than in the cyanosis and control groups. However, malondialdehyde levels in the coronary sinus and myocardial antioxidant reserve capacity were not significantly different among the groups. CONCLUSION: Recovery of left ventricular function after deep hypothermic circulatory arrest in neonatal lambs with chronic cyanosis was slightly worse than that found in acyanotic animals. Acute hypoxia before bypass was associated with significantly worse recovery of left ventricular function, and the mechanism of injury may be related to an impairment of nitric oxide production. Free radical injury does not appear to explain any differences among cyanotic, acyanotic, and acutely hypoxic animals in recovery of left ventricular function after ischemia.     

Does hypothermic fibrillatory arrest improve myocardial protection during emergency revascularization?

Hypothermic fibrillatory arrest (HFA) was compared with conventional hypothermic cardioplegic arrest (HCA) in a model of acute regional ischemia. In 20 pigs, the left anterior descending coronary artery was occluded for 30 minutes before cardiopulmonary bypass. In the HCA group (n = 10), the heart was arrested with a hyperkalemic cold crystalloid solution, whereas in HFA animals (n = 10), the heart was vented and allowed to fibrillate spontaneously without cross-clamping. Miniature pH probes monitored intramyocardial pH during 45 minutes of arrest (HCA or HFA, both with systemic and topical myocardial cooling) and during two hours of coronary reperfusion. Hypothermic fibrillatory arrest did not ameliorate the acidosis in the ischemic (left anterior descending) region; indeed, after two hours of coronary reperfusion, there was a trend toward more acidosis in the postischemic left anterior descending territory in the HFA group. However, HFA did prevent acidosis in the nonischemic (left circumflex) territory. Infarct size expressed as percent of region at risk was 18.1% +/- 3.2% (mean +/- standard error of the mean) in the HCA animals and 18.8% +/- 4.4% in the HFA animals. These results demonstrate that HFA offers no advantage over HCA in protection of regionally ischemic myocardium in a model with minimal collateral circulation.     

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.     

Deep hypothermic circulatory arrest and global reperfusion injury: avoidance by making a pump prime reperfusate--a new concept

OBJECTIVE: We sought to determine whether damage after deep hypothermic circulatory arrest can be diminished by changing pump prime components when reinstituting cardiopulmonary bypass. METHODS: Fifteen piglets (2-3 months old) were cooled to 19 degrees C by using the alpha-stat pH strategy. Five were cooled and rewarmed without ischemia (control animals), and the other 10 piglets underwent 90 minutes of deep hypothermic circulatory arrest. Of these, 5 were rewarmed and reperfused without altering the cardiopulmonary bypass circuit blood prime. In the other 5 animals, the bypass blood prime was modified (leukocyte depleted, hypocalcemic, hypermagnesemic, pH-stat, normoxic, mannitol, and an Na(+)/H(+) exchange inhibitor) during circulatory arrest before starting warm reperfusion. Oxidant injury was assessed on the basis of conjugated dienes, vascular changes on the basis of endothelin levels, myocardial function on the basis of cardiac output and dopamine need, lung injury on the basis of pulmonary vascular resistance and oxygenation, and cellular damage on the basis of release of creatine kinase and aspartate aminotransferase. Neurologic assessment (score 0, normal; score 500, brain death) was done 6 hours after discontinuing cardiopulmonary bypass. RESULTS: Compared with animals undergoing cardiopulmonary bypass without ischemia (control animals), deep hypothermic circulatory arrest without modification of the reperfusate produced an oxidant injury (conjugated dienes increased 0.78 vs 1.71 absorbance (Abs) 240 nmol/L per 0.5 mL, P <.001 vs control animals), depressed cardiac output (6.0 vs 4.0 L/min, P <.05 vs control subjects), prolonged dopamine need (P <.001 vs control subjects), elevated pulmonary vascular resistance (74% vs 197%, P <.05 vs control subjects), reduced oxygenation (P <.01 vs control subjects), increased neurologic injury (56 vs 244, P <.001 vs control subjects), and increased release of creatine kinase (2695 vs 6974 U/L, P <.05 vs control subjects), aspartate aminotransferase (144 vs 229 U/L), and endothelin (1.02 vs 2.56 pg/mL, P <.001 vs control subjects). Conversely, the oxidant injury was markedly limited (conjugated dienes of 0.85 +/- 0.09 Abs 240 nmol/L per 0.5 mL, P <.001 vs unmodified pump prime) with modification of cardiopulmonary bypass prime, resulting in increased cardiac output (5.1 +/- 0.8 L/min), minimal dopamine need (P <.001 vs unmodified pump prime), no increase in pulmonary vascular resistance (44% +/- 31%, P <.01 vs unmodified pump prime) or endothelin levels (0.64 +/- 0.15 pg/mL, P <.001 vs unmodified pump prime), complete recovery of oxygenation (P <.01 vs unmodified pump prime), reduced neurologic damage (144 +/- 33, P <.05 vs unmodified pump prime), and lower release of aspartate aminotransferase (124 +/- 23 U/L, P <.05 vs unmodified pump prime) and creatine kinase (3366 +/- 918, P <.05 vs unmodified pump prime). CONCLUSIONS: A global reperfusion injury after deep hypothermic circulatory arrest was identified and changed. The injury is mediated by oxygen-derived free radicals, resulting in organ and endothelial dysfunction. Modification of global organ and endothelial damage is achieved by modifying the blood prime in the cardiopulmonary bypass circuit to deliver a controlled global reperfusate when reinstituting bypass.     

The Role of Cerebral Microdialysis in Predicting the Outcome after Experimental Hypothermic Circulatory Arrest

Objective –To evaluate whether and which of the cerebral microdialysis parameters are predictive of postoperative outcome after an experimental 75-min period of hypothermic circulatory arrest (HCA) in a chronic porcine model. Design –Seventy-four juvenile female pigs underwent a 75-min period of HCA at 20°C. A microdialysis catheter was placed into the cortex gray matter and brain extracellular concentrations of glucose, lactate, glycerol and glutamate were measured throughout the experiment by enzymatic methods using a microdialysis analyzer. Surviving animals were sacrificed on the 7th postoperative day and histopathological examination of the brain was performed. Results –Brain glucose concentrations were higher in animals that survived ( p = 0.017), especially from the 90-min until the 7-h interval after the start of rewarming. The blood venous concentrations of glucose were also higher among survivors, and correlated significantly with the brain glucose levels at 2-h and 4-h intervals after the start of rewarming. Higher concentrations of brain lactate, glycerol and glutamate were observed throughout the study among animals that died postoperatively. Brain glutamate and glycerol concentrations were significantly, negatively correlated with brain glucose concentrations. The lactate/glucose ratio was significantly lower among survivors during the postoperative period ( p = 0.014). Furthermore, brain glucose concentrations were higher and brain glycerol concentrations lower among the animals that did not develop brain infarction, but such differences did not reach statistical significance. Conclusion –Cerebral microdialysis is a useful tool for cerebral monitoring during experimental HCA. Low brain glucose concentrations and high brain lactate/glucose ratios after HCA are strong predictors of postoperative death. Brain glucose concentrations are negatively correlated with brain glycerol and glutamate concentrations.     

The methodologies of hypothermic circulatory arrest and of antegrade and retrograde cerebral perfusion for aortic arch surgery

In spite of recent advances in thoracic aortic surgery, postoperative neurological injury still remains the main cause of mortality and morbidity after aortic arch operation. The use of cardiopulmonary bypass (CPB) and hypothermic circulatory arrest, temporary interruption of brain circulation, transient cerebral hypoperfusion, and manipulations on the frequently atheromatic aorta all produce neurological damages. The basic established techniques and perfusion strategies during aortic arch replacement number three: hypothermic circulatory arrest (HCA), antegrade cerebral perfusion (ACP), and retrograde cerebral perfusion (RCP). During the past decade and after several experimental studies, RCP lost its previous place in the armamentarium of brain protection, giving it up to ACP as a major method of brain perfusion during HCA. HCA should be applied at a temperature of asymptotically equal to 20 degrees C with long-lasting cooling and rewarming and should not exceed by itself the time of 20-25 min. RCP does not seem to prolong safe brain-ischemia time beyond 30 min, but it appears to enhance cerebral hypothermia by its massive concentration inside the brain vein sinuses. HCA combined with ACP, however, could prolong safe brain-ischemia time up to 80 min. Cold ACP at 10 degrees -13 degrees C should be initially applied through the right subclavian or axillary artery and continued bihemispherically through the left common carotid artery at first and later the anastomosed graft, with a mean perfusion pressure of 40-70 mm Hg. The safety of temporary perfusion is being confirmed by the meticulous monitoring of brain perfusion through internal jugular bulb O2 saturation, electroencephalogram, and transcranial comparative Doppler velocity of the middle cerebral arteries.     

Neonatal brain protection and deep hypothermic circulatory arrest: pathophysiology of ischemic neuronal injury and protective strategies

Deep hypothermic circulatory arrest (DHCA) has been used for the past 50 years in the surgical repair of complex congenital cardiac malformations and operations involving the aortic arch; it enables the surgeon to achieve precise anatomical reconstructions by creating a bloodless operative field. Nevertheless, DHCA has been associated with immediate and late neurodevelopmental morbidities. This review provides an overview of the pathophysiology of neonatal hypoxic brain injury after DHCA, focusing on cellular mechanisms of necrosis, apoptosis, and glutamate excitotoxicity. Techniques and strategies in neonatal brain protection include hypothermia, acid base blood gas management during cooling, and pharmacologic interventions such as the use of volatile anesthetics. Surgical techniques consist of intermittent cerebral perfusion during periods of circulatory arrest and continuous regional brain perfusion.     

Aneurysm formation after patch aortoplasty repair (Vossschulte): reoperation in adults with and without hypothermic circulatory arrest

BACKGROUND: Aortic aneurysm formation is common after patch aortoplasty repair of coarctation of the aorta. Its incidence varies between 5% and 38%. The majority of patients show progressive aneurysmal dilation within 6 to 18 years and reoperation is necessary to avoid rupture of the aneurysm. METHODS: Ten patients were reoperated on for patch aneurysm formation. Femorofemoral cardiopulmonary bypass (CPB) with a heparinized system was used in all patients. Decision to initiate hypothermic circulatory arrest (HCA) was made intraoperatively. All patients received a Dacron graft replacement of the aneurysmatic thoracic aorta. RESULTS: HCA was initiated in 5 patients owing to extreme adhesions in vicinity to the aneurysm. There was no significant intergroup difference regarding time interval after first operation, age, operation time, and postoperative blood loss. Only minor neurologic events were present in 2 patients with cross-clamping the aorta. CONCLUSIONS: Patch aneurysms after Vossschulte aortoplasty can safely be operated on with femorofemoral CPB. Initiation of HCA is recommended to prevent rupture of the aneurysm during preparation and injury of adjacent nerves and vessels.