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Ann Thorac Surg 1998;66:38-50
© 1998 The Society of Thoracic Surgeons
a Department of Cardiothoracic Surgery,, The Mount Sinai Medical Center, New York, New York, USA
b Department of Neuropathology, The Mount Sinai Medical Center, New York, New York, USA
c Department of Neurosurgery, The Mount Sinai Medical Center, New York, New York, USA
d Department of Biomathematics, The Mount Sinai Medical Center, New York, New York, USA
Address reprint requests to Dr Juvonen, Department of Surgery, Oulu University Hospital, FIN 90220, Oulu, Finland
e-mail: (tatu.juvonen{at}oulu.fi)
Presented at the Poster Session of the Thirty-fourth Annual Meeting of The Society of Thoracic Surgeons, New Orleans, LA, Jan 26–28, 1998.
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Abstract |
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Methods. Sixty-two pigs (27 to 30 kg) were randomly assigned to undergo one of the following for 90 minutes at 20°C: antegrade cerebral perfusion (ACP); conventional RCP (RCP); RCP with occlusion of the inferior vena cava (RCP-O), or HCA with the head packed in ice. RCP flow was regulated to a sagittal sinus pressure of 20 mm Hg. Hemodynamic, electrophysiologic, and metabolic monitoring were carried out until 4 hours after rewarming, daily behavioral and neurologic assessments until elective sacrifice on day 7, and histologic analysis of the brain after death.
Results. Complete behavioral recovery was seen in all surviving animals by day 5 after ACP or RCP, but in only 83% after RCP-O and 50% after HCA (p = 0.001). A histopathologic score of 2 or more, indicating more than mild injury, was not found in any animal after ACP, in 27% after RCP, in 47% after HCA, and in 68% after RCP-O (p = 0.002). The median oxygen consumption was 6.66 mL/min after ACP, 1.37 mL/min with RCP, and 1.02 mL/min with RCP-O (p < 0.0001). The median amount of fluid sequestered was 2,450 mL after RCP-O, 760 mL after RCP, and -200 mL after ACP (p < 0.0001).
Conclusions. Conventional RCP without inferior vena caval occlusion results in a significantly better outcome than RCP-O after prolonged HCA, despite more efficient cerebral perfusion during RCP-O, and also provides cerebral protection superior to prolonged HCA alone, but care must be taken during its implementation to minimize cerebral edema and other possible causes of retroperfusion-related cerebral injury.
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Introduction |
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TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
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We have been studying various ways of implementing RCP in a chronic porcine model, in which the metabolic and physiologic consequences of our interventions can be evaluated intraoperatively, and the cerebral sequelae can be assessed by means of neurologic and behavioral evaluation, electrophysiologic recovery, and histologic examination after elective sacrifice 1 week postoperatively [4–6]. Our studies have thus far indicated that RCP may enhance cerebral protection during prolonged hypothermic circulatory arrest when compared with HCA alone, even when the head is packed in ice, and that RCP can remove particulate emboli after their experimental administration [4, 6]. In addition to these encouraging results, however, our studies have also revealed mild cerebral injury even after relatively short intervals of RCP without prior embolization, and they have not unequivocally demonstrated improved neurologic and behavioral or histologic outcome after embolization followed by RCP, even after successful reduction in residual emboli. The studies have also shown that the way in which RCP is implemented has a definite impact on its efficacy and safety: when RCP is instituted with occlusion of the inferior vena cava (IVC), cerebral perfusion is enhanced, but the incidence of adverse sequelae also appears to be higher.
The current study was undertaken to compare conventional RCP, RCP with occlusion of the IVC (RCP-O), and HCA with the head packed in ice with regard to their effectiveness in preserving cerebral function for extended intervals, because RCP, RCP-O, and HCA are possible alternatives when prolonged interruption of the antegrade circulation is required to repair aortic aneurysms in adults or complex congenital heart lesions in infants. We wished to clarify whether either way of implementing RCP provides cerebral protection superior to conventional HCA during prolonged intervals of antegrade circulatory arrest under hypothermic conditions, as indicated by our earlier studies, and to explore how each of these alternatives compares with continued antegrade perfusion [4].
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Material and methods |
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All animals received humane care in accordance with the "Principles of Laboratory Animal Care" formulated by the National Society for Medical Research and the "Guide for the Care and Use of Laboratory Animals" prepared by the Institute of Laboratory Animal Resources and published by the National Institutes of Health (NIH publication 85-23, revised 1985). The protocol for these experiments was approved by the Mount Sinai Institutional Animal Care and Use Committee.
Anesthesia and hemodynamic monitoring
Anesthesia was induced with ketamine hydrochloride (10 mg/kg intramuscularly) and muscular paralysis maintained with pancuronium (0.1 mg/kg intravenously). After endotracheal intubation, the animals were maintained on positive pressure ventilation with 100% oxygen; anesthesia was maintained with isoflurane (1%). Appropriate catheters were positioned in the femoral artery and vein to allow sampling and pressure monitoring, in the pulmonary artery for determination of cardiac output, in the esophagus and rectum for temperature determinations, and in the bladder to monitor urine output. Sagittal sinus cannulation was undertaken as previously described, and epidural temperature was also monitored [4–6].
Electroencephalography and evoked potential monitoring
Cortical electrical activity was monitored via four stainless steel screw electrodes implanted in the skull as previously described in detail, and processed as in an earlier study [6]. In addition, a stainless steel electrode was positioned as near to the hippocampus as possible to measure deep cortical potentials. Continuous electroencephalographic activity was recorded for 3 minutes at the time of each measurement. Electrical activity that was less than 5 µV was defined as electrocerebral silence.
Somatosensory evoked potentials
Somatosensory evoked potentials were recorded from the cervical spine and bilateral skull sites in response to stimulation of the median nerve, as described in detail in earlier studies [6]. Two sets of somatosensory evoked potentials were recorded for each median nerve at six of the seven measurement time points, and their amplitudes are reported as a percentage of baseline recordings.
Auditory brainstem evoked responses
Auditory brainstem evoked responses were recorded from all animals by averaging the responses to 1,000 presentations of an auditory click stimulus (95 db) that was presented to the right ear through a Cadwell ear insert, also as described in previous studies [6]. The total power of the auditory brainstem evoked response at the first measurement time point was used as a baseline for all subsequent measurements.
Cardiopulmonary bypass
Through a right thoracotomy in the fourth intercostal space, the heart and great vessels were exposed, and the azygos and hemiazygos veins were ligated. The superior vena cava and aortic arch were mobilized, and the descending aorta just distal to the left subclavian artery was exposed using a retroesophageal approach. Twenty-gauge catheters were positioned in the isolated aortic arch, the superior vena cava, and the inferior vena cava for monitoring pressures during antegrade and retrograde perfusion.
After heparinization (300 IU/kg), the ascending aorta was cannulated with a 16-F arterial cannula, and the right atrial appendage with a single 24-F atrial cannula. Nonpulsatile cardiopulmonary bypass (CPB) was initiated at a flow rate 100 mL/kg per minute. A cannula was passed from the right superior pulmonary vein into the left ventricle to permit the decompression of the left heart during CPB. A heat exchanger was utilized for core cooling, and surface cooling was achieved with a cooling blanket. A membrane oxygenator (VPCML plus; Cobe Laboratories Inc, Lakewood, CO) was primed with 1 L of 0.9% sodium chloride, 1 unit of 5% albumin, furosemide (1 mg/kg), heparin (5,000 IU) and potassium chloride (1 mEq/kg). The pH was maintained, using alpha-stat principles, at 7.40 ± 0.05 with an arterial CO2 tension of 35 to 40 mm Hg, uncorrected for temperature.
Cardiopulmonary bypass with perfusion cooling was carried out for 45 minutes to attain an epidural temperature of 20°C. Cardiac arrest was induced by adding potassium chloride (1 mEq/kg) to the perfusate, and topical cardiac cooling was then begun and maintained throughout the procedure. The ascending aorta was cross-clamped just proximal to the aortic cannula, and the descending aorta was cross-clamped just distal to the left subclavian artery, thereby isolating the transverse aortic arch.
Experimental protocol
After isolating the aortic arch, animals underwent a 90-minute interval of ACP, RCP, RCP-O, or HCA as dictated by the randomization protocol. In the ACP group, a pressure of 50 mm Hg in the aortic arch was maintained throughout the 90-minute experimental interval. In animals assigned to undergo HCA, CPB was discontinued and ice packs were placed on the head to maintain an epidural temperature of 19°C to 20°C. The packs were removed if the temperature decreased below this level.
Preparations for RCP involved inserting a 14-F cannula into the SVC, advancing it as cranially as possible, snaring it in place, and connecting it to the arterial line with a Y connector. In the RCP-O groups, the IVC was also snared, and a 10-F cannula was inserted into the descending aorta just distal to the second cross-clamp to permit collection of descending aortic return. Retrograde flow was slowly increased and regulated to achieve a pressure of 20 mm Hg in the sagittal sinus during the first 30 minutes (prestable period) of RCP. During the subsequent 60 minutes, the CPB flow was kept constant despite slight alterations in sagittal sinus pressure (stable period). In animals undergoing RCP-O, maintenance of adequate retrograde flow required infusion of 200 to 300 mL of blood obtained from donor pigs. In the retrograde groups, perfusate returning from the upper body to the isolated aortic arch, right atrium (and descending aorta in RCP-O) was drained to collecting chambers and returned to the pump once its volume had been measured. The amount of sequestered fluid was assessed in all groups.
After 90 minutes of selective perfusion, all animals were switched to ACP and rewarming was initiated as previously described [6]. Weaning from CPB occurred approximately 60 minutes after the beginning of rewarming, with cardiac support provided by dobutamine and with administration of furosemide (40 mg), mannitol (12.5 g), and 200 mg of hydrocortisone. Animals were extubated 4 hours after the last measurement and moved into a recovery incubator. All animals were kept sedated with intravenous acepromacin, butorphenol, and diazepam during the first night postoperatively. A second dose of furosemide (60 mg) was also administered.
During the experiments, hemodynamic, metabolic, and electrophysiologic measurements were recorded at 7 different times:
Postoperative evaluation
Postoperatively, all animals were evaluated daily according to a previously described quantitative behavioral score in which the highest numbers reflect normal neurologic function and lower numbers indicate substantial neurologic damage. A score of 8 or higher means that the animals are able to stand unassisted, and are likely to recover fully [4].
On postoperative day 7 each surviving animal was electively sacrificed. After weighing, the brain was immediately immersed in 4% formalin for subsequent histologic analysis.
Histopathologic analysis
After fixation, the brain was examined grossly, and then the cerebrum, the brainstem, the cerebellum, and 1.5 inches of the spinal cord were sectioned as previously described [5, 6]. Sections were then processed into paraffin, and 5 µm sections were stained with hematoxylin and eosin.
Alternate coronal sections of the entire brain of each animal were systematically examined by a single experienced senior neuropathologist (D.W.), blinded both to the experimental design and to the identity and treatment status of individual animals. He carefully screened each section for the presence or absence of any infarctive or other damage.
Definition of the anatomic regions scored was as previously described in detail [6]. Morphometric analysis of the volume of ischemic injury of the cortex was classified into 5 groups as follows:
For all other anatomic regions: 0 = no microscopic ischemic damage identified, 1 = a single or multiple small infarctive lesions, and 2 = a large area of infarctive damage.
To allow quantitative comparisons, a total histologic score was calculated by adding all the regional scores, although we recognize that this is by no means a rigorous quantitative assessment. A score greater than 4 means that the animal had significant extracortical as well as cortical injury.
Other measurements
Systemic arterial, venous, and sagittal sinus blood samples were obtained to determine pH, partial pressure of oxygen, partial pressure of carbon dioxide, O2 saturation, O2 content, hematocrit, and hemoglobin (Ciba-Corning Diagnostic Corp, Medfield, MA). Glucose and lactate levels were analyzed by using a YSI 2300 Stat (Yellow Springs Instrument Co, Yellow Springs, OH). Temperatures were recorded at intervals throughout the study.
Statistical analysis
Summary statistics for continuous or ordinal variables are expressed as the median and interquartile ranges, mean ± standard error of mean (in the figures). Statistical significance was determined by one-way analysis of variance between the treatment groups. Comparisons between each time point and baseline were done by a set of paired t tests or Wilcoxon signed-rank tests. Normality was tested first, and if it failed, the analysis was performed utilizing the corresponding nonparametric tests (Wilcoxon or Kruskal-Wallis tests). If significant differences were found by the analysis of variance, then relevant pairwise comparisons were performed and the significance levels reported. Categoric variables were compared using 
2 tests. Significance levels are reported for comparisons with p less than 0.05. However, the levels of statistical significance should be interpreted with caution, given the large number of statistical tests performed. Analyses were performed using a standard statistical program (SigmaStat).
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Results |
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Rectal temperature measurements (Fig 1) showed a slight increase from baseline in all groups, but there were almost no significant differences between experimental groups (only between RCP-O and HCA at 80 and 90 minutes).
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Hemodynamic data (Table 1) show that all animals were stable before, during, and after cardiopulmonary bypass, although mean arterial pressure and cardiac output decreased significantly in all groups with cooling, and remained lower than baseline levels even 4 hours after the start of rewarming.
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Blood gas and hematocrit measurements (Table 2) did not differ significantly between groups except during the period of the different interventions. All groups had a significant decrease in pH and in hematocrit during cooling. The highly significant subsequent increase in pH in the RCP group probably reflects the large volume of blood infused into the superior vena cava that is shunted into the IVC during RCP if the IVC is not clamped and the blood is then recirculated without having perfused any tissues. In contrast to the slight decrease in pH and in arterial carbon dioxide tension in the ACP group even after 90 minutes, the RCP-O group showed a progressively severe acidosis after 45 minutes, reaching a mean pH of 7.12 after 90 minutes, despite significant hyperventilation (which might have been expected to correct the pH). All but the RCP-O group, in which pH remained slightly acidotic, showed return of pH to baseline levels by 4 hours after the intervention.
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Hemodynamic data
Flow rates during the stable period of selective antegrade or retrograde perfusion are shown in Table 3. In order to achieve the specified aortic arch or sagittal sinus pressures, flow rates were significantly different in each of the groups, with a significantly higher flow rate during antegrade perfusion than with either method of retrograde perfusion. When the IVC was clamped during RCP, flow rates to achieve a sagittal sinus pressure of 20 mm Hg were significantly lower than when RCP was carried out with the IVC open, but superior vena caval pressures were comparable. Despite the higher flow rate during conventional RCP with the IVC open, aortic arch return was somewhat higher in the RCP-O group, although this was not a statistically significant difference. Much of the blood from the superior vena cava is shunted into the IVC during RCP if the IVC is not clamped.
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In the HCA group, the oxygen saturations immediately upon rewarming were slightly higher than at baseline, suggesting reactive hyperemia during rewarming, as has been observed after HCA in earlier studies. Saturations were never significantly below baseline levels during recovery from HCA.
Cerebral venous oxygen saturations during RCP (marked "sagittal sinus," but actually from the aortic arch) decreased markedly in both groups to levels significantly less than those during ACP at both 45 and 90 minutes. Slightly lower levels of cerebral venous oxygen saturation were present in the RCP than in the RCP-O group, most likely reflecting the slightly lower effective cerebral perfusion, documented by the smaller amount of aortic arch return seen in this group. The cerebral venous oxygen saturation returned to levels higher than baseline during rewarming, and remained at levels significantly higher than baseline (and higher than those seen after ACP) as late as 2 hours after the start of rewarming, suggesting that cerebral blood flow was not restrictive either during rewarming after RCP or for several hours thereafter despite somewhat reduced cardiac output.
Oxygen consumption was significantly greater in the ACP group than in either of the groups perfused retrograde (Table 5). By 90 minutes after the start of selective perfusion, oxygen consumption was significantly greater with RCP than with RCP-O, although still much less than the levels sustained during ACP.
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Glucose extraction data followed a pattern similar to that of oxygen extraction, but much greater variation in individual numbers prevented the apparent trends from being statistically significant.
Fluid sequestration and urine output
As can be seen in Figure 2, the amount of fluid sequestered (the difference between fluid input and output) is significantly different for each of the perfused groups, with a negative fluid balance in the ACP group and significant fluid retention by both RCP groups, with especially marked fluid sequestration during RCP-O. The retention of fluid in the RCP-O group is also documented by urine output in the various experimental groups: urine output is significantly less after RCP-O than after ACP (Fig 3).
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Morbidity and mortality
All animals were stable during the surgical procedures. Forty-three (69%) of the 62 animals survived for the full duration of the experiment, with daily behavioral scores recorded until their elective sacrifice on the seventh postoperative day.
The 7-day mortality in the various groups differed significantly between the groups: ACP = 1/11 (9%), HCA-HP = 5/16 (31%), RCP = 6/16 (38%), RCP-O = 7/19 (37%), with a significantly lower mortality rate in the group that underwent ACP (p < 0.0001). Some animals died spontaneously within the first few days postoperatively, but others were sacrificed to minimize excessive suffering resulting from severe brain damage: many were unable to stand or to eat. Because of the high morbidity and mortality (which was in retrospect almost inevitable with so prolonged an interval of circulatory arrest at this temperature, designed to result in some neurologic sequelae), the experiment was extended so that each group had at least 10 animals that survived for the entire duration of the experiment. The only animal in the ACP group that did not survive for the full 7 days exhibited substantial neurologic impairment, and postmortem examination revealed a large subdural hematoma that covered the entire cortex and brainstem and extended along the spinal cord.
Behavioral outcome
The results of neurologic and behavioral scoring for each animal in each group are shown in Figure 4. A score of 9 indicates a completely normal outcome. Animals that died or were sacrificed early were given a score of zero beginning at the time of sacrifice. As expected, complete behavioral recovery was seen in all surviving animals after ACP. In the RCP group, significant behavioral and neurologic abnormalities were seen early in the postoperative period, but much of this impairment was transient: by day 5, all surviving animals had recovered completely. In contrast, animals showed more severe initial neurologic and behavioral impairment after both RCP-O and HCA, and complete recovery was seen in only 83% of survivors after RCP-O, and in 50% of survivors after HCA (p = 0.001). The difference in behavioral outcome between RCP and HCA groups was highly significant (p = 0.01).
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Histopathologic results
The total histopathologic score, arrived at by adding the quantitative assessment of histopathologic findings in the neocortex to the scores in other regions of the brain for each of the animals is shown in Figure 5. The median score is indicated for each group. As is evident from the graph, no animal had any significant histopathologic abnormality after ACP. Of the animals that underwent RCP without IVC occlusion, only 4 (27%) of 15 showed evidence of more than mild histopathologic damage as indicated by a total histopathologic score of 2 or more, in contrast to 7 (47%) of 15 with moderate to severe damage after HCA, and 13 (68%) of 19 with significant histopathologic abnormalities after RCP-O (p = 0.002).
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Electroencephalography and evoked potentials
Quantitative electroencephalography
Two animals were excluded from quantitative electroencephalography analysis because their baseline recordings contained high levels of artifact. No differences were found in total electroencephalographic (EEG) power (0.5 to 2.0 Hz) between any of the groups at baseline or at the end of cooling: EEG was isoelectric at 20°C in all the animals. During rewarming, and at 2 and 4 hours after the start of rewarming, only the ACP group showed any significant return of EEG, reaching approximately 70% of baseline by 4 hours after the start of rewarming (Fig 6). Only 3 of 49 animals in any of the other experimental groups showed a 10% or greater return of EEG within the period of EEG surveillance, and there was no significant difference among the RCP, RCP-O, or HCA groups.
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As expected, the cervical somatosensory evoked potential showed greater recovery than did the cortical potential. During early rewarming and at 2 hours, as seen in Figure 7, there were significant differences among the groups (p = 0.005 at 30°C, and p = 0.007 at 2 hours). Pairwise comparisons showed that the ACP group had significantly greater recovery than did any of the other groups. By 4 hours after the start of rewarming, there were no significant differences in recovery among the groups. At no time were there any differences in the recovery of the RCP, RCP-O, or HCA groups in the return of the cervical potential.
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Comment |
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As in our previous study, the animals had slightly but significantly lower epidural temperatures during RCP than during HCA, which may have contributed to their improved outcome after interruption of antegrade circulation [4]. Better temperature control is clearly not the only factor leading to improved outcome, since epidural temperature was highest in the group undergoing antegrade perfusion, which had the best behavioral and histologic result.
The aspect of the study that we found most surprising was the superiority of the outcome after conventional RCP over RCP with the IVC occluded (RCP-O). In a recent study, we demonstrated that retrograde perfusion with IVC occlusion, but not conventional RCP with the IVC open, was successful in removing particulate emboli from the brain. In the current study we confirm that RCP-O results in more efficient cerebral perfusion than conventional RCP, with greater flow returning to the aortic arch despite lower rates of flow into the superior vena cava and comparable sagittal sinus pressure [6]. However, as in our previous study, cerebral outcome was less favorable after RCP-O than after conventional RCP with the IVC open. In the current study, both neurologic and behavioral assessment and histologic examination showed better results after conventional RCP than with RCP-O. Oxygen extraction is initially (after 45 minutes) lower after RCP-O than with RCP, at a time when the rates of oxygen consumption are not significantly different in the two groups, suggesting that cerebral perfusion during RCP-O is initially more effective than during RCP. By 90 minutes, however, oxygen consumption with RCP-O decreased significantly to a level lower than that with conventional RCP, suggesting better sustenance of cerebral function by RCP than by RCP-O.
We suspect, as in our previous study, that the poor outcome after RCP-O may be attributable to the development of progressively severe cerebral edema. We have again demonstrated that fluid sequestration after RCP-O is greater than after conventional RCP, and we have some evidence that this fluid accumulation may be associated with significant morbidity. When we compared the urine output in animals that died and those that survived, urine output was significantly less in the animals that did not survive (2,700 ± 140 mL versus 3,200 ± 170 mL in survivors, p < 0.05). In our earlier study, brain weights were significantly higher in animals that died or required sacrifice before completion of the protocol at 7 days, suggesting that cerebral edema may be one of the consequences of the fluid sequestration that occurs after RCP [6]. Other investigators have documented the occurrence of severe cerebral edema after RCP and have demonstrated improved outcome after treating cerebral edema vigorously [7–9]. The importance of the potential injurious impact of cerebral edema was not appreciated at the time this study was designed, so the administration of diuretics and corticosteroids early in the postoperative course were the only measures used to combat this possible complication.
In addition to differing rates of effective cerebral flow and of fluid sequestration between various perfusion methods, differences in pH during the interval of cerebral perfusion are also quite striking and may have contributed to differences in outcome. During ACP, the pH remained stable, dropping to a mean of 7.38, only modestly lower than baseline levels. In contrast, the pH during retrograde perfusion without IVC occlusion became very alkalotic, with a mean value of 7.63 after 45 minutes; it remained high (7.58) even after 90 minutes of perfusion. In contrast, with RCP-O the pH remained stable for the first 45 minutes of perfusion (with a mean of 7.43), but became acidotic at 90 minutes, with a mean of 7.12.
The significance of the pH during RCP is not completely obvious. The presence of fairly extreme alkalosis may have limited cerebral blood flow in the RCP group, which might limit aerobic metabolism, which is demonstrably much lower in the RCP group than in the ACP group at the same temperature. Conversely, the alkalosis in this circumstance might also be beneficial by decreasing intracranial pressure and also combatting the intracellular acidosis that is likely to result from the hypoxemia and anaerobic metabolism, which usually occur when antegrade flow is interrupted [10, 11]. The absence of severe acidosis in the animals that underwent conventional RCP may explain why they had a significantly higher oxygen consumption at 90 minutes than did the RCP-O group, as well as higher cardiac output and a better outcome. A slightly higher rate of metabolic activity, implying better sustenance of cerebral function, in the RCP group versus the RCP-O group at the end of the experimental interval is suggested both by the increased oxygen consumption in the RCP group and by somewhat higher levels of residual lactate in the RCP group during rewarming.
As in the previous study, we found that the behavioral scores in the early postoperative period are lower than the level at which the animals ultimately stabilize. We suspect that this improvement reflects the resolution of postoperative cerebral edema. We also suspect that more vigorous and sustained attempts to combat cerebral edema during RCP and immediately thereafter might improve outcome. What seems clear from the experiments undertaken up to this point is that RCP holds some promise as a method for improving cerebral outcome after operations that require prolonged interruption of antegrade flow. It is equally clear that the details of implementing RCP are very critical in order to provide benefit without inducing harm. Further investigations need to be undertaken to determine how best to implement RCP while also preventing damage from cerebral edema, which seems to be an almost inevitable consequence of its use.
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TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
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C. Hagl, N. Khaladj, D. J. Weisz, N. Zhang, L. J. Guo, C. A. Bodian, D. Spielvogel, and R. B. Griepp Impact of high intracranial pressure on neurophysiological recovery and behavior in a chronic porcine model of hypothermic circulatory arrest Eur. J. Cardiothorac. Surg., October 1, 2002; 22(4): 510 - 516. [Abstract] [Full Text] [PDF]
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O. Tasdemir, A. Saritas, S. Kucuker, M. A. Ozatik, and E. Sener Aortic arch repair with right brachial artery perfusion Ann. Thorac. Surg., June 1, 2002; 73(6): 1837 - 1842. [Abstract] [Full Text] [PDF]
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J. M. Slater, T. A. Orszulak, K. J. Zehr, and D. J. Cook Use of the Cobra catheter for targeted temperature management during cardiopulmonary bypass in swine J. Thorac. Cardiovasc. Surg., May 1, 2002; 123(5): 936 - 942. [Abstract] [Full Text] [PDF]
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Z. Li, L. Yang, M. Jackson, R. Summers, M. Donnelly, R. Deslauriers, and J. Ye Increased pressure during retrograde cerebral perfusion in an acute porcine model improves brain tissue perfusion without increase in tissue edema Ann. Thorac. Surg., May 1, 2002; 73(5): 1514 - 1521. [Abstract] [Full Text] [PDF]
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C. Hagl, N. A. Tatton, N. Khaladj, N. Zhang, S. Nandor, S. Insolia, D. J. Weisz, D. Spielvogel, and R. B. Griepp Involvement of apoptosis in neurological injury after hypothermic circulatory arrest: a new target for therapeutic intervention? Ann. Thorac. Surg., November 1, 2001; 72(5): 1457 - 1464. [Abstract] [Full Text] [PDF]
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D. L. Reich, S. Uysal, M. A. Ergin, and R. B. Griepp Retrograde cerebral perfusion as a method of neuroprotection during thoracic aortic surgery Ann. Thorac. Surg., November 1, 2001; 72(5): 1774 - 1782. [Abstract] [Full Text] [PDF]
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M. P. Ehrlich, C. Hagl, J. N. McCullough, N. Zhang, H. Shiang, C. Bodian, and R. B. Griepp Retrograde cerebral perfusion provides negligible flow through brain capillaries in the pig J. Thorac. Cardiovasc. Surg., August 1, 2001; 122(2): 331 - 338. [Abstract] [Full Text] [PDF]
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C. Hagl, N. A. Tatton, D. J. Weisz, N. Zhang, D. Spielvogel, H. H. Shiang, C. A. Bodian, and R. B. Griepp Cyclosporine A as a potential neuroprotective agent: a study of prolonged hypothermic circulatory arrest in a chronic porcine model Eur. J. Cardiothorac. Surg., June 1, 2001; 19(6): 756 - 764. [Abstract] [Full Text] [PDF]
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C. Hagl, M. A. Ergin, J. D. Galla, S. L. Lansman, J. N. McCullough, D. Spielvogel, P. Sfeir, C. A. Bodian, and R. B. Griepp Neurologic outcome after ascending aorta-aortic arch operations: Effect of brain protection technique in high-risk patients J. Thorac. Cardiovasc. Surg., June 1, 2001; 121(6): 1107 - 1121. [Abstract] [Full Text] [PDF]
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D. L. Reich, S. Uysal, M. A. Ergin, C. A. Bodian, S. Hossain, and R. B. Griepp Retrograde cerebral perfusion during thoracic aortic surgery and late neuropsychological dysfunction Eur. J. Cardiothorac. Surg., May 1, 2001; 19(5): 594 - 600. [Abstract] [Full Text] [PDF]
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R. B. Griepp Cerebral protection during aortic arch surgery J. Thorac. Cardiovasc. Surg., March 1, 2001; 121(3): 425 - 427. [Full Text] [PDF]
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 P. Sekaran, M. Ehrlich, C. Hagl, M. L. Leavitt, R. Jacobs, J. N. McCullough, and E. Bennett-Guerrero A Comparison of Complete Blood Replacement With Varying Hematocrit Levels on Neurological Recovery in a Porcine Model of Profound Hypothermic (<5{degrees}C) Circulatory Arrest Anesth. Analg., February 1, 2001; 92(2): 329 - 334. [Abstract] [Full Text] [PDF]
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P. Dong, Y. Guan, J. Yang, M. He, and C. Wan Fundus microvascular flow monitoring during retrograde cerebral perfusion: an experimental study Ann. Thorac. Surg., November 1, 2000; 70(5): 1478 - 1482. [Abstract] [Full Text] [PDF]
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U. S. Boston, H. Sungurtekin, C. G.A. McGregor, J. A. Macoviak, and D. J. Cook Differential perfusion: a new technique for isolated brain cooling during cardiopulmonary bypass Ann. Thorac. Surg., May 1, 2000; 69(5): 1346 - 1350. [Abstract] [Full Text] [PDF]
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V. Anttila, M. Pokela, K. Kiviluoma, M. Makiranta, J. Hirvonen, and T. Juvonen Is maintained cranial hypothermia the only factor leading to improved outcome after retrograde cerebral perfusion? An experimental study with a chronic porcine model J. Thorac. Cardiovasc. Surg., May 1, 2000; 119(5): 1021 - 1029. [Abstract] [Full Text] [PDF]
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V. Anttila, K. Kiviluoma, M. Pokela, J. Rimpilainen, M. Makiranta, V. Jantti, J. Hirvonen, and T. Juvonen COLD RETROGRADE CEREBRAL PERFUSION IMPROVES CEREBRAL PROTECTION DURING MODERATE HYPOTHERMIC CIRCULATORY ARREST: A LONG-TERM STUDY IN A PORCINE MODEL J. Thorac. Cardiovasc. Surg., November 1, 1999; 118(5): 938 - 945. [Abstract] [Full Text] [PDF]
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 N. Oshikiri, T Watanabe, H Saitou, Y Iijima, T Minowa, K Inui, and Y Shimazaki Retrograde cerebral perfusion: experimental approach to brain oedema Perfusion, July 1, 1999; 14(4): 257 - 262. [PDF]
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