Neuronal damage after hypothermic circulatory arrest and retrograde cerebral perfusion in the pig

7.0 tesla high resolution MRI study on intracerebral migration of magnet-labeled neural stem cells in a mouse model of Alzheimer's disease

OBJECTIVE

To observe the migration characteristics of neural stem cells (NSCs) labeled with the MRI contrast agent superparamagnetic iron oxide (SPIO) in the brain of APP/PS1 transgenic mice with Alzheimer's disease (AD) by 7.0 T high resolution MRI.

METHODS

C57BL/6 mouse NSCs were cultured, amplified, labeled with Feridex and Poly-l-lysine (FE-PLL) and evaluated by transmission electron microscopy (TEM). Using the random number table method, 24 APP/PS1 transgenic AD mice aged 12 months were equally assigned to two groups: animals in group A were transplanted with FE-PLL labeled NSCs and those in group B were transplanted with non-labeled NSCs in the right hippocampus. Twelve wild-type mice of the same age and born from the same litter were used as the control group (group C) and transplanted with FE-PLL labeled NSCs. Using the 7.0 T high resolution MR scanner, the transplanted NSCs were traced in vivo at 1 day, 1 and 2 weeks after cell transplantation. The MRI findings were compared with the histopathological findings.

RESULTS

C57BL/6 mouse NSCs were cultured and amplified successfully. TEM showed large amounts of iron-containing particles in the cytoplasm of transplanted cells. MRI in group A showed the presence of spheroid low signals at the injection point of the hippocampus on T₂*WI one day after transplantation; one weeks later, the low signals were seen diffusing to the surroundings along the injection point, and covering almost the whole hippocampal area but the intensity of the low signals became weaker gradually; two weeks after transplantation, almost all low signals disappeared. In group B, no significant change in low signals was observed in the transplantation area at all designated time points. Although low signals were also observed in the hippocampus after transplantation of FE-PLL labeled NSCs in group C, their size and location remained almost unchanged. Prussian blue staining showed that migration of the FE-PLL labeled NSCs in the hippocampus of the AD mice was consistent with the MRI findings at all designated time points.

CONCLUSION

NSCs underwent diffuse and non-directional migration to the surroundings after they were transplanted to the hippocampus of APP/PS1 transgenic AD mice, and this migration pattern could be traced in vivo by MRI when they were labeled with magnet.

Neuroprotective Strategies in Repair and Replacement of the Aortic Arch

Aortic arch surgery is a technical challenge, and cerebral protection during distal anastomosis is a continued topic of controversy and discussion. The physiologic effects of hypothermic arrest and adjunctive cerebral perfusion have yet to be fully defined, and the optimal strategies are still undetermined. This review highlights the historical context, physiological rationale, and clinical efficacy of various neuroprotective strategies during arch operations.

Optimal temperature management in aortic arch operations

Hypothermic circulatory arrest is a critical component of aortic arch procedures, without which these operations could not be safely performed. Despite the use of hypothermia as a protective adjunct for organ preservation, aortic arch surgery remains complex and is associated with numerous complications despite years of surgical advancement. Deep hypothermic circulatory arrest affords the surgeon a safe period of time to perform the arch reconstruction, but this interruption of perfusion comes at a high clinical cost: stroke, paraplegia, and organ dysfunction are all potential-associated complications. Retrograde cerebral perfusion was subsequently developed as a technique to improve upon the rates of neurologic dysfunction, but was done with only modest success. Selective antegrade cerebral perfusion, on the other hand, has consistently been shown to be an effective form of cerebral protection over deep hypothermia alone, even during extended periods of circulatory arrest. A primary disadvantage of using deep hypothermic circulatory arrest is the prolonged bypass times required for cooling and rewarming which adds significantly to the morbidity associated with these procedures, especially coagulopathic bleeding and organ dysfunction. In an effort to mitigate this problem, the degree of hypothermia at the time of the initial circulatory arrest has more recently been reduced in multiple centers across the globe. This technique of moderate hypothermic circulatory arrest in combination with adjunctive brain perfusion techniques has been shown to be safe when performing aortic arch operations. In this review, we will discuss the evolution of these protection strategies as well as their relative strengths and weaknesses.

Cannulation and Cardiopulmonary Bypass Produce Selective Brain Lesions in Pigs

Whether cardiopulmonary bypass alone or together with manipulation of the aorta produces neurologic complications remains controversial. Using a pig model, the immediate effects of aortic cannulation and cardiopulmonary bypass on neural injury in different brain regions were investigated in 3 experimental groups: non-operated controls; operated controls with aortic cannulation without cardiopulmonary bypass; and operated animals undergoing cardiopulmonary bypass. Immunohistochemistry using a monoclonal antibody against calretinin was used to show possible ischemic damage in the hippocampal formation which is one of the most vulnerable regions to ischemia. Both cannulation of the aorta alone and cardiopulmonary bypass resulted in numerous argyrophilic neurons in discrete regions of the prefrontal and cerebellar cortex. Decreased calretinin immunoreaction and a reduced number of calretinin-positive neurons were observed following aortic cannulation or cardiopulmonary bypass compared to the non-operated controls. This suggests that both cannulation of the aorta alone and cardiopulmonary bypass affect a selected population of neurons. Therefore, off-pump, aorta no-touch technique may prevent neurologic complications.

Attenuation of regional cerebral blood flow during memory processing after coronary artery bypass surgery

Reports of memory impairment after cardiac surgery are controversial. To address this controversy, we used positron emission tomography to examine changes in regional cerebral blood flow (rCBF) during memory processing before and after elective coronary artery bypass grafting surgery. In postoperative scans, we observed significantly reduced rCBF in 2 of the most important memory processing areas: the medial temporal lobe (P = 0.023) and the prefrontal cortex (P = 0.002). The results suggest postoperative attenuation of rCBF in brain areas involved in memory processing. These reductions could be used to evaluate severity of memory impairment after coronary artery bypass grafting surgery in patients at risk.

[Neuroimaging of a 39-year-old woman with transient global amnesia accompanied by cerebral venous reflow abnormalities]

We present a 39-year-old woman with transient global amnesia (TGA) who showed sudden onset amnesia immediately following sexual intercourse after taking a bath. Her amnesia resolved within 6 hours. Three-Tesla (3T) diffusion weighted magnetic resonance imaging (DWI) taken 80 hours after the onset revealed hyperintense spots in the CA1 subfields of the bilateral hippocampi. No abnormalities were noted in 3T DWI, T(2) weighted imaging (T(2) WI) and fluid attenuated inversion recovery (FLAIR) at 3 weeks after the onset. She had no cardiovascular diseases. Magnetic resonance venography (MRV) revealed hypoplasia of the right transverse sinus and stenosis of the bilateral brachiocephalic veins. Ultrasound sonographic studies revealed a prolonged retrograde flow component of the right internal jugular vein during a Valsalva maneuver. The vast majority of TGA attacks occur between the ages of 50 and 80, and very rarely under the age of 40 years, which is mostly not exposed to vascular risks. We therefore speculate that in conjunction with a decreased vascular beds from the brain, a Valsalva-like maneuver might have precipitated cerebral venous ischemia in the bilateral hippocampi, which are the most vulnerable to ischemic insults.

What is the best method for brain protection in surgery of the aortic arch? Selective antegrade cerebral perfusion

Despite considerable progress in the operative management of lesions involving the transverse aortic arch, replacement of this portion of the vessel remains a surgical challenge and is still associated with mortality and morbidity. This situation is due not only to the technical difficulties of the procedure but, often, to the unsatisfactory preservation of the integrity of the central nervous system during the period of arch exclusion. The techniques of cerebral protection during surgery of the aortic arch can be divided into those aimed at suppressing the metabolic demand of the central nervous system and those aimed at maintaining the metabolic supply during the time of exclusion of the cerebral vessels. Whichever technique is used, it must maintain the normal metabolism of the central nervous system or, at least, allow restoration of the physiologic conditions of its function. In this regard, selective antegrade cerebral perfusion has demonstrated experimentally and clinically its superiority over the other proposed protective techniques.

[Three patients with transient global amnesia following an increased venous pressure: a study using 3.0 Tesla diffusion-weighted magnetic resonance imaging]

We present 3 patients with transient global amnesia (TGA). Patient 1 was a 67-year-old man who had developed TGA 5 years ago. He showed sudden onset amnesia immediately after he quarreled with his wife loudly during driving. Three-Tesla (3T) diffusion-weighted magnetic resonance imaging (DWI) taken 18 hours after onset revealed a small hyperintense signal area in the right CA1 subfield of the hippocampus. Patient 2 was a 66-year-old woman who showed sudden onset amnesia immediately after she walked for about 20 minutes holding a heavy luggage with her arms. 3T DWI taken 64 hours after onset revealed a small hyperintense signal area in the left CA1 subfield of the hippocampus. Patient 3 was a 68-year-old woman who showed sudden onset amnesia immediately after she hurriedly cleaned up her house with a cleaner. 3T DWI taken 48 hours after onset revealed small hyperintense signal areas in the left CA1 subfield and the right subiculum proper of the hippocampus. She developed TGA recurrence 6 months after the first episode of TGA. All these 3 patients had no cardiovascular diseases. Their amnesia resolved within 5-6 hours. Magnetic resonance venography (MRV) revealed hypoplasia of the left transverse sinus in Patient 1 and Patient 3, and aplasia of the left transverse sinus in Patient 2. Ultrasound studies revealed a retrograde flow component of internal jugular vein during Valsalva maneuver in Patient 2. We speculate that an increased venous pressure might have precipitated cerebral venous ischemia in the hippocampus, which is most vulnerable to ischemic insults.

Classical diseases revisited: transient global amnesia

Transient global amnesia usually affects patients between the ages of 40 and 80. Patients with this condition are often described--wrongly--as being confused. It presents classically with an abrupt onset of severe anterograde amnesia. It is usually accompanied by repetitive questioning. The patient does not have any focal neurological symptoms. Patients remain alert, attentive, and cognition is not impaired. However, they are disoriented to time and place. Attacks usually last for 1-8 h but should be less than 24 h. It is possible that it may result from different mechanisms such as venous congestion with valsalva-like activities before symptom onset, arterial thromboembolic ischaemia and vasoconstriction due to hyperventilation. Diagnosis may be made safely in the presence of a characteristic collateral history. No specific treatment is indicated for a typical episode.

Lipopolysaccharide preconditioning induces robust protection against brain injury resulting from deep hypothermic circulatory arrest

OBJECTIVE

Delayed preconditioning genetically reprograms the response to ischemic injury. Subclinical bacterial lipopolysaccharide acts through preconditioning, powerfully protecting against experimental stroke. We investigated the potential for lipopolysaccharide to protect against brain injury related to cardiopulmonary bypass.

METHODS

Neonatal piglets were blindly and randomly preconditioned with lipopolysaccharide (n = 6) or saline (n = 6). Three days later, they experienced 2 hours of deep hypothermic circulatory arrest before being weaned and supported anesthetized for 20 hours in an intensive care setting. Controls included cardiopulmonary bypass without deep hypothermic circulatory arrest (n = 3) and no cardiopulmonary bypass (n = 3). Brain injury was quantified by light and fluorescent microscopy (Fluoro-Jade; Histo-Chem, Inc, Jefferson, Ark).

RESULTS

All animals were clinically indistinguishable before surgery. Perioperative and postoperative parameters between experimental groups were similar. No control animal scored falsely positive. Histologic scores were 0.33 +/- 0.21, 0.66 +/- 0.42, and 0.5 +/- 0.24 in the cortex, basal ganglia, and hippocampus, respectively, in the lipopolysaccharide-treated animals but significantly worse in all saline control animals (1.33 +/- 0.21, P < .01; 1.66 +/- 0.33, P = .09; and 6.0 +/- 1.5, P < .01). One lipopolysaccharide-treated brain was histologically indistinguishable from controls.

CONCLUSION

This is the first evidence that lipopolysaccharide can precondition against cardiopulmonary bypass-related injury. Because lipopolysaccharide preconditioning is a systemic phenomenon offering proven protection against myocardial, hepatic, and pulmonary injury, this technique offers enormous potential for protecting against systemic neonatal injury related to cardiopulmonary bypass.

Effect of profound hypothermia during circulatory arrest on neurologic injury and apoptotic repressor protein Bcl-2 expression in an acute porcine model

OBJECTIVES

We reported that the neocortex and hippocampus are selectively vulnerable to injury in an acute porcine model of hypothermic circulatory arrest at 18 degrees C. We hypothesize that further cooling to 10 degrees C could reduce neurologic injury in these regions. To further elucidate the mechanisms of neurologic injury and protection, we assessed the expression of the anti-apoptotic protein Bcl-2.

METHODS

Twelve piglets underwent 75 minutes of hypothermic circulatory arrest at 18 degrees C (n = 6) and 10 degrees C (n = 6). After gradual rewarming and reperfusion, animals were put to death and brains were perfusion-fixed and cryopreserved. Regional patterns of neuronal apoptosis after hypothermic circulatory arrest were characterized by in situ DNA fragmentation with terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) histochemistry. Bcl-2 protein expression was characterized with immunohistochemistry. Statistical comparisons were made by t test, analysis of variance, and Mann-Whitney U test, as appropriate.

RESULTS

Concentrations of TUNEL(+) cells were significantly lower after profound hypothermia at 10 degrees C compared with 18 degrees C hypothermia in the sensory and motor neocortex and hippocampus (t test, P < .0001; P < .006; P < .006, respectively). Positive Bcl-2 immunostaining was observed only in the motor and sensory neocortex and hippocampus after 18 degrees C hypothermic circulatory arrest. Profound cooling to 10 degrees C resulted in a significant increase in Bcl-2 immunostaining in the motor and sensory cortex as compared with 18 degrees C (Mann-Whitney U test, P < .05).

CONCLUSIONS

Deep hypothermia at 10 degrees C protects the neocortex and hippocampus from insult during hypothermic circulatory arrest as suggested by significantly reduced TUNEL(+) staining in these areas. Although a concomitant increase in Bcl-2 expression was observed in the neocortex at 10 degrees C, it remains unclear whether profound hypothermia deters from neuronal injury by activation of the anti-apoptotic protein Bcl-2.

Increased pressure during retrograde cerebral perfusion provides better preservation of the Na+, K+-ATPase activity

This study was carried out to determine if increased perfusion pressure during retrograde cerebral perfusion (RCP) provides better preservation of the brain Na+, K+-ATPase activity. Twenty pigs were subjected to anesthesia alone (control group, n =5), hypothermic circulatory arrest (HCA) (HCA group, n =5), HCA+RCP at perfusion pressures of 24-29 mmHg (Low-pressure group, n= 5), or HCA+RCP at perfusion pressures of 34-40 mmHg (High-pressure group, n =5). The brain was harvested for the measurement of tissue Na+, K+-ATPase activity. Relative to the control pigs (67.29∓2.1%), significant impairment of Na+, K+-ATPase activity was observed in all three experimental groups (29.89∓7.4% in HCA group, 33.59∓2.9% in the Low-pressure group, and 52.09∓1.8% in the High-pressure group, p <0.01). The best preservation of the enzyme, particularly in the cortex and cerebellum regions, was observed in the High-pressure group (p <0.01). In conclusion, HCA causes severe impairment of Na+, K+-ATPase activity, and increasing perfusion pressures from 24 +29 to 34 +40 mmHg during RCP significantly improves preservation of Na+, K+-ATPase activity, and the improvement of the protection varies in different regions of the brain.

Retrograde cerebral perfusion with intermittent pressure augmentation provides adequate neuroprotection: Diffusion- and perfusion-weighted magnetic resonance imaging study in an experimental canine model

OBJECTIVE

Diffusion- and perfusion-weighted magnetic resonance imaging can identify ischemic brain injury in the hyperacute stage. For neuroprotection during thoracic aortic surgery, we developed a novel retrograde cerebral perfusion with intermittent pressure augmentation. The purpose of this study was to assess the efficiency of this novel method for neuroprotection in real time by using diffusion- and perfusion-weighted magnetic resonance imaging.

METHODS

Sixteen beagle dogs were randomly divided into 4 groups: the antegrade selective cerebral perfusion group (n = 4; antegrade selective cerebral perfusion at a flow rate of 10 mL x kg(-1) x min(-1)); the intermittent retrograde cerebral perfusion group (n = 4; retrograde cerebral perfusion at a baseline pressure of 15 mm Hg with intermittent pressure augmentation to 45 mm Hg every 30 seconds); the conventional retrograde cerebral perfusion group (n = 4; conventional retrograde cerebral perfusion at a fixed pressure of 25 mm Hg); and the circulatory arrest group (n = 4; only circulatory arrest). Diffusion- and perfusion-weighted magnetic resonance images were acquired during each session of cerebral perfusion. Regions of interest were defined, and the apparent diffusion coefficient and relative regional cerebral blood volume were calculated in these regions of interest. Finally, the brain was evaluated for its histopathologic damage score.

RESULTS

The best apparent diffusion coefficient values were observed in the intermittent retrograde cerebral perfusion group in all the regions of interest, although the relative regional cerebral blood volume values were mostly lower than those in the antegrade selective cerebral perfusion group. The total Histopathologic Damage Score (0, normal; 32, worst) in the intermittent retrograde cerebral perfusion group (8.0 +/- 0.6) was significantly lower than that in the conventional retrograde cerebral perfusion (17.5 +/- 1.7; P < .01) and circulatory arrest (25 +/- 1.0; P < 0.01) groups and was equivalent to that in the antegrade selective cerebral perfusion group (7.8 +/- 0.8; P = .9).

CONCLUSION

Intermittent retrograde cerebral perfusion provides adequate neuroprotection by allowing high apparent diffusion coefficient values to be maintained.

Intermittent pressure augmentation during retrograde cerebral perfusion under moderate hypothermia provides adequate neuroprotection: An experimental study

OBJECTIVE

For cerebral protection during aortic surgery, we introduced a novel retrograde cerebral perfusion method with intermittent pressure augmentation. We then assessed whether this novel method provides benefits similar to those provided by antegrade selective cerebral perfusion.

METHODS

Eighteen dogs were randomly divided into 3 groups: the RCP-INT group, intermittent-retrograde cerebral perfusion at 15 mm Hg with intermittent pressure augmentation to 45 mm Hg (n = 6); the ASCP group, antegrade selective cerebral perfusion at a flow rate of 10 mL x kg(-1) x min(-1) (n = 6); and the sham group, no circulatory arrest (n = 6). Cooling (26 degrees C) with cardiopulmonary bypass and 60 minutes of circulatory arrest were performed in the RCP-INT and ASCP groups. The levels of tau protein in the cerebrospinal fluid and the diameters of the retinal vessels were measured. The neurologic deficit scores and the histopathologic damage scores of the brains were determined.

RESULTS

The total postoperative tau protein levels (calculated as the area under the curve) did not differ significantly between the RCP-INT and ASCP groups (203 +/- 87 pg x mL(-1) x h vs 154 +/- 69 pg x mL(-1) x h, P = .95). The retinal vessels were effectively dilated at an augmented pressure of 45 mm Hg in the RCP-INT group. The total neurologic deficit score (0 = normal, 500 = brain death) and histopathologic damage score (0 = normal, 40 = worst) were not significantly different between the RCP-INT and ASCP groups (neurologic deficit score: 75 +/- 21 vs 70 +/- 21, P = .98; histopathologic damage score: 13.5 +/- 1.5 vs 14.2 +/- 1.3, P = .84).

CONCLUSIONS

Intermittent augmented pressure dilated the cerebral vessels, allowing adequate blood supply without injuring the brain. This retrograde cerebral perfusion method provides adequate neuroprotection during moderate hypothermia.

Erythropoietin protects the central nervous system during prolonged hypothermic circulatory arrest: An experimental study in a canine model

OBJECTIVE

Current data suggest that erythropoietin protects the brain and the spinal cord from ischemic and traumatic injury. In this study, we determined whether erythropoietin protects the central nervous system during prolonged hypothermic circulatory arrest in an experimental canine model.

METHODS

Ten adult beagle dogs were randomly and intravenously injected with either 5000 U/kg recombinant human erythropoietin or normal saline. Each dog was then subjected to a cardiopulmonary bypass and 120 minutes of deep hypothermic circulatory arrest (18 degrees C). The level of tau proteins in the cerebrospinal fluid, a modified marker of neurologic deficit in dogs, and the histopathologic characteristics of the brains and spinal cords were then examined.

RESULTS

The level of tau proteins was significantly lower in the erythropoietin-treated group than in the untreated group at 6 hours (20 +/- 12 vs 144 +/- 54 pg/mL; P = .036) and 12 hours (64 +/- 35 vs 478 +/- 103 pg/mL; P = .01) after the operation. The total Neurologic Deficit Score was 59 +/- 31 (0, normal; 500, brain death) in the erythropoietin-treated group, compared with 376 +/- 30 in the untreated group (P = .0117). Histopathologic examination revealed that ischemic neuronal changes and apoptosis in the hippocampus CA1 were significantly lower in the erythropoietin-treated group (P < .01 and P = .028, respectively).

CONCLUSIONS

This study showed that erythropoietin protected the central nervous system during prolonged hypothermic circulatory arrest, partly by preventing both necrosis (ischemic neuronal changes) and apoptosis.

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.

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

BACKGROUND

Although it is well documented that the use of a pH-stat strategy during hypothermic cardiopulmonary bypass improves cerebral blood flow, an alpha-stat strategy has been almost exclusively used during retrograde cerebral perfusion. We investigated the effects of pH-stat and alpha-stat management on brain tissue blood flow and oxygenation during retrograde cerebral perfusion in a porcine model to determine if the use of a pH-stat strategy during retrograde cerebral perfusion improves brain tissue perfusion.

METHODS

Fourteen pigs were managed by an alpha-stat strategy (alpha-stat group, n = 7) or by a pH-stat strategy (pH-stat group, n = 7) during 120 minutes of hypothermic retrograde cerebral perfusion. Retrograde cerebral perfusion was established through the superior vena cava. Brain tissue blood flow and oxygenation were measured continuously with a laser flowmeter and near infrared spectroscopy, respectively. Brain tissue water content was determined at the end of the experiments.

RESULTS

During cooling, brain tissue blood flow was significantly higher with use of the pH-stat strategy than with the alpha-stat strategy (86% +/- 10% versus 40% +/- 3% of baseline). During retrograde cerebral perfusion, brain tissue blood flow was also significantly higher (about three times higher) in the pH-stat group than in the alpha-stat group (15% +/- 4% versus 5% +/- 1% of baseline at 60 minutes of retrograde cerebral perfusion). Tissue oxygen saturation appeared to be higher during retrograde cerebral perfusion in the pH-stat group than in the alpha-stat group. Brain tissue blood flow during rewarming remained significantly higher with the use of pH-stat than with the use of alpha-stat. Brain tissue water contents were similar in both groups.

CONCLUSIONS

In our pig model, the use of a pH-stat strategy during retrograde cerebral perfusion significantly improves brain tissue perfusion. Therefore, to improve retrograde cerebral blood flow during retrograde cerebral perfusion, it may be preferable to use a pH-stat strategy, rather than an alpha-stat strategy.

Is Maintenance of Cerebral Hypothermia the Principal Mechanism by which Retrograde Cerebral Perfusion Provides Better Brain Protection than Hypothermic Circulatory Arrest? A Study in a Porcine Model

OBJECTIVE

Retrograde cerebral perfusion (RCP) provides better brain protection than hypothermic circulatory arrest (HCA) alone. The mechanism by which RCP improves brain protection during circulatory arrest remains unknown. The purpose of the study in pigs was to determine if RCP improves brain protection mainly as a result of its ability to maintain cerebral hypothermia.

METHODS

Fifteen pigs were subjected to 120 minutes of HCA alone (HCA group, n = 5), HCA + RCP at perfusion pressures of 23 to 29 mmHg (RCP-low group, n = 5), or at perfusion pressures of 34-40 mmHg (RCP-high group, n = 5) at 15 degrees C, followed by 60 minutes of normothermic cardiopulmonary bypass (CPB). After brain temperature reached 15 degrees C, HCA was initiated with or without RCP. Temperatures in the brain, esophagus, and perfusate/blood were monitored continuously. Brain tissue blood flow was measured continuously using a laser flowmeter. Brain oxygen extraction was calculated from the oxygen contents in arterial and venous blood samples.

RESULTS

During cooling and rewarming, the change in temperature was slower in the brain than in the esophagus. A similar degree of spontaneous rewarming (from 15 degrees C to 17/18 degrees C) occurred in the brain during HCA and RCP. This indicates that RCP does not provide better maintenance of cerebral hypothermia during circulatory arrest than HCA alone. The esophageal temperature rose more slowly during RCP than during HCA alone, indicating that RCP maintains better hypothermia in the body. During RCP, the brain extracted oxygen continuously from the blood, indicating that RCP may provide nutrient flow to the brain.

CONCLUSION

In an acute pig model, maintenance of cerebral hypothermia does not appear to be the principal mechanism by which RCP provides better brain protection than HCA alone. Retrograde cerebral perfusion provides nutrient flow/oxygen to brain tissue, leading to better brain protection than HCA alone.

Transient global amnesia: a clinical and sonographic study

BACKGROUND

The aetiology of transient global amnesia (TGA) is still unknown. The aim of this study was to identify potential risk factors for TGA, vascular risk factors, the role of patent foramen ovale (PFO) and of retrograde jugular venous flow.

METHODS

138 subjects entered the study, including 48 patients with TGA, 42 age-matched patients with transient ischaemic attack (TIA) and 48 controls. PFO was studied by contrast transcranial duplex sonography. Retrograde jugular venous flow was tested with air contrast ultrasound venography (ACUV).

RESULTS

TGA patients and controls showed a lower prevalence for vascular risk factors than TIA patients. No statistical difference was found between the 3 groups with regard to PFO. ACUV detected jugular valve incompetence in 72.9% TGA, 35.7% TIA and 39.5% controls (TGA vs. TIA and TGA vs. controls p < 0.01).

CONCLUSIONS

TGA patients have fewer vascular risk factors than TIA patients. Paradoxical embolism due to PFO as a cause of TGA is not confirmed in our study. Cerebral venous hypertension due to incompetence of the internal jugular valve may play a role in the pathogenesis of TGA.

Increased pressure during retrograde cerebral perfusion in an acute porcine model improves brain tissue perfusion without increase in tissue edema

BACKGROUND

There is a significant lack of scientific data to support the clinically accepted view that 25 to 30 mm Hg is the maximum safe perfusion pressure during retrograde cerebral perfusion (RCP). This study was designed to investigate whether perfusion pressure greater than 30 mm Hg during RCP is beneficial to the brain during prolonged HCA in an acute porcine model.

METHODS

Sixteen pigs underwent 120 minutes of circulatory arrest in conjunction with RCP at a perfusion pressure of either 23 to 29 mm Hg (group L, n = 8) or 34 to 40 mm Hg (group H, n = 8) at 15 degrees C, followed by 60 minutes of normothermic cardiopulmonary bypass. Cortical blood flow and oxygenation were measured continuously with a laser flowmeter and near-infrared spectroscopy, respectively. Tissue water content was measured at the end of the experiments.

RESULTS

Brain tissue blood flow was significantly higher in group H than in group L (16.8% +/- 4.1% vs 4.8% +/- 0.9% of baseline, p < 0.01) during RCP. Brain oxygen extraction in group L reached a maximum (approximately 70%) immediately after starting RCP, whereas in group H it increased gradually and reached a maximum at 120 minutes of RCP, indicating a greater supply of oxygen to tissue in group H than in group L. After RCP, the ability of brain tissue to use oxygen was better preserved in group H than in group L, as indicated by tissue oxygen saturation and the deoxyhemoglobin level. There was no significant increase in tissue water content in either group (group H 79.2% +/- 0.3%, group L 79.1% +/- 0.4%) relative to normal control pigs (78.7% +/- 0.1%).

CONCLUSIONS

In this acute porcine model, increasing perfusion pressure from 23-29 to 34-40 mm Hg during RCP increases tissue blood flow and provides better tissue oxygenation, without increasing tissue edema. The optimal perfusion pressure for RCP needs to be further investigated.

Brain protection during surgery of the aortic arch

Deep hypothermia with circulatory arrest is the usual method of cerebral protection during replacement of the aortic arch. It has the enormous advantage of allowing the surgical repair to be carried out in a complete bloodless field with no aortic cross-clamping. However, this method only gives the surgeon a limited period of time to carry out the aortic repair. It also requires that cardiopulmonary bypass be prolonged to cool and rewarm the patient which may be the cause of various complications. It has been proposed to improve the efficiency and the results of deep hypothermia, by associating it with retrograde cerebral perfusion of the brain with oxygenated blood through the superior vena cava. This technique improves the tolerance of the brain to cold ischemia and increases the time of repair allowed to the surgeon. Antegrade selective cerebral perfusion has also been in use for more than three decades. When the perfusion is derived from the main arterial line and performed at moderate hypothermia, the aorta must be cross-clamped to perform the repair. In addition, there is some uncertainty as to what constitutes adequate perfusion flow at normal or moderate hypothermic conditions. To reconcile the advantages of both approaches while avoiding their major drawbacks, in 1986 we proposed an original method of selective antegrade brain perfusion. The principle is to perfuse selectively the brain with cold blood (10 to 12 degrees C) while maintaining the central temperature in moderate hypothermia (25-28 degrees C). During the time of the distal anastomosis the cardiopulmonary bypass is stopped, maintaining only the cerebral perfusion at a flow rate of about 400 to 500 mL/mn and a pressure of about 70 mmHg. As soon as the distal anastomosis is completed the main perfusion is resumed. Two hundred and six patients with a mean age of 57 years (22 to 83) were operated on with this technique between October 1984 and March 2001. One hundred forty three patients underwent an elective procedure and 63 patients were operated on in emergency, mainly for acute type A dissection (54 of 63). The hospital mortality was 17% (34 patients). Death was directly related to neurological injury in 9 patients (4.4%). All others patients awoke within 6 to 8 hours and were conscious at 24 hours postoperatively. Thirteen nonfatal neurological complications were observed. The type of lesion, gender, age, duration of CPB, cerebral perfusion, and circulatory arrest had no influence on the neurological outcome of the patients. In our experience, antegrade selective perfusion of the brain with cold blood and moderate hypothermic central temperature constitutes the method of choice for cerebral protection during surgery of the aortic arch as it requires no prolonged CPB and does not limit the time available to perform the aortic repair.

Neurological Complications of Aortic Surgery

Surgery of the aortic arch involves an inherently high risk of neurological complications. A number of factors have been identified which may predispose the patient to brain injury, and various techniques employed in an attempt to counteract these are outlined. In particular the vulnerability of the brain to ischemia has led to the development of three adjunctive cerebral protective techniques, hypothermic circulatory arrest, retrograde cerebral perfusion and selective antegrade cerebral perfusion, all based upon brain cooling and metabolic inhibition. The relative merits and disadvantages of these techniques are therefore discussed. Finally, pharmacologic adjuncts and potential future developments in aortic arch surgery are discussed.

Retrograde cerebral perfusion as a method of neuroprotection during thoracic aortic surgery

Retrograde cerebral perfusion is commonly used as an adjunct to hypothermic circulatory arrest to enhance cerebral protection during thoracic aortic surgery. This review summarizes a large number of studies that demonstrate a spectrum of beneficial, neutral, and detrimental effects of retrograde cerebral perfusion in humans and experimental animal models. It remains unclear whether retrograde cerebral perfusion provides effective cerebral perfusion, metabolic support, washout of embolic material, and improved neurological and neuropsychological outcome.

Retrograde cerebral perfusion during thoracic aortic surgery and late neuropsychological dysfunction

OBJECTIVE

Retrograde cerebral perfusion (RCP) is commonly used in thoracic aortic surgery, ostensibly to provide metabolic support, maintain cerebral hypothermia and/or wash out particulate emboli. We tested the hypothesis that RCP would affect neuropsychological outcome in a clinical cohort.

METHODS

Ninety-four patients undergoing elective thoracic aortic repairs requiring deep hypothermic circulatory arrest consented to participate in this study. These patients underwent preoperative neuropsychological evaluation and comprise the reference group. Fifty-six of these patients also underwent neuropsychological evaluation several weeks postoperatively, 12 of whom (21%) had RCP. The neuropsychological domains tested were attention, processing speed, memory, executive function, and fine motor function. A global assessment of impairment, negative neuropsychological outcome (NNO), was defined as a postoperative decrease in function in two or more neuropsychological domains for patients with at least three domains tested both pre- and postoperatively (n=48). The relationship of three potential predictors (RCP, cerebral ischemia time and patient age) to negative outcomes was analyzed using Wilcoxon two-sample tests, chi(2) tests, Mantel-Haenszel tests and multiple logistic regression. P<0.05 was considered significant.

RESULTS

Memory dysfunction and NNO had strong associations with RCP. This effect remained significant when controlling separately for age and cerebral ischemia time.

CONCLUSIONS

The effects of RCP are difficult to distinguish from those of age and prolonged cerebral ischemia time, because complex thoracic aortic repairs are associated with advanced age, prolonged cerebral ischemia and use of RCP. Despite this limitation, these preliminary data indicated that RCP had no beneficial effect (and most likely a negative effect) upon cognitive outcome.

Animal models for studies on cold-induced platelet activation in human beings

When human platelets are chilled below about 20 degrees C, they spontaneously activate, a phenomenon that limits their storage lifetime. We have previously shown that this activation in chilled human platelets is associated with passage through a lipid phase transition. Because animal models are necessary for Investigating methods for cold storage of platelets, it is essential to determine whether such phase transitions and chilling-induced activation are found in these models. In this study we examined platelets from some commonly used animal models-pigs, rhesus monkeys, mice, dogs, and rabbits. Using Fourier transform infrared spectroscopy (FTIR), we detected the thermotropic membrane phase transition in Intact platelets and assessed the morphologic response of the platelets to chilling. Statistical analysis of both FTIR and shape change show that of the animal models tested, pig platelets are most similar to human platelets. These studies suggest that pigs and pig platelets are the models of choice for the study of cold-induced platelet activation in human beings.

Surgical techniques. Aortic arch and deep hypothermic circulatory arrest: real-life suspended animation

Surgical reconstruction of the aortic arch is a complex procedure requiring careful preoperative analysis of the pathology and forethought toward surgical approach. Development of surgical techniques has brought dramatic improvement survival and reduction of neurological events associated with these procedures, yet significant morbidity is still encountered. New approaches to the patient with these pathologies include antegrade and retrograde perfusions to the brain. Continued research into physiology of hypothermic circulatory arrest offers the promise of pharmacological protection of the brain during aortic reconstruction and potentially development of therapeutic modalities to treat and limit ischemic brain damage.

Hippocampal neuronal death following deep hypothermic circulatory arrest in dogs: involvement of apoptosis

This study was undertaken to evaluate the histological nature of brain damage caused by deep hypothermic circulatory arrest during cardiopulmonary bypass. Total body cooling to 15 degrees C and rewarming were performed with a conventional cardiopulmonary bypass technique using the femoral artery and vein. Dogs were assigned to one of three groups. In group 1 (n = 4), cardiopulmonary bypass was maintained in a state of deep hypothermia (15 degrees C) for 90 min, group 2 animals (n = 5) underwent 60 min of deep hypothermic circulatory arrest at 15 degrees C, and group 3 (n = 6) underwent 90 min of deep hypothermic circulatory arrest at 15 degrees C. All dogs were killed by perfusion fixation 72 h after cardiopulmonary bypass. The CA1 regions of the hippocampi were examined by light and electron microscopy. Biotinylated dUTP was used for nick-end labeling of apoptotic cells mediated by terminal deoxytransferase. No morphological change was observed in group 1 dogs, and very little in group 2 dogs. More severe neuronal damage was observed in group 3. The nuclei of many cells were shrunken and showed nick-end labeling. Dense chromatin masses were detected electron microscopically in the nuclei of CA1 pyramidal cells. Neuronal cell death observed in CA1 pyramidal cells 72 h after 90 min of deep hypothermic circulatory arrest at 15 degrees C involves apoptosis. Therefore, according to this model, the maximum duration of deep hypothermic circulatory arrest should not be allowed to exceed 60 min.

Temporary neurological dysfunction after deep hypothermic circulatory arrest: a clinical marker of long-term functional deficit

BACKGROUND

With increasing clinical experience, it has become clear that two distinct forms of neurological injury occur after operations on the thoracic aorta that require temporary exclusion of the cerebral circulation. Traditionally, evaluation of neurological outcome was limited to reporting the incidence of postoperative stroke related to ischemic infarcts due to particulate embolization. More recently, the symptom complex defined as "temporary neurological dysfunction" (TND) was recognized as a functional manifestation of subtle and presumably transient brain injury, but whether this early postoperative syndrome is associated with long-term deficits of cognitive and intellectual functions has not been established.

METHODS

With Institution Review Board approval, 105 patients undergoing elective thoracic aortic surgery were entered into a protocol involving neuropsychological evaluation with a battery of tests preoperatively, and 1 and 6 weeks postoperatively. Patients who could not be tested adequately or had documented strokes were eliminated from final analysis. Seventy-one patients completed the neuropsychological evaluation, which consisted of eight tests consolidated into five domains: attention, cognitive speed, memory, executive function, and fine motor function. Independent observers also determined whether temporary dysfunction was present, and graded its severity based on a fixed but subjective clinical scale, ranging from simple disorientation and lethargy or confusion (grade 1-2) to prolonged extreme agitation or psychotic behavior requiring treatment with psychotropic drugs (grade 3-5). Data were normalized to baseline values, and were analyzed using analysis of variance, analysis of covariance (ANCOVA), and chi2 as necessary.

RESULTS

A previous analysis had shown that patients who could not be tested or had poor scores 1 week postoperatively were more likely to perform poorly at 6 weeks (odds ratio 5.27, p < 0.01). In the current study, in order to determine the clinical relevance of TND, patients were analyzed retrospectively according to their performance in neuropsychological testing: patients with no change or a decline of less than 50% in tests of memory, motor function, and attention 1 week postoperatively (group 1, n = 49) were compared with those with a negative change exceeding 50% in the same functions at 1 week (group 2, n = 22). The overall incidence of TND was 28.1% (20/71). The incidence of TND in group 2 (14/22, 63%) was significantly higher than in group 1 (6/49, 12%; p = 0.0006). Similarly, the severity of TND (as assessed by clinical score > 2) was also significantly higher in group 2 (11/14) compared with group 1 (0/6; p = 0.006.)

CONCLUSIONS

The incidence and severity of clinically apparent temporary neurological dysfunction correlates significantly with poor performance on neuropsychological tests 1 week postoperatively. Such poor performance predicts continued deficits in memory and motor function at 6 weeks. Thus, TND may not be a benign self-limited condition as previously supposed, but rather a clinical marker for insidious but significant neurological injury associated with measurable long-term deficits in cerebral function. A concerted effort to reduce the incidence of this complication is therefore necessary.

Antegrade cerebral perfusion with cold blood: a 13-year experience

BACKGROUND

In 1986 we introduced the technique of antegrade selective perfusion of the brain with cold blood during surgery of the aortic arch.

METHODS

Between January 1984 and March 1998, 171 patients (118 males and 53 females) aged 25 to 83 years (mean 56.5 +/- 17), underwent replacement of the transverse aortic arch with the aid of cold blood antegrade selective perfusion. One hundred twenty two patients (71.3%) with chronic lesions were operated on electively; 49 patients (28.6%) were operated on urgently for acute aortic dissection (42 patients) or for a ruptured chronic aneurysm (7 patients). Fifty-one patients (29.8%) had previously undergone a surgical procedure on the thoracic aorta. Mean duration of cardiopulmonary bypass was 121 minutes (range: 65-248); mean duration of cerebral perfusion was 60 minutes (range: 15-90), and mean duration of systemic circulatory arrest circuit was 32 minutes (range: 10-57). The electroencephalogram, routinely recorded, showed disappearance of electrical activity in a mean of 9 minutes (range: 3-16) initial return of electrical activity after a mean of 12 minutes (range: 1-35) and normalization in a mean time of 66 minutes.

RESULTS

All patients but 7 (4%) showed signs of normal awakening within 8 hours postoperatively. Six patients (3.5%) had fatal neurologic complications, and 16 patients (9.3%) had a non-fatal neurologic complications. Twenty-nine patients (16.9%) died during the postoperative hospital course. There was a significant difference between patients aged less than 60 years (9%) and patients older than 60 years (mortality rate 26.4%, p < 0.02). There was also a significant difference between patients undergoing an isolated replacement of the arch, and those in whom the replacement was extended to the descending aorta in whom mortality was 36.4% (chi2, p < 0.02). Lesion and gender had no significant influence on the outcome of the patients, nor had the duration of cardiopulmonary bypass, circulatory arrest, and cerebral perfusion. In particular, no correlation could be established between the duration of cerebral perfusion and the occurrence of neurologic complications.

CONCLUSION

The clinical results obtained throughout this experience have demonstrated that selective antegrade cerebral perfusion with cold blood provides excellent protection during surgery of the transverse aortic arch. In addition, it avoids the use of deep hypothermia and prolonged cardiopulmonary bypass and does not limit the time allowed to perform the aortic repair. In our opinion it is the technique of choice, especially in frail patients or those requiring a long and difficult procedure.

Retrograde cerebral perfusion versus selective cerebral perfusion as evaluated by cerebral oxygen saturation during aortic arch reconstruction

BACKGROUND

Time limits for neuroprotection by retrograde cerebral perfusion (RCP) and selective cerebral perfusion (SCP) in aortic arch aneurysm repair or dissection are undergoing definition.

METHODS

Using near-infrared optical spectroscopy, changes in regional cerebrovascular oxygen saturation (rSO2) were compared between the two perfusion methods.

RESULTS

Immediately before cardiopulmonary bypass, baseline rSO2 was 63.9%+/-6.9% for the RCP and 66.1%+/-5.3% for the SCP group (no significant difference). As patients were core-cooled to 20 degrees C, rSO2 increased to 73.1%+/-8.8% and 74.1%+/-7.9% in the RCP and SCP groups, respectively. With circulatory arrest, rSO2 suddenly decreased. After starting cerebral perfusion, rSO2 returned to prearrest values in the SCP group but continued decreasing steadily in the RCP group, to levels below baseline after about 25 minutes. At the end of perfusion, rSO2 was 57.4%+/-12.2% for the RCP group and 71.7%+/-6.9% for the SCP group, and the ratio of rSO2 to baseline value was 0.89 for RCP and 1.08 for SCP despite a shorter brain perfusion time for RCP (38.8+/-18.0 versus 103.3+/-43.3 minutes). Three of 5 patients whose ratios of rSO2 to baseline at the end of brain protection were 0.7 or less had neurologic deficits.

CONCLUSIONS

Although SCP showed no clinically important time limitation, rSO2 continued to decrease with time during RCP. An rSO2 ratio less than 0.7 could represent a critical lower limit.

Distribution of cerebral flow using retrograde versus antegrade cerebral perfusion

BACKGROUND

This study compared flow to the brain with retrograde and antegrade cerebral perfusion during circulatory arrest.

METHODS

Twenty-four rabbits were injected with 5 mCi of technetium-99 macroaggregated albumin, a tracer trapped in the capillaries. Group I (n = 6) were maintained normothermic, and the tracer was injected into the ascending aorta. Group II (n = 6) were maintained normothermic, and underwent cannulation of the superior vena cava (SVC), exsanguination through the aorta, and injection of the tracer into the SVC, which was proximally occluded. In group III (n = 6), the animal was cooled to 25 degrees C. The animal was exsanguinated through the aorta and tracer was injected into the ascending aorta. In group IV (n = 6), animals were cooled to 25 degrees C. The animal was exsanguinated through the ascending aorta and tracer was injected into the SVC. Three animals (group V) were exsanguinated through the ascending aorta and a retrograde venogram of the SVC was performed. Scintigraphy of groups I to IV was carried out on a digital gamma camera. Brain trapping of tracer was graded from 0 to 5, with 0 being no tracer in the brain and 5 being dominant tracer trapping in the brain.

RESULTS

Tracer trapping in the brain showed group I, 3.67+/-0.82; group II, 0; group III, 4.67+/-0.41; group IV, 0.17+/-0.41 (p<0.0001). Retrograde venogram of the SVC showed flow into the cerebral veins.

CONCLUSIONS

Retrograde flow through the SVC reaches the cerebral venous system. Flow arriving in retrograde fashion does not go through the capillary system.

[Surgical treatment of acute dissection of the ascending aorta (20 years experience)]

PURPOSE

In 1977, the use of gelatine-resorcine-formaline (GRF) biological glue during surgery of acute type A aortic dissection was proposed. The present study retrospectively analyses the late results obtained with this adjunct in an experience extending over a 20-year period.

PATIENTS AND METHODS

From January 1977 to July 1997, 193 patients (139 males and 54 females) aged from 15 to 79 years (mean age: 53 +/- 14 years) underwent an emergency operation for type A aortic dissection in our institution. All patients suffering from acute type A dissection and 162 (84%) were operated on within 48 hours after the onset of symptoms. Twenty-eight patients (15.2%) had Marfan's syndrome. In all patients the ascending aorta was replaced and the aortic stumps were reinforced with the GRF glue. In 43 patients (22.2%), the aortic valve was replaced either independently (5 cases-2.5%) or by means of a composite graft (35 cases-19.5%). Recently three patients underwent a complete replacement of the ascending aorta and coronary reimplantation with preservation of the native aortic valve. Because of the location of the intimal tear, the aortic replacement was extended to the transverse arch in 58 patients (30%).

RESULTS

Hospital mortality amounted to 21% (40 patients) (22.8% in patients with arch replacement and 20.3% in patients without arch replacement) (ns). The survivors were surveyed from 2 months to 20 years post-operatively (cumulative follow-up: 856 pt/years, mean follow-up: 85 +/- 66 months). During this period of time, 23 patients (15%) had to be reoperated on for a total of 29 procedures. Six of those patients (26%) died at reoperation. At univariate analysis, presence of Marfan's syndrome (P < 0.05) and absence of arch replacement (P < 0.02) were determinant risk factors for reoperation. Emergency (P < 0.01) and thoraco-abdominal replacement (P < 0.04) were determinant risk-factors of death at reoperation. The actuarial freedom from reoperation (Kaplan-Meier, CI: 95%) was: 96.5% (90.9-98.2), 87.6% (79.8-92.7), 80.9% (70.8-88.1), 66.4% (51.1-78.9) at one, 5, 10 and 15 years, respectively. A total of 36 patients (27.7%) died during follow-up. Presence of Marfan's syndrome (P < 0.01), reoperation (P < 0.02), stroke (P < 0.05), cardiac failure (P < 0.05) were determinant risk factors of late mortality. The actuarial late survival rate (Kaplan-Meier. CI: 95%), including hospital mortality, was: 71.5% (64.3-77.8), 66% (58.3-73), 56.4% (47.7-64.7), 46.3% (36.4-56.5) at one, 5, 10 and 15 years.

CONCLUSION

The GRF glue has proved to be extremely useful during initial emergency surgery for acute type A dissection, making the procedure much easier and safer. Through this operative improvement, the use of the GRF glue seems to have a beneficial influence on the late results which, however, depend mainly on the patient's basic condition.

Deep hypothermic intermittent circulatory arrest--an adjunct technique for operations on aneurysms involving the aortic arch

Aneurysms involving the aortic arch were repaired in 12 patients using a technique known as deep hypothermic intermittent circulatory arrest (DHICA). This technique consists of repeated cycles of 20 min of circulatory arrest and 10 min of cerebral and systemic reperfusion. Aneurysms were of the following types: 2 true atherosclerotic aneurysm, 8 aortic dissections, and 2 traumatic aneurysm. There were 2 operative deaths caused by coagulopathy as a result of hepatic failure and difficulty with left ventricular venting. The frequency of circulatory arrest ranged from 2 to 5 cycles, and total circulatory arrest ranged from 20 to 71 min (mean 43.6 min). The lowest tympanic temperature ranged from 17.7 to 19.2 degrees C. No permanent cerebral complications occurred in 10 patients. We believe that this adjunct technique offers excellent results in the surgical treatment of aneurysms involving the aortic arch.

Retrograde cerebral perfusion provides limited distribution of blood to the brain: a study in pigs

OBJECTIVE

The objective of this study was to investigate flow distribution during retrograde and antegrade cerebral perfusion with India ink as a marker.

METHODS

Ten pigs received cerebral perfusion with a solution containing 50% filtered India ink for 5 minutes either antegradely through both internal carotid arteries at a flow of 180 to 200 ml/min (n = 5) or retrogradely via the superior vena cava at a flow of 300 to 500 ml/min (n = 5). The brains were then fixed for quantitative measurement of the density of ink-filled capillaries (reported as a percentage of the total selected area). The assessment was done with the use of an in-house software program.

RESULTS

In the antegrade cerebral perfusion group, the intracranial arterial and venous systems were completely filled with ink. The gray matter was colored uniformly black, and light coloring was observed in the white matter. During retrograde cerebral perfusion, the majority of ink was returned to the inferior vena cava, and only a small amount of ink was found in the innominate artery draining from the brain. Massive ink filling was observed in the sagittal sinus and other venous sinuses in all the pigs. Vessels on the surface of the brain and large vessels in the brain were also well filled with ink. However, only 10% of capillaries were filled with ink during retrograde cerebral perfusion relative to the number observed with antegrade cerebral perfusion.

CONCLUSIONS

Retrograde cerebral perfusion supplies a limited amount of blood to brain tissue, which flows mainly through superficial and large deep cerebral vessels.

The effect of circulatory arrest and retrograde cerebral perfusion on microtubule-associated protein 2: an immunohistochemical study in pig hippocampus

Microtubule-associated protein 2 (MAP2) immunohistochemical labeling in the hippocampus was studied to assess the protective effect of brain perfusion during surgery requiring hypothermic circulatory arrest in 24 pigs exposed to anesthesia alone (control), 120 min of complete circulatory arrest at 15 degrees C, min of retrograde cerebral perfusion at 15 degrees C, or 120 min of anterograde cerebral perfusion at 15 degrees C. Pigs were reperfused for 60 min and sacrificed. In the control anterograde perfusion groups, the intensity of MAP2 labeling was similar in all regions of the hippocampus. Circulatory arrest and retrograde perfusion resulted in significant reduction of MAP2 labeling (28% and 38% respectively of control, P < 0.001) of neurons in the CA1 region. MAP2 labeling may be useful for assessing early damage in the hippocampus in this model.

Cerebral protection during moderate hypothermic circulatory arrest: histopathology and magnetic resonance spectroscopy of brain energetics and intracellular pH in pigs

OBJECTIVE

We evaluated the effect of antegrade and retrograde brain perfusion during moderate hypothermic circulatory arrest at 28 degrees C.

METHODS

Phosphorus 31-magnetic resonance spectroscopy was used to follow brain energy metabolites and intracellular pH in pigs during 2 hours of ischemia and 1 hour of reperfusion. Histopathologic analysis of brain tissue fixed at the end of the experimental protocol was performed. Fourteen pigs were divided into two experimental groups subjected to antegrade (n = 6) or retrograde (n = 8) brain perfusion. Anesthesia (n = 8) and hypothermic cardiopulmonary bypass groups (15 degrees C, n = 8) served as control subjects. In the antegrade and retrograde brain perfusion groups, the initial bypass flow rate was 60 to 100 ml x kg(-1) x min(-1). In the antegrade group, the brain was perfused through the carotid arteries at a flow rate of 180 to 210 ml x min(-1) during circulatory arrest at 28 degrees C. In the retrograde group, the brain was perfused through the superior vena cava at a flow rate of 300 to 500 ml x min(-1) during circulatory arrest at 28 degrees C.

RESULTS

The intracellular pH was 7.1 +/- 0.1 and 7.2 +/- 0.1 in the anesthesia and hypothermic bypass groups, respectively. Brain intracellular pH and high-energy metabolites (adenosine triphosphate, phosphocreatine) did not change during the course of the 3.5-hour study. In the antegrade group, adenosine triphosphate and intracellular pH were unchanged throughout the protocol. In the retrograde perfusion group, the intracellular pH level decreased to 6.4 +/- 0.1, and adenosine triphosphate and phosphocreatine levels decreased within the first 30 minutes of circulatory arrest and remained at low levels until the end of reperfusion. High-energy phosphates did not return to their initial levels during reperfusion. Histopathologic analysis of nine regions of the brain showed good preservation of cell structure in the anesthesia, hypothermic bypass, and antegrade perfusion groups. The retrograde perfusion group showed changes in all the regions examined.

CONCLUSIONS

The study shows that moderate hypothermic circulatory arrest at 28 degrees C with antegrade brain perfusion during circulatory arrest protects the brain but that retrograde cerebral perfusion at 28 degrees C does not protect the brain.