Is maintained cranial hypothermia the only factor leading to improved outcome after retrograde cerebral perfusion? An experimental study with a chronic porcine model

Safety of retrograde cerebral perfusion under moderate hypothermia for hemiarch replacement

OBJECTIVES

Aortic surgeries performed under moderate hypothermia require antegrade cerebral perfusion. The influence of retrograde cerebral perfusion under moderate hypothermic circulatory arrest remains unknown. To clarify this effect, this study aimed to compare the early outcomes of retrograde versus antegrade cerebral perfusion under moderate hypothermia for hemiarch replacement.

METHODS

Between March 2009 and April 2020, 391 hemiarch replacements under moderate hypothermic circulatory arrest via median sternotomy were performed at our institution. Of these, 70 involved retrograde perfusion and 162 involved antegrade perfusion. Propensity score matching was used to compare 61 pairs of retrograde and antegrade cases.

RESULTS

Retrograde and antegrade strategy under moderate hypothermia resulted in comparable operative mortality (3.3% vs. 1.6%, P > 0.99), permanent neurological deficits (8.5% vs. 6.6%, P > 0.99), and temporary neurological deficits (24.6% vs. 39.3%, P = 0.33). Retrograde surgery was associated with shorter circulatory arrest times (31.4 ± 8.2 min vs. 37.4 ± 12.2 min, P = 0.005) and fewer red blood cell transfusions (4.6 ± 3.9 units vs. 8.2 ± 5.1 units, P < 0.001) than those with antegrade surgery.

CONCLUSIONS

Retrograde cerebral perfusion under moderate hypothermia for hemiarch replacement yields excellent operative outcomes, equivalent to those achieved using an antegrade strategy.

Review of cerebral perfusion strategies for aortic surgery with application for minimally invasive approaches

Aortic arch and hemiarch surgery necessitate the temporary interruption of blood perfusion to the brain. Despite its complexity, hemiarch and ascending aortic surgery can be performed via a minimally invasive approach. Due to the higher risk of neurological injury during a circulatory arrest, several techniques were developed to further protect the brain during this surgery. We searched the Embase, Medline, and Cochrane databases and identified articles reporting outcomes of antegrade and retrograde cerebral perfusion strategies. Herein, we outline surgical approaches, intra-operative technical considerations, and clinical outcomes of hemiarch and ascending aortic surgery. Hemiarch and ascending aortic surgery is associated with a higher risk of mortality and morbidity. Attention to the optimal approach and cerebral protection strategy has been shown to significantly affect outcomes and mitigate risk.

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.

Management of potential gas embolus during closure of an atrial septal defect in a three-year-old

Gas embolism occurring in adult patients supported with cardiopulmonary bypass is usually associated with mechanical complications. Management of gas embolism is less often described for the pediatric or neonatal patient. Measures to counteract gas embolism must be undertaken immediately if a satisfactory outcome is to be achieved. Here, the management of a three-year-old female patient, who was undergoing repair of a secundum atrial septal defect when the aortic cannula became dislodged and air entered the aorta, is described. Immediate implementation of an air embolism protocol, including (among other maneuvers) removal of air from the circuit, retrograde cerebral perfusion via the superior vena cava, and induction of cerebral hypothermia, may have aided in an acceptable outcome.

Italian multicentre study on type A acute aortic dissection: a 33-year follow-up†

OBJECTIVES

Despite substantial progress in surgical techniques and perioperative management, the treatment and long-term follow-up of type A acute aortic dissection (AAD) still remain a major challenge. The objective of this retrospective, multicentre study was to assess in a large series of patients the early and long-term results after surgery for type A AAD.

METHODS

We analysed the preoperative, intraoperative and postoperative conditions of 1.148 consecutive patients surgically treated in seven large referral centres from 1981 to 2013. We applied to each patient three different multi-parameter risk profiles (preadmission risk, admission risk and post-surgery risk) in order to compare risk factors and outcome. Long-term Kaplan-Meier survival was evaluated.

RESULTS

The median age was 64 years and the male population was predominant (66%). Identified diagnosis of collagen disease was present in 9%, and Marfan syndrome in 5%. Bicuspid aortic valve was present in 69 patients (6%). Previous cardiac surgery was identified in 10% of the patients. During surgery, the native aortic valve was preserved in 72% of the cases, including leaflet resuspension in 23% and David operation in 1.2%. Considering aortic valve replacement (AVR: 28%), bioprosthesis implantation was performed in 14.7% of the subjects. Neurological impairment at discharge was shown in 23% of the cases among which 21% of patients had new neurological impairment versus preoperative conditions. The overall 30-day mortality rate was 25.7%. All risk profiles remained independently associated with in-hospital mortality. During the available follow-up of hospital survivors (median: 70 months, interquartile range: 34-113, maximum: 396), cardiac-related death occurred in 7.9% of the subjects. The cumulative survival rate for cardiac death was 95.3% at 5 years, 92.8% at 10 years and 52.8% at 20 years. Severe aortic regurgitation (AR) (grade 3-4) at the time of surgery showed to be a significant risk factor for reintervention during the follow-up (P < 0.001). Among risk profiles, only the preadmission risk was independently associated with late mortality after multivariate analysis. Unexpectedly, there was no difference in freedom from cardiac death between patients with and without AVR.

CONCLUSIONS

Although surgery for type A has remained challenging over more than three decades, there is a positive trend in terms of hospital mortality and long-term follow-up. About 90% of patients were free from reoperation in the long term, although late AR remains a critical issue, suggesting that a thorough debate on surgical options, assessment and results of a conservative approach should be considered.

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.

Preliminary results of intermittent retrograde cerebral perfusion during proximal aortic arch surgery

OBJECTIVE

Continuous retrograde cerebral perfusion during aortic arch surgery is associated with cerebral edema. In this report, we describe the clinical use of a new type of intermittent retrograde cerebral perfusion.

SUBJECTS AND METHODS

Fourteen patients with a Stanford type A dissection were included in this study. With the usual method of retrograde cerebral perfusion, about 2,500 mL venous blood is drained from bicaval cannulae into a hard-shell reservoir, and oxygenated blood is perfused through the superior vena caval cannula. The flow rate is 300 mL/min. After about 15 min, retrograde perfusion is discontinued, and drainage from the bicaval cannulae is restarted. When a bloodless field is necessary, perfusion also is discontinued.

RESULTS

Two to seven cycles of intermittent retrograde cerebral perfusion were administered (average, 3.1+/-0.4, mean+/-SD). The total retrograde perfusion time was 36.0+/-1.9 min which was equivalent to 74.8% of the circulatory arrest time. No patient developed edema of the upper body. The time to wake-up was 3 to 14 h (average, 6.5+/-1.0 h). No patient suffered any neurologic complications even though the time of circulatory arrest was greater than 60 min in four cases. Head magnetic resonance imaging or computed tomography was performed in 12 cases, and no evidence of hypoxic brain injury was detected.

CONCLUSIONS

Our clinical experience using a moderate amount of intermittent retrograde cerebral perfusion is superior to continuous retrograde cerebral perfusion for protecting the brain during aortic arch surgery.

Neuropsychometric outcome following aortic arch surgery: a prospective randomized trial of retrograde cerebral perfusion

BACKGROUND

Aortic surgery requiring hypothermic circulatory arrest is associated with a high incidence of brain injury. However, knowledge of neuropsychometric outcome is limited. Retrograde cerebral perfusion has become a popular adjunctive technique to hypothermic circulatory arrest. The aim of this study was to assess neuropsychometric outcome and compare the 2 techniques.

METHODS

In a prospective randomized trial, 38 patients requiring elective aortic arch surgery were allocated to either hypothermic circulatory arrest plus retrograde cerebral perfusion or hypothermic circulatory arrest alone. Neuropsychometric testing was performed preoperatively, and at 6 weeks and 12 to 24 weeks postoperatively. Deficit was defined as a 20% decline in 2 tests or more. Standardized Z scores were calculated for each patient and test. Eighteen patients underwent hypothermic circulatory arrest and 20 patients underwent hypothermic circulatory arrest plus retrograde cerebral perfusion. The mean cardiopulmonary bypass, hypothermic circulatory arrest, and retrograde cerebral perfusion durations were 169, 30, and 25 minutes, respectively.

RESULTS

There were 2 deaths and 2 neurological deficits. At 6 weeks postoperatively, 77% of the hypothermic circulatory arrest group and 93% of the hypothermic circulatory arrest plus retrograde cerebral perfusion group had a deficit (P =.22). At 12 weeks this was reduced to 55% and 56%, respectively (P =.93). There was a worse total Z test score in the hypothermic circulatory arrest plus retrograde cerebral perfusion group at 12 weeks (P =.05). Neuropsychometric change did not correlate with hypothermic circulatory arrest duration, presence of aortic atheroma, cannulation technique, or procedure.

CONCLUSIONS

Hypothermic circulatory arrest plus/minus retrograde cerebral perfusion is associated with a high incidence of neuropsychometric change despite ostensibly normal clinical outcomes and apparently safe arrest duration. Retrograde cerebral perfusion did not improve outcome in this small study.

Direct visualization of minimal cerebral capillary flow during retrograde cerebral perfusion: an intravital fluorescence microscopy study in pigs

BACKGROUND

Retrograde cerebral perfusion (RCP) is used in some centers during aortic arch surgery for brain protection during hypothermic circulatory arrest. It is still unclear however whether RCP provides adequate microcirculatory blood flow at a capillary level. We used intravital microscopy to directly visualize the cerebral capillary blood flow in a piglet model of RCP.

METHODS

Twelve pigs (weight 9.7 +/- 0.9 kg) were divided into two groups (n = 6 each): deep hypothermic circulatory arrest (DHCA) and RCP. After the creation of a window over the parietal cerebral cortex, pigs underwent 10 minutes of normothermic bypass and 40 minutes of cooling to 15 degrees C on cardiopulmonary bypass ([CPB] pH-stat, hemocrit 30%, pump flow 100 mL x kg(-1) x min(-1)). This was followed by 45 minutes of DHCA and rewarming on CPB to 37 degrees C. In the RCP group the brain was retrogradely perfused (pump flow 30 mL x kg(-1) x min(-1)) during DHCA through the superior vena cava after inferior vena cava occlusion. Plasma was labeled with fluorescein-isothiocyanate-dextran for assessing microvascular diameter and functional capillary density (FCD), defined as total length of erythrocyte-perfused capillaries per observation area. Cerebral tissue oxygenation was determined by nicotinamide adenine dinucleotide hydrogen (NADH) autofluorescence, which increases during tissue ischemia.

RESULTS

During normothermic and hypothermic antegrade cerebral perfusion the FCD did not significantly change from base line (97% +/- 14% and 96% +/- 12%, respectively). During retrograde cerebral perfusion the FCD decreased highly significantly to 2% +/- 2% of base line values (p < 0.001). Thus there was no evidence of significant capillary blood flow during retrograde cerebral perfusion. The microvascular diameter of cerebral arterioles that were slowly perfused significantly decreased to 27% +/- 6% of base line levels during RCP. NADH fluorescence progressively and significantly increased during RCP, indicating poorer tissue oxygenation. At the end of retrograde cerebral perfusion there was macroscopic evidence of significant brain edema.

CONCLUSIONS

RCP does not provide adequate cerebral capillary blood flow and does not prevent cerebral ischemia. Prolonged RCP induces brain edema. However, there might be a role for a short period of RCP to remove air and debris from the cerebral circulation after DHCA because retrograde flow could be detected in cerebral arterioles.

Antegrade selective cerebral perfusion during operations on the thoracic aorta: factors influencing survival and neurologic outcome in 413 patients

OBJECTIVE

We retrospectively analyzed hospital mortality and neurologic outcome after operations on the thoracic aorta with the aid of antegrade selective cerebral perfusion to determine a predictive risk model.

METHODS

Between October 1995 and May 2001, 413 patients (mean age, 63.0 +/- 11.5 years) underwent operations on the thoracic aorta with antegrade selective cerebral perfusion. Indications for surgical intervention were acute type A dissection in 116 (28.1%) patients, degenerative aneurysm in 227 (55.0%) patients, and postdissection aneurysm in 70 (16.9%) patients. One hundred twenty-five (30.3%) patients were operated on urgently; concomitant procedures were performed in 171 (41.4%) patients. Mean cerebral perfusion time was 63.0 +/- 38.7 minutes (range, 16-220 minutes). Preoperative and intraoperative factors were evaluated by means of univariate and multivariate analysis to identify predictors of hospital mortality and neurologic outcome.

RESULTS

The hospital mortality was 9.4%. Stepwise logistic regression revealed urgency status (P =.000; odds ratio, 19.9) and recent history of a recent central neurologic event (P =.004; odds ratio, 8.0) to be independent determinants for hospital mortality. Temporary neurologic dysfunction occurred in 20 (5.1%) patients. Urgency status (P =.005; odds ratio, 7.5), history of a central neurologic event (P =.003; odds ratio, 8.6), and coronary artery bypass grafting (P =.019; odds ratio, 6.0) were independent determinants of temporary neurologic dysfunction. Urgency status (P =.003; odds ratio, 8.6) was the only independent determinant for permanent neurologic dysfunction, and it occurred in 15 (3.7%) patients.

CONCLUSION

Antegrade selective cerebral perfusion is an effective method of brain protection. Cerebral perfusion times of longer than 90 minutes were not associated with an increased risk of hospital mortality or poorer neurologic outcome. Urgency status and recent history of central neurologic events were retained as important risk factors for hospital mortality and neurologic outcome.

Cerebral Protection During Surgery of the Aortic Arch

The most significant challenge in surgical repair of the aortic arch (transverse thoracic aorta) is to protect the brain from ischemic injury. During the portion of the procedure when the brachiocephalic vessels are at tached to a graft, there is an obligatory interruption in the normal path of circulation to the brain. Various strategies are used to overcome the potential for brain injury during discontinuity between the aorta and the cerebral circulation. These include deep hypothermic circulatory arrest, retrograde cerebral perfusion, and selective anterograde cerebral perfusion. Pharmaco logic adjuncts to these procedures are also used to further enhance brain protection. This review ad dresses the relative merits of these techniques as means of cerebral protection.

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.

Neurologic outcome after ascending aorta-aortic arch operations: effect of brain protection technique in high-risk patients

OBJECTIVE

We sought to assess the optimal strategy for avoiding neurologic injury after aortic operations requiring hypothermic circulatory arrest.

METHODS

All 717 patients who survived ascending aorta-aortic arch operations through a median sternotomy since 1986 were examined for factors influencing stroke. Temporary neurologic dysfunction was assessed in all patients who survived the operation without stroke since 1993. Multivariate analyses were carried out to determine independent risk factors for neurologic injury.

RESULTS

Independent risk factors for stroke were as follows: age greater than 60 years (P <.001; odds ratio, 4.5); emergency operation (P =.02; odds ratio, 2.2); new preoperative neurologic symptoms (P =.05; odds ratio, 2.9); presence of clot or atheroma (P <.001; odds ratio, 4.4); mitral valve replacement or other concomitant procedures (P =.055; odds ratio, = 3.7); and total cerebral protection time, defined as the sum of hypothermic circulatory arrest and any retrograde or antegrade cerebral perfusion (P =.001; odds ratio, 1.02/min). In 453 patients surviving operations without stroke after 1993, independent risk factors for temporary neurologic dysfunction included age (P <.001; odds ratio, 1.06/y), dissection (P =.001; odds ratio, 2.2), need for coronary artery bypass grafting (P =.006; odds ratio, 2.1) or other procedures (P =.023; odds ratio, 3.4), and total cerebral protection time (P <.001; odds ratio, 1.02/min). When all patients with total cerebral protection times between 40 and 80 minutes were examined, the method of cerebral protection did not influence the occurrence of stroke, but antegrade cerebral perfusion resulted in a significant reduction in incidence on temporary neurologic dysfunction (P =.05; odds ratio, 0.3).

CONCLUSIONS

The occurrence of stroke is principally determined by patient- and disease-related factors, but use of antegrade cerebral perfusion can significantly reduce the occurrence of temporary neurologic dysfunction.

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.

Leukocyte filtration improves brain protection after a prolonged period of hypothermic circulatory arrest: A study in a chronic porcine model

BACKGROUND

Ischemic cerebral injury follows a well-attested sequence of events, including 3 phases: depolarization, biochemical cascade, and reperfusion injury. Leukocyte infiltration and cytokine-mediated inflammatory reaction are known to play a pivotal role in the reperfusion phase. These events exacerbate the brain injury by impairing the normal microvascular perfusion and through the release of cytotoxic enzymes. The aim of the present study was to determine whether a leukocyte-depleting filter (LeukoGuard LG6, Pall Biomedical, Portsmouth, United Kingdom) could improve the cerebral outcome after hypothermic circulatory arrest.

METHODS

Twenty pigs (23-30 kg) were randomly assigned to undergo cardiopulmonary bypass with or without a leukocyte-depleting filter before and after a 75-minute period of hypothermic circulatory arrest at 20 degrees C. Electroencephalographic recovery, S-100beta protein levels, and cytokine levels (interleukin 1beta, interleukin 8, and tumor necrosis factor alpha) were recorded up to the first postoperative day. Postoperatively, all animals were evaluated daily until death or until electively being put to death on day 7 by using a quantitative behavioral score. A postmortem histologic analysis of the brain was carried out on all animals.

RESULTS

The rate of mortality was 2 of 10 in the leukocyte-depletion group and 5 of 10 in control animals. The risk for early death in control animals was 2.5 (95% confidence interval, 0.63-10.0) times higher than that of the leukocyte-depleted animals. The median behavioral score at day 7 was higher in the leukocyte-depletion group (8.5 vs 3.5; P =.04). The median of total histopathologic score was 8.5 in the leukocyte-depletion group and 15.5 in the control group (P =.005).

CONCLUSION

A leukocyte-depleting filter improves brain protection after a prolonged period of hypothermic circulatory arrest.