Challenging Paradigm Limits of Retrograde Cerebral Perfusion During Lower Body Circulatory Arrest.

INTRODUCTION: Retrograde cerebral perfusion (RCP) is a safe and effective technique to augment cerebral protection during lower body circulatory arrest in patients undergoing elective hemiarch replacement. However, recommendations guiding optimal temperature, flow rate, and perfusion pressure are outdated and potentially overly limiting. We report our experience using RCP for elective hemiarch replacement with parameters that challenge the currently accepted paradigm. METHODS: This was a single-center, retrospective analysis of 319 adult patients who underwent elective hemiarch replacement between February 2010 and 2021 using hypothermic lower body circulatory arrest with RCP alone, RCP followed by antegrade cerebral perfusion (ACP), or ACP alone. Flow rates were adjusted to maintain cerebral perfusion pressure between 30 and 50 mm Hg for RCP and between 40 and 60 mm Hg for ACP. RESULTS: RCP was used in 22.6% (n = 72) of cases, whereas ACP alone was performed in 77.4% (n = 247) of cases. Baseline patient characteristics were similar between groups. Patients undergoing RCP demonstrated shorter cross-clamp time (97.0 min versus 100.0 min, P = 0.034) and shorter lower body circulatory arrest time (7.0 min versus 10.0 min, P < 0.0001) compared with ACP alone. Nadir bladder temperature was equivalent between groups (27.3°C versus 27.5°C, P = 0.752). There were no significant differences in postoperative complications, neurologic outcomes, or mortality. CONCLUSIONS: Moderate hypothermic lower body circulatory arrest combined with RCP at target perfusion pressures of 30-50 mm Hg in patients undergoing elective hemiarch replacement results in equivalent neurologic outcomes and overall morbidity to cases using ACP alone. These results challenge the currently accepted paradigm for RCP, which typically uses deep hypothermia while keeping perfusion pressures below 25 mm Hg.

Retrograde cerebral perfusion for intracardiac air embolism in Fontan procedure.

We report the case of a 5-year-old boy who suffered from an intracardiac air influx with suspected cerebral air embolism during the Fontan procedure. We immediately transformed the cardiopulmonary bypass circuit to perform a retrograde cerebral perfusion, which resulted in successful neuroprotection. He was extubated in the operating room without any neurological defects.

Perfusion of brain and viscera using modified retrograde cerebral perfusion for aortic arch surgery.

Anterograde or retrograde cerebral perfusion can protect the brain from ischemic injury during hypothermic circulatory arrest (HCA), but neither type of perfusion provides blood flow to the abdominal viscera. Here, we report a modified retrograde cerebral perfusion (RCP) technique in which we tethered both superior and inferior venae cavae with bands around the cannula and clamped the distal ends of the drainage tubes of both venae cavae. Modified RCP may provide greater blood flow to the brain and lower body than conventional RCP during HCA in hemiarch surgery.

Does deep hypothermic circulatory arrest with versus without retrograde cerebral perfusion affect the outcomes after proximal aortic arch aneurysm and acute type A aortic dissection repair? Different pathologies and cerebral protection techniques with similar results.

Hypothermic circulatory arrest is used for proximal and total aortic arch correction in patients with aortic arch aneurysm and acute or chronic type A aortic dissection. Different cerebral perfusion techniques have been proposed for reducing morbidity and mortality rate. The study of Arnaoutakis et al. showed that deep hypothermic circulatory arrest with or without retrograde cerebral perfusion for proximal aortic aneurysm and acute type A aortic dissection correction had similar results with regard to morbidity and mortality rate. In addition, the short circulatory arrest time contributes for favorable outcomes of these patients. Although antegrade cerebral perfusion with hypothermic circulatory is widely used by many cardiac surgeons, deep hypothermic circulatory arrest with or without retrograde cerebral perfusion remains an alternative and safe method for brain protection in patients undergoing proximal aortic arch aneurysm or acute type A aortic dissection repair.

Application of retrograde cerebral perfusion in aortic root replacement combined with right half aortic arch replacement. / é€†è¡Œè„‘çŒæ³¨åœ¨ä¸»åŠ¨è„‰æ ¹éƒ¨å’Œå³åŠå¼“ç½®æ¢æ‰‹æœ¯ä¸­çš„åº”ç”¨.

OBJECTIVES: After cardiac surgery involving the aortic arch, the incidence of neurological complications remains high, therefore it is very important to take measures to protect brain. This study is to investigate the safety and effectiveness of deep hypothermic circulatory arrest and retrograde cerebral perfusion for aortic root combined with right half aortic arch replacement. METHODS: Clinical data of 31 patients, who underwent aortic root and right half aortic arch replacement with deep hypothermic circulatory arrest and retrograde cerebral perfusion in Xiangya Hospital, Central South University, were retrospectively analyzed. This cohort included 23 aortic aneurysms and 8 aortic dissections. Aortic root replacement was conducted in 26 patients by Bentall procedures, and 5 patients by David procedures. Time of deep hypothermic circulatory arrest and retrograde cerebral perfusion in surgery was (21.9±5.2) min. The in-hospital mortality, postoperative neurological dysfunction and other major adverse complications were observed and recorded. RESULTS: No in-hospital death and permanent neurological dysfunction occurred. Two patients had transient neurological dysfunction and 2 patients with aortic dissection requiring long-time ventilation due to hypoxemia, 1 patient underwent resternotomy. During 6-36 months of follow-up, all patients recovered satisfactorily. CONCLUSIONS: Deep hypothermic circulatory arrest and retrograde cerebral perfusion can be safely and effectively applied in aortic root and right half aortic arch replacement, and which can simplify the surgical procedures and be worth of clinical promotion.

New frontiers in aortic therapy: focus on deep hypothermic circulatory arrest.

There is currently a paradigm shift in the conduct of adult aortic arch repair. Although deep hypothermic circulatory arrest has been the classic perfusion platform for adult aortic arch repair, recent developments have challenged this aortic arch paradigm. There has been a gradual clinical drift towards moderate, and even mild, hypothermic circulatory arrest combined with antegrade cerebral perfusion. This paradigm shift appears to be associated with equivalent clinical outcomes, and in certain settings, with improved outcomes. The advent of endovascular therapy has challenged even further the concept that circulatory arrest is required for adult aortic arch repair. These dramatic advances have resulted in the emergence of an international aortic arch surgery study group that aims to advance this dynamic field through consensus statements, meta-analysis, clinical database analysis, prospective registries, and randomized controlled trials.

Retrograde cerebral perfusion reduces embolic and watershed lesions after acute type a aortic dissection repair with deep hypothermic circulatory arrest.

BACKGROUND: To assess whether retrograde cerebral perfusion reduces neurological injury and mortality in patients undergoing surgery for acute type A aortic dissection. METHODS: Single-center, retrospective, observational study including all patients undergoing acute type A aortic dissection repair with deep hypothermic circulatory arrest between January 1998 and December 2022 with or without the adjunct of retrograde cerebral perfusion. 515 patients were included: 257 patients with hypothermic circulatory arrest only and 258 patients with hypothermic circulatory arrest and retrograde cerebral perfusion. The primary endpoints were clinical neurological injury, embolic lesions, and watershed lesions. Multivariable logistic regression was performed to identify independent predictors of the primary outcomes. Survival analysis was performed using Kaplan-Meier estimates. RESULTS: Clinical neurological injury and embolic lesions were less frequent in patients with retrograde cerebral perfusion (20.2% vs. 28.4%, p = 0.041 and 13.7% vs. 23.4%, p = 0.010, respectively), but there was no significant difference in the occurrence of watershed lesions (3.0% vs. 6.1%, p = 0.156). However, after multivariable logistic regression, retrograde cerebral perfusion was associated with a significant reduction of clinical neurological injury (OR: 0.60; 95% CI 0.36-0.995, p = 0.049), embolic lesions (OR: 0.55; 95% CI 0.31-0.97, p = 0.041), and watershed lesions (OR: 0.25; 95%CI 0.07-0.80, p = 0.027). There was no significant difference in 30-day mortality (12.8% vs. 11.7%, p = ns) or long-term survival between groups. CONCLUSION: In this study, we showed that the addition of retrograde cerebral perfusion during hypothermic circulatory arrest in the setting of acute type A aortic dissection repair reduced the risk of clinical neurological injury, embolic lesions, and watershed lesions.

Persistent left superior vena cava in right hemiarch replacement under deep hypothermic circulatory arrest: A case report.

BACKGROUND: Persistent left superior vena cava (PLSVC), a relatively rare thoracic vascular malformation, can inconvenience perfusionists and operators when encountered during deep hypothermic circulatory arrest (DHCA). CASE SUMMARY: Herein, we describe the case of a patient with concurrent giant aortic arch aneurysm, aortic stenosis, and PLSVC. To treat these conditions, we performed right hemiarch and aortic valve replacements under DHCA. Notably, we applied "bilateral superior vena cava retrograde cerebral perfusion (RCP)" for cerebral protection, which significantly optimized the surgical procedure and reduced the risk of postoperative complications. The patient was discharged 14 d after surgery with no complications. CONCLUSION: Surgical intervention for PLSVC under DHCA can be performed using the bilateral superior vena cava RCP approach.

Intraoperative neurophysiologic monitoring during aortic arch surgery.

OBJECTIVE: To evaluate the ability of intraoperative neurophysiologic monitoring (IONM) during aortic arch reconstruction with hypothermic circulatory arrest (HCA) to predict early (<48 hours) adverse neurologic events (ANE; stroke or transient ischemic attack) and operative mortality. METHODS: This was an observational study of aortic arch surgeries requiring HCA from 2010 to 2018. Patients were monitored with electroencephalogram (EEG) and somatosensory evoked potentials (SSEP). Baseline characteristics and postoperative outcomes were compared according to presence or absence of IONM changes, which were defined as any acute variation in SSEP or EEG, compared with baseline. Multivariable logistic regression analysis was used to assess the association of IONM changes with operative mortality and early ANE. RESULTS: A total of 563 patients underwent aortic arch reconstruction with HCA and IONM. Of these, 119 (21.1%) patients had an IONM change, whereas 444 (78.9%) did not. Patients with IONM changes had increased operative mortality (22.7% vs 4.3%) and increased early ANE (10.9% vs 2.9%). In multivariable analysis, SSEP changes were correlated with early ANE (odds ratio [OR], 4.68; 95% confidence interval [CI], 1.51-14.56; P = .008), whereas EEG changes were not (P = .532). Permanent SSEP changes were correlated with early ANE (OR, 4.56; 95% CI, 1.51-13.77; P = .007), whereas temperature-related SSEP changes were not (P = .997). Finally, any IONM change (either SSEP or EEG) was correlated with operative mortality (OR, 5.82; 95% CI, 2.72-12.49; P < .001). CONCLUSIONS: Abnormal IONM events during aortic arch reconstruction with HCA portend worse neurologic outcomes and operative mortality and have a negative predictive value of 97.1%. SSEP might be more sensitive than EEG for predicting early ANE, especially when SSEP changes are permanent.

Long-term outcomes of hemiarch replacement with hypothermic circulatory arrest and retrograde cerebral perfusion.

OBJECTIVE: This study sought to report outcomes of hemiarch replacement with hypothermic circulatory arrest and retrograde cerebral perfusion, and secondarily, to report outcomes of this operative approach by type of underlying aortic disease. METHODS: This was an observational study of aortic surgeries from 2010 to 2018. All patients who underwent hemiarch replacement with retrograde cerebral perfusion were included, whereas patients undergoing partial or total arch replacement or concomitant elephant trunk procedures were excluded. Patients were dichotomized into 2 groups by underlying aortic disease; that is, acute aortic dissection (AAD) or aneurysmal degeneration of the aorta. These groups were analyzed for differences in short-term postoperative outcomes, including stroke and operative mortality (Society of Thoracic Surgeons definition). Multivariable Cox analysis was performed to identify variables associated with long-term survival after hemiarch replacement. RESULTS: A total of 500 patients undergoing hemiarch replacement with hypothermic circulatory arrest plus retrograde cerebral perfusion were identified, of whom 53.0% had aneurysmal disease and 47.0% had AAD. For the entire cohort, operative mortality was 6.4%, whereas stroke occurred in 4.6% of patients. Comparing AAD with aneurysm, operative mortality and stroke rates were similar across each group. Five-year survival was 84.4% ± 0.02% for the entire hemiarch cohort, whereas 5-year survival was 88.0% ± 0.02% for the aneurysm subgroup and was 80.5% ± 0.03% for the AAD subgroup. On multivariable analysis, AAD was not associated with an increased hazard of death, compared with aneurysm (P = .790). CONCLUSIONS: Morbidity and mortality after hemiarch replacement with hypothermic circulatory arrest plus retrograde cerebral perfusion are acceptably low, and this operative approach may be as advantageous for AAD as it is for aneurysm.

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.

Optimal brain protection in aortic arch surgery.

There is considerable debate with regard to the optimal cerebral protection strategy during aortic arch surgery. There are three contemporary techniques in use which include straight deep hypothermic circulatory arrest (DHCA), DHCA with retrograde cerebral perfusion (DHCA + RCP), and moderate hypothermic circulatory arrest with antegrade cerebral perfusion (MHCA + ACP). Appropriate application of these methods ensures appropriate cerebral, myocardial, and visceral protection. Each of these techniques has benefits and drawbacks and ensuring coordinated circulation management strategy is critical to safe performance of aortic arch surgery. In this report, we will review various cannulation strategies, review logistics of hypothermia, and review the relevant literature to outline the strengths and weaknesses of these various cerebral protection strategies.

Aortic and arch branch vessel cannulation in acute type A aortic dissection repair.

Objective: To evaluate central aortic cannulation and arch branch vessel (ABV) cannulation in acute type A aortic dissection repair. Methods: From 2015 to April 2020, 298 patients underwent open repair of an acute type A aortic dissection. Patients undergoing femoral cannulation for cardiopulmonary bypass (n = 34) were excluded. Patients were then divided based on initial cannulation for cardiopulmonary bypass into central aortic cannulation (n = 72) and ABV cannulation (n = 192) groups. ABV sites included cannulation of the axillary, innominate, right/left common carotid, and intrathoracic right subclavian arteries. Results: The aortic cannulation group was younger (59 vs 62 years; P = .02), more likely to be men (76% vs 60%; P = .02), and had more peripheral vascular disease (60% vs 37%; P = .0009). ABV dissection was similar between central and ABV cannulation groups (53% vs 60%; P = .51). The aortic cannulation group underwent less aggressive arch replacement, had shorter cardiopulmonary bypass times (200 vs 222 minutes; P = .01), less utilization of antegrade cerebral perfusion (93% vs 98%; P = .04), and received less blood transfusion (0 vs 1 U; P = .001). Postoperative outcomes were similar between aortic and ABV cannulation groups, including stroke (5.6% vs 5.2%; P = 1.0) and operative mortality (4.2% vs 6.3%; P = .77). In addition, postoperative strokes were similar in location (right-brain, left-brain, or bilateral), etiology (embolic vs hemorrhagic), and presence of permanent deficits. Aortic cannulation was not a risk factor for postoperative stroke (odds ratio, 0.94; P = .91) or operative mortality (odds ratio, 0.70; P = .64). Short-term survival was similar between central and ABV cannulation groups. Conclusions: Both aortic and ABV cannulation were safe and effective cannulation strategies in acute type A aortic dissection repair.

Rapid cooling is a safe technique in patients undergoing circulatory arrest for aortic repair.

Objective: To evaluate our institutional experience with rapid cooling for hypothermic circulatory arrest in proximal aortic repair. Methods: We retrospectively reviewed data from 2171 patients who underwent proximal aortic surgery requiring hypothermic circulatory arrest between 1991 and 2020. Cooling times were divided into quartiles and clinical outcome event rates were compared across quartiles using contingency table methods. Incremental effect of cooling time was assessed in the context of other perfusion time variables using multiple logistic regression analysis. Results: Median age was 61 years (interquartile range, 49-70 years) and 34.1% of patients were women. The procedure was emergent in 33.5% of patients, 22.9% had a previous sternotomy. The median circulatory arrest time was 22 minutes, with retrograde cerebral perfusion used in 94% of cases. Median cardiopulmonary bypass time was 149 minutes, with an aortic crossclamp time of 90 minutes. Patients were cooled to deep hypothermia. The first quartile had cooling times ranging from 5 to 13 minutes, second 14 to 18 minutes, third 19-23 minutes, and fourth 24-81 minutes. Overall, 30-day mortality was 9.4%, and was not significantly different across quartiles. There was a statistically significant trend toward lower rates of postoperative encephalopathy, gastrointestinal complications, and respiratory failure with shorter cooling times (P < .001, .006, and < .001, respectively). There was no significant difference in rates of postoperative stroke or dialysis. Conclusions: Rapid cooling can be performed safely in patients undergoing aortic surgery requiring circulatory arrest without increasing mortality or stroke. There were significantly lower rates of coagulopathy, respiratory failure, and postoperative encephalopathy with shorter cooling times.

Retrograde cerebral perfusion for surgery of type A aortic dissection.

BACKGROUND: For type A aortic dissection (TAAD), antegrade cerebral perfusion (ACP) was proposed as a more physiological method than retrograde cerebral perfusion (RCP) for intra-operative brain protection, but it is still debatable whether antegrade cerebral perfusion (ACP) or retrograde cerebral perfusion (RCP) is related to the better clinical outcome. The present study was undertaken to compare the results in our patients receiving surgery for TAAD with ACP or RCP. The primary aim of this study was focused on the incidence of and the factors associated with surgical mortality, post-operative neurological outcomes and long-term survival. METHODS: From February 2001 to March 2019, there were 223 consecutive patients with TAAD treated surgically at our hospital. The median age at presentation was 56 years (range 29-88 years) and 70 patients (31.4%) over 65 years of age. There were 168 patients treated with RCP and 55 patients treated with ACP. The primary endpoints were surgical mortality and neurological outcome. Propensity score matching was used to compare the treatment results of surgeries with RCP or ACP. The long-term survival was also analyzed. RESULTS: The overall in-hospital mortality rate and the overall 30-day mortality rate were 15.6% and 14.3% respectively. For the patients without pre-operative shock (n = 184), the in-hospital mortality rate was 10.3% and the 30-day mortality rate was 8.7% and higher long-term survival rates (88.3% for 5 years, 86.5% for 10 years, 86.5% for 15 years) were documented for this patient group. There was no significant difference on the surgical mortality between the ACP group and the RCP group. In the entire cohort, there were 23 patients (10.3%) who suffered from post-operative neurological deficits (PND) and there were less PND for the patients with RCP than the patients with ACP (7.7% vs 18.1%, p = 0.027). After propensity score matching, there was still higher incidence of PND in the ACP group than in the RCP group but without statistical significance (18.5% vs 11.1%, p = 0.279). CONCLUSIONS: Aortic surgery carries high risk for the patients with TAAD and PND is not an unusual post-operative morbidity. In our series, pre-operative shock, pre-operative CPR, CRI, past history with CAD are related to higher surgical mortality. The younger patients (<65 years old) without pre-operative shock got better surgical outcome and long-term survival. RCP could provide acceptable cerebral protection during aortic surgery for the TAAD patients. Old age, pre-operative shock, CRI and past history of CAD are independent risk factors for long-term survival.

The role of diffuse correlation spectroscopy and frequency-domain near-infrared spectroscopy in monitoring cerebral hemodynamics during hypothermic circulatory arrests.

OBJECTIVES: Real-time noninvasive monitoring of cerebral blood flow (CBF) during surgery is key to reducing mortality rates associated with adult cardiac surgeries requiring hypothermic circulatory arrest (HCA). We explored a method to monitor cerebral blood flow during different brain protection techniques using diffuse correlation spectroscopy (DCS), a noninvasive optical technique which, combined with frequency-domain near-infrared spectroscopy (FDNIRS), also provides a measure of oxygen metabolism. METHODS: We used DCS in combination with FDNIRS to simultaneously measure hemoglobin oxygen saturation (SO2), an index of cerebral blood flow (CBFi), and an index of cerebral metabolic rate of oxygen (CMRO2i) in 12 patients undergoing cardiac surgery with HCA. RESULTS: Our measurements revealed that a negligible amount of blood is delivered to the cerebral cortex during HCA with retrograde cerebral perfusion, indistinguishable from HCA-only cases (median CBFi drops of 93% and 95%, respectively) with consequent similar decreases in SO2 (mean decrease of 0.6 ± 0.1% and 0.9 ± 0.2% per minute, respectively); CBFi and SO2 are mostly maintained with antegrade cerebral perfusion; the relationship of CMRO2i to temperature is given by CMRO2i = 0.052e0.079T. CONCLUSIONS: FDNIRS-DCS is able to detect changes in CBFi, SO2, and CMRO2i with intervention and can become a valuable tool for optimizing cerebral protection during HCA.

Intraoperative inadvertent piercing of the aortic arch: case report.

Aortic injury is a rarely encountered complication of spinal surgery. The authors report a case of a 32-year-old woman with a T3 tumor who experienced an intraoperative aortic arch injury during T3 spondylectomy. The patient was successfully treated with no postoperative neurological deficits.

Optimal Cerebral Protection Strategies in Aortic Surgery.

Cerebral protection strategies in aortic surgery have undergone significant evolution over the years, but its tenets remain rooted in maintenance of hypothermia and cerebral perfusion to limit adverse neurologic outcomes. While deep hypothermic circulatory arrest alone remains a viable approach in many instances, the need for prolonged duration of circulatory arrest and increasing case complexity have driven the utilization of adjunctive cerebral perfusion strategies. In this review, we present the most recent studies published on this topic over the last few years investigating the efficacy of deep hypothermic circulatory arrest, retrograde cerebral perfusion, and unilateral and bilateral antegrade cerebral perfusion, as well as the emerging trend toward mild and moderate HCA temperatures. We highlight the ongoing controversies in the field that underscore the need for large-scale randomized trials using well-defined neurologic endpoints to optimize evidence-based practice in cerebral protection.

Simple retrograde cerebral perfusion is as good as complex antegrade cerebral perfusion for hemiarch replacement.

Cerebral complication is a major concern after aortic arch surgery, which may lead to death. Thus, cerebral protection strategy plays the key role to obtain respectable results in aortic arch repair. Deep hypothermic circulatory arrest was introduced in 1970s to decrease the ischemic insults to the brain. However, safe duration of circulatory arrest time was limited to 30 minutes. The 1990s was the decade of evolution for cerebral protection, in which two adjuncts for deep hypothermic circulatory arrest were introduced: retrograde and antegrade cerebral perfusion (ACP) techniques. These two cerebral perfusion techniques significantly decreased incidence of postoperative neurological dysfunction and mortality after aortic arch surgery. Although there are no large prospective studies that demonstrate which perfusion technique provide better outcomes, multiple retrospective studies implicate that ACP may decrease cerebral complications compared to retrograde cerebral perfusion (RCP) when a long circulatory arrest time is required during aortic arch reconstructions. To date, many surgeons favor ACP over RCP during a complex aortic arch repair, such as total arch replacement and hybrid arch replacement. However, the question is whether the use of ACP is necessary during a short, limited circulatory arrest time, such as hemiarch replacement? There is a paucity of data that proves the advantages of a complex ACP over a simple RCP for a short circulatory arrest time. RCP with deep hypothermic circulatory arrest is the simple, efficient cerebral protection technique with minimal interference to the surgical field-and it potentially allows to flush atheromatous debris out from the arch vessels. Thus, it is the preferred adjunct to deep hypothermic circulatory arrest during hemiarch replacement in our institution.