Impact of pump flow rate during selective cerebral perfusion on cerebral hemodynamics and metabolism

Development and validation of a prediction model for postoperative ischemic stroke following total arch replacement and frozen elephant trunk under mild hypothermia

Background

Early identification of postoperative ischemic stroke among patients with acute DeBakey type I aortic dissection (ADIAD) is of great significance to taking timely effective treatment. We aimed to develop and validate a prediction model for postoperative ischemic stroke in ADIAD patients who underwent total arch replacement (TAR) and frozen elephant trunk (FET) under mild hypothermia.

Methods

ADIAD patients who underwent TAR and FET between January 2017 and April 2023 were enrolled in our study. Preoperative and intraoperative variables were selected using pairwise comparisons, the Least Absolute Shrinkage and Selection Operator (LASSO), and logistic regression to construct a prediction model for postoperative ischemic stroke. The accuracy and calibration of the model were assessed using 1000 bootstrap resamples for internal validation, with the area under the receiver operating characteristic curve (AUC) and the Hosmer-Lemeshow test. The AUC was also used to evaluate the model's accuracy in the validation cohort.

Results

The development cohort included 246 patients. The mean [standard deviation (SD)] age of patients in the cohort was 50.7 (11.2) years, 196 (79.7%) were men, and 22 (8.9%) were diagnosed with postoperative ischemic stroke. The validation cohort included 73 patients with a mean (SD) age of 52.5 (11.9) years, 58 (79.5%) were men and 3 (4.1%) were diagnosed with postoperative ischemic stroke. Three variables out of the initial 40 potential predictors were included in the final prediction model: the platelet count [odd ratio (OR), 0.992; 95% confidence interval (CI), 0.983-1.000], the presence of innominate artery dissection (OR, 3.400; 95% CI, 1.027-11.260), and the flow of selective cerebral perfusion (OR, 0.147; 95% CI, 0.046-0.469). The mean AUC in the development cohort was 0.77 (95% CI, 0.68-0.87), and calibration was checked with the Hosmer-Lemeshow test (P = 0.78). In the validation cohort, the AUC was 0.98 (95% CI, 0.94-1.00). A prediction model and a clinical impact curve were developed for practical purposes.

Conclusions

In this study, we have developed a prediction model with competent discriminative ability and calibration. This model can be used for early assessment of the risk of postoperative ischemic stroke in patients with ADIAD following TAR and FET under mild hypothermia.

Optimal antegrade cerebral perfusion flow in patients undergoing surgery for acute type A aortic dissection: A retrospective single-center analysis

BACKGROUND

Systemic hypothermia with bilateral antegrade selective cerebral perfusion (ASCP) is the preferred cerebral protective strategy for type A aortic dissection surgery. The optimal ASCP flow rate remains uncertain and the target flow cannot always be reached due to pressure limitations. The aim of this study was to assess the correlation between ASCP flow and regional cerebral oxygen saturation (rSO2).

METHODS

A retrospective analysis was performed on 140 patients with acute type A aortic dissection who underwent surgery with moderate hypothermic circulatory arrest and bilateral ASCP between 2015 and 2021. Pearson correlation analysis was performed between ASCP flow and rSO2.

RESULTS

The median circulatory arrest duration was 46.5 (IQR:37.0-61.0) minutes. There was no significant correlation between ASCP flow and rSO2 for both the right (r = -.02, p = .851), and the left hemisphere (r = - .04, p = .618). The rSO2 values for ten patients who received > 10 mL/kg/min flow did not differ significantly from 130 patients who received 10 mL/kg/min or less for both the left hemisphere (p = .135), and the right hemisphere (p = .318). The ASCP flow was 5.1 (IQR:5.0- 6.5) mL/kg/min in five patients with, and 7.2 (IQR:5.8-8.3) mL/kg/min in 135 patients without a watershed infarction (p = .098).

CONCLUSIONS

There was no correlation between ASCP flow rate and rSO2 in patients with acute type A aortic dissection. Furthermore, ASCP flow below 10 mL/kg/min was not associated with a reduction in rSO2. Definitive associations between ASCP flow and neurological outcome after type A aortic dissection surgery need further investigation.

Neuroprotection during Open Aortic Arch Surgery: Cerebral Perfusion Methods and Temperature

Neuroprotection is important in open aortic arch surgery because of the dependence of brain tissues on cerebral perfusion. Therefore, several techniques have been developed to reduce cerebral ischemia and improve outcomes in open aortic arch surgery. In this review, I describe various neuroprotective strategies, such as profound and deep hypothermic circulatory arrest, selective antegrade cerebral perfusion, retrograde cerebral perfusion, and lower body circulatory arrest; compare their advantages and disadvantages, and discuss their evolution and current status by reviewing relevant literature.

Elective aortic arch surgery: cerebral perfusion flows and transient neurological dysfunctions

AIMS

Selective antegrade cerebral perfusion technique is a method of cerebral protection used worldwide during aortic arch surgery. This study was designed to identify a potential correlation between perfusion flows and the development of postoperative transient neurological dysfunctions.

METHODS

From January 2015 to May 2020, 175 patients underwent elective surgical replacement of the aortic arch using selective antegrade cerebral perfusion at the Cardiac Surgery Unit of Sant'Orsola Hospital in Bologna. Considering that patients who developed a permanent neurological dysfunction and those who died before a possible evaluation of neurological status were excluded, the study population included 160 patients. The perfusion flows were collected and analyzed. Univariate and multivariate analyses were performed to identify the statistical risk factors involved in the onset of transient neurological dysfunctions.

RESULTS

The study population was divided into two groups: 138 patients (86.3%) without and 22 (13.8%) with postoperative transient neurological complications. Among the intra-operative parameters collected in the study, the univariate analysis showed that the indexed medium perfusion flow of selective antegrade cerebral perfusion was significantly lower in the transient neurological dysfunctions group (11.63 ± 2.41 ml/kg/min vs 12.62 ± 2.39 ml/kg/min, P -value = 0.03). The multivariate logistic regression analysis showed that the female gender ( P  = 0.004, OR = 4.816, IC = 1.636-14.174) was predictor of transient neurological dysfunctions.

CONCLUSION

The results of the study showed that lower perfusion flows seem to be related to a higher probability of developing transient neurological dysfunctions. However, the analysis of a wider population is required to confirm these preliminary data.

Effects of circulatory arrest and cardiopulmonary bypass on cerebral autoregulation in neonatal swine

BACKGROUND

Cerebral autoregulation mechanisms help maintain adequate cerebral blood flow (CBF) despite changes in cerebral perfusion pressure. Impairment of cerebral autoregulation, during and after cardiopulmonary bypass (CPB), may increase risk of neurologic injury in neonates undergoing surgery. In this study, alterations of cerebral autoregulation were assessed in a neonatal swine model probing four perfusion strategies.

METHODS

Neonatal swine (n = 25) were randomized to continuous deep hypothermic cardiopulmonary bypass (DH-CPB, n = 7), deep hypothermic circulatory arrest (DHCA, n = 7), selective cerebral perfusion (SCP, n = 7) at deep hypothermia, or normothermic cardiopulmonary bypass (control, n = 4). The correlation coefficient (LDx) between laser Doppler measurements of CBF and mean arterial blood pressure was computed at initiation and conclusion of CPB. Alterations in cerebral autoregulation were assessed by the change between initial and final LDx measurements.

RESULTS

Cerebral autoregulation became more impaired (LDx increased) in piglets that underwent DH-CPB (initial LDx: median 0.15, IQR [0.03, 0.26]; final: 0.45, [0.27, 0.74]; p = 0.02). LDx was not altered in those undergoing DHCA (p > 0.99) or SCP (p = 0.13). These differences were not explained by other risk factors.

CONCLUSIONS

In a validated swine model of cardiac surgery, DH-CPB had a significant effect on cerebral autoregulation, whereas DHCA and SCP did not.

IMPACT

Approximately half of the patients who survive neonatal heart surgery with cardiopulmonary bypass (CPB) experience neurodevelopmental delays. This preclinical investigation takes steps to elucidate and isolate potential perioperative risk factors of neurologic injury, such as impairment of cerebral autoregulation, associated with cardiac surgical procedures involving CPB. We demonstrate a method to characterize cerebral autoregulation during CPB pump flow changes in a neonatal swine model of cardiac surgery. Cerebral autoregulation was not altered in piglets that underwent deep hypothermic circulatory arrest (DHCA) or selective cerebral perfusion (SCP), but it was altered in piglets that underwent deep hypothermic CBP.

Protection of multiple ischemic organs by controlled reperfusion

Reperfusion injury (RI) is a harmful complication that takes place during recanalization treatment of ischemic organs. Currently, there are no efficacious treatments for protecting the organs against RI. Therefore, it is necessary to discover new strategies to prevent RI. As a novel intervention technique, controlled reperfusion has promising effects on protecting multiple organs from RI, and it is done by adjusting physical parameters of blood flow or chemical compositions of the reperfusion liquid. In this brief review, the status of various controlled reperfusion methods is presented, as well as their application in the protection of ischemic organs.

Different hypothermic and cerebral perfusion strategies in extended arch replacement for acute type a aortic dissection: a retrospective comparative study

BACKGROUND

The optimal hypothermic level in total arch replacement with stented elephant trunk implantation for acute type A aortic dissection (aTAAD) has not been established, and the superiority of unilateral or bilateral cerebral perfusion remains a controversial issue. Therefore, we evaluated the application of moderate hypothermic circulatory arrest (MHCA) with a core temperature of 29 °C and bilateral selective antegrade cerebral perfusion in aTAAD treated by total arch replacement with stented elephant trunk implantation.

METHODS

From July 2019 to January 2020, 25 aTAAD patients underwent total arch replacement with stented elephant trunk implantation via MHCA (29 °C) and bilateral selective antegrade cerebral perfusion (modified group). Thirty-six patients treated by the same procedure with MHCA (25 °C) and unilateral selective antegrade cerebral perfusion during this period were selected as controls.

RESULTS

There were no differences between the two groups of patients in terms of age, sex, incidence of hypertension, malperfusion, and pericardial effusion, although the incidence of cardiac tamponade was higher in the modified group (control 2.8%, modified 20%; P = 0.038). The lowest mean circulatory arrest temperature was 24.6 ± 0.9 °C in the control group, and 29 ± 0.8 °C in the modified group (P <  0.001). In-hospital mortality was 4.9% (3/61) for the entire cohort (control 8.3%, modified 0; P = 0.262). The incidence of permanent neurologic deficit was 4.9% (control 8.3%, modified 0; P = 0.262). There were no significant differences in the occurrence of temporary neurological deficit, renal failure, and paraplegia between groups. The rate of major adverse events in the modified group was lower (30.6% vs. 4%, P = 0.019). A shorter duration of ventilation and ICU stay was identified in the modified group, as well as a reduced volume of drainage within the first 48 h and red blood cell transfusion.

CONCLUSIONS

The early results of MHCA (29 °C) and bilateral selective antegrade cerebral perfusion applied in total arch replacement with stented elephant trunk implantation for aTAAD were acceptable, providing similar inferior cerebral and visceral protection compared with that of the conventional strategy. A higher core temperature may account for the shorter duration of ventilation and ICU stay, as well as a reduced volume of drainage and red blood cell transfusion.

Impact of Regional Cerebral Perfusion on Outcomes Among Neonates Undergoing Norwood Operation

OBJECTIVES

To evaluate the impact of regional cerebral perfusion (RCP) during heart operation on outcomes in neonates undergoing Norwood operation.

METHODS

We performed a retrospective cohort study using data from the Single Ventricle Reconstruction trial data set. The adjusted effect of RCP use on each outcome was studied using a penalized logistic regression model with bootstrap validation.

RESULTS

Of 549 patients included in the study, 252 patients (45.9%) received RCP during their heart operation. In univariate comparisons, the majority of the baseline characteristics and preoperative risk factors were similar in the RCP and No RCP group. The total cardiopulmonary bypass (CPB) time and the total cross-clamp (CC) time were longer in the RCP group (RCP vs No RCP, median CPB time: 161 minutes vs 109 minutes; median CC time: 63 minutes vs 43 minutes). In adjusted models, the use of RCP was not associated with decreased mortality and/or need for heart transplant at hospital discharge (odds ratio [OR]: 0.73; 95% confidence interval [CI]: 0.43-1.25) or prolonged mechanical ventilation (OR: 1.20, 95% CI: 0.62-2.28) or prolonged hospital length of stay (OR: 1.30, 95% CI: 0.73-2.30). We demonstrated that use of RCP was associated with longer CPB times, increased use of ultrafiltration, and higher probability of open chest after Norwood operation.

CONCLUSIONS

This study did not demonstrate any impact of RCP on in-hospital mortality and/or heart transplantation, prolonged mechanical ventilation, and prolonged hospital length of stay among neonates undergoing Norwood operation.

Relative cerebral hyperperfusion during cardiopulmonary bypass is associated with risk for postoperative delirium: a cross-sectional cohort study

Background

Our objective was to evaluate if changes in on-pump cerebral blood flow, relative to the pre-bypass baseline, are associated with the risk for postoperative delirium (POD) following cardiac surgery.

Methods

In 47 consecutive adult patients, right middle cerebral artery blood flow velocity (MCAV) was assessed using transcranial Doppler sonography. Individual values, measured during cardiopulmonary bypass (CPB), were normalized to the pre-bypass baseline value and termed MCAV_rel. An MCAV_rel > 100% was defined as cerebral hyperperfusion. Prevalence of POD was assessed using the Confusion Assessment Method for the Intensive Care Unit.

Results

Overall prevalence of POD was 27%. In the subgroup without POD, 32% of patients had experienced relative cerebral hyperperfusion during CPB, compared to 67% in the subgroup with POD (p < 0.05). The mean averaged MCAV_rel was 90 (±21) % in the no-POD group vs. 112 (±32) % in the POD group (p < 0.05), and patients developing delirium experienced cerebral hyperperfusion during CPB for about 39 (±35) min, compared to 6 (±11) min in the group without POD (p < 0.001). In a subcohort with pre-bypass baseline MCAV (MCAV_bas) below the median MCAV_bas of the whole cohort, prevalence of POD was 17% when MCAV_rel during CPB was kept below 100%, but increased to 53% when these patients actually experienced relative cerebral hyperperfusion.

Conclusions

Our results suggest a critical role for cerebral hyperperfusion in the pathogenesis of POD following on-pump open-heart surgery, recommending a more individualized hemodynamic management, especially in the population at risk.

Electronic supplementary material

The online version of this article (10.1186/s12871-019-0705-y) contains supplementary material, which is available to authorized users.

Neuroprotective effect of pressure-oriented flow regulation and pH-stat management in selective antegrade brain perfusion during total aortic arch repair

OBJECTIVES

The aim of this study was to assess the safety and effectiveness of our selective antegrade brain perfusion (SABP) strategy, which is characterized by moderate hypothermic and low-pressure management under pH-stat using a completely closed cardiopulmonary bypass circuit with a single centrifugal pump.

METHODS

Forty-nine consecutive patients (median age, 74) underwent total aortic arch replacement using a 4-branched graft. SABP was conducted with individual cannulation in all arch vessels. The SABP flow rate was monitored, and the flow rates of each arch vessel were also measured in patients with available data.

RESULTS

One patient died of cerebral infarction, and 7 had transient neurological deficits without apparent findings on postoperative imaging studies and without residual sequels at hospital discharge. The operation, cardiopulmonary bypass, cardiac arrest, circulatory arrest and SABP times were 327 min (interquartile range, 292-381), 211 (184-247), 107 (84.8-138.3), 54.0 (48-68) and 137 (114-158), respectively. The total flow of the SABP was 18.1 ml/kg/min (15.7-20.9). The flow rates of the brachiocephalic, the left carotid and the left subclavian arteries were 9.5 ml/kg/min (7.7-11.5), 4.2 (2.8-5.7) and 4.5 (3.7-5.5), respectively. Only the flow rate of the brachiocephalic artery was significantly correlated with the total SABP flow rate (Spearman rank correlation coefficient, r = 0.58, P < 0.01).

CONCLUSIONS

The moderate hypothermic, high-flow, low-pressure SABP strategy with pH-stat management can be applied in adult aortic surgery; however, the feasibility and effectiveness of this concept need further evaluation in a prospective controlled study.

Aortic Surgery and Deep-Hypothermic Circulatory Arrest: Anesthetic Update

Aortic arch surgery has become increasingly complex, and novel surgical approaches have been utilized. Efforts aimed at improving neurological outcomes in this patient population have been numerous, with varying degrees of success. This article summarizes the anesthetic considerations for procedures on the aortic arch, including evidence-based outcomes with respect to temperature management, perfusion strategies, hemodynamic goals, adjunct agents, and neuromonitoring.

Blood Flow Quantitation by Positron Emission Tomography During Selective Antegrade Cerebral Perfusion

BACKGROUND

Perfusion strategies during aortic surgery usually comprise hypothermic circulatory arrest (HCA), often combined with selective antegrade cerebral perfusion (SACP) or retrograde cerebral perfusion. Cerebral blood flow (CBF) is a fundamental parameter for which the optimal level has not been clearly defined. We sought to determine the CBF at a pump flow level of 6 mL/kg/min, previously shown likely to provide adequate SACP at 20°C in pigs.

METHODS

Repeated positron emission tomography (PET) scans were used to quantify the CBF and glucose metabolism throughout HCA and SACP including cooling and rewarming. Eight pigs on cardiopulmonary bypass were assigned to either HCA alone (n = 4) or HCA+SACP (n = 4). The CBF was measured by repeated [¹⁵O]water PET scans from baseline to rewarming. The cerebral glucose metabolism was examined by [¹⁸F]fluorodeoxyglucose PET scans after rewarming to 37°C.

RESULTS

Cooling to 20°C decreased the cortical CBF from 0.31 ± 0.06 at baseline to 0.10 ± 0.02 mL/cm³/min (p = 0.008). The CBF was maintained stable by SACP of 6 mL/kg/min during 45 minutes. After rewarming to 37°C, the mean CBF increased to 0.24 ± 0.07 mL/cm³/min, without significant differences between the groups at any time-point exclusive of the HCA period. The net cortical uptake (K_i) of [¹⁸F]fluorodeoxyglucose after rewarming showed no significant difference between the groups.

CONCLUSIONS

Cooling autoregulated the CBF to 0.10 mL/cm³/min, and 45 minutes of SACP at 6 mL/kg/min maintained the CBF in the present model. Cerebral glucose metabolism after rewarming was similar in the study groups.

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.

How to Perfuse: Concepts of Cerebral Protection during Arch Replacement

Arch surgery remains undoubtedly among the most technically and strategically challenging endeavors in cardiovascular surgery. Surgical interventions of thoracic aneurysms involving the aortic arch require complete circulatory arrest in deep hypothermia (DHCA) or elaborate cerebral perfusion strategies with varying degrees of hypothermia to achieve satisfactory protection of the brain from ischemic insults, that is, unilateral/bilateral antegrade cerebral perfusion (ACP) and retrograde cerebral perfusion (RCP). Despite sophisticated and increasingly individualized surgical approaches for complex aortic pathologies, there remains a lack of consensus regarding the optimal method of cerebral protection and circulatory management during the time of arch exclusion. Many recent studies argue in favor of ACP with various degrees of hypothermic arrest during arch reconstruction and its advantages have been widely demonstrated. In fact ACP with more moderate degrees of hypothermia represents a paradigm shift in the cardiac surgery community and is widely adopted as an emergent strategy; however, many centers continue to report good results using other perfusion strategies. Amidst this important discussion we review currently available surgical strategies of cerebral protection management and compare the results of recent European multicenter and single-center data.

Effects of phentolamine infusion during selective cerebral perfusion in neonatal piglets

BACKGROUND

An optimal selective cerebral perfusion protocol in pediatric cardiac surgery is unknown. Phentolamine is frequently used in pediatric cardiopulmonary bypass. We sought to determine the effects of continuous phentolamine infusion during selective cerebral perfusion.

METHODS

Twenty-seven neonatal piglets (3.38 ± 0.32 kg) were randomly assigned to 3 groups; sham (n = 7, anesthesia alone, no surgery or bypass), control (n = 10, saline infusion), or experimental (n = 10, phentolamine infusion 0.1 mg/kg per hour). Animals underwent 90 minutes of selective cerebral perfusion. Cerebral vascular resistance index (CVRI) and metabolic rate of oxygen (CMRO2) were determined every 15 minutes. Standardized sections of hippocampus, basal ganglia, and neo-cortex were obtained. Tissue samples were stained for caspase-3 and analyzed for positive apoptotic cell count. Data were analyzed with repeated measures and one-way analysis of variance.

RESULTS

The CVRI tended to increase over time in the control group and decrease over time in the experimental group, but difference was not statically significant (0.46 ± 0.24 vs 0.39 ± 0.10 mm Hg × min × kg(2/3)/mL, p = 0.15). Mean CMRO2 was higher in the control group compared with the experimental group (0.90 ± 0.27 vs 0.59 ± 0.12 mLO2/min × kg(2/3), p = 0.005) and decreased over time in both groups. The percentage of caspase-3 positive cells was significantly different among regions (hippocampus = 16.9 ± 8.8; basal ganglia = 14.6 ± 7.5; neocortex = 10.8 ± 6.3; p < 0.0001) but not significantly different among sham (11.8% ± 2.68%), control (14.4% ± 2.24%), and experimental (15.5% ± 2.24%) groups.

CONCLUSIONS

A continuous infusion of phentolamine during selective cerebral perfusion significantly decreases CMRO2 and tends to decrease CVRI when compared with control. At the dose studied and at the time of tissue sampling, phentolamine does not appear to decrease apoptosis during or early after selective cerebral perfusion.

Selective cerebral perfusion for cerebral protection: what we do know

Selective antegrade cerebral perfusion (SACP) for aortic arch surgery has evolved considerably since it was first reported. Various pressure rates have been investigated through animal models, as has the effect of warmer perfusate temperatures and hematocrit. Clinical research into pH management, the role of unilateral and bilateral perfusion, and core temperatures have further refined the procedure. We recommend the following protocol for SACP: perfusion pressure between 40-60 mmHg, flow rates between 6-10 mL/kg/min, and perfusate temperature of 20-28 °C; core cooling to 18-30 °C contingent on duration of arrest; alpha-stat pH management; hematocrit between 25-30%; near infrared spectroscopy to monitor cerebral perfusion; and bilateral perfusion when prolonged durations of SACP is anticipated.

Modern temperature management in aortic arch surgery: the dilemma of moderate hypothermia

Arch surgery is undoubtedly among the most technically and strategically challenging endeavours in aortic surgery, requiring thorough understanding not only of cardiovascular physiology, but also in particular, of neurophysiology (cerebral and spinal cord), and is still associated with significant mortality and morbidity. In the late 1980s, when deep hypothermic circulatory arrest (HCA) had gained widespread acceptance as the standard approach for arch surgery, antegrade selective cerebral perfusion (SCP), as an adjunct to deep HCA, began its triumphal march, offering excellent neuroprotection and improved overall outcome. This encouraged the use of antegrade SCP in combination with steadily increasing body core temperatures--a trend culminating in the progressive advocation of moderate-to-mild temperatures up to 35 °C, and even normothermia. The impetus for progressive temperature elevation was the limitation of adverse effects of profound hypothermia and the most welcome side effect of significantly shorter cooling and rewarming periods on cardiopulmonary bypass (CPB), and thereby, potentially, the alleviation of the systemic inflammatory response and, in particular, the risk of severe postoperative bleeding (and other organ dysfunctions). The safe limits of prolonged distal circulatory arrest, particularly with regard to the ischaemic tolerance of the viscera and the spinal cord, have not yet been clearly defined. Adverse outcomes due to inappropriate temperature management (core temperatures too high for the required duration of distal arrest) are probably highly underreported. Complications historically associated with hypothermia, namely excessive bleeding, are possibly overestimated. Trading effective neuroprotection and excellent outcomes for the risk of prolonged 'warm' distal ischaemia might constitute a significant step back, jeopardizing visceral and, in particular, spinal cord integrity, with unpredictable consequences for long-term outcome and quality of life, particularly affecting those in need of more complex surgery or with previous neurological deficits.

The impact of temperature and pump flow rate during selective cerebral perfusion on regional blood flow in piglets

OBJECTIVE

Ideal temperature and flow rate for selective cerebral perfusion (SCP) are not known. We examined regional organ perfusion in a piglet SCP model.

METHODS

Three groups underwent SCP at 30 mL/kg/min at different temperatures (15°C, 25°C, and 32°C) and 4 groups remained at 25°C for SCP at different flow rates (10, 30, 50 and 75 mL/kg/min). Fluorescent microspheres were injected at 5 minutes of normothermic cardiopulmonary bypass (CPB), immediately before SCP, SCP 45 minutes, SCP 90 minutes, and 2 hours after CPB. Brain and lower body organs were collected to examine regional blood flow (RBF, mL/min/g).

RESULTS

At 2 hours after CPB, RBF of the 32°C group was higher than that of the 15°C group (P < .05) at the caudate nucleus and hippocampus; RBF of the 32°C group was higher than that of the 25°C and 15°C groups (P < .05) at the neocortex. No significant difference in RBF was observed among any of the 25°C groups at different flow rates. Also, there was no significant difference between the RBF to the left and right sides of brain in either the temperature or flow rate groups. RBF did significantly increase with temperature in the liver and quadriceps during SCP (P < .05). At the kidney, RBF at SCP 90 minutes was significantly higher than that at SCP 45 minutes when all temperature groups were combined (P < .05).

CONCLUSIONS

SCP at 32°C provides higher brain RBF 2 hours after CPB. Increasing SCP flow rate does not increase RBF significantly at 25°C. Higher temperature during SCP results in improved RBF to the liver and quadriceps.

Selective cerebral perfusion using moderate flow in complex cardiac surgery provides sufficient neuroprotection. Are children young adults?

OBJECTIVE

Selective cerebral perfusion (SCP) is commonly applied during the correction of complex congenital cardiac defects. In this study, we assessed the impact of different flow levels of SCP on potential brain ischaemia.

METHODS

Fifteen piglets (7-10 kg, age 3-4 weeks) received SCP via the right common carotid artery during cardiopulmonary bypass at 25°C for 90 min. Regular brain perfusion (1 ml/g brain weight/min), moderate hypoperfusion (0.5 ml/g/min) and extensive hypoperfusion (0.25 ml/g/min) were evaluated. Clinical parameters and tissue oxygenation index (TOI) were registered online until 3 h of reperfusion. Hematoxylin and eosin (HE) staining and immunohistological analyses for apoptosis inducing factor (AIF) and nitrotyrosine (NO-Tyr) were performed on sections of the hippocampus.

RESULTS

Intracerebral pressure remained stable throughout the study. Haemodynamic parameters, blood gas and lactate measurements were stable until the end of the study. Extensive hypoperfusion led to a moderate reduction of TOI. NO-Tyr immuno-positive cells were 15.7% at regular cerebral perfusion, 23.9% at moderate hypoperfusion (P = n.s.) and 46.1% at extensive hypoperfusion (P < 0.05). AIF immuno-positive nuclei were present in 8.3% of the hippocampus cells after regular perfusion, in 10.8% after moderate hypoperfusion (P = n.s.) and in 17.9% after extensive hypoperfusion (P < 0.05).

CONCLUSIONS

SCP using a moderate SCP flow regime demonstrates comparable results to normal brain perfusion while after extensive hypoperfusion significant morphological brain injury could be found. Thus moderate, but not extensive, hypoperfusion might have the potential to prevent perfusion-related cerebral oedema and an increasing risk of brain injury.

State of the art in neuroprotection during acute type A aortic dissection repair

Temporary (TND) or permanent neurologic dysfunctions (PND) represent the main neurological complications following acute aortic dissection repair. The aim of our experimental and clinical research was the improvement and update of the most common neuroprotective strategies which are in present use.

Hypothermic circulatory arrest (HCA): Cerebral metabolic suppression at the clinically most used temperatures (18-22°C) is less complete than had been assumed previously. If used as a ‘stand-alone’ neuroprotective strategy, cooling to 15-20°C with a jugular SO2 ≥ 95% is needed to provide sufficient metabolic suppression. Regardless of the depth of cooling, the HCA interval should not exceed 25 min. After 40 min of HCA, the incidence of TND and PND increases, after 60 min, the mortality rate increases.

Antegrade selective cerebral perfusion (ASCP): At moderate hypothermia (25-28°C), ASCP should be performed at a pump flow rate of 10ml/kg/min, targeting a cerebral perfusion pressure of 50-60mmHg. Experimental data revealed that these conditions offer an optimal regional blood flow in the cortex (80±27ml/min/100g), the cerebellum (77±32ml/min/100g), the pons (89±5ml/min/100g) and the hippocampus (55±16ml/min/100g) for 25 minutes. If prolonged, does ASCP at 32°C provide the same neuroprotective effect?

Cannulation strategy: Direct axillary artery cannulation ensures the advantage of performing both systemic cooling and ASCP through the same cannula, preventing additional manipulation with the attendant embolic risk. An additional cannulation of the left carotid artery ensures a bi-hemispheric perfusion, with a neurologic outcome of only 6% TND and 1% PND.

Neuromonitoring: Near-infrared spectroscopy and evoked potentials may prove the effectiveness of the neuroprotective strategy used, especially if the trend goes to less radical cooling.

Conclusion: A short interval of HCA (5 min) followed by a more extended period of ASCP (25 min) at moderate hypothermia (28°C), with a pump flow rate of 10ml/kg/min and a cerebral perfusion pressure of 50 mmHg, represents safe conditions for open arch surgery.