Comparative study of retrograde and selective cerebral perfusion with transcranial Doppler

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.

Open aortic arch surgery: the gold standard method

Aortic arch pathologies are complex and treating them requires close team collaboration and technical skills to provide safe outcomes with low morbidity and mortality rates. Such challenges are facing both aortic and vascular surgeons. Open aortic arch repair has been the standard method of practice in all cases of aortic arch pathologies for the last four decades since the very first successful published case series by Griepp et al. during 1975. However, since then, repair of multi-segmented thoracic aortic pathologies has been explored through endovascular techniques; this is with or without open repair as a one-stage procedure especially in high-risk and elderly patients. Although the role of endovascular techniques in thoracoabdominal aorta is well established, its utilization as solo technique in aortic arch pathologies remains debatable. In this review, we highlight current evidences behind using open, endovascular, and hybrid procedures in aortic arch surgery.

Cerebral Circulation During Retrograde Cerebral Perfusion: Evaluation Using Laser Speckle Flowgraphy

BACKGROUND

The cerebroprotective effect of retrograde cerebral perfusion (RCP) and selective antegrade cerebral perfusion (SCP) still remains controversial. Laser speckle flowgraphy has shown much promise for novel perioperative neuromonitoring by assessing blood flow of the optic nerve head. This study aimed to evaluate the cerebral microcirculation in humans using laser speckle flowgraphy during simple circulatory arrest, RCP, and SCP under moderate hypothermia and to investigate whether RCP under moderate hypothermia is a reliable method of cerebral protection.

METHODS

A total of 23 consecutive patients who underwent a scheduled aortic arch or hemiarch surgical procedure on thoracic aorta aneurysm were enrolled. The laser speckle flowgraphy measurement that calculates mean blur ratio, a parameter of cerebral circulation, was obtained 6 times: after induction of anesthesia, baseline (T1), after initiation of cardiopulmonary bypass with cardiac arrest (T2), simple circulatory arrest (T3), RCP (T4), SCP (T5), and after the termination of cardiopulmonary bypass (T6).

RESULTS

Both mean blur ratios of simple circulatory arrest and RCP were significantly decreased compared with baseline. In contrast, no significant differences were observed between simple circulatory arrest and RCP. The mean blur ratio of SCP was significantly increased compared with both simple circulatory arrest and RCP.

CONCLUSIONS

In conclusion, no significant difference was observed in the cerebral circulation between RCP and simple circulatory arrest without adjunctive strategy under moderate hypothermia. In contrast, the cerebral circulation during SCP was significantly higher than simple circulatory arrest and RCP. These results suggest that cerebral microcirculation may not be adequate during RCP compared with SCP under moderate hypothermia.

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.

Varying Evidence on Deep Hypothermic Circulatory Arrest in Thoracic Aortic Aneurysm Surgery

Cardiovascular surgeons have long debated the safe duration of deep hypothermic circulatory arrest during thoracic aortic aneurysm surgery. The rationale for using adjunctive cerebral perfusion (or not) is to achieve the best technical aortic repair with the lowest risk of morbidity and death. In this literature review, we highlight the debates surrounding these issues, evaluate the disparate findings on deep hypothermic circulatory arrest durations and temperatures, and consider the usefulness of adjunctive perfusion.

Retrograde perfusion through superior vena cava reaches the brain during circulatory arrest

Background

The optimal technique for brain perfusion during circulatory arrest remains controversial. Concern exists that retrograde cerebral perfusion (RCP) via the superior vena cava (SVC) is unable to perfuse the brain. We evaluated whether RCP blood circulates through the brain parenchyma in humans during deep hypothermic circulatory arrest (DHCA). We hypothesized that a significant difference in the levels of S-100β (a protein with very high neuro-sensitivity) between the blood infused in the SVC and the effluent blood returning in the left carotid artery (CA) during RCP, should be regarded as a sign of the circulation of RCP blood through the brain parenchyma.

Methods

We enrolled 10 non-consecutive patients undergoing elective arch-surgery using DHCA and RCP. Circulating S-100β levels were measured at baseline and immediately before DHCA. During DHCA and RCP the difference in S-100β between the SVC and the CA was evaluated after 10 minutes of arrest and immediately before resumption of the circulation. S-100β levels were evaluated using enzyme-linked immunosorbent assay (ELISA).

Results

Mean DHCA duration was 22.4±7.9 minutes. Mean S-100β level at baseline was 92.5±54.9 µg/L. After 10 minutes of DHCA the level of S-100β in the CA was significantly higher than in the SVC (936.9±326.3 vs. 810.9±307.4 µg/L, P=0.0021). This difference was enhanced at the second DHCA sample (1113.8±334.2 vs. 920.5±340.0 µg/L, P=0.0002). There was a statistically significant correlation between the duration of DHCA and the percent difference in S-100β level between the SVC and the CA (Pearson's correlation coefficient =0.902).

Conclusions

RCP is able to perfuse the brain parenchyma in humans during DHCA.

Brain protection in aortic arch aneurysm: antegrade or retrograde?

During open aortic arch repair, there is an interruption of cerebral perfusion and to prevent neurological sequelae, the hypothermic circulatory arrest has been established to provide sufficient brain protection coupled with adjuncts including retrograde and antegrade cerebral perfusion. To date, brain protection during open aortic arch repair is a contested topic as to which provides superior brain protection with little evidence existing to suggest supremacy of one modality over the other. This article reviews current literature reflecting on key and emerging studies in brain protection and their associated outcomes in patients undergoing open aortic arch surgery.

A Protocol for Diagnosis and Management of Aortic Atherosclerosis in Cardiac Surgery Patients

In patients undergoing cardiac surgery, use of perioperative screening for aortic atherosclerosis with modified TEE (A-View method) was associated with lower postoperative mortality, but not stroke, as compared to patients operated on without such screening. At the time of clinical implementation and validation, we did not yet standardize the indications for modified TEE and the changes in patient management in the presence of aortic atherosclerosis. Therefore, we designed a protocol, which combined the diagnosis of atherosclerosis of thoracic aorta and the subsequent considerations with respect to the intraoperative management and provides a systematic approach to reduce the risk of cerebral complications.

Intraoperative Transcranial Ultrasonic Monitoring for Cardiac and Vascular Surgery

The brain is the only organ not routinely monitored by any direct method during the administration of anesthesia. Anesthesiologists rely primarily on indirect physiologic evidence provided by blood pressure, peripheral pulse oximetry, heart rate, and respiratory and anesthetic gas concentrations to determine that brain blood flow and oxygenation are adequate. The reasons for this practice are that: (1) after millions of anesthetics significant numbers of adverse neurologic outcomes have not occurred, (2) the interpretation of transcranial Doppler, electroencephalogram, and near-infrared cerebral oximetry requires experienced personnel, and (3) the evidence of cost-benefit to support monitoring is limited. Brain monitoring generally has been confined to procedures where the brain is exposed to unique insults and risks specific to the procedures and where reliance on indirect physiologic evidence of cerebral integrity has been proven to be unreliable. Transcranial Doppler monitoring is valuable in the assessment of established surgical techniques, refinement of recent surgical techniques, and development of new techniques and instrumentation. Brain monitoring with transcranial Doppler is of particular value when deviations from established surgical or anesthetic techniques may place the brain at risk for cerebral hyper-or hypoperfusion, gaseous or particulate embolization, or their combined effects. This paper discusses applications of transcranial Doppler in coronary artery bypass surgery, aortic arch procedures, pediatric cardiac surgery, carotid endarterectomy, and a few other special cases. The insight into cerebral physiology is unique to the continuous window on the brain that transcranial Doppler provides.

Antegrade versus retrograde cerebral perfusion for hemiarch replacement with deep hypothermic circulatory arrest: does it matter? A propensity-matched analysis

OBJECTIVE

The choice of cerebral perfusion strategy for aortic arch surgery has been debated, and the superiority of antegrade (ACP) or retrograde (RCP) cerebral perfusion has not been shown. We examined the early and late outcomes for ACP versus RCP in proximal (hemi-) arch replacement using deep hypothermic circulatory arrest (DHCA).

METHODS

A retrospective analysis of a prospectively maintained database was performed for all patients undergoing elective and nonelective hemiarch replacement at a single referral institution from June 2005 to February 2013. Total arch cases were excluded to limit the analysis to shorter DHCA times and a more uniform patient population for whom clinical equipoise regarding ACP versus RCP exists. A total of 440 procedures were identified, with 360 (82%) using ACP and 80 (18%) using RCP. The endpoints included 30-day/in-hospital and late outcomes. A propensity score with 1:1 matching of 40 pre- and intraoperative variables was used to adjust for differences between the 2 groups.

RESULTS

All 80 RCP patients were propensity matched to a cohort of 80 similar ACP patients. The pre- and intraoperative characteristics were not significantly different between the 2 groups after matching. No differences were found in 30-day/in-hospital mortality or morbidity outcomes. The only significant difference between the 2 groups was a shorter mean operative time in the RCP cohort (P = .01). No significant differences were noted in late survival (P = .90).

CONCLUSIONS

In proximal arch operations using DHCA, equivalent early and late outcomes can be achieved with RCP and ACP, although the mean operative time is significantly less with RCP, likely owing to avoidance of axillary cannulation. Questions remain regarding comparative outcomes with straight DHCA and lesser degrees of hypothermia.

A reappraisal of retrograde cerebral perfusion

Brain protection during aortic arch surgery by perfusing cold oxygenated blood into the superior vena cava was first reported by Lemole et al. In 1990 Ueda and associates first described the routine use of continuous retrograde cerebral perfusion (RCP) in thoracic aortic surgery for the purpose of cerebral protection during the interval of obligatory interruption of anterograde cerebral flow. The beneficial effects of RCP may be its ability to sustain brain hypothermia during hypothermic circulatory arrest (HCA) and removal of embolic material from the arterial circulation of the brain. RCP can offer effective brain protection during HCA for about 40 to 60 minutes. Animal experiments revealed that RCP provided inadequate cerebral perfusion and that neurological recovery was improved with selective antegrade cerebral perfusion (ACP), however, both RCP and ACP provide comparable clinical outcomes regarding both the mortality and stroke rates by risk-adjusted and case-matched comparative study. RCP still remains a valuable adjunct for brain protection during aortic arch repair in particular pathologies and patients.

Deep hypothermic circulatory arrest: Alternative strategies for cerebral perfusion. A review article

Deep hypothermic circulatory arrest is an essential tool in the surgeon’s armamentarium. There are essentially three strategies to address cerebral ischemia during arrest periods. Early surgical case series pioneered the option of complete anoxia with deep hypothermia. Subsequent innovators introduced the concept of retrograde perfusion of the cerebral vessels through the venous system, and others have advocated the use of selective and non-selective antegrade perfusion of the cerebral arteries. Clinical studies assessing outcomes of the three approaches are compromised by small patient numbers, retrospective design and surgeon bias.

In this review, the authors will briefly discuss the conceptual basis of these strategies and the literature comparing these approaches in terms of key neurologic outcomes. The importance of this topic will emphasize the key role the perfusion community plays in establishing guidelines for best practice in circulatory arrest to go forward with education and research in this area.

Ascending and Transverse Aortic Arch Repair

Background— The benefit of retrograde cerebral perfusion (RCP) with profound hypothermic circulatory arrest has been subject to much debate. We examined our experience with ascending and transverse arch repairs to determine the impact of retrograde cerebral perfusion on stroke and mortality.

Methods and Results— Between August 1991 and June 2007, we performed 1107 repairs of the ascending and transverse aortic arch. RCP was used in 82% of cases (907 of 1107). Sixty-two percent were men (682 of 1107); median age was 64 years (range, 16 to 93 years). Perioperative variables were evaluated using univariate and multivariable analysis for mortality and stroke. Thiry-day mortality was 10.4% (115 of 1107). Stroke occurred in 2.8% (31 of 1107) of patients. Univariate risk factors for mortality were increasing age ( P <0.0001), history of coronary artery disease ( P =0.02), previous coronary artery bypass ( P =0.02), emergency status ( P <0.0001), acute dissection ( P =0.02), rupture ( P =0.0001), preoperative glomerular filtration rate, bypass time ( P <0.0001), crossclamp time ( P <0.007), RCP time ( P <0.0001), and packed red blood cell transfusions ( P =0.0001). Univariate risk factors for stroke included emergency status ( P <0.02), cerebrovascular disease ( P <0.02), and crossclamp time ( P <0.04). Independent risk factors for mortality were glomerular filtration rate <90 mL/min ( P =0.0004), emergency status ( P =0.006), rupture ( P =0.004), cardiopulmonary bypass time >120 minutes ( P <0.04), and packed red blood cell transfusions ( P =0.0002). Risk factors for stroke were emergency status ( P <0.009) and hypertension ( P <0.05). RCP was protective against mortality and stroke.

Conclusions— The use of RCP with profound hypothermic circulatory arrest was associated with a reduction in mortality and stroke. The use of RCP remains warranted during repairs of the ascending and transverse aortic arch.

Methods of cerebral protection in surgery of the thoracic aorta

During the last decade, a considerable increase in the number of operations on the thoracic aorta has been observed. Although patient's outcomes have improved considerably, this surgery is still associated with significant morbidity and mortality due to neurological complications. Various methods have been proposed and widely used as means to protect the brain from ischemic damage. This review summarizes the principal methods of cerebral protection, describes the advantages and disadvantages of each method and their impact on patient outcomes, and discusses the different surgical techniques proposed to minimize the risk of cerebral injuries.

Assessment of Cerebral Blood Flow With Transcranial Doppler in Right Brachial Artery Perfusion Patients

BACKGROUND

Antegrade selective cerebral perfusion as a method of cerebral protection during the correction of aortic arch aneurysms and dissections is considered as a safe method for cerebral protection. There are still some questions remaining to be answered; such as whether cerebral perfusion through contralateral hemisphere is adequate.

METHOD

Fifteen consecutive patients (mean age of 53 +/- 3.3 years) underwent surgical reconstruction of aortic arch with antegrade selective cerebral perfusion through the right brachial artery. We monitored maximum, minimum and mean blood flow velocities of bilateral middle cerebral arteries using the transcranial Doppler technique at four different time periods: after induction of anesthesia, during cardiopulmonary bypass, during antegrade selective cerebral perfusion, and after termination of cardiopulmonary bypass. We compared the results of brachial cannulation group with aortic group.

RESULTS

Following induction, no significant differences were observed in the right and left middle cerebral artery blood flow velocity measurements in and between the groups. During cardiopulmonary bypass, V(max) and V(mean) decreased significantly in both groups. When two groups were compared there was a significant decrease in the left V(max) values of brachial group (p = 0.048). In-group comparisons revealed that V(max) values were lower in left middle cerebral artery than right middle cerebral artery in brachial group (p = 0.002). With the initiation of antegrade selective cerebral perfusion in brachial group, significant decrease occurred in V(max) and V(mean) when compared with cardiopulmonary bypass values. When left and right sides were compared, although V(min) values remained similar, V(max) and V(mean) values decreased significantly in the left side (p = 0.001 and p = 0.003, respectively). After cardiopulmonary bypass, in both groups, all values restored to initial values and indicated no difference between left and right middle cerebral artery in the groups as well as between the groups. No neurologic deficit was observed in any patient postoperatively.

CONCLUSIONS

Antegrade selective cerebral perfusion through the right brachial artery, as a method of cerebral protection for aortic arch repair, seems to provide adequate perfusion for both right and left cerebral hemispheres.

Determination of cerebral blood flow dynamics during retrograde cerebral perfusion using power M-mode transcranial Doppler

BACKGROUND

Retrograde cerebral perfusion (RCP) during profound hypothermic circulatory arrest has been used as an adjunct for cerebral protection for repairs of the ascending and transverse aortic arch. Transcranial Doppler ultrasound has been used to monitor cerebral blood flow during RCP with varying success. The purpose of this study was to characterize cerebral blood flow dynamics during RCP using a new mode of monitoring known as transcranial power motion-mode (M-mode) Doppler ultrasound.

METHODS

Data on pump-flow characteristics and patient outcomes were collected prospectively for patients undergoing ascending and transverse aortic arch repair. Retrograde cerebral perfusion during profound hypothermic circulatory arrest was used for all operations. Intraoperative cerebral blood flow dynamics were monitored and recorded using transcranial power M-mode Doppler ultrasound.

RESULTS

Between August 2001 and March 2002, we used transcranial power M-mode Doppler ultrasound monitoring for 40 ascending and transverse aortic arch repairs during RCP. Mean RCP time was 32.2 +/- 13.8 minutes. Mean RCP pump flow and RCP peak pressure for identification of cerebral blood flow were 0.66 +/- 0.11 L/min and 31.8 +/- 9.7 mm Hg, respectively. Retrograde cerebral blood flow during RCP was detected in 97.5% of cases (39 of 40 patients) with a mean transcranial power M-mode Doppler ultrasound flow velocity of 15.5 +/- 12.3 cm/s. In the study group, 30-day mortality was 10.0% (4 of 40 patients). The incidence of stroke was 7.6% (3 of 40 patients); the incidence of temporary neurologic deficit was 35.0% (14 of 40 patients).

CONCLUSIONS

Transcranial power M-mode Doppler ultrasound consistently demonstrated retrograde middle cerebral artery blood flow during RCP. Transcranial power M-mode Doppler ultrasound can provide optimal RCP with individualized settings of pump flow.

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.

Replacement of the ascending and transverse aortic arch: determinants of long-term survival

BACKGROUND

Although little has been published on the natural history of aneurysms of the ascending aorta and aortic arch, long-term prognosis of untreated aneurysms is generally poor. We reviewed our 10-year experience in the repair of the ascending aorta and aortic arch to evaluate long-term outcome.

METHODS

Between January 1991 and May 2001, we repaired 423 aneurysms of the ascending aorta or aortic arch using profound hypothermic circulatory arrest. Median age was 65 years. Retrograde cerebral perfusion (RCP) was used in 357 cases. Mean pump and RCP times were 139 and 33.9 minutes, respectively. Survival was ascertained by direct patient contact or by searching the social security death index. Survival was analyzed by Kaplan-Meier stratified analysis and by multivariate Cox regression.

RESULTS

Overall actuarial survival was 72% at 5 years and 71% at 10 years after surgery. Univariate analysis identified increasing age (p < 0.0001), chronic obstructive pulmonary disease (p < 0.014), concurrent unoperated aneurysm (p < 0.005), arch involvement (p < 0.042), pump time (p < 0.0004), concurrent aortic valve replacement (p < 0.009), and postoperative renal failure (p < 0.0002) as factors that negatively influenced survival. Multivariate analysis identified increasing age (p < 0.0001) and pump time (p < 0.0001). RCP did not have a significant independent effect on the long-term survival.

CONCLUSIONS

Our experience indicates that repair of the ascending aorta and aortic arch can be accomplished with good long-term survival.

Failure of retrograde cerebral perfusion to attenuate metabolic changes associated with hypothermic circulatory arrest

OBJECTIVES

Although retrograde cerebral perfusion has become a popular adjunctive technique and may improve cerebral ischemic tolerance during hypothermic circulatory arrest, direct cerebral metabolic benefit has yet to be demonstrated in human subjects. We investigated the post-arrest metabolic phenomena with and without retrograde cerebral perfusion in patients.

METHODS

In a prospective randomized trial, 42 patients undergoing aortic surgery requiring hypothermic circulatory arrest were allocated to receive hypothermic circulatory arrest alone (n = 21) or hypothermic circulatory arrest with additional retrograde cerebral perfusion (n = 21). Circulatory arrest was commenced at 15 degrees C, and retrograde perfusion was instituted through the superior vena cava at a maximum jugular bulb pressure of 25 mm Hg. Transcranial, paired, repeated samples of the arterial and jugular bulb blood were analyzed for oxygen and glucose. Velocity in the right middle cerebral artery was also measured simultaneously.

RESULTS

There were 3 (7.1%) deaths and 3 (7.1%) episodes of neurologic deficit. Mean bypass and circulatory arrest duration (in minutes) were similar between groups (P =.4 and.14). The mean retrograde perfusion duration was 23 minutes. Post-arrest nasopharyngeal temperature was similar (15.3 degrees C vs. 15.3 degrees C). Retrograde perfusion did not affect post-arrest oxygen extraction, glucose extraction, or jugular bulb Po(2). There was no immediate lactate release immediately after hypothermic circulatory arrest.

CONCLUSIONS

Retrograde cerebral perfusion did not influence immediate post-arrest nasopharyngeal temperature or cerebral metabolic recovery. The low jugular bulb Po(2) suggests equivalent ischemia. These findings cast doubt on the effectiveness of retrograde cerebral perfusion as a metabolic adjunct to hypothermic circulatory arrest.

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.

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.

Cerebral hemodynamics changes during retrograde brain perfusion in dogs

The objective of this study was to examine cerebral hemodynamics changes during hypothermic circulatory arrest (HCA) with and without retrograde cerebral perfusion (RCP). Thirteen colony-bred hound dogs were placed on cardiopulmonary bypass (CPB) and cooled to 18 degrees C. Five dogs underwent 2 hours of HCA without RCP and 8 with RCP. The animals were then rewarmed on CPB until normothermic and weaned. Cerebral blood flow velocity (CBFV) and Gosling Pulsatility Index (PI) in the middle cerebral artery (MCA) were studied using trans-cranial Doppler ultrasound (TCD). At baseline and during pre- and postarrest CPB, there was anterograde direction of blood flow in the MCA. During HCA with RCP, there was retrograde direction of blood flow in the MCA. There was no difference in CBFV between pre-, during, and postarrest CPB in the group with RCP; however, there was significantly increased CBFV during postarrest CPB in the group without RCP compared to the dogs with RCP. Later, at 3 hours after postarrest CPB, there was decreased CBFV in all animals accompanied by increased PI (2.4 +/- 0.4 and 2.2 +/- 0.6 for animals with RCP and without RCP, respectively) and abnormal TCD waveform changes including decreased diastolic compartment and sharp systolic peak. During hypothermic circulatory arrest, RCP provides CBFV in the MCA comparable to MCA CBFV during CPB. HCA dogs without RCP showed immediate hyperemia on reperfusion. The decreased CBFV and increased PI at 1 hour after postarrest CPB could be an indicator of progressive ischemic injury due to the increased intracranial pressure despite the implementation of RCP.