Retrograde cerebral perfusion: anatomic study of the distribution of blood to the brain

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.

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.

Evaluation of Different Cannulation Strategies for Aortic Arch Surgery Using a Cardiovascular Numerical Simulator

Aortic disease has a significant impact on quality of life. The involvement of the aortic arch requires the preservation of blood supply to the brain during surgery. Deep hypothermic circulatory arrest is an established technique for this purpose, although neurological injury remains high. Additional techniques have been used to reduce risk, although controversy still remains. A three-way cannulation approach, including both carotid arteries and the femoral artery or the ascending aorta, has been used successfully for aortic arch replacement and redo procedures. We developed circuits of the circulation to simulate blood flow during this type of cannulation set up. The CARDIOSIM© cardiovascular simulation platform was used to analyse the effect on haemodynamic and energetic parameters and the benefit derived in terms of organ perfusion pressure and flow. Our simulation approach based on lumped-parameter modelling, pressure-volume analysis and modified time-varying elastance provides a theoretical background to a three-way cannulation strategy for aortic arch surgery with correlation to the observed clinical practice.

Preservation of the Aortic Root During Type A Aortic Dissection Surgery: An Effective Strategy?

Background  Management of the aortic root during acute Type A aortic dissection (TAAD) repair remains controversial in term of long-term evolution and reoperation. The aim of this study was to assess the long-term outcomes of the aortic root after conservative management during primary surgery.

Methods  One hundred sixty-four consecutive patients were included in this monocentric retrospective study. The primary endpoint was reoperation on the aortic root during long-term follow-up. Forty-six patients had aortic root replacement (ARR) and 118 had supracoronary aortic replacement (SCR). The 10-year survival, occurrence of significant aortic regurgitation, and radiologic aortic root dilatation in each group were assessed during follow-up.

Results  Patients from ARR group were younger than those from SCR group ( p  < 0.0001). Median follow-ups of ARR group and SCR group are 4.4 (interquartile range [IR]: 2.6–8.3) and 6.15 (IR: 2.8–10.53) years, respectively. Reoperation of the aortic root during long-term follow-up was similar in both groups (ARR group: 5.1%, SCR group: 3.3%, p  = 0.636). The 10-year survivals of ARR and SCR groups were 64.8 ± 12.3% and 46.3 ± 5.8% ( p  = 0.012), respectively. Long-term significant aortic regurgitation occurred in one patient (1.7%) and seven patients (7.6%) of the ARR and SCR groups ( p  = 0.176), respectively. Radiologic aortic root diameters in the SCR group were similar between postoperative period and follow-up studies ( p  = 0.58). Reoperation on the distal aorta ( p  = 0.012) and patent radiologic false lumen of the descending aorta ( p  = 0.043) were independent risk factors of late death.

Conclusion  SCR is an effective technique for primary TAAD surgery and does not increase the rate of late reoperation on the aortic root.

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.

Alternative Approach for Cerebral Protection during Complex Aortic Arch and Redo Surgery

Total arch replacement remains a very demanding surgical procedure. It can be associated with reasonable long-term outcomes but carries serious perioperative complications. Aortic arch surgery has progressed in recent years to a wider adoption of reproducible and reliable techniques. Conventional open, surgical aortic arch replacement is currently offered to the majority of patients, although hybrid and wholly endovascular techniques are gaining popularity. With regards to open arch replacement, the nuances of surgical technique, the mode of cannulation and the optimal cerebral protection protocols remain a matter of debate. We propose an alternative cannulation approach facilitated by the cooperation between cardiac and vascular surgeons. A three-way arterial cannulation including both carotid arteries and the femoral artery (or ascending aorta) is the key feature of this approach. A case series of complex patients is presented to show both the feasibility and relative safety of a standardised new approach with a 100% technical success rate and a 16% 30-day mortality. The three-way cannulation approach may have a role to play for complex and extensive procedures requiring prolonged cerebral protection. We believe that a shared skill set from cardiac and vascular specialists is essential for the safe management and successful outcomes using this adaptive technique.

Open repair techniques in the aortic arch are still superior

Conventional arch replacement can be carried out in a great majority of patients. Hybrid procedures are often as invasive and technically difficult as conventional ones. Moreover, their immediate results are, in many reported experiences, not better and their long-term results less favourable than the ones observed with conventional methods. So, yes, the open conventional arch replacement is still "the gold standard".

Evolution of surgical therapy for Stanford acute type A aortic dissection

Acute type A aortic dissection (AcA-AoD) is a surgical emergency associated with very high morbidity and mortality. Unfortunately, the early outcome of emergency surgical repair has not improved substantially over the last 20 years. Many of the same debates occur repeatedly regarding operative extent and optimal conduct of the operation. The question remains: are patients suffering from too large an operation or too small? The pendulum favoring routine aortic valve resuspension, when feasible, has swung towards frequent aortic root replacement. This already aggressive approach is now being challenged with the even more extensive valve-sparing aortic root replacement (V-SARR) in selected patients. Distally, open replacement of most of the transverse arch is best in most patients. The need for late aortic re-intervention has not been shown to be affected by more extensive distal operative procedures, but the contemporary enthusiasm for a distal frozen elephant trunk (FET) only seems to build. It must be remembered that the first and foremost goal of the operation is to have an operative survivor; additional measures to reduce late morbidity are secondary aspirations. With increasing experience, true contraindications to emergency surgical operation have dwindled, but patients with advanced age, multiple comorbidities, and major neurological deficits do not fare well. The endovascular revolution, moreover, has spawned innovative options for modern practice, including ascending stent graft and adaptations of the old flap fenestration technique. Despite the increasingly complex operations and ever expanding therapies, this life-threatening disease remains a stubborn challenge for all cardiovascular surgeons. Development of specialized thoracic aortic teams and regionalization of care for patients with AcA-AoD offers the most promise to improve overall results.

Implications from neurologic assessment of brain protection for total arch replacement from a randomized trial

OBJECTIVE

The study objective was to perform a randomized trial of brain protection during total aortic arch replacement and identify the best way to assess brain injury.

METHODS

From June 2003 to January 2010, 121 evaluable patients were randomized to retrograde (n = 60) or antegrade (n = 61) brain perfusion during hypothermic circulatory arrest. We assessed the sensitivity of clinical neurologic evaluation, brain imaging, and neurocognitive testing performed preoperatively and 4 to 6 months postoperatively to detect brain injury.

RESULTS

A total of 29 patients (24%) experienced neurologic events. Clinical stroke was evident in 1 patient (0.8%), and visual changes were evident in 2 patients; all had brain imaging changes. A total of 14 of 95 patients (15%) undergoing both preoperative and postoperative brain imaging had evidence of new white or gray matter changes; 10 of the 14 patients had neurocognitive testing, but only 2 patients experienced decline. A total of 17 of 96 patients (18%) undergoing both preoperative and postoperative neurocognitive testing manifested declines of 2 or more reliable change indexes; of these 17, 11 had neither imaging changes nor clinical events. Thirty-day mortality was 0.8% (1/121), with no neurologic deaths and a similar prevalence of neurologic events after retrograde and antegrade brain perfusion (22/60, 37% and 15/61, 25%, respectively; P = .2).

CONCLUSIONS

Although this randomized clinical trial revealed similar neurologic outcomes after retrograde or antegrade brain perfusion for total aortic arch replacement, clinical examination for postprocedural neurologic events is insensitive, brain imaging detects more events, and neurocognitive testing detects even more. Future neurologic assessments for cardiovascular procedures should include not only clinical examination but also brain imaging studies, neurocognitive testing, and long-term assessment.

"Open" approach to aortic arch aneurysm repair

Aortic arch aneurysm is a relatively rare entity in cardiac surgery. Repair of such aneurysms, either in isolation or combined with other cardiac procedures, remains a challenging task. The need to produce a relatively bloodless surgical field with circulatory arrest, while at the same time protecting the brain, is the hallmark of this challenge. However, a clear understanding of the topic allows a better and less morbid approach to such a complex surgery. Literature has shown the advantage of selective cerebral perfusion techniques in comparison with only circulatory arrest. Ability to perfuse the brain has allowed circulatory arrest temperatures at moderate hypothermia without the need for deep hypothermia. Even though cannulation site selection appears to be a minor issue, literature has shown that the subclavian/axillary route has the best outcomes and that femoral cannulation should only be reserved for no access patients. Although different techniques for arch anastomosis have been described, we routinely perform the distal first technique as we find it to be less cumbersome and easiest to reproduce. In this review our aim is to outline a systematic approach to aortic arch surgery. Starting with indications for intervention and proceeding with approaches on site of cannulation, approaches to brain protection with hypothermia and selective cerebral perfusion and finally surgical steps in performing the distal and arch vessels anastomosis.

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.

Visualization of macroscopic cerebral vessel anatomy--a new and reliable technique in mice

Visualizing rodent cerebral vasculature is an important tool in experimental stroke research. Intravascular perfusion with colored latex has been the method of choice until recently. However, latex perfusion has some technical limitations which compromise its reproducibility. We therefore describe a simple and reproducible method to visualize cerebral vessels in mice. A mixture of two commercially available carbon black inks is injected into the thoracic aorta resulting in efficient filling and high contrast visualization of cerebral vessels. Feasibility of this technique has been validated by identifying anastomotic points between anterior and middle cerebral arteries. Furthermore, perfusion with combined carbon inks allows visualization of significantly smaller vessel diameters at a higher vessel density in comparison to perfusion with diluted/undiluted latex. Thus, perfusion with combined carbon inks offers a simple, cost-effective and reproducible technique in order to visualize cerebral vasculature.

Novel technique of retrograde cerebral perfusion for descending aortic repair: direct cannulation into left internal jugular vein

We performed descending thoracic aortic repair via posterolateral thoracotomy using retrograde cerebral perfusion with direct cannulation into the left internal jugular vein. No postoperative neurological dysfunction was observed. This patient was discharged without any adverse events.

Total aortic arch replacement under intermittent pressure-augmented retrograde cerebral perfusion

Kitahori, Kawata, Takamoto et al. described the effectiveness of a novel protocol for retrograde cerebral perfusion that included intermittent pressure augmentation for brain protection in a canine model. Based on their report, we applied this novel technique clinically. Although the duration of circulatory arrest with retrograde cerebral perfusion was long, the patient recovered consciousness soon after the operation and had no neurological deficit. Near-infrared oximetry showed recovery of intracranial blood oxygen saturation every time the pressure was augmented.

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

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

Continuous selective bilateral antegrade cerebral perfusion through anomalous innominate artery for repair of root, ascending aortic and arch aneurysm – challenges, vagaries and opportunities of bovine arch variant anatomy and review of literature

We describe the repair of a root, ascending aortic and arch aneurysm in a 69-year-old man with a bioprosthetic Shelhigh conduit and cylinder, employing continuous bilateral antegrade cerebral perfusion through an anomalous innominate artery with a bovine arch variant anatomy. The origin of both the innominate artery and the left common carotid artery from a common stem from the arch in this bovine arch variant puts the whole cerebral circulation at risk, on one hand, yet provides an opportunity of continuous bilateral antegrade cerebral perfusion through the right brachial, right axillary, right subclavian or innominate artery, during arch reconstruction under lower body, deep hypothermic circulatory arrest. Safety and adequacy of selective cerebral perfusion through the right axillary artery in patients with normal arch vessel origin depends on an intact circle of Willis. In this bovine arch variant, both cerebral hemispheres can be perfused through the right brachial, right axillary, right subclavian or the innominate artery, independent of the integrity of the circle of Willis, because of the origin of the left common carotid artery from the innominate artery, except for the area supplied by the left vertebral artery. Although this is the first report of innominate artery perfusion for arch reconstruction for aneurysm in a bovine arch variant, we believe the method described has important implications for cerebral protection in light of the generally reported incidence of bovine arch from 13 to 35 percent.

Straight deep hypothermic arrest: experience in 394 patients supports its effectiveness as a sole means of brain preservation

BACKGROUND

The three methods of brain preservation for aortic arch surgery--straight deep hypothermic circulatory arrest (DHCA) without perfusion adjuncts, retrograde cerebral perfusion, and antegrade cerebral perfusion--remain controversial. Patients in this report underwent surgery solely with DHCA.

METHODS

Straight DHCA at 19 degrees C was used in 394 patients (267 males, 127 females) during a 10-year period. Mean age was 61.3 years (range, 15 to 88 years). Eighty-seven cases (22.1%) were urgent or emergencies. Thirty-eight (9.6%) were performed for descending or thoracoabdominal pathology and the rest for ascending/arch (102 hemiarch, 49 total arch). Ninety-one patients (23.1%) had dissections. The head was packed in ice. No barbiturate coma was used.

RESULTS

DHCA lasted a mean of 31.0 minutes (range, 10 to 66 minutes). Reexploration for bleeding was required in 4.5% (18/394). Overall mortality was 6.3% (25/394). Mortality was 3.6% (11/307) for elective cases and 16% (14/87) for emergency cases. The stroke rate was 4.8% (19/394). The seizure rate was 3.1% (12/394). Forty-five patients with high professional cognitive demands (MD, PhD, attorney, etc) performed without detriment postoperatively. Among patients with DHCA exceeding 40 minutes, the stroke rate was 13.1% (8/61); a neuroradiologist's review of brain computed tomography scans found 62.5% of these strokes (5/8) to be embolic and 37.5% (3/8) hypoperfusion related. By multivariable logistic regression, emergency operation and descending location increased morbidity and mortality.

CONCLUSIONS

Straight DHCA without adjunctive perfusion suffices as a sole means of cerebral protection. Stroke and seizure rates are low. Cognitive function, by clinical assessment, is excellent. Especially for straightforward ascending/arch reconstructions, there is little need for the added complexity of brain perfusion strategies.

[Current treatment of acute type A aortic dissection. Surgical treatment and treatment of malperfusion syndrome]

Acute type A aortic dissection is a surgical emergency. Treatment is based on dissected ascending aortic replacement and correction of an associated aortic insufficiency. Catheterization of the axillary artery, open distal anastomosis and systematic resection of the intimal tear are the main surgical evolutions of the last years. They allowed to significantly reduce intraoperative mortality rate particularly due to bleeding. Thirty days mortality rate of operated aortic dissection is about 20 to 30%. Visceral malperfusion syndromes induced by aortic dissection represent an important cause of postoperative death. An early diagnosis and treatment appears necessary. Thoracoabdominal CT scan allows understanding mechanisms inducing malperfusion. Aortography and an emergency endovascular procedure allow restoring arterial blood flow before renal or mesenteric irreversible ischemia. Collaboration between radiologist, anesthesiologist and surgeon is necessary to optimize survival of acute type A aortic dissection.

Does retrograde cerebral perfusion via superior vena cava cannulation protect the brain?

OBJECTIVE

The retrograde cerebral perfusion via cannulation of the superior vena cava is a widespread method for optimising protection of the brain during hypothermic circulatory arrest.

METHODS

In 14 cadavers (8 females, 6 males) of the local department of pathology, an examination was performed to check the competence of the valves of the internal jugular veins. After a complete preparation of the superior vena cava, the innominate vein and both internal jugular veins, ligating all side branches, a retrograde perfusion on 7 cadavers was installed, documenting flow and pressure of each internal jugular vein (IJV) in vitro. Afterwards, the veins were opened and their valves inspected.

RESULTS

In all 14 cadavers, anatomically and functionally competent valves on the right proximal IJV were found. Only 1/14 cadaver had no valve in the left proximal IJV. Additional rudimentary and incompetent valves could be identified in 1/14 cadaver on the distal right IJV, and in 2/14 cadavers on the left IJV. Retrograde flow measurement of 7/14 cadavers revealed 0 ml/min in 4/7 cadavers, 6 ml/min in 1/7, 340 ml/min in 1/7 and 2500 ml/min in 1/7 cadaver.

CONCLUSIONS

As a rule, anatomically and functionally competent valves in the proximal IJV are present. In human beings, they obstruct the direct retrograde inlet to the intracranial venous system, which suggests an unbalanced and unreliable perfusion of the brain. Therefore, retrograde cerebral perfusion by cannulating the superior vena cava may help flushing out embolism and supporting 'the cold jacket' of the brain. However, its effect of retrograde backflow cannot be a sign of adequate cerebral perfusion.

Aortic Arch Replacement Using a Trifurcated Graft: Simple, Versatile, and Safe

BACKGROUND

Hypothermic selective antegrade cerebral perfusion during aortic arch replacement may prevent adverse neurologic sequelae. It can be provided via balloon-tipped catheters or a branched graft sewn to the brachiocephalic vessels. We report a consecutive series of total arch replacement using a trifurcated graft.

METHODS

From September 1999 through October 2004, 109 patients underwent nonemergent total arch replacement using this technique. The graft, placed during a period of hypothermic circulatory arrest, was used for selective cerebral perfusion during the arch reconstruction.

RESULTS

Adverse outcomes were seen in 9 (8.3%) patients: hospital death in 5 (4.6%), and stroke in 5 (4.6%). Transient neurologic dysfunction was noted in 6 (5.5%) patients. Mean duration of hypothermic circulatory arrest was 31.2 +/- 6.6 minutes and selective cerebral perfusion was 65.3 +/- 20.9 minutes. Reoperation for bleeding was required in 3 (2.8%) patients and prolonged intubation in 15 (13.8%). Median intensive care unit stay was 3 days (interquartile range 2-4; range, 1 to 108) and hospital stay was 9 (interquartile range 8-15; range, 5 to 108).

CONCLUSIONS

The trifurcated graft technique results in low rates of perioperative mortality, temporary neurologic dysfunction, and stroke. It may reduce cerebral embolization as it requires no instrumentation of the aortic arch to establish selective cerebral perfusion and, although it mandates hypothermic circulatory arrest to place the graft, this interval is reliably brief enough to fall within accepted safe limits. This strategy leaves no residual arch tissue behind, and allows placement of an elephant trunk proximal to one or more arch vessels if anatomically indicated.

Rapid Brain Cooling by Hypothermic Retrograde Jugular Vein Flush

BACKGROUND

Although whole-body hypothermia recently has been reported effective in improving the neurologic outcome after cardiac arrest, it is contraindicated in the management of trauma patients with hemorrhagic shock. To provide selective brain cooling in this situation, the authors speculated about the feasibility of hypothermic retrograde jugular vein flush (HRJVF). This preliminary study was conducted to test the effectiveness of brain cooling after HRJVF in rats without hemorrhagic shock.

METHODS

After jugular vein cannulation with cranial direction, Sprague-Dawley rats were randomized into a normal control group, a group that underwent flush with cold saline at 4 degrees C, or a group that underwent flush with saline at a room temperature of 24 degrees C. A Servo-controlled heat lamp was applied for all the rats to keep their rectal temperature at 37 +/- 0.5 degrees C. Their brain temperature and cerebral blood flow were checked.

RESULTS

Within the 10-minute period of cold saline flush (1.7 mL/100 g), brain temperature was immediately decreased, and this cooling effect could be maintained for at least 20 minutes. Cerebral blood flow was significantly increased after HRJVF, then returned gradually to the baseline as brain temperature elevated.

CONCLUSIONS

This study successfully demonstrated a significant cooling effect in rat brain by HRJVF. For preservation of brain function, HRJVF may be useful in resuscitation for trauma patients with hemorrhagic shock after further studies on animals with shock.

Hypothermic retrograde jugular perfusion reduces brain damage in rats with heatstroke

OBJECTIVE

To determine whether direct retrograde ice saline infusion in the jugular vein without cardiopulmonary bypass protects rat brains after heatstroke.

DESIGN

Randomized, controlled, prospective study.

SETTING

University physiology research laboratory.

SUBJECTS

Sprague-Dawley rats (270-320 g, males).

INTERVENTIONS

Rats were randomized into three groups and given a) no resuscitation after onset of heat stroke (HS, n = 8); b) ice saline infusion in the femoral vein after onset of heat stroke (HS + F, n = 8); or c) retrograde ice saline infusion in the external jugular vein after onset of heat stroke (HS + J, n = 8). Rats were exposed to an ambient temperature of 43 degrees C after vessel cannulation. Their mean arterial pressure, heart rate, colonic temperature, and brain temperature were continuously recorded. Survival time and brain pathology were checked.

MEASUREMENTS AND MAIN RESULTS

Although colonic temperature decreased 0.8-1.0 degrees C 15 mins after heatstroke in all groups, no treatment-related changes in colonic temperature were noted in any group. However, significant changes were observed in brain temperature. Fifteen minutes after heatstroke, brain temperature was 37.6 +/- 0.4 degrees C, 36.1 +/- 0.4 degrees C, and 33.6 +/- 0.8 degrees C in HS, HS + F, and HS + J, respectively. Survival time was 16.1 +/- 2.1, 33.0 +/- 3.8, and >120 mins in these groups, respectively. Neuron damage score was significantly lower in HS + J and without lateralization.

CONCLUSIONS

We successfully demonstrated that direct retrograde hypothermic perfusion via the jugular vein without cardiopulmonary bypass protected the brain after heat stroke. This technique cooled the brain but did not significantly interfere with body temperature.

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.

Brain protection during surgery of the aortic arch

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

Neurological Complications of Aortic Surgery

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

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

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

Retrograde cerebral perfusion provides negligible flow through brain capillaries in the pig

OBJECTIVES

Although retrograde cerebral perfusion is being used clinically during aortic arch surgery, whether retrograde flow perfuses the brain effectively is still uncertain.

METHODS

Fourteen pigs were cooled to 20 degrees C with cardiopulmonary bypass and perfused retrogradely via the superior vena cava for 30 minutes: 7 underwent standard retrograde cerebral perfusion and 7 underwent retrograde perfusion with occlusion of the inferior vena cava. Antegrade and retrograde cerebral blood flow were calculated by quantitating fluorescent microspheres trapped in brain tissue after the animals were put to death; microspheres returning to the aortic arch, the inferior vena cava, and the descending aorta were also analyzed during retrograde cerebral perfusion.

RESULTS

Antegrade cerebral blood flow was 16 +/- 7.7 mL. min(-1). 100 g(-1) before retrograde cerebral perfusion and 22 +/- 6.3 mL. min(-1). 100 g(-1) before perfusion with caval occlusion (P =.14). During retrograde perfusion, calculations based on the number of microspheres trapped in the brain showed negligible flows (0.02 +/- 0.02 mL. min(-1). 100 g(-1) with retrograde cerebral perfusion and 0.04 +/- 0.02 mL. min(-1). 100 g(-1) with perfusion with caval occlusion; P =.09): only 0.01% and 0.02% of superior vena caval inflow, respectively. Less than 13% of retrograde superior vena caval inflow blood returned to the aortic arch with either technique. During retrograde cerebral perfusion, more than 90% of superior vena caval input was shunted to the inferior vena cava and was then recirculated, as indicated by rapid development of an equilibrium in microspheres between the superior and inferior venae cavae. With retrograde perfusion and inferior vena caval occlusion, less than 12% of inflow returned to the descending aorta and only 0.01% of microspheres.

CONCLUSIONS

The paucity of microspheres trapped within the brain indicates that retrograde cerebral perfusion, either alone or combined with inferior vena caval occlusion, does not provide sufficient cerebral capillary perfusion to confer any metabolic benefit. The slightly improved outcome previously reported with retrograde cerebral perfusion during prolonged circulatory arrest in this model may be a consequence of enhanced cooling resulting from perfusion of nonbrain capillaries and from venoarterial and venovenous shunting.

Results of aortic arch repair with hypothermic circulatory arrest and retrograde cerebral perfusion

BACKGROUND

Repair of aortic arch pathology is reliably performed with hypothermic circulatory arrest, but the best method of brain protection is controversial.

METHODS

We reviewed a consecutive series of 67 patients who had aortic arch repair with hypothermic circulatory arrest. Retrograde perfusion of arterial blood into the superior vena cava (SVC) during systemic arrest was used in 87%. Average age was 65 years. Acute dissection was present in 25%. Average circulatory arrest time was 37 minutes, and average temperature 17.7 degrees C.

RESULTS

Hospital mortality was 1.5%. Strokes occurred in 4.5%. Temporary neurological dysfunction occurred in 16%. Multivariate logistic regression analysis showed that acute dissection was the only independent predictor of the combined risk of stroke and temporary neurological dysfunction (odds ratio 8.5). Duration of circulatory arrest and patient age were not risk factors for adverse neurological outcome.

CONCLUSION

Continuous arterial perfusion of the SVC during hypothermic circulatory arrest provides excellent cerebral protection for aortic arch repair. Acute dissection is an independent risk factor for adverse neurological outcome. Arrest time is not a predictor of neurological dysfunction.

Intermittent retrograde cerebral perfusion during prolonged period of hypothermic circulatory arrest: a study in a chronic porcine model

Previous studies have shown that although retrograde cerebral perfusion (RCP) improves cerebral outcome during hypothermic circulatory arrest (HCA), RCP exposes the brain to subsequent edema. In this study, we have compared intermittent RCP (I-RCP) with continuous RCP (C-RCP) and HCA alone to determine whether the rate of fluid sequestration can be decreased without losing the beneficial effects of RCP. Eighteen pigs were randomly assigned to undergo 75 min of I-RCP, C-RCP or HCA at 20 degrees C. Hemodynamic and metabolic measurements were carried out for upto 20 h. Behavioral assessments were examined until day 7, when histopathologic analysis of the brain was performed. The median amount of fluid sequestered was 145 ml after C-RCP and -50 ml after I-RCP (p = 0.04). The mean brain weight of the animals that died within the first postoperative day was significantly higher than that in electively sacrificed animals in the C-RCP group (p = 0.04). These data suggest that if RCP is implemented intermittently, the rate of cerebral edema can be decreased, without compromising the benefits of this strategy.

Comparison of two sites of inflow pressure measurement during retrograde cerebral perfusion

OBJECTIVE

To determine whether internal jugular venous valves influence inflow pressure during retrograde cerebral perfusion.

DESIGN

Prospective study.

SETTING

Community hospital, university setting, single institution.

PARTICIPANTS

Ten patients undergoing reconstructive aortic arch surgery with profound hypothermic circulatory arrest.

INTERVENTIONS

During retrograde cerebral perfusion, inflow pressure was continuously measured at 2 separate sites relative to the left internal jugular venous valve (ie, superior vena cava inflow catheter [infravalvular pressure] and rostral left internal jugular vein [supravalvular pressure]).

MEASUREMENTS AND MAIN RESULTS

Infravalvular pressure of 29.8 +/- 3.5 mmHg and supravalvular pressure of 22.7 +/- 0.8 mmHg were significantly different (mean difference, 7.1 +/- 3.6 mmHg; p = 0.041). In 8 patients, the pressure difference was <6 mmHg; whereas in 2 patients, the pressure difference was >20 mmHg. Bland and Altman analysis revealed 95% limits of agreement on mean bias of -12.9 to 27.8 mmHg.

CONCLUSION

Internal jugular venous valves can obstruct retrograde cerebral perfusion inflow, manifest by an inflow pressure difference between the superior vena cava and internal jugular vein. In the presence of competent internal jugular venous valves, measurement of inflow pressure in the superior vena cava may be an inaccurate estimate of actual cerebral perfusion pressure. Internal jugular vein pressure should be monitored to avoid inadvertent cerebral hypoperfusion.

Retrograde cerebral perfusion in human brains

Retrograde cerebral perfusion via the superior vena cava during deep hypothermic circulatory arrest has evolved as a means of cerebral protection in aortic-arch surgery. We showed, with use of fluorescein retinal angiography, that during retrograde cerebral perfusion, fluorescein injected into the superior vena cava entered the retinal venules, flowed to the capillaries, and subsequently, to the retinal arterioles. Since the retina is embryologically part of the brain, we conclude that this procedure does allow blood to perfuse in a retrograde way through the human brain.

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

BACKGROUND

Previous studies have shown that retrograde cerebral perfusion can improve neurologic outcome after prolonged hypothermic circulatory arrest. Here we have compared two temperatures of retrograde cerebral perfusion (15 degrees C and 25 degrees C) with hypothermic circulatory arrest at systemic hypothermia of 25 degrees C to clarify whether the possible benefit of retrograde cerebral perfusion may only be due to improved cooling effect.

METHODS

Eighteen pigs (23-27 kg) were randomly assigned to undergo 15 degrees C retrograde cerebral perfusion at systemic hypothermia of 25 degrees C, 25 degrees C retrograde cerebral perfusion at 25 degrees C systemic hypothermia, or hypothermic circulatory arrest at 25 degrees C for 40 minutes. Flow was adjusted to maintain superior vena cava pressure at 20 mm Hg during retrograde cerebral perfusion. Hemodynamic, electrophysiologic, metabolic, and temperature monitoring were performed until 4 hours after the start of rewarming. Daily behavioral assessment was done until death or until the animals were killed on day 7. Histopathologic analysis of the brain was carried out on all animals.

RESULTS

Epidural temperatures were lower in the 15 degrees C retrograde cerebral perfusion group during the intervention (P <.05). In the 15 degrees C retrograde cerebral perfusion group, 4 (67%) of 6 animals survived for 7 days compared with 3 (50%) of 6 in both the 25 degrees C retrograde cerebral perfusion and hypothermic circulatory arrest groups. The median total histopathologic score was 5 in the 15 degrees C retrograde cerebral perfusion group and 7 in the 25 degrees C retrograde cerebral perfusion group (P =.04).

CONCLUSIONS

These findings suggest that enhanced cranial hypothermia is the major beneficial factor of retrograde cerebral perfusion when careful attention is paid to its implementation.

Retrograde perfusion and true reverse brain blood flow in humans

OBJECTIVE

Reversal of brain blood flow is necessary for retrograde cerebral perfusion (RCP) to have any metabolic benefit, but RCP is commonly used with little clinical evidence of the true incidence of reverse brain blood flow and impact. S-100B is exclusive to the brain and spinal cord and released during hypothermic circulatory arrest (HCA). True reverse brain blood flow (tRBBF) during RCP may be determined by demonstrating an excess of S-100B in the effluent blood from the common carotid artery compared to blood entering the brain.

METHODS

Simultaneous blood samples were drawn from the jugular bulb and left common carotid artery during RCP at 5 min intervals in ten patients undergoing aortic surgery, utilizing HCA and subjected to blood gas, glucose and S-100B quantification. RCP was instituted at maximum pressure of 25 mmHg. Trans-cranial Doppler (TCD) continuously monitored the middle cerebral artery velocity (MCAV).

RESULTS

The mean HCA and RCP durations were 31 min (20-50 min). Reversal of MCAV was demonstrated in only 6/10 cases (mean, 6 cm/s). Veno-arterial (V-A) extraction of oxygen and glucose occurred in all cases (P<0.001), with the mean effluent pO(2) falling to 14 mmHg. V-A S-100 gradients greater than 5% were demonstrated in 8/10 cases and correlated with higher oxygen extraction (P<0.01). In patients with and without MCAV reversal, the S-100 gradients were 1. 7 and 0.3 micromol/l, respectively (P<0.01).

CONCLUSIONS

tRBBF occurred in nearly all patients. MCAV reversal appears to be a specific but insensitive guide to reverse perfusion. The de-saturation of effluent blood is not a reliable guide to true brain perfusion, and despite RCP, the brain remains ischaemic.

Blood flow velocities in the vertebral veins of healthy subjects: a duplex sonographic study

Along with the jugular veins, the vertebral veins serve as an important pathway for venous blood returning from the brain. In this study, the authors report duplex sonographic findings in 138 healthy subjects without central nervous disease. Successful insonation was possible in 70.7% of all examined vessels. Bilateral insonation was achieved in 86 subjects (62.3%). Only 1 vertebral vein was detected in 23 persons (16.7%), whereas no vein was found in 29 persons (21%). The authors observed a marked variation of peak flow velocities ranged (5-81 cm/s, mean +/- standard deviation, 23.9 +/- 12.3 cm/s). No significant gender-related or side-to-side differences or age influences on flow velocities were detected. The authors' findings may be of relevance when discussing flow velocities in the vertebral veins in cases of cerebrovenous disorders (e.g., dural sinus thrombosis) or in patients after neck dissection.

Retrograde perfusion of the spinal cord during aortic crossclamping: initial observations in the swine model

BACKGROUND

Retrograde perfusion has emerged as a useful technique for the preservation of the heart and brain when arterial circulation is interrupted. Herein, this study was designed to test the hypothesis that retrograde perfusion of the azygos vein is sufficient to maintain viability of the spinal cord during aortic occlusion in the swine model.

METHODS

Female swine, 17 to 22 kg, underwent left thoracotomy, creation of a shunt between the aortic arch and the azygos vein, and aortic crossclamping for 60 minutes: the shunt was open in the retrograde perfusion group (n = 5) and closed in the control group (n = 4). The animals were evaluated for neurologic function for 8 days and killed. Spinal cords were processed for histologic examination. Additional animals underwent left thoracotomy and injection of a casting solution in the azygos vein (n = 2), left thoracotomy and angiography of the azygos vein (n = 2), and a compartmentalization procedure to separate the azygos vein from the caval system followed by angiography (n = 2).

RESULTS

Differences in the neurologic (2-sample t test, P =.11) and histologic (2-sample t test, P =.65) scores of retrograde perfusion and control groups were likely due to chance. Casting and angiography groups showed extensive collaterals between azygos and caval systems, only partially interrupted by compartmentalization.

CONCLUSIONS

Retrograde perfusion does not protect the spinal cord from ischemic injury. The collateral network between the azygos and caval systems prevents the oxygenated blood from reaching the cord. Surgical separation between the 2 systems was only partially successful in this study.

Risk analysis for aortic surgery using hypothermic circulatory arrest with retrograde cerebral perfusion

BACKGROUND

Retrospective analysis of 144 patients undergoing aortic arch reconstruction using hypothermic circulatory arrest (HCA) with retrograde cerebral perfusion (RCP) for cerebral protection was performed.

METHODS

The diagnosis, procedure, and anatomic site of the arch anastomosis were analyzed to see if they were independent predictors of mortality or morbidity. In addition age, gender, HCA-RCP times, preoperative malperfusion (both treated and untreated), surgical status, and redo surgery status were also examined to determine their influence on the incidence of death and complications. Both multivariate and univariate analysis were performed using linear regression and cross-tabulation with either chi2 or Fisher's exact test where appropriate.

RESULTS

Preoperative surgical status (emergent) and the presence of untreated preoperative malperfusion were the only variables that were significant independent predictors for mortality (p <0.05). No variable was significant for the prediction of stroke or other complications. The severity of surgery had no bearing on the patient outcome.

CONCLUSIONS

Complex aortic surgery using HCA-RCP can be performed with acceptable risk to the patients.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Assessment of arteriovenous blood flow during retrograde cerebral perfusion

OBJECTIVE

This study examined arterial and venous blood flow during retrograde cerebral perfusion (RCP) to quantify what proportion of arterial inflow is not recovered as venous outflow.

DESIGN

Prospective.

SETTING

Community hospital, university setting, single institution.

PARTICIPANTS

Twelve patients undergoing reconstructive aortic arch surgery with profound hypothermic circulatory arrest and RCP.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

RCP arterial inflow and venous outflow measurements were recorded at 2-minute intervals for 10 minutes, averaged, and then compared. Only 44.9%+/-16.3% of RCP inflow returned through the aortic arch. The remainder was not recovered.

CONCLUSION

Internal jugular venous valves, sequestration, and shunting may contribute to arterial inflow diversion during RCP.

Distribution of cerebral flow using retrograde versus antegrade cerebral perfusion

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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