Cerebral metabolism and circulatory arrest: effects of duration and strategies for protection

Direct Innominate Artery Cannulation versus Side Graft for Selective Antegrade Cerebral Perfusion during Aortic Hemiarch Replacement

Background  Selective antegrade cerebral perfusion (SACP) has become our preferred method for cerebral protection during open arch cases. While the initial approach involved sewing a graft to the innominate artery as the arterial cannulation site, our access strategy has since evolved to central aortic cannulation with use of a percutaneous cannula in the innominate for SACP. We hypothesized that SACP delivered via direct innominate cannulation using a 12- or 14-Fr cannula results in equivalent outcomes to cases utilizing a side graft.

Methods  This was a single-center, retrospective analysis of 211 adult patients who underwent elective hemiarch replacement using hypothermic circulatory arrest with SACP via the innominate artery between 2012 and 2020. Urgent and emergent cases were excluded.

Results  A side graft sutured to the innominate was utilized in 81% ( n  = 171) of patients, while direct innominate artery cannulation was performed in 19% ( n  = 40) of patients. Baseline patient characteristics were similar between groups aside from a higher baseline creatinine in the direct cannulation group (1.3 vs. 0.9, p  = 0.032). Patients undergoing direct cannulation demonstrated shorter cardiopulmonary bypass time (132.7 vs. 154.9 minutes, p  = 0.020) and shorter circulatory arrest time (8.1 vs. 10.9 minutes, p  = 0.004). Nadir bladder temperature did not significantly differ between groups (27.2°C for side graft vs. 27.6°C for direct cannulation, p  = 0.088). There were no significant differences in postoperative outcomes.

Conclusion  Direct cannulation of the innominate artery with a 12- or 14-Fr cannula for SACP during hemiarch replacement is a safe alternative to using a sutured side graft. While cardiopulmonary bypass and circulatory arrest times appear improved, this is likely attributable to accumulation of experience and proficiency in technique. However, direct innominate artery cannulation may facilitate quicker completion of these procedures by eliminating the time necessary to suture a graft to the innominate artery.

Brain Protection in Aortic Arch Surgery: An Evolving Field

Despite advances in cardiac surgery and anesthesia, the rates of brain injury remain high in aortic arch surgery requiring circulatory arrest. The mechanisms of brain injury, including permanent and temporary neurologic dysfunction, are multifactorial, but intraoperative brain ischemia is likely a major contributor. Maintaining optimal cerebral perfusion during cardiopulmonary bypass and circulatory arrest is the key component of intraoperative management for aortic arch surgery. Various brain monitoring modalities provide different information to improve cerebral protection. Electroencephalography gives crucial data to ensure minimal cerebral metabolism during deep hypothermic circulatory arrest, transcranial Doppler directly measures cerebral arterial blood flow, and near-infrared spectroscopy monitors regional cerebral oxygen saturation. Various brain protection techniques, including hypothermia, cerebral perfusion, pharmacologic protection, and blood gas management, have been used during interruption of systemic circulation, but the optimal strategy remains elusive. Although deep hypothermic circulatory arrest and retrograde cerebral perfusion have their merits, there have been increasing reports about the use of antegrade cerebral perfusion, obviating the need for deep hypothermia. With controversy and variability of surgical practices, moderate hypothermia, when combined with unilateral antegrade cerebral perfusion, is considered safe for brain protection in aortic arch surgery performed with circulatory arrest. The neurologic outcomes of brain protection in aortic arch surgery largely depend on the following three major components: cerebral temperature, circulatory arrest time, and cerebral perfusion during circulatory arrest. The optimal brain protection strategy should be individualized based on comprehensive monitoring and stems from well-executed techniques that balance the major components contributing to brain injury.

Non-invasive optical neuromonitoring of the temperature-dependence of cerebral oxygen metabolism during deep hypothermic cardiopulmonary bypass in neonatal swine

Management of deep hypothermic (DH) cardiopulmonary bypass (CPB), a critical neuroprotective strategy, currently relies on non-invasive temperature to guide cerebral metabolic suppression during complex cardiac surgery in neonates. Considerable inter-subject variability in temperature response and residual metabolism may contribute to the persisting risk for postoperative neurological injury. To characterize and mitigate this variability, we assess the sufficiency of conventional nasopharyngeal temperature (NPT) guidance, and in the process, validate combined non-invasive frequency-domain diffuse optical spectroscopy (FD-DOS) and diffuse correlation spectroscopy (DCS) for direct measurement of cerebral metabolic rate of oxygen (CMRO₂). During CPB, n = 8 neonatal swine underwent cooling from normothermia to 18℃, sustained DH perfusion for 40 min, and then rewarming to simulate cardiac surgery. Continuous non-invasive and invasive measurements of intracranial temperature (ICT) and CMRO₂ were acquired. Significant hysteresis (p < 0.001) between cooling and rewarming periods in the NPT versus ICT and NPT versus CMRO₂ relationships were found. Resolution of this hysteresis in the ICT versus CMRO₂ relationship identified a crucial insufficiency of conventional NPT guidance. Non-invasive CMRO₂ temperature coefficients with respect to NPT (Q₁₀ = 2.0) and ICT (Q₁₀ = 2.5) are consistent with previous reports and provide further validation of FD-DOS/DCS CMRO₂ monitoring during DH CPB to optimize management.

Design of a Physiologic Pulsatile Flow Cardiopulmonary Bypass System for Neonates and Infants

Cardiopulmonary bypass surgical techniques that allow a surgeon to operate on the infant's heart use an extracorporeal circuit consisting of a pump, oxygenator, arterial and venous reservoirs, cannulae, an arterial filter, and tubing. The extracorporeal technique currently used in infants and neonates is sometimes associated with neurologic damage. We are developing a modified cardiopulmonary bypass system for neonates that has been tested in vitro and in one animal in vivo. Unlike other extracorporeal circuits which use steady flow, this system utilizes pulsatile flow, a low prime volume (500ml) and a closed circuit. During in vitro experiments, the pseudo patient's mean arterial pressure was kept constant at 40 mmHg and the extracorporeal circuit pressure did not exceed a mean pressure of 200 mmHg. In our single in vivo experiment, the primary objective was to determine whether physiologic pulsatility with a 10F (3.3 mm) aortic cannula could be achieved. The results suggest that this is possible.

Deep Hypothermia and Circulatory Arrest in Adults

Brain protection during cardiopulmonary bypass has been the subject of intense research. Deep hypothermic circulatory arrest (DHCA) continues to be used for that goal during complex aortic arch and large intracranial aneurysm surgeries. The anesthetic management for adult patients undergoing these types of procedures requires specific knowledge and expertise. Based on our experience and review of the current literature, the authors highlight the key areas of the anesthetic plan, discussing the risk factors associated with adverse neurologic outcome as well as the rationale for decisions regarding specific monitors and medications. In the conclusion an anesthetic protocol for adult patients undergoing DHCA is suggested.

Cerebral injury during paediatric heart surgery: perfusion issues

Suboptimal neurodevelopmental outcome is common in children who have congenital heart disease. Its aetiology is often multifactorial. This review focuses on the role of cardiopulmonary bypass. Hypothermia is the mainstay of cerebral protection. Low flow and regional low flow are preferred to deep hypothermic circulatory arrest in many situations. Cooling and rewarming, aortopulmonary collaterals, pH, air emboli, the systemic inflammatory response, haematocrit, oxygenation, glucose and ultrafiltration can influence neurodevelopmental outcome. Although no pharmacological agents have been shown to have a beneficial effect on neurodevelopmental outcome in clinical practice in children, animal work on the use of steroids several hours before surgery is encouraging.

Paediatric CPB: Bypass in a High Risk Group

Children and particularly neonates present unique challenges during CPB. Patient age, size, underlying anatomy and surgical strategy influence the perfusion techniques and the construction of the CPB circuit. The normal changes in physiology in the first weeks of life impact upon surgical technique and outcome of repair.

Limited surgical access necessitates alternative cannulation strategies. Deep hypothermia, low flow CPB and circulatory arrest are frequently used. An understanding of the related pathophysiology is therefore required to make the correct choices and to optimise patient outcome.

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.

Outcomes of Aortic Arch Replacement Performed Without Circulatory Arrest or Deep Hypothermia

BACKGROUND

Aortic arch replacement using standard techniques, including deep hypothermic circulatory arrest and selective antegrade cerebral perfusion, is still associated with significant mortality and cerebral morbidity. We have previously described the "branch-first" technique that avoids circulatory arrest or profound hypothermia with excellent outcomes. We now describe our clinical experience with a larger cohort of patients as well as follow-up of our earlier results. We also describe a further technical simplification to this technique.

METHODS

From 2005 to 2010, 43 patients underwent a "branch-first continuous perfusion" technique for aortic arch replacement. In this technique, arterial perfusion is peripheral, usually by femoral inflow. Disconnection of each arch branch and anastomosis to a perfused trifurcation graft proceeds sequentially from the innominate to the left subclavian artery, with uninterrupted perfusion of the heart and viscera by the peripheral cannula. In the first cohort perfusion to the trifurcation graft was by right axillary cannulation. Since 2009, a modification was introduced such that perfusion is supplied directly by a sidearm on the trifurcation graft. This was used in the last 18 patients of this series. After reconstruction of the debranched arch and ascending aorta, the common stem of the trifurcation graft is anastomosed to the arch graft. In this series, there were 27 males, and mean age was 63 ± 13 years. Fifteen cases (35%) were performed with urgent/emergent priority. Nineteen patients (44%) were operated for aortic dissection, and the remainder for aneurysms. Seven patients (16%) had previously undergone a cardiac surgical procedure.

RESULTS

There were two (4.7%) early mortalities while one patient (2.3%) experienced a permanent stroke. One patient (2%) required mechanical support while three (7%) required hemofiltration for renal support. Extubation was achieved within 24 hours in 21 patients (49%) while 19 (42%) were discharged from the Intensive Care Unit (ICU) within two days. Eight patients (19%) did not require any transfusion of red cells or platelets. Mean follow-up duration was 21 ± 19 months and was 100% complete. At three years, survival was 95 ± 3.2%. No patients required subsequent aortic reoperation during this early follow-up period.

CONCLUSIONS

This modified branch-first continuous perfusion technique brings us closer to the goal of arch surgery without cerebral or visceral circulatory arrest and the morbidity of deep hypothermia. Our early experience is encouraging although greater numbers and longer follow-up will reveal the full potential of this approach.

Is it worth packing the head with ice in patients undergoing deep hypothermic circulatory arrest?

A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was: Is it worth packing the head with ice in patients undergoing deep hypothermic circulatory arrest (DHCA)? Altogether more than 34 papers were found using the reported search, of which 7 represented the best evidence to answer the clinical question, 5 of which were animal studies, 1 was a theoretical laboratory study and 1 study looked at the ability to cool using circulating water 'jackets' in humans. There were no available human studies looking at the neurological outcome with or without topical head cooling with ice without further adjunct methods of cerebral protection. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. Four papers studied animals undergoing DHCA for 45 min-2 h depending on the study design, with or without packing the head with ice. The studies all demonstrated improved cerebral cooling when the head was packed with ice during DHCA. They also illustrated an improved neurological outcome, with better behavioural scores (P < 0.05), and in some, survival, when compared with animals whose heads were not packed in ice. One study examined selective head cooling with the use of packing the head with ice during rewarming after DHCA. However, they demonstrated worse neurological outcomes in these animals, possibly due to the loss of cerebral vasoregulation and cerebral oedema. One study involved a laboratory experiment showing improved cooling using circulating cool water in cryotherapy braces than by using packed ice. They extrapolated that newer devices to cool the head may improve cerebral cooling during DHCA. The final study discussed here demonstrated the use of circulating water to the head in humans undergoing pulmonary endarterectomy. They found that tympanic membrane temperatures could be maintained significantly lower than bladder or rectal temperatures when using circulating water to cool the head. We conclude that topical head cooling with ice is of use during DHCA but not during rewarming following DHCA and that it may be possible to advance topical head cooling techniques using circulating water rather than packed ice.

Brief review on systematic hypothermia for the protection of central nervous system during aortic arch surgery: a double-sword tool?

Antegrade selective cerebral perfusion in conjunction with hypothermia attenuate postoperative neurological injury, which in turn still remains the main cause of mortality and morbidity following aortic arch surgery. Hypothermic circulatory arrest however could be a useful tool during arch surgery, surgery for chronic thromboembolic disease, air on the arterial line during CPB, during cavotomy for extraction of renal cell carcinoma with level IV extension, or when dealing with difficult trauma to the SVC or IVC. Cerebral protective effects with hypothermic procedures including inhibition of neuron excitation, and discharge of excitable amino acids, and thereby, prevention of an increase in intercellular calcium ions, hyperoxidation of lipids in cell membranes, and free radical production.The authors are briefly discussing the fundamental principles of using hypothermia as an adjunct tool of the cardiothoracic surgeon's practice. The relationship between temperature, flow, metabolic requirements and adverse effects is addressed.

Interrupted Aortic Arch or Extreme Coarctation? A Case Report and Review of the Literature

The hallmark feature of aortic interruption that is useful in differentiating it from aortic coarctation is the "complete absence" of continuity between both parts of the interrupted segment. In this study, we reviewed the 28 patients diagnosed with isolated interrupted aortic arch (IAA) who reached adult age (> 20 years), aimed to review the validity of the Celoria-Patton classification in the literature, and reported the first microscopic pathology of the IAA in an adult.

Factors influencing neurologic outcome after neonatal cardiopulmonary bypass: what we can and cannot control

Advances in cardiopulmonary bypass and surgical techniques have led to progress in the early repair of congenital heart defects in children. However, as increasing numbers survive their initial cardiac operation, an awareness is emerging that significant early and late neurologic morbidities continue to complicate otherwise successful operative repairs. Adverse neurologic outcomes after neonatal cardiac surgery are multifactorial and relate to both fixed and modifiable mechanisms. The purpose of this review is to (1) review mechanisms of brain injury after neonatal cardiopulmonary bypass, (2) examine risk factors, and (3) speculate on how investigations may improve our understanding of neurologic injury.

Cerebral Perfusion

Aortic arch surgery necessitates interrupted brain perfusion and carries a risk of brain injury. Various brain protective techniques have been advocated to reduce risk including hypothermic arrest and retrograde or selective antegrade perfusion. Knowledge of the pathophysiologic consequences of deep hypothermia, may aid the surgeon in deciding when to initiate circulatory arrest and for how long. Retrograde cerebral perfusion use was advocated to prolong safe arrest durations but may not improve outcomes. Selective antegrade cerebral perfusion appears to have become the preferred method of brain protection. However, the delivery conditions and optimal perfusate constitution require further study.

Specific bypass conditions determine safe minimum flow rate

BACKGROUND

The purpose of this study is to define a safe minimum flow rate for specific bypass conditions using continuous monitoring with near-infrared spectroscopy and direct observation of the cerebral microcirculation.

METHODS

Two series of experiments (n = 72 in each) were conducted in which piglets were cooled to a temperature of 15 degrees, 25 degrees, or 34 degrees C on cardiopulmonary bypass with hematocrit 20% or 30%, pH-stat management in all, followed by 1 or 2 hours of reduced flow (10, 25, or 50 mL.kg(-1).min(-1)). Animals in series one had a cranial window placed over the parietal cortex to evaluate the microcirculation with intravital microscopy. Plasma was labeled with fluorescein-isothiocyanate-dextran for assessment of functional capillary density (FCD) and microvascular diameter. In series two, near-infrared spectroscopy was utilized to detect tissue oxygenation index (TOI). Outcome measures included histologic and neurologic injury scores.

RESULTS

The TOI during low flow and FCD during rewarming and after weaning from cardiopulmonary bypass were associated with neurologic injury. Failure of FCD to return to baseline during rewarming predicted worse functional and histologic outcome (p < 0.001). Regression analysis indicated that temperature and low-flow rate were multivariable predictors of TOI and FCD during rewarming (p < 0.001).

CONCLUSIONS

Tissue oxygen index derived from near-infrared spectroscopy is a useful real-time monitor for detecting inadequate cerebral perfusion during cardiopulmonary bypass. Minimal safe pump flow rate varies according to the conditions of bypass: using pH stat management and with an hematocrit of either 20% or 30%, a flow rate as low as 10 mL.kg(-1).min(-1) is safe for as long as 2 hours at a temperature of 15 degrees C. However, under the same conditions at 34 degrees C, a flow rate of 10 mL.kg(-1).min(-1) is very likely to be associated with neurologic injury.

Aortic Arch Reconstruction: Safety of Moderate Hypothermia and Antegrade Cerebral Perfusion During Systemic Circulatory Arrest

BACKGROUND AND AIM

The ideal strategy for cerebral protection during aortic arch (AA) reconstructive surgery remains undefined. Antegrade cerebral perfusion (ACP) during systemic circulatory arrest (SCA) may provide superior results; however, optimal systemic temperature is undetermined. Our objective was to determine whether "deep" hypothermia is necessary during ACP with SCA, and whether the degree of hypothermia is associated with neurologic outcomes postoperatively.

METHODS

Retrospective series of 72 consecutive patients (aged 65.9 +/- 3.2 years) who underwent AA reconstructive surgery at Vancouver General Hospital using a cerebral protection strategy of ACP with SCA between December 1995 and December 2002. Patients were divided into two groups according to lowest systemic temperature: <22 degrees C (n = 52) and > or =22 degrees C (n = 20).

RESULTS

ACP was via right axillary or innominate artery, +/- left common carotid cannulation. Median SCA time with ACP was not different between groups. There were four hospital deaths (5.6%) (three from the <22 degrees C group). Eight patients (11.2%) had major neurologic injuries (seven from the <22 degrees C group): 4 (5.6%) permanent (1 fatal) and 4 (5.6%) temporary. There was a trend toward a significantly higher incidence of delirium in the <22 degrees C group than the > or =22 degrees C group (30.8 vs 10.0%, respectively, p = 0.07).

CONCLUSIONS

In our experience, SCA with ACP was a safe technique for AA reconstructive surgery. The observation of a larger number of major neurologic injuries, and a trend toward a higher incidence of delirium in the <22 degrees C group, suggests that systemic temperatures below 22 degrees C may not be necessary and may be associated with a higher incidence of neurologic injury when using ACP during SCA.

Current insights regarding neurological and developmental abnormalities in children and young adults with complex congenital cardiac disease

Over a decade ago, I co-authored a review in Cardiology in the Young regarding neurological outcomes following surgery for congenital cardiac disease.1In that review, I placed much emphasis on the conduct of cardiopulmonary bypass, and its role in neurodevelopmental disabilities. Much has been learned in the intervening years regarding the multifactorial causes of abnormal school-age development, in particular, the role of prenatal, perioperative, socioeconomic, and genetic influences. In this update, I will highlight some of the recent advances in our understanding of the protean causes of neurological, behavioral, and developmental abnormalities in children and young adults with complex forms of congenital cardiac disease. In addition, I will summarize the current data on patients at particular high-risk for adverse neurodevelopmental outcomes, specifically those with a functionally univentricular heart who have had staged reconstruction with ultimate conversion to the Fontan circulation.

Cardiac Output Augmentation During Hypoxemia Improves Cerebral Metabolism After Hypothermic Cardiopulmonary Bypass

BACKGROUND

Hypothermic circulatory arrest (HCA) impairs cerebral oxygen delivery (CDO2) and cerebral oxygen consumption (CMRO2), which are further reduced by perioperative hypoxemia. This study investigates if continuous hypothermic low-flow cardiopulmonary bypass (HLF) or intermittent hypothermic low-flow cardiopulmonary bypass (IHLF) can prevent reductions in CDO2 and CMRO2 during hypoxemia.

METHODS

Eighteen neonatal piglets, cooled to 16 degrees to 18 degrees C with cardiopulmonary bypass (CPB), were randomly assigned into three groups: HCA, HLF (50 cc.kg(-1).min(-1)), or IHLF (1 minute of HLF for every 15 minutes of HCA). After 60 minutes of hypothermia, normothermic CPB (100 cc.kg(-1).min(-1)) was established and cerebral perfusion data measured at hyperoxemia (PaO2 150 to 250 mm Hg), hypoxemia (PaO2 50 to 60 mm Hg), and severe hypoxemia (PaO2 30 to 40 mm Hg), and with increased CPB flow (200 cc.kg(-1).min(-1)) during severe hypoxemia.

RESULTS

The CMRO2 (in mL O2.100 g(-1).min(-1)) was lower after HCA (2.5 +/- 0.3), compared with HLF (4.1 +/- 0.5, p = 0.02) and IHLF (6.2 +/- 0.8, p = 0.002). Within groups, the change from hyperoxemia to severe hypoxemia resulted in decreased CMRO2: HCA (1.3 +/- 0.2, p = 0.004), HLF (3.0 +/- 0.5, p = 0.01), and IHLF (2.9 +/- 0.5, p = 0.01). During severe hypoxemia, increasing CPB flow (from 100 cc.kg(-1).min(-1) to 200 cc.kg(-1).min(-1)) improved CMRO2: HCA (1.9 +/- 0.5, p = 0.05), HLF (4.2 +/- 0.5, p = 0.05), and IHLF (7.4 +/- 0.5, p = 0.04).

CONCLUSIONS

Hypoxemia reduces CDO2 and CMRO2 despite the method of hypothermic CPB. Increased CPB flow during hypoxemia can restore both CDO2 and CMRO2 to values found with hyperoxemia and slower CPB flows. Augmenting cardiac output during periods of perioperative hypoxemia may prevent cerebral injury after exposure to hypothermic cardiopulmonary bypass.

Postoperative hypoxemia exacerbates potential brain injury after deep hypothermic circulatory arrest

BACKGROUND

Deep hypothermic circulatory arrest (DHCA) is often used in infants undergoing the Norwood procedure. These infants are hypoxic after surgery. Previous investigations into the cerebral metabolic response and oxygen utilization after DHCA examined animals with normal arterial oxygenation. This study reports the cerebral metabolic consequences if hypoxemic conditions are present after DHCA.

METHODS

Eighteen neonatal piglets were randomly assigned to three groups. The control group was ventilated; the cardiopulmonary bypass group underwent 60 minutes of normothermic cardiopulmonary bypass, and the DHCA group underwent cardiopulmonary bypass and 60 minutes of DHCA (16 degrees to 18 degrees C) followed by rewarming. Hemodynamic and cerebral perfusion data were measured at an arterial partial pressure of oxygen (PaO2) of 150 to 250 mm Hg, and then at moderate hypoxemia (PaO2, 50 to 60 mm Hg) and severe hypoxemia (PaO2, 25 to 35 mm Hg).

RESULTS

Cerebral oxygen delivery decreased by 44% from PaO2 150 to 250 mm Hg to severe hypoxemia (p < 0.001). Cerebral oxygen extraction increased from moderate hypoxemia to severe hypoxemia in the control (57.9% +/- 3.7% to 71.8% +/- 3.8%; p = 0.002) and cardiopulmonary bypass groups (61.2% +/- 2.6% to 70.6% +/- 1.2%; p = 0.035); however, the cerebral oxygen extraction of the DHCA group did not increase under these conditions (82.8% +/- 1.8% to 77.9% +/- 4.3%; p = 0.32). The cerebral metabolic rate of oxygen consumption of the DHCA group decreased from PaO2 150 to 250 mm Hg to severe hypoxemia (1.86 +/- 0.20 to 0.99 +/- 0.24 mL O2 x 100 g(-1) x min(-1); p = 0.02), whereas the cerebral metabolic rate of oxygen consumption did not change under these conditions in the control and cardiopulmonary bypass groups.

CONCLUSIONS

Under hypoxemic conditions cerebral metabolic rate of oxygen consumption deteriorates after DHCA. Infants exposed to DHCA may be at greater risk of brain injury when postoperative hypoxemia is present. Because maximal cerebral oxygen extraction after DHCA occurs at moderate hypoxemia, techniques that increase cerebral oxygen delivery may reduce the risk of hypoxic brain injury.

Practice patterns in neonatal cardiopulmonary bypass

This article reviews practice patterns of numerous congenital heart surgeons, as collected from surveys (the Congenital Heart Surgeon's Society) and from audience response at the American Association of Thoracic Surgery (May 2003) and the Society of Thoracic Surgeons (January 2004). The information shows that there are numerous practice patterns, with unanimity only in the use of cardioplegia, although the delivery, type, and timing of doses varies. Hypothermic circulatory arrest continues to be used by the majority of congenital heart surgeons, although strategies for delivery have evolved in a way that reflects research contributions over the past decade.

Brain injury in children with congenital heart disease

The incidence of neurodevelopmental impairment in children with congenital heart disease is high. Its aetiology is multiple and complex. Prevention and treatment must start during the preoperative period and continue through the intra- and postoperative periods. Research has resulted in a clearer understanding of the relationship between congenital heart disease and the brain, and of the effects of cardiopulmonary bypass, hypothermia and circulatory arrest. This has led to modifications in management which may improve neurological outcome in the future.

Cardiopulmonary bypass in infants and children

Cardiopulmonary bypass (CPB) systems have evolved from futuristic visions of surgical pioneers to a safe and efficient tool in the therapy of treatment of cardiac disorders. There are many significant differences in the physiology between neonates and adult patients. There are currently very few congenital cardiac malformations that cannot be addressed effectively with surgical therapy. Yet, the necessity of CPB in the repair of these patients can still result in significant morbidity. A clearer understanding of the effects of CPB, hypothermia, and circulatory arrest is evolving and there is a considerable amount of research in these areas. It seems likely that modification of current CPB systems, minimization of exposure, and surgical techniques to avoid or limit the adverse effects may reduce mortality and morbidity in the future. The problems faced in these complex patients and procedures require that infant and neonatal cardiac surgery be performed in specialized centers with a multidisciplinary approach and specialized personnel. Future improvements in technology will likely result in improved long term outcome for children with congenital cardiac disease. Copyright 2000 by W.B. Saunders Company

Intermittent perfusion protects the brain during deep hypothermic circulatory arrest

BACKGROUND

Deep hypothermic circulatory arrest (DHCA) has been shown to cause impairment in recovery of cerebral blood flow (CBF) and cerebral metabolism (CMRO2) proportional to the duration of the DHCA period. This effect on CMRO2 may be a marker for brain injury, because CMRO2 recovers normally after cardiopulmonary bypass (CPB) when DHCA is not used. The aim of this study was to investigate the effects of intermittent perfusion during DHCA on the recovery of CMRO2 after CPB and to correlate these findings with electron microscopy (EM) of the cerebral microcirculatory bed.

METHODS

Fifteen neonatal piglets were placed on CPB and cooled to 18 degrees C. Each animal then underwent either: (1) 60 minute continuous CPB (control), (2) 60 minute uninterrupted DHCA (UI-DHCA), or (3) 60 minute DHCA with intermittent perfusion (1 minute every 15 minutes) (I-DHCA). All animals were then rewarmed and weaned from CPB. Measurements of CBF and CMRO2 were taken before and after CPB. A further 9 animals underwent CPB without DHCA (2 animals) or with DHCA (7 animals), under various conditions of arterial blood gas management, intermittent perfusion, and reperfusion time.

RESULTS

UI-DHCA resulted in significant impairment to recovery of CMRO2 after CPB (p < 0.05). Regardless of the blood gas strategy used, the EM after UI-DHCA revealed extensive damage characterized by perivascular intracellular and organelle edema, and vascular collapse. I-DHCA, on the other hand, produced a pattern of normal CMRO2 recovery identical to controls, and the EM was normal for both these groups.

CONCLUSIONS

Intermittent perfusion during DHCA is clinically practical and results in normal cerebral metabolic and ultrastructural recovery. Furthermore, the correlation between brain structure and CMRO2 suggests that monitoring CMRO2 during the operation may be an outstanding way to investigate new strategies for neuroprotection designed to reduce cerebral damage in children undergoing correction of congenital cardiac defects.

Cerebral physiology in paediatric cardiopulmonary bypass

PURPOSE

To analyze studies of neurological injury after open-heart surgery in infants and children and to discuss the effects of cardiopulmonary bypass, hypothermia and deep hypothermic circulatory arrest on cerebral blood flow, cerebral metabolism and brain temperature.

SOURCE

Articles were obtained from the databases, Current Science and Medline, from 1966 to present. Search terms include cardiopulmonary bypass (CPB), hypothermia, cerebral blood flow (CBF), cerebral metabolism and brain temperature. Information and abstracts obtained from meetings on the topic of brain and cardiac surgery helped complete the collection of information.

PRINCIPAL FINDINGS

In adults the incidence of neurological morbidity is between 7 to 87% with stroke in about 2-5%, whereas the incidence of neurological morbidity increases to 30% in infants and children undergoing cardiopulmonary bypass. Besides the medical condition of the patient, postoperative cerebral dysfunction and neuronal ischaemia associated with cardiac surgery in infants and small children are a combination of intraoperative factors. Deep hypothermic circulatory arrest impairs CBF and cerebral metabolism even after termination of CPB. Inadequate and/or non-homogenous cooling of the brain before circulatory arrest, as well as excessive rewarming of the brain during reperfusion are also major contributory factors.

CONCLUSION

Newer strategies, including the use of low-flow CPB, pulsatile CPB, pH-stat acid-base management and a cold reperfusion, are being explored to ensure better cerebral protection. Advances in monitoring technology and better understanding of the relationship of cerebral blood flow and metabolism during the different modalities of cardiopulmonary bypass management will help in the medical and anaesthetic development of strategies to improve neurological and developmental outcomes.

Effects of cardiopulmonary bypass and use of modified ultrafiltration

BACKGROUND

Hemodilution is a prominent problem in cardiopulmonary bypass in a pediatric population. Ultrafiltration is a method used to reduce fluid volume and tissue edema and to increase hematocrit without the need for blood products. Modified ultrafiltration may offer advantages in comparison with conventional ultrafiltration.

METHODS

This article reviews the technique of modified ultrafiltration and its use, results, complications, and safety in pediatric cardiopulmonary bypass.

RESULTS

Modified ultrafiltration in pediatric cardiopulmonary bypass reduces total body water and serum levels of inflammatory mediators. It results in an elevated hematocrit without the need for transfusion, improved pulmonary compliance in the immediate postbypass period, and probably improved cerebral metabolic recovery after deep hypothermic circulatory arrest.

CONCLUSIONS

Modified ultrafiltration can be performed safely in neonatal patients after cardiopulmonary bypass and offers advantages in comparison with conventional ultrafiltration.

Endothelial dysfunction in cerebral microcirculation during hypothermic cardiopulmonary bypass in newborn lambs

OBJECTIVES

Inflammatory stimuli or mechanical stresses associated with hypothermic cardiopulmonary bypass could potentially impair cerebrovascular function, resulting in inadequate cerebral perfusion. We hypothesize that hypothermic cardiopulmonary bypass is associated with endothelial or vascular smooth muscle dysfunction and associated cerebral hypoperfusion. Therefore we studied the cerebrovascular response to endothelium-dependent vasodilator, acetylcholine, endothelium-independent nitric oxide donor, sodium nitroprusside, and vasoactive amine, serotonin, in newborn lambs undergoing hypothermic cardiopulmonary bypass (nasopharygeal temperature = 18 degrees C).

METHODS

Studies were performed on 13 newborn lambs equipped with a closed cranial window, allowing for direct visualization of surface pial arterioles. Six animals were studied while undergoing hypothermic cardiopulmonary bypass, whereas seven served as nonbypass, warm (37 degrees C) controls. Pial arteriolar caliber (range = 111 to 316 microm diameter) was monitored using video microscopy.

RESULTS

Topical application of acetylcholine caused a dose-dependent increase in arteriolar diameter in the control group that was absent in animals undergoing hypothermic cardiopulmonary bypass. Hypothermic cardiopulmonary bypass did not alter the vasodilation in response to sodium nitroprusside. Furthermore, the contractile response to serotonin was fully expressed during hypothermic cardiopulmonary bypass.

CONCLUSIONS

The specific loss of acetylcholine-induced vasodilation suggests endothelial cell dysfunction rather than impaired ability of vascular smooth muscle to respond to nitric oxide. It is speculated that loss of endothelium-dependent regulatory factors in the cerebral microcirculation during hypothermic cardiopulmonary bypass may enhance vasoconstriction, and impaired cerebrovascular function may be a basis for associated neurologic injury during or after hypothermic cardiopulmonary bypass.

Topical ice slurry prevents brain rewarming during deep hypothermic circulatory arrest in newborn sheep

OBJECTIVES

To measure the effect of ice slurry topical cooling on brain surface temperature during deep hypothermic circulatory arrest.

DESIGN

This was a prospective, controlled experiment.

SETTING

Animal laboratory at a university hospital.

PARTICIPANTS

Five control lambs, five treatment (ice slurry) lambs.

INTERVENTIONS

Animals were studied in two groups: the study group had topical cooling of the head with ice slurry started immediately before circulatory arrest and continued throughout the period of circulatory arrest; control group lambs received no supplemental topical cooling.

MEASUREMENTS AND MAIN RESULTS

Brain surface temperature, scalp, nasopharyngeal, and rectal temperatures were measured at 5-minute intervals during 45 minutes of circulatory arrest. Lambs receiving topical cooling of the head with ice slurry had a statistically significant decrease in brain surface temperature of 2.2 +/- 1.2 degrees C during circulatory arrest, whereas brain surface temperature increased 1.2 +/- 0.3 degrees C, in control lambs. Equilibration of temperature between the scalp and brain in control lambs produced rewarming of the brain surface.

CONCLUSIONS

Topical cooling of the head with ice slurry in newborn lambs lowers brain surface temperature during deep hypothermic circulatory arrest. Surrogate temperature monitoring locations such as nasopharyngeal and rectal temperatures varied significantly and do not accurately reflect changes in brain surface temperature.

Thromboxane A2-receptor blockade improves cerebral protection for deep hypothermic circulatory arrest

OBJECTIVE

Following the use of deep hypothermic circulatory arrest in cardiac surgery, cerebral blood flow and cerebral oxygen metabolism are impaired. These may result from abnormal cerebral vasospasm. Powerful vasoconstrictors including endothelins and thromboxane A2 could mediate these processes. We investigated possible involvement of these two factors by assessing the effects of (a) phosphoramidon-an inhibitor of endothelin converting enzyme, and (b) vapiprost (GR32191B)-a specific thromboxane A2-receptor antagonist, on the recovery of cerebral blood flow and cerebral oxygen metabolism following deep hypothermic circulatory arrest.

METHODS

A total of 18 1-week-old piglets were randomised into three groups (n = 6 per group). At induction, the control group received saline; group PHOS received phosphoramidon 30 mg kg-1 intravenously. Group VAP received vapiprost 2 mg kg-1 at induction and at 30 min intervals thereafter. All groups underwent cardiopulmonary bypass cooling to 18 degrees C, exposed to 60 min of deep hypothermic circulatory arrest, rewarmed and reperfused for 1 h. Cerebral blood flow was measured with radio-labeled microspheres: cerebral oxygen metabolism was calculated at baseline before deep hypothermic circulatory arrest and at 1 h of reperfusion and rewarming.

RESULTS

In the control group, cerebral blood flow decreased to 40.2 +/- 2.0% of baseline after deep hypothermic circulatory arrest and cerebral oxygen metabolism decreased to 50.0 +/- 5.5% (P < 0.0005). The responses in group PHOS were similar. In group VAP, cerebral blood flow and cerebral oxygen metabolism were 64.3 +/- 10.6 and 80.1 +/- 9.8% of baseline, respectively, after deep hypothermic circulatory arrest. Thus, treatment with vapiprost significantly improved recovery of cerebral blood flow (P = 0.046) and cerebral oxygen metabolism (P = 0.020) following deep hypothermic circulatory arrest. No such improvement was seen after treatment with phosphoramidon.

CONCLUSIONS

Thromboxane A2 mediates impairments in cerebral perfusion and metabolism following deep hypothermic circulatory arrest. These changes were attenuated by blockade of thromboxane A2-receptors using vapiprost. Endothelins are not shown to be involved. Better knowledge of injury mechanisms will enable development of more effective cerebral protection strategies and allow safer application of deep hypothermic circulatory arrest.

Regional blood flow during pulsatile cardiopulmonary bypass and after circulatory arrest in an infant model

BACKGROUND

Pulsatile perfusion systems have been proposed as a means of improving end-organ perfusion during and after cardiopulmonary bypass. Few attempts have been made to study this issue in an infant model.

METHODS

Neonatal piglets were subjected to nonpulsatile (n = 6) or pulsatile (n = 7) cardiopulmonary bypass and 60 minutes of circulatory arrest. Cerebral, renal, and myocardial blood flow measurements were obtained at baseline, on bypass before and after circulatory arrest, and after bypass.

RESULTS

Cerebral blood flow did not differ between groups at any time and was diminished equally in both groups after circulatory arrest. Renal blood flow was diminished in both groups during bypass but was significantly better in the pulsatile group than in the nonpulsatile group prior to, but not after, circulatory arrest. Myocardial blood flow was maintained at or above baseline in the pulsatile group throughout the study, but in the nonpulsatile group, it was significantly lower than baseline during CPB prior to circulatory arrest and lower compared with baseline and with the pulsatile group 60 minutes after CPB.

CONCLUSIONS

Pulsatile bypass does not improve recovery of cerebral blood flow after circulatory arrest, may improve renal perfusion during bypass but does not improve its recovery after ischemia, and may have beneficial effects on myocardial blood flow during bypass and after ischemia compared with nonpulsatile bypass in this infant model.

Surgery of the thoracic aorta using deep hypothermic total circulatory arrest. Are there neurological consequences other than frank cerebral defects?

OBJECTIVE

Deep hypothermic total circulatory arrest has reduced primary morbidity and mortality in thoracic aortic surgery. Although frank neurological deficits have been proven to be a rare complication of this technique, the rate of subtle but irreversible neuropsychological disorders remains unknown.

METHODS

A total of 23 patients (15 male, 8 female) who had undergone surgery for dissection or aneurysm of the thoracic aorta using deep hypothermic total circulatory arrest (mean 25.5 min, range 10-75 min) were studied retrospectively. The mean follow-up was 17 months. The following psychometric tests were conducted: a computer-based test battery to assess tonic alertness and sustained attention, the trail making test (TMT part A and B), the Münchner Gedächtnistest and a verbal learning test. In addition, a cerebral dopamine D2 receptor scintigraphy (using the SPECT technique) was performed. For comparison, 10 healthy subjects were studied.

RESULTS

With regard to tonic alertness, 69.6 and 30.4% were below the 50th and 10th centiles, respectively, according to age- and education-corrected standard values. The impairment in sustained attention correlated significantly with the duration of the circulatory arrest. On the tests assessing short-term memory, the patients scored 30% below their age- and education-corrected peers. In terms of long-term memory, 60.9 and 39.1% of the patients were below one and two standard deviations, respectively. Concerning speed of information processing whilst 78.3% of the patients were below the 50th and 21.7% below the 10th centile. Indicative of some persistent and functional brain alteration, the dopamine D2 receptor binding was significantly reduced when compared with healthy subjects.

CONCLUSIONS

These data prove a substantial and chronic reduction of higher cognitive function in some of the patients who underwent cardiac surgery using deep hypothermic total circulatory arrest; this was accompanied by a depression of the cerebral dopamine D2 receptor binding.

Nitric oxide production affects cerebral perfusion and metabolism after deep hypothermic circulatory arrest

BACKGROUND

Use of deep hypothermic circulatory arrest (DHCA) in infant cardiac surgery is associated with reduced cerebral perfusion and metabolism during the recovery period. We investigated the impairment of nitric oxide production as a possible cause.

METHODS

A group of 1-week-old piglets underwent normothermic cardiopulmonary bypass (group A); three other groups (B, C, and D; n = 6 per group) underwent 60 minutes of DHCA at 18 degrees C and 60 minutes of rewarming. The animals were then treated as follows: Groups A and B received L-omega-nitro-arginine-methyl-ester (L-NAME, 50 mg.kg-1); group C, saline solution; and group D, L-arginine (600 mg.kg-1).

RESULTS

In group A, global cerebral blood flow decreased to 37.3% +/- 4.2% of baseline after L-NAME administration (p < 0.005). In group B, global cerebral blood flow decreased to 44.6% +/- 4.4% of baseline after DHCA and 28.9% +/- 3.4% after L-NAME administration (p < 0.001). Following L-arginine treatment after DHCA (group D), global cerebral blood flow increased from 43.8% +/- 3.0% of baseline to 61.6% +/- 9.1% (p < 0.05); cerebral oxygen metabolism increased from 1.93 +/- 0.16 mL.min-1.100 g-1 after DHCA to 2.42 +/- 0.25 mL.min-1.100 g-1 (p < 0.05).

CONCLUSIONS

Tonal production of nitric oxide is impaired in the brain after DHCA and is partly responsible for the circulatory and metabolic changes observed. Stimulation of nitric oxide production (L-arginine) significantly improved recovery of cerebral blood flow and cerebral oxygen metabolism after DHCA.

Blood gas management and degree of cooling: effects on cerebral metabolism before and after circulatory arrest

This study investigated the effects of different cooling strategies on cerebral metabolic response to circulatory arrest. In particular, it examined the impact of blood gas management and degree of cooling on cerebral metabolism before and after deep hypothermic circulatory arrest. Sixty-nine 1-week-old piglets (2 to 3 kg) were placed on cardiopulmonary bypass (37 degrees C) at 100 ml/kg per minute. Animals were cooled to 18 degrees or 14 degrees C as follows: alpha-stat strategy to 18 degrees C (n = 9) or 14 degrees C (n = 6), pH-stat strategy to 18 degrees C (n = 12) or 14 degrees C (n = 10). Animals underwent 60 minutes of circulator arrest followed by rewarming with alpha-stat strategy to 36 degrees C. Control animals were cooled with alpha-stat strategy to 18 degrees C (n = 10) or 14 degrees C (n = 3) and then maintained on cold cardiopulmonary bypass (100 ml/kg per minute) for 60 minutes. Three animals were excluded (see text). With the use of xenon 133 clearance methods, cerebral blood flow was measured at the following points: point I, cardiopulmonary bypass (37 degrees C); point II, cardiopulmonary bypass before circulatory arrest or control flow (18 degrees or 14 degrees C); and point III, cardiopulmonary bypass after rewarming (36 degrees C). Cerebral metabolic rate of oxygen consumption was calculated for each point. At point II, cerebral metabolism was more suppressed at 14 degrees C compared with that at 18 degrees C. At any given temperature (18 degrees or 14 degrees C), pH-stat strategy provided the greatest suppression of of cerebral metabolism. In control animals, cerebral metabolic oxygen consumption of point III returned to baseline values after 60 minutes of cold bypass. Sixty minutes of circulatory arrest resulted in a significant reduction in cerebral metabolic oxygen consumption at point III compared with that at point I regardless of cooling temperature or blood gas strategy. The amount of cerebral metabolic recovery was significantly reduced in the pH-stat 14 degrees C group compared with that in the pH-stat 18 degrees C group at point III. The use of pH-stat strategy followed by a switch to alpha-stat at 14 degrees C provided better cerebral metabolic recovery compared with either strategy used alone. The use of pH-stat strategy during initial cooling may provide the animal with maximal cerebral metabolic suppression. The cerebral acidosis produced with pH-stat cooling may worsen cerebral metabolic injury from circulatory arrest, but this affect is eliminated with the use of alpha-stat just before the period of circulatory arrest.

Effects of aortopulmonary collaterals on cerebral cooling and cerebral metabolic recovery after circulatory arrest

BACKGROUND

Aortopulmonary collaterals (APC) have been associated with an increased risk of choreoathetosis after deep hypothermic circulatory arrest (DHCA). To study the effects of APC on cerebral hemodynamics and metabolism before and after DHCA, a piglet model was developed.

METHODS AND RESULTS

Protocol 1: Eight 4- to 6-week-old piglets underwent placement of a left subclavian-to-main pulmonary artery shunt. Control shunts (n = 4) were ligated, APC shunts (n = 4) were left patent. All animals were placed on cardiopulmonary bypass (CPB) and cooled in identical fashion for 20 minutes. Temperature probes were placed in the nasopharynx, cortex, and deep brain. Control animals achieved significantly lower temperatures in all three areas by the end of cooling (17.5 degrees C versus 20.1 degrees C, 19.0 degrees C versus 22.3 degrees C, and 17.5 degrees C versus 21.0 degrees C, respectively, P < .005). Protocol 2: Six control and six APC animals were instrumented as described. All were placed on CPB, cooled to 18 degrees C, arrested for 90 minutes, and rewarmed to 37 degrees C. Cerebral blood flow (CBF) was measured with radioactive microspheres while warm on CPB, after cooling, and after rewarming. Arterial and sagittal sinus blood gases and CBF were used to calculate the cerebral metabolic rate of oxygen consumption (CMRO2). Both CBF and CMRO2 were significantly higher after rewarming to 37 degrees C in control versus APC animals (28 +/- 3 versus 14 +/- 2 mL/100 g per minute and 1.72 +/- 0.21 versus 1.04 +/- 0.14 mL O2/100 g per minute, respectively, P < .05).

CONCLUSIONS

APC decrease the rate of cerebral cooling on CPB and even if temperature is controlled result in increased cerebral metabolic derangement after DHCA. Patients with such collaterals may need additional measures to optimize cerebral protection.

Continuous retrograde cerebral perfusion supplies substrates for brain metabolism during hypothermic circulatory arrest

Ten patients underwent replacement of ascending aorta and/or aortic arch with aneurysm or dissection, using hypothermic circulatory arrest (HCA) with retrograde cerebral perfusion (RCP). RCP was administered through the superior vena cava cannula continuously during HCA (15 degrees C to 20 degrees C). Mean HCA time was 32 minutes (range, 18-45 minutes). To assess the metabolic changes during RCP, blood samples were taken from carotid arteries and the superior vena cava cannula simultaneously, five minutes after the onset and five minutes prior to termination of continuous retrograde cerebral perfusion (CRCP) for analysis of blood gas and glucose level. One patient died intraoperatively due to left ventricular failure. Nine patients survived their operations and all except one with stroke due to partial intimal flap obstruction of innominate artery awoke neurologically intact within four to six hours. One patient died on the postoperative fifth day due to septic shock following resection of ischaemic bowel due to dissection involving the mesenteric artery. Oxygen saturation, pH and glucose level were all found to be lower in blood back-bleeding from the carotid arteries than in blood perfused through the superior vena cava cannula at all sampling times during HCA and CRCP (p < 0.05). Although oxygen and glucose extraction is not only from brain tissue, these data demonstrate the efficacy of CRCP in supplying substrates for brain protection. CRCP is a reliable method as an adjunct to HCA for brain protection.

A 31p-magnetic resonance study of antegrade and retrograde cerebral perfusion during aortic arch surgery in pigs

To evaluate the effect of hypothermic circulatory arrest on brain metabolism, we used 31P-magnetic resonance spectroscopy to monitor brain metabolites in pigs during 2 hours of ischemia and 1 hour of reperfusion. Twenty-eight pigs were divided into five groups. Anesthesia (n = 5) and hypothermic cardiopulmonary bypass groups (n = 5) served as controls. In the circulatory arrest (n = 6), antegrade perfusion (n = 6), and retrograde (n = 6) brain perfusion groups, the bypass flow rate was 60 to 100 ml.kg-1.min-1. In the antegrade group, the brain was perfused via the carotid arteries at a blood flow rate of 180 to 200 ml.min-1 during circulatory arrest at 15 degrees C. In the retrograde group, the brain was perfused through the superior vena cava at a flow rate of 300 to 500 ml.min-1 during circulatory arrest at 15 degrees C. The intracellular pH was 7.1 +/- 0.1 and 7.3 +/- 0.1 in the anesthesia and hypothermic cardiopulmonary bypass groups, respectively. In the circulatory arrest group, the intracellular pH decreased to 6.2 +/- 0.1 and did not recover to its initial value (7.0 +/- 0.1) during reperfusion (p < 0.05 compared with the value obtained from the control groups at the corresponding time). Inorganic phosphate did not return to its initial level during reperfusion. In three animals in this group, levels of high-energy phosphates, adenosine triphosphate and phosphocreatine, recovered partially but did not reach the levels observed before arrest. In the group receiving antegrade perfusion, cerebral metabolites and intracellular pH were unchanged throughout the protocol. During circulatory arrest in the retrograde perfusion group the intracellular pH decreased to 6.4 +/- 0.1 and recovered fully during reperfusion (7.1 +/- 0.1). High-energy phosphates also returned to their initial levels during reperfusion. These studies show that deep hypothermic circulatory arrest with antegrade brain perfusion provides the best brain protection of the options investigated.

Pharmacologic intervention for ischemic brain edema after retrograde cerebral perfusion

Retrograde cerebral perfusion has recently been the focus of interest as a simple new technique of brain protection during aortic arch operations. We undertook the experimental protocol of 120 minutes of retrograde cerebral perfusion followed by antegrade reperfusion. Eighteen mongrel dogs were used. Retrograde cerebral perfusion was maintained at a flow rate of 150 to 250 ml/min to keep the perfusion pressure from 15 to 25 mm Hg. Animals were divided into three groups as follows: in group I, no treatment was received during and after retrograde cerebral perfusion; in group II, mannitol (2 gm/kg) was administered before cardiopulmonary bypass was restarted; and in group III, antivasospastic substance (1,2-bis nicotinamido]-propane) was continuously injected during and after retrograde cerebral perfusion (1 mg/kg per minute). Cerebral blood flow decreased during retrograde cerebral perfusion in all three groups. Cerebrovascular resistance showed marked increases 30 and 60 minutes after cardiopulmonary bypass was restarted in group I compared with the values in groups II and III (group I: 3.35 +/- 0.73 and 5.00 +/- 1.57 mm Hg/ml per 100 gm per minute; group II: 1.30 +/- 0.33 and 1.03 +/- 0.17 mm Hg/ml per 100 gm per minute; group III: 1.24 +/- 0.41 and 0.98 +/- 0.24 mm Hg/ml per 100 gm per minute). The oxygen extraction level was reduced by cooling, but it rose to a higher level as a result of significant desaturation of returned blood even in deep hypothermia during retrograde cerebral perfusion. Both cerebral metabolic rate of oxygen and cerebral metabolic rate of glucose remained at low levels during retrograde cerebral perfusion. Ratios of cerebral blood flow to cerebral metabolic rate of oxygen and cerebral blood flow to cerebral metabolic rate of glucose were markedly reduced during retrograde cerebral perfusion. Intracranial pressure showed significant increases 30 and 60 minutes after cardiopulmonary bypass was restarted in group I compared with values in group II or group III (group I: 22.7 +/- 2.8 and 20.6 +/- 5.1 mm Hg; group II: 6.3 +/- 1.8 and 5.3 +/- 1.3 mm Hg; group III: 4.2 +/- 1.7 and 7.7 +/- 2.8 mm Hg). Water content of the brain tissue in group I (77.54% +/- 0.29%) was significantly higher than that in group II (74.71% +/- 0.76%) or group III (74.14% +/- 0.48%). These data suggest that the supply of oxygen or glucose by retrograde cerebral perfusion is not enough to maintain sufficient cerebral metabolism, which may cause brain edema during antegrade reperfusion.(ABSTRACT TRUNCATED AT 400 WORDS)