Intermittent hypothermic asanguineous cerebral perfusion (cerebroplegia) protects the brain during prolonged circulatory arrest

Emergency preservation and resuscitation with profound hypothermia, oxygen, and glucose allows reliable neurological recovery after 3 h of cardiac arrest from rapid exsanguination in dogs

We have used a rapid induction of profound hypothermia (<10 degrees C) with delayed resuscitation using cardiopulmonary bypass (CPB) as a novel approach for resuscitation from exsanguination cardiac arrest (ExCA). We have defined this approach as emergency preservation and resuscitation (EPR). We observed that 2 h but not 3 h of preservation could be achieved with favorable outcome using ice-cold normal saline flush to induce profound hypothermia. We tested the hypothesis that adding energy substrates to saline during induction of EPR would allow intact recovery after 3 h CA. Dogs underwent rapid ExCA. Two minutes after CA, EPR was induced with arterial ice-cold flush. Four treatments (n=6/group) were defined by a flush solution with or without 2.5% glucose (G+ or G-) and with either oxygen or nitrogen (O+ or O-) rapidly targeting tympanic temperature of 8 degrees C. At 3 h after CA onset, delayed resuscitation was initiated with CPB, followed by intensive care to 72 h. At 72 h, all dogs in the O+G+ group regained consciousness, and the group had better neurological deficit scores and overall performance categories than the O-groups (both P<0.05). In the O+G- group, four of the six dogs regained consciousness. All but one dog in the O-groups remained comatose. Brain histopathology in the O-G+ was worse than the other three groups (P<0.05). We conclude that EPR induced with a flush solution containing oxygen and glucose allowed satisfactory recovery of neurological function after a 3 h of CA, suggesting benefit from substrate delivery during induction or maintenance of a profound hypothermic CA.

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.

Intermittent circulatory arrest for repairing postoperative mycotic pseudoaneurysm in the ascending aorta

Postoperative mycotic pseudoaneurysm in the ascending aorta associated with mediastinitis is one of the most serious complications after cardiovascular surgery. Circulatory arrest is usually needed for repairing this lesion; it is likely that the procedure needs unpredictably prolonged arrest time due to uncontrollable bleeding or serious adhesion. With this reason we employed intermittent circulatory arrest instead. The purpose of this paper is to describe 2 cases which demonstrated the method of intermittent circulatory arrest for repairing postoperative mycotic pseudoaneurysm in the ascending aorta.

Pathophysiologic changes and effects of hypothermia on outcome in elective surgery and trauma patients

Generally, hypothermia is defined as a core temperature <35 degrees C. In elective surgery, induced hypothermia has beneficial effects. It is recommended to diminish complications attributable to ischemia reperfusion injury. Experimental studies have shown that hypothermia during hemorrhagic shock has beneficial effects on outcome. In contrast, clinical experience with hypothermia in trauma patients has shown accidental hypothermia to be a cause of posttraumatic complications. The different etiology of hypothermia might be one reason for this disparity because induced therapeutic hypothermia, with induction of poikilothermia and shivering prevention, is quite different from accidental hypothermia, which results in physiological stress. Other studies have shown evidence that this contradictory effect is related to the plasma concentration of high-energy phosphates (e.g., adenosine triphosphate [ATP]). Induced hypothermia preserves ATP storage, whereas accidental hypothermia causes depletion. Hypothermia also has an impact on the immunologic response after trauma and elective surgery by decreasing the inflammatory response. This might have a beneficial effect on outcome. Nevertheless, posttraumatic infectious complications may be higher because of an immunosuppressive profile. Further studies are needed to investigate the impact of induced hypothermia on outcome in trauma patients.

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

Neurological evaluation and intelligence testing in the child with operated congenital heart disease

BACKGROUND

The immediate and intermediate-term neurodevelopmental outcome in infants undergoing open heart procedures using deep hypothermic cardiopulmonary bypass was assessed prospectively.

METHODS

One hundred consecutive infants (age 2 to 174 days) were operated on using either deep hypothermic bypass only (group A, n = 28), or with associated circulatory arrest (group B, n = 72). Early neurological outcome was recorded. Survivors underwent mental development evaluation after 31 to 55 months. Fifty other children of similar demographic profile but without heart disease were also tested as controls.

RESULTS

In group A, there were two neurological deaths. In group B, 5 patients had clinical seizures, 1 had monoparesis and 1 had hyperkinetic syndrome with decreased attention span. Mean mental performance quotient was 90.0+/-8.2 in group A, and 89.1+/-6.8 in group B, (group A vs. B, p = 0.60). Mean mental performance quotient in the control group was 101.4+/-8.4, which was significantly higher than the patient population (p << 0.001). No correlation was found between duration of circulatory arrest and postoperative mental performance quotient.

CONCLUSIONS

There was significant retardation of mental development in infants operated with deep hypothermic cardiopulmonary bypass. However, use of total circulatory arrest and its duration did not affect clinical outcome up to preschool age.

Impact of retrograde cerebral perfusion on aortic arch aneurysm repair

OBJECTIVE

Protection of the brain is a primary concern in aortic arch surgery. Retrograde cerebral perfusion is a relatively new technique used for cerebral protection during profound hypothermic circulatory arrest. This study was designed to compare, retrospectively, the outcome of 109 patients undergoing aortic arch operation with and without the use of retrograde cerebral perfusion.

METHODS

Fifty-five patients had profound hypothermic circulatory arrest alone, and 54 patients had supplemental cerebral protection with retrograde cerebral perfusion. Mean age was 61 +/- 13 years and 58 +/- 14 years, respectively (mean +/- standard deviation). Twenty-two preoperative and intraoperative characteristics, including age, sex, acuity, presence of aortic dissection, and aneurysm rupture, were similar in the 2 groups (P >.05).

RESULTS

Mean circulatory arrest times (in minutes) were 30 +/- 19 in the group without retrograde cerebral perfusion and 33 +/- 19 in the group with retrograde cerebral perfusion, respectively. chi(2) Analysis revealed that patients operated on with the use of retrograde cerebral perfusion had significantly lower hospital mortality (15% vs 31%; P =.04) and in-hospital permanent neurologic complications (9% vs 27%; P =.01). Retrograde cerebral perfusion failed to reduce the prevalence of temporary neurologic dysfunction (17% vs 18%; P =.9). Stepwise multiple logistic regression revealed that extracorporeal circulation time, age, and lack of retrograde cerebral perfusion were statistically significant independent risk factors for hospital mortality. The same analysis revealed that lack of retrograde cerebral perfusion was the only significant independent risk factor for permanent neurologic dysfunction.

CONCLUSION

Retrograde cerebral perfusion decreased the prevalence of permanent neurologic complications and the hospital mortality in patients undergoing aortic arch operations.

Neuronal damage in gerbils caused by intermittent forebrain ischemia

OBJECT

The purpose of this study was to investigate the possibility of preventing cumulative neuronal damage after repetitive severe ischemia.

METHODS

The authors monitored ischemic depolarization in the gerbil hippocampus, which has recently been shown to be a good experimental model of the effects of brief ischemia on the brain, and evaluated neuronal damage in the CA1 subregion 7 days after the ischemic insult. In a single-ischemia paradigm, the results indicate that induction of ischemia-induced neuronal damage depended on the duration of ischemic depolarization. Neuronal damage can be detected in the CA1 subregion after a period of depolarization lasting 210 seconds. Using a double-ischemia paradigm in which the animals were subjected to two periods of ischemia, there was apparently no accumulation of neuronal damage from the first ischemic episode to the second, provided the duration of the first period of ischemic depolarization did not exceed 90 seconds. Neuronal damage accumulated when the duration of the first ischemia episode exceeded 90 seconds, regardless of the duration of the reperfusion interval between the two ischemic insults. Finally, when the ischemic insult was spread over four separate episodes, each lasting 90 seconds (with a reperfusion interval of 5 minutes), neuronal damage was not found when the total depolarization period was less than 420 seconds.

CONCLUSIONS

The authors conclude that cumulative neuronal damage may be avoided by adopting an intermittent ischemia approach. The implications of these results for human surgery requiring temporary occlusion of the cerebral arteries are discussed.

Adenosine-triphosphate in trauma-related and elective hypothermia

BACKGROUND

In trauma patients, hypothermia is a frequent event. According to the literature, the majority of trauma patients are presenting a core temperature of less than 34 degrees C at admission. In contrast to the benefit of hypothermia in elective surgery, clinical experience with hypothermia in trauma patients has identified hypothermia to be one major cause of severe posttraumatic complications. It was hypothesized that this diverse effect of hypothermia is related to depletion of high-energy phosphates like adenosine triphosphate (ATP) in trauma patients. To verify this hypothesis, the relation of ATP plasma levels and hypothermia was examined in a clinical study.

METHODS

Three different groups of patients were under study. The first group (group A, normothermic control group) included patients (n = 15) undergoing elective surgery of the lower limb with a mean operation time of 113 minutes. The second study group (group B, hypothermic control) was composed of patients (n = 15) who were subjected to elective coronary artery bypass operation under hypothermia (31 degrees C for 48 minutes, mean total operation time being 205 minutes). The third study group (group C) included trauma patients (n = 23, mean Injury Severity Score [ISS] of 24.7). At the time of admission, 10 patients presented a core temperature more than or equal to 34 degrees C (group C1, mean ISS, 25.2; mean T(A), 34.5 degrees C), 13 patients presented a T(A) less than 34 degrees C (group C2, mean ISS, 26.0; mean T(A), 32.9 degrees C). In both groups of surgical patients, the ATP plasma level was measured preoperatively, at 2, 4, and 24 hours postoperatively. For trauma patients, this measurement was performed at admission and 24 hours later. Within the same schedule, body core temperature was recorded and the clinical course was documented as well.

RESULTS

Elective limb surgery in normothermic patients resulted only in a transient decrease in ATP plasma levels (preoperative, 87.8 micromol/dL; 4 hours postoperative, 52.0 micromol/dL). At 24 hours, the ATP plasma level (62.6 +/- 10.0 micromol/dL) has increased toward baseline level. Elective hypothermia in patients subjected to coronary bypass also resulted only in a transient decrease in ATP plasma levels. During the operation period, including hypothermia, the ATP plasma level was comparable (50.4 micromol/dL) to group A and also returned back toward normal values at 24 hours (58.2 micromol/dL). All trauma patients revealed a significant low ATP plasma level at admission compared with both control groups. Looking at subdivided groups the most significant drop in ATP plasma level (28.5 micromol/dL) was noted in patients presenting an initial core temperature less than 34 degrees C and ISS more than 30. Even 24 hours later, the ATP level of this subgroup was significantly diminished, despite a rise up to 44.4 micromol/dL. In contrast, only a moderate drop in ATP plasma concentration (59.2 micromol/dL) was noted in the group of T(A) more than or equal to 34 degrees C and ISS less than 20. This group revealed almost normal values (68.3 micromol/dL) 24 hours after trauma. In addition to hypothermia, the metabolic state, reflected by the plasma lactate levels, significantly influenced the ATP plasma levels, as high lactate levels were paralleled by low ATP levels. Also, the overall outcome was related to injury severity and hypothermia.

CONCLUSION

Hypothermia in elective surgery, established by active cooling, preserves the ATP storage and maintains an aerobic metabolism, which both contribute to the beneficial effect of hypothermia in ischemia/reperfusion in cardiovascular surgery. However, in trauma patients hypothermia is caused by insufficient heat production due to utilization of ATP under anaerobic metabolic conditions. Low ATP plasma levels combined with hypothermia seem to be a predisposition for post-traumatic complications like organ failure.

Prolongation of total permissible circulatory arrest duration by deep hypothermic intermittent circulatory arrest

OBJECTIVE

We determined whether the duration of permissible circulatory arrest could be prolonged by deep hypothermic intermittent circulatory arrest.

METHODS

Twenty-five beagles were cooled on bypass to 18 degrees C to initiate deep hypothermia that was maintained for 3 hours. Five protocols were then studied: group 1, uninterrupted bypass during hypothermia; group 2, arrest for 40 minutes during hypothermia; group 3, arrest for 60 minutes during hypothermia; group 4, arrest for 80 minutes during hypothermia; and group 5, intermittent circulatory arrest, consisting of six cycles of 20 minutes of arrest followed by 10 minutes of systemic recirculation during hypothermia (total, 120 minutes of arrest). The oxyhemoglobin concentration in the brain was measured with near infrared spectrophotometry.

RESULTS

In groups 2, 3, and 4, the oxyhemoglobin concentration in the brain decreased continuously after arrest, finally reaching a plateau after 24.9 +/- 1.2 minutes. This finding suggested that the available cerebral oxyhemoglobin was depleted. In contrast, the available cerebral oxyhemoglobin was not depleted during hypothermic intermittent arrest in group 5. The mitochondrial respiratory control index was significantly lower in group 4 than in the other groups (p < 0.05). However, there were no significant differences in the respiratory control index for groups 1, 2, 3, and 5. Moreover, the formation of brain edema was significantly lower in group 5 than in the other groups (p < 0.05).

CONCLUSIONS

These results indicate that deep hypothermic intermittent arrest can increase the duration of total permissible circulatory arrest and will be a useful modality when prolonged arrest is anticipated.

Cerebral hemodynamics and metabolism during infant cardiac surgery. Mechanisms of injury and strategies for protection

There is an established link between congenital heart disease and acquired brain injury, which relates to the dependence of the nervous system on a consistent and responsive supply of oxygen and glucose. The advances in the field of infant cardiac surgery have presented new and different challenges to the arena of child neurology. This review provides an overview of the mechanisms of neurologic injury and cerebral hemodynamics and metabolism during cardiac surgery. This review discusses current and future strategies for the management of children with congenital heart disease.

Hypothermia, circulatory arrest, and the pediatric brain

A review has been conducted of ongoing clinical and laboratory studies of hypothermic circulatory arrest (HCA) and low-flow cardiopulmonary bypass (LFB) at a children's hospital in Boston. A prospective randomized clinical trial of HCA versus LFB has shown a higher incidence of perioperative seizures in patients randomized to HCA. At 1 year of age, neurologic and developmental studies have shown an association between seizures and worse outcome. Longer duration of HCA is associated with a worse score on the Bayley scale assessment of gross and fine motor function in particular, as well as a higher probability of neurologic abnormality. A retrospective review of development after HCA for Senning procedure has shown a correlation between more alkaline pH (alpha-stat strategy) during cooling before HCA and lower developmental score relative to a more acidotic strategy (pH stat). The institutional change to alpha-stat was accompanied by several cases of choreoathetosis after HCA. Currently, patients are being randomized between alpha-stat and pH-stat. Laboratory studies have used a piglet model with assessment of cerebral blood flow and metabolism as well as high-energy phosphates and cerebral pH determined by magnetic resonance spectroscopy. High-energy phosphates are maintained by a flow rate of 50 mL/kg/min but are undetectable after approximately 35 minutes of HCS. A pH-stat is associated with more rapid recovery of high-energy phosphates after HCA than alpha-stat. Recent studies have examined the role of nitric oxide in the causation of brain injury after HCA as well as the potential utility of cerebroplegia in increasing the safe duration of circulatory arrest.

Magnetic resonance studies of the effects of cardiovascular surgery on brain metabolism and function

Neurologic and neuropsychologic impairment are important sequelae of cardiac surgery in general and of coronary artery bypass graft surgery in particular. Although estimates of incidence vary, the numbers affected are considerable. Despite the ubiquity of such effects and the general consensus that impairments originate from ischemic injury secondary to microemboli produced during surgery, the nature of the underlying brain injuries remains poorly understood. Precise, and preferably quantitative, definition of the localization and nature of the underlying injuries is a precondition for the rigorous evaluation of the efficacy of prophylactic measures. The ability of magnetic resonance imaging (MRI) to detect surgically related lesions and the course of brain swelling is described, as are potential improvements in imaging sensitivity. Results of an experimental program studying chemical sequelae of surgery in a pig model are presented. MR spectroscopy can provide noninvasive information on the biochemical changes in brain and brain metabolism that permit empirical evaluation of various neuroprotective interventions. Functional MRI provides a means of studying the neuropsychologic mechanisms most often affected by cardiac surgery. Experimental data are presented that demonstrate that two such mechanisms, selective attention and working memory, can be imaged successfully. Perfusion mapping, combined with functional imaging, allows for the quantitative study of flow and functional activation. Applied to structures such as the cingulate, these techniques permit comparison of surgical sequelae with processes such as normal aging. MRI technology offers the possibility of improved anatomic, chemical, and functional definition of the effects of cardiac surgery on the brain.

Cerebrovascular assessment of the high-risk patient: the role of transcranial Doppler ultrasound

With increased attention to the causes and effects of neurologic injury related to cardiopulmonary bypass anesthesia and surgery, multiple modality examination and monitoring of cerebral function and perfusion in the perioperative period may prove to be advantageous. Transcranial Doppler examination and monitoring is inexpensive, noninvasive, safe, provides unique information about the functional status of the intracranial circulation, and complements the duplex Doppler study of the extracranial carotid vessels of the neck for preoperative evaluation of the surgical patient. The transcranial Doppler examination permits quantitation of blood flow velocity of the intracranial vessels, evaluation of autoregulatory capacity and vasomotor reserve, determination of symmetry of flow velocity in the circle of Willis, assessment of collateral circulatory capacity, examination of vessels not accessible to the duplex Doppler and serves as a baseline for intraoperative monitoring and the postoperative examination. Noninvasive, unilateral or bilateral, continuous monitoring of brain blood flow velocity intraoperatively or postoperatively with trending, storage, and correlation with other physiologic variables provides evidence of cerebral perfusion, occurrence and rate of cerebral embolism, and continuous monitoring of therapeutic interventions. A review of the incidence of stroke and neuropsychologic deficit after bypass surgery is focused on parameters amenable to diagnosis using transcranial Doppler. Patient-specific risk factors for neurologic injury derived from previous studies are discussed as well as risk factors that are related to anesthetic and surgical management and equipment. A description of Doppler technology and the correlation of transcranial Doppler findings with angiography and radionucleotide scans establishes the accuracy of the Doppler examination. The preoperative examination, provocative tests of vasomotor reserve, the evaluation of cerebral collateral circulation, and examples of Doppler applications are discussed.

Quantitation of phosphorus metabolites in newborn human brain using internal water as reference standard

A new method for noninvasive, in vivo quantitation of cerebral phosphorus (31P) metabolites is described. The technique employs point-resolved spectroscopy (PRESS) to obtain both 31P-metabolite and proton (1H) water spectra: brain water is used as an internal concentration reference. Spin-spin relaxation times (T2s) of cerebral 31P metabolites are much longer than the minimum echo time (TE) usable on a spectrometer equipped with actively shielded gradient coils. With short-TE (approximately 10 ms) 31P PRESS, T2 relaxation is minimal and phase modulation of the nucleotide triphosphate (NTP) multiplets can be accounted for 1H water spectra were acquired using several TEs so that extra- and intracellular water signals could be separated from that due to cerebrospinal fluid. Prior calibration of the 31P and 1H spectrometer channels and an assumed brain-water concentration enabled estimations of metabolite concentrations. Using this method, mean 31P metabolite concentrations in the brains of eight normal infants of gestational plus postnatal age 34 to 39 wk were: phosphomonoester (PME) 5.6 (SD 0.9); inorganic phosphate 1.4 (0.4); mobile phosphodiester 2.3 (0.6); phosphocreatine 2.9 (0.3); nucleotide triphosphate 2.8 (0.6); and total mobile phosphate 21.4 (2.8) mmol/kg wet.

University of Wisconsin cerebroplegia in a piglet survival model of circulatory arrest

BACKGROUND

Previous acute studies in immature piglets at our institution have demonstrated improved recovery of cerebral blood flow, intracellular pH, and high-energy phosphates with the administration of multidose University of Wisconsin solution as cerebroplegia during a period of deep hypothermic circulatory arrest (HCA). In an effort to define further the clinical applicability of this technique, we have developed a survival model of swine cardiopulmonary bypass (CPB) and HCA.

METHODS

12 Yorkshire pigs (age 4 to 5 weeks) were placed on CPB via the right femoral artery and right atrium. Animals were cooled to a rectal temperature of 15 degrees C and submitted to 90 minutes of HCA. Group UW (n = 6) received a single infusion of 50 mL/kg of 4 degrees C University of Wisconsin solution delivered antegrade to the cerebral circulation. The control group (n = 6) received no intervention. Animals were reperfused, rewarmed to 35 degrees C, and weaned from CPB. Neurologic assessments using neurologic deficit scoring (0 = normal, 500 = brain death) and overall performance categories (1 = normal, 5 = brain death) were performed at 24-hour intervals for 5 days. On the 5th postoperative day all brains were perfusion-fixed and examined for histologic evidence of neuronal injury (0 = normal, 5 = severe injury).

RESULTS

All animals were extubated 18 to 20 hours postoperatively. There was no significant difference between the mean neurologic score of the two groups. The mean day 5 neurologic deficit score was 108 for the UW group and 68 for the control group (p > 0.05). The day 5 overall performance category was 2.8 for the UW group and 2.0 for the control group (p > 0.05). Three of the UW animals but none of the control animals experienced generalized seizures. Histologic examination revealed more severe damage in UW animals, primarily in the cerebral cortex. Injury was more widespread in UW animals, involving cerebellum and hippocampus. The mean histologic injury score was 3.8 for UW animals and 2.4 for the control group (p = 0.06).

CONCLUSIONS

A clinically relevant survival model of CPB with HCA in immature swine is feasible. Cold UW solution as single-dose cerebroplegia is not beneficial, and may be injurious to the immature swine brain subjected to CPB and HCA. Further studies are indicated to determine optimal composition and administration of cerebroplegic solutions.

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.

pH strategies and cerebral energetics before and after circulatory arrest

The pH-stat strategy compared with the alpha-stat strategy provides more rapid recovery of brain high-energy phosphate stores and intracellular pH after 1 hour of hypothermic circulatory arrest in pigs. Possible mechanisms for this difference are (1) improved oxygen delivery and homogeneity of brain cooling before deep hypothermic circulatory arrest and (2) greater cerebral blood flow and reduced reperfusion injury owing to extracellular acidosis during the rewarming phase. To identify which of these mechanisms is predominant, we studied 49 4-week-old piglets undergoing 1 hour of deep hypothermic circulatory arrest. Four groups were defined according to cooling/rewarming strategy: alpha/alpha, alpha/pH, pH/alpha, and pH/pH. In 24 animals cerebral high-energy phosphate levels and intracellular pH were measured by magnetic resonance spectroscopy (alpha/alpha group 7, alpha/pH group 5, pH/alpha group 7, pH/pH group 5). In 25 animals cerebral blood flow was measured by labeled microspheres, cerebral metabolic rate by oxygen and glucose extraction, and the redox state of cytochrome aa3 and hemoglobin oxygenation by near infrared spectroscopy (alpha/alpha group 7, alpha/pH group 5, pH/alpha group 7, pH/pH group 6). Cerebral blood flow was greater with pH-stat than alpha-stat during cooling (56.3% +/- 3.7% versus 32.9% +/- 2.1% of normothermic baseline values, p < 0.001). Cytochrome aa3 values became more reduced during cooling with alpha-stat than with pH-stat (p = 0.049). Recovery of adenosine triphosphate levels in the initial 45 minutes of reperfusion was more rapid in group pH/pH compared with that in the other groups (p = 0.029). Recovery of cerebral intracellular pH in the initial 30 minutes was faster in group pH/pH compared with that in group alpha/alpha (p = 0.026). Intracellular pH became more acidic during early reperfusion only in group alpha/alpha, whereas it showed continuous recovery in the other groups. This study suggests that there are mechanisms in effect during both the cooling and rewarming phases before and after deep hypothermic circulatory arrest that could contribute to an improved cerebral outcome with pH-stat relative to more alkaline strategies.

Retrograde cerebral perfusion during profound hypothermia and circulatory arrest in pigs

The purpose of this study was to evaluate the use of retrograde cerebral perfusion via the superior vena cava during profound hypothermia and circulatory arrest (CA) in pigs. In three groups of 5 pigs each, group A (control) underwent cardiopulmonary bypass and normothermic CA for 1 hour, group B underwent cardiopulmonary bypass, profound hypothermia, and CA (15 degrees C nasopharyngeal) for 1 hour, and group C underwent the same procedure as group B plus retrograde cerebral perfusion. In group A none awoke. In group B, 2 of 5 did not awake and 3 of 5 awoke unable to stand, 2 with perceptive hind limb movement and 1 moving all extremities. In group C all awoke, 4 of 5 able to stand and 1 of 5 unable to stand but moving all limbs. In neurologic evaluation group B had significantly lower Tarlov scores than group C (p = 0.0090). Group B mean wake-up time, plus or minus standard error of the mean, was 124.6 +/- 4.6 minutes versus 29.2 +/- 5.1 in group C (p = 0.0090). In group B late phase CA cerebral blood flow dropped 30.9% +/- 4.8%, but in group C it rose 24.7% +/- 9.3% (p = 0.0007, pooled variance t test, two-tailed). In group B late phase CA brain oxygenation decreased 46.0% +/- 13.9% but it increased 26.1% +/- 5.4% in group C (p = 0.0013). This difference was reduced somewhat during rewarming (B, -21.2% +/- 14.9%; C, 16.4% +/- 4.7%; p = 0.043). Group B rewarming jugular venous O2 saturation was 30.8% +/- 2.5% versus 56.0% +/- 4.4% in group C (p = 0.0011). We conclude that in pigs retrograde cerebral perfusion combined with profound hypothermia during CA significantly reduces neurologic dysfunction, providing superior brain protection.

AMPA glutamate receptor antagonism reduces neurologic injury after hypothermic circulatory arrest

Pharmacologic inhibition of the N-methyl-D-aspartate (NMDA) glutamate receptor can reduce the neurologic injury associated with hypothermic circulatory arrest; however, other receptor subtypes, such as the alpha-amino-3-hydroxy-5-methylisoazole-4-propionic acid/kainate or AMPA/kainate subtype, may predominate in the adult brain. In this experiment, a selective AMPA antagonist, NBQX, was used in a canine survival model of hypothermic circulatory arrest. Twelve male dogs (20 to 25 kg) were placed on closed-chest cardiopulmonary bypass, subjected to 2 hours of hypothermic circulatory arrest at 18 degrees C, and rewarmed on cardiopulmonary bypass. All were mechanically ventilated and monitored for 20 hours before extubation and survived for 3 days. Six dogs received NBQX beginning 2 hours after arrest (3 mg/kg for 3 hours then 1.5 mg/kg for 2 hours). Control dogs received vehicle only. Neurologic recovery was assessed every 12 hours using a species-specific behavior scale that yielded a neurodeficit score ranging from 0 (normal) to 500 (brain dead). After sacrifice at 72 hours, brains were examined by receptor autoradiography and histologically for patterns of selective neuronal necrosis and scored blindly from 0 (normal) to 100 (severe injury). Dogs given NBQX had better neurologic function compared with controls (neurodeficit score, 58.6 +/- 15 versus 204 +/- 30; p < 0.004) and had less neuronal injury (18.2 +/- 3 versus 52.5 +/- 6; p < 0.004). Densitometric receptor autoradiography revealed preservation of neuronal NMDA receptor expression only in dogs given NBQX. These results suggest that antagonism of the non-NMDA glutamate receptor AMPA may be neuroprotective in adults after hypothermic circulatory arrest.

Optimal perfusion pressure for experimental retrograde cerebral perfusion

We evaluated cerebral metabolism during retrograde cerebral perfusion (RCP) and circulatory arrest during profound hypothermia, and also investigated the effects of perfusion pressure on RCP. Twenty-four adult mongrel dogs were placed on cardiopulmonary bypass and cooled to a nasopharyngeal temperature of 20 degrees C. At this temperature, hypothermic circulatory arrest (HCA; n = 6), and RCP with a perfusion pressure of 10 mmHg (RCP10; n = 6), 20 mmHg (RCP20; n = 6), and 30 mmHg (RCP30; n = 6) were carried out for 60 minutes. RCP was performed with oxygenated blood via the bilateral maxillary veins, and the retrograde flow rate was regulated to maintain a mean perfusion pressure of 10, 20, or 30 mmHg in the external jugular vein. At 60 minutes of RCP, we measured nasopharyngeal temperature; regional cerebral blood flow (rCBF); cerebral oxygen consumption, carbon dioxide excretion, and excess lactate; cerebral tissue adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP) and energy charge; and cerebral tissue water content. In the RCP10 group, there was excess cerebral lactate, and ATP and energy charge were low. In the RCP30 group, the water content of cerebral tissue was significantly higher than in other groups. In the RCP20 group, temperature was maintained in a narrow range, oxygen consumption and carbon dioxide excretion could be observed, there was no excess lactate, and ATP and energy charge were significantly higher than in the HCA group. In conclusion, RCP can provide adequate metabolic support for the brain during circulatory arrest, and a perfusion pressure of 20 mmHg is most appropriate for RCP.

Cerebral injury and cardiac operations

Cerebral complications constitute the leading source of morbidity and disability after cardiac operations. The incidence of stroke after coronary artery bypass grafting has increased in tandem with the mean age of the patient population. Although many cerebral deficits resolve with time, others remain sources of disability for otherwise functional patients and detract from an otherwise successful procedure. The clinical spectrum of cerebral complications includes both neurologic and neuropsychologic deficits. Neurologic deficits include fatal cerebral injury, stroke, impaired level of consciousness, and seizures. The incidence of these deficits is 1% to 6%. Neuropsychologic deficits refer to cognitive changes, and are quantitated with tests of memory and learning and speed of visual-motor response. The incidence of these deficits is 60% to 80% at 1 week after operation and 20% to 40% at 8 weeks after operation. Central nervous system complications after cardiac operations have been attributed in large part to the effects of cardiopulmonary bypass on the brain. Potential mechanisms include macroembolization of air or particulate matter; microembolization of gas, fat, aggregates of blood cells, platelets or fibrin, and particles of silicone or polyvinylchloride tubing; and inadequate cerebral perfusion pressure. Methods of assessment include those applied during the procedure (clinical observation, assessment of cerebral blood flow and metabolism, intraoperative electroencephalography, transcranial and carotid Doppler echography, quantitative embolic measurement, and fluorescein angiography) and those performed to measure outcome (neurologic and neuropsychologic testing, computed tomographic scans, magnetic resonance imaging, and cerebrospinal fluid studies). Much of the literature regarding cerebral injury and cardiopulmonary bypass is descriptive, relating patient risk factors to the incidence of postoperative stroke.(ABSTRACT TRUNCATED AT 250 WORDS)

EEG and prognosis of neurologic recovery of dogs under profound hypothermic circulatory arrest

Deep hypothermia (18-20 degrees C) (DH) during prolonged circulatory arrest and cardiopulmonary bypass is used to repair complex intracardiac lesions and vascular neurosurgical lesions. DH diminishes the risk of ischemic damage and multiorgan failure after circulatory arrest. Profound hypothermia (PH) to 6-7 degrees C has recently been reported to improve the neurological outcome of dogs after 2 h of circulatory arrest. There are no reports of the possible utility of EEG activity to predict the neurological outcome. As a part of a controlled study of cardiopulmonary bypass and 2 h of circulatory arrest we compared EEG recovery to the neurological outcome in 2 groups of dogs: 4 under DH and 4 under PH. All of the dogs under PH had a good outcome: mean neurodeficit score was 6.25/500 in PH and 139.25/500 in DH dogs (P < 0.03); mean histopathological score was 19.25/100 for DH and 47.75/100 in PH dogs (P < 0.03). EEG activity 2 h after reperfusion and starting of rewarming correlated with eventual neurological outcome. EEG variables associated with good outcome were: main final frequency and degree of rhythmicity of the activity. We conclude that PH exerted a protective effect for animals undergoing 2 h of circulatory arrest. EEG was a useful tool for predicting neurological outcome under the studied conditions.

Superior cerebral protection with profound hypothermia during circulatory arrest

The optimal temperature for cerebral protection during hypothermic circulatory arrest is not known. This study was undertaken to test the hypothesis that deeper levels of cerebral hypothermia (< 10 degrees C) confer better protection against neurologic injury during prolonged hypothermic circulatory arrest ("colder is better"). Twelve male dogs (20 to 25 kg) were placed on closed-chest cardiopulmonary bypass via femoral artery and femoral/external jugular vein. Using surface and core cooling, tympanic membrane temperature was lowered to 18 degrees to 20 degrees C (deep hypothermia, n = 6) or 5 degrees to 7 degrees C (profound hypothermia, n = 6). After 2 hours of hypothermic circulatory arrest, animals were rewarmed to 35 degrees to 37 degrees C on cardiopulmonary bypass. All were mechanically ventilated and monitored in an intensive care unit setting for 20 hours. Neurologic assessment was performed every 12 hours using a species-specific behavior scale that yielded a neurodeficit score ranging from 0% to 100%, where 0 = normal and 100% = brain dead. After 72 hours, animals were sacrificed and examined histologically for neurologic injury. Histologic injury scores were assigned to each animal (range, 0 [normal] to 100 [severe injury]). At the end of the observation period, profoundly hypothermic animals had better neurologic function (neurodeficit score, 5.7% +/- 4.0%) compared with deeply hypothermic animals (neurodeficit score, 41% +/- 9.3%; p < 0.006). Every animal had histologic evidence of neurologic injury, but profoundly hypothermic animals had significantly less injury (histologic injury score, 19.2 +/- 1.2 versus 48.3 +/- 1.5; p < 0.0001).

Inorganic phosphate compartmentation in the normal isolated canine brain

In vivo 31P magnetic resonance spectra of 16 isolated dog brains were studied by using a 9.4-T wide-bore superconducting magnet. The observed Pi peak had an irregular shape, which implied that it represented more than one single homogeneous pool of Pi. To evaluate our ability to discriminate between single and multiple peaks and determine peak areas, we designed studies of simulated 31Pi spectra with the signal-to-noise (S/N) ratios ranging from infinity to 4.4 with reference to the simulated Pi peak. For the analysis we used computer programs with a linear prediction algorithm (NMR-Fit) and a Marquardt-Levenberg nonlinear curve-fit algorithm (Peak-Fit). When the simulated data had very high S/N levels, both methods located the peak centers precisely; however, the Marquardt-Levenberg algorithm (M-L algorithm) was the more reliable at low S/N levels. The linear prediction method was poor at determining peak areas; at comparable S/N levels, the M-L algorithm determined all peak areas relatively accurately. Application of the M-L algorithm to the individual experimental in vivo dog brain data resolved the Pi peak into seven or more separate components. A composite spectrum obtained by averaging all spectral data from six of the brains with normal O2 utilization was fitted using the M-L algorithm. The results suggested that there were eight significant peaks with the following chemical shifts: 4.07, 4.29, 4.45, 4.62, 4.75, 4.84, 4.99, and 5.17 parts per million (ppm). Although linear prediction demonstrated the presence of only three peaks, all corresponded to values obtained using the M-L algorithm. The peak indicating a compartment at 5.17 ppm (pH 7.34) was assigned to venous pH on the basis of direct simultaneous electrode-based measurements. On the basis of earlier electrode studies of brain compartmental pH, the peaks at 4.99 ppm (pH 7.16) and 4.84 ppm (pH 7.04) were thought to represent interstitial fluid and the astrocyte cytoplasm, respectively.

Effects of pH on brain energetics after hypothermic circulatory arrest

The pH management that provides optimal organ protection during hypothermic circulatory arrest is uncertain. Recent retrospective clinical data suggest that the pH-stat strategy (maintenance of pH at 7.40 corrected to core temperature) may improve brain protection during hypothermic cardiopulmonary bypass with a period of circulatory arrest in infants. The impact of alpha-stat (group A) and pH-stat (group P) strategies on recovery of cerebral high-energy phosphates and intracellular pH measured by magnetic resonance spectroscopy (A, n = 7; P, n = 5), organ blood flow measured by microspheres, cerebral metabolic rate measured by oxygen and glucose extraction (A, n = 7; P, n = 6), and cerebral edema was studied in 25 4-week-old piglets undergoing core cooling and 1 hour of circulatory arrest at 15 degrees C. Group P had greater cerebral blood flow during core cooling (54.3% +/- 4.7% versus 34.2% +/- 1.5% of normothermic baseline, respectively; p = 0.001). The intracellular pH during core cooling showed an alkaline shift in both groups but became more alkaline in group A than in group P at the end of cooling (7.08 to 7.63 versus 7.09 to 7.41, respectively; p = 0.013). Recovery of cerebral adenosine triphosphate (p = 0.046) and intracellular pH (p = 0.014) in the initial 30 minutes of reperfusion was faster in group P. The cerebral intracellular pH became more acidotic during early reperfusion in group A, whereas it showed continuous recovery in group P. Brain water content postoperatively was less in group P (0.8075) than in group A (0.8124) (p = 0.05). These results suggest that compared with alpha-stat, the pH-stat strategy provides better early brain recovery after deep hypothermic cardiopulmonary bypass with circulatory arrest in the immature animal. Possible mechanisms include improved brain cooling by increased blood flow to subcortical areas, improved oxygen delivery, and reduction of reperfusion injury, as well as an alkaline shift in intracellular pH with hypothermia in spite of a stable blood pH.

Cerebral consequences of hypothermic circulatory arrest in adults

Despite widespread use of hypothermic circulatory arrest (HCA) in aneurysm surgery and for repair of congenital heart defects, there is continued concern about possible adverse cerebral sequelae. The search for ways to improve implementation of HCA has inspired retrospective clinical studies to try to identify risk factors for cerebral injury, and clinical and laboratory investigations to explore the physiology of HCA. At present, risk factors associated with less favorable cerebral outcome after HCA include: prolonged duration of HCA (usually greater than 60 min); advanced patient age; rapid cooling (less than 20 min); hyperglycemia either before HCA or during reperfusion; preoperative cyanosis or lack of adequate hemodilution; evidence of increased oxygen extraction before HCA or during reperfusion; and delayed reappearance of electroencephalogram (EEG) or marked EEG abnormality. Strategies advocated to increase safety of HCA include: pretreatment with barbiturates and steroids; use of alpha-stat pH regulation during cooling and rewarming; intraoperative monitoring of EEG; slow and adequate cooling, including packing of the head in ice; monitoring of jugular venous oxygen content; hemodilution; and avoidance of hyperglycemia. Current investigation focuses on delineating the relationship of cerebral blood flow (CBF) to cerebral oxygen consumption and glucose metabolism during cooling, HCA, rewarming, and later recovery, and identifying changes in acute intraoperative parameters, including the presence of intracerebral enzymes in cerebral spinal fluid, with cerebral outcome as assessed by neurological evaluation, quantitative EEG, and postmortem histology. Clinically, intraoperative monitoring of EEG and measurement of CBF by tracer washout or Doppler flows are contributing to better understanding of the physiology of HCA, and in the laboratory, nuclear magnetic resonance (NMR) spectroscopy has provided valuable insights into the kinetics of intracerebral energy metabolism. Promising strategies for the future include investigation of other pharmacological agents to increase cerebral protection, and use of "cerebroplegia" or intermittent perfusion between intervals of HCA to improve cerebral tolerance for longer durations of HCA.

Distribution of intracellular pH in the rat brain cortex after global ischemia as measured by color film histophotometry of neutral red

Tissue acidosis is an important determinant of cell viability following cerebral ischemia. Because of the heterogeneity of tissue response to metabolic stress, a method for measuring intracellular pH (pHi) that preserves spatial information would be desirable. Histophotometry of the pH indicator dye Neutral red offers such a possibility. The purpose of our study was to determine the distribution of pHi following complete irreversible ischemia and show the correlation of mean pHi measured by Neutral red and [31P]NMR in the same brain. Three rats were studied in the anesthetized state. A pHi range was obtained by total cerebral ischemia at various pre-arrest plasma glucose concentrations. The data show that mean pHi calculated by Neutral red was strongly correlated to pHi determined from [31P]NMR (slope: 0.99 +/- 0.08; P less than 0.001, r2 = 0.96). Within each brain, 80-110 discrete samples were analyzed by histophotometry. The pHi distribution of those samples broadened in those rat brains with greater acidosis, suggesting a heterogeneity of response by the tissue to ischemia and the presence of multiple pHi pools. Our results demonstrate the need to use methods which maintain spatial resolution such as is available with histophotometry.

Brain protection during circulatory arrest

Previous nuclear magnetic resonance studies in this laboratory have shown a beneficial biochemical effect of antegrade cerebroplegia (CP-A) during hypothermic circulatory arrest. This study compared CP-A with other methods of cerebral protection during hypothermic circulatory arrest to assess the clinical utility of this technique. Twenty-three sheep were divided into four groups: systemic hypothermia alone (SYST) and systemic hypothermia combined with external cranial cooling (EXTNL), retrograde cerebroplegia (CP-R), or CP-A. Cardiopulmonary bypass was started, and the sheep were cooled to 15 degrees C and subjected to 2 hours of circulatory arrest. Cardiopulmonary bypass was restarted, and the animals were rewarmed and weaned from cardiopulmonary bypass. Serial neurological examinations were performed and hourly scores assigned until the animals were extubated. Postanesthetic neurological scores improved in all groups throughout the 6-hour recovery period except the CP-R group. The improvement over time for these scores was similar for the EXTNL and CP-A groups and significantly better than for the SYST or CP-R groups (p = 0.004). The CP-A group had 5 of 7 animals with deficit-free survival despite the similarity in recovery of baseline brainstem function. We conclude that both antegrade infusion of cerebroplegia and external cranial cooling confer distinct cerebroprotective effects after a protracted period of hypothermic circulatory arrest when compared with the other methods studied.

New horizons in management of hypothermia and frostbite injury

Diagnosing hypothermia requires a high index of suspicion. Restoring lost heat with careful attention to hemodynamics usually results in complete recovery. Frostbite is best treated by physicians who are cognizant of the pathophysiology of cold injury. Although alternative methods of intervention are being tested, rapid rewarming and anti-inflammatory agents are integral to treatment protocols.

Metabolism of the heart and brain during hypothermic cardiopulmonary bypass

The alterations in tissue metabolism induced by hypothermic cardiopulmonary bypass are not completely known. Phosphorus-31 nuclear magnetic resonance spectroscopy was used to determine the effect of hypothermic cardiopulmonary bypass on energy states and intracellular pH of the heart and brain. Sheep were instrumented for cardiopulmonary bypass and had a radiofrequency coil placed over either the heart or skull. The animals were placed in a 4.7-T magnet at 37 degrees C and spectra obtained. The animals were cooled on cardiopulmonary bypass to either 26 degrees C (n = 17) or 18 degrees C (n = 14) for brain studies and to 26 degrees C (n = 12) for heart studies. Hypothermia increased the phosphocreatine/adenosine triphosphate ratio in the heart (2.38 +/- 0.23 versus 3.18 +/- 0.37, 37 degrees versus 26 degrees C, respectively, p = 0.03). The brain phosphocreatine/adenosine triphosphate ratio increased from 1.70 +/- 0.09 at 37 degrees C to 2.00 +/- 0.12 at 26 degrees C (p = 0.009) and 2.10 +/- 0.07 at 18 degrees C (p = 0.0001). Intracellular pH increased during hypothermia (heart: 7.05 +/- 0.02 to 7.18 +/- 0.02, 37 degrees versus 26 degrees C, p = 0.0001; and brain: 7.07 +/- 0.02 versus 7.32 +/- 0.02, 37 degrees versus 18 degrees C, p = 0.0001). The adenosine triphosphate resonance position is known to be sensitive to magnesium binding as well as temperature and was shifted upfield (p less than 0.01) in both the heart and brain. This effect could be totally explained by the temperature dependence of this process.(ABSTRACT TRUNCATED AT 250 WORDS)