The protective effect of profound hypothermia on the canine central nervous system during one hour of circulatory arrest

Duration of deep hypothermic circulatory arrest for aortic arch surgery: is it a myth, fiction, or scientific leap?

INTRODUCTION

The use of deep hypothermic circulatory arrest (DHCA) to provide aortic surgeons with a bloodless operative field while simultaneously protecting the brain and peripheries from ischemic damage revolutionized cardiac and aortic surgery, and is currently used in specialist centers across the globe. However, it is associated with manifold adverse outcomes, including neurocognitive dysfunction and mortality. This review seeks to analyze the relationship between DHCA duration and clinical outcome, and evaluate the controversies and limitations surrounding its use.

EVIDENCE ACQUISITION

We performed a review of available literature with statistical analysis to evaluate the relationship between DHCA duration (<40 min and >40 min) and key clinical outcomes, including mortality, permanent and temporary neurological deficit, renal damage, admission length, and reintervention rate. The controversies surrounding DHCA use and future directions for care are also explored.

EVIDENCE SYNTHESIS

Statistical analysis revealed no significant association (P>0.05) between DHCA duration and clinical outcomes (early and late mortality rates, neurological deficit, admission length, and reintervention rate), both with and without adjunctive perfusion techniques.

CONCLUSIONS

Available literature suggests that the relationships between DHCA duration (with and without adjunctive perfusion) and clinical outcomes are unclear, and at present not statistically significant. Alternative surgical and endovascular techniques have been identified as promising novel approaches not requiring DHCA, as have the use of biomarkers to enable early diagnosis and intervention for aortic pathologies.

Brain injury in canine models of cardiac surgery

Neuropathology and neurologic impairment were characterized in a clinically relevant canine model of hypothermic (18°C) circulatory arrest (HCA) and cardiopulmonary bypass (CPB). Adult dogs underwent 2 hours of HCA (n = 39), 1 hour of HCA (n = 20), or standard CPB (n = 22) and survived 2, 8, 24, or 72 hours. Neurologic impairment and neuropathology were much more severe after 2-hour HCA than after 1-hour HCA or CPB; histopathology and neurologic deficit scores were significantly correlated. Apoptosis developed as early as 2 hours after injury and was most severe in the granule cells of the hippocampal dentate gyrus. Necrosis evolved more slowly and was most severe in amygdala and pyramidal neurons in the cornu ammonis hippocampus. Neuronal injury was minimal up to 24 hours after 1-hour HCA, but 1 dog that survived to 72 hours showed substantial necrosis in the hippocampus, suggesting that, with longer survival time, the injury was worse. Although neuronal injury was minimal after CPB, we observed rare apoptotic and necrotic neurons in hippocampi and caudate nuclei. These results have important implications for CPB in humans and may help explain the subtle cognitive changes experienced by patients after CPB.

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

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

Suspended animation for delayed resuscitation

'Suspended animation for delayed resuscitation' is a new concept for attempting resuscitation from cardiac arrest of patients who currently (totally or temporarily) cannot be resuscitated, such as traumatic exsanguination cardiac arrest. Suspended animation means preservation of the viability of brain and organism during cardiac arrest, until restoration of stable spontaneous circulation or prolonged artificial circulation is possible. Suspended animation for exsanguination cardiac arrest of trauma victims would have to be induced within the critical first 5 min after the start of cardiac arrest no-flow, to buy time for transport and resuscitative surgery (hemostasis) performed during no-flow. Cardiac arrest is then reversed with all-out resuscitation, usually requiring cardiopulmonary bypass. Suspended animation has been explored and documented as effective in dogs in terms of long-term survival without brain damage after very prolonged cardiac arrest. In the 1990s, the Pittsburgh group achieved survival without brain damage in dogs after cardiac arrest of up to 90 min no-flow at brain (tympanic) temperature of 10 degrees C, with functionally and histologically normal brains. These studies used emergency cardiopulmonary bypass with heat exchanger or a single hypothermic saline flush into the aorta, which proved superior to pharmacologic strategies. For the large number of normovolemic sudden cardiac death victims, which currently cannot be resuscitated, more research in large animals is needed.

Fifty Years of Thoracic Aortic Surgery: Lessons Learned and Future Directions

During the past 50 years, the genetic basis and natural history of aortic disease has been defined. Surgical methods evolved to reduce mortality and morbidity from bleeding, renal impairment, cerebral injury, and paraplegia. Aortic surgery is now a specialty in itself. Experienced groups achieve a mortality rate of less than 2% for root operations and less than 15% for arch surgery and aortic dissection. The introduction of stent grafts has changed the approach to vascular pathology. These are less intimidating for the patient but have unsolved risks with uncertain long-term outcome. In the future, an evidence-based balance between conventional surgical procedures versus interventional strategies is required.

Interaction of temperature with hematocrit level and pH determines safe duration of hypothermic circulatory arrest

OBJECTIVE

Previous studies have demonstrated that both hematocrit level and pH influence the protection afforded by deep hypothermic circulatory arrest. The current study examines how temperature modulates the effect of hematocrit level and pH in determining a safe duration of circulatory arrest. The study also builds on previous work investigating the utility of near-infrared spectroscopy as a real-time monitor of cerebral protection during circulatory arrest.

METHODS

Seventy-six piglets (9.3 +/- 1.2 kg) underwent circulatory arrest under varying conditions with continuous monitoring by means of near-infrared spectroscopy (hematocrit level of 20% or 30%; pH-stat or alpha-stat strategy; temperature of 15 degrees C or 25 degrees C; arrest time of 60, 80, or 100 minutes). Neurologic recovery was evaluated daily by a veterinarian, and the brain was fixed in situ on postoperative day 4 to be examined on the basis of histologic score in a blinded fashion.

RESULTS

Multivariable analysis of total histologic score revealed that higher temperature, lower hematocrit level, more alkaline pH, and longer hypothermic circulatory arrest duration were predictive of more severe damage to the brain (P <.01). Regression modeling revealed that higher temperature exacerbated the disadvantage of a lower hematocrit level and longer arrest times but not pH strategy. Normalized oxyhemoglobin nadir time, derived from near-infrared spectroscopy, was positively correlated with neurologic recovery on the fourth postoperative day and with total histologic injury score (P <.0001).

CONCLUSION

Hematocrit level and pH, as well as temperature, determine the safe duration of hypothermic circulatory arrest. Near-infrared spectroscopy is a useful real-time monitor of safe duration of circulatory arrest.

Survival without brain damage after clinical death of 60-120 mins in dogs using suspended animation by profound hypothermia

OBJECTIVES

This study explored the limits of good outcome of brain and organism achievable after cardiac arrest (no blood flow) of 60-120 mins, with preservation (suspended animation) induced immediately after the start of exsanguination cardiac arrest.

DESIGN

Prospective experimental comparison of three arrest times, without randomization.

SETTING

University research laboratory.

SUBJECTS

Twenty-seven custom-bred hunting dogs (17-25 kg).

INTERVENTIONS

Dogs were exsanguinated over 5 mins to cardiac arrest no-flow of 60 mins, 90 mins, or 120 mins. At 2 mins of cardiac arrest, the dogs received, via a balloon-tipped catheter, an aortic flush of isotonic saline at 2 degrees C (at a rate of 1 L/min), until tympanic temperature reached 20 degrees C (for 60 mins of cardiac arrest), 15 degrees C (for 60 mins of cardiac arrest), or 10 degrees C (for 60, 90, or 120 mins of cardiac arrest). Resuscitation was by closed-chest cardiopulmonary bypass, postcardiac arrest mild hypothermia (tympanic temperature 34 degrees C) to 12 hrs, controlled ventilation to 20 hrs, and intensive care to 72 hrs.

MEASUREMENTS AND MAIN RESULTS

We assessed overall performance categories (OPC 1, normal; 2, moderate disability; 3, severe disability; 4, coma; 5, death), neurologic deficit scores (NDS 0-10%, normal; 100%, brain death), regional and total brain histologic damage scores at 72 hrs (total HDS >0-40, mild; 40-100, moderate; >100, severe damage), and morphologic damage of extracerebral organs. For 60 mins of cardiac arrest (n = 14), tympanic temperature 20 degrees C (n = 6) was achieved after flush of 3 mins and resulted in two dogs with OPC 1 and four dogs with OPC 2: median NDS, 13% (range 0-27%); and median total HDS, 28 (range, 4-36). Tympanic temperature of 15 degrees C (n = 5) was achieved after flush of 7 mins and resulted in all five dogs with OPC 1, NDS 0% (0-3%), and HDS 8 (0-48). Tympanic temperature 10 degrees C (n = 3) was achieved after flush of 11 mins and resulted in all three dogs with OPC 1, NDS 0%, and HDS 16 (2-18). For 90 mins of cardiac arrest (n = 6), tympanic temperature 10 degrees C was achieved after flush of 15 mins and resulted in all six dogs with OPC 1, NDS 0%, and HDS 8 (0-37). For 120 mins of cardiac arrest (n = 7), three dogs had to be excluded. In the four dogs within protocol, tympanic temperature 10 degrees C was achieved after flush of 15 mins. This resulted in one dog with OPC 1, NDS 0%, and total HDS 14; one with OPC 1, NDS 6%, and total HDS 20; one with OPC 2, NDS 13%, and total HDS 10; and one with OPC 3, NDS 39%, and total HDS 22.

CONCLUSIONS

In a systematic series of studies in dogs, the rapid induction of profound cerebral hypothermia (tympanic temperature 10 degrees C) by aortic flush of cold saline immediately after the start of exsanguination cardiac arrest-which rarely can be resuscitated effectively with current methods-can achieve survival without functional or histologic brain damage, after cardiac arrest no-flow of 60 or 90 mins and possibly 120 mins. The use of additional preservation strategies should be pursued in the 120-min arrest model.

Brain protection during surgery of the aortic arch

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

Prediction of safe duration of hypothermic circulatory arrest by near-infrared spectroscopy

OBJECTIVE

Hypothermic circulatory arrest is widely used for adults with aortic arch disease as well as for children with congenital heart disease. At present, no method exists for monitoring safe duration of circulatory arrest. Near-infrared spectroscopy is a new technique for noninvasive monitoring of cerebral oxygenation and energy state. In the current study, the relationship between near-infrared spectroscopy data and neurologic outcome was evaluated in a survival piglet model with hypothermic circulatory arrest.

METHODS

Thirty-six piglets (9.36 +/- 0.16 kg) underwent circulatory arrest under varying conditions with continuous monitoring by near-infrared spectroscopy (temperature 15 degrees C or 25 degrees C, hematocrit value 20% or 30%, circulatory arrest time 60, 80, or 100 minutes). Each setting included 3 animals. Neurologic recovery was evaluated daily by neurologic deficit score and overall performance category. Brain was fixed in situ on postoperative day 4 and examined by histologic score.

RESULTS

Oxygenated hemoglobin signal declined to a plateau (nadir) during circulatory arrest. Time to nadir was significantly shorter with lower hematocrit value (P <.001) and higher temperature (P <.01). Duration from reaching nadir until reperfusion ("oxygenated hemoglobin signal nadir time") was significantly related to histologic score (r (s) = 0.826), neurologic deficit score (r (s) = 0.717 on postoperative day 1; 0.716 on postoperative day 4), and overall performance category (r (s) = 0.642 on postoperative day 1; 0.702 on postoperative day 4) (P <.001). All animals in which oxygenated hemoglobin signal nadir time was less than 25 minutes were free of behavioral or histologic evidence of brain injury.

CONCLUSION

Oxygenated hemoglobin signal nadir time determined by near-infrared spectroscopy monitoring is a useful predictor of safe duration of circulatory arrest. Safe duration of hypothermic circulatory arrest is strongly influenced by perfusate hematocrit value and temperature during circulatory arrest.

Surgical techniques. Aortic arch and deep hypothermic circulatory arrest: real-life suspended animation

Surgical reconstruction of the aortic arch is a complex procedure requiring careful preoperative analysis of the pathology and forethought toward surgical approach. Development of surgical techniques has brought dramatic improvement survival and reduction of neurological events associated with these procedures, yet significant morbidity is still encountered. New approaches to the patient with these pathologies include antegrade and retrograde perfusions to the brain. Continued research into physiology of hypothermic circulatory arrest offers the promise of pharmacological protection of the brain during aortic reconstruction and potentially development of therapeutic modalities to treat and limit ischemic brain damage.

Surgical management of hemorrhage from rupture of the aortic arch

BACKGROUND

Control of hemorrhage in patients with active bleeding from rupture of the aortic arch is difficult, because of the location of the bleeding and the impossibility of cross-clamping the aorta without interfering with cerebral perfusion. A precise and swift plan of management helped us salvage some patients and prompted us to review our experience.

METHODS

Six patients with active bleeding of the aortic arch in the mediastinum and pericardial cavity (5 patients) or left pleural cavity (1 patient), treated between 1992 and 1996, were reviewed. Bleeding was reduced by keeping the mediastinum under local tension (3 patients) or by applying compression on the bleeding site (2 patients), or both (1 patient) while circulatory support, retransfusion of aspirated blood, and hypothermia were established. The diseased aortic arch was replaced during deep hypothermic circulatory arrest, which ranged from 25 to 40 minutes. In 3 patients, the brain was further protected by retrograde (2 patients) or antegrade (1 patient) cerebral perfusion.

RESULTS

Hemorrhage from the aortic arch was controlled in all patients. Two patients died postoperatively, one of respiratory failure and the other of abdominal sepsis. Recovery of neurologic function was assessed and complete in all patients. The 4 survivors are well 8 to 49 months after operation.

CONCLUSIONS

An approach relying on local tamponade to reduce bleeding, rapid establishment of circulatory support and hypothermia, retransfusion of aspirated blood, and swift repair of the aortic arch under circulatory arrest allows salvage of patients with active bleeding from an aortic arch rupture.

Deep hypothermic intermittent circulatory arrest--an adjunct technique for operations on aneurysms involving the aortic arch

Aneurysms involving the aortic arch were repaired in 12 patients using a technique known as deep hypothermic intermittent circulatory arrest (DHICA). This technique consists of repeated cycles of 20 min of circulatory arrest and 10 min of cerebral and systemic reperfusion. Aneurysms were of the following types: 2 true atherosclerotic aneurysm, 8 aortic dissections, and 2 traumatic aneurysm. There were 2 operative deaths caused by coagulopathy as a result of hepatic failure and difficulty with left ventricular venting. The frequency of circulatory arrest ranged from 2 to 5 cycles, and total circulatory arrest ranged from 20 to 71 min (mean 43.6 min). The lowest tympanic temperature ranged from 17.7 to 19.2 degrees C. No permanent cerebral complications occurred in 10 patients. We believe that this adjunct technique offers excellent results in the surgical treatment of aneurysms involving the aortic arch.

Cerebral perfusion and hypothermic circulatory arrest

Since DeBakey's replacement of an aortic arch aneurysm using cardiopulmonary bypass and individual perfusion of the brachiocephalic and carotid arteries, selective cerebral perfusion has been used as an effective method of cerebral protection. Although interest in this technique waned with the evolution of hypothermic circulatory arrest, complications arising from long and challenging aortic procedures have led to a renewed interest in perfusion of the cerebral circulation. During aortic arch surgery, antegrade and retrograde cerebral perfusion techniques have been used in an effort to prolong the "safe" duration during which conventional cardiopulmonary bypass flow to the brain is interrupted. Although the degree to which retrograde cerebral flow is able to perfuse cerebral tissue remains controversial, its use may afford protection through other mechanisms as well. This paper will review techniques, benefits, and limitations of antegrade and retrograde cerebral perfusion and their role in conjunction with hypothermic systemic circulatory arrest.

Profound systemic hypothermia inhibits the release of neurotransmitter amino acids in spinal cord ischemia

Profound hypothermia induced with cardiopulmonary bypass has a protective effect on spinal cord function during operations on the thoracoabdominal aorta. The mechanism of this protection remains unknown. It has been proposed that the release of excitatory amino acids in the extracellular space plays a causal role in irreversible neuronal damage. We investigated the changes in extracellular neurotransmitter amino acid concentrations with the use of in vivo microdialysis in a swine model of spinal cord ischemia. All animals underwent left thoracotomy and right atrium-femoral artery cardiopulmonary bypass with additional aortic arch perfusion. Lumbar laminectomies were then done and microdialysis probes were inserted stereotactically in the anterior horn of the second and fourth segments of the lumbar spinal cord. The probes were perfused with artificial cerebrospinal fluid at a rate of 2 microliters/min and 15-minute samples were assayed by high-performance liquid chromatography. Group 1 animals (n = 6) underwent aortic clamping distal to the left subclavian artery and proximal to the renal arteries for 60 minutes at normothermia (37 degrees C) and group 2 animals (n = 5) were cooled to a rectal temperature of 20 degrees C before application of aortic clamps, maintained at this level during cardiopulmonary bypass until the aorta was unclamped, and then slowly rewarmed to 37 degrees C. Seven amino acids were studied, including two excitatory neurotransmitters (glutamate and aspartate) and five putative inhibitory neurotransmitters (glycine, gamma-aminobutyric acid, serine, adenosine, and taurine). Glutamate exhibited a threefold increase in extracellular concentration during normothermic ischemia compared with baseline values and remained elevated until 60 minutes after reperfusion. The increase in aspartate concentration was not significant. The extracellular concentrations of glycine and gamma-aminobutyric acid also increased significantly during ischemia and reperfusion. Hypothermia uniformly prevented the release of amino acids in the extracellular space. Glutamate levels remained significantly decreased even after rewarming to normothermia whereas glycine levels returned to baseline values. These results are consistent with a role for excitatory amino acids in the production of ischemic spinal cord injury and suggest that the mechanism of hypothermic protection may be related to decreased release of these amino acids in the ischemic spinal cord.

Retrograde cerebral perfusion with hypothermic blood provides efficient protection of the brain: a neuropathological study

Retrograde cerebral perfusion is a method that is recently being used for protection of the brain during operations on the aortic arch. This method is useful but is said to provide a limited time for protecting the brain. We designed an experiment in dogs to investigate neuropathologically the effect of protecting the brain for 120 minutes under: (1) circulatory arrest (CA); (2) retrograde cerebral perfusion with moderately cooled blood (RCPMC); and (3) retrograde cerebral perfusion with deeply cooled blood (RCPDC). We calculated the number of the abnormal cells of 400 hippocampal neurons per dog light microscopically. The number was 199 +/- 23 (mean +/- 1 SD) in the CA group, 149 +/- 50 in the RCPMC group, and 72 +/- 33 in the RCPDC group. The difference between the CA group and the RCPMC group was not statistically significant (p < 0.05), but there was a significant difference between the RCPMC and RCPDC groups (p < 0.05). The degree of cerebral protection provided by retrograde cerebral perfusion for 120 minutes is not sufficient when using moderately cooled blood. If we use deeply cooled blood at a temperature of about 10 degrees C, we should obtain a sufficient degree of protection of the brain.

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.

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.

Differences in intraischemic temperature influence neurological outcome after deep hypothermic circulatory arrest in newborn dogs

BACKGROUND AND PURPOSE

Hypothermia to core temperatures ranging from 16 degrees C to 24 degrees C has become an established procedure to extend the "safe" interval of cardiac arrest during open heart surgery in human infants. The present experiment was designed to ascertain whether differences in core (rectal) temperature during hypothermic circulatory arrest influence the presence and extent of ischemic brain damage in newborn dogs.

METHODS

Newborn dogs (postnatal age, 3 to 5 days) were anesthetized with halothane (4% induction; 0.5% maintenance), intubated, paralyzed, and artificially ventilated with 70% nitrous oxide/30% oxygen. Thereafter, the dogs were surface cooled with ice packs to either 16 degrees C (n = 6), 20 degrees C (n = 8), or 24 degrees C (n = 6). The dogs then were subjected to circulatory arrest for 1.75 hours by the intravenous injection of KCl, following which they were resuscitated with intravenous NaHCO3 and epinephrine, artificial ventilation, and closed chest cardiac massage. Those dogs that survived for 8 hours of recovery (n = 16) underwent neurobehavioral examination followed by perfusion-fixation of their brains for pathological analysis.

RESULTS

All newborn dogs were successfully resuscitated after 1.75 hours of cardiac arrest, rewarmed to 37 degrees C, and ultimately weaned from anesthesia and ventilatory support. Four dogs sustained secondary systemic complications with death at 4 to 7 hours. All surviving dogs remained stable, with systemic blood pressure, heart rate, arterial oxygen, and acid-base balance within the normal, normothermic range. Of the 16 surviving dogs, all except 1 showed histological evidence of brain damage at 8 hours of recovery. Morphometric analysis of the number of necrotic neurons in the vulnerable gray matter structures showed the greatest damage to cerebral cortex at 24 degrees C and the least damage to this structure at 16 degrees C by either regression analysis (r = .62; P = .01) or a repeated-measures model (P = .008). The extent of damage to the caudate nucleus was similar in the three temperature groups, while damage to the amygdaloid nucleus was greater at 24 degrees C compared with 20 degrees C but with no difference in the severity of damage between 20 degrees C and 16 degrees C. A close correlation existed between neurobehavioral deficits in the surviving dogs and the severity of damage to the cerebral cortex (r = .72; P = .001).

CONCLUSIONS

The findings indicate that differences in intraischemic core temperature during deep hypothermic circulatory arrest influence the severity of damage to the cerebral cortex of newborn dogs. Specifically, the lower the temperature below 24 degrees C, the more protected the structure from ischemic injury. Furthermore, the greater the cortical damage, the more severe the neurobehavioral deficits. Such was not the case for the amygdaloid nucleus and especially for the caudate nucleus. Accordingly, differences in core temperature, even at very low levels, appear critical for optimal protection of the newborn brain during hypothermic circulatory arrest.

The effect of focal cerebral cooling on perinatal hypoxic-ischemic brain damage

We describe a method of focal cooling of the head and its effects on hypoxic-ischemic cerebral damage in neonatal rat. Focal cooling of the head was obtained by positioning a catheter under the scalp ipsilateral to the ligated common carotid artery and by running cold water through the catheter during 2 h of systemic hypoxia. Hypoxia was produced in neonatal rats by breathing 8% oxygen for 2 h in a 37 degrees C chamber. Animals underwent focal cooling with ipsilateral scalp temperatures ranging from 22 degrees C to 35 degrees C. Temperature recordings from the ipsilateral scalp, cerebral hemisphere (dorsal hippocampus) and core (rectal) were obtained. The results suggest that the method is effective in cooling of brain and also to a lesser extent in lowering of the core temperature. At a mean scalp temperature of 28 degrees C, mean hippocampal temperature in hypoxic rat was 29.5 degrees C and mean core temperature in hypoxic rat was 32.8 degrees C. At a lower scalp temperature of 22 degrees C, mean hippocampal temperature in hypoxic rat was 24.7 degrees C and mean core temperature was 31.3 degrees C. Neuropathologic examination 3-4 days following hypoxia-ischemia showed that focal cooling with a scalp temperature of lower than 28 degrees C completely protected from brain damage, and that there was a trend towards greater damage with higher scalp temperatures.

Continuous retrograde hypothermic low flow cerebral perfusion during aortic arch surgery

Continuous retrograde hypothermic low flow cerebral perfusion (CRCP) with deep hypothermic systemic circulatory arrest (DHSCA) during aortic arch surgery was employed in six patients, aged 21-79 years. From August 1991 to November 1992, five of these patients were operated for ascending and arch aortic dissection type I, and one patient was operated for an aneurysm extending from the ascending aorta into the arch. Cardiopulmonary bypass (CPB) technology included a centrifugal pump and low-dose aprotinin. Venous drainage was established via the superior and inferior caval veins and arterial return via the femoral artery. Prior to CPB, a bypass line connecting the arterial line with the superior vena cava cannula was implemented. Prior to DHSCA, the patients were systemically cooled to a mean nasopharyngeal temperature of 15.2 degrees C. After induction of systemic circulatory arrest, the femoral artery cannula was clamped. Thereafter, the implemented bypass line was opened to achieve reverse flow into the superior vena cava to allow venoarterial perfusion. The perfusate was returned to the CPB circuit through drainage from the inferior caval vein and by aspiration of blood from the opened aortic arch. CRCP flow rate ranged from 250 to 450 ml/min (mean 375 ml/min) maintaining an internal jugular vein pressure between 18 and 25 mmHg. The duration of CRCP ranged from 24 to 55 minutes (mean 39 minutes). Postoperatively, one patient died of cardiac failure. The other five patients regained full consciousness without neurological deficits, as defined by the Glasgow coma score, within 48 hours after the operation. Neither did we see other major organ complications.(ABSTRACT TRUNCATED AT 250 WORDS)

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).

Replacement of the transverse aortic arch for type A acute aortic dissection

Surgical treatment of acute aortic dissection involving the segment of transverse aortic arch is difficult and often associated with a high mortality and morbidity. The high mortality and morbidity are primarily related to anatomic features and techniques of cerebral protection employed during the period of aortic branch occlusion needed for reconstruction. This study reports our experience of 20 consecutive cases of acute type A aortic dissection treated by repair or replacement of the transverse aortic arch during emergency operation. Ages of the patients ranged from 56 to 76 years. All patients were referred to us within 2 weeks of onset (mean time, 58 hours). Selective cerebral perfusion or deep hypothermia with complete circulatory arrest was employed during the period of aortic branch occlusion. Duration of cerebral perfusion, circulatory arrest, myocardial ischemia, and cardiopulmonary bypass averaged 106 minutes, 32 minutes, 127 minutes, and 248 minutes, respectively. There were three operative deaths. All three dissections were ruptured ones, and the patients died of hemorrhage, deep coma, or multiple organ failure. One patient died of infection 3 months after operation. The remaining patients are alive and well without any detectable neurological deficit 1 month to 4 years postoperatively. This experience emphasizes that repair or replacement of acute type A aortic dissection involving the aortic arch can be performed safely by adequate selection of patients, supportive measures, and operative methods.

Selective jugular cannulation of safer retrograde cerebral perfusion

Hypothermic retrograde cerebral perfusion is a new technique for protecting the brain. Satisfactory cerebral protection should be possible even for periods of retrograde perfusion greater than 60 minutes. However, there are some concerns that functioning venous valves at the jugular-subclavian junction may impede retrograde flow to the brain and consequently cerebral protection may not be adequate. To overcome this obstacle, we have developed an easy and safe technique of selective jugular cannulation through the right atrium using a central venous catheter and a guidewire. We have employed this technique successfully in 15 patients who underwent operation on the aortic arch.

Partial brachiocephalic perfusion in aortic arch replacement

Eleven patients who underwent replacement of the aortic arch or adjacent areas for aneurysmal disease between 1989 and 1991, using hypothermic cardiopulmonary bypass at 20 degrees to 23 degrees C with partial brachiocephalic perfusion, were studied. Selective perfusion of the innominate artery was performed in all 11 patients through the right axillary artery, while partial brachiocephalic perfusion was carried out using a separate arterial roller pump with a perfusion flow rate of 10 ml/kg per min. Direct cannulation to the left common carotid and left subclavian artery was not performed in this method. There were 4 men and 7 women who ranged in age from 26 to 78 years, with a mean age of 56 years. The etiology of aneurysmal disease was aortic dissection in 10 patients, and aortitis syndrome in 1. The cardiopulmonary bypass time was 214.3 +/- 39.3 min, aortic cross-clamp time 131.5 +/- 33.4 min, and partial brachiocephalic perfusion time 57.6 +/- 15.1 min. There were three operative deaths (27.3%), the causes being multiple organ failure, acute peritonitis, and infection of the composite graft in the ascending aorta, in one patient each, respectively. However, there were no deaths related to the technique of partial brachiocephalic perfusion and no neurological complications were seen in this series. Thus, we believe that partial brachiocephalic perfusion under hypothermic cardiopulmonary bypass is safe and effective in surgery for aortic aneurysms involving the aortic arch.

Retrograde cerebral perfusion with circulatory arrest in aortic arch aneurysms

Two surgical cases of aortic arch aneurysms are presented. Retrograde (venoarterial) cerebral perfusion during circulatory arrest under deep hypothermia was performed to evacuate air and debris in cerebral vessels and preserve cerebral tissue. On postoperative day 1, the patients were conscious and alert with no neurological deficit. This technique is simple and can be applied during standard cardiopulmonary bypass. The technique is useful to avoid cerebral air and thromboembolisms.

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.

Selective cerebral perfusion during operation for aneurysms of the aortic arch: a reassessment

Thirty-two consecutive patients with thoracic aortic aneurysms who required aortic arch reconstruction were operated on with the aid of extracorporeal circulation and selective cerebral perfusion between January 1986 and August 1990. For selective cerebral perfusion, blood was infused into both the innominate and left common carotid arteries at a rate of 10 mL.kg-1.min-1 using a single roller pump separately from the systemic circulation. In 9 patients treated before March 1987, the operations were performed without open aortic anastomosis (group 1), whereas in 23 patients treated from March 1987 onward we used open aortic anastomosis (group 2). The extracorporeal circulation and cardiac arrest times were significantly longer in group 2, but there was no significant difference in the cerebral perfusion time. Early death occurred in 1 patient in group 1 and 2 in group 2. No serious cerebrospinal neurological complications occurred in either group, and there were similar rates of postoperative hepatic and renal dysfunction in both groups. The present data suggest that selective cerebral perfusion and open aortic anastomosis are useful methods for thoracic aortic aneurysm operation requiring complex repair of the aortic arch.

Retrograde cerebral perfusion through a superior vena caval cannula protects the brain

Retrograde cerebral perfusion through a superior vena caval cannula is a new technique for protecting the brain during aortic arch operations. In mongrel dogs (n = 10; 13 to 15 kg) we have performed retrograde cerebral perfusion (300 mL/min) by infusing blood through a superior vena caval cannula with aortic and inferior vena caval drainage. We have measured the cerebral tissue blood flow, oxygen consumption, and carbon dioxide exudation during retrograde cerebral perfusion at normothermia (NT, 37 degrees C) and hypothermia (HT, 20 degrees C) and have compared these values with values obtained in dogs during cardiopulmonary bypass (1,200 mL/min). Cerebral tissue blood flow was measured by the hydrogen clearance method. During retrograde cerebral perfusion about 20% of the superior vena caval perfusate was returned through the aorta and the rest drained from the inferior vena cava. Cerebral vascular resistance during retrograde cerebral perfusion was lower than that during cardiopulmonary bypass (NT, 63.8 +/- 52.5 versus 126.9 +/- 58.4; HT, 28.4 +/- 32.8 versus 69.5 +/- 28.7 x 10(3) dynes.s.cm(-5). Retrograde cerebral perfusion provided half the cerebral tissue blood flow of cardiopulmonary bypass (NT, 14.7 +/- 6.4 versus 34.3 +/- 7.8; HT, 17.6 +/- 5.6 versus 37.2 +/- 10.6 mL/min). Retrograde cerebral perfusion also provided a third of the oxygen (NT, 4.4 +/- 2.1 versus 12.3 +/- 7.1; HT, 1.4 +/- 0.8 versus 4.2 +/- 1.3 mL/min) and discharged 20% of the carbon dioxide (NT, 0.24 +/- 0.08 versus 1.19 +/- 0.58; HT, 0.15 +/- 0.06 versus 0.51 +/- 0.17 mmol/min) when compared with cardiopulmonary bypass. Retrograde cerebral perfusion may reduce ischemic damage during interruption of cerebral blood flow.

Ultraprofound hypothermia with complete blood substitution in a canine model

The potential for hypothermia to prevent or ameliorate ischemic injury to the central nervous system is well known. To determine if a more prolonged period of metabolic suppression with blood substitution is possible, a method was developed to lower body temperature to near the freezing point. Eight adult mongrel dogs underwent closed-chest extracorporeal circulation with both external and internal body cooling. As they were cooled, progressive hemodilution was employed until complete exsanguination and blood substitution with an aqueous solution was accomplished. Continuous circulation and a core temperature at a mean of 1.7 degrees C were maintained from 2 1/2 to 3 hours. After rewarming to 20 degrees C, the animals were autotransfused and allowed to recover. Of the eight animals, two died due to technical factors related to cardiac defibrillation. Of the six surviving animals, five survived over a long period and one died on the 10th postoperative day with hepatorenal failure resulting from a presumed blood transfusion incompatability reaction. All six showed normal neurological function and kennel behavior, except one dog with mild weakness of a hindlimb. When the dogs were sacrificed 1 to 2 months postoperatively, all organs were histologically normal. Specifically, there was no gross or microscopic evidence of ischemic or hypoxic injury to any central nervous system structures. This pilot study demonstrates that it is possible to successfully achieve complete exsanguination, blood substitution, and ultraprofound body temperature, while continuous circulation of the blood substitute is maintained. With the capability of controlling and repeatedly performing washout of the extracellular environment and by reaching lower temperatures, it may be possible to attain greater cellular metabolic suppression. This perhaps will extend the allowable times for circulatory arrest procedures. In addition, "bloodless ischemia" may be beneficial in removing both blood substances and formed elements which may mediate organ ischemia. With replacement of blood at warm temperatures, coagulopathy is avoided. This preliminary evidence demonstrates potential in the combination of ultraprofound hypothermia and complete blood component substitution. However, further study is required to confirm the potential of achieving circulatory arrest of longer duration.

Operative management of acute aortic arch dissection using profound hypothermia and circulatory arrest

Six consecutive patients with acute aortic dissection involving the transverse aortic arch underwent surgical repair using profound hypothermia and circulatory arrest. All patients survived without neurological deficit. Postoperative angiographic evaluation has revealed complete resection or obliteration of patent false lumen within the aortic arch and ascending aorta in all patients. Use of this adjunct in the operative management of aortic arch dissection has allowed bloodless inspection and repair of extensive intimal tears, complete intimal adventitial reapproximation or resection, avoidance of clamp injury to fragile dissected aortic tissue, and assurance of patent arch-cerebral revascularization.