Cerebral effects of circulatory arrest at 20 degrees c in the infant pig

Relevance of Porcine Stroke Models to Bridge the Gap from Pre-Clinical Findings to Clinical Implementation

In the search of animal stroke models providing translational advantages for biomedical research, pigs are large mammals with interesting brain characteristics and wide social acceptance. Compared to rodents, pigs have human-like highly gyrencephalic brains. In addition, increasingly through phylogeny, animals have more sophisticated white matter connectivity; thus, ratios of white-to-gray matter in humans and pigs are higher than in rodents. Swine models provide the opportunity to study the effect of stroke with emphasis on white matter damage and neuroanatomical changes in connectivity, and their pathophysiological correlate. In addition, the subarachnoid space surrounding the swine brain resembles that of humans. This allows the accumulation of blood and clots in subarachnoid hemorrhage models mimicking the clinical condition. The clot accumulation has been reported to mediate pathological mechanisms known to contribute to infarct progression and final damage in stroke patients. Importantly, swine allows trustworthy tracking of brain damage evolution using the same non-invasive multimodal imaging sequences used in the clinical practice. Moreover, several models of comorbidities and pathologies usually found in stroke patients have recently been established in swine. We review here ischemic and hemorrhagic stroke models reported so far in pigs. The advantages and limitations of each model are also discussed.

Current incidence of acute neurologic complications after open-heart operations in children

BACKGROUND

Previously, neurologic dysfunction was estimated to complicate 25% or less of pediatric open-heart operations. We sought to determine the current incidence and spectrum of early postoperative neurologic complications.

METHODS

We undertook a retrospective review of all patients undergoing open heart operations in 1 year at our institution with the goal to identify all neurologic complications occurring in the early postoperative period.

RESULTS

Open-heart operations were performed in 706 children. Sixteen children (2.3%) had neurologic complications develop, including 9 (1.3%) with definite clinical seizures, 1 with suspected seizures and bilateral subdural hemorrhage, 2 with coma after cardiac arrest, 2 with transient mild choreoathetosis, 1 with facial palsy, and 1 with persistent irritability. Causes of seizure were cyclosporin A toxicity posttransplant (4), cerebral ischemia post cardiac arrest (3), and unknown (2). In infants less than 1 year of age, the incidence of seizures was 1.2%.

CONCLUSIONS

This review suggests a decrease in acute neurologic morbidity after pediatric open heart operation. Clinical seizures remain the most common complication. Posttransplant, cyclosporin-associated seizures have emerged as an important etiologic category, coincident with an increase in cardiac transplantation in children.

The pursuit of effective neuroprotection during infant cardiac surgery

Advances in infant cardiac surgery have resulted in a dramatic decline in mortality rates; however, neurological morbidity remains an important concern. The effectiveness of a number of interventional strategies to prevent or minimize brain injury during open heart surgery are currently being investigated. This article provides an overview of two approaches: (1) interventions to enhance intraoperative cerebral oxygenation so as to prevent hypoxic-ischemic insults, and (2) the application of cerebral rescue therapies to attenuate the cascade of brain injury. Infant cardiac surgery provides a controlled environment in which to apply these neuroprotective approaches, so as to optimize the quality of life of these vulnerable children.

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.

Perioperative electroencephalographic seizures in infants undergoing repair of complex congenital cardiac defects

Many infants with cardiac anomalies undergo repair early in life. Both commonly used support techniques, deep hypothermic circulatory arrest (DHCA) and low-flow cardiopulmonary bypass (LFB), may be associated with adverse neurological outcomes, including seizures. In a single center study, 171 infants undergoing correction for D-transposition of the great arteries were randomized to one of these support techniques. Incidence and onset times of EEG seizures during continuous EEG-video monitoring in the first 48 h postoperatively and clinical seizures in the first postoperative week were compared. EEG seizures were characterized by time, duration, and localization of onset. Incidence of EEG seizures (20%) was more than 3 times that of clinical seizures (6%). Most infants with EEG seizures had multiple seizures beginning between 13 and 36 h postoperatively. Durations ranged from 6 s to 980 min. Onset of EEG seizures occurred most commonly in frontal and central regions. Factors associated with EEG seizures included randomization to DHCA, longer duration of circulatory arrest, and diagnosis of VSD. In this study EEG seizures were common following this type of cardiac surgery, illustrating the importance of EEG monitoring in detecting seizures. This data adds insight into mechanisms of seizures in infants undergoing cardiac surgery.

A comparison of the perioperative neurologic effects of hypothermic circulatory arrest versus low-flow cardiopulmonary bypass in infant heart surgery

BACKGROUND

Hypothermic circulatory arrest is a widely used support technique during heart surgery in infants, but its effects on neurologic outcome have been controversial. An alternative method, low-flow cardiopulmonary bypass, maintains continuous cerebral circulation but may increase exposure to known pump-related sources of brain injury, such as embolism or inadequate cerebral perfusion.

METHODS

We compared the incidence of perioperative brain injury after deep hypothermia and support consisting predominantly of total circulatory arrest with the incidence after deep hypothermia and support consisting predominantly of low-flow cardiopulmonary bypass in a randomized, single-center trial. The criteria for eligibility included a diagnosis of transposition of the great arteries with an intact ventricular septum or a ventricular septal defect and a planned arterial-switch operation before the age of three months.

RESULTS

Of 171 patients with D-transposition of the great arteries, 129 (66 of whom were assigned to circulatory arrest and 63 to low-flow bypass) had an intact ventricular septum, and 42 (21 assigned to circulatory arrest and 21 to low-flow bypass) had a ventricular septal defect. After adjustment for diagnosis, assignment to circulatory arrest as compared with low-flow bypass was associated with a higher risk of clinical seizures (odds ratio, 11.4; 95 percent confidence interval, 1.4 to 93.0), a tendency to a higher risk of ictal activity on continuous electroencephalographic (EEG) monitoring during the first 48 hours after surgery (odds ratio, 2.5; 95 percent confidence interval, 1.0 to 6.4), a longer recovery time to the first reappearance of EEG activity (only in the group with an intact ventricular septum, P < 0.001), and greater release of the brain isoenzyme of creatine kinase in the first 6 hours after surgery (P = 0.046). Analyses comparing durations of circulatory arrest produced results similar to those of analyses comparing treatments.

CONCLUSIONS

In heart surgery in infants, a strategy consisting predominantly of circulatory arrest is associated with greater central nervous system perturbation in the early postoperative period than a strategy consisting predominantly of low-flow cardiopulmonary bypass. Assessment of the effect of these findings on later outcomes awaits follow-up of this cohort.

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

Hypothermic total circulatory arrest (CA) is commonly used to facilitate repair of complex congenital heart defects. However, the "safe" period of CA remains to be defined. Extended periods of hypothermic total circulatory arrest may impair cerebral metabolism and cause ischemic brain injury. This study defines the relationship between increasing durations of CA at 18 degrees C and cerebral metabolism, and examines the protective value of topical cooling of the head or continuous "trickle" flow (5 to 10 mL.kg-1.min-1). Thirty-three 1-week-old piglets were randomized to six experimental groups: control; 15, 30, or 60 minutes of CA; 60 minutes of CA with topical cooling of the head; and 60 minutes of trickle flow. Animals were placed on cardiopulmonary bypass (CPB) at 100 mL.kg-1.min-1 and cooled to 18 degrees C. After the experimental period of CA or trickle flow (or 60 minutes of CPB at normal flow for the control group), animals were rewarmed to 37 degrees C and weaned from CPB. Data were obtained before and immediately after CPB at 37 degrees C, and before and immediately after the experimental period at 18 degrees C. Parameters measured included cerebral blood flow by xenon 133 clearance, arterial and sagittal sinus blood gases, and cerebral metabolism. Hypothermic total circulatory arrest caused an impairment of cerebral metabolism that was directly proportional to CA duration (r2 = 0.73; p = 0.0001), and recovery of metabolic function after 60 minutes of CA improved more than 50% if the head was packed in ice.(ABSTRACT TRUNCATED AT 250 WORDS)

Somatic and psychomotor development of children after hypothermic open-heart surgery

One hundred and seven patients with ventricular septal defect who survived one and a half to thirteen years after hypothermic open-heart surgery were reviewed with respect to somatic, intellectual, and psychomotor development. There were no negative effects associated with deep hypothermic arrest in any of these areas. Abnormal electroencephalograms were seen in one-half the number of patients examined, but there was no close relation between the circulatory arrest period and electroencephalographic findings. CT scanning of the brain indicated that the abnormality decreased with the lapse of the time after hypothermic open-heart surgery. It would appear that hypothermic open-heart surgery with limited circulatory arrest is a useful method, providing that the circulatory arrest is not allowed to exceed a limited period. However electroencephalographic assessment suggests that postoperative cerebral abnormalities may occur more frequently than previously suspected, despite the lack of preoperative abnormalities on the electroencephalograms.

Local cerebral blood flow following transient cerebral ischemia. I. Onset of impaired reperfusion within the first hour following global ischemia

Using the hydrogen clearance technique, local cerebral blood flow (LCBF) in 22 dogs was estimated at 6 parietal sites prior to and following 5 min of total global ischemia. Ischemia was immediately followed by an initial reactive hyperemia during which the electrocorticogram (ECoG) usually began to recover, and within the first 30 min, most of the LCBF's decreased to subnormal values. This onset of hypoperfusion was accompanied by a concomitant decrease in ECoG activity. Two animals that maintained normal local perfusion after the initial hyperemia recovered ECoG activity quickly. These results suggest that the subsequent poor reperfusion was caused by an increased microvascular resistance rather than by blood aggregates, increased blood viscosity, or a variety of other mechanism which have been proposed. Increased vascular tonus was, at least, partly responsible for the increased vascular resistance. This report supports the hypothesis that impaired reperfusion (which occurs some time after an initial hyperemia) may be responsible for ultimate neuronal death, rather than the period of global ischemic hypoxia per se.

Early intracardiac repair of large ventricular septal defects with conventional cardiopulmonary bypass and moderate hypothermia

With the use of conventional cardiopulmonary bypass and moderate hypothermia, primary intracardiac repair of large ventricular septal defects was performed in 30 children below the age of two years. All babies were falling to thrive and suffered from cardiac failure resistant to medical therapy, or had evidence of early pulmonary vascular disease. Two patients died after the operation, giving an operative mortality of 6.7%. Twenty-eight survivors have been followed for periods of one month to two and a half years. All are thriving and have normal or mildly enlarged hearts on their chest skiagrams. Primary intracardiac repair of large ventricular septal defects can be performed in infants and small children with a low operative risk when the standard cardiopulmonary bypass technique is being used.

The influence of duration of circulatory arrest at 20 degrees C on cerebral changes

In infants and piglets subjected to periods of circulatory arrest at 20 degrees C there was close correlation between duration of arrest and delay in return of electroencephalographic activity. Post mortem studies demonstrated histological evidence of brain damage in patients after circulatory arrest at 20 degrees C. Similar histological changes were demonstrated in piglets, including some who had complete E.E.G. and clinical recovery from circulatory arrest.