Deep hypothermic arrest: Observations on later development in children

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

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

An MRI Study of Neurological Injury Before and After Congenital Heart Surgery

Background Neuorological deficits are observed in patients with congenital heart disease (CHD) before and after neonatal surgery, the etiology being multifactorial. To understand the impact of preoperative events and to characterize the evaluation of neurological injury, we performed serial magnetic resonance imaging (MRI) studies of the brain in a cohort of neonates undergoing open-heart surgery.

Methods and Results Twenty-four term neonates with CHD were studied prospectively with brain MRI: before surgery, within 2 weeks of surgery, and several months after surgery. Preoperative MRI examinations showed periventricular leukomalacia (PVL) in 4 patients (16%) and infarct in 2 subjects (8%). MR spectroscopy was performed in 19 subjects preoperatively and revealed elevated brain lactate in 53%. An early postoperative MRI (n=21) identified new PVL in 48%, new infarct in 19%, and new parenchymal hemorrhage in 33%. New lesions or worsening of preoperative lesions occurred in 67% of subjects. No patient- or procedure-related factors for the development of early postoperative lesions were identified. A late postoperative MRI (n=17) demonstrated resolution of early lesions in 8 and mild cerebral atrophy in 2.

Conclusions Mild ischemic lesions, primarily in the form of PVL, occur in a number of neonates with CHD before surgery and >50% of patients postoperatively. Resolution of these lesions is common 4 to 6 months after surgery. Longer-term follow-up is needed to determine the significance of perioperative ischemic lesions on functional outcome.

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.

Neurodevelopmental outcome and lifestyle assessment in school-aged and adolescent children with hypoplastic left heart syndrome

OBJECTIVES

The purposes of this study are to describe the quality of life and cognitive function in school-aged children who have undergone staged palliation for hypoplastic left heart syndrome (HLHS), and to identify factors that are predictive of neurodevelopmental outcome in this population.

METHODS

School-aged survivors with HLHS who had undergone palliative surgery at our institution were identified and mailed a questionnaire to assess subjectively quality of life, school performance, and incidence of medical complications. A subgroup of local patients underwent standardized testing of cognitive function and neurologic examination. These patients were compared with the larger (remote) group of questionnaire respondents to determine whether results may be generalizable to the entire HLHS population. Potential predictors of neurologic and cognitive outcome were tested for their association with test scores using multivariate regression analysis.

RESULTS

Questionnaire results were obtained from 115 of 138 eligible children (83%; mean age: 9.0 +/- 2.0 years). Standardized testing was performed in 28 of 34 (82%) eligible local patients (mean age: 8.6 +/- 2.1 years). The majority of parents or guardians described their child's health as good (34%) or excellent (45%) and their academic performance as average (42%) or above average (42%). One third of the children, however, were receiving some form of special education. Chronic medication usage was common (64%); the incidence of medical complications was comparable to that previously reported in children with Fontan physiology. Cognitive testing of the local group demonstrated a median full scale IQ of 86 (range: 50-116). Mental retardation (IQ: <70) was noted in 18% of patients. In multivariate analysis, only the occurrence of preoperative seizures predicted lower full scale IQ.

CONCLUSIONS

Although the majority of school-aged children with HLHS had IQ scores within the normal range, mean performance for this historical cohort of survivors was lower than that in the general population.

Developmental and neurological status of children at 4 years of age after heart surgery with hypothermic circulatory arrest or low-flow cardiopulmonary bypass

BACKGROUND

It is not known whether developmental and neurological outcomes in the preschool period differ depending on whether the predominant vital organ support strategy used in infant heart surgery was total circulatory arrest (CA) or low-flow cardiopulmonary bypass.

METHODS AND RESULTS

Infants with D-transposition of the great arteries who underwent an arterial-switch operation were randomly assigned to a support method consisting predominantly of CA or low-flow cardiopulmonary bypass. Developmental and neurological status were evaluated blindly at 4 years of age in 158 of 163 eligible children (97%). Neither IQ scores nor overall neurological status were significantly associated with either treatment group or duration of CA. The CA group scored lower on tests of motor function (gross motor, P=0.01; fine motor, P=0.03) and had more severe speech abnormalities (oromotor apraxia, P=0.007). Seizures in the perioperative period, detected either clinically or by continuous electroencephalographic monitoring, were associated with lower mean IQ scores (12.6 and 7.7 points, respectively) and increased risk of neurological abnormalities (odds ratios, 8.4 and 5.6, respectively). The performance of the full cohort was below expectations in several domains, including IQ, expressive language, visual-motor integration, motor function, and oromotor control.

CONCLUSIONS

Use of CA to support vital organs during open heart surgery in infancy is associated, at the age of 4 years, with worse motor coordination and planning but not with lower IQ or with worse overall neurological status.

Neuropsychologic outcome after deep hypothermic circulatory arrest in adults

INTRODUCTION

Pediatric patients undergoing prolonged periods of deep hypothermic circulatory arrest have been found to experience long-term deficits in cognitive function. However, there is limited information of this type in adult patients who are undergoing deep hypothermic circulatory arrest for thoracic aortic repairs.

METHODS

One hundred forty-nine patients undergoing elective cardiac or thoracic aortic operations were evaluated preoperatively; 106 patients were evaluated early in the postoperative period (EARLY), and 77 patients were evaluated late in the postoperative period (LATE) with a battery of neuropsychologic tests. Seventy-three patients had routine cardiac operations without deep hypothermic circulatory arrest, and 76 patients with deep hypothermic circulatory arrest were divided into 2 subgroups: those with 1 to 24 minutes of deep hypothermic circulatory arrest (n = 36 patients) and those with 25 minutes or more of deep hypothermic circulatory arrest (n = 40 patients). The neuropsychologic test battery consisted of 8 tests encompassing 5 domains: attention, processing speed, memory, executive function, and fine motor function. Data were normalized to baseline values, and changes from baseline were analyzed by analysis of covariance, multivariate logistic regression, and survival functions.

RESULTS

In all domains, poor performance or inability to be tested EARLY were significant predictors of poor performance LATE (odds ratio, 5.27; P <.01). Deep hypothermic circulatory arrest of 25 minutes or more and advanced age were significant predictors of poor performance LATE for the memory and fine motor domains. Deep hypothermic circulatory arrest of 25 minutes or more (odds ratio, 4. 0; P =.02) was a determinant of prolonged hospital stay (>21 days).

CONCLUSION

Deep hypothermic circulatory arrest of 25 minutes or more and advanced age were associated with memory and fine motor deficits and with prolonged hospital stay.

Predictors of developmental outcomes in children with complete transposition

Cognitive, functional, educational achievement and behavioural measures were employed to assess neurobehavioral status in 57 of 60 participants who were initially enrolled in the Baltimore-Washington Infant Study, and who survived surgical correction of complete transposition (concordant atrioventricular and discordant ventriculo-arterial connections). Charts were reviewed to investigate the relationship between birth variables, surgical strategy and developmental outcomes. Higher preoperative weight was associated with better outcomes on the Stanford-Binet Short-term Memory subtest, while lower preoperative oxygen tension was associated with better outcomes on the Abstract/Visual Reasoning subtest and a test of Visual-Motor Integration. Longer total bypass time was associated with poor outcomes on the Short-term Memory subtests. Higher average flow rates during cooling and rewarming were associated with higher scores in the test of short term memory but poorer outcomes on a test for visual motor integration. Longer cooling times were associated with higher scores on the test for Visual-Motor Integration. Patients suffering seizures scored lower on the Stanford-Binet Composite, as well as in their tests of achievement. The data indicate that non-verbal skills may be particularly sensitive to variations in surgical strategies employed to correct complete transposition. Overt neurological events, such as seizures, were related to global deficits in intellectual functioning. Prospective studies evaluating systemic variations in surgical procedures and attempts to prevent and manage perioperative neurological events are important for further investigation of neurodevelopmental outcomes in children surviving surgical correction.

Cognitive and motor development in preschool and school-aged children after neonatal arterial switch operation

OBJECTIVE

The developmental status of children beyond 3 years of age after the neonatal arterial switch operation has not yet been systematically evaluated and is the topic of the present work.

METHODS

Seventy-seven unselected children operated on as neonates with combined deep hypothermic circulatory arrest and low-flow cardiopulmonary bypass were examined at an age of 3.2 to 9.4 years (5.4 +/- 1.6 years, mean +/- standard deviation). Clinical neurologic status, standard scores of intelligence, acquired abilities and vocabulary, and standardized tests on gross motor and fine motor functions were carried out, and the results were related to preoperative, perioperative, and postoperative status and management.

RESULTS

Neurologic impairment was more frequent (9.1%) than in the normal population. Intelligence was not different in these patients compared with normal children (p = 0.11), but motor function, vocabulary, and acquired abilities were poorer. Reduced intelligence was found in 9.1%, fine motor dysfunction in 22.1%, and gross motor dysfunction in 23.4% of the children. Intelligence was weakly but significantly inversely related to the duration of bypass (Spearman correlation coefficient -0.25, p = 0.03) and tended to be inversely related to the duration of circulatory arrest (-0.21, p = 0.07), but not to core cooling time on bypass or degree of hypothermia. Gross motor function, vocabulary, and acquired abilities were not significantly related to any of the perioperative parameters considered. No correlation was found between the test results and the variables perinatal asphyxia, perioperative and postoperative cardiocirculatory insufficiency, resuscitation events, and plexal or intraventricular cerebral hemorrhage.

CONCLUSIONS

The neonatal arterial switch operation with combined circulatory arrest and low-flow bypass in our experience is associated with neurologic as well as fine and gross motor impairment but appears to be well tolerated concerning cognitive functions as based on formal intelligence testing.

Neurologic sequelae of deep hypothermic circulatory arrest in cardiac transplant infants

BACKGROUND

Considerable controversy exists experimentally and clinically regarding adverse neurologic effects that may follow deep hypothermic circulatory arrest. Moreover, the techniques of DHCA have never been standardized.

METHODS

We prospectively studies the neurodevelopmental outcome in 38 infants undergoing cardiac transplantation using DHCA before the age of 4 months (mean age, 37.0 days). Neurodevelopmental outcome in the 22 boys and 16 girls was tested up to 2.5 years after transplantation using Bayley scale of infant development. Bayley scores were compared with the rate of core cooling and the length of DHCA in all patients. Deep hypothermic circulatory arrest was accomplished using an asanguineous prime resulting in hematocrits of 5% +/- 5% and ionized Ca2+, 0.4 +/- 0.1 mmol/L. No surface precooling was used, but the head was packed in ice. Mean cooling time was 14.0 +/- 3.5 minutes, resulting in rectal temperatures of 18 degrees +/- 2.5 degrees C. Duration of DHCA ranged from 42 to 70 minutes (mean duration, 56.0 +/- 6.6 minutes).

RESULTS

Postoperatively, the mean Bayley psychomotor development index was 91 (range, 50 to 130) and mental development index was 88 (range, 50 to 130). No relationship was found between either the rate of cooling or the duration of DHCA and Bayley scores (r = 0.227 and r = 0.322, respectively).

CONCLUSIONS

These data suggest that neither the rate of cooling nor DHCA times between 42 and 70 minutes using profoundly low hematocrits and low ionized calcium levels has any measurable effect on neurologic outcome up to 2.5 years postoperatively. It is possible that adverse neurologic outcomes from DHCA reflect particular methods of achieving DHCA.

Developmental and neurologic status of children after heart surgery with hypothermic circulatory arrest or low-flow cardiopulmonary bypass

BACKGROUND

Deep hypothermia with either total circulatory arrest or low-flow cardiopulmonary bypass is used to support vital organs during heart surgery in infants. We compared the developmental and neurologic sequelae of these two strategies one year after surgery.

METHODS

Infants with D-transposition of the great arteries who underwent an arterial-switch operation were randomly assigned to a method of support consisting predominantly of circulatory arrest or a method consisting predominantly of low-flow bypass. Developmental and neurologic evaluations and magnetic resonance imaging (MRI) were performed at one year of age.

RESULTS

Of the 171 patients enrolled in the study, 155 were evaluated. After adjustment for the presence or absence of a ventricular septal defect, the infants assigned to circulatory arrest, as compared with those assigned to low-flow bypass, had a lower mean score on the Psychomotor Development Index of the Bayley Scales of Infant Development (a 6.5-point deficit, P = 0.01) and a higher proportion had scores < or = 80 (i.e., 2 SD or more below the population mean) (27 percent vs. 12 percent, P = 0.02). The score on the Psychomotor Development Index was inversely related to the duration of circulatory arrest (P = 0.02). The risk of neurologic abnormalities increased with the duration of circulatory arrest (P = 0.04). The method of support was not associated with the prevalence of abnormalities on MRI scans of the brain, scores on the Mental Development Index of the Bayley Scale, or scores on a test of visual-recognition memory. Perioperative electroencephalographic seizure activity was associated with lower scores on the Psychomotor Development Index (P = 0.002) and an increased likelihood of abnormalities on MRI scans of the brain (P < 0.001).

CONCLUSIONS

Heart surgery performed with circulatory arrest as the predominant support strategy is associated with a higher risk of delayed motor development and neurologic abnormalities at the age of one year than is surgery with low-flow bypass as the predominant support strategy.

Marked protection by moderate hypothermia after experimental traumatic brain injury

These experiments examined the effects of moderate hypothermia on mortality and neurological deficits observed after experimental traumatic brain injury (TBI) in the rat. Brain temperature was measured continuously in all experiments by intraparenchymal probes. Brain cooling was induced by partial immersion (skin protected by a plastic barrier) in a water bath (0 degrees C) under general anesthesia (1.5% halothane/70% nitrous oxide/30% oxygen). In experiment I, we examined the effects of moderate hypothermia induced prior to injury on mortality following fluid percussion TBI. Rats were cooled to 36 degrees C (n = 16), 33 degrees C (n = 17), or 30 degrees C (n = 11) prior to injury and maintained at their target temperature for 1 h after injury. There was a significant (p less than 0.04) reduction in mortality by a brain temperature of 30 degrees C. The mortality rate at 36 degrees C was 37.5%, at 33 degrees C was 41%, and at 30 degrees C was 9.1%. In experiment II, we examined the effects of moderate hypothermia or hyperthermia initiated after TBI on long-term behavioral deficits. Rats were cooled to 36 degrees C (n = 10), 33 degrees C (n = 10), or 30 degrees C (n = 10) or warmed to 38 degrees C (n = 10) or 40 degrees C (n = 12) starting at 5 min after injury and maintained at their target temperatures for 1 h. Hypothermia-treated rats had significantly less beam-walking, beam-balance, and body weight loss deficits compared to normothermic (38 degrees C) rats. The greatest protection was observed in the 30 degrees C hypothermia group.(ABSTRACT TRUNCATED AT 250 WORDS)

The relation between EEG and mental development following cardiac surgery performed under simple deep hypothermia in children

In order to assess the accuracy of electroencephalography (EEG), in children who have undergone cardiac surgery under simple deep hypothermia, the relation between IQ or schoolwork achievement and the duration of circulatory arrest was investigated in 75 such children. Abnormal preoperative EEG's were found in 16 per cent of the children while abnormal postoperative EEG's were found in 17 per cent. The children were divided into 4 groups, according to pre- and postoperative EEG results. Schoolwork achievement scores ranged between 3.0 and 3.2, the difference among the groups being insignificant. Moreover, no significant shift in IQ was found among the groups. Finally, regarding the number of children who were able to go on to a higher level of education, including high school then college or university, again no significant differences were found among the 4 groups. In a comparison with the number of such children in neighboring Nagasaki prefecture able to continue on to a higher level of education, no significant differences were seen either. The findings and statistics of this investigation therefore indicate that pre- and postoperative EEG's are not always a reliable reference for assessing the prognosis of cerebral activity.

The motor performance of preschool-aged children after surgery for congenital heart disease

This study compared the motor performance of preschool-aged children who had undergone surgery for congenital heart disease with that of a group of children matched for age, sex, preschool experience, racial and socio-economic background. Analysis of the results indicated that the performances of the children with congenital heart disease were significantly immature compared to the performances of the control children on the total assessment and in the areas of gross motor, muscle strength, fine motor, tone and postural reactions. Sex, age at first surgical intervention and presence of a cyanotic heart defect did not influence the performances of the study group children. Age at assessment and socio-economic background were found to influence motor performances. The need for physiotherapists to be involved in the follow-up of children with congenital heart disease is supported.

Surgical hypothermia

Induced hypothermia is an interesting and useful adjunct to therapy in many areas of surgery and medicine. To paraphrase Professor Swan (1973), clinical hypothermia 'has a past and some promise for the future'.

The use of VEPs for CNS monitoring during continuous cardiopulmonary bypass and circulatory arrest

Cerebral function was monitored with the use of visual evoked potentials (VEPs) in 16 infants (mean age 9.9 +/- 4.3 months) during surgery for congenital cardiac anomalies. While hypothermia was employed in all patients, half (8) remained on continuous cardiopulmonary bypass (CCB) while the rest were cooled to lower temperatures before the induction of circulatory stasis and venous exsanguination (CA), i.e., profound hypothermic circulatory arrest (PHCA). VEPs were recorded before, during and after surgical intervention. Latency changes occurred in both the N100 and P145 components of the VEP as a function of systemic temperature during cooling in both groups. Differences in the VEPs were found between the two groups post-operatively, with the most interesting result being a greater increase in P145 latency in the CA group after rewarming. To the extent that VEPs reflect neurological status, our findings suggested that CCB was associated with less perturbation in acute neurological status than PHCA, and shorter arrest times and lower temperatures during CA were associated with the most favourable post-operative VEPs. Hence, intraoperative monitoring of VEPs appeared to be useful as an objective measure of the short-term effects of various cardiopulmonary procedures on neurophysiological function.

The effect of low-flow cardiopulmonary bypass on cerebral function: an experimental and clinical study

Systemic flow rates (Q) during nonpulsatile hypothermic cardiopulmonary bypass (CPB) that are consistent with preservation of cerebral function have not to our knowledge been objectively defined. The effect of a sequential reduction in flow rates on cerebral cortical metabolism and function was evaluated in 6 mongrel dogs during hypothermic (25 degrees C) CPB. Cerebral function was assessed using somatosensory cortical evoked potentials (SSEP); cerebral metabolism was assessed by adenosine triphosphate (ATP) and lactate content of snap-frozen gray matter biopsies taken from the hemisphere contralateral to that monitored for SSEP. A progressive decline in ATP levels was observed during flow reduction with virtually complete depletion of ATP at 0.25 L min-1 m-2(p = .0003). The significant (p = .028) dependence of cortical ATP levels on perfusion pressure was no longer evident after adjusting for the effects of flow rate. Lactate levels increased during flow reduction (p = .028), especially at flow rates less than 0.5 L min-1 m-2. Somatosensory neural transmission remained intact until flow was reduced to 0.25 L min-1 m-2 in 5 animals and until total circulatory arrest in 1, at which time loss of the signal occurred. In addition, 5 patients were subjected to brief periods of low-flow CPB (Q = 1.0 L min-1 m-2) at 21 degrees to 25 degrees C. SSEPs remained intact during flow reduction, and postoperative neurologic evaluation was normal in all patients. We conclude that, in the absence of cerebral vascular disease, the flow rate threshold for incurring functional cerebral injury during hypothermic (25 degrees C) nonpulsatile CPB is less than 1.0 L min-1 m-2.(ABSTRACT TRUNCATED AT 250 WORDS)

The value of early repair for total anomalous pulmonary venous drainage

A total of 20 children with total anomalous pulmonary venous drainage (TAPVD) underwent complete repair within the past six years. The drainage was supracardiac in 11, infracardiac in seven, and into the coronary sinus in two. At repair mean age was nine weeks, and weight was 3.7 km. Operative technique in extracardiac types included complete mobilization of the common vein with division of anomalous channel when possible. The incision in the confluent vein was extended into the lobar veins when necessary to permit extensive incorporation of this structure into the posterior wall of the left atrium and resulted in a nonobstructing stellate-type anastomosis. Operative mortality was 10% (2 of 20). Deaths occurred only in the group of infants in whom severe obstruction to pulmonary venous return required emergency operation, and one of these patients has persistent neurologic deficit. Late cardiac catheterization has been performed in 11 of 18 survivors. Nine had no or only minor abnormalities and two required reoperation. There have been no late deaths with follow-up of 2-8 years (mean = 4 years). Currently, all of the survivors are without cardiac symptoms and only one requires cardiac medication. Our experience identifies pulmonary venous obstruction with critical symptoms as the major operative risk factor in patients with TAPVD. With early operation prior to onset of critical symptoms, mortality is low and functional results are excellent.

Anaesthesia for aortic arch aneurysm repair: experience with 17 patients

Mortality and morbidity during aortic arch aneurysm repair is high despite improvements in surgical technique which attempt to assure brain protection during surgery. We successfully managed 17 patients using deep hypothermia and circulatory arrest. Anaesthesia consisted of pancuronium, fentanyl, plus isoflurane or halothane if needed. Pulmonary artery and arterial catheters were inserted. Surface cooling was performed followed by core cooling on cardiopulmonary bypass, using a heat exchanger. Total circulatory arrest was performed when esophageal temperature reached 12-14 degrees C after previous administration of thiopentone 30 mg X kg-1, methylprednisolone 2 gm, furosemide 40 mg and mannitol 25 gm. At that time the head was packed in ice and surgical correction performed. Mean arrest time was 36.5 +/- 13 minutes at a mean oesophageal temperature of 12.5 +/- 0.75 degrees C. No serious, permanent neurological deficit was found. Tracheostomy was required in five patients of whom two had chronic obstructive pulmonary disease (COPD). Two of these patients died of adult respiratory distress syndrome (ARDS) and renal failure. The reported technique is safe and can be easily used in patients undergoing aortic arch aneurysm repair.

Monitoring of multimodality evoked potentials during open heart surgery under hypothermia

Multimodality evoked responses (ERs) were monitored in 16 adults who had cardiac surgery under cardiopulmonary bypass and moderate hypothermia (19-25 degrees C). Cooling affected all sensory ERs by progressively increasing the latencies of the major components. The effect was more profound on the later than on the earlier ER components. Visual evoked responses (VERs) were most inconsistent and always disappeared at temperatures below 25 degrees C. The later components of the long latency somatosensory evoked responses (SERs) also attenuated or disappeared rather early during hypothermia. On the other hand, short latency SERs were more resistant to the effects of hypothermia. They were always recordable at temperatures of 25 degrees C or above; and usually persisted even at temperatures between 20 and 25 degrees C. Brain-stem auditory evoked responses (BAERs) were consistently present at temperatures above 25 degrees C, wave V was recordable in majority between 20 and 25 degrees C. All sensory ERs disappeared with severe hypothermia (20 degrees C or less) except the components generated more peripherally such as N10 of the short latency SERs. We feel that BAERs and short latency SERs may serve as useful intraoperative monitors of brain function during hypothermia.

Middle-latency auditory evoked responses during open-heart surgery with hypothermia

Middle-latency auditory evoked responses (MLRs) were recorded from infants and adults before and during open heart surgery. Hypothermia was induced through perfusion cooling by cardiopulmonary bypass. In infants deep hypothermia (to 15 degrees C nasopharyngeal temp.) was often followed by the induction of total circulatory arrest. In adults nasopharyngeal temperatures of 25 degrees C were reached. The MLRs were elicited by unfiltered clicks presented through an insert type earphone and recorded with a vertex to ipsilateral earlobe electrode configuration. The MLRs proved to be resistant to muscle relaxation induced by pancuronium and to anesthesia induced and maintained in most cases by fentanyl. In most cases MLR peak latencies were progressively delayed as temperature decreased. Hypotension resulted in decreased MLR (Pa) amplitude.

Brain damage after deep hypothermia in dogs

Histopathological and succinic acid dehydrogenase (SAD) activity changes, and the electron spin resonance (ESR) were examined in the brains of dogs exposed to various hypothermic conditions. A simple hypothermic cardiac arrest of 5 min duration occurred in the group subjected to 28 degrees C, and normal SAD activity was noted in dogs exposed 1-hour extracorporeal circulation under normothermia. In cases of a hypothermia below 28 degrees C, a decrease in enzyme activity, marked histopathological changes and the disappearance of the ESR signal were observed. In dogs killed immediately after induction of 20 degrees C hypothermia, the histopathological changes were primarily ischemic in nature, while in dogs killed at 1-12 month intervals after the experiments, irreversible gliosis was dominant. Our findings suggest that, to avoid brain damage under conditions of deep hypothermic circulatory arrest, the critical range is between 26-28 degrees C for rectal, and approximately 28-30 degrees C for brain temperature.

Cerebral blood flow and cerebral metabolism in children following cardiac surgery with deep hypothermia and circulatory arrest. Clinical course and follow-up of psychomotor development

Between November 1975 and June 1977, 49 children underwent repair of complicated cardiac defects with the aid of deep hypothermia. Circulatory arrest was used in 28 cases. Nine children died (18%) due to early postoperative heart failure. A decisive cause of death in terms of important cardiovascular defects, which were either unknown or not correctable at the time of repair, was found in 6 patients. Children with complicated forms of congenital heart disease requiring an extensive repair were overrepresented among those who died. Hence, there was an excess in the duration of bypass among nonsurvivors (p less than 0.01) whereas the patient's age at operation, the use of circulatory arrest and the duration of aortic occlusion had no bearing on operative mortality. Cerebral blood flow (CBF) and cerebral metabolism were studied in 9 survivors. A negative correlation (r = -0.67) was found between the duration of circulatory arrest and CBF measured directly after surgery. CBF was reduced to values below 0.2 ml . g-1 . min-1 in 3 children with long periods of circulatory arrest. The cerebral uptake of oxygen and glucose was normal both before and after surgery. Two separate interviews with the parents were performed, the first one 3-22 months and the second one about 3 years after surgery. No serious neurological symptoms or psychomotor disturbances were reported. However, in 3 children operated with circulatory arrest, difficulties in performing more delicate motor activities were noted by the parents. The findings indicate that circulatory arrest should be used with caution and total arrest periods exceeding 60 min avoided.

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.

Developmental progress after cardiac surgery in infancy using hypothermia and circulatory arrest

Seventy-two of 76 long-term survivors who had surgical repair of congenital heart lesions at 11 days to 26 months of age using profound hypothermia and circulatory arrest underwent psychometric testing (Stanford-Binet) late postoperatively. The mean IQ of the 72 patients was 92.9 +r16.5 (SD). Stanford-Binet scores bore no relationship to the duration of circulatory arrest or other aspects of surgical technique. Scores were significantly lower in those who had a low birth weight for gestational age, important neurologic problems preoperatively or were in the lower socioeconomic classes. An "ideal" control group of 69 children randomly selected from patients satisfying certain criteria based on birth and neonatal characteristics had a mean IQ of 106.2 +r11.6. Twenty-five patients who had surgical treatment of cogenital heart disease met the criteria for the control group except for their heart lesions. Their mean IQ was 101.4 +r15.0(NS). We could not demonstrate any significant deleterious effect that could be attributed to the surgical methods. Rather, the postoperative IQ scores reflected characteristics related to individual patients.

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.