Profound hypothermia with alpha-stat pH management during open-heart surgery is associated with choreoathetosis

Vitreoretinal Surgery with Temperature Management: A Preliminary Study in Rabbits

The present study aimed to evaluate the structure of the rabbit retina after vitreoretinal surgery using prolonged irrigation with solutions of different temperatures. Thirty-six rabbits (72 eyes) were included in this study and randomly divided into 3 equal groups according to the temperature of the intraocular irrigating fluid they received during vitrectomy. Vitreoretinal surgery was performed with a 5°C irrigation solution in group 1 (12 rabbits, 24 eyes), a 22°C irrigation solution in group 2 (12 rabbits, 24 eyes), and a 36°C irrigation solution in group 3 (12 rabbits, 24 eyes). In each group of animals, the mean irrigation/aspiration time was 30 minutes for left eyes and 60 minutes for right eyes. Histological examination of the retina was performed 1, 7, and 30 days after surgery. During surgery, the temperature in the vitreous cavity of the eyes of rabbits of groups 1, 2, and 3 dropped by 26.0°C, 11.2°C (deep hypothermia), and 1.0°C (mild hypothermia), respectively. The highest rewarming rate was detected in group 1 (0.9°C/min) compared with group 2 (0.7°C/min) and group 3 (0.2°C/min). After 60 minutes of irrigation, retinal structural changes were detected in the animals of groups 1 and 2 (in contrast to the animals of group 3). After surgery with irrigation lasting 30 minutes, no retinal structural changes were observed. This study showed that temperature management, avoidance of intraoperative deep hypothermia, and prevention of rapid uncontrolled rewarming may protect the retinal morphology and increase the safety of prolonged vitreoretinal surgery.

Inherited and Acquired Choreas

Chorea is a symptom of a broad array of genetic, structural, and metabolic disorders. While chorea can result from systemic illness and damage to diverse brain structures, injury to the basal ganglia, especially the putamen or globus pallidus, appears to be a uniting features of these diverse neuropathologies. The timing of onset, rate of progression, and the associated neurological or systemic symptoms can often narrow the differential diagnosis to a few disorders. Recognizing the correct etiology for childhood chorea is critical, as numerous disorders in this category are potentially curable, or are remediable, with early treatment.

Is postoperative encephalopathy with choreoathetosis an acquired form of neuroacanthocytosis?

Postoperative encephalopathy with choreoathetosis ("postpump chorea") is a rare complication of open-heart surgery and, in particular, the employment of a cardiopulmonary bypass pump. It almost exclusively occurs in young children. While risk factors and the underlying histopathology have been identified, the pathogenesis of postpump chorea, crucially, remains largely unknown. Transient cerebral hypoperfusion associated with cardiopulmonary bypass is considered a likely candidate mechanism, but the evidence is insufficient and inconclusive. It is hypothesized in this article, that postpump chorea may be caused by mechanical trauma to red blood cells and resulting acanthocytosis. These dysfunctional erythrocytes could then lead to damage to the globus pallidus and disease development akin to that presumed in neuroacanthocytosis. In patients with neuroacanthocytosis an association between acanthocytosis and basal ganglia pathology has been suggested. To test the mechanism hypothesized here, the effects of cardiopulmonary bypass on erythrocyte morphology and function could be systematically tested in children undergoing cardiac surgery. Ideally, the extent of erythrocyte damage could be correlated with the risk of developing postpump chorea. Finally, if the proposed hypothesis is supported by empirical findings, efforts to reduce blood cell damage during extracorporeal circulation in children might prevent this devastating complication.

Limitations of Mild, Moderate, and Profound Hypothermia in Protecting Developing Hippocampal Neurons After Simulated Ischemia

Mild hypothermia (33°C-34°C) after cerebral ischemia in intact animals or ischemia-like conditions in vitro reduces neuron death. However, it is now clear that more profound hypothermia or delayed hypothermia may not provide significant protection. To further define the limitations of hypothermia after cerebral ischemia, we used hippocampal slice cultures to examine the effects of various degrees, durations, and delays of hypothermia on neuron death after an ischemia-like insult. Organotypic cultures of the hippocampus from 7- to 8 day-old rat pups were cooled to 32°C, 23°C, 17°C, or 4°C immediately or after a 2-4 hour delay from an injurious insult of oxygen and glucose deprivation (OGD). Cell death in CA1, CA3 and dentate regions of the cultures was assessed 24 hours later with SYTOX® or propidium iodide, both of which are fluorescent markers labeling damaged cells. OGD caused extensive cell death in CA1, CA3, and dentate regions of the hippocampal cultures. Hypothermia (32°C, 23°C and 17°C) for 4-6 hours immediately after OGD was protective at 24 hours, but when hypothermia was applied for longer periods or delayed after OGD, no protection or increased death was seen. Ultra-profound hypothermia (4°C) increased cell death in all cell areas of the hippocampus even when after a milder insult of only hypoxia. In an in vitro model of recovery after an ischemia-like insult, mild to profound hypothermia is protective only when applied without delay and for limited periods of time (6-8 hours). Longer durations of hypothermia, or delayed application of the hypothermia can increase neuron death. These findings may have implications for clinical uses of therapeutic hypothermia after hypoxic or ischemic insults, and suggest that further work is needed to elucidate the limitations of hypothermia as a protective treatment after ischemic stress.

Anesthetic protection of neurons injured by hypothermia and rewarming: roles of intracellular Ca2+ and excitotoxicity

BACKGROUND

Mild hypothermia is neuroprotective after cerebral ischemia but surgery involving profound hypothermia (PH, temperature less than 18°C) is associated with neurologic complications. Rewarming (RW) from PH injures hippocampal neurons by glutamate excitotoxicity, N-methyl-D-aspartate receptors, and intracellular calcium. Because neurons are protected from hypoxia-ischemia by anesthetic agents that inhibit N-methyl-D-aspartic acid receptors, we tested whether anesthetics protect neurons from damage caused by PH/RW.

METHODS

Organotypic cultures of rat hippocampus were used to model PH/RW injury, with hypothermia at 4°C followed by RW to 37°C and assessment of cell death 1 or 24 h later. Cell death and intracellular Ca were assessed with fluorescent dye imaging and histology. Anesthetic agents were present in the culture media during PH and RW or only RW.

RESULTS

Injury to hippocampal CA1, CA3, and dentate neurons after PH and RW involved cell swelling, cell rupture, and adenosine triphosphate (ATP) loss; this injury was similar for 4 through 10 h of PH. Isoflurane (1% and 2%), sevoflurane (3%) and xenon (60%) reduced cell loss but propofol (3 μM) and pentobarbital (100 μM) did not. Isoflurane protection involved reduction in N-methyl-D-aspartate receptor-mediated Ca influx during RW but did not involve γ-amino butyric acid receptors or KATP channels. However, cell death increased over the next day.

CONCLUSION

Anesthetic protection of neurons rewarmed from 4°C involves suppression of N-methyl-D-aspartate receptor-mediated Ca overload in neurons undergoing ATP loss and excitotoxicity. Unlike during hypoxia/ischemia, anesthetic agents acting predominantly on γ-aminobutyric acid receptors do not protect against PH/RW. The durability of anesthetic protection against cold injury may be limited.

Hypothermia and rewarming injury in hippocampal neurons involve intracellular Ca2+ and glutamate excitotoxicity

This study examines the causes of hypothermia and rewarming injury in CA1, CA3, and dentate neurons in rat hippocampal slice cultures. Neuronal death, assessed with propidium iodide or Sytox fluorescence, Fluoro-Jade labeling, and Cresyl Violet staining, depended on the severity and duration of hypothermia. More than 6 h at temperatures less than 12 °C followed by rewarming to 37 °C (profound hypothermia and rewarming, PH/RW) caused swelling and death in large number of neurons in CA1, CA3, and dentate. During PH, [ATP] decreased and [Ca(2+)](I) and extracellular [glutamate] increased, with neuron rupture and nuclear condensation following RW. The data support the hypothesis that neuronal death from PH/RW is excitotoxic, due to ATP loss, glutamate receptor activation and Ca(2+) influx. We found that antagonism of N-methyl-D-aspartate (NMDA) receptors, but not 2-amino-3-(5-methyl-3-oxo-1,2- oxazol-4-yl) propanoic acid or metabotropic glutamate receptors, decreased neuron death and prevented increases in [Ca(2+)](I) caused by PH/RW. Chelating extracellular Ca(2+) decreased PH/RW injury, but inhibiting L- and T-type voltage-gated Ca(2+) channels, K+ channels, Ca(2+) release from the endoplasmic reticulum, and reverse Na(+)/Ca(2+) exchange did not affect the Ca(2+) changes or cell death. We conclude that the mechanism of PH/RW neuronal injury in hippocampal slices primarily involves intracellular Ca(2+) accumulation mediated by NMDA receptors that activates necrotic, but not apoptotic processes.

Movement disorder emergencies in childhood

The literature on paediatric acute-onset movement disorders is scattered. In a prospective cohort of 52 children (21 male; age range 2mo-15y), the commonest were chorea, dystonia, tremor, myoclonus, and Parkinsonism in descending order of frequency. In this series of mainly previously well children with cryptogenic acute movement disorders, three groups were recognised: (1) Psychogenic disorders (n = 12), typically >10 years of age, more likely to be female and to have tremor and myoclonus (2) Inflammatory or autoimmune disorders (n = 22), including N-methyl-d-aspartate receptor encephalitis, opsoclonus-myoclonus, Sydenham chorea, systemic lupus erythematosus, acute necrotizing encephalopathy (which may be autosomal dominant), and other encephalitides and (3) Non-inflammatory disorders (n = 18), including drug-induced movement disorder, post-pump chorea, metabolic, e.g. glutaric aciduria, and vascular disease, e.g. moyamoya. Other important non-inflammatory movement disorders, typically seen in symptomatic children with underlying aetiologies such as trauma, severe cerebral palsy, epileptic encephalopathy, Down syndrome and Rett syndrome, include dystonic posturing secondary to gastro-oesophageal reflux (Sandifer syndrome) and Paroxysmal Autonomic Instability with Dystonia (PAID) or autonomic 'storming'. Status dystonicus may present in children with known extrapyramidal disorders, such as cerebral palsy or during changes in management e.g. introduction or withdrawal of neuroleptic drugs or failure of intrathecal baclofen infusion; the main risk in terms of mortality is renal failure from rhabdomyolysis. Although the evidence base is weak, as many of the inflammatory/autoimmune conditions are treatable with steroids, immunoglobulin, plasmapheresis, or cyclophosphamide, it is important to make an early diagnosis where possible. Outcome in survivors is variable. Using illustrative case histories, this review draws attention to the practical difficulties in diagnosis and management of this important group of patients.

Brain temperature: heat production, elimination and clinical relevance

Neurological insults are a leading cause of morbidity and mortality, both in adults and especially in children. Among possible therapeutic strategies to limit clinical cerebral damage and improve outcomes, hypothermia remains a promising and beneficial approach. However, its advantages are still debated after decades of use. Studies in adults have generated conflicting results, whereas in children recent data even suggest that hypothermia may be detrimental. Is it because brain temperature physiology is not well understood and/or not applied properly, that hypothermia fails to convince clinicians of its potential benefits? Or is it because hypothermia is not, as believed, the optimal strategy to improve outcome in patients affected with an acute neurological insult? This review article should help to explain the fundamental physiological principles of brain heat production, distribution and elimination under normal conditions and discuss why hypothermia cannot yet be recommended routinely in the management of children affected with various neurological insults.

Postoperative encephalopathy with choreoathetosis

Since the 1980s, survival of children with CHD has increased significantly with the introduction of new surgical techniques that incorporate cardiorespiratory arrest (CRA), extracorporeal circulation (ECC), and deep hypothermia. However, an increase in survival has been associated with an increase in recognized postoperative neurological complications. Postoperative encephalopathy with choreoathetosis, also known as "postpump chorea", is one of these well-defined neurological complications and was first reported in 1961. Postpump chorea is considered one of the most devastating neurological complications following cardiac surgery. However, the exact etiology and pathophysiology of this complication is unknown. Several factors may contribute to the postoperative development of choreoathetoid movements, including deep hypothermia (core body temperature < 20ºC) with total circulatory arrest, use of cardiopulmonary bypass, and variability in blood pH and PaCO(2) resulting in fluctuations in cerebral blood flow. The length of time children are affected by choreoathetoid movements and long-term neurological outcome in these children varies and largely depends upon the form of postoperative encephalopathy that they develop, described as either mild or severe. Several groups suggest that age at time of surgery plays a role in the risk of developing postpump chorea, with a tendency for older children to develop the severe persistent form.

Perioperative hypothermia: use and therapeutic implications

Perioperative cerebral ischemic insults are common in some surgical procedures. The notion that induced hypothermia can be employed to improve outcome in surgical patients has persisted for six decades. Its principal application has been in the context of cardiothoracic and neurosurgery. Mild (32-35 degrees C) and moderate (26-31 degrees C) hypothermia have been utilized for numerous procedures involving the heart, but intensive research has found little or no benefit to outcome. This may, in part, be attributable to confounding effects associated with rewarming and lack of understanding of the mechanisms of injury. Evidence of efficacy of mild hypothermia is absent for cerebral aneurysm clipping and carotid endarterectomy. Deep hypothermia (18-25 degrees C) during circulatory arrest has been practiced in the repair of congenital heart disease, adult thoracic aortas, and giant intracranial aneurysms. There is little doubt of the protective efficacy of deep hypothermia, but continued efforts to refine its application may serve to enhance its utility. Recent evidence that mild hypothermia is efficacious in out-of-hospital cardiac arrest has implications for patients incurring anoxic or global ischemic brain insults during anesthesia and surgery, or perioperatively. Advances in preclinical models of ischemic/anoxic injury and cardiopulmonary bypass that allow definition of optimal cooling strategies and study of cellular and subcellular events during perioperative ischemia can add to our understanding of mechanisms of hypothermia efficacy and provide a rationale basis for its implementation in humans.

Pediatric warm open heart surgery and prolonged cross-clamp time

BACKGROUND

The safety of normothermic pediatric cardiac surgery remains controversial. This study evaluated the performance of normothermic cardiopulmonary bypass (CPB) associated with intermittent warm blood cardioplegia during prolonged aortic cross-clamp time (CCT).

METHODS

This retrospective study included 234 consecutive patients weighing less than 10 kg operated under CPB from August 2006 to November 2007. Patients were divided into two groups: group 1 contained 38 patients with CCT exceeding 90 minutes, and group 2 had 196 patients with shorter CCT. Classic factors were used to analyze outcomes, and outcomes were compared with those from the Society of Thoracic Surgeons-European Association for Cardio-Thoracic Surgery database.

RESULTS

Results, expressed as values for group 1 vs those for group 2, were mortality rate, 5.3% vs 2%; length of hospital stay exceeding 21 days, 5% vs 0.5%; delayed chest closure, 21% vs 2.6%; epinephrine infusion, 45% vs 11%; organ failure, 13% vs 2%; reoperation due to bleeding, 3% vs 0.5%; heart block, 3% vs 1%; time to extubation, in hours, 64 +/- 94 vs 19 +/- 48; plasma lactate concentrations after bypass, 2.6 vs 1.9 mmol/L; length of stay in intensive care, in hours, 100 +/- 105 vs 52 +/- 48.

CONCLUSIONS

Despite expected differences between the two groups, our results were within the range of values described in the literature. This led us to conclude that warm pediatric cardiac surgery with a long CCT is safe. A large, multicenter, randomized prospective study comparing normothermic and hypothermic pediatric cardiac surgery is underway.

Acute brain injury and therapeutic hypothermia in the PICU: A rehabilitation perspective

Acquired brain injury from traumatic brain injury, cardiac arrest (CA), stroke, and central nervous system infection is a leading cause of morbidity and mortality in the pediatric population and reason for admission to inpatient rehabilitation. Therapeutic hypothermia is the only intervention shown to have efficacy from bench to bedside in improving neurological outcome after birth asphyxia and adult arrhythmia-induced CA, thought to be due to its multiple mechanisms of action. Research to determine if therapeutic hypothermia should be applied to other causes of brain injury and how to best apply it is underway in children and adults. Changes in clinical practice in the hospitalized brain-injured child may have effects on rehabilitation referral practices, goals and strategies of therapies offered, and may increase the degree of complex medical problems seen in children referred to inpatient rehabilitation.

Therapeutic hypothermia

Therapeutic hypothermia, introduced more than 5 decades ago, remains an important neuroprotective factor in the surgery for the correction of congenital heart disease, in particular when intraoperative circulatory arrest is required. Hypothermia decreases cerebral metabolism and energy consumption and reduces the extent of degenerative processes such as the excitotoxic cascade, apoptotic and necrotic cell death, microglial activation, oxidative stress, and inflammation. Neurological outcome has become the focus of several studies in the recent years, and deep hypothermic circulatory arrest durations of more than 40 minutes are associated with increased mid- and long-term disability. Physiologic cerebral flow-metabolism coupling seems to be preserved with moderate and mild hypothermia, but cerebral blood flow autoregulation is probably altered after deep hypothermic circulatory arrest, suggesting disordered cerebral metabolism and oxygen use. Although evidence from animal studies suggests potential benefit from very low temperatures, postoperative development of choreoathetosis has been found to correlate with the degree of intraoperative hypothermia, recommending the use of central temperatures greater than 15 degrees C in the clinical practice. Cooling times longer than 20 minutes are needed to obtain homogeneous brain cooling and effective neuroprotection. Finally, there is evidence that the sites of temperature monitoring used in the clinical practice may underestimate brain temperature after cardiopulmonary bypass, with the risk of postoperative hyperthermic brain damage.