Blood-brain barrier disruption after cardiopulmonary resuscitation in immature swine

Feasibility and Preliminary Efficacy of α-Calcium Sulfate Hemihydrate in Socket Preservation: Protocol for a Pilot Randomized Controlled Trial

BACKGROUND

Tooth extraction procedures often lead to bone resorption, which can have adverse effects on the dimensions of the alveolar ridge. Research has shown that socket preservation techniques using bone graft substitutes can effectively minimize early bone loss in such cases. α-calcium sulfate hemihydrate (α-CSH) has garnered significant attention as a potential bone graft material due to its favorable properties, including osteoconductivity, angiogenic potential, and biocompatibility. Considering these facts, we developed a preliminary protocol for applying α-CSH in addressing alveolar bone loss following tooth extraction.

OBJECTIVE

This research's general objective is to evaluate the feasibility and initial effectiveness of α-CSH as bone-inducing graft material for socket preservation after tooth extraction.

METHODS

This preliminary clinical trial will involve 30 fresh extraction sockets from individuals aged 18-35 years. The participants will be divided into 2 groups: one group will receive α-CSH graft material after tooth extraction for socket preservation, while the other group will not receive any graft material. Throughout the study, the participants will be closely monitored for safety measures, which will include clinical examinations, radiographic imaging, and blood tests. Radiographic imaging will be used extensively to assist the progress of bone formation.

RESULTS

The study commenced enrollment in August 2022 and is scheduled to conclude post assessments and analyses by the end of 2023. The results of the study are anticipated to be accessible in late 2024.

CONCLUSIONS

This clinical study represents the initial investigation in humans to assess the feasibility and efficacy of α-CSH in alveolar bone regeneration. We hypothesize that the inclusion of α-CSH can greatly expedite the process of bone formation within fresh sockets, resulting in a swift restoration of bone height without the disadvantages associated with harvesting autogenous bone graft.

TRIAL REGISTRATION

Indonesia Registry Center INA-D02FAHP; https://tinyurl.com/2jnf6n3s.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/49922.

Epinephrine vs placebo in neonatal resuscitation: ROSC and brain MRS/MRI in term piglets

BACKGROUND

We aimed to investigate the effect of epinephrine vs placebo on return of spontaneous circulation (ROSC) and brain magnetic resonance spectroscopy and imaging (MRS/MRI) in newborn piglets with hypoxic cardiac arrest (CA).

METHODS

Twenty-five piglets underwent hypoxia induced by endotracheal tube clamping until CA. The animals were randomized to CPR + intravenous epinephrine or CPR + placebo (normal saline). The primary outcome was ROSC, and secondary outcomes included time-to-ROSC, brain MRS/MRI, and composite endpoint of death or severe brain MRS/MRI abnormality.

RESULTS

ROSC was more frequent in animals treated with epinephrine than placebo; 10/13 vs 4/12, RR = 2.31 (95% CI: 1.09-5.77). We found no difference in time-to-ROSC (120 (113-211) vs 153 (116-503) seconds, p = 0.7) or 6-h survival (7/13 vs 3/12, p = 0.2). Among survivors, there was no difference between groups in brain MRS/MRI. We found no difference in the composite endpoint of death or severe brain MRS/MRI abnormality; RR = 0.7 (95% CI: 0.37-1.19).

CONCLUSIONS

Resuscitation with epinephrine compared to placebo improved ROSC frequency after hypoxic CA in newborn piglets. We found no difference in time-to-ROSC or the composite endpoint of death or severe brain MRS/MRI abnormality.

IMPACT

In a newborn piglet model of hypoxic cardiac arrest, resuscitation with epinephrine compared to placebo improved the rate of return of spontaneous circulation and more than doubled the 6-h survival. Brain MRS/MRI biomarkers were used to evaluate the effect of epinephrine vs placebo. We found no difference between groups in the composite endpoint of death or severe brain MRS/MRI abnormality. This study adds to the limited evidence regarding the effect and safety of epinephrine; the lack of high-quality evidence from randomized clinical trials was highlighted in the latest ILCOR 2020 guidelines, and newborn animal studies were specifically requested.

Regulation of the Cerebral Circulation During Development

The cerebral microcirculation undergoes dynamic changes in parallel with the development of neurons, glia, and their energy metabolism throughout gestation and postnatally. Cerebral blood flow (CBF), oxygen consumption, and glucose consumption are as low as 20% of adult levels in humans born prematurely but eventually exceed adult levels at ages 3 to 11 years, which coincide with the period of continued brain growth, synapse formation, synapse pruning, and myelination. Neurovascular coupling to sensory activation is present but attenuated at birth. By 2 postnatal months, the increase in CBF often is disproportionately smaller than the increase in oxygen consumption, in contrast to the relative hyperemia seen in adults. Vascular smooth muscle myogenic tone increases in parallel with developmental increases in arterial pressure. CBF autoregulatory response to increased arterial pressure is intact at birth but has a more limited range with arterial hypotension. Hypoxia-induced vasodilation in preterm fetal sheep with low oxygen consumption does not sustain cerebral oxygen transport, but the response becomes better developed for sustaining oxygen transport by term. Nitric oxide tonically inhibits vasomotor tone, and glutamate receptor activation can evoke its release in lambs and piglets. In piglets, astrocyte-derived carbon monoxide plays a central role in vasodilation evoked by glutamate, ADP, and seizures, and prostanoids play a large role in endothelial-dependent and hypercapnic vasodilation. Overall, homeostatic mechanisms of CBF regulation in response to arterial pressure, neuronal activity, carbon dioxide, and oxygenation are present at birth but continue to develop postnatally as neurovascular signaling pathways are dynamically altered and integrated. © 2021 American Physiological Society. Compr Physiol 11:1-62, 2021.

Microbleeds in the Corpus Callosum in Anoxic Brain Injury

Purpose

This study was performed to evaluate the relationship between callosal microbleeds and anoxic brain injury.

Materials and Methods

Twenty-seven patients with anoxic brain injuries were analyzed and retrospectively compared to the control group of patients without a history of anoxic brain injury using Fisher's exact test regarding comorbidities and cerebral microbleeds. The patient group was subdivided according to the presence of callosal microbleeds. Fisher's exact test was used to compare the presence of typical MRI findings of anoxic brain injury, use of cardiopulmonary resuscitation, and prognosis. The Mann-Whitney U test was used to compare the interval between the occurrence of anoxic brain injury to MRI acquisition.

Results

The prevalence of cerebral microbleeds in the patient group was 29.6%, which was significantly higher than that in the control group at 3.7% (p = 0.012). All cerebral microbleeds in the patient group were in the corpus callosum. Compared with the callosal microbleed-absent group, the callosal microbleed-present group showed a tendency of good prognosis (6/8 vs. 11/19), fewer typical MRI findings of anoxic brain injury (2/8 vs. 10/19), and more cardiopulmonary resuscitation (6/8 vs. 12/19), although these differences did not reach statistical significance (p = 0.35, p = 0.19, and p = 0.45, respectively).

Conclusion

Callosal microbleeds may be an adjunctive MRI marker for anoxic brain injury.

Effect of mild hypothermia on cerebral microcirculation in a murine cardiopulmonary resuscitation model

BACKGROUND

We hypothesized that mild hypothermia may improve brain microcirculation by reducing cerebral microvascular endothelial cells apoptosis, and this effect may be maximized by moving up the initiation of mild hypothermia from after return of spontaneous circulation (ROSC) to the start of cardiopulmonary resuscitation (CPR).

METHODS

A total of 35 rats were randomized into the intra-arrest hypothermia group (IAH), post-resuscitation hypothermia group (PRH), normothermia group (NT), or the sham control group. A craniotomy exposed the parietal cortex for visualization of microcirculation. Ventricular fibrillation was electrically induced and untreated for 8 minutes, followed by 8 minutes of precordial compression and mechanical ventilation. Hypothermia (33 ± 0.5°C) in the IAH and PRH group was induced and maintained for 6 hours at the beginning of CPR or after ROSC, respectively. At baseline, 1, 3, and 6 hours, hemodynamic parameters were measured and the pial microcirculations were visualized with a sidestream dark field imaging video microscope. Microvascular flow index and perfused microvessel density (PMD) were calculated. Rats were euthanized, and brain tissues were removed at 3 and 6 hours separately. Expression of Bax, Bcl-2, and Caspase 3 in brain microvascular endothelial cells was examined by Western blot.

RESULTS

Microvascular flow index and PMD were significantly reduced after cardiac arrest and resuscitation (all P < 0.05), and the former was largely preserved by hypothermia regardless when the hypothermia treatment was induced (P < 0.05). Bax and Caspase 3 increased and Bcl-2 decreased significantly after resuscitation, and hypothermia treatment reversed the trend partly (all P < 0.05). A moderate correlation was observed between MFI and those proteins (Bcl-2/BAX: 3 hours: r = 0.730, P = 0.002; 6 hours: r = 0.743, P = 0.002).

CONCLUSION

Mild hypothermia improves cerebral microcirculatory blood supply, partly by inhibiting endothelial cell apoptosis. Mild hypothermia induced simultaneously with CPR has shown no additional benefit in microcirculation or endothelial cell apoptosis.

Blood brain barrier is impermeable to solutes and permeable to water after experimental pediatric cardiac arrest

Pediatric asphyxial cardiac arrest (CA) results in unfavorable neurological outcome in most survivors. Development of neuroprotective therapies is contingent upon understanding the permeability of intravenously delivered medications through the blood brain barrier (BBB). In a model of pediatric CA we sought to characterize BBB permeability to small and large molecular weight substances. Additionally, we measured the percent brain water after CA. Asphyxia of 9 min was induced in 16-18 day-old rats. The rats were resuscitated and the BBB permeability to small (sodium fluorescein and gadoteridol) and large (immunoglobulin G, IgG) molecules was assessed at 1, 4, and 24 h after asphyxial CA or sham surgery. Percent brain water was measured post-CA and in shams using wet-to-dry brain weight. Fluorescence, gadoteridol uptake, or IgG staining at 1, 4h and over the entire 24 h post-CA did not differ from shams, suggesting absence of BBB permeability to these solutes. Cerebral water content was increased at 3h post-CA vs. sham. In conclusion, after 9 min of asphyxial CA there is no BBB permeability over 24h to conventional small or large molecule tracers despite the fact that cerebral water content is increased early post-CA indicating the development of brain edema. Evaluation of novel therapies targeting neuronal death after pediatric CA should include their capacity to cross the BBB.

Adrenaline increases blood-brain-barrier permeability after haemorrhagic cardiac arrest in immature pigs

BACKGROUND

Adrenaline (ADR) and vasopressin (VAS) are used as vasopressors during cardiopulmonary resuscitation. Data regarding their effects on blood-brain barrier (BBB) integrity and neuronal damage are lacking. We hypothesised that VAS given during cardiopulmonary resuscitation (CPR) after haemorrhagic circulatory arrest will preserve BBB integrity better than ADR.

METHODS

Twenty-one anaesthetised sexually immature male piglets (with a weight of 24.3 ± 1.3 kg) were bled 35% via femoral artery to a mean arterial blood pressure of 25 mmHg in the period of 15 min. Afterwards, the piglets were subjected to 8 min of untreated ventricular fibrillation followed by 15 min of open-chest CPR. At 9 min of circulatory arrest, piglets received amiodarone 1.0 mg/kg and hypertonic-hyperoncotic solution 4 ml/kg infusions for 20 min. At the same time, VAS 0.4 U/kg was given intravenously to the VAS group (n = 9) while the ADR group received ADR 20 μg/kg (n = 12). Internal defibrillation was attempted from 11 min of cardiac arrest to achieve restoration of spontaneous circulation. The experiment was terminated 3 h after resuscitation.

RESULTS

The intracranial pressure (ICP) in the post-resuscitation phase was significantly greater in ADR group than in VAS group. VAS group piglets exhibited a significantly smaller BBB disruption compared with ADR group. Cerebral pressure reactivity index showed that cerebral blood flow autoregulation was also better preserved in VAS group.

CONCLUSIONS

Resuscitation with ADR as compared with VAS after haemorrhagic circulatory arrest increased the ICP and impaired cerebrovascular autoregulation more profoundly, as well as exerted an increased BBB disruption though no significant difference in neuronal injury was observed.

Striatal neuroprotection from neonatal hypoxia-ischemia in piglets by antioxidant treatment with EUK-134 or edaravone

Striatal neurons are highly vulnerable to hypoxia-ischemia (HI) in term newborns. In a piglet model of HI, striatal neurons develop oxidative stress and organelle disruption by 3-6 h of recovery and ischemic cytopathology over 6-24 h of recovery. We tested the hypothesis that early treatment with the antioxidants EUK-134 (a manganese-salen derivative that acts as a scavenger of superoxide, hydrogen peroxide, nitric oxide or NO and peroxynitrite) or edaravone (MCI-186, a scavenger of hydroxyl radical and NO) protects striatal neurons from HI. Anesthetized newborn piglets were subjected to 40 min of hypoxia and 7 min of airway occlusion. At 30 min after resuscitation, the piglets received vehicle, EUK-134 or edaravone. Drug treatment did not affect arterial blood pressure, blood gases, blood glucose or rectal temperature. At 4 days of recovery, the density of viable neurons in the putamen of vehicle-treated piglets was 12 ± 6% (±SD) of sham-operated control density. Treatment with EUK-134 increased viability to 41 ± 17%, and treatment with edaravone increased viability to 39 ± 19%. In the caudate nucleus, neuronal viability was increased from 54 ± 11% in the vehicle group to 78 ± 15% in the EUK-134 group and to 73 ± 13% in the edaravone group. Antioxidant drug treatment accelerated recovery from neurologic deficits and decreased oxidative and nitrative damage to nucleic acids. Treatment with EUK-134 reduced the HI-induced formation of protein carbonyl groups and tyrosine nitration at 3 h of recovery. We conclude that systemic administration of antioxidant agents by 30 min after resuscitation from HI can reduce oxidative stress and salvage neurons in the highly vulnerable striatum in a large-animal model of neonatal HI. Therefore, oxidative stress is an important mechanism for this injury, and antioxidant therapy is a rational, mechanism-based approach to neuroprotection in the newborn brain.

Sex differences in cerebral injury after severe haemorrhage and ventricular fibrillation in pigs

BACKGROUND

Experimental studies of haemorrhagic shock have documented a superior haemodynamic response and a better outcome in female animals as compared with male controls. Such sexual dimorphism has, nevertheless, not been reported after circulatory arrest that follows exsanguination and shock. We aimed to study differences in cerebral injury markers after exsanguination cardiac arrest in pre-pubertal piglets. The hypothesis was that cerebral injury is less extensive in female animals, and that this difference is independent of sexual hormones or choice of resuscitative fluid.

METHODS

Thirty-two sexually immature piglets (14 males and 18 females) were subjected to 5 min of haemorrhagic shock followed by 2 min of ventricular fibrillation and 8 min of cardiopulmonary resuscitation, using three resuscitation fluid regimens (whole blood, hypertonic saline and dextran, or acetated Ringers' solution plus whole blood and methylene blue). Haemodynamic values, cellular markers of brain injury and brain histology were studied.

RESULTS

After successful resuscitation, female piglets had significantly greater cerebral cortical blood flow, tended to have lower S-100beta values and a lower cerebral oxygen extraction ratio. Besides, in female animals, systemic and cerebral venous acidosis were mitigated. Female piglets exhibited a significantly smaller increase in neuronal nitric oxide synthase (nNOS) and inducible nitric oxide synthase (iNOS) expression in their cerebral cortex, smaller blood-brain-barrier (BBB) disruption and significantly smaller neuronal injury.

CONCLUSION

After resuscitation from haemorrhagic circulatory arrest, cerebral reperfusion is greater, and BBB permeability and neuronal injury is smaller in female piglets. An increased cerebral cortical iNOS and nNOS expression in males implies a mechanistic relationship with post-resuscitation neuronal injury and warrants further investigation.

Blood-brain barrier integrity in a rat model of emergency preservation and resuscitation

Emergency Preservation and Resuscitation (EPR) represents a novel approach to treat exsanguination cardiac arrest (CA) victims, using an aortic flush to induce hypothermia during circulatory arrest, followed by delayed resuscitation with cardiopulmonary bypass (CPB). The status of the blood-brain barrier (BBB) integrity after prolonged hypothermic CA is unclear. The objective of this study was to assess BBB permeability in two EPR models in rats, associated with poor outcome. Rats subjected to traumatic brain injury (TBI) and naïve rats served as positive and negative controls, respectively.

HYPOTHESIS

The BBB will be disrupted after TBI, but intact after prolonged hypothermic CA.

METHODS

Four groups were studied: (1) EPR-IC (ice cold)-75 min CA at 15 degrees C; (2) EPR-RT (room temperature)-20 min CA at 28 degrees C; (3) TBI; (4) sham. Rats in EPR groups were subjected to rapid hemorrhage, followed by CA. Rats in the TBI group had a controlled cortical impact to the left hemisphere. Naïves were subjected to the same anesthesia and surgery. 1h after insult, rats were injected with Evans Blue (EB), a marker of BBB permeability for albumin. Rats were sacrificed after 5h and EB absorbance was quantified in brain samples.

RESULTS

TBI produced an approximately 10-fold increase in EB absorbance in the left (injured) hemisphere vs. left hemisphere for all other groups (p=0.001). In contrast, EB absorbance in either EPR group did not differ from sham.

CONCLUSION

BBB integrity to albumin is not disrupted early after resuscitation from prolonged CA treated with EPR. Neuroprotective adjuncts to hypothermia in this setting should focus on agents that penetrate the BBB. These findings also have implications for deep hypothermic circulatory arrest.

Magnetic resonance imaging assessment of regional cerebral blood flow after asphyxial cardiac arrest in immature rats

Cerebral blood flow (CBF) alterations after asphyxial cardiac arrest (CA) are not defined in developmental animal models or humans. We characterized regional and temporal changes in CBF from 5 to 150 mins after asphyxial CA of increasing duration (8.5, 9, 12 min) in postnatal day (PND) 17 rats using the noninvasive method of arterial spin-labeled magnetic resonance imaging (ASL-MRI). We also assessed blood-brain barrier (BBB) permeability, and evaluated the relationship between CBF and mean arterial pressure after resuscitation. After all durations of asphyxia CBF alterations were region dependent. After 8.5- and 9-min asphyxia, intense subcortical hyperemia at 5 min was followed by return of CBF to baseline values by 10 mins. After 12-min asphyxia, hyperemia was absent and hypoperfusion reached a nadir of 38% to 65% of baselines with the lowest values in the cortex. BBB was impermeable to gadoteridol 150 mins after CA. CBF in the 12-min CA group was blood pressure passive at 60 min assessed via infusion of epinephrine. ASL-MRI assessment of CBF after asphyxial CA in PND 17 rats reveals marked duration and region-specific reperfusion patterns and identifies possible new therapeutic targets.

Neuro- and cardioprotective effects of blockade of nitric oxide action by administration of methylene blue

Methylene blue (MB), generic name methylthioninium (C(16)H(18)ClN(3) S . 3H(2)O), is a blue dye synthesized in 1876 by Heinrich Caro for use as a textile dye and used in the laboratory and clinically since the 1890s, with well-known toxicity and pharmacokinetics. It has experimentally proven neuroprotective and cardioprotective effects in a porcine model of global ischemia-reperfusion in experimental cardiac arrest. This effect has been attributed to MB's blocking effect on nitric oxide synthase and guanylyl cyclase, the latter blocking the synthesis of the second messenger of nitric oxide. The physiological effects during reperfusion include stabilization of the systemic circulation without significantly increased total peripheral resistance, moderately increased cerebral cortical blood flow, a decrease of lipid peroxidation and inflammation, and less anoxic tissue injury in the brain and the heart. The last two effects are recorded as less increase in plasma concentrations of astroglial protein S-100beta, as well as troponin I and creatine kinase isoenzyme MB, respectively.

Cardio-cerebral and metabolic effects of methylene blue in hypertonic sodium lactate during experimental cardiopulmonary resuscitation

BACKGROUND

Methylene blue (MB) administered with a hypertonic-hyperoncotic solution reduces the myocardial and cerebral damage due to ischaemia and reperfusion injury after experimental cardiac arrest and also increases short-term survival. As MB precipitates in hypertonic sodium chloride, an alternative mixture of methylene blue in hypertonic sodium lactate (MBL) was developed and investigated during and after cardiopulmonary resuscitation (CPR).

METHODS

Using an experimental pig model of cardiac arrest (12 min cardiac arrest and 8 min CPR) the cardio-cerebral and metabolic effects of MBL (n=10), MB in normal saline (MBS; n=10) or in hypertonic saline dextran (MBHSD; n=10) were compared. Haemodynamic variables and cerebral cortical blood flow (CCBF) were recorded. Biochemical markers of cerebral oxidative injury (8-iso-PGF2alpha), inflammation (15-keto-dihydro-PGF2alpha), and neuronal damage (protein S-100beta) were measured in blood from the sagittal sinus, whereas markers of myocardial injury, electrolytes, and lactate were measured in arterial plasma.

RESULTS

There were no differences between groups in survival, or in biochemical markers of cerebral injury. In contrast, the MBS group exhibited not only increased CKMB (P<0.001) and troponin I in comparison with MBHSD (P=0.019) and MBL (P=0.037), but also greater pulmonary capillary wedge pressure 120 min after return of spontaneous circulation (ROSC). Lactate administration had an alkalinizing effect started 120 min after ROSC.

CONCLUSIONS

Methylene blue in hypertonic sodium lactate may be used against reperfusion injury during experimental cardiac arrest, having similar effects as MB with hypertonic saline-dextran, but in addition better myocardial protection than MB with normal saline. The neuroprotective effects did not differ.

Methylene blue added to a hypertonic–hyperoncotic solution increases short-term survival in experimental cardiac arrest*

OBJECTIVE

Methylene blue (MB), a free-radical scavenger inhibiting the production and actions of nitric oxide, may counteract excessive vasodilatation induced by nitric oxide during cardiac arrest. Effects of MB in cardiac arrest and cardiopulmonary resuscitation were investigated.

DESIGN

Randomized, prospective, laboratory animal study.

SETTING

University animal research laboratory.

SUBJECTS

A total of 63 piglets of both sexes.

INTERVENTIONS

A pig model of extended cardiac arrest (12 mins of untreated cardiac arrest and 8 mins of cardiopulmonary resuscitation) was employed to assess the addition or no addition of MB to a hypertonic saline-dextran solution. These two groups (MB and hypertonic saline-dextran group [MB group] and hypertonic saline-dextran-only group) of 21 animals were each compared with a group receiving isotonic saline (n = 21).

MEASUREMENTS AND MAIN RESULTS

Although the groups were similar in baseline values, 4-hr survival in the MB group was increased (p = .02) in comparison with the isotonic saline group. Hemodynamic variables were somewhat improved at 15 mins after restoration of spontaneous circulation in the MB group compared with the other two groups. The jugular bulb levels of 8-isoprostane-prostaglandin F2alpha and 15-keto-dihydro-prostaglandin F2alpha (indicators of peroxidation and inflammation) were significantly decreased in the MB group compared with the isotonic saline group. Significant differences were recorded between the three groups in levels of protein S-100beta (indicator of neurologic injury), with lower levels in the MB group compared with the isotonic saline and hypertonic saline-dextran-only groups. Troponin I and myocardial muscle creatine kinase isoenzyme arterial concentrations (indicators of myocardial damage) were also significantly lower in the MB group.

CONCLUSIONS

MB co-administered with a hypertonic-hyperoncotic solution increased 4-hr survival vs. saline in an experimental porcine model of cardiac arrest and reduced oxidative, inflammatory, myocardial, and neurologic injury.

Pediatric traumatic brain injury: quo vadis?

In this review, five questions serve as the framework to discuss the importance of age-related differences in the pathophysiology and therapy of traumatic brain injury (TBI). The following questions are included: (1) Is diffuse cerebral swelling an important feature of pediatric TBI and what is its etiology? (2) Is the developing brain more vulnerable than the adult brain to apoptotic neuronal death after TBI and, if so, what are the clinical implications? (3) If the developing brain has enhanced plasticity versus the adult brain, why are outcomes so poor in infants and young children with severe TBI? (4) What contributes to the poor outcomes in the special case of inflicted childhood neurotrauma and how do we limit it? (5) Should both therapeutic targets and treatments of pediatric TBI be unique? Strong support is presented for the existence of unique biochemical, molecular, cellular and physiological facets of TBI in infants and children versus adults. Unique therapeutic targets and enhanced therapeutic opportunities, both in the acute phase after injury and in rehabilitation and regeneration, are suggested.

Energy metabolism in mammalian brain during development

Production of energy for the maintenance of ionic disequilibria necessary for generation and transmission of nerve impulses is one of the primary functions of the brain. This review attempts to link the plethora of information on the maturation of the central nervous system with the ontogeny of ATP metabolism, placing special emphasis on variations that occur during development in different brain regions and across the mammalian species. It correlates morphological events and markers with biochemical changes in activities of enzymes and pathways that participate in the production of ATP. The paper also evaluates alterations in energy levels as a function of age and, based on the tenet that ATP synthesis and utilization cannot be considered in isolation, investigates maturational profiles of the key processes that utilize energy. Finally, an attempt is made to assess the relevance of currently available animal models to improvement of our understanding of the etiopathology of various disease states in the human infant. This is deemed essential for the development and testing of novel strategies for prevention and treatment of several severe neurological deficits.

Traumatic brain injury in infants and children: mechanisms of secondary damage and treatment in the intensive care unit

Unfortunately no specific pharmacologic therapies are available for the treatment of TBI in patients. Current investigation of contemporary therapies for the treatment of TBI consists of recycling of previously tested therapies in the era of contemporary neurointensive care. These therapies include hypothermia, decompressive craniectomy, osmotherapy, and controlled hyperventilation. It is hoped that more detailed knowledge regarding the dominant pathophysiologic mechanisms associated with TBI-excitotoxicity, CBF dysregulation, oxidative stress, and programmed cell death-will catapult an efficacious intervention from the laboratory bench to the bedside. This intervention may be a potent agent targeting a single dominant pathway, a broad-spectrum intervention such as hypothermia, or, more likely, a combination of therapies. Meanwhile, practitioners must offer meticulous supportive neurointensive care using clinically proven therapies aimed at minimizing cerebral swelling for the management of pediatric patients who are victims of TBI.

[Cerebral oedema in children compared to cerebral oedema in adults]

About 50% of deaths, in the pediatric population between 1-15 years of age, are due to trauma. This high mortality rate, associated with the frequent sequelae, leading sometimes to severe handicaps, constitutes a major problem for public health in the developed countries. Pediatric trauma has some particularities, due to anatomic and physiologic differences, and to specific injury mechanisms. In a busy traumatology center, a child will be admitted daily in the emergency department with head trauma injury. The anaesthesiologist must have a complete understanding of the pathophysiology involved in this clinical presentation if one wishes to develop a practical knowledge of initial management of such patients. Traumatic brain injury may have intracranial and systemic effects that combine to give global cerebral ischaemia.

Blood-brain barrier permeability during dopamine-induced hypertension in fetal sheep

Dopamine is often used as a pressor agent in sick newborn infants, but an increase in arterial blood pressure could disrupt the blood-brain barrier (BBB), especially in the preterm newborn. Using time-dated pregnant sheep, we tested the hypothesis that dopamine-induced hypertension increases fetal BBB permeability and cerebral water content. Barrier permeability was assessed in nine brain regions, including cerebral cortex, caudate, thalamus, brain stem, cerebellum, and spinal cord, by intravenous injection of the small tracer molecule [(14)C]aminoisobutyric acid at 10 min after the start of dopamine or saline infusion. We studied 23 chronically catheterized fetal sheep at 0.6 (93 days, n = 10) and 0.9 (132 days, n = 13) gestation. Intravenous infusion of dopamine increased mean arterial pressure from 38 +/- 3 to 53 +/- 5 mmHg in 93-day fetuses and from 55 +/- 5 to 77 +/- 8 mmHg in 132-day fetuses without a decrease in arterial O(2) content. These 40% increases in arterial pressure are close to the maximum hypertension reported for physiological stresses at these ages in fetal sheep. No significant increases in the brain transfer coefficient of aminoisobutyric acid were detected in any brain region in dopamine-treated fetuses compared with saline controls at 0.6 or 0.9 gestation. There was also no significant increase in cortical water content with dopamine infusion at either age. We conclude that a 40% increase in mean arterial pressure during dopamine infusion in normoxic fetal sheep does not produce substantial BBB disruption or cerebral edema even as early as 0.6 gestation.

The effects of alpha-human atrial natriuretic peptide and milrinone on pial vessels during blood-brain barrier disruption in rabbits

The effects of alpha-human atrial natriuretic peptide (HANP) and milrinone on cerebral pial vessels, especially during blood-brain barrier (BBB) disruption, are not clear. We studied topical HANP (10(-14), 10(-12), and 10(-10) M) or milrinone (10(-7), 10(-5), and 10(-3) M), and IV HANP (0.1, 0.2, and 1.0 microg. kg(-1). min(-1)) or milrinone (0.5, 5.0, and 20.0 microg. kg(-1). min(-1)) with or without hyperosmolar BBB disruption, using a rabbit cranial window preparation. At 10(-12) and 10(-10) M topical HANP produced significant arteriolar (16%, 20%, respectively), but no venular dilation. Topical milrinone (10(-3) M) produced significant arteriolar and venular dilation (21%, 8%, respectively). IV HANP produced no arteriolar or venular changes at any dose except during BBB disruption, when it caused a significant arteriolar (16%, 16%, and 17%, respectively), but no venular dilation. In contrast, IV milrinone caused small but significant arteriolar and venular dilation without BBB disruption (arterioles, 6%, 7% and 8%, respectively; venules, 6% at 20.0 microg. kg(-1). min(-1)). During BBB disruption, these responses to milrinone were similar. Although HANP and milrinone each have a direct vasodilator effect on arterioles, their systemic administration at clinical doses could induce different effects. BBB disruptive conditions could increase the response of pial vessels to systemically administered HANP.

IMPLICATIONS

Although alpha-human atrial natriuretic peptide (HANP) and milrinone each have a direct vasodilator effect on cerebral pial arterioles, their systemic administration at clinical doses could have different effects and blood-brain-barrier disruptive conditions could alter the response of pial vessels to HANP, but not to milrinone.

Hemodynamic effects of nitric oxide synthase inhibition before and after cardiac arrest in infant piglets

Using infant piglets, we studied the effects of nonspecific inhibition of nitric oxide (NO) synthase by NG-nitro-L-arginine methyl ester (L-NAME; 3 mg/kg) on vascular pressures, regional blood flow, and cerebral metabolism before 8 min of cardiac arrest, during 6 min of cardiopulmonary resuscitation (CPR), and at 10 and 60 min of reperfusion. We tested the hypotheses that nonspecific NO synthase inhibition 1) will attenuate early postreperfusion hyperemia while still allowing for successful resuscitation after cardiac arrest, 2) will allow for normalization of blood flow to the kidneys and intestines after cardiac arrest, and 3) will maintain cerebral metabolism in the face of altered cerebral blood flow after reperfusion. Before cardiac arrest, L-NAME increased vascular pressures and cardiac output and decreased blood flow to brain (by 18%), heart (by 36%), kidney (by 46%), and intestine (by 52%) compared with placebo. During CPR, myocardial flow was maintained in all groups to successfully resuscitate 24 of 28 animals [P value not significant (NS)]. Significantly, L-NAME attenuated postresuscitation hyperemia in cerebellum, diencephalon, anterior cerebral, and anterior-middle watershed cortical brain regions and to the heart. Likewise, cerebral metabolic rates of glucose (CMRGluc) and of lactate production (CMRLac) were not elevated at 10 min of reperfusion. These cerebral blood flow and metabolic effects were reversed by L-arginine. Flows returned to baseline levels by 60 min of reperfusion. Kidney and intestinal flow, however, remained depressed throughout reperfusion in all three groups. Thus nonspecific inhibition of NO synthase did not adversely affect the rate of resuscitation from cardiac arrest while attenuating cerebral and myocardial hyperemia. Even though CMRGluc and CMRLac early after resuscitation were decreased, they were maintained at baseline levels. This may be clinically advantageous in protecting the brain and heart from the damaging effects of hyperemia, such as blood-brain barrier disruption.

Early endothelial damage and leukocyte accumulation in piglet brains following cardiac arrest

This study examined the early microvascular and neuronal consequences of cardiac arrest and resuscitation in piglets. We hypothesized that early morphological changes occur after cardiac arrest and reperfusion, and that these findings are partly caused by post-resuscitation hypertension. Three groups of normothermic piglets (37.5 degrees - 38.5 degrees C) were investigated: group 1, non-ischemic time controls; group 2, piglets undergoing 8 min of cardiac arrest by ventricular fibrillation, 6 min of cardiopulmonary resuscitation (CPR) and 4 h of reperfusion; and group 3, non-ischemic hypertensive controls, receiving 6 min of CPR after only 10 s of cardiac arrest followed by 4-h survival. Immediately following resuscitation, acute hypertension occurred with peak systolic pressure equal to 197 +/- 15 mm Hg usually lasting less than 10 min. In reacted vibratome sections, isolated foci of extravasated horseradish peroxidase were noted throughout the brain within surface cortical layers and around penetrating vessels in group 2. Stained plastic sections of leaky sites demonstrated variable degrees of tissue injury. While many sections were unremarkable except for luminal red blood cells and leukocytes, other specimens contained abnormal neurons, some appearing irreversibly injured. The number of vessels containing leukocytes was higher in group 2 than in controls (3.8 +/- 0.6% vs 1.4 +/- 0.4% of vessels, P < 0.05). Evidence for irreversible neuronal injury was only seen in group 2. Endothelial vacuolization was higher in groups 2 and 3 than in group 1 (P < 0.05). Ultrastructural examination of leaky sites identified mononuclear and polymorphonuclear leukocytes adhering to the endothelium of venules and capillaries only in group 2. The early appearance of luminal leukocytes in ischemic animals indicates that these cells may contribute to the genesis of ischemia reperfusion injury in this model. In both groups 2 and 3 endothelial cells demonstrated vacuolation and luminal discontinuities with evidence of perivascular astrocytic swelling. Widespread microvascular and neuronal damage is present as early as 4 h after cardiac arrest in infant piglets. Hypertension appears to play a role in the production of some of the endothelial changes.

Norepinephrine-induced hypertension following cardiac arrest: effects on myocardial oxygen use in a swine model

STUDY OBJECTIVE

Recent studies suggest that norepinephrine-induced hypertension early after cardiac arrest ameliorates cerebral hypoperfusion and improves neurologic outcome. The purpose of this study was to evaluate the effects of early norepinephrine-induced hypertension on postresuscitation myocardial blood flow and oxygen use.

DESIGN

Prospective, controlled laboratory study.

PARTICIPANTS

Ten swine.

INTERVENTIONS

All animals underwent 10 minutes of ventricular fibrillation cardiac arrest followed by 5 minutes of low-flow cardiopulmonary bypass (10 mL/kg.min), norepinephrine (0.12 mg/kg), and defibrillation. Animals then were assigned to a hypertension group (mean aortic pressure, 95 mm Hg) or a control group (mean aortic pressure, 75 mm Hg) by titrating a norepinephrine infusion to attain the prescribed aortic pressure.

RESULTS

Myocardial blood flow, perfusion pressure, and oxygen metabolism were compared between groups at different times using analysis of variance with a post-hoc Tukey test. Groups had similar myocardial blood flow during ventricular fibrillation, total defibrillation energy, and time to restoration of spontaneous circulation. Fifteen minutes after restoration of spontaneous circulation, the hypertension group had significantly elevated myocardial blood flow, 965 +/- 314 mL/min.100 g versus 325 +/- 67 mL/min.100 g in the control group (P < .001), myocardial oxygen consumption of 51.2 +/- 26.9 mL O2/min.100 g versus 6.4 +/- 3.4 mL O2/min.100 g (P < .001), and myocardial oxygen extraction of 46% +/- 20% versus 14% +/- 4% (P < .01).

CONCLUSION

In the early resuscitation period, increasing the norepinephrine dose to induce mild hypertension significantly increases oxygen use in the postischemic myocardium.

Early cerebrovascular response to head injury in immature and mature rats

Clinical studies suggest that children respond to head injury with more pronounced cerebral edema and hyperemia than do adults. We hypothesized that these age-related differences could be demonstrated in an animal model. Anesthetized and ventilated mature (2-3 months) and immature (3.5-4.5 weeks) male Wistar rats were traumatized by weight drop onto the exposed right parietal cortex. Trauma severity was adjusted to keep the ratio of force to brain weight constant. This resulted in an energy delivered to the brain of about 9 x 10(3) ergs.mm-2.g-1 brain in both age groups. Percent right hemispheric brain water (%RBW) was measured at 2, 24, 48, and 168 h posttrauma. Infarct area, intracranial pressure (ICP), and 14C-iodoantipyrine autoradiographic local cerebral blood flow (ICBF) were measured at 2 h or 24 h posttrauma. In mature rats, %RBW was unchanged at 2 h, but increased at 24 and 48 h (both p < 0.05). In immature rats, %RBW increased at 2 h and remained elevated at 24 and 48 h (all p < 0.05). Traumatic infarct area as a percent of hemispheric area at 24 h did not differ between age groups. In mature rats, at 2 h posttrauma ICBF was reduced (p < 0.05) in 16 of 17 regions but in only 4 of 17 regions in immature rats. ICBF as a percent of age-matched control values showed a greater reduction in mature vs immature rats in 9 of 16 regions (p < 0.05). ICP increased at 24 h posttrauma in both age groups. In immature rats posttrauma, brain water increased earlier and cerebral hypoperfusion was less marked than in mature rats.