Quantitative electroencephalography in a swine model of cerebral arterial gas embolism

Multimodal Neuromonitoring and Neurocritical Care in Swine to Enhance Translational Relevance in Brain Trauma Research

Neurocritical care significantly impacts outcomes after moderate-to-severe acquired brain injury, but it is rarely applied in preclinical studies. We created a comprehensive neurointensive care unit (neuroICU) for use in swine to account for the influence of neurocritical care, collect clinically relevant monitoring data, and create a paradigm that is capable of validating therapeutics/diagnostics in the unique neurocritical care space. Our multidisciplinary team of neuroscientists, neurointensivists, and veterinarians adapted/optimized the clinical neuroICU (e.g., multimodal neuromonitoring) and critical care pathways (e.g., managing cerebral perfusion pressure with sedation, ventilation, and hypertonic saline) for use in swine. Moreover, this neurocritical care paradigm enabled the first demonstration of an extended preclinical study period for moderate-to-severe traumatic brain injury with coma beyond 8 h. There are many similarities with humans that make swine an ideal model species for brain injury studies, including a large brain mass, gyrencephalic cortex, high white matter volume, and topography of basal cisterns, amongst other critical factors. Here we describe the neurocritical care techniques we developed and the medical management of swine following subarachnoid hemorrhage and traumatic brain injury with coma. Incorporating neurocritical care in swine studies will reduce the translational gap for therapeutics and diagnostics specifically tailored for moderate-to-severe acquired brain injury.

Challenges and demand for modeling disorders of consciousness following traumatic brain injury

Following severe traumatic brain injury (TBI), many patients experience coma - an unresponsive state lacking wakefulness or awareness. Coma rarely lasts more than two weeks, and emergence involves passing through a state of wakefulness without awareness of self or environment. Patients that linger in these Disorders of Consciousness (DoC) undergo clinical assessments of awareness for diagnosis into Unresponsive Wakefulness Syndrome (no awareness, also called vegetative state) or Minimally Conscious State (periodic increases in awareness). These diagnoses are notoriously inaccurate, offering little prognostic value. Recovery of awareness is unpredictable, returning within weeks, years, or never. This leaves patients' families with difficult decisions and little information on which to base them. Clinical studies have made significant advancements, but remain encumbered by high variability, limited data output, and a lack of necessary controls. Herein we discuss the clear and present need to establish a preclinical model of TBI-induced DoC, the significant challenges involved, and how such a model can be applied to support DoC research.

Quantitative electroencephalography in a swine model of blast-induced brain injury

OBJECTIVE

Electroencephalography (EEG) was used to examine brain activity abnormalities earlier after blast exposure using a swine model to develop a qEEG data analysis protocol.

METHODS

Anaesthetized swine were exposed to 420-450 Kpa blast overpressure and survived for 3 days after blast. EEG recordings were performed at 15 minutes before the blast and 15 minutes, 30 minutes, 2 hours and 1, 2 and 3 days post-blast using surface recording electrodes and a Biopac 4-channel data acquisition system. Off-line quantitative EEG (qEEG) data analysis was performed to determine qEEG changes.

RESULTS

Blast induced qEEG changes earlier after blast exposure, including a decrease of mean amplitude (MAMP), an increase of delta band power, a decrease of alpha band root mean square (RMS) and a decrease of 90% spectral edge frequency (SEF90).

CONCLUSIONS

This study demonstrated that qEEG is sensitive for cerebral injury. The changes of qEEG earlier after the blast indicate the potential of utilization of multiple parameters of qEEG for diagnosis of blast-induced brain injury. Early detection of blast induced brain injury will allow early screening and assessment of brain abnormalities in soldiers to enable timely therapeutic intervention.

Thrombolytic-Enhanced Extracorporeal Cardiopulmonary Resuscitation After Prolonged Cardiac Arrest

OBJECTIVE

To investigate the effects of the combination of extracorporeal cardiopulmonary resuscitation and thrombolytic therapy on the recovery of vital organ function after prolonged cardiac arrest.

DESIGN

Laboratory investigation.

SETTING

University laboratory.

SUBJECTS

Pigs.

INTERVENTIONS

Animals underwent 30-minute untreated ventricular fibrillation cardiac arrest followed by extracorporeal cardiopulmonary resuscitation for 6 hours. Animals were allocated into two experimental groups: t-extracorporeal cardiopulmonary resuscitation (t-ECPR) group, which received streptokinase 1 million units, and control extracorporeal cardiopulmonary resuscitation (c-ECPR), which did not receive streptokinase. In both groups, the resuscitation protocol included the following physiologic targets: mean arterial pressure greater than 70 mm Hg, cerebral perfusion pressure greater than 50 mm Hg, PaO2 150 ± 50 torr (20 ± 7 kPa), PaCO2 40 ± 5 torr (5 ± 1 kPa), and core temperature 33°C ± 1°C. Defibrillation was attempted after 30 minutes of extracorporeal cardiopulmonary resuscitation.

MEASUREMENTS AND MAIN RESULTS

A cardiac resuscitability score was assessed on the basis of success of defibrillation, return of spontaneous heart beat, weanability from extracorporeal cardiopulmonary resuscitation, and left ventricular systolic function after weaning. The addition of thrombolytic to extracorporeal cardiopulmonary resuscitation significantly improved cardiac resuscitability (3.7 ± 1.6 in t-ECPR vs 1.0 ± 1.5 in c-ECPR). Arterial lactate clearance was higher in t-ECPR than in c-ECPR (40% ± 15% vs 18% ± 21%). At the end of the experiment, the intracranial pressure was significantly higher in c-ECPR than in t-ECPR. Recovery of brain electrical activity, as assessed by quantitative analysis of electroencephalogram signal, and ischemic neuronal injury on histopathologic examination did not differ between groups. Animals in t-ECPR group did not have increased bleeding complications, including intracerebral hemorrhages.

CONCLUSIONS

In a porcine model of prolonged cardiac arrest, t-ECPR improved cardiac resuscitability and reduced brain edema, without increasing bleeding complications. However, early electroencephalogram recovery and ischemic neuronal injury were not improved.

A standardized model of brain death, donor treatment, and lung transplantation for studies on organ preservation and reconditioning

BACKGROUND

We set a model of brain death, donor management, and lung transplantation for studies on lung preservation and reconditioning before transplantation.

METHODS

Ten pigs (39.7 ± 5.9 Kg) were investigated. Five animals underwent brain death and were treated as organ donors; the lungs were then procured and cold stored (Ischemia). Five recipients underwent left lung transplantation and post-reperfusion follow-up (Graft). Cardiorespiratory and metabolic parameters were collected. Lung gene expression of cytokines (tumor necrosis factor alpha (TNFα), interleukin-1 beta (IL-1β), interleukin-6 (IL-6), interferon gamma (IFNγ), high mobility group box-1 (HMGB-1)), chemokines (chemokine CC motif ligand-2 (CCL2-MCP-1), chemokine CXC motif ligand-10 (CXCL-10), interleukin-8 (IL-8)), and endothelial activation markers (endothelin-1 (EDN-1), intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), selectin-E (SELE)) was assessed by real-time polymerase chain reaction (PCR).

RESULTS

Tachycardia and hypertension occurred during brain death induction; cardiac output rose, systemic vascular resistance dropped (P < 0.05), and diabetes insipidus occurred. Lung-protective ventilation strategy was applied: 9 h after brain death induction, PaO2 was 192 ± 12 mmHg at positive end-expiratory pressure (PEEP) 8.0 ± 1.8 cmH2O and FiO2 of 40%; wet-to-dry ratio (W/D) was 5.8 ± 0.5, and extravascular lung water (EVLW) was 359 ± 80 mL. Procured lungs were cold-stored for 471 ± 24 min (Ischemia) at the end of which W/D was 6.1 ± 0.9. Left lungs were transplanted and reperfused (warm ischemia 98 ± 14 min). Six hours after controlled reperfusion, PaO2 was 192 ± 23 mmHg (PEEP 8.7 ± 1.5 cmH2O, FiO2 40%), W/D was 5.6 ± 0.4, and EVLW was 366 ± 117 mL. Levels of IL-8 rose at the end of donor management (BD, P < 0.05); CCL2-MCP-1, IL-8, HMGB-1, and SELE were significantly altered after reperfusion (Graft, P < 0.05).

CONCLUSIONS

We have set a standardized, reproducible pig model resembling the entire process of organ donation that may be used as a platform to test in vivo and ex vivo strategies of donor lung optimization before transplantation.

Detection of cerebral arterial gas embolism using regional cerebral oxygen saturation, quantitative electroencephalography, and brain oxygen tension in the swine

BACKGROUND

Cerebral air emboli occur as a complication of invasive medical procedures. The sensitivity of cerebral monitoring methods for the detection of air emboli is not known. This study investigates the utility of electroencephalography and non-invasively measured cerebral oxygen saturation in the detection of intracerebrovascular air.

NEW METHOD

In 12 pigs oxygen saturation was continuously measured using transcranial near-infrared spectroscopy and oxygen tension was continuously measured using intraparenchymal probes. Additionally, quantitative electroencephalography and microdialysis were performed. Doses of 0.2, 0.4, 0.8, and 1.6 ml of air were injected into the cerebral arterial vasculature through a catheter.

RESULTS

Oxygen saturation and electroencephalography both reacted almost instantaneously on the air emboli, but were less sensitive than the intraparenchymal oxygen tension. There was reasonable correlation (ρ ranging from 0.417 to 0.898) between oxygen saturation, oxygen tension, electroencephalography and microdialysis values.

COMPARISON WITH EXISTING METHODS

Our study is the first to demonstrate the effects of cerebral air emboli using multimodal monitoring, specifically on oxygen saturation as measured using near-infrared spectroscopy.

CONCLUSIONS

Our results show that non-invasively measured oxygen saturation and quantitative electroencephalography can detect the local effects of air emboli on cerebral oxygenation, but with reduced sensitivity as compared to intraparenchymal oxygen tension. Prospective human studies using multimodal monitoring incorporating electroencephalography and oxygen saturation should be performed.

Age-dependence of sensorimotor and cerebral electroencephalographic asymmetry in rats subjected to unilateral cerebrovascular stroke

BACKGROUND

The human population mostly affected by stroke is more than 65 years old. This study was designed to meet the recommendation that models of cerebral ischemia in aged animals are more relevant to the clinical setting than young animal models. Until now the majority of the pre-clinical studies examining age effects on stroke outcomes have used rats of old age. Considering the increasing incidence of stroke among younger than old human population, new translational approaches in animal models are needed to match the rejuvenation of stroke. A better knowledge of alterations in stroke outcomes in middle-aged rats has important preventive and management implications providing clues for future investigations on effects of various neuroprotective and neurorestorative drugs against cerebrovascular accidents that may occur before late senescence.

METHODS

We evaluated the impact of transient focal ischemia, induced by intracerebral unilateral infusion of endothelin-1 (Et-1) near the middle cerebral artery of conscious rats, on volume of brain damage and asymmetry in behavioral and electroencephalographic (EEG) output measures in middle-aged (11-12 month-old) rats.

RESULTS

We did not find any age-dependent difference in the volume of ischemic brain damage three days after Et-1 infusion. However, age was an important determinant of neurological and EEG outcomes after stroke. Middle-aged ischemic rats had more impaired somatosensory functions of the contralateral part of the body than young ischemic rats and thus, had greater left-right reflex/sensorimotor asymmetry. Interhemispheric EEG asymmetry was more evident in middle-aged than in young ischemic rats, and this could tentatively explain the behavioral asymmetry.

CONCLUSIONS

With a multiparametric approach, we have validated the endothelin model of ischemia in middle-aged rats. The results provide clues for future studies on mechanisms underlying plasticity after brain damage and motivate investigations of novel neuroprotective strategies against cerebrovascular accidents that may occur before late senescence.

Hyperbaric oxygen does not improve cerebral function when started 2 or 4 hours after cerebral arterial gas embolism in swine

OBJECTIVE

Hyperbaric oxygenation is the accepted treatment for cerebral arterial gas embolism. Although earlier start of hyperbaric oxygenation is associated with better outcome, it is unknown how much delay can be tolerated before start of hyperbaric oxygenation. This study investigates the effect of hyperbaric oxygenation on cerebral function in swine when initiated 2 or 4 hours after cerebral arterial gas embolism.

DESIGN

Prospective interventional animal study.

SETTING

Surgical laboratory and hyperbaric chamber.

SUBJECTS

Twenty-two Landrace pigs.

INTERVENTIONS

Under general anesthesia, probes to measure intracranial pressure, brain oxygen tension (PbtO2), and brain microdialysis, and electrodes for electroencephalography were placed. The electroencephalogram (quantified using temporal brain symmetry index) was suppressed during 1 hour by repeated injection of air boluses through a catheter placed in the right ascending pharyngeal artery. Hyperbaric oxygenation was administered using U.S. Navy Treatment Table 6 after 2- or 4-hour delay. Control animals were maintained on an inspiratory oxygen fraction of 0.4.

MEASUREMENTS AND MAIN RESULTS

Intracranial pressure increased to a mean maximum of 19 mm Hg (SD, 4.5 mm Hg) due to the embolization procedure. Hyperbaric oxygenation significantly increased PbtO2 in both groups treated with hyperbaric oxygenation (mean maximum PbtO2, 390 torr; SD, 177 torr). There were no significant differences between groups with regard to temporal brain symmetry index (control vs 2-hr delay, p = 0.078; control vs 4-hr delay, p = 0.150), intracranial pressure, and microdialysis values.

CONCLUSIONS

We did not observe an effect of hyperbaric oxygenation on cerebral function after a delay of 2 or 4 hours. The injury caused in our model could be too severe for a single session of hyperbaric oxygenation to be effective. Our study should not change current hyperbaric oxygenation strategies for cerebral arterial gas embolism, but further research is necessary to elucidate our results. Whether less severe injury benefits from hyperbaric oxygenation should be investigated in models using smaller amounts of air and clinical outcome measures.

Animal models of cerebral arterial gas embolism

Cerebral arterial gas embolism is a dreaded complication of diving and invasive medical procedures. Many different animal models have been used in research on cerebral arterial gas embolism. This review provides an overview of the most important characteristics of these animal models. The properties discussed are species, cerebrovascular anatomy, method of air embolization, amount of air, bubble size, outcome parameters, anesthesia, blood glucose, body temperature and blood pressure.