Five percent CO₂ is a potent, fast-acting inhalation anticonvulsant

Brief apnea with hypoventilation reduces seizure duration and shifts seizure location for several hours in a model of severe traumatic brain injury

OBJECTIVE

Seizures can be difficult to control in infants and toddlers. Seizures with periods of apnea and hypoventilation are common following severe traumatic brain injury (TBI). We previously observed that brief apnea with hypoventilation (A&H) in our severe TBI model acutely interrupted seizures. The current study is designed to determine the effect of A&H on subsequent seizures and whether A&H has potential therapeutic implications.

METHODS

Piglets (1 week or 1 month old) received multifactorial injuries: cortical impact, mass effect, subdural hematoma, subarachnoid hemorrhage, and seizures induced with kainic acid. A&H (1 min apnea, 10 min hypoventilation) was induced either before or after seizure induction, or control piglets received subdural/subarachnoid hematoma and seizure without A&H. In an intensive care unit, piglets were sedated, intubated, and mechanically ventilated, and epidural electroencephalogram was recorded for an average of 18 h after seizure induction.

RESULTS

In our severe TBI model, A&H after seizure reduced ipsilateral seizure burden by 80% compared to the same injuries without A&H. In the A&H before seizure induction group, more piglets had exclusively contralateral seizures, although most piglets in all groups had seizures that shifted location throughout the several hours of seizure. After 8-10 h, seizures transitioned to interictal epileptiform discharges regardless of A&H or timing of A&H.

SIGNIFICANCE

Even brief A&H may alter traumatic seizures. In our preclinical model, we will address the possibility of hypercapnia with normoxia, with controlled intracranial pressure, as a therapeutic option for children with status epilepticus after hemorrhagic TBI.

Cerebral perfusion and metabolism with mild hypercapnia vs. normocapnia in a porcine post cardiac arrest model with and without targeted temperature management

Aim

To determine whether targeting mild hypercapnia (PaCO2 7 kPa) would yield improved cerebral blood flow and metabolism compared to normocapnia (PaCO2 5 kPa) with and without targeted temperature management to 33 °C (TTM33) in a porcine post-cardiac arrest model.

Methods

39 pigs were resuscitated after 10 minutes of cardiac arrest using cardiopulmonary bypass and randomised to TTM33 or no-TTM, and hypercapnia or normocapnia. TTM33 was managed with intravasal cooling. Animals were stabilized for 30 minutes followed by a two-hour intervention period. Hemodynamic parameters were measured continuously, and neuromonitoring included intracranial pressure (ICP), pressure reactivity index, cerebral blood flow, brain-tissue pCO2 and microdialysis. Measurements are reported as proportion of baseline, and areas under the curve during the 120 min intervention period were compared.

Results

Hypercapnia increased cerebral flow in both TTM33 and no-TTM groups, but also increased ICP (199% vs. 183% of baseline, p = 0.018) and reduced cerebral perfusion pressure (70% vs. 84% of baseline, p < 0.001) in no-TTM animals. Cerebral lactate (196% vs. 297% of baseline, p < 0.001), pyruvate (118% vs. 152% of baseline, p < 0.001), glycerol and lactate/pyruvate ratios were lower with hypercapnia in the TTM33 group, but only pyruvate (133% vs. 150% of baseline, p = 0.002) was lower with hypercapnia among no-TTM animals.

Conclusion

In this porcine post-arrest model, hypercapnia led to increased cerebral flow both with and without hypothermia, but also increased ICP and reduced cerebral perfusion pressure in no-TTM animals. The effects of hypercapnia were different with and without TTM.(Institutional protocol number: FOTS, id 14931).

Seizure control via pH manipulation: a phase II double-blind randomised controlled trial of inhaled carbogen as adjunctive treatment of paediatric convulsive status epilepticus (Carbogen for Status Epilepticus in Children Trial (CRESCENT))

BACKGROUND

Paediatric convulsive status epilepticus is the most common neurological emergency presenting to emergency departments. Risks of resultant neurological morbidity and mortality increase with seizure duration. If the seizure fails to stop within defined time-windows, standard care follows an algorithm of stepwise escalation to more intensive treatments, ultimately resorting to induction of general anaesthesia and ventilation. Additionally, ventilatory support may also be required to treat respiratory depression, a common unwanted effect of treatment. There is strong pre-clinical evidence that pH (acid-base balance) is an important determinant of seizure commencement and cessation, with seizures tending to start under alkaline conditions and terminate under acidic conditions. These mechanisms may be particularly important in febrile status epilepticus: prolonged fever-related seizures which predominantly affect very young children. This trial will assess whether imposition of mild respiratory acidosis by manipulation of inhaled medical gas improves response rates to first-line medical treatment.

METHODS

A double-blind, placebo-controlled trial of pH manipulation as an adjunct to standard medical treatment of convulsive status epilepticus in children. The control arm receives standard medical management whilst inhaling 100% oxygen; the active arm receives standard medical management whilst inhaling a commercially available mixture of 95% oxygen, 5% carbon dioxide known as 'carbogen'. Due to the urgent need to treat the seizure, deferred consent is used. The primary outcome is success of first-line treatment in seizure cessation. Planned subgroup analyses will be undertaken for febrile and non-febrile seizures. Secondary outcomes include rates of induction of general anaesthesia, admission to intensive care, adverse events, and 30-day mortality.

DISCUSSION

If safe and effective 95% oxygen, 5% carbon dioxide may be an important adjunct in the management of convulsive status epilepticus with potential for pre-hospital use by paramedics, families, and school staff.

TRIAL REGISTRATION

EudraCT: 2021-005367-49. CTA: 17136/0300/001.

ISRCTN

52731862. Registered on July 2022.

Two-lung ventilation with artificial pneumothorax on cerebral desaturation and early postoperative cognitive outcome: a randomized controlled trial

BACKGROUND

The effect of two lung ventilation (TLV) with carbon dioxide artificial pneumothorax on cerebral desaturation and postoperative neurocognitive changes in elderly patients undergoing elective minimally invasive esophagectomy (MIE) is unclear.

OBJECTIVES

The first aim of this study was to compare the effect of TLV and one lung ventilation (OLV) on cerebral desaturation. The second aim was to assess changes in early postoperative cognitive outcomes of two ventilation methods.

METHODS

This prospective, randomized, controlled trial enrolled patients 65 and older scheduled for MIE. Patients were randomly assigned (1:1) to TLV group or OLV group. The primary outcome was the incidence of cerebral desaturation events (CDE). Secondary outcomes were the cumulative area under the curve of desaturation for decreases in regional cerebral oxygen saturation (rSO2) values below 20% relative to the baseline value (AUC.20) and the incidence of delayed neurocognitive recovery.

RESULTS

Fifty-six patients were recruited between November 2019 and August 2020. TLV group had a lower incidence of CDE than OLV group [3 (10.71%) vs. 13 (48.14%), P = 0.002]. TLV group had a lower AUC.20 [0 (0-35.86) % min vs. 0 (0-0) % min, P = 0.007], and the incidence of delayed neurocognitive recovery [2 (7.4%) vs. 11 (40.7%), P = 0.009] than OLV group. Predictors of delayed neurocognitive recovery on postoperative day 7 were age (OR 1.676, 95% CI 1.122 to 2.505, P = 0.006) and AUC.20 (OR 1.059, 95% CI 1.025 to 1.094, P < 0.001).

CONCLUSION

Compared to OLV, TLV had a lower incidence of CDE and delayed neurocognitive recovery in elderly patients undergoing MIE. The method of TLV combined with carbon dioxide artificial pneumothorax may be an option for these elderly patients. Chinese Clinical Trial Registry (identifier: ChiCTR1900027454).

Effects of carbonic anhydrase activity on the excitability of hippocampal axons during high-frequency firing

Epileptic activity is known to cause a lowering of intraneuronal pH, which has been suggested to serve as a feedback signal to terminate seizures. The mechanism of such signaling is unclear, but likely involves an altered function of several types of ligand- and voltage-gated channels in postsynaptic membranes caused by increasing cytosolic and extracellular [H+]. In addition, axonal conduction properties may be altered by endogenous pH signals, but this has not been investigated. In the present study, we have recorded the axonal compound action potential (fiber volley) in hippocampal slices in the presence of glutamatergic and GABAergic antagonists. During high-frequency stimulation (HFS) of the Schaffer collaterals, the fiber volley was depressed and its latency from stimulus to peak increased. In the CA1 stratum radiatum these changes were enhanced when the carbonic anhydrase inhibitor acetazolamide (1 mM) was co-perfused. The enhancing effect of acetazolamide was absent after lowering of [Ca2+] in the perfusion medium. Acetazolamide had no detectable effect on HFS-evoked fiber volleys recorded from a more proximal site along the Schaffer collaterals (at the CA2-CA3 border) or from axons in the alveus of CA1. Intracellular acidification imposed by washout of NH4Cl (5 mM) had qualitatively similar effects on fiber volleys evoked at low frequency as those observed with acetazolamide during HFS in CA1 stratum radiatum. The results suggest that carbonic anhydrase-dependent pH regulation counteracts activity-induced reduction of the excitability of Schaffer collateral axons in CA1. A possible influence from local synaptic terminals on this effect is discussed.

Causal relationship between addictive behaviors and epilepsy risk: A mendelian randomization study

BACKGROUND

Previous studies have reported inconsistent results regarding the potential relationships between addictive behaviors and the risk of epilepsy.

OBJECTIVE

To assess whether genetically predicted addictive behaviors are causally associated with the risk of epilepsy outcomes.

METHODS

The causation between five addictive behaviors (including cigarettes per day, alcoholic drinks per week, tea intake, coffee intake, and lifetime cannabis use) and epilepsy was evaluated by using a two-sample Mendelian Randomization (MR) analysis. The inverse-variance weighted (IVW) method was used as the primary outcome. The other MR analysis methods (MR Egger, weighted median, simulation extrapolation corrected MR-Egger, and Mendelian Randomization Pleiotropy Residual Sum and Outlier (MR-PRESSO)) were performed to complement IVW. In addition, the robustness of the MR analysis results was assessed by leave-one-out analysis.

RESULTS

The IVW analysis method indicated an approximately 20% increased risk of epilepsy per standard deviation increase in lifetime cannabis use (odds ratio [OR], 1.20; 95% confidence interval [CI]), 1.02-1.42, P = 0.028). However, there is no causal association between the other four addictive behaviors and the risk of epilepsy (cigarettes per day: OR, 1.04; 95% CI, 0.92-1.18, P = 0.53; alcoholic drinks per week: OR, 1.31; 95% CI, 0.93-1.84, P = 0.13; tea intake: OR, 1.15; 95% CI, 0.84-1.56, P = 0.39; coffee intake: OR, 0.86; 95% CI, 0.59-1.23, P = 0.41). The other MR analysis methods and further leave-one-out sensitivity analysis suggested the results were robust.

CONCLUSION

This MR study indicated a potential genetically predicted causal association between lifetime cannabis use and higher risk of epilepsy. As for the other four addictive behaviors, no evidence of a causal relationship with the risk of epilepsy was found in this study.

Obstructive sleep apnea and epilepsy: understanding the pathophysiology of the comorbidity

Obstructive sleep apnea (OSA) is a sleep disorder of significant health concern with a high prevalence in the general population. It has been found to exhibit a high incidence of comorbidity with epilepsy, the exact underlying pathophysiology of which still remains poorly understood. OSA is characterized by apnea/hypopnea spells and arousals, leading to intermittent hypoxemia and sleep deprivation. Both sleep deprivation and hypoxemia adversely affect the cortical excitability and favor epileptogenesis and worsening of pre-existing epilepsy, if any. In patients with OSA, deprivation of rapid eye movement sleep (REMS) phase (known for its strong antiepileptic influence) is relatively more than that non rapid eye movement sleep phase leading to postulation of REMS deprivation as a significant factor in the development of epilepsy as a comorbidity in patients with OSA. Furthermore, OSA and epilepsy both have shown to exercise a bidirectional influence on one another and are also likely to exacerbate each other through a positive feedback mechanism. This is especially based on the reports of improved control of epilepsy upon treatment of comorbid OSA. This brief paper attempts to present an underlying pathophysiological basis of the comorbidity of OSA and epilepsy based upon sleep deprivation and hypoxemia that are characteristic features observed in patients with OSA.

Carbogen-Induced Respiratory Acidosis Blocks Experimental Seizures by a Direct and Specific Inhibition of NaV1.2 Channels in the Axon Initial Segment of Pyramidal Neurons

Brain pH is a critical factor for determining neuronal activity, with alkalosis increasing and acidosis reducing excitability. Acid shifts in brain pH through the breathing of carbogen (5% CO2/95% O2) reduces seizure susceptibility in animal models and patients. The molecular mechanisms underlying this seizure protection remain to be fully elucidated. Here, we demonstrate that male and female mice exposed to carbogen are fully protected from thermogenic-triggered seizures. Whole-cell patch-clamp recordings revealed that acid shifts in extracellular pH (pHo) significantly reduce action potential firing in CA1 pyramidal neurons but did not alter firing in hippocampal inhibitory interneurons. In real-time dynamic clamp experiments, acidification reduced simulated action potential firing generated in hybrid model neurons expressing the excitatory neuron predominant NaV1.2 channel. Conversely, acidification had no effect on action potential firing in hybrid model neurons expressing the interneuron predominant NaV1.1 channel. Furthermore, knockdown of Scn2a mRNA in vivo using antisense oligonucleotides reduced the protective effects of carbogen on seizure susceptibility. Both carbogen-mediated seizure protection and the reduction in CA1 pyramidal neuron action potential firing by low pHo were maintained in an Asic1a knock-out mouse ruling out this acid-sensing channel as the underlying molecular target. These data indicate that the acid-mediated reduction in excitatory neuron firing is mediated, at least in part, through the inhibition of NaV1.2 channels, whereas inhibitory neuron firing is unaffected. This reduction in pyramidal neuron excitability is the likely basis of seizure suppression caused by carbogen-mediated acidification.SIGNIFICANCE STATEMENT Brain pH has long been known to modulate neuronal excitability. Here, we confirm that brain acidification reduces seizure susceptibility in a mouse model of thermogenic seizures. Extracellular acidification reduced excitatory pyramidal neuron firing while having no effect on interneuron firing. Acidification also reduced dynamic clamp firing in cells expressing the NaV1.2 channel but not in cells expressing NaV1.1 channels. In vivo knockdown of Scn2a mRNA reduced seizure protection of acidification. In contrast, acid-mediated seizure protection was maintained in the Asic1a knock-out mouse. These data suggest NaV1.2 channel as an important target for acid-mediated seizure protection. Our results have implications on how natural variations in pH can modulate neuronal excitability and highlight potential antiseizure drug development strategies based on the NaV1.2 channel.

Pregabalin for Recurrent Seizures in Critical Illness: A Promising Adjunctive Therapy, Especially for cyclic Seizures

BACKGROUND

Pregabalin (PGB) is an effective adjunctive treatment for focal epilepsy and acts by binding to the alpha2-delta subunit of voltage-gated calcium channels to reduce excitatory neurotransmitter release. Limited data exist on its use in the neurocritical care setting, including cyclic seizures-a pattern of recurrent seizures occurring at nearly regular intervals. Although the mechanism underpinning cyclic seizures remains elusive, spreading excitation linked to spreading depolarizations may play a role in seizure recurrence and periodicity. PGB has been shown to increase spreading depolarization threshold; hence, we hypothesized that the magnitude of antiseizure effect from PGB is more pronounced in patients with cyclic versus noncyclic seizures in a critically ill cohort with recurrent seizures.

METHODS

We conducted a retrospective case series of adults admitted to two academic neurointensive care units between January 2017 and March 2019 who received PGB for treatment of seizures. Data collected included demographics, etiology of brain injury, antiseizure medications, and outcome. Continuous electroencephalogram recordings 48 hours before and after PGB administration were reviewed by electroencephalographers blinded to the administration of antiseizure medications to obtain granular data on electrographic seizure burden. Cyclic seizures were determined quantitatively (i.e., < 50% variation of interseizure intervals for at least 50% of consecutive seizures). Coprimary outcomes were decrease in hourly seizure burden in minutes and decrease in seizure frequency in the 48 hours after PGB initiation. We used nonparametric tests for comparison of seizure frequency and burden and segmented linear regression to assess PGB effect.

RESULTS

We included 16 patients; the median age was 69 years, 11 (68.7%) were women, three (18.8%) had undergone a neurosurgical procedure, and five (31%) had underlying epilepsy. All seizures had focal onset; ten patients (62.5%) had cyclic seizures. The median hourly seizure burden over the 48 hours prior to PGB initiation was 1.87 min/hour (interquartile range 1.49-8.53), and the median seizure frequency was 1.96 seizures/hour (interquartile range 1.06-3.41). In the 48 hours following PGB (median daily dose 300 mg, range 75-300 mg), the median number of seizures per hour was reduced by 0.80 seizures/hour (95% confidence interval 0.19-1.40), whereas the median hourly seizure burden decreased by 1.71 min/hour (95% confidence interval 0.38-3.04). When we compared patients with cyclic versus noncyclic seizures, there was a relative decrease in hourly seizure frequency (- 86.7% versus - 2%, p = 0.04) and hourly seizure burden (- 89% versus - 7.8%, p = 0.03) at 48 hours.

CONCLUSIONS

PGB was associated with a relative reduction in seizure burden in neurocritically ill patients with recurrent seizures, especially those with cyclic seizures, and may be considered in the therapeutic arsenal for refractory seizures. Whether this effect is mediated via modulation of spreading depolarization requires further study.

Bumetanide for neonatal seizures: no light in the pharmacokinetic/dynamic tunnel

In his editorial, Kevin Staley criticizes our recent work demonstrating the lack of effect of bumetanide in a novel model of neonatal seizures. The main points in our response are that (1) our work is on an asphyxia model, not one on "hypercarbia only"; (2) clinically relevant parenteral doses of bumetanide applied in vivo lead to concentrations in the brain parenchyma that are at least an order of magnitude lower than what would be sufficient to exert any direct effect—even a transient one—on neuronal functions, including neonatal seizures; and (3) moreover, bumetanide's molecular target in the brain is the Na‐K‐2Cl cotransporter NKCC1, which has vital functions in neurons, astrocytes, and oligodendrocytes as well as microglia. This would make it impossible even for highly brain‐permeant NKCC1 blockers to specifically target depolarizing and excitatory actions of γ‐aminobutyric acid in principal neurons of the brain, which is postulated as the rationale of clinical trials on neonatal seizures.

Carbon dioxide inhibits COVID-19-type proinflammatory responses through extracellular signal-regulated kinases 1 and 2, novel carbon dioxide sensors

Mitogen-activated protein kinase (MAPK) signalling pathways are crucial for developmental processes, oncogenesis, and inflammation, including the production of proinflammatory cytokines caused by reactive oxygen species and upon severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. There are no drugs that can effectively prevent excessive inflammatory responses in endothelial cells in the lungs, heart, brain, and kidneys, which are considered the main causes of severe coronavirus disease 2019 (COVID-19). In this work, we demonstrate that human MAPKs, i.e. extracellular signal-regulated kinases 1 and 2 (ERK1/2), are CO₂ sensors and CO₂ is an efficient anti-inflammatory compound that exerts its effects through inactivating ERK1/2 in cultured endothelial cells when the CO₂ concentration is elevated. CO₂ is a potent inhibitor of cellular proinflammatory responses caused by H₂O₂ or the receptor-binding domain (RBD) of the spike protein of SARS-CoV-2. ERK1/2 activated by the combined action of RBD and cytokines crucial for the development of severe COVID-19, i.e. interferon-gamma (IFNγ) and tumour necrosis factor-α (TNFα), are more effectively inactivated by CO₂ than by dexamethasone or acetylsalicylic acid in human bronchial epithelial cells. Previously, many preclinical and clinical studies showed that the transient application of 5–8% CO₂ is safe and effective in the treatment of many diseases. Therefore, our research indicates that CO₂ may be used for the treatment of COVID-19 as well as the modification of hundreds of cellular pathways.

Anticonvulsant Effects of Carbonic Anhydrase Inhibitors: The Enigmatic Link Between Carbonic Anhydrases and Electrical Activity of the Brain

Acetazolamide (ACZ), a sulfonamide carbonic anhydrase (CA) inhibitor, was first introduced into medical use as a diuretic in the1950s. Shortly after its introduction, its antiglaucoma and anticonvulsant properties came to light. Subsequently, studies of ACZ have explored a plethora of neurophysiological functions of CAs in the CNS. In addition, topiramate (TPM) and zonisamide (ZNS), which were developed as antiepileptic drugs (AEDs) in the1990s, were found to have the ability to inhibit CAs. How CA inhibition prevents seizures is elusive. CA expression and activity are extensively detected in neurons, the choroid plexus, oligodendrocytes and astrocytes. TPM and ZNS appear to produce multimodal actions in the CNS as well as CA inhibition unlike ACZ. Nonetheless, CA inhibitors share some common denominators. They do not only affect the fine equilibrium among CO₂, H⁺ and HCO₃^- in the extraneuronal and intraneuronal milieu, but also modulate the activity of ligand gated ion channels at the neuronal level such as GABA-A signaling through inhibiting CA-replenished HCO₃^- efflux. In addition, there are studies reporting their ability to alter Ca²⁺ kinetics through modulation of ligand gated Ca²⁺ channels, voltage gated Ca²⁺ channels (VGCC) or Ca²⁺-induced Ca²⁺ release channels (CICRC). The present study will review the involvement of CAs in the formation of epileptogenesis, and likely mechanisms by which CA inhibitors suppress the electrical activity of the brain. The common properties of CA inhibitors provide some clues for a possible link among metabolism, CAs, Ca²⁺ and GABA signaling.

Carbonic anhydrase inhibitors suppress seizures in a rat model of birth asphyxia

OBJECTIVE

Seizures are common in neonates recovering from birth asphyxia but there is general consensus that current pharmacotherapy is suboptimal and that novel antiseizure drugs are needed. We recently showed in a rat model of birth asphyxia that seizures are triggered by the post-asphyxia recovery of brain pH. Here our aim was to investigate whether carbonic anhydrase inhibitors (CAIs), which induce systemic acidosis, block the post-asphyxia seizures.

METHODS

The CAIs acetazolamide (AZA), benzolamide (BZA), and ethoxzolamide (EZA) were administered intraperitoneally or intravenously to 11-day-old rats exposed to intermittent asphyxia (30 min; three 7+3 min cycles of 9% and 5% O₂ at 20% CO₂ ). Electrode measurements of intracortical pH, Po₂ , and local field potentials (LFPs) were made under urethane anesthesia. Convulsive seizures and blood acid-base parameters were examined in freely behaving animals.

RESULTS

The three CAIs decreased brain pH by 0.14-0.17 pH units and suppressed electrographic post-asphyxia seizures. AZA, BZA, and EZA differ greatly in their lipid solubility (EZA > AZA > BZA) and pharmacokinetics. However, there were only minor differences in the delay (range 0.8-3.7 min) from intraperitoneal application to their action on brain pH. The CAIs induced a modest post-asphyxia elevation of brain Po₂ that had no effect on LFP activity. AZA was tested in freely behaving rats, in which it induced a respiratory acidosis and decreased the incidence of convulsive seizures from 9 of 20 to 2 of 17 animals.

SIGNIFICANCE

AZA, BZA, and EZA effectively block post-asphyxia seizures. Despite the differences in their pharmacokinetics, they had similar effects on brain pH, which indicates that their antiseizure mode of action was based on respiratory (hypercapnic) acidosis resulting from inhibition of blood-borne and extracellular vascular carbonic anhydrases. AZA has been used for several indications in neonates, suggesting that it can be safely repurposed for the treatment of neonatal seizures as an add-on to the current treatment regimen.

Association Between Arterial Carbon Dioxide Tension and Clinical Outcomes in Venoarterial Extracorporeal Membrane Oxygenation

OBJECTIVES

The manipulation of arterial carbon dioxide tension is associated with differential mortality and neurologic injury in intensive care and cardiac arrest patients; however, few studies have investigated this relationship in patients on venoarterial extracorporeal membrane oxygenation. We investigated the association between the initial arterial carbon dioxide tension and change over 24 hours on mortality and neurologic injury in patients undergoing venoarterial extracorporeal membrane oxygenation for cardiac arrest and refractory cardiogenic shock.

DESIGN

Retrospective cohort analysis of adult patients recorded in the international Extracorporeal Life Support Organization Registry.

SETTING

Data reported to the Extracorporeal Life Support Organization from all international extracorporeal membrane oxygenation centers during 2003-2016.

PATIENTS

Adult patients (≥ 18 yr old) supported with venoarterial extracorporeal membrane oxygenation.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A total of 7,168 patients had sufficient data for analysis at the initiation of venoarterial extracorporeal membrane oxygenation, 4,918 of these patients had arterial carbon dioxide tension data available at 24 hours on support. The overall in-hospital mortality rate was 59.9%. A U-shaped relationship between arterial carbon dioxide tension tension at extracorporeal membrane oxygenation initiation and in-hospital mortality was observed. Increased mortality was observed with a arterial carbon dioxide tension less than 30 mm Hg (odds ratio, 1.26; 95% CI, 1.08-1.47; p = 0.003) and greater than 60 mm Hg (odds ratio, 1.28; 95% CI, 1.10-1.50; p = 0.002). Large reductions (> 20 mm Hg) in arterial carbon dioxide tension over 24 hours were associated with important neurologic complications: intracranial hemorrhage, ischemic stroke, and/or brain death, as a composite outcome (odds ratio, 1.63; 95% CI, 1.03-2.59; p = 0.04), independent of the initial arterial carbon dioxide tension.

CONCLUSIONS

Initial arterial carbon dioxide tension tension was independently associated with mortality in this cohort of venoarterial extracorporeal membrane oxygenation patients. Reductions in arterial carbon dioxide tension (> 20 mm Hg) from the initiation of extracorporeal membrane oxygenation were associated with neurologic complications. Further prospective studies testing these associations are warranted.

Alkaline brain pH shift in rodent lithium-pilocarpine model of epilepsy with chronic seizures

Brain pH is thought to be important in epilepsy. The regulation of brain pH is, however, still poorly understood in animal models of chronic seizures (SZ) as well as in patients with intractable epilepsy. We used chemical exchange saturation transfer (CEST) MRI to noninvasively determine if the pH is alkaline shifted in a rodent model of the mesial temporal lobe (MTL) epilepsy with chronic SZ. Taking advantage of its high spatial resolution, we determined the pH values in specific brain regions believed to be important in this model produced by lithium-pilocarpine injection. All animals developed status epilepticus within 90 min after the lithium-pilocarpine administration, but one animal died within 24 hrs. All the surviving animals developed chronic SZ during the first 2 months. After SZ developed, brain pH was determined in the pilocarpine and control groups (n = 8 each). Epileptiform activity was documented in six pilocarpine rats with scalp EEG. The brain pH was estimated using two methods based on magnetization transfer asymmetry and amide proton transfer ratio. The pH was alkaline shifted in the pilocarpine rats (one outlier excluded) compared to the controls in the hippocampus (7.29 vs 7.17, t-test, p < 0.03) and the piriform cortex (7.34 vs. 7.06, p < 0.005), marginally more alkaline in the thalamus (7.13 vs. 7.01, p < 0.05), but not in the cerebral cortex (7.18 vs. 7.08, p > 0.05). Normalizing the brain pH may lead to an effective non-surgical method for treating intractable epilepsy as it is known that SZ can be eliminated by lowering the pH.

A physiologically validated rat model of term birth asphyxia with seizure generation after, not during, brain hypoxia

OBJECTIVE

Birth asphyxia (BA) is often associated with seizures that may exacerbate the ensuing hypoxic-ischemic encephalopathy. In rodent models of BA, exposure to hypoxia is used to evoke seizures, that commence already during the insult. This is in stark contrast to clinical BA, in which seizures are typically seen upon recovery. Here, we introduce a term-equivalent rat model of BA, in which seizures are triggered after exposure to asphyxia.

METHODS

Postnatal day 11-12 male rat pups were exposed to steady asphyxia (15 min; air containing 5% O2  + 20% CO2 ) or to intermittent asphyxia (30 min; three 5 + 5-min cycles of 9% and 5% O2 at 20% CO2 ). Cortical activity and electrographic seizures were recorded in freely behaving animals. Simultaneous electrode measurements of intracortical pH, Po2 , and local field potentials (LFPs) were made under urethane anesthesia.

RESULTS

Both protocols decreased blood pH to <7.0 and brain pH from 7.3 to 6.7 and led to a fall in base excess by 20 mmol·L-1 . Electrographic seizures with convulsions spanning the entire Racine scale were triggered after intermittent but not steady asphyxia. In the presence of 20% CO2 , brain Po2 was only transiently affected by 9% ambient O2 but fell below detection level during the steps to 5% O2 , and LFP activity was nearly abolished. Post-asphyxia seizures were strongly suppressed when brain pH recovery was slowed down by 5% CO2 .

SIGNIFICANCE

The rate of brain pH recovery has a strong influence on post-asphyxia seizure propensity. The recurring hypoxic episodes during intermittent asphyxia promote neuronal excitability, which leads to seizures only after the suppressing effect of the hypercapnic acidosis is relieved. The present rodent model of BA is to our best knowledge the first one in which, consistent with clinical BA, behavioral and electrographic seizures are triggered after and not during the BA-mimicking insult.

Discovery of Potent Carbonic Anhydrase Inhibitors as Effective Anticonvulsant Agents: Drug Design, Synthesis, and In Vitro and In Vivo Investigations

Two sets of benzenesulfonamide-based effective human carbonic anhydrase (hCA) inhibitors have been developed using the tail approach. The inhibitory action of these novel molecules was examined against four isoforms: hCA I, hCA II, hCA VII, and hCA XII. Most of the molecules disclosed low to medium nanomolar range inhibition against all tested isoforms. Some of the synthesized derivatives selectively inhibited the epilepsy-involved isoforms hCA II and hCA VII, showing low nanomolar affinity. The anticonvulsant activity of selected sulfonamides was assessed using the maximal electroshock seizure (MES) and subcutaneous pentylenetetrazole (sc-PTZ) in vivo models of epilepsy. These potent CA inhibitors effectively inhibited seizures in both epilepsy models. The most effective compounds showed long duration of action and abolished MES-induced seizures up to 6 h after drug administration. These sulfonamides were found to be orally active anticonvulsants, being nontoxic in neuronal cell lines and in animal models.

Carbogen inhalation during non-convulsive status epilepticus: A quantitative exploratory analysis of EEG recordings

Objective

To quantify the effect of inhaled 5% carbon-dioxide/95% oxygen on EEG recordings from patients in non-convulsive status epilepticus (NCSE).

Methods

Five children of mixed aetiology in NCSE were given high flow of inhaled carbogen (5% carbon dioxide/95% oxygen) using a face mask for maximum 120s. EEG was recorded concurrently in all patients. The effects of inhaled carbogen on patient EEG recordings were investigated using band-power, functional connectivity and graph theory measures. Carbogen effect was quantified by measuring effect size (Cohen’s d) between “before”, “during” and “after” carbogen delivery states.

Results

Carbogen’s apparent effect on EEG band-power and network metrics across all patients for “before-during” and “before-after” inhalation comparisons was inconsistent across the five patients.

Conclusion

The changes in different measures suggest a potentially non-homogeneous effect of carbogen on the patients’ EEG. Different aetiology and duration of the inhalation may underlie these non-homogeneous effects. Tuning the carbogen parameters (such as ratio between CO₂ and O₂, duration of inhalation) on a personalised basis may improve seizure suppression in future.

A critical analysis of the purported role of hypoxaemia in the comorbidity of obstructive sleep apnoea and epilepsy

Obstructive sleep apnoea (OSA) is a globally prevalent sleep disorder of significant health concern and confounded with several comorbidities resulting in adverse effect(s) on quality of life in patients afflicted with it. Of particular interest is the enigmatic high comorbidity of OSA with epilepsy, the exact underlying pathophysiology of which remains elusive despite a multitude of research performed in the last four decades. Hypoxaemia, which is an important characteristic feature found in OSA during apnoeic spells, has been implicated in the high comorbidity of OSA with epilepsy, the basis of which rests upon hypoxaemia-mediated brain damage, subcortical release phenomenon, oxidative stress and neuroinflammatory reactions. However, several studies present contradictory evidences that potentially refute the hypoxaemia-based mechanism. Additionally, the role of hypercapnia thatgenerally accompanies hypoxaemia during apnoeic spells, cannot be overlooked and is known to be potentially protective against neuronal hyperexcitability. Thus, hypoxaemia theory implicated in the high comorbidity of OSA and epilepsy appears weak and refutable. This brief paper studies and critically analyses the role of hypoxaemia in conjunction with hypercapnia in the underlying pathophysiology of the comorbidity.

The therapeutic importance of acid-base balance

Baking soda and vinegar have been used as home remedies for generations and today we are only a mouse-click away from claims that baking soda, lemon juice, and apple cider vinegar are miracles cures for everything from cancer to COVID-19. Despite these specious claims, the therapeutic value of controlling acid-base balance is indisputable and is the basis of Food and Drug Administration-approved treatments for constipation, epilepsy, metabolic acidosis, and peptic ulcers. In this narrative review, we present evidence in support of the current and potential therapeutic value of countering local and systemic acid-base imbalances, several of which do in fact involve the administration of baking soda (sodium bicarbonate). Furthermore, we discuss the side effects of pharmaceuticals on acid-base balance as well as the influence of acid-base status on the pharmacokinetic properties of drugs. Our review considers all major organ systems as well as information relevant to several clinical specialties such as anesthesiology, infectious disease, oncology, dentistry, and surgery.

The effects of arterial CO2 on the injured brain: Two faces of the same coin

Serum levels of carbon dioxide (CO₂) closely regulate cerebral blood flow (CBF) and actively participate in different aspects of brain physiology such as hemodynamics, oxygenation, and metabolism. Fluctuations in the partial pressure of arterial CO₂ (PaCO₂) modify the aforementioned variables, and at the same time influence physiologic parameters in organs such as the lungs, heart, kidneys, and the gastrointestinal tract. In general, during acute brain injury (ABI), maintaining normal PaCO₂ is the target to be achieved. Both hypercapnia and hypocapnia may comprise secondary insults and should be avoided during ABI. The risks of hypocapnia mostly outweigh the potential benefits. Therefore, its therapeutic applicability is limited to transient and second-stage control of intracranial hypertension. On the other hand, inducing hypercapnia could be beneficial when certain specific situations require increasing CBF. The evidence supporting this claim is very weak. This review attempts providing an update on the physiology of CO₂, its risks, benefits, and potential utility in the neurocritical care setting.

Inhaled H2 or CO2 Do Not Augment the Neuroprotective Effect of Therapeutic Hypothermia in a Severe Neonatal Hypoxic-Ischemic Encephalopathy Piglet Model

Hypoxic-ischemic encephalopathy (HIE) is still a major cause of neonatal death and disability as therapeutic hypothermia (TH) alone cannot afford sufficient neuroprotection. The present study investigated whether ventilation with molecular hydrogen (2.1% H₂) or graded restoration of normocapnia with CO₂ for 4 h after asphyxia would augment the neuroprotective effect of TH in a subacute (48 h) HIE piglet model. Piglets were randomized to untreated naïve, control-normothermia, asphyxia-normothermia (20-min 4%O₂–20%CO₂ ventilation; T_core = 38.5 °C), asphyxia-hypothermia (A-HT, T_core = 33.5 °C, 2–36 h post-asphyxia), A-HT + H₂, or A-HT + CO₂ treatment groups. Asphyxia elicited severe hypoxia (pO₂ = 19 ± 5 mmHg) and mixed acidosis (pH = 6.79 ± 0.10). HIE development was confirmed by altered cerebral electrical activity and neuropathology. TH was significantly neuroprotective in the caudate nucleus but demonstrated virtually no such effect in the hippocampus. The mRNA levels of apoptosis-inducing factor and caspase-3 showed a ~10-fold increase in the A-HT group compared to naïve animals in the hippocampus but not in the caudate nucleus coinciding with the region-specific neuroprotective effect of TH. H₂ or CO₂ did not augment TH-induced neuroprotection in any brain areas; rather, CO₂ even abolished the neuroprotective effect of TH in the caudate nucleus. In conclusion, the present findings do not support the use of these medical gases to supplement TH in HIE management.

The association of partial pressures of oxygen and carbon dioxide with neurological outcome after out-of-hospital cardiac arrest: an explorative International Cardiac Arrest Registry 2.0 study

BACKGROUND

Exposure to extreme arterial partial pressures of oxygen (PaO2) and carbon dioxide (PaCO2) following the return of spontaneous circulation (ROSC) after out-of-hospital cardiac arrest (OHCA) is common and may affect neurological outcome but results of previous studies are conflicting.

METHODS

Exploratory study of the International Cardiac Arrest Registry (INTCAR) 2.0 database, including 2162 OHCA patients with ROSC in 22 intensive care units in North America and Europe. We tested the hypothesis that exposure to extreme PaO2 or PaCO2 values within 24 h after OHCA is associated with poor neurological outcome at discharge. Our primary analyses investigated the association between extreme PaO2 and PaCO2 values, defined as hyperoxemia (PaO2 > 40 kPa), hypoxemia (PaO2 < 8.0 kPa), hypercapnemia (PaCO2 > 6.7 kPa) and hypocapnemia (PaCO2 < 4.0 kPa) and neurological outcome. The secondary analyses tested the association between the exposure combinations of PaO2 > 40 kPa with PaCO2 < 4.0 kPa and PaO2 8.0-40 kPa with PaCO2 > 6.7 kPa and neurological outcome. To define a cut point for the onset of poor neurological outcome, we tested a model with increasing and decreasing PaO2 levels and decreasing PaCO2 levels. Cerebral Performance Category (CPC), dichotomized to good (CPC 1-2) and poor (CPC 3-5) was used as outcome measure.

RESULTS

Of 2135 patients eligible for analysis, 700 were exposed to hyperoxemia or hypoxemia and 1128 to hypercapnemia or hypocapnemia. Our primary analyses did not reveal significant associations between exposure to extreme PaO2 or PaCO2 values and neurological outcome (P = 0.13-0.49). Our secondary analyses showed no significant associations between combinations of PaO2 and PaCO2 and neurological outcome (P = 0.11-0.86). There was no PaO2 or PaCO2 level significantly associated with poor neurological outcome. All analyses were adjusted for relevant co-variates.

CONCLUSIONS

Exposure to extreme PaO2 or PaCO2 values in the first 24 h after OHCA was common, but not independently associated with neurological outcome at discharge.

Endogenous brain-sparing responses in brain pH and PO2 in a rodent model of birth asphyxia

AIM

To study brain-sparing physiological responses in a rodent model of birth asphyxia which reproduces the asphyxia-defining systemic hypoxia and hypercapnia.

METHODS

Steady or intermittent asphyxia was induced for 15-45 minutes in anaesthetized 6- and 11-days old rats and neonatal guinea pigs using gases containing 5% or 9% O₂ plus 20% CO₂ (in N₂ ). Hypoxia and hypercapnia were induced with low O₂ and high CO₂ respectively. Oxygen partial pressure (PO₂ ) and pH were measured with microsensors within the brain and subcutaneous ("body") tissue. Blood lactate was measured after asphyxia.

RESULTS

Brain and body PO₂ fell to apparent zero with little recovery during 5% O₂ asphyxia and 5% or 9% O₂ hypoxia, and increased more than twofold during 20% CO₂ hypercapnia. Unlike body PO₂ , brain PO₂ recovered rapidly to control after a transient fall (rat), or was slightly higher than control (guinea pig) during 9% O₂ asphyxia. Asphyxia (5% O₂ ) induced a respiratory acidosis paralleled by a progressive metabolic (lact)acidosis that was much smaller within than outside the brain. Hypoxia (5% O₂ ) produced a brain-confined alkalosis. Hypercapnia outlasting asphyxia suppressed pH recovery and prolonged the post-asphyxia PO₂ overshoot. All pH changes were accompanied by consistent shifts in the blood-brain barrier potential.

CONCLUSION

Regardless of brain maturation stage, hypercapnia can restore brain PO₂ and protect the brain against metabolic acidosis despite compromised oxygen availability during asphyxia. This effect extends to the recovery phase if normocapnia is restored slowly, and it is absent during hypoxia, demonstrating that exposure to hypoxia does not mimic asphyxia.

Impact of low and high partial pressure of carbon dioxide on neuron-specific enolase derived from serum and cerebrospinal fluid in patients who underwent targeted temperature management after out-of-hospital cardiac arrest: A retrospective study

AIM

In a previous study, low and high-normal arterial carbon dioxide tension (PaCO₂) were not associated with serum neuron-specific enolase (NSE) in cardiac arrest survivors. We assessed the effect of PaCO₂ on NSE in cerebrospinal fluid (CSF) and serum.

METHODS

This was a retrospective study. PaCO₂ for the first 24 h was analysed in four means, qualitative exposure state (qES), time-weighted average (TWA), median, and minimum-maximum (Min-Max). These subgroups were divided into low (LCO₂) and high PaCO₂ (HCO₂) groups defined as PaCO₂ ≤ 35.3 and PaCO₂ > 43.5 mmHg, respectively. NSE was measured at 24, 48, and 72 h (sNSE_24,48,72 and cNSE_24,48,72) from return of spontaneous circulation (ROSC). The primary outcome was the association between PaCO₂ and the NSE measured at 24 h after ROSC.

RESULTS

Forty-two subjects (male, 33; 78.6%) were included in total cohort. PaCO₂ in TWA subgroup was associated with cNSE_24,48,72, while PaCO₂ in the other subgroup were only associated with cNSE₂₄. PaCO₂ and cNSE in qES subgroup showed good correlation (r = -0.61; p < 0.01), and in TWA, median, and Min-Max subgroup showed moderate correlations (r = -0.57, r = -0.48, and r = -0.60; p < 0.01). Contrastively, sNSE was not associated and correlated with PaCO₂ in all analysis. Poor neurological outcome in LCO₂ was significantly higher than HCO₂ in qES, TWA, and median subgroups (p < 0.01, p < 0.01, and p = 0.02).

CONCLUSION

Association was found between NSE and PaCO₂ using CSF, despite including normocapnic ranges; TWA of PaCO₂ may be most strongly associated with CSF NSE levels. A prospective, multi-centre study is required to confirm our results.

Extracellular pH modulation of excitatory synaptic transmission in hippocampal CA3 neurons

In this study, the effect of extracellular pH on glutamatergic synaptic transmission was examined in mechanically dissociated rat hippocampal CA3 pyramidal neurons using a whole-cell patch-clamp technique under voltage-clamp conditions. Native synaptic boutons were isolated without using any enzymes, using a so-called "synapse bouton preparation," and preserved for the electrical stimulation of single boutons. Both the frequency and amplitude of spontaneous excitatory postsynaptic currents (sEPSCs) were found to decrease and increase in response to modest acidic (~pH 6.5) and basic (~pH 8.5) solutions, respectively. These changes in sEPSC frequency were not affected by the addition of TTX but completely disappeared by successive addition of Cd²⁺. However, changes in sEPSC amplitude induced by acidic and basic extracellular solutions were not affected by the addition of neither TTX nor Cd²⁺. The glutamate-induced whole-cell currents were decreased and increased by acidic and basic solutions, respectively. Acidic pH also decreased the amplitude and increased the failure rate (R_f) and paired-pulse rate (PPR) of glutamatergic electrically evoked excitatory postsynaptic currents (eEPSCs), while a basic pH increased the amplitude and decreased both the R_f and PPR of eEPSCs. The kinetics of the currents were not affected by changes in pH. Acidic and basic solutions decreased and increased voltage-gated Ca²⁺ but not Na⁺ channel currents in the dentate gyrus granule cell bodies. Our results indicate that extracellular pH modulates excitatory transmission via both pre- and postsynaptic sites, with the presynaptic modulation correlated to changes in voltage-gated Ca²⁺ channel currents.NEW & NOTEWORTHY The effects of external pH changes on spontaneous, miniature, and evoked excitatory synaptic transmission in CA3 hippocampal synapses were examined using the isolated nerve bouton preparation, which allowed for the accurate regulation of extracellular pH at the synapses. Acidification generally reduced transmission, partly via effects on presynaptic Ca²⁺ channel currents, while alkalization generally enhanced transmission. Both pre- and postsynaptic sites contributed to these effects.

Excitatory GABAergic signalling is associated with benzodiazepine resistance in status epilepticus

Status epilepticus is defined as a state of unrelenting seizure activity. Generalized convulsive status epilepticus is associated with a rapidly rising mortality rate, and thus constitutes a medical emergency. Benzodiazepines, which act as positive modulators of chloride (Cl-) permeable GABAA receptors, are indicated as first-line treatment, but this is ineffective in many cases. We found that 48% of children presenting with status epilepticus were unresponsive to benzodiazepine treatment, and critically, that the duration of status epilepticus at the time of treatment is an important predictor of non-responsiveness. We therefore investigated the cellular mechanisms that underlie acquired benzodiazepine resistance, using rodent organotypic and acute brain slices. Removing Mg2+ ions leads to an evolving pattern of epileptiform activity, and eventually to a persistent state of repetitive discharges that strongly resembles clinical EEG recordings of status epilepticus. We found that diazepam loses its antiseizure efficacy and conversely exacerbates epileptiform activity during this stage of status epilepticus-like activity. Interestingly, a low concentration of the barbiturate phenobarbital had a similar exacerbating effect on status epilepticus-like activity, while a high concentration of phenobarbital was effective at reducing or preventing epileptiform discharges. We then show that the persistent status epilepticus-like activity is associated with a reduction in GABAA receptor conductance and Cl- extrusion capability. We explored the effect on intraneuronal Cl- using both gramicidin, perforated-patch clamp recordings and Cl- imaging. This showed that during status epilepticus-like activity, reduced Cl- extrusion capacity was further exacerbated by activity-dependent Cl- loading, resulting in a persistently high intraneuronal Cl-. Consistent with these results, we found that optogenetic stimulation of GABAergic interneurons in the status epilepticus-like state, actually enhanced epileptiform activity in a GABAAR dependent manner. Together our findings describe a novel potential mechanism underlying benzodiazepine-resistant status epilepticus, with relevance to how this life-threatening condition should be managed in the clinic.

Nest Carbon Dioxide Masks GABA-Dependent Seizure Susceptibility in the Naked Mole-Rat

African naked mole-rats were likely the first mammals to evolve eusociality, and thus required adaptations to conserve energy and tolerate the low oxygen (O₂) and high carbon dioxide (CO₂) of a densely populated fossorial nest. As hypercapnia is known to suppress neuronal activity, we studied whether naked mole-rats might demonstrate energy savings in GABAergic inhibition. Using whole-colony behavioral monitoring of captive naked mole-rats, we found a durable nest, characterized by high CO₂ levels, where all colony members spent the majority of their time. Analysis of the naked mole-rat genome revealed, uniquely among mammals, a histidine point variation in the neuronal potassium-chloride cotransporter 2 (KCC2). A histidine missense substitution mutation at this locus in the human ortholog of KCC2, found previously in patients with febrile seizures and epilepsy, has been demonstrated to diminish neuronal Cl^- extrusion capacity, and thus impairs GABAergic inhibition. Seizures were observed, without pharmacological intervention, in adult naked mole-rats exposed to a simulated hyperthermic surface environment, causing systemic hypocapnic alkalosis. Consistent with the diminished function of KCC2, adult naked mole-rats demonstrate a reduced efficacy of inhibition that manifests as triggering of seizures at room temperature by the GABA_A receptor (GABA_AR) positive allosteric modulator diazepam. These seizures are blocked in the presence of nest-like levels of CO₂ and likely to be mediated through GABA_AR activity, based on in vitro recordings. Thus, altered GABAergic inhibition adds to a growing list of adaptations in the naked mole-rat and provides a plausible proximate mechanism for nesting behavior, where a return to the colony nest restores GABA-mediated inhibition.

Impaired CO2-Induced Arousal in SIDS and SUDEP

Premature, sudden death is devastating. Certain patient populations are at greater risk to succumb to sudden death. For instance, infants under 1year of age are at risk for sudden infant death syndrome (SIDS), and patients with epilepsy are at risk for sudden unexpected death in epilepsy (SUDEP). Deaths are attributed to these syndromic entities in these select populations when other diagnoses have been excluded. There are a number of similarities between these syndromes, and the commonalities suggest that the two syndromes may share certain etiological features. One such feature may be deficiency of arousal to CO₂. Under normal conditions, CO₂ is a potent arousal stimulus. Circumstances surrounding SIDS and SUDEP deaths often facilitate CO₂ elevation, and faulty CO₂ arousal mechanisms could, at least in part, contribute to death.

A miniaturized push-pull-perfusion probe for few-second sampling of neurotransmitters in the mouse brain

Measuring biomolecule concentrations in the brain of living animals, in real time, is a challenging task, especially when detailed information at high temporal resolution is also required. Traditionally, microdialysis probes are used that generally have sampling areas in the order of about 1 mm2, and provide information on concentrations with a temporal resolution of at least several minutes. In this paper, we present a novel miniaturized push-pull perfusion sampling probe that uses an array of small 3 μm-wide sampling channels to sample neurotransmitters at a typical recovery rate of 61%, with a reduced risk of clogging. The added feature to segment the dialysate inside the probe into small water-in-decane droplets enables the detection of concentrations with a temporal resolution of a few seconds. Here we used the probe for in vivo recordings of neurotransmitter glutamate released upon electrical stimulation in the brain of a mouse to demonstrate the feasibility of the probe for real-time neurochemical brain analysis.

Targeting two different levels of both arterial carbon dioxide and arterial oxygen after cardiac arrest and resuscitation: a randomised pilot trial

Purpose

We assessed the effects of targeting low-normal or high-normal arterial carbon dioxide tension (PaCO₂) and normoxia or moderate hyperoxia after out-of-hospital cardiac arrest (OHCA) on markers of cerebral and cardiac injury.

Methods

Using a 2³ factorial design, we randomly assigned 123 patients resuscitated from OHCA to low-normal (4.5–4.7 kPa) or high-normal (5.8–6.0 kPa) PaCO₂ and to normoxia (arterial oxygen tension [PaO₂] 10–15 kPa) or moderate hyperoxia (PaO₂ 20–25 kPa) and to low-normal or high-normal mean arterial pressure during the first 36 h in the intensive care unit. Here we report the results of the low-normal vs. high-normal PaCO₂ and normoxia vs. moderate hyperoxia comparisons. The primary endpoint was the serum concentration of neuron-specific enolase (NSE) 48 h after cardiac arrest. Secondary endpoints included S100B protein and cardiac troponin concentrations, continuous electroencephalography (EEG) and near-infrared spectroscopy (NIRS) results and neurologic outcome at 6 months.

Results

In total 120 patients were included in the analyses. There was a clear separation in PaCO₂ (p < 0.001) and PaO₂ (p < 0.001) between the groups. The median (interquartile range) NSE concentration at 48 h was 18.8 µg/l (13.9–28.3 µg/l) in the low-normal PaCO₂ group and 22.5 µg/l (14.2–34.9 µg/l) in the high-normal PaCO₂ group, p = 0.400; and 22.3 µg/l (14.8–27.8 µg/l) in the normoxia group and 20.6 µg/l (14.2–34.9 µg/l) in the moderate hyperoxia group, p = 0.594). High-normal PaCO₂ and moderate hyperoxia increased NIRS values. There were no differences in other secondary outcomes.

Conclusions

Both high-normal PaCO₂ and moderate hyperoxia increased NIRS values, but the NSE concentration was unaffected.

Registration

ClinicalTrials.gov, NCT02698917. Registered on January 26, 2016.

Electronic supplementary material

The online version of this article (10.1007/s00134-018-5453-9) contains supplementary material, which is available to authorized users.

Bioenergetic Mechanisms of Seizure Control

Epilepsy is characterized by the regular occurrence of seizures, which follow a stereotypical sequence of alterations in the electroencephalogram. Seizures are typically a self limiting phenomenon, concluding finally in the cessation of hypersynchronous activity and followed by a state of decreased neuronal excitability which might underlie the cognitive and psychological symptoms the patients experience in the wake of seizures. Many efforts have been devoted to understand how seizures spontaneously stop in hope to exploit this knowledge in anticonvulsant or neuroprotective therapies. Besides the alterations in ion-channels, transmitters and neuromodulators, the successive build up of disturbances in energy metabolism have been suggested as a mechanism for seizure termination. Energy metabolism and substrate supply of the brain are tightly regulated by different mechanisms called neurometabolic and neurovascular coupling. Here we summarize the current knowledge whether these mechanisms are sufficient to cover the energy demand of hypersynchronous activity and whether a mismatch between energy need and supply could contribute to seizure control.

Physiological and Pathological Brain Activation in the Anesthetized Rat Produces Hemodynamic-Dependent Cortical Temperature Increases That Can Confound the BOLD fMRI Signal

Anesthetized rodent models are ubiquitous in pre-clinical neuroimaging studies. However, because the associated cerebral morphology and experimental methodology results in a profound negative brain-core temperature differential, cerebral temperature changes during functional activation are likely to be principally driven by local inflow of fresh, core-temperature, blood. This presents a confound to the interpretation of blood-oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) data acquired from such models, since this signal is also critically temperature-dependent. Nevertheless, previous investigation on the subject is surprisingly sparse. Here, we address this issue through use of a novel multi-modal methodology in the urethane anesthetized rat. We reveal that sensory stimulation, hypercapnia and recurrent acute seizures induce significant increases in cortical temperature that are preferentially correlated to changes in total hemoglobin concentration (Hbt), relative to cerebral blood flow and oxidative metabolism. Furthermore, using a phantom-based evaluation of the effect of such temperature changes on the BOLD fMRI signal, we demonstrate a robust inverse relationship between both variables. These findings suggest that temperature increases, due to functional hyperemia, should be accounted for to ensure accurate interpretation of BOLD fMRI signals in pre-clinical neuroimaging studies.

Association of Hypercapnia and Hypercapnic Acidosis With Clinical Outcomes in Mechanically Ventilated Patients With Cerebral Injury

IMPORTANCE

Clinical studies investigating the effects of hypercapnia and hypercapnic acidosis in acute cerebral injury are limited. The studies performed so far have mainly focused on the outcomes in relation to the changes in partial pressure of carbon dioxide and pH in isolation and have not evaluated the effects of partial pressure of carbon dioxide and pH in conjunction.

OBJECTIVE

To review the association of compensated hypercapnia and hypercapnic acidosis during the first 24 hours of intensive care unit admission on hospital mortality in adult mechanically ventilated patients with cerebral injury.

DESIGN, SETTING, AND PARTICIPANTS

Multicenter, binational retrospective review of patients with cerebral injury (traumatic brain injury, cardiac arrest, and stroke) admitted to 167 intensive care units in Australia and New Zealand between January 2000 and December 2015. Patients were classified into 3 groups based on combination of arterial pH and arterial carbon dioxide (normocapnia and normal pH, compensated hypercapnia, and hypercapnic acidosis) during the first 24 hours of intensive care unit stay.

MAIN OUTCOMES AND MEASURES

Hospital mortality.

RESULTS

A total of 30 742 patients (mean age, 55 years; 21 827 men [71%]) were included. Unadjusted hospital mortality rates were highest in patients with hypercapnic acidosis. Multivariable logistic regression analysis and Cox proportional hazards analysis in 3 diagnostic categories showed increased odds of hospital mortality (cardiac arrest odds ratio [OR], 1.51; 95% CI, 1.34-1.71; stroke OR, 1.43; 95% CI, 1.27-1.6; and traumatic brain injury OR, 1.22; 95% CI, 1.06-1.42; P <.001) and hazard ratios (HR) (cardiac arrest HR, 1.23; 95% CI, 1.14-1.34; stroke HR, 1.3; 95% CI, 1.21-1.4; traumatic brain injury HR, 1.13; 95% CI, 1-1.27), in patients with hypercapnic acidosis compared with normocapnia and normal pH. There was no difference in mortality between patients who had compensated hypercapnia compared with patients who had normocapnia and normal pH. In patients with hypercapnic acidosis, the adjusted OR of hospital mortality increased with increasing partial pressure of carbon dioxide, while no such increase was noted in patients with compensated hypercapnia.

CONCLUSIONS AND RELEVANCE

Hypercapnic acidosis was associated with increased risk of hospital mortality in patients with cerebral injury. Hypercapnia, when compensated to normal pH during the first 24 hours of intensive care unit admission, may not be harmful in mechanically ventilated patients with cerebral injury.

Association of Hypocapnia in Children with Febrile Seizures

Introduction:

Febrile seizure is a benign condition in children. Susceptibility genes associated with febrile convulsions have been identified, but the precise pathophysiologic mechanism that triggers febrile seizure is unclear. Using animal models, it has been demonstrated that hyperthermia causes respiratory alkalosis with consequent brain alkalosis and seizures. This study was conducted to find out any association of febrile seizures with fever induced hypocapnia.

Methods:

We conducted a cross sectional observational study and enrolled 45 children presenting with febrile seizures. Axillary temperature was measured and venous blood gas analysis was done soon after admission and within 24 hour of seizure onset. Mean pH and pCO2 from venous blood gas analysis was measured and compared with standard normal values. Data was analyzed using SPSS software version 17.0 software.

Results:

The mean pCO2 (27.95 ± 5.31mmHg) was much below normal range, and 91% of children had hypocapnia (pCO2 <35) after the febrile seizures. However alkalosis (pH > 7.45) was demonstrated in only 20% of children. Also pCO2 levels in samples drawn before 2 hours were significantly less than those taken after 2 hours (23.24 ± 3.44 vs 29.29 ± 4.99 respectively; p = 0.001).

Conclusion:

Our data indicates that febrile seizures may be associated with fever induced hyperventilation and ensuing hypocapnia may be one of the precipitating factor in inducing seizures. However, well-structured human trials are needed to demonstrate the same.

Seizure epicenter depth and translaminar field potential synchrony underlie complex variations in tissue oxygenation during ictal initiation

Whether functional hyperemia during epileptic activity is adequate to meet the heightened metabolic demand of such events is controversial. Whereas some studies have demonstrated hyperoxia during ictal onsets, other work has reported transient hypoxic episodes that are spatially dependent on local surface microvasculature. Crucially, how laminar differences in ictal evolution can affect subsequent cerebrovascular responses has not been thus far investigated, and is likely significant in view of possible laminar-dependent neurovascular mechanisms and angioarchitecture. We addressed this open question using a novel multi-modal methodology enabling concurrent measurement of cortical tissue oxygenation, blood flow and hemoglobin concentration, alongside laminar recordings of neural activity, in a urethane anesthetized rat model of recurrent seizures induced by 4-aminopyridine. We reveal there to be a close relationship between seizure epicenter depth, translaminar local field potential (LFP) synchrony and tissue oxygenation during the early stages of recurrent seizures, whereby deep layer seizures are associated with decreased cross laminar synchrony and prolonged periods of hypoxia, and middle layer seizures are accompanied by increased cross-laminar synchrony and hyperoxia. Through comparison with functional activation by somatosensory stimulation and graded hypercapnia, we show that these seizure-related cerebrovascular responses occur in the presence of conserved neural-hemodynamic and blood flow-volume coupling. Our data provide new insights into the laminar dependency of seizure-related neurovascular responses, which may reconcile inconsistent observations of seizure-related hypoxia in the literature, and highlight a potential layer-dependent vulnerability that may contribute to the harmful effects of clinical recurrent seizures. The relevance of our findings to perfusion-related functional neuroimaging techniques in epilepsy are also discussed.

Targeting low- or high-normal Carbon dioxide, Oxygen, and Mean arterial pressure After Cardiac Arrest and REsuscitation: study protocol for a randomized pilot trial

Background

Arterial carbon dioxide tension (PaCO₂), oxygen tension (PaO₂), and mean arterial pressure (MAP) are modifiable factors that affect cerebral blood flow (CBF), cerebral oxygen delivery, and potentially the course of brain injury after cardiac arrest. No evidence regarding optimal treatment targets exists.

Methods

The Carbon dioxide, Oxygen, and Mean arterial pressure After Cardiac Arrest and REsuscitation (COMACARE) trial is a pilot multi-center randomized controlled trial (RCT) assessing the feasibility of targeting low- or high-normal PaCO₂, PaO₂, and MAP in comatose, mechanically ventilated patients after out-of-hospital cardiac arrest (OHCA), as well as its effect on brain injury markers. Using a 2³ factorial design, participants are randomized upon admission to an intensive care unit into one of eight groups with various combinations of PaCO₂, PaO₂, and MAP target levels for 36 h after admission.

The primary outcome is neuron-specific enolase (NSE) serum concentration at 48 h after cardiac arrest. The main feasibility outcome is the between-group differences in PaCO2, PaO2, and MAP during the 36 h after ICU admission. Secondary outcomes include serum concentrations of NSE, S100 protein, and cardiac troponin at 24, 48, and 72 h after cardiac arrest; cerebral oxygenation, measured with near-infrared spectroscopy (NIRS); potential differences in epileptic activity, monitored via continuous electroencephalogram (EEG); and neurological outcomes at six months after cardiac arrest.

Discussion

The trial began in March 2016 and participant recruitment has begun in all seven study sites as of March 2017. Currently, 115 of the total of 120 patients have been included. When completed, the results of this trial will provide preliminary clinical evidence regarding the feasibility of targeting low- or high-normal PaCO₂, PaO₂, and MAP values and its effect on developing brain injury, brain oxygenation, and epileptic seizures after cardiac arrest. The results of this trial will be used to evaluate whether a larger RCT on this subject is justified.

Trial registration

ClinicalTrials.gov, NCT02698917. Registered on 26 January 2016.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-017-2257-0) contains supplementary material, which is available to authorized users.

Neonatal Hypoxia Ischaemia: Mechanisms, Models, and Therapeutic Challenges

Neonatal hypoxia-ischaemia (HI) is the most common cause of death and disability in human neonates, and is often associated with persistent motor, sensory, and cognitive impairment. Improved intensive care technology has increased survival without preventing neurological disorder, increasing morbidity throughout the adult population. Early preventative or neuroprotective interventions have the potential to rescue brain development in neonates, yet only one therapeutic intervention is currently licensed for use in developed countries. Recent investigations of the transient cortical layer known as subplate, especially regarding subplate's secretory role, opens up a novel set of potential molecular modulators of neonatal HI injury. This review examines the biological mechanisms of human neonatal HI, discusses evidence for the relevance of subplate-secreted molecules to this condition, and evaluates available animal models. Neuroserpin, a neuronally released neuroprotective factor, is discussed as a case study for developing new potential pharmacological interventions for use post-ischaemic injury.

Cyclic seizures in critically ill patients: Clinical correlates, DC recordings and outcomes

OBJECTIVE

To describe EEG and clinical correlates, DC recordings and prognostic significance of cyclic seizures (CS).

METHODS

We reviewed our prospective continuous EEG database to identify patients with CS, controls with non-cyclic status epilepticus (SE) and controls without seizure matched for age and etiology. EEG was reviewed with DC settings.

RESULTS

39/260 (15%) patients with electrographic seizures presented with CS. These patients were older (62 vs. 54years; p=0.04) and more often had acute or progressive brain injury (77% vs. 52%; p=0.03) than patients with non-cyclic SE and had a lower level of consciousness, were more severely ill, than matched controls. CS almost always had focal onset, often from posterior regions. Patients with CS trended towards worse prognosis. When available (12 patients), DC recordings showed an infraslow cyclic oscillation of EEG baseline synchronized to the seizures in all cases.

CONCLUSIONS

CS occur mostly in older patients with acute or progressive brain injury, are more likely to be associated with poor outcome than patients with other forms of nonconvulsive SE, and are accompanied by synchronous oscillations of the EEG baseline on DC recordings.

SIGNIFICANCE

CS are a common form of non-convulsive status epilepticus in critically ill patients and provide further insights into the relationship between infraslow activity and seizures; further study on this relationship may shed light on the mechanisms of seizure initiation and termination.

Reduced Efficacy of the KCC2 Cotransporter Promotes Epileptic Oscillations in a Subiculum Network Model

Pharmacoresistant epilepsy is a chronic neurological condition in which a basal brain hyperexcitability results in paroxysmal hypersynchronous neuronal discharges. Human temporal lobe epilepsy has been associated with dysfunction or loss of the potassium-chloride cotransporter KCC2 in a subset of pyramidal cells in the subiculum, a key structure generating epileptic activities. KCC2 regulates intraneuronal chloride and extracellular potassium levels by extruding both ions. Absence of effective KCC2 may alter the dynamics of chloride and potassium levels during repeated activation of GABAergic synapses due to interneuron activity. In turn, such GABAergic stress may itself affect Cl- regulation. Such changes in ionic homeostasis may switch GABAergic signaling from inhibitory to excitatory in affected pyramidal cells and also increase neuronal excitability. Possibly these changes contribute to periodic bursting in pyramidal cells, an essential component in the onset of ictal epileptic events. We tested this hypothesis with a computational model of a subicular network with realistic connectivity. The pyramidal cell model explicitly incorporated the cotransporter KCC2 and its effects on the internal/external chloride and potassium levels. Our network model suggested the loss of KCC2 in a critical number of pyramidal cells increased external potassium and intracellular chloride concentrations leading to seizure-like field potential oscillations. These oscillations included transient discharges leading to ictal-like field events with frequency spectra as in vitro Restoration of KCC2 function suppressed seizure activity and thus may present a useful therapeutic option. These simulations therefore suggest that reduced KCC2 cotransporter activity alone may underlie the generation of ictal discharges.

SIGNIFICANCE STATEMENT

Ion regulation in the brain is a major determinant of neural excitability. Intracellular chloride in neurons, a partial determinant of the resting potential and the inhibitory reversal potentials, is regulated together with extracellular potassium via kation chloride cotransporters. During temporal lobe epilepsy, the homeostatic regulation of intracellular chloride is impaired in pyramidal cells, yet how this dysregulation may lead to seizures has not been explored. Using a realistic neural network model describing ion mechanisms, we show that chloride homeostasis pathology provokes seizure activity analogous to recordings from epileptogenic brain tissue. We show that there is a critical percentage of pathological cells required for seizure initiation. Our model predicts that restoration of the chloride homeostasis in pyramidal cells could be a viable antiepileptic strategy.

5% Carbon Dioxide is safe but of limited efficacy as a treatment for paediatric non-convulsive status epilepticus: An open label observational study

OBJECTIVE

To establish the efficacy and tolerability of inhaled 5% carbon dioxide/95% oxygen as a treatment for paediatric non-convulsive status epilepticus (NCSE).

METHODS

In an open label clinical trial, children in NCSE were given high flow inhaled 5% carbon dioxide/95% oxygen by face mask for 120 s under EEG control.

RESULTS

Six children (five male; ages 3-13; all with severe underlying epilepsy and disability) were recruited. Inhalation was well tolerated in all cases. Capillary blood gasses showed no significant derangements at the end of the inhalation. Effects on EEG normalisation were limited and transient, and no clinical improvements were noted. No adverse effects occurred.

CONCLUSION

Inhaled 5% carbon dioxide/95% oxygen has been suggested as a potent, well tolerated anticonvulsant. An anticonvulsant without sedating and respiration-depressing effects would be particularly welcome in the management of NCSE where the justification for aggressive anticonvulsant therapy is often uncertain, however it appears that 5% carbon dioxide is of limited efficacy in this context.

Targeted therapeutic mild hypercapnia after cardiac arrest: A phase II multi-centre randomised controlled trial (the CCC trial)

BACKGROUND

In intensive care observational studies, hypercapnia after cardiac arrest (CA) is independently associated with improved neurological outcome. However, the safety and feasibility of delivering targeted therapeutic mild hypercapnia (TTMH) for such patients is untested.

METHODS

In a phase II safety and feasibility multi-centre, randomised controlled trial, we allocated ICU patients after CA to 24h of targeted normocapnia (TN) (PaCO2 35-45mmHg) or TTMH (PaCO2 50-55mmHg). The primary outcome was serum neuron specific enolase (NSE) and S100b protein concentrations over the first 72h assessed in the first 50 patients surviving to day three. Secondary end-points included global measure of function assessment at six months and mortality for all patients.

RESULTS

We enrolled 86 patients. Their median age was 61 years (58, 64 years) and 66 (79%) were male. Of these, 50 patients (58%) survived to day three for full biomarker assessment. NSE concentrations increased in the TTMH group (p=0.02) and TN group (p=0.005) over time, with the increase being significantly more pronounced in the TN group (p(interaction)=0.04). S100b concentrations decreased over time in the TTMH group (p<0.001) but not in the TN group (p=0.68). However, the S100b change over time did not differ between the groups (p(interaction)=0.23). At six months, 23 (59%) TTMH patients had good functional recovery compared with 18 (46%) TN patients. Hospital mortality occurred in 11 (26%) TTMH patients and 15 (37%) TN patients (p=0.31).

CONCLUSIONS

In CA patients admitted to the ICU, TTMH was feasible, appeared safe and attenuated the release of NSE compared with TN. These findings justify further investigation of this novel treatment.

Seizures and brain regulatory systems: consciousness, sleep, and autonomic systems

Research into the physiologic underpinnings of epilepsy has revealed reciprocal relationships between seizures and the activity of several regulatory systems in the brain. This review highlights recent progress in understanding and using the relationships between seizures and the arousal or consciousness system, the sleep-wake and associated circadian system, and the central autonomic network.

Emerging roles of Na⁺/H⁺ exchangers in epilepsy and developmental brain disorders

Epilepsy is a common central nervous system (CNS) disease characterized by recurrent transient neurological events occurring due to abnormally excessive or synchronous neuronal activity in the brain. The CNS is affected by systemic acid-base disorders, and epileptic seizures are sensitive indicators of underlying imbalances in cellular pH regulation. Na(+)/H(+) exchangers (NHEs) are a family of membrane transporter proteins actively involved in regulating intracellular and organellar pH by extruding H(+) in exchange for Na(+) influx. Altering NHE function significantly influences neuronal excitability and plays a role in epilepsy. This review gives an overview of pH regulatory mechanisms in the brain with a special focus on the NHE family and the relationship between epilepsy and dysfunction of NHE isoforms. We first discuss how cells translocate acids and bases across the membrane and establish pH homeostasis as a result of the concerted effort of enzymes and ion transporters. We focus on the specific roles of the NHE family by detailing how the loss of NHE1 in two NHE mutant mice results in enhanced neuronal excitability in these animals. Furthermore, we highlight new findings on the link between mutations of NHE6 and NHE9 and developmental brain disorders including epilepsy, autism, and attention deficit hyperactivity disorder (ADHD). These studies demonstrate the importance of NHE proteins in maintaining H(+) homeostasis and their intricate roles in the regulation of neuronal function. A better understanding of the mechanisms underlying NHE1, 6, and 9 dysfunctions in epilepsy formation may advance the development of new epilepsy treatment strategies.

On the contribution of KCC2 and carbonic anhydrase to two types of in vitro interictal discharge

GABAA receptor-mediated inhibition--which is due to Cl(-) and HCO3 (-) currents controlled by KCC2 and carbonic anhydrase activity, respectively--contributes to short- and long-lasting interictal events recorded from the CA3 region of hippocampus during application of 4-aminopyridine (4AP, 50 μM). Here, we employed field potential recordings in an in vitro brain slice preparation to establish the effects induced by the KCC2 blockers VU0240551 (10 μM) or bumetanide (50 μM) and by the carbonic anhydrase inhibitor acetazolamide (10 μM) on the two types of interictal events. We found that blocking KCC2 activity decreased the amplitude of the short-lasting events. In addition, this pharmacological procedure increased the interval of occurrence of the long-lasting events and reduced their amplitude. Blocking carbonic anhydrase activity with acetazolamide reduced the interval of occurrence and the duration of the short-lasting events while increasing their amplitude; acetazolamide also reduced the duration and amplitude of the long-lasting events. Finally, blocking either KCC2 or carbonic anhydrase activity increased the interval of occurrence of pharmacologically isolated synchronous GABAergic events and decreased their duration and amplitude. These data substantiate further the role of GABAA receptor-mediated signaling in driving neuronal populations toward hypersynchronous states presumably by increasing extracellular [K(+)].

Ion dynamics during seizures

Changes in membrane voltage brought about by ion fluxes through voltage and transmitter-gated channels represent the basis of neural activity. As such, electrochemical gradients across the membrane determine the direction and driving force for the flow of ions and are therefore crucial in setting the properties of synaptic transmission and signal propagation. Ion concentration gradients are established by a variety of mechanisms, including specialized transporter proteins. However, transmembrane gradients can be affected by ionic fluxes through channels during periods of elevated neural activity, which in turn are predicted to influence the properties of on-going synaptic transmission. Such activity-induced changes to ion concentration gradients are a feature of both physiological and pathological neural processes. An epileptic seizure is an example of severely perturbed neural activity, which is accompanied by pronounced changes in intracellular and extracellular ion concentrations. Appreciating the factors that contribute to these ion dynamics is critical if we are to understand how a seizure event evolves and is sustained and terminated by neural tissue. Indeed, this issue is of significant clinical importance as status epilepticus—a type of seizure that does not stop of its own accord—is a life-threatening medical emergency. In this review we explore how the transmembrane concentration gradient of the six major ions (K⁺, Na⁺, Cl⁻, Ca²⁺, H⁺and HCO3−) is altered during an epileptic seizure. We will first examine each ion individually, before describing how multiple interacting mechanisms between ions might contribute to concentration changes and whether these act to prolong or terminate epileptic activity. In doing so, we will consider how the availability of experimental techniques has both advanced and restricted our ability to study these phenomena.