Potassium Leak Channels and Mitochondrial Complex I Interact in Glutamatergic Interneurons of the Mouse Spinal Cord

BACKGROUND

Volatile anesthetics induce hyperpolarizing potassium currents in spinal cord neurons that may contribute to their mechanism of action. They are induced at lower concentrations of isoflurane in noncholinergic neurons from mice carrying a loss-of-function mutation of the Ndufs4 gene, required for mitochondrial complex I function. The yeast NADH dehydrogenase enzyme, NDi1, can restore mitochondrial function in the absence of normal complex I activity, and gain-of-function Ndi1 transgenic mice are resistant to volatile anesthetics. The authors tested whether NDi1 would reduce the hyperpolarization caused by isoflurane in neurons from Ndufs4 and wild-type mice. Since volatile anesthetic behavioral hypersensitivity in Ndufs4 is transduced uniquely by glutamatergic neurons, it was also tested whether these currents were also unique to glutamatergic neurons in the Ndufs4 spinal cord.

METHODS

Spinal cord neurons from wild-type, NDi1, and Ndufs4 mice were patch clamped to characterize isoflurane sensitive currents. Neuron types were marked using fluorescent markers for cholinergic, glutamatergic, and γ-aminobutyric acid-mediated (GABAergic) neurons. Norfluoxetine was used to identify potassium channel type. Neuron type-specific Ndufs4 knockout animals were generated using type-specific Cre-recombinase with floxed Ndufs4.

RESULTS

Resting membrane potentials (RMPs) of neurons from NDi1;Ndufs4, unlike those from Ndufs4, were not hyperpolarized by 0.6% isoflurane (Ndufs4, ΔRMP -8.2 mV [-10 to -6.6]; P = 1.3e-07; Ndi1;Ndufs4, ΔRMP -2.1 mV [-7.6 to +1.4]; P = 1). Neurons from NDi1 animals in a wild-type background were not hyperpolarized by 1.8% isoflurane (wild-type, ΔRMP, -5.2 mV [-7.3 to -3.2]; P = 0.00057; Ndi1, ΔRMP, 0.6 mV [-1.7 to 3.2]; P = 0.68). In spinal cord slices from global Ndufs4 animals, holding currents (HC) were induced by 0.6% isoflurane in both GABAergic (ΔHC, 81.3 pA [61.7 to 101.4]; P = 2.6e-05) and glutamatergic (ΔHC, 101.2 pA [63.0 to 146.2]; P = 0.0076) neurons. In neuron type-specific Ndufs4 knockouts, HCs were increased in cholinergic (ΔHC, 119.5 pA [82.3 to 156.7]; P = 0.00019) and trended toward increase in glutamatergic (ΔHC, 85.5 pA [49 to 126.9]; P = 0.064) neurons but not in GABAergic neurons.

CONCLUSIONS

Bypassing complex I by overexpression of NDi1 eliminates increases in potassium currents induced by isoflurane in the spinal cord. The isoflurane-induced potassium currents in glutamatergic neurons represent a potential downstream mechanism of complex I inhibition in determining minimum alveolar concentration.

EDITOR’S PERSPECTIVE

Preventing Prolonged Times to Awakening While Mitigating the Risk of Patient Awareness: Gas Man Computer Simulations of Sevoflurane Consumption From Brief, High Fresh Gas Flow Before the End of Surgery

Prolonged times to tracheal extubation are associated with adverse patient and economic outcomes. We simulated awakening patients from sevoflurane after long-duration surgery at 2% end-tidal concentration, 1.0 minimum alveolar concentration (MAC) in a 40-year-old. Our end-of-surgery target was 0.5 MAC, the Michigan Awareness Control Study's threshold for intraoperative alerts. Consider an anesthetist who uses a 1 liter/minute gas flow until surgery ends. During surgical closure, the inspired sevoflurane concentration is reduced from 2.05% to 0.62% (i.e., MAC-awake). The estimated time to reach 0.5 MAC is 28 minutes. From a previous study, 28 minutes exceeded ≥95% of surgical closure times for all 244 distinct surgical procedures (N=23,343 cases). Alternatively, the anesthetist uses 8 liters/minute gas flow with the vaporizer at MAC-awake for 1.8 minutes, which reduces the end-tidal concentration to 0.5 MAC. The anesthetist then increases the vaporizer to keep end-tidal 0.5 MAC until the surgery ends. An additional simulation shows that, compared with simulated end-tidal agent feedback control, this approach consumed 0.45 mL extra agent. Simulation results are the same for an 80-year-old patient. The extra 0.45 mL has a global warming potential comparable to driving 26 seconds at 40 kilometers (25 miles) per hour, comparable to route modification to avoid potential roadway hazards.

Veterinarians exposed to inhaled anesthetic present chromosome damage, apoptosis and cell cycle changes

This cross-sectional study evaluated, for the first time, DNA damage, viability, and cell death of lymphocytes and cell cycle phases of mononuclear and polymorphonuclear cells in veterinarians exposed to the volatile anesthetic isoflurane. Veterinarians who were occupationally exposed to isoflurane (exposed group; n = 20) and matched-unexposed individuals (volunteers without occupational exposure; n = 20) were enrolled in the study. DNA damage was assessed in lymphocytes by micronucleus (MN) and phosphorylated histone gamma-H2AX (γ-H2AX). Cell viability, cytotoxicity, and the cell cycle were evaluated by flow cytometry. Isoflurane was detected in urine samples by headspace gas chromatography-mass spectrometry. Compared with unexposed subjects, veterinarians occupationally exposed to isoflurane (25.7 ± 23.7 μg/L urine) presented statistically higher MN frequencies, lymphocytic apoptosis rates, and numbers of polymorphonuclear cells in the G0/G1 stage. Additionally, the exposed group presented statistically lower proportions of viable lymphocytes and G2/M polymorphonuclear cells. Our findings indicate that veterinarians who are frequently exposed to inhaled anesthetic exhibit chromosomal and cell damage in addition to changes in peripheral blood cell proliferation.

The effects of volatile anesthetics and propofol in patients undergoing off-pump coronary artery bypass grafting: a systematic review and meta-analysis

Background

Studies investigating the cardioprotective effect of volatile anesthetics on cardiac troponins in off-pump coronary artery bypass grafting (OPCAB) surgery remain controversial. This current study was conducted to systematically evaluate the impact of volatile anesthetics and propofol on patients undergoing OPCAB surgery.

Methods

A computerized search of electronic databases was conducted up to July 21, 2023, to identify relevant studies using appropriate search terms. The primary outcomes of interest were the levels of myocardial injury biomarkers (e.g., cTnI, cTnT), while secondary outcomes included extubation time, length of ICU stay, 30-day mortality, transfusion and thrombosis, and postoperative recovery, which were compared between two anesthesia techniques.

Results

A search of databases produced 14 relevant studies with a combined total of 703 patients. Among them, 355 were allocated to the volatile anesthetics group and 348 to the propofol group. Our study reveals a statistically significant reduction in myocardial injury biomarkers among patients who received volatile anesthetics compared to those who received propofol (P < .001). Subgroup analysis showed that patients using sevoflurane had lower postoperative cardiac troponins levels compared to propofol (P = .01). However, desflurane and isoflurane currently have no significant advantage over propofol (all P > 0.05). There was no significant difference in postoperative mechanical ventilation time, length of ICU stay, and mortality between the two groups (all P > 0.05).

Conclusions

This study suggested that volatile anesthetics, specifically sevoflurane, in adult OPCAB surgery provide a better cardioprotective effect than propofol.

Systematic Review Registration

PROSPERO (CRD42023444277).

Volatile anesthetic and outcome in acute trauma care: planned secondary analysis of the PROPPR study

Background

This retrospective analysis of prospectively collected data from the PROPPR study describes volatile anesthetic use in severely injured trauma patients undergoing anesthesia.

Methods

After exclusions, 402 subjects were reviewed of the original 680, and 292 had complete data available for analysis. Anesthesia was not protocolized, so analysis was of contemporary practice.

Results

The small group who received no volatile anesthetic (n = 25) had greater injury burden (Glasgow Coma Scale P = 0.05, Injury Severity Score P = 0.001, Revised Trauma Score P = 0.03), higher 6- and 24-hour mortality (P < 0.001), and higher incidence of systemic inflammatory response syndrome (P = 0.003) and ventilator-associated pneumonia (P = 0.02) than those receiving any volatile (n = 267). There were no differences in mortality between volatile agents at 6 hours (P = 0.51) or 24 hours (P = 0.35). The desflurane group was less severely injured than the isoflurane group. Mean minimum alveolar concentration was < 0.6 and lowest in the isoflurane group compared to the sevoflurane and desflurane groups (both P < 0.01). The incidence of systemic inflammatory response syndrome was lower in the desflurane group than in the isoflurane group (P = 0.007).

Conclusion

In this acutely injured trauma population, choice of volatile anesthetic did not appear to influence short-term mortality and morbidity. Subjects who received no volatile were more severely injured with greater mortality, representing hemodynamic compromise where volatile agent was limited until stable. As anesthetic was not protocolized, these findings that choice of specific volatile was not associated with short-term survival require prospective, randomized evaluation.

Ventilatory Effects of Isoflurane Sedation via the Sedaconda ACD-S versus ACD-L: A Substudy of a Randomized Trial

Devices used to deliver inhaled sedation increase dead space ventilation. We therefore compared ventilatory effects among isoflurane sedation via the Sedaconda ACD-S (internal volume: 50 mL), isoflurane sedation via the Sedaconda ACD-L (100 mL), and propofol sedation with standard mechanical ventilation with heat and moisture exchangers (HME). This is a substudy of a randomized trial that compared inhaled isoflurane sedation via the ACD-S or ACD-L to intravenous propofol sedation in 301 intensive care patients. Data from the first 24 h after study inclusion were analyzed using linear mixed models. Primary outcome was minute ventilation. Secondary outcomes were tidal volume, respiratory rate, arterial carbon dioxide pressure, and isoflurane consumption. In total, 151 patients were randomized to propofol and 150 to isoflurane sedation; 64 patients received isoflurane via the ACD-S and 86 patients via the ACD-L. While use of the ACD-L was associated with higher minute ventilation (average difference (95% confidence interval): 1.3 (0.7, 1.8) L/min, p < 0.001), higher tidal volumes (44 (16, 72) mL, p = 0.002), higher respiratory rates (1.2 (0.1, 2.2) breaths/min, p = 0.025), and higher arterial carbon dioxide pressures (3.4 (1.2, 5.6) mmHg, p = 0.002), use of the ACD-S did not significantly affect ventilation compared to standard mechanical ventilation and sedation. Isoflurane consumption was slightly less with the ACD-L compared to the ACD-S (-0.7 (-1.3, 0.1) mL/h, p = 0.022). The Sedaconda ACD-S compared to the ACD-L is associated with reduced minute ventilation and does not significantly affect ventilation compared to a standard mechanical ventilation and sedation setting. The smaller ACD-S is therefore the device of choice to minimize impact on ventilation, especially in patients with a limited ability to compensate (e.g., COPD patients). Volatile anesthetic consumption is slightly higher with the ACD-S compared to the ACD-L.

Knowledge Gaps in Anesthetic Gas Utilization in a Large Academic Hospital System: A Multicenter Survey

Inhaled anesthetics account for a significant portion of the greenhouse gases generated by perioperative services within the healthcare systems. This cross-sectional study aimed to identify knowledge gaps and practice patterns related to carbon dioxide (CO₂) absorbents and intraoperative delivery of fresh gas flows (FGF) for future sustainability endeavors. Secondary aims focused on differences in these knowledge gaps based on the level of training. Surveys were distributed at five large academic medical centers. In addition to site-specific CO₂ absorbent use and practice volume and experience, respondents at each institution were queried about individual practice with FGF rates during anesthetic maintenance as well as the cost-effectiveness and environmental impact of different volatile anesthetics. Results were stratified and analyzed by the level of training. In total, 368 (44% physicians, 30% residents, and 26% nurse anesthetists) respondents completed surveys. Seventy-six percent of respondents were unaware or unsure about which type of CO₂ absorbent was in use at their hospital. Fifty-nine percent and 48% of respondents used sevoflurane and desflurane with FGF ≥1 L/min, respectively. Most participants identified desflurane as the agent with the greatest environmental impact (89.9%) and a greater proportion of anesthesiologists correctly identified isoflurane as a cost-effective anesthetic (78.3%, p=0.02). Knowledge gaps about in-use CO₂ absorbent and optimal FGF usage were identified within the anesthesia care team. Educational initiatives to increase awareness about the carbon emissions from anesthesia and newer CO₂ absorbents will impact the environmental and economic cost per case and align anesthesia providers toward healthcare decarbonization.

Developing a Real-Time Electroencephalogram-Guided Anesthesia-Management Curriculum for Educating Residents: A Single-Center Randomized Controlled Trial

BACKGROUND

Different anesthetic drugs and patient factors yield unique electroencephalogram (EEG) patterns. Yet, it is unclear how best to teach trainees to interpret EEG time series data and the corresponding spectral information for intraoperative anesthetic titration, or what effect this might have on outcomes.

METHODS

We developed an electronic learning curriculum (ELC) that covered EEG spectrogram interpretation and its use in anesthetic titration. Anesthesiology residents at a single academic center were randomized to receive this ELC and given spectrogram monitors for intraoperative use versus standard residency curriculum alone without intraoperative spectrogram monitors. We hypothesized that this intervention would result in lower inhaled anesthetic administration (measured by age-adjusted total minimal alveolar concentration [MAC] fraction and age-adjusted minimal alveolar concentration [aaMAC]) to patients ≥60 old during the postintervention period (the primary study outcome). To study this effect and to determine whether the 2 groups were administering similar anesthetic doses pre- versus postintervention, we compared aaMAC between control versus intervention group residents both before and after the intervention. To measure efficacy in the postintervention period, we included only those cases in the intervention group when the monitor was actually used. Multivariable linear mixed-effects modeling was performed for aaMAC fraction and hospital length of stay (LOS; a non-prespecified secondary outcome), with a random effect for individual resident. A multivariable linear mixed-effects model was also used in a sensitivity analysis to determine if there was a group (intervention versus control group) by time period (post- versus preintervention) interaction for aaMAC. Resident EEG knowledge difference (a prespecified secondary outcome) was compared with a 2-sided 2-group paired t test.

RESULTS

Postintervention, there was no significant aaMAC difference in patients cared for by the ELC group (n = 159 patients) versus control group (N = 325 patients; aaMAC difference = -0.03; 95% confidence interval [CI], -0.09 to 0.03; P =.32). In a multivariable mixed model, the interaction of time period (post- versus preintervention) and group (intervention versus control) led to a nonsignificant reduction of -0.05 aaMAC (95% CI, -0.11 to 0.01; P = .102). ELC group residents (N = 19) showed a greater increase in EEG knowledge test scores than control residents (N = 20) from before to after the ELC intervention (6-point increase; 95% CI, 3.50-8.88; P < .001). Patients cared for by the ELC group versus control group had a reduced hospital LOS (median, 2.48 vs 3.86 days, respectively; P = .024).

CONCLUSIONS

Although there was no effect on mean aaMAC, these results demonstrate that this EEG-ELC intervention increased resident knowledge and raise the possibility that it may reduce hospital LOS.

Volatile anesthetic agents for life-threatening pediatric asthma: A multicenter retrospective cohort study and narrative review

BACKGROUND

Volatile anesthetic agents are described as rescue therapy for children invasively ventilated for critical asthma. Yet, data are currently limited to case series.

AIMS

Using the Virtual Pediatric Systems database, we assessed children admitted to a pediatric intensive care unit invasively ventilated for life-threatening asthma and hypothesized ventilation duration and mortality rates would be lower for subjects exposed to volatile anesthetics compared with those without exposure.

METHODS

We performed a multicenter retrospective cohort study among nine institutions including children 5-17 years of age invasively ventilated for asthma from 2013 to 2019 with and without exposure to volatile anesthetics. Primary outcomes were ventilation duration and mortality. Secondary outcomes included patient characteristics, length of stay, and anesthetic-related adverse events. A subgroup analysis was performed evaluating children intubated ≥2 days.

RESULTS

Of 203 children included in study, there were 29 (14.3%) with and 174 (85.7%) without exposure to volatiles. No differences in odds of mortality (1.1, 95% CI: 0.3-3.9, p > .999) were observed. Subjects receiving volatiles experienced greater median difference in length of stay (4.8, 95% CI: 1.9-7.8 days, p < .001), ventilation duration (2.3, 95% CI: 1-3.3 days, p < .001), and odds of extracorporeal life support (9.1, 95% CI: 1.9-43.2, p = .009) than those without volatile exposure. For those ventilated ≥2 days, no differences were detected in mortality, ventilation duration, length of stay, arrhythmias, or acute renal failure. However, the odds of extracorporeal life support remained greater for those receiving volatiles (7.6, 95% CI: 1.3-44.5, p = .027). No children experienced malignant hyperthermia or hepatic failure after volatile exposure.

CONCLUSIONS

For intubated children for asthma, no differences in mechanical ventilation duration or mortality between those with and without volatile anesthetic exposure were observed. Although volatiles may represent a viable rescue therapy for severe cases of asthma, definitive, and prospective trials are still needed.

The Use of Bispectral Index Monitoring Does Not Change Intraoperative Exposure to Volatile Anesthetics in Children

The exposure of infants and children to volatile anesthetics, such as sevoflurane, has been a topic of concern with respect to the potential risk for long term neurocognitive effects. The primary objective of this study was to determine whether the perioperative utilization of Bispectral Index (BIS) monitoring alters the sevoflurane delivery and exposure to children. This is a prospective randomized trial of two groups of healthy ambulatory day surgery patients (2 to 12 years). The patients in both groups had the BIS applied soon after the induction of general anesthesia, but only the anesthesiologists in the group randomized to BIS visible were able to see the BIS values. All of the patients received general anesthesia with sevoflurane. This study found no difference in the overall exposure to sevoflurane between both groups (mean end-tidal sevoflurane level of 1.8 in both groups, P = 084). The duration of time in the recovery room, the time to meet discharge criteria, the Pediatric Agitation Emergence Delirium (PAED) scores and the Face, Legs, Activity, Cry, Consolability (FLACC) scores were not statistically different between the groups. The application and utilization of intraoperative BIS monitoring does not alter the sevoflurane administration nor the discharge readiness nor the recovery profile in healthy ambulatory children.

Sevoflurane exerts protective effects on liver ischemia/reperfusion injury by regulating NFKB3 expression via miR-9-5p

Hepatic ischemia/reperfusion (IR) injury is a critical contraindication of hepatobiliary surgery and results in severe liver damage. It is imperative to identify underlying pathophysiological mechanisms. In the current study, a rat model of liver IR was established to explore the mechanisms of sevoflurane during surgical intervention on IR. The detection of cytokines was performed using ELISA and reverse transcription-quantitative polymerase chain reaction and western blot assays were used to detect mRNA and protein expression levels, respectively. The target protein of microRNA (miR)-9-5p was identified by in vitro luciferase reporter assay. Cell apoptosis was detected by Annexin-V/propidium iodide and TUNEL staining assays. The results demonstrated that sevoflurane exerted protective effect against liver IR. Sevoflurane administration ameliorated a cytokine storm by decreasing serum levels of interleukin (IL)-1 and −6 and tumor necrosis factor (TNF)-α, and improved liver function was determined. IR-induced damage was mediated by an increase in transcription factor p65 expression and activation of the nuclear factor (NF)-κB signaling pathway, which were suppressed by sevoflurane treatment. In situ analysis predicted that NFKB3, encoding for p65, may be targeted by miR-9-5p and the hypothesis was verified by in vitro reporter assays using wild type and mutant sequences of the NFKB3 3′-untranslated region. Furthermore, pretreatment of hepatic tissue with a miR-9-5p mimic inhibited IR-associated injury as suggested by the decrease in the Suzuki score and decreased serum levels of TNF-α, IL-1 and IL-6. The results indicated that sevoflurane protected the liver from IR injury by increasing miR-9-5p expression and miR-9-5p may be a potential treatment target in IR.

Ferroptosis Contributes to Isoflurane Neurotoxicity

The underlying mechanisms of isoflurane neurotoxicity in the developing brain remain unclear. Ferroptosis is a recently characterized form of programmed cell death distinct from apoptosis or autophagy, characterized by iron-dependent reactive oxygen species (ROS) generation secondary to failure of glutathione-dependent antioxidant defenses. The results of the present study are the first to demonstrate in vitro that ferroptosis is a central mechanism contributing to isoflurane neurotoxicity. We observed in embryonic mouse primary cortical neuronal cultures (day-in-vitro 7) that 6 h of 2% isoflurane exposure was associated with decreased transcription and protein expression of the lipid repair enzyme glutathione peroxidase 4. In parallel, isoflurane exposure resulted in increased ROS generation, disruption in mitochondrial membrane potential, and cell death. These effects were significantly attenuated by pre-treatment with the selective ferroptosis inhibitor ferrostatin-1 (Fer-1). Collectively, these observations provide a novel mechanism for isoflurane-induced injury in the developing brain and suggest that pre-treatment with Fer-1 may be a potential clinical intervention for neuroprotection.

Comparison of the Analgesic Properties of Sevoflurane and Desflurane Using Surgical Pleth Index at Equi-Minimum Alveolar Concentration

Background: Traditionally, minimum alveolar concentration (MAC) has been used as the standard measure to compare the potencies of volatile anesthetics. However, it reflects the spinal mechanism of immobility rather than the subcortical mechanism of analgesia. Recently, the surgical pleth index (SPI) derived from photoplethysmographic waveform was shown to reflect the intraoperative analgesic component. This study was designed to compare the SPI values produced by equi-MAC of two commonly used volatile anesthetics, sevoflurane and desflurane. Methods: Seventy-two patients undergoing arthroscopic shoulder surgery were randomly assigned to two groups receiving either sevoflurane (n = 36) or desflurane (n = 36). General anesthesia was maintained with the respective volatile anesthetic only. A vaporizer was adjusted to maintain end-tidal anesthetic concentration at age-corrected 1.0 MAC throughout the study period. The SPI value as an analgesic estimate and the bispectral index (BIS) value as a hypnotic estimate were recorded at predefined time points during the standardized surgical procedure. Results: During the steady state of age-corrected 1.0 MAC, mean SPI values throughout the entire study period were significantly higher in the sevoflurane group than in the desflurane group (38.1 ± 12.8 vs. 30.7 ± 8.8, respectively, P = 0.005), and mean BIS values were significantly higher in the sevoflurane group than in the desflurane group (40.7 ± 5.8 vs. 36.8 ± 6.2, respectively, P = 0.008). Conclusions: Equi-MAC of sevoflurane and desflurane did not produce similar surgical pleth index values. Therefore, sevoflurane and desflurane may have different analgesic properties at equipotent concentrations.

Differential Effects of Toluene and Ethanol on Dopaminergic Neurons of the Ventral Tegmental Area

Drugs of abuse increase the activity of dopaminergic neurons of the ventral tegmental area (VTA), and output from the VTA is critical for both natural and drug-induced reward and reinforcement. Ethanol and the abused inhalant toluene both enhance VTA neuronal firing, but the mechanisms of this effect is not fully known. In this study, we used extracellular recordings to compare the actions of toluene and ethanol on DA VTA neurons. Both ethanol and toluene increased the firing rate of DA neurons, although toluene was ~100 times more potent than ethanol. The mixed ion channel blocker quinine (100 μM) blocked the increases in firing produced by ethanol and toluene, indicating some similarity in mechanisms of excitation. A mixture of antagonists of GABA and cholinergic receptors did not prevent toluene-induced or ethanol-induced excitation, and toluene-induced excitation was not altered by co-administration of ethanol, suggesting independent mechanisms of excitation for ethanol and toluene. Concurrent blockade of NMDA, AMPA, and metabotropic glutamate receptors enhanced the excitatory effect of toluene while having no significant effect on ethanol excitation. Nicotine increased firing of DA VTA neurons, and this was blocked by the nicotinic antagonist mecamylamine (1 μM). Mecamylamine did not alter ethanol or toluene excitation of firing but the muscarinic antagonist atropine (5 μM) or a combination of GABA antagonists (bicuculline and CGP35348, 10 μM each) reduced toluene-induced excitation without affecting ethanol excitation. The Ih current blocker ZD7288 abolished the excitatory effect of toluene but unlike the block of ethanol excitation, the effect of ZD7288 was not reversed by the GIRK channel blocker barium, but was reversed by GABA antagonists. These results demonstrate that the excitatory effects of ethanol and toluene have some similarity, such as block by quinine and ZD7288, but also indicate that there are important differences between these two drugs in their modulation by glutamatergic, cholinergic, and GABAergic receptors. These findings provide important information regarding the actions of abused inhalants on central reward pathways, and suggest that regulation of the activation of central dopamine pathways by ethanol and toluene partially overlap.

Attenuation of Isoflurane Preconditioning-Induced Acute Cardioprotection in Hypertensive Hypertrophied Hearts

OBJECTIVES

To evaluate the efficiency of isoflurane-induced anesthetic preconditioning and the role of mitochondrial manganese superoxide dismutase (MnSOD) in hypertensive hypertrophied hearts.

DESIGN

A prospective animal investigation.

SETTING

Medical center hospital research laboratory.

PARTICIPANTS

Male spontaneously hypertensive rats (SHRs) and normotensive control Wistar-Kyoto (WKY) rats.

INTERVENTIONS

All pentobarbital-anesthetized open-chest rats were subjected to a 45-minute left coronary artery occlusion followed by a 120-minute reperfusion. Before ischemia, both SHR and WKY rats were assigned randomly to receive a 30-minute exposure to 0.9% saline or 1.0 minimum alveolar concentration isoflurane.

MEASUREMENTS AND MAIN RESULTS

The myocardial infarct size, assessed as a percentage of the area at risk, was significantly greater in the hypertrophied SHRs than in the WKY rats (65.3%±8.7% v 51.8%±7.2%, p<0.05). Isoflurane preconditioning appreciably reduced the infarct size in the WKY hearts (30.9%±10.5%, p<0.05) but not in the SHR hearts. MnSOD protein expression and enzymatic activity were increased drastically in response to isoflurane exposure in the hearts of the WKY rats (p<0.05) but not in the SHRs.

CONCLUSIONS

Isoflurane-induced anesthetic preconditioning is attenuated in hypertensive hypertrophied hearts. This impairment may be associated with the loss of MnSOD augmentation during ischemia and reperfusion.

Case report: proximal tubule impairment following volatile anesthetic exposure

The safety of contemporary volatile anesthetic agents with respect to kidney function is well established, and growing evidence suggests that volatile anesthetics even protect against ischemic nephropathy. However, studies examining effects of volatile anesthetics on kidney function frequently demonstrate transient proteinuria and glycosuria following exposure to these agents, although the cause of these findings has not been thoroughly examined. We describe the case of a patient who underwent a neurosurgical procedure, then experienced glycosuria without hyperglycemia that resolved within days. Following a second neurosurgical procedure, the patient again developed glycosuria, now associated with ketonuria. Further examination demonstrated nonalbuminuric proteinuria in conjunction with urinary wasting of phosphate and potassium, indicative of proximal tubule impairment. We suggest that transient proximal tubule impairment may play a role in the proteinuria and glycosuria described following volatile anesthetic exposure and discuss the relationship between these observations and the ability of these agents to protect against ischemic nephropathy.

Isoflurane protects against human endothelial cell apoptosis by inducing sphingosine kinase-1 via ERK MAPK. Int J Mol Sci. 2012;13:977-993. [PMID: 22312298 PMCID: PMC3269732 DOI: 10.3390/ijms13010977]

Endothelial dysfunction is a major clinical problem affecting virtually every patient requiring critical care. Volatile anesthetics are frequently used during the perioperative period and protect the heart and kidney against ischemia and reperfusion injury. We aimed to determine whether isoflurane, the most commonly used volatile anesthetic in the USA, protects against endothelial apoptosis and necrosis and the mechanisms involved in this protection. Human endothelial EA.hy926 cells were pretreated with isoflurane or carrier gas (95% room air + 5% CO₂) then subjected to apoptosis with tumor necrosis factor-α or to necrosis with hydrogen peroxide. DNA laddering and in situ Terminal Deoxynucleotidyl Transferase Biotin-dUTP Nick-End Labeling (TUNEL) staining determined EA.hy926 cell apoptosis and percent LDH released determined necrosis. We also determined whether isoflurane modulates the expression and activity of sphingosine kinase-1 (SK1) and induces the phosphorylation of extracellular signal regulated kinase (ERK MAPK) as both enzymes are known to protect against cell death. Isoflurane pretreatment significantly decreased apoptosis in EA.hy926 cells as evidenced by reduced TUNEL staining and DNA laddering without affecting necrosis. Mechanistically, isoflurane induces the phosphorylation of ERK MAPK and increased SK1 expression and activity in EA.hy926 cells. Finally, selective blockade of SK1 (with SKI-II) or S1P₁ receptor (with W146) abolished the anti-apoptotic effects of isoflurane. Taken together, we demonstrate that isoflurane, in addition to its potent analgesic and anesthetic properties, protects against endothelial apoptosis most likely via SK1 and ERK MAPK activation. Our findings have significant clinical implication for protection of endothelial cells during the perioperative period and patients requiring critical care.

The use of a volatile anesthetic regimen protects against acute normovolemic hemodilution induced myocardial depression in patients with coronary artery disease

BACKGROUND

Previous studies indicated that acute normovolemic hemodilution (ANH) was associated with a depression of myocardial function in coronary surgery patients with baseline heart rate faster than 90 bpm. It was suggested that this phenomenon could be explained by the occurrence of myocardial ischemia. In the present study, we hypothesized that the cardioprotective properties of a volatile anesthetic regimen might protect against the ANH related myocardial functional impairment.

MATERIALS AND METHODS

Forty elective coronary surgery patients with baseline heart rate faster than 90 bpm were randomly allocated to receive different anesthetic regimens. Group A (n = 20) received midazolam-based anesthesia. Group B (n = 20) received a sevoflurane-based anesthesia. Five-lead electrocardiogram, pulse oximetry, capnography, radial arterial pressure, and Swan Ganz continuous thermodilution cardiac output via right internal jugular vein were monitored. Measurements were obtained before and after ANH. Data were compared using paired t test. All data were expressed as mean +/- SD. Data were considered significant if P < 0.05.

RESULTS

After ANH, systemic vascular resistance was slightly decreased in group A while there was a significant decrease in group B. In group A, cardiac output was slightly decreased from 5.07+/-1.17 l/min to 5.02+/-1.28 l/min after ANH, whereas in group B, cardiac output was significantly increased from 4.84+/-1.21 l/min to 6.02+/-1.28 l/min after ANH.

CONCLUSION

In coronary surgery patients, with baseline heart rate faster than 90 bpm, anesthesia with sevoflurane during ANH was associated with an improvement in myocardial function after ANH, which was not present in patients anesthetized with midazolam.

The TASK-1 two-pore domain K+ channel is a molecular substrate for neuronal effects of inhalation anesthetics

Despite widespread use of volatile general anesthetics for well over a century, the mechanisms by which they alter specific CNS functions remain unclear. Here, we present evidence implicating the two-pore domain, pH-sensitive TASK-1 channel as a target for specific, clinically important anesthetic effects in mammalian neurons. In rat somatic motoneurons and locus coeruleus cells, two populations of neurons that express TASK-1 mRNA, inhalation anesthetics activated a neuronal K(+) conductance, causing membrane hyperpolarization and suppressing action potential discharge. These membrane effects occurred at clinically relevant anesthetic levels, with precisely the steep concentration dependence expected for anesthetic effects of these compounds. The native neuronal K(+) current displayed voltage- and time-dependent properties that were identical to those mediated by the open-rectifier TASK-1 channel. Moreover, the neuronal K(+) channel and heterologously expressed TASK-1 were similarly modulated by extracellular pH. The decreased cellular excitability associated with TASK-1 activation in these cell groups probably accounts for specific CNS effects of anesthetics: in motoneurons, it likely contributes to anesthetic-induced immobilization, whereas in the locus coeruleus, it may support analgesic and hypnotic actions attributed to inhibition of those neurons.

Presynaptic and postsynaptic actions of halothane at glutamatergic synapses in the mouse hippocampus

Whole-cell patch-clamp recordings in adult mouse hippocampal slices were used to test the mechanism by which the volatile anesthetic halothane inhibits glutamate receptor-mediated synaptic transmission. Non-N-methyl-D-aspartate (nonNMDA) and NMDA receptor-mediated currents in CA1 pyramidal cells were pharmacologically isolated by bath application of D,L-2-amino-5-phosphonovaleric acid (APV; 100 microM) or 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX; 5 microM), respectively. Halothane blocked both nonNMDA and NMDA receptor-mediated excitatory postsynaptic currents (EPSCs) to a similar extent (IC50 values of 0.66 and 0.57 mM, respectively). Partial blockade of the EPSCs by lowering the extracellular concentration of calcium ([Ca2+]o), but not by application of CNQX (1 microM), was accompanied by an increase in paired-pulse facilitation (PPF). Halothane-induced blockade of the EPSCs also was associated with an increase in PPF. The effects of halothane on alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) and NMDA receptor-mediated currents induced by agonist iontophoresis, were compared. AMPA-induced currents were blocked with an IC50 of 1.7 mM. NMDA-induced currents were significantly less sensitive to halothane (IC50 of 5.9 mM). The effect of halothane on iontophoretic AMPA dose-response curves was tested. Halothane suppressed the maximal response to AMPA without affecting its EC50, suggesting a noncompetitive mechanism of inhibition. All effects of halothane were reversible upon termination of the exposure to the drug. These data suggest that halothane blocks central glutamatergic synaptic transmission by presynaptically inhibiting glutamate release and postsynaptically blocking the AMPA subtype of glutamate receptors.