Flumazenil improves cognitive and neuromotor emergence and attenuates shivering after halothane-, enflurane- and isoflurane-based anesthesia

Preoperative frailty tendency predicts delirium occurrence in older people undergoing spinal surgery

BACKGROUND

This prospective cohort study focused on the predictive value of frailty or pre-frailty assessed by Edmonton Frailty Scale (EFS) for postoperative delirium in spinal surgery patients.

METHODS

The primary outcome measurement was postoperative delirium (POD) evaluated by Confusion Assessment Method at day 1, day 2, and day 3 after the surgery. Secondary outcomes included severity and duration of POD, severe postoperative pain measured by Faces Pain Scale-Revised. Patients scheduled for elective spinal surgery were enrolled and assessed for frailty by EFS before surgery. Demographic data, preoperative, intraoperative, and postoperative information were collected.

RESULTS

231 out of 325 patients were enrolled and analyzed in this study at last. The cohort with 36.8% being frail and 28.5% being vulnerable. Postoperative delirium was detected in 41 in 231 patients. Multivariate logistic regression analysis revealed that vulnerable to frailty (OR = 4.681, 95% CI: 1.199 to 18.271, P = 0.026), after adjusted duration of surgery more than 3 h, using flumazenil at the end of surgery, using butorphanol only in postoperative patient-controlled intravenous analgesia, moderate-to-severe pain at day 1 and 2, is a strong predictor of postoperative delirium. Frailty was associated with longer duration (frailty vs. fit, P = 0.364) and stronger severity of postoperative delirium in the first two days (P < 0.001). High EFS score was independent risk factor of severe postoperative pain (Frailty vs. Fit: OR = 5.007, 95% CI: 1.903 to 13.174, P = 0.001; Vulnerable vs. Fit: OR = 2.525, 95% CI: 1.008 to 6.329, P = 0.048). In stratified tests, Sufentanil regimen in intravenous PCA significantly increase the proportion of POD in vulnerable group (P = 0.030), instead of frailty group (P = 0.872) or fit group (P = 0.928).

CONCLUSIONS

Frailty can increase the risk, severity, duration of delirium and severe postoperative pain in the first 3 days after surgery of patients.

TRIAL REGISTRATION

The protocol of this study has been approved by the Ethic Committee of Shanghai Changzheng Hospital (Approval file number: 2022SL044) and informed consent was obtained from all the patients. The trial was retrospectively registered at chictr.org.cn (ChiCTR2300073306) on 6th July 2023.

Effect of Flumazenil on Emergence Agitation after Orthognathic Surgery: A Randomized Controlled Trial

Flumazenil, a gamma-aminobutyric acid receptor antagonist, can promote arousal even under general anesthesia without the use of benzodiazepines. We hypothesized that flumazenil could promote arousal and reduce emergence agitation in patients undergoing orthognathic surgery with sevoflurane anesthesia. One hundred and two patients were randomly allocated to the control or flumazenil group. Saline or flumazenil was administered at the end of the surgery. The incidence of emergence agitation was measured by using Aono’s four-point scale, with scores of 3 and 4 indicating emergence agitation. The primary outcome was the incidence of emergence agitation. Secondary outcomes included duration of emergence agitation and time intervals between the discontinuation of anesthetics, first response, extubation, and post-anesthesia care-unit discharge readiness. The incidence of emergence agitation was 58.3% and 38.9% in the control and flumazenil groups, respectively, but it was not statistically significant. However, the duration of emergence agitation was shorter in the flumazenil group (p = 0.012). There were no significant differences in the time intervals between the discontinuation of anesthetics, first response, and extubation. Although flumazenil did not reduce the incidence of emergence agitation in patients undergoing orthognathic surgery with sevoflurane anesthesia, it can be considered as an option for awakening patients in terms of improving emergence profiles.

The Neural Circuits Underlying General Anesthesia and Sleep

General anesthesia is characterized by loss of consciousness, amnesia, analgesia, and immobility. Important molecular targets of general anesthetics have been identified, but the neural circuits underlying the discrete end points of general anesthesia remain incompletely understood. General anesthesia and natural sleep share the common feature of reversible unconsciousness, and recent developments in neuroscience have enabled elegant studies that investigate the brain nuclei and neural circuits underlying this important end point. A common approach to measure cortical activity across the brain is electroencephalogram (EEG), which can reflect local neuronal activity as well as connectivity among brain regions. The EEG oscillations observed during general anesthesia depend greatly on the anesthetic agent as well as dosing, and only some resemble those observed during sleep. For example, the EEG oscillations during dexmedetomidine sedation are similar to those of stage 2 nonrapid eye movement (NREM) sleep, but high doses of propofol and ether anesthetics produce burst suppression, a pattern that is never observed during natural sleep. Sleep is primarily driven by withdrawal of subcortical excitation to the cortex, but anesthetics can directly act at both subcortical and cortical targets. While some anesthetics appear to activate specific sleep-active regions to induce unconsciousness, not all sleep-active regions play a significant role in anesthesia. Anesthetics also inhibit cortical neurons, and it is likely that each class of anesthetic drugs produces a distinct combination of subcortical and cortical effects that lead to unconsciousness. Conversely, arousal circuits that promote wakefulness are involved in anesthetic emergence and activating them can induce emergence and accelerate recovery of consciousness. Modern neuroscience techniques that enable the manipulation of specific neural circuits have led to new insights into the neural circuitry underlying general anesthesia and sleep. In the coming years, we will continue to better understand the mechanisms that generate these distinct states of reversible unconsciousness.

The effects of flumazenil on ventilatory and recovery characteristics in horses following midazolam-ketamine induction and isoflurane anaesthesia

BACKGROUND

Flumazenil antagonises the actions of benzodiazepines. There has been no prior research specifically investigating this anaesthetic reversal agent for horses.

OBJECTIVES

To determine the effects of flumazenil administration in horses on (a) ventilatory parameters after midazolam-ketamine induction and maintenance with isoflurane in oxygen and on (b) the characteristics of recovery from general anaesthesia.

STUDY DESIGN

Blinded, randomised, crossover experiment.

METHODS

Six horses were randomly assigned to receive high-dose flumazenil (F_high , 20 µg/kg), low-dose flumazenil (F_low , 10 µg/kg) and saline (control). Cardioventilatory parameters were monitored. After 90 minutes of isoflurane anaesthesia, a bolus of F_high , F_low or saline was administered i.v. The horses were recovered using head and tail rope assistance. The times to first movement, to achievement of sternal recumbency, to the first attempt to stand and the total recovery time were determined. The recovery quality was evaluated using a 115-point recovery scoring system. The cardioventilatory parameters and recovery times were analysed using mixed-effects regression analyses. Intraclass correlation (ICC) analysis was used to evaluate the recovery scores. A Mann-Whitney U test assessed the relationship between recovery score and flumazenil administration.

RESULTS

A significant difference with flumazenil administration was found for SpO₂ , mean arterial pressure, I:E ratio, minute volume of ventilation (MV) and peak inspiratory pressure. There was a significant difference with flumazenil administration for the time to sternal recumbency, the time to the first attempt to rise and the total recovery time. There was no significant difference in total recovery score with flumazenil administration.

MAIN LIMITATIONS

Plasma levels of midazolam and flumazenil were not obtained.

CONCLUSIONS

Flumazenil has a dose-dependent effect on MV and recovery time, which may make it useful in cases for which a prolonged anaesthetic recovery is undesirable.

Escape From Oblivion: Neural Mechanisms of Emergence From General Anesthesia

The question of how general anesthetics suppress consciousness has persisted since the mid-19th century, but it is only relatively recently that the field has turned its focus to a systematic understanding of emergence. Once assumed to be a purely passive process, spontaneously occurring as residual levels of anesthetics dwindle below a critical value, emergence from general anesthesia has been reconsidered as an active and controllable process. Emergence is driven by mechanisms that can be distinct from entry to the anesthetized state. In this narrative review, we focus on the burgeoning scientific understanding of anesthetic emergence, summarizing current knowledge of the neurotransmitter, neuromodulators, and neuronal groups that prime the brain as it prepares for its journey back from oblivion. We also review evidence for possible strategies that may actively bias the brain back toward the wakeful state.

Effects of γ-Aminobutyric Acid Type A Receptor Modulation by Flumazenil on Emergence from General Anesthesia

BACKGROUND

Transitions into conscious states are partially mediated by inactivation of sleep networks and activation of arousal networks. Pharmacologic hastening of emergence from general anesthesia has largely focused on activating subcortical monoaminergic networks, with little attention on antagonizing the γ-aminobutyric acid type A receptor (GABAAR). As the GABAAR mediates the clinical effects of many common general anesthetics, the authors hypothesized that negative GABAAR modulators would hasten emergence, possibly via cortical networks involved in sleep.

METHODS

The authors investigated the capacity of the benzodiazepine rescue agent, flumazenil, which had been recently shown to promote wakefulness in hypersomnia patients, to alter emergence. Using an in vivo rodent model and an in vitro GABAAR heterologous expression system, they measured flumazenil's effects on behavioral, neurophysiologic, and electrophysiologic correlates of emergence from isoflurane anesthesia.

RESULTS

Animals administered intravenous flumazenil (0.4 mg/kg, n = 8) exhibited hastened emergence compared to saline-treated animals (n = 8) at cessation of isoflurane anesthesia. Wake-like electroencephalographic patterns occurred sooner and exhibited more high-frequency electroencephalography power after flumazenil administration (median latency ± median absolute deviation: 290 ± 34 s) compared to saline administration (473 ± 186 s; P = 0.042). Moreover, in flumazenil-treated animals, there was a decreased impact on postanesthesia sleep. In vitro experiments in human embryonic kidney-293T cells demonstrated that flumazenil inhibited isoflurane-mediated GABA current enhancement (n = 34 cells, 88.7 ± 2.42% potentiation at 3 μM). Moreover, flumazenil exhibited weak agonist activity on the GABAAR (n = 10 cells, 10.3 ± 3.96% peak GABA EC20 current at 1 μM).

CONCLUSIONS

Flumazenil can modulate emergence from isoflurane anesthesia. The authors highlight the complex role GABAARs play in mediating consciousness and provide mechanistic links between emergence from anesthesia and arousal.

Effect of flumazenil on recovery from anesthesia and the bispectral index after sevoflurane/fentanyl general anesthesia in unpremedicated patients

Background

Benzodiazepines have a hypnotic/sedative effect through the inhibitory action of γ-aminobutyric acid type A receptor. Flumazenil antagonizes these effects via competitive inhibition, so it has been used to reverse the effect of benzodiazepines. Recently, flumazenil has been reported to expedite recovery from propofol/remifentanil and sevoflurane/remifentanil anesthesia without benzodiazepines. Endogenous benzodiazepine ligands (endozepines) were isolated in several tissues of individuals who had not received benzodiazepines.

Methods

Forty-five healthy unpremedicated patients were randomly allocated to either flumazenil or a control groups. Each patient received either a single dose of 0.3 mg of flumazenil (n = 24) or placebo (n = 21). After drug administration, various recovery parameters and bispectral index (BIS) values in the flumazenil and control groups were compared.

Results

Mean time to spontaneous respiration, eye opening on verbal command, hand squeezing on verbal command, extubation and time to date of birth recollection were significantly shorter in the flumazenil group than in the control group (P = 0.004, 0.007, 0.005, 0.042, and 0.016, respectively). The BIS value was significantly higher in flumazenil group than in the control group beginning 6 min after flumazenil administration.

Conclusions

Administration of a single dose of 0.3 mg of flumazenil to healthy, unpremedicated patients at the end of sevoflurane/fentanyl anesthesia without benzodiazepines resulted in earlier emergence from anesthesia and an increase in the BIS value. This may indicate that flumazenil could have an antagonistic effect on sevoflurane or an analeptic effect through endozepine-dependent mechanisms.

Flumazenil expedites recovery from sevoflurane/remifentanil anaesthesia when administered to healthy unpremedicated patients

BACKGROUND AND OBJECTIVE

To investigate the hypothesis that 0.3 mg flumazenil administered to healthy unpremedicated patients at the end of deep surgical sevoflurane/remifentanil anaesthesia would expedite recovery. Flumazenil, an imidazobenzodiazepine derivative, antagonizes the hypnotic/sedative effects of benzodiazepines on γ-aminobutyric acid receptors. However, endogenous benzodiazepine ligands (endozepines) were isolated in mammalian tissues of individuals who had not received benzodiazepines.

METHODS

Twenty-four healthy unpremedicated patients, scheduled to undergo elective surgery requiring general anaesthesia, were randomly allocated to receive either a single dose of 0.3 mg flumazenil (n = 14) or placebo (n = 10) intravenously at the end of the surgical procedure just before the discontinuation of the volatile anaesthetic. After study drug administration, the authors compared various recovery parameters in the flumazenil and control groups.

RESULTS

Median time to spontaneous respiration, eye opening on verbal command, extubation and time to date of birth recollection was significantly shorter in the flumazenil group than in the control group [2.5 min (2.0-3.0) vs. 7.0 min (6.8-8.3), 3.4 min (3.0-4.0) vs. 8.1 min (6.9-10.2), 4.0 min (3.0-5.0) vs. 9.0 min (7.0-10.8) and 4.7 min (4.0-5.0) vs. 10.3 min (8.0-12.0), respectively].

CONCLUSION

Administration of a single dose of 0.3 mg flumazenil to healthy unpremedicated patients at the end of sevoflurane/remifentanil anaesthesia results in earlier emergence from anaesthesia and significantly expedites recovery. This could redefine the role of flumazenil in general anaesthesia, implicating endozepine-dependent mechanisms.

GABA(A) positive modulator and NMDA antagonist-like discriminative stimulus effects of isoflurane vapor in mice

RATIONALE

Several neurotransmitter systems have been hypothesized to be involved in the in vivo effects of volatile anesthetics. Drug discrimination may represent a novel procedure to explore the neurochemical systems underlying the sub-anesthetic behavioral effects of these compounds.

OBJECTIVES

The purpose of the present study was to examine the contribution of GABA(A) and NMDA receptors to the discriminative stimulus effects of a behaviorally active sub-anesthetic concentration of isoflurane vapor.

METHODS

Sixteen B6SJLF1/J mice were trained to discriminate 10 min of exposure to 6,000 ppm isoflurane vapor from air. Substitution tests were conducted with volatile anesthetics, abused vapors, GABA(A) positive modulators, NMDA antagonists, and nitrous oxide.

RESULTS

The volatile anesthetics, enflurane and halothane as well as the abused vapors toluene and 1,1,1-trichloroethane fully substituted for isoflurane. The GABA(A) positive modulators, pentobarbital, midazolam, and zaleplon but not the direct GABA(A) agonist, muscimol, produced high levels of partial substitution for isoflurane. The anticonvulsant, valproic acid fully substituted for isoflurane but a second, tiagabine, did not substitute. The competitive NMDA antagonist, CGS-19755, fully and the non-competitive NMDA antagonist, dizocilpine, partially substituted for isoflurane. The glycine-site NMDA antagonist, L-701,324 did not substitute for isoflurane. Gamma-hydroxybutric acid and nitrous oxide gas also failed to substitute for isoflurane.

CONCLUSIONS

The discriminative stimulus effects of sub-anesthetic concentrations of isoflurane vapor are shared by other vapor anesthetics and abused inhalants. The discriminative stimulus effects of isoflurane vapor appear to be mediated by both positive allosteric modulation of GABA(A) receptors as well as antagonism of NMDA receptors.

Single-Dose Parenteral Pharmacological Interventions for the Prevention of Postoperative Shivering: A Quantitative Systematic Review of Randomized Controlled Trials

Shivering is a frequent complication in the postoperative period. The relative efficacy of pharmacological interventions to prevent this phenomenon is not well understood. We performed a systematic search for full reports of randomized comparisons of prophylactic, parenteral, single-dose antishivering interventions with inactive control (placebo or no treatment). Variable doses were converted to fixed doses. Dichotomous data on the absence of shivering were analyzed by using relative benefit (RB) and number needed to treat (NNT) with 95% confidence intervals (CI). Data from 27 trials (1348 adults received an antishivering intervention; 931 were controls) were analyzed. The average incidence of shivering in controls was extremely frequent (52%). Clonidine 65-300 microg (1078 patients), meperidine 12.5-35 mg (250 patients), tramadol 35-220 mg (250 patients), and nefopam 6.5-11 mg (204 patients) were tested in at least 3 trials each. All were more effective than control. For clonidine, meperidine, and nefopam, there was some weak evidence of dose responsiveness. For small-dose clonidine (65-110 microg), the RB compared with control was 1.32 (95% CI, 1.16-1.51); for medium-dose clonidine (140-150 microg), the RB was 1.83 (95% CI, 1.47-2.27); and for large-dose clonidine (220-300 microg), the RB was 1.52 (95% CI, 1.30-1.78). For all clonidine regimens combined, the RB was 1.58 (95% CI, 1.43-1.74), with an NNT of 3.7. For all meperidine regimens combined, the RB was 1.67 (95% CI, 1.37-2.03), with an NNT of 3. For all tramadol regimens combined, the RB was 1.93 (95% CI, 1.56-2.39), with an NNT of 2.2. For all nefopam regimens combined, the RB was 2.62 (95% CI, 2.02-3.40), with an NNT of 1.7. Methylphenidate, midazolam, dolasetron, ondansetron, physostigmine, urapidil, and flumazenil were tested in no more than 3 trials each, with a limited number of patients.