Towards a better understanding of anesthesia emergence mechanisms: Research and clinical implications

Regulating the activity of GABAergic neurons in the ventral pallidum alters the general anesthesia effect of propofol

The full mechanism of action of propofol, a commonly administered intravenous anesthetic drug in clinical practice, remains elusive. The focus of this study was the role of GABAergic neurons which are the main neuron group in the ventral pallidum (VP) closely associated with anesthetic effects in propofol anesthesia. The activity of VP GABAergic neurons following propofol anesthesia in Vgat-Cre mice was observed via detecting c-Fos immunoreactivity by immunofluorescence and western blotting. Subsequently, chemogenetic techniques were employed in Vgat-Cre mice to regulate the activity of VP GABAergic neurons. The role of VP GABAergic neurons in generating the effects of general anesthesia induced by intravenous propofol was further explored through behavioral tests of the righting reflex. The results revealed that c-Fos expression in VP GABAergic neurons in Vgat-Cre mice dramatically decreased after propofol injection. Further studies demonstrated that chemogenetic activation of VP GABAergic neurons during propofol anesthesia shortened the duration of anesthesia and promoted wakefulness. Conversely, the inhibition of VP GABAergic neurons extended the duration of anesthesia and facilitated the effects of anesthesia. The results obtained in this study suggested that regulating the activity of GABAergic neurons in the ventral pallidum altered the effect of propofol on general anesthesia.

Development and validation of a reinforcement learning model for ventilation control during emergence from general anesthesia

Ventilation should be assisted without asynchrony or cardiorespiratory instability during anesthesia emergence until sufficient spontaneous ventilation is recovered. In this multicenter cohort study, we develop and validate a reinforcement learning-based Artificial Intelligence model for Ventilation control during Emergence (AIVE) from general anesthesia. Ventilatory and hemodynamic parameters from 14,306 surgical cases at an academic hospital between 2016 and 2019 are used for training and internal testing of the model. The model's performance is also evaluated on the external validation cohort, which includes 406 cases from another academic hospital in 2022. The estimated reward of the model's policy is higher than that of the clinicians' policy in the internal (0.185, the 95% lower bound for best AIVE policy vs. -0.406, the 95% upper bound for clinicians' policy) and external validation (0.506, the 95% lower bound for best AIVE policy vs. 0.154, the 95% upper bound for clinicians' policy). Cardiorespiratory instability is minimized as the clinicians' ventilation matches the model's ventilation. Regarding feature importance, airway pressure is the most critical factor for ventilation control. In conclusion, the AIVE model achieves higher estimated rewards with fewer complications than clinicians' ventilation control policy during anesthesia emergence.

The effect of aminophylline on the recovery profile after hysterectomy: A randomized controlled double-blinded study

Background and Aims

In anesthesia practice, aminophylline is clinically used to treat bronchospasm. However, due to its antagonistic effect on adenosine, studies have recently focused on the drug's ability to enhance the recovery profile. The aim of this study was to investigate the hypothesis that the administration of aminophylline leads to better recovery after general anesthesia in hysterectomy.

Methods

This randomized controlled double-blinded study, was conducted at Alzahra academic hospital in Guilan, Iran. During December 2022 to March 2023, 70 eligible women scheduled for elective abdominal hysterectomy were divided into two groups. Group A: received 3 mg/kg IV aminophylline diluted in 100 mL of normal saline and Group C: received 100 mL IV normal saline. The time to recovery of consciousness, tracheal extubation and discharge from post anesthesia care unit were recorded. In addition, heart rate, and mean arterial blood pressure were measured at 10 point times including; baseline (T0), immediately before the administration of aminophylline (T1), every 5 min until the end of the surgery(T2,T3,T4,T5,T6), and every 15 min in PACU(T7,T8,T9).

Results

There was no significant difference in terms of demographic data between the study groups. Comparing the two groups, the time of ROC was shorter in Group A than group C; 5.95 ± 1.12 and 8.5 ± 1.77 for Groups A and C, respectively (p < 0.001). The extubation time was shorter in Group A than group C; 7.79 ± 1.48 and 10.55 ± 3.02, for Groups A and C, respectively (p < 0.001). In addition, the discharge time was also shorter in group A than Group C; 30.17 ± 5.24 and 37.57 ± 4.41 for Groups A and C, respectively (p < 0.001). Not serious side effects were reported among 71.4% of cases in Group A and 51.4% in Group C (p = 0.086).

Conclusion

Administration of aminophylline at a dose of 3 mg/kg IV improves the recovery profile after abdominal hysterectomy without serious adverse effects.

The impact of emergence delirium on hospital length of stay for children who underwent tonsillectomy/adenotonsillectomy: an observational retrospective study

BACKGROUND

Emergence Delirium (ED) is a combination of disturbance of perception and psychomotor agitation that is common in pediatric patients after general anesthesia, especially at preschool age. Since the effect of ED on the length of stay has been studied in adults but infrequently in children, the aim of this study was to investigate the relationship between ED and length of stay in this population.

METHODS

A single center, retrospective, observational study was carried out in children who underwent tonsillectomy or adenotonsillectomy. The Pediatric Anesthesia Emergence Delirium (PAED) scale was used to assess ED. In addition to the time to hospital discharge (time frame 24 hours), drugs used, comorbidities, early postoperative complications, and pain were investigated if potentially associated with the complication.

RESULTS

Four hundred sixteen children aged from 1.5 to 10 years (183 female, 233 male) were included. ED occurred in 25.5% of patients (n = 106). Patients were divided into the ED group and the No-ED group. The discharge time was similar in both groups. No significant differences were observed in the frequency of postoperative complications. The use of fentanyl or dexmedetomidine did not affect ED occurrence. The frequency of pain was greater in the ED group, both in the recovery room and in the ward (p = 0.01).

CONCLUSIONS

The occurrence of ED in children after tonsillectomy/adenotonsillectomy did not extend the length of stay.

Spectral EEG correlations from the different phases of general anesthesia

Introduction

Electroencephalography (EEG) signals contain transient oscillation patterns commonly used to classify brain states in responses to action, sleep, coma or anesthesia.

Methods

Using a time-frequency analysis of the EEG, we search for possible causal correlations between the successive phases of general anesthesia. We hypothesize that it could be possible to anticipate recovery patterns from the induction or maintenance phases. For that goal, we track the maximum power of the α-band and follow its time course.

Results and discussion

We quantify the frequency shift of the α-band during the recovery phase and the associated duration. Using Pearson coefficient and Bayes factor, we report non-significant linear correlation between the α-band frequency and duration shifts during recovery and the presence of the δ or the α rhythms during the maintenance phase. We also found no correlations between the α-band emergence trajectory and the total duration of the flat EEG epochs (iso-electric suppressions) induced by a propofol bolus injected during induction. Finally, we quantify the instability of the α-band using the mathematical total variation that measures possible deviations from a flat line. To conclude, the present correlative analysis shows that EEG dynamics extracted from the initial and maintenance phases of general anesthesia cannot anticipate both the emergence trajectory and the extubation time.

Complexity of Brain Dynamics as a Correlate of Consciousness in Anaesthetized Monkeys

The use of anaesthesia is a fundamental tool in the investigation of consciousness. Anesthesia procedures allow to investigate different states of consciousness from sedation to deep anesthesia within controlled scenarios. In this study we use information quantifiers to measure the complexity of electrocorticogram recordings in monkeys. We apply these metrics to compare different stages of general anesthesia for evaluating consciousness in several anesthesia protocols. We find that the complexity of brain activity can be used as a correlate of consciousness. For two of the anaesthetics used, propofol and medetomidine, we find that the anaesthetised state is accompanied by a reduction in the complexity of brain activity. On the other hand we observe that use of ketamine produces an increase in complexity measurements. We relate this observation with increase activity within certain brain regions associated with the ketamine used doses. Our measurements indicate that complexity of brain activity is a good indicator for a general evaluation of different levels of consciousness awareness, both in anesthetized and non anesthetizes states.

Historical and Modern Evidence for the Role of Reward Circuitry in Emergence

Increasing evidence supports a role for brain reward circuitry in modulating arousal along with emergence from anesthesia. Emergence remains an important frontier for investigation, since no drug exists in clinical practice to initiate rapid and smooth emergence. This review discusses clinical and preclinical evidence indicating a role for two brain regions classically considered integral components of the mesolimbic brain reward circuitry, the ventral tegmental area and the nucleus accumbens, in emergence from propofol and volatile anesthesia. Then there is a description of modern systems neuroscience approaches to neural circuit investigations that will help span the large gap between preclinical and clinical investigation with the shared aim of developing therapies to promote rapid emergence without agitation or delirium. This article proposes that neuroscientists include models of whole-brain network activity in future studies to inform the translational value of preclinical investigations and foster productive dialogues with clinician anesthesiologists.

EEG monitoring during anesthesia in children aged 0 to 18 months: amplitude-integrated EEG and age effects

Background

The amplitude-integrated EEG (aEEG) is a widely used monitoring tool in neonatology / pediatric intensive care. It takes into account the amplitudes, but not the frequency composition, of the EEG. Advantages of the aEEG are clear criteria for interpretation and time compression. During the first year of life, the electroencephalogram (EEG) during sedation / anesthesia changes from a low-differentiated to a differentiated EEG; higher-frequency waves develop increasingly. There are few studies on the use of aEEG during pediatric anesthesia. A systematic evaluation of the aEEG in defined EEG stages during anesthesia / sedation is not yet available. Parameters of pediatric EEGs (power, median frequency, spectral edge frequency) recorded during anesthesia and of the corresponding aEEGs (upper and lower value of the aEEG trace) should be examined for age-related changes. Furthermore, it should be examined whether the aEEG can distinguish EEG stages of sedation / anesthesia in differentiated EEGs.

Methods

In a secondary analysis of a prospective observational study EEGs and aEEGs (1-channel recordings, electrode positions on forehead) of 50 children (age: 0–18 months) were evaluated. EEG stages: A (awake), Slow EEG, E2, F0, and F1 in low-differentiated EEGs and A (awake), B0–2, C0–2, D0–2, E0–2, F0–1 in differentiated EEGs.

Results

Median and spectral edge frequency increased significantly with age (p < 0.001 each). In low-differentiated EEGs, the power of the Slow EEG increased significantly with age (p < 0.001). In differentiated EEGs, the power increased significantly with age in each of the EEG stages B1 to E1 (p = 0.04, or less), and the upper and lower values of the aEEG trace increased with age (p < 0.001). A discriminant analysis using the upper and lower values of the aEEG showed that EEG epochs from the stages B1 to E1 were assigned to the original EEG stage in only 19.3% of the cases. When age was added as the third variable, the rate of correct reclassifications was 28.5%.

Conclusions

The aEEG was not suitable for distinguishing EEG stages above the burst suppression range. For this purpose, the frequency composition of the EEG should be taken into account.

Dopamine D1 Receptor in the Nucleus Accumbens Modulates the Emergence from Propofol Anesthesia in Rat

It has been reported that systemic activation of D1 receptors promotes emergence from isoflurane-induced unconsciousness, suggesting that the central dopaminergic system is involved in the process of recovering from general anesthesia. The nucleus accumbens (NAc) contains abundant GABAergic medium spiny neurons (MSNs) expressing the D1 receptor (D1R), which plays a key role in sleep-wake behavior. However, the role of NAc D1 receptors in the process of emergence from general anesthesia has not been identified. Here, using real-time in vivo fiber photometry, we found that neuronal activity in the NAc was markedly disinhibited during recovery from propofol anesthesia. Subsequently, microinjection of a D1R selective agonist (chloro-APB hydrobromide) into the NAc notably reduced the time to emerge from propofol anesthesia with a decrease in δ-band power and an increase in β-band power evident in the cortical electroencephalogram. These effects were prevented by pretreatment with a D1R antagonist (SCH-23390). Whole-cell patch clamp recordings were performed to further explore the cellular mechanism underlying the modulation of D1 receptors on MSNs under propofol anesthesia. Our data primarily demonstrated that propofol increased the frequency and prolonged the decay time of spontaneous inhibitory postsynaptic currents (sIPSCs) and miniature IPSCs (mIPSCs) of MSNs expressing D1 receptors. A D1R agonist attenuated the effect of propofol on the frequency of sIPSCs and mIPSCs, and the effects of the agonist were eliminated by preapplication of SCH-23390. Collectively, these results indicate that modulation of the D1 receptor on the activity of NAc MSNs is vital for emergence from propofol-induced unconsciousness.

Preoptic Area Modulation of Arousal in Natural and Drug Induced Unconscious States

The role of the hypothalamic preoptic area (POA) in arousal state regulation has been studied since Constantin von Economo first recognized its importance in the early twentieth century. Over the intervening decades, the POA has been shown to modulate arousal in both natural (sleep and wake) as well as drug-induced (anesthetic-induced unconsciousness) states. While the POA is well known for its role in sleep promotion, populations of wake-promoting neurons within the region have also been identified. However, the complexity and molecular heterogeneity of the POA has made distinguishing these two populations difficult. Though multiple lines of evidence demonstrate that general anesthetics modulate the activity of the POA, the region's heterogeneity has also made it challenging to determine whether the same neurons involved in sleep/wake regulation also modulate arousal in response to general anesthetics. While a number of studies show that sleep-promoting POA neurons are activated by various anesthetics, recent work suggests this is not universal to all arousal-regulating POA neurons. Technical innovations are making it increasingly possible to classify and distinguish the molecular identities of neurons involved in sleep/wake regulation as well as anesthetic-induced unconsciousness. Here, we review the current understanding of the POA's role in arousal state regulation of both natural and drug-induced forms of unconsciousness, including its molecular organization and connectivity to other known sleep and wake promoting regions. Further insights into the molecular identities and connectivity of arousal-regulating POA neurons will be critical in fully understanding how this complex region regulates arousal states.

Delayed Emergence from Anesthesia: What We Know and How We Act

The emergence from anesthesia is the stage of general anesthesia featuring the patient's progression from the unconsciousness status to wakefulness and restoration of consciousness. This complex process has precise neurobiology which differs from that of induction. Despite the medications commonly used in anesthesia allow recovery in a few minutes, a delay in waking up from anesthesia, called delayed emergence, may occur. This phenomenon is associated with delays in the operating room, and an overall increase in costs. Together with the emergence delirium, the phenomenon represents a manifestation of inadequate emergence. Nevertheless, in delayed emergence, the transition from unconsciousness to complete wakefulness usually occurs along a normal trajectory, although slowed down. On the other hand, this awakening trajectory could proceed abnormally, possibly culminating in the manifestation of emergence delirium. Clinically, delayed emergence often represents a challenge for clinicians who must make an accurate diagnosis of the underlying cause to quickly establish appropriate therapy. This paper aimed at presenting an update on the phenomenon, analyzing its causes. Diagnostic and therapeutic strategies are addressed. Finally, therapeutic perspectives on the "active awakening" are reported.

Awareness during emergence from anesthesia: Features and future research directions

The anesthesia awareness with recall (AAWR) phenomenon represents a complication of general anesthesia consisting of memorization of intraoperative events reported by the patient immediately after the end of surgery or at a variable distance from it. Approximately 20% of AAWR cases occur during emergence from anesthesia. Clinically, these unexpected experiences are often associated with distress especially due to a sense of paralysis. Indeed, although AAWR at the emergence has multiple causes, in the majority of cases the complication develops when the anesthesia plan is too early lightened at the end of anesthesia and there is a lack of use, or misuse, of neuromuscular monitoring with improper management of the neuromuscular block. Because the distress caused by the sense of paralysis represents an important predictor for the development of severe psychological complications, the knowledge of the phenomenon, and the possible strategies for its prophylaxis are aspects of considerable importance. Nevertheless, a limited percentage of episodes of AAWR cannot be prevented. This paradox holds also during the emergence phase of anesthesia which represents a very complex neurophysiological process with many aspects yet to be clarified.

Failure to awaken from general anesthesia due to infratentorial hemorrhage after cervical spine surgery: A case report

RATIONALE

Emergence is not simply the reverse process of induction. Many dynamic situations could occur in this period by distinct neurobiology as recent studies indicated. Herein we report a rare case of failure of emergence from general anesthesia after cervical spine surgery.

PATIENT CONCERNS

Despite the perioperative vital signs and laboratory results were unremarkable, the patient could not recover his mental status and spontaneous breathing during emergence. 20 minutes after cessation of anesthetic drug administration, his blood pressure suddenly began to decrease requiring transfusion and vasopressor.

DIAGNOSIS

After thorough inspection of intraoperative alterations of hemodynamic and metabolic values, which showed no significant changes except possible signs of delayed volume loss, cerebrovascular bleeding was most suspected as the cause of the event. Computed tomography was performed and infratentorial hemorrhage after cervical spine surgery was checked.

INTERVENTIONS

Decompression operation was required for removing the hemorrhage. However, the patient's family refused further management considering his limited life expectancy.

OUTCOMES

The patient expired on postoperative day 5.

LESSONS

Failure to awaken is a relatively rare event. It could be confused with simple delayed emergence, which is often caused by residual drug effect. However, when it occurs, the result could be devastating. Therefore, appropriate recognition and prompt response are required to decrease the mortality and morbidity of the patient.

Anesthetics influence concussive head injury induced blood-brain barrier breakdown, brain edema formation, cerebral blood flow, serotonin levels, brain pathology and functional outcome

Several lines of evidences show that anesthetics influence neurotoxicity and neuroprotection. The possibility that different anesthetic agents potentially influence the pathophysiological and functional outcome following neurotrauma was examined in a rat model of concussive head injury (CHI). The CHI was produced by an impact of 0.224N on the right parietal bone by dropping a weight of 114.6g from a 20cm height under different anesthetic agents, e.g., inhaled ether anesthesia or intraperitoneally administered ketamine, pentobarbital, equithesin or urethane anesthesia. Five hour CHI resulted in profound volume swelling and brain edema formation in both hemispheres showing disruption of the blood-brain barrier (BBB) to Evans blue and radioiodine. A marked decrease in the cortical CBF and a profound increase in plasma or brain serotonin levels were seen at this time. Neuronal damages were present in several parts of the brain. These pathological changes were most marked in CHI under ether anesthesia followed by ketamine (35mg/kg, i.p.), pentobarbital (50mg/kg, i.p.), equithesin (3mL/kg, i.p.) and urethane (1g/kg, i.p.). The functional outcome on Rota Rod performances or grid walking tests was also most adversely affected after CHI under ether anesthesia followed by pentobarbital, equithesin and ketamine. Interestingly, the plasma and brain serotonin levels strongly correlated with the development of brain edema in head injured animals in relation to different anesthetic agents used. These observations suggest that anesthetic agents are detrimental to functional and pathological outcomes in CHI probably through influencing the circulating plasma and brain serotonin levels, not reported earlier. Whether anesthetics could also affect the efficacy of different neuroprotective agents in CNS injuries is a new subject that is currently being examined in our laboratory.