A Subanesthetic Concentration of Sevoflurane Increases Regional Cerebral Blood Flow and Regional Cerebral Blood Volume and Decreases Regional Mean Transit Time and Regional Cerebrovascular Resistance in Volunteers

Sevoflurane Ameliorates Schizophrenia in a Mouse Model and Patients: A Pre-Clinical and Clinical Feasibility Study

BACKGROUND

GABAergic deficits have been considered to be associated with the pathophysiology of schizophrenia, and hence, GABA receptors subtype A (GABA_ARs) modulators, such as commonly used volatile anesthetic sevoflurane, may have therapeutic values for schizophrenia. The present study investigates the therapeutic effectiveness of low-concentration sevoflurane in MK801-induced schizophrenia-like mice and schizophrenia patients.

METHODS

Three weeks after MK801 administration (0.5 mg kg^-1, i.p. twice a day for 5 days), mice were exposed to 1% sevoflurane 1hr/day for 5 days. Behavioral tests, immunohistochemical analysis, western blot assay, and electrophysiology assessments were performed 1-week post-exposure. Ten schizophrenia patients received 1% sevoflurane 5 hrs per day for 6 days and were assessed with the Positive and Negative Syndrome Scale (PANSS) and the 18-item Brief Psychiatric Rating Scale (BPRS-18) at week 1 and week 2.

RESULTS

MK801 induced hypolocomotion and social deficits, downregulated expression of NMDARs subunits and postsynaptic density protein 95 (PSD95), reduced parvalbumin - and GAD67-positive neurons, altered amplitude and frequency of mEPSCs and mIPSCs, and increased the excitation/inhibition ratio. All these changes induced by MK-801 were attenuated by sevoflurane administration. Six and eight patients achieved a response defined as a reduction of at least 30% in the PANSS total score at 1st and 2nd week after treatments. The BPRS-18 total score was found to be significantly decreased by 38% at the 2nd week (p < 0.01).

CONCLUSION

Low-concentration sevoflurane effectively reversed MK801-induced schizophrenialike disease in mice and alleviated schizophrenia patients' symptoms. Our work suggests sevoflurane to be a valuable therapeutic strategy for treating schizophrenia patients.

Acquisition of sensorimotor fMRI under general anaesthesia: Assessment of feasibility, the BOLD response and clinical utility

We evaluated whether task-related fMRI (functional magnetic resonance imaging) BOLD (blood oxygenation level dependent) activation could be acquired under conventional anaesthesia at a depth enabling neurosurgery in five patients with supratentorial gliomas. Within a 1.5 T MRI operating room immediately prior to neurosurgery, a passive finger flexion sensorimotor paradigm was performed on each hand with the patients awake, and then immediately after the induction and maintenance of combined sevoflurane and propofol general anaesthesia. The depth of surgical anaesthesia was measured and confirmed with an EEG-derived technique, the Bispectral Index (BIS). The magnitude of the task-related BOLD response and BOLD sensitivity under anaesthesia were determined. The fMRI data were assessed by three fMRI expert observers who rated each activation map for somatotopy and usefulness for radiological neurosurgical guidance. The mean magnitudes of the task-related BOLD response under a BIS measured depth of surgical general anaesthesia were 25% (tumour affected hemisphere) and 22% (tumour free hemisphere) of the respective awake values. BOLD sensitivity under anaesthesia ranged from 7% to 83% compared to the awake state. Despite these reductions, somatotopic BOLD activation was observed in the sensorimotor cortex in all ten data acquisitions surpassing statistical thresholds of at least p < 0.001_uncorr. All ten fMRI activation datasets were scored to be useful for radiological neurosurgical guidance. Passive task-related sensorimotor fMRI acquired in neurosurgical patients under multi-pharmacological general anaesthesia is reproducible and yields clinically useful activation maps. These results demonstrate the feasibility of the technique and its potential value if applied intra-operatively. Additionally these methods may enable fMRI investigations in patients unable to perform or lie still for awake paradigms, such as young children, claustrophobic patients and those with movement disorders.

Effects of anesthesia on cerebral blood flow, metabolism, and neuroprotection

Administration of anesthetic agents fundamentally shifts the responsibility for maintenance of homeostasis from the patient and their intrinsic physiological regulatory mechanisms to the anesthesiologist. Continuous delivery of oxygen and nutrients to the brain is necessary to prevent irreversible injury and arises from a complex series of regulatory mechanisms that ensure uninterrupted cerebral blood flow. Our understanding of these regulatory mechanisms and the effects of anesthetics on them has been driven by the tireless work of pioneers in the field. It is of paramount importance that the anesthesiologist shares this understanding. Herein, we will review the physiological determinants of cerebral blood flow and how delivery of anesthesia impacts these processes.

Esmolol reduces anesthetic requirements thereby facilitating early extubation; a prospective controlled study in patients undergoing intracranial surgery

BACKGROUND

Adequate cerebral perfusion pressure with quick and smooth emergence from anesthesia is a major concern of the neuroanesthesiologist. Anesthesia techniques that minimize anesthetic requirements and their effects may be beneficial. Esmolol, a short acting hyperselective β-adrenergic blocker is effective in blunting adrenergic response to several perioperative stimuli and so it might interfere in the effect of the anesthetic drugs on the brain. This study was designed to investigate the effect of esmolol on the consumption of propofol and sevoflurane in patients undergoing craniotomy.

METHOD

Forty-two patients that underwent craniotomy for aneurysm clipping or tumour dissection were randomly divided in two groups (four subgroups). Anesthesia was induced with propofol, fentanyl and a single dose of cis-atracurium, followed by continuous infusion of remifentanil and either propofol or sevoflurane. Patients in the esmolol group received 500 mcg/kg of esmolol bolus 10 min before induction of anesthesia, followed by additional 200 mcg/kg/min of esmolol. Monitoring of the depth of anesthesia was also performed using the Bispectral Index-BIS and cardiac output. The inspired concentration of sevoflurane and the infusion rate of propofol were adjusted in order to maintain a BIS value between 40-50. Intraoperative emergence was detected by the elevation of BIS value, HR or MAP.

RESULTS

The initial and the intraoperative doses of propofol and sevoflurane were 18-50 mcg/kg/min and 0.2-0.5 MAC respectively in the esmolol group, whereas in the control group they where 100-150 mcg/kg/ and 0.9-2.0 MAC respectively (p = 0.000 for both groups). All procedures were anesthesiologically uneventful with no episodes of intraoperative emerge.

CONCLUSIONS

Esmolol is effective not only in attenuating intraoperative hemodynamic changes related to sympathetic overdrive but also in minimizing significant propofol and sevoflurane requirements without compromising the hemodynamic status. ClinicalTrials.gov Identifier: NCT02455440 . Registered 26 May 2015.

Cerebral blood flow is an earlier indicator of perfusion abnormalities than cerebral blood volume in Alzheimer's disease

The purpose of this study was to elucidate whether cerebral blood flow (CBF) can better characterize perfusion abnormalities in predementia stages of Alzheimer's disease (AD) than cerebral blood volume (CBV) and whether cortical atrophy is more associated with decreased CBV or with decreased CBF. We compared measurements of CBV, CBF, and mean cortical thickness obtained from magnetic resonance images in a group of healthy controls, patients with mild cognitive impairment (MCI) who converted to AD after 2 years of clinical follow-up (MCI-c), and patients with mild AD. A significant decrease in perfusion was detected in the parietal lobes of the MCI-c patients with CBF parametric maps but not with CBV maps. In the MCI-c group, a negative correlation between CBF values and cortical thickness in the right parahippocampal gyrus suggests an increase in CBF that depends on cortical atrophy in predementia stages of AD. Our study also suggests that CBF deficits appear before CBV deficits in the progression of AD, as CBV abnormalities were only detected at the AD stage, whereas CBF changes were already detected in the MCI stage. These results confirm the hypothesis that CBF is a more sensitive parameter than CBV for perfusion abnormalities in MCI-c patients.

Relationship between regional cerebral blood flow and electrocorticographic activities under sevoflurane and isoflurane anesthesia

The aims of this study are (1) to assess the effects of volatile anesthetics on regional cerebral blood flow (rCBF) and electrocorticography (ECoG), and (2) to investigate the relationship between rCBF and ECoG influenced by volatile anesthetics. The authors measured rCBF using laser Doppler flowmetry and ECoG simultaneously and continuously from the same cortex during craniotomy, using the specially arranged probe. Patients received intravenous anesthetics with nitrous oxide until craniotomy, and after opening of dura, volatile anesthetic, either isoflurane or sevoflurane, was started and was gradually increased for the measurement. Four of the nine cases (44.4%) of the sevoflurane group showed no change both in rCBF and ECoG. In three cases (33.3%), rCBF increased as the frequency of the paroxysmal activities increased. In two cases (22.2%), decreased rCBF was accompanied by slow waves. In 12 cases of the isoflurane group, no apparent rCBF and ECoG changes were seen, except a case with decreased rCBF and slow waves. This is the first report of simultaneous recordings of regional CBF and neuronal activity under general anesthesia. During sevoflurane and isoflurane anesthesia <2.5 minimum alveolar anesthetic concentration, rCBF is affected by ECoG activities rather than pharmacologic action of inhalational anesthetics.

Regional cerebral glucose metabolism during sevoflurane anaesthesia in healthy subjects studied with positron emission tomography

BACKGROUND

The precise mechanism by which sevoflurane exerts its effects in the human brain remains unknown. In the present study, we quantified the effects of sevoflurane on regional cerebral glucose metabolism (rGMR) in the human brain measured with positron emission tomography.

METHODS

Eight volunteers underwent two dynamic 18F-fluorodeoxyglucose positron emission tomography (PET) scans. One scan assessed conscious-baseline metabolism and the other scan assessed metabolism during 1 minimum alveolar concentration (MAC) sevoflurane anaesthesia. Cardiovascular and respiratory parameters were monitored and bispectral index responses were registered. Statistical parametric maps and conventional regions of interest analysis were used to determine rGMR differences.

RESULTS

All subjects were unconsciousness at 1.0 MAC sevoflurane. Cardiovascular and respiratory parameters were constant over time. In the awake state, rGMR ranged from 0.24 to 0.35 mumol/g/min in the selected regions. Compared with the conscious state, total GMR decreased 56% in sevoflurane anaesthesia. In white and grey matter, GMR was averaged 42% and 58% of normal, respectively. Sevoflurane reduced the absolute rGMR in all selected areas by 48-71% of the baseline (P< or = 0.01), with the most significant reductions in the lingual gyrus (71%), occipital lobe in general (68%) and thalamus (63%). No increases in rGMR were observed.

CONCLUSIONS

Sevoflurane caused a global whole-brain metabolic reduction of GMR in all regions of the human brain, with the most marked metabolic suppression in the lingual gyrus, thalamus and occipital lobe.

Why we still use intravenous drugs as the basic regimen for neurosurgical anaesthesia

PURPOSE OF REVIEW

Evolution of neurosurgery mainly trends towards minimally invasive and functional procedures including endoscopies, small-size craniotomies, intraoperative imaging and stereotactic interventions. Consequently, new adjustments of anaesthesia should aim at providing brain relaxation, minimal interference with electrophysiological monitoring, rapid recovery, patients' cooperation during surgery and neuroprotection.

RECENT FINDINGS

In brain tumour patients undergoing craniotomy, propofol anaesthesia is associated with lower intracranial pressure and cerebral swelling than volatile anaesthesia. Hyperventilation used to improve brain relaxation may decrease jugular venous oxygen saturation below the critical threshold. It decreases the cerebral perfusion pressure in patients receiving sevoflurane, but not in those receiving propofol. The advantage of propofol over volatile agents has also been confirmed regarding interference with somatosensory, auditory and motor evoked potentials. Excellent and predictable recovery conditions as well as minimal postoperative side-effects make propofol particularly suitable in awake craniotomies. Finally, the potential neuroprotective effect of this drug could be mediated by its antioxidant properties which can play a role in apoptosis, ischaemia-reperfusion injury and inflammatory-induced neuronal damage.

SUMMARY

Although all the objectives of neurosurgical anaesthesia cannot be met by one single anaesthetic agent or technique, propofol-based intravenous anaesthesia appears as the first choice to challenge the evolution of neurosurgery in the third millennium.

Comparison of the effects of sevoflurane and propofol anaesthesia on regional cerebral glucose metabolism in humans using positron emission tomography

This study compared brain glucose metabolism during sevoflurane anaesthesia and propofol anaesthesia using positron emission tomography (PET) in the same eight human volunteers. All the volunteers were anaesthetized twice, with a 1-week interval. Half of the volunteers received sevoflurane on the first occasion and propofol on the second; the other half received the two anaesthetics in the reverse order. PET scans using 18F-fluorodeoxyglucose were performed after sevoflurane or propofol anaesthesia. The relative glucose metabolic rate (rGMR) in the brain was assessed with statistical parametric mapping. Propofol suppressed the rGMR of the neocortex area more than sevoflurane, and sevoflurane suppressed the rGMR of the paleocortex and telencephalon more than propofol. These findings suggest that these two anaesthetics act via different mechanisms and may provide an important clue to the relationship between anaesthesia and the brain.

Effect of sevoflurane on cerebral blood flow and cerebrovascular resistance at surgical level of anaesthesia: a transcranial Doppler study

BACKGROUND AND OBJECTIVE

It is widely accepted that sevoflurane affects cerebral circulation, but there are uncertainities regarding the magnitude of its effect. The aim of the present work was to assess the effect of sevoflurane on the cerebral circulation at surgical levels of anaesthesia.

METHODS

Twenty patients undergoing elective lumbar discectomies were investigated. Anaesthesia was induced with propofol and maintained with sevoflurane. The level of surgical anaesthesia was determined by bispectral index, the target level was 45-55. Transcranial Doppler (TCD) measurement was performed before induction and after reaching the surgical level of anaesthesia. Besides routine parameters (middle cerebral artery mean blood flow velocity (MCAV) and pulsatility index (PI)) derived parameters (estimated cerebral perfusion pressure (eCPP), cerebral blood flow index (CBFI) and resistance area product (RAP)) were calculated by taking changes of mean arterial pressure also into account.

RESULTS

MCAV decreased from 54.1 +/- 13.3 to 43.7 +/- 18.5 cm s-1, P < 0.01 and PI increased from 0.79 +/- 0.2 to 0.92 +/- 0.2, P < 0.01 after reaching the surgical level of anaesthesia. As a result eCPP decreased by 18.2%, CBFI by 25.5% and RAP increased by 15% respectively.

CONCLUSIONS

Our data indicate a vasodilatory effect of sevoflurane at surgical level of anaesthesia on large cerebral vessels or a vasoconstriction of the resistance arterioles likely caused by decreased brain metabolism.

Effect of nitrous oxide on cerebrovascular reactivity to carbon dioxide in children during sevoflurane anaesthesia

BACKGROUND

Sevoflurane and nitrous oxide have intrinsic cerebral vasodilatory activity. To determine the effects of nitrous oxide on cerebrovascular reactivity to carbon dioxide (CCO(2)R) during sevoflurane anaesthesia in children, middle cerebral artery blood flow velocity (V(mca)) was measured over a range of end-tidal carbon dioxide concentrations (E'(CO(2))), using transcranial Doppler (TCD) ultrasonography.

METHODS

Ten children aged 1.5-6 yr were anaesthetized with sevoflurane and received a caudal block. Patients were allocated randomly to receive either air-nitrous oxide or nitrous oxide-air. Further randomization determined the sequence of E'(CO(2)) (25, 35, 45, and 55 mm Hg) and sevoflurane (1.0 then 1.5 MAC or 1.5 then 1.0 MAC) concentrations. Once steady state had been reached, three measurements of V(mca), mean arterial pressure (MAP), and heart rate (HR) were recorded.

RESULTS

Cerebrovascular carbon dioxide reactivity was reduced in the 25-35 mm Hg E'(CO(2)) range on the addition of nitrous oxide to 1.5 MAC, but not 1.0 MAC sevoflurane. A plateau in CCO(2)R of 0.4-0.6% per mm Hg was seen in all groups between E'(CO(2)) values of 45 and 55 mm Hg. Mean HR and MAP remained constant throughout the study period.

CONCLUSIONS

Cerebrovascular carbon dioxide reactivity is reduced at and above an E'(CO(2)) of 45 mm Hg during 1.0 and 1.5 MAC sevoflurane anaesthesia. The addition of nitrous oxide to 1.5 MAC sevoflurane diminishes CCO(2)R in the hypocapnic range. This should be taken into consideration when hyperventilation techniques for reduction of brain bulk are being contemplated in children with raised intracranial pressure.

Asymmetric regional cerebral blood flow in sedated baboons measured by positron emission tomography (PET)

The analysis of structural brain asymmetry has been a focal point in anthropological theories of human brain evolution and the development of lateralized behaviors. While physiological brain asymmetries have been documented for humans and animals presenting with pathological conditions or under certain activation tasks, published studies on baseline asymmetries in healthy individuals have produced conflicting results. We tested for the presence of cerebral blood flow asymmetries in 7 healthy, sedated baboons using positron emission tomography, a method of in vivo autoradiography. Five of the 7 baboons exhibited hemispheric asymmetries in which left-sided flow was significantly greater than right-sided flow. Furthermore, the degree of asymmetry in 8 of 24 brain regions was found to be significantly correlated with age; older individuals exhibited a higher degree of asymmetry than younger individuals. Cerebral blood flow itself was uncorrelated with age, and differences between males and females were not significant.