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

Propofol Versus Sevoflurane General Anaesthesia for Selective Impairment of Attention Networks After Gynaecological Surgery in Middle-Aged Women: A Randomised Controlled Trial

PURPOSE

Attention is an essential component of cognitive function that may be impaired after surgery with anaesthesia. Propofol intravenous anaesthesia and sevoflurane inhalational anaesthesia are frequently used in gynaecological surgery. However, which type of anaesthetic has fewer cognitive effects postoperatively remains unclear. We compared the differences in attention network impairment after surgery in women receiving propofol versus sevoflurane general anaesthesia.

PATIENTS AND METHODS

Eighty-three patients with gynaecological diseases who were 40-60 years of age were involved in the study. All patients underwent elective gynaecological surgery under either total intravenous anaesthesia or sevoflurane inhalational anaesthesia, depending on randomisation. The efficiencies of the three attention networks were captured using the attention network test preoperatively and on the 1st and 5th postoperative days.

RESULTS

Both groups of patients showed differences in impairments on the 1st and 5th postoperative days. Pairwise comparisons indicated that the alerting and orienting networks of patients in the propofol group were impaired to a greater extent than those of patients in the sevoflurane group on the 1st postoperative day, while the executive control network was impaired to a lesser extent. On the 5th postoperative day, the alerting networks of both groups recovered to the baseline level. Patients in the propofol group still showed impairment of the orienting network, while patients in the sevoflurane group recovered to baseline. For the executive control network, patients in the sevoflurane group still exhibited more severe impairment than those in the propofol group.

CONCLUSION

In middle-aged women, propofol impaired orienting and alerting networks more than sevoflurane, while sevoflurane showed more residual impairment of the executive control network.

Validation of a new approach for distinguishing anesthetized from awake state in patients using directed transfer function applied to raw EEG

We test whether a measure based on the directed transfer function (DTF) calculated from short segments of electroencephalography (EEG) time-series can be used to monitor the state of the patients also during sevoflurane anesthesia as it can for patients undergoing propofol anesthesia. We collected and analyzed 25-channel EEG from 7 patients (3 females, ages 41–56 years) undergoing surgical anesthesia with sevoflurane, and quantified the sensor space directed connectivity for every 1-s epoch using DTF. The resulting connectivity parameters were compared to corresponding parameters from our previous study (n = 8, patients anesthetized with propofol and remifentanil, but otherwise using a similar protocol). Statistical comparisons between and within studies were done using permutation statistics, a data driven algorithm based on the DTF-parameters was employed to classify the epochs as coming from awake or anesthetized state. According to results of the permutation tests, DTF-parameter topographies were significantly different between the awake and anesthesia state at the group level. However, the topographies were not significantly different when comparing results computed from sevoflurane and propofol data, neither in the awake nor in anesthetized state. Optimizing the algorithm for simultaneously having high sensitivity and specificity in classification yielded an accuracy of 95.1% (SE = 0.96%), with sensitivity of 98.4% (SE = 0.80%) and specificity of 94.8% (SE = 0.10%). These findings indicate that the DTF changes in a similar manner when humans undergo general anesthesia caused by two distinct anesthetic agents with different molecular mechanisms of action.

The PET Sandwich: Using Serial FDG-PET Scans with Interval Burst Suppression to Assess Ictal Components of Disease

BACKGROUND

Determining the cause of refractory seizures and/or interictal continuum (IIC) findings in the critically ill patient remains a challenge. These electrographic abnormalities may represent primary ictal pathology or may instead be driven by an underlying infectious, inflammatory, or neoplastic pathology that requires targeted therapy. In these cases, it is unclear whether escalating antiepileptic therapy will be helpful or harmful. Herein, we report the use of serial [F-18] fluorodeoxyglucose positron emission tomography (FDG-PET) coupled with induced electrographic burst suppression to distinguish between primary and secondary ictal pathologies. We propose that anesthetic suppression of hypermetabolic foci suggests clinical responsiveness to escalating antiepileptic therapy, whereas non-suppressible hypermetabolic foci are suggestive of non-ictal pathologies that likely require multimodal therapy.

METHODS

We describe 6 patients who presented with electrographic findings of seizure or IIC abnormalities, severe neurologic injury, and clinical concern for confounding pathologies. All patients were continuously monitored on video electroencephalography (cvEEG). Five patients underwent at least two sequential FDG-PET scans of the brain: one in a baseline state and the second while under electrographic burst suppression. FDG-avid loci and EEG tracings were compared pre- and post-burst suppression. One patient underwent a single FDG-PET scan while burst-suppressed.

RESULTS

Four patients had initially FDG-avid foci that subsequently resolved with burst suppression. Escalation of antiepileptic therapy in these patients resulted in clinical improvement, suggesting that the foci were related to primary ictal pathology. These included clinical diagnoses of electroclinical status epilepticus, new-onset refractory status epilepticus, stroke-like migraine attacks after radiotherapy, and epilepsy secondary to inflammatory cerebral amyloid angiopathy. Conversely, two patients with high-grade EEG abnormalities had FDG-avid foci that persisted despite burst suppression. The first presented with a poor examination, fever, and concern for encephalitis. Postmortem pathology confirmed suspicion of herpes simplex virus encephalitis. The second patient presented with concern for checkpoint inhibitor-induced autoimmune encephalitis. The persistence of the FDG-avid focus, despite electrographic burst suppression, guided successful treatment through escalation of immunosuppressive therapy.

CONCLUSIONS

In appropriately selected patients, FDG-PET scans while in burst suppression may help dissect the underlying pathophysiologic cause of IIC findings observed on EEG and guide tailored therapy.

Effects of isoflurane, sevoflurane, propofol and alfaxalone on brain metabolism in dogs assessed by proton magnetic resonance spectroscopy (1H MRS)

Background

The purpose of this study was to determine the effects of isoflurane, sevoflurane, propofol and alfaxalone on the canine brain metabolite bioprofile, measured with single voxel short echo time proton magnetic resonance spectroscopy at 3 Tesla. Ten adult healthy Beagle dogs were assigned to receive isoflurane, sevoflurane, propofol and alfaxalone at 3 different dose rates each in a randomized cross-over study design. Doses for isoflurane, sevoflurane, propofol and alfaxalone were F_E’Iso 1.7 vol%, 2.1 vol%, 2.8 vol%, F_E’Sevo 2.8 vol%, 3.5 vol% and 4.7 vol%, 30, 45 and 60 mg kg^− 1 h^− 1 and 10, 15 and 20 mg kg^− 1 h^− 1 respectively. A single voxel Point Resolved Spectroscopy Sequence was performed on a 3 T MRI scanner in three brain regions (basal ganglia, parietal and occipital lobes). Spectral data were analyzed with LCModel. Concentration of total N-acetylaspartate (tNAA), choline, creatine, inositol and glutamine and glutamate complex (Glx) relative to water content was obtained. Plasma concentration of lactate, glucose, triglycerides, propofol and alfaxalone were determined. Statistics were performed using repeated measures ANOVA or Wilcoxon Sign Rank test with alpha = 5%.

Results

Plasma glucose increased with isoflurane, sevoflurane and alfaxalone but decreased with propofol. Plasma lactate increased with all anesthetics (isoflurane > sevoflurane > propofol > alfaxalone). Cerebral lactate could not be detected. Only minor changes in cerebral metabolite concentrations of tNAA, choline, inositol, creatine and Glx occurred with anesthetic dose changes.

Conclusion

The metabolomic profile detected with proton magnetic resonance spectroscopy at 3 Tesla of canine brain showed only minor differences between doses and anesthetics related to tNAA, choline, creatine, inositol and Glx.

Decoupled temporal variability and signal synchronization of spontaneous brain activity in loss of consciousness: An fMRI study in anesthesia

Two aspects of the low frequency fluctuations of spontaneous brain activity have been proposed which reflect the complex and dynamic features of resting-state activity, namely temporal variability and signal synchronization. The relationship between them, especially its role in consciousness, nevertheless remains unclear. Our study examined the temporal variability and signal synchronization of spontaneous brain activity, as well as their relationship during loss of consciousness. We applied an intra-subject design of resting-state functional magnetic resonance imaging (rs-fMRI) in two conditions: during wakefulness, and under anesthesia with clinical unconsciousness. In addition, an independent group of patients with disorders of consciousness (DOC) was included in order to test the reliability of our findings. We observed a global reduction in the temporal variability, local and distant brain signal synchronization for subjects during anesthesia. Importantly, we found a link between temporal variability and both local and distant signal synchronizations during wakefulness: the higher the degree of temporal variability, the higher its intra-regional homogeneity and inter-regional functional connectivity. In contrast, this link was broken down under anesthesia, implying a decoupling between temporal variability and signal synchronization; this decoupling was reproduced in patients with DOC. Our results suggest that there exist some as yet unclear physiological mechanisms of consciousness which "couple" the two mathematically independent measures, temporal variability and signal synchronization of spontaneous brain activity. Our findings not only extend our current knowledge of the neural correlates of anesthetic-induced unconsciousness, but have implications for both computational neural modeling and clinical practice, such as in the diagnosis of loss of consciousness in patients with DOC.

Anesthetic effects of propofol in the healthy human brain: functional imaging evidence

Functional imaging methods, including positron emission tomography (PET) and functional magnetic resonance imaging (fMRI), have become important tools for studying how anesthetic drugs act in the human brain to induce the state of general anesthesia. Recent imaging studies using fMRI and PET techniques have demonstrated the regional effects of propofol on the brain. However, the pharmacological mechanism of the action of propofol in the intact human central nervous system is unclear. To explore the possible action targets of propofol in the human brain, a systematic review of the literature was performed. The literature search was performed with limiting factors of "propofol," "functional imaging," "positron emission tomography", and "functional magnetic resonance imaging" from 1966 to July 2013 (using Medline, EMBASE, CINAHL and hand searches of references). Studies meeting the inclusion criteria were reviewed and critiqued for the purpose of this literature research. Eighteen researches meeting the inclusion criteria were reviewed in terms of the appropriateness of valuation technique. In the unconscious state, propofol sharply reduces the regional glucose metabolism rate (rGMR) and regional cerebral blood flow (rCBF) in all brain regions, particularly in the thalamus. However, GMR, such as in the occipital, temporal, and frontal lobes, was obviously decreased at a sedative dosage of propofol, whereas, changes in the thalamus were not obvious. Using fMRI, several studies observed a decrease of connectivity of the thalamus versus an increase of connectivity within the pons of the brainstem during propofol-induced mild sedation. During deep sedation, propofol preserves cortical sensory reactivity, the specific thalamocortical network is moderately affected, whereas the nonspecific thalamocortical network is severely suppressed. In contrast, several recent fMRI studies are consistent on the systemic decreased effects of propofol in the frontoparietal network. Accumulating evidence suggest that propofol-induced unconsciousness is associated with a global metabolic and vascular depression in the human brain and especially with a significant reduction in the thalamocortical network and the frontoparietal network.

Regional cerebral blood flow and glucose metabolism during propofol anaesthesia in healthy subjects studied with positron emission tomography

BACKGROUND

General anaesthetics can alter the relationship between regional cerebral glucose metabolism rate (rGMR) and regional cerebral blood flow (rCBF). With the present study, we wanted to assess quantitatively the effects of propofol on rCBF and rGMR in the same healthy volunteers measured with positron emission tomography (PET).

METHODS

(15)O-labelled water and (18)F fluorodeoxyglucose were used as PET tracers to determine rCBF and rGMR, respectively, in eight healthy volunteers during the waking state (baseline) and during propofol anaesthesia. Propofol was titrated to keep a constant hypnotic depth (Bispectral Indes 35-40) throughout the anaesthesia. Changes in rGMR and rCBF were quantified using region-of-interest and voxel-based analyses.

RESULTS

The measured mean propofol concentration was 4.1 ± 0.8 μg/ml during anaesthesia. Compared with the conscious state, total CBF and GMR decreased during the anaesthetic state with 47% and 54%, respectively. In the white and grey matter, rCBF and rGMR were reduced by 37% and 49%, and by 45% and 57%, respectively. Propofol decreased rCBF in all brain structures by 46-55% (P ≤ 0.01) with highest significant decreases in the thalamus and parietal lobe. Regional GMR was reduced in all brain areas to 48-66% (P ≤ 0.01) with highest significant reductions in the occipital lobe, the lingual gyrus, parietal lobe, temporal lobe and thalamus. No increases in rCBF or rGMR happened anywhere.

CONCLUSIONS

General anaesthesia with propofol is associated with a global metabolic and vascular depression in the human brain, with significant shifts in regional blood flow and metabolism indicating marked metabolic and vascular responsiveness in some cortical areas and thalamus.

Pharmacologic amelioration of severe hypoglycemia-induced neuronal damage

Hypoglycemia is a common complication for insulin treated people with diabetes. Severe hypoglycemia, which occurs in the setting of excess or ill-timed insulin administration, has been shown to cause brain damage. Previous pre-clinical studies have shown that memantine (an N-methyl-d-aspartate receptor antagonist) and erythropoietin can be neuroprotective in other models of brain injury. We hypothesized that these agents might also be neuroprotective in response to severe hypoglycemia-induced brain damage. To test this hypothesis, 9-week old, awake, male Sprague-Dawley rats underwent hyperinsulinemic (0.2 U kg(-1)min(-1)) hypoglycemic clamps to induce severe hypoglycemia (blood glucose 10-15 mg/dl for 90 min). Animals were randomized into control (vehicle) or pharmacological treatments (memantine or erythropoietin). One week after severe hypoglycemia, neuronal damage was assessed by Fluoro-Jade B and hematoxylin and eosin staining of brain sections. Treatment with both memantine and erythropoietin significantly decreased severe hypoglycemia-induced neuronal damage in the cortex by 35% and 39%, respectively (both p<0.05 vs. controls). These findings demonstrate that memantine and erythropoietin provide a protective effect against severe hypoglycemia-induced neuronal damage.

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.

Recurrent moderate hypoglycemia ameliorates brain damage and cognitive dysfunction induced by severe hypoglycemia

OBJECTIVE

Although intensive glycemic control achieved with insulin therapy increases the incidence of both moderate and severe hypoglycemia, clinical reports of cognitive impairment due to severe hypoglycemia have been highly variable. It was hypothesized that recurrent moderate hypoglycemia preconditions the brain and protects against damage caused by severe hypoglycemia.

RESEARCH DESIGN AND METHODS

Nine-week-old male Sprague-Dawley rats were subjected to either 3 consecutive days of recurrent moderate (25-40 mg/dl) hypoglycemia (RH) or saline injections. On the fourth day, rats were subjected to a hyperinsulinemic (0.2 units x kg(-1) x min(-1)) severe hypoglycemic ( approximately 11 mg/dl) clamp for 60 or 90 min. Neuronal damage was subsequently assessed by hematoxylin-eosin and Fluoro-Jade B staining. The functional significance of severe hypoglycemia-induced brain damage was evaluated by motor and cognitive testing.

RESULTS

Severe hypoglycemia induced brain damage and striking deficits in spatial learning and memory. Rats subjected to recurrent moderate hypoglycemia had 62-74% less brain cell death and were protected from most of these cognitive disturbances.

CONCLUSIONS

Antecedent recurrent moderate hypoglycemia preconditioned the brain and markedly limited both the extent of severe hypoglycemia-induced neuronal damage and associated cognitive impairment. In conclusion, changes brought about by recurrent moderate hypoglycemia can be viewed, paradoxically, as providing a beneficial adaptive response in that there is mitigation against severe hypoglycemia-induced brain damage and cognitive dysfunction.

Diabetes increases brain damage caused by severe hypoglycemia

Insulin-induced severe hypoglycemia causes brain damage. The hypothesis to be tested was that diabetes portends to more extensive brain tissue damage following an episode of severe hypoglycemia. Nine-week-old male streptozotocin-diabetic (DIAB; n = 10) or vehicle-injected control (CONT; n = 7) Sprague-Dawley rats were subjected to hyperinsulinemic (0.2 U.kg(-1).min(-1)) severe hypoglycemic (10-15 mg/dl) clamps while awake and unrestrained. Groups were precisely matched for depth and duration (1 h) of severe hypoglycemia (CONT 11 +/- 0.5 and DIAB 12 +/- 0.2 mg/dl, P = not significant). During severe hypoglycemia, an equal number of episodes of seizure-like activity were noted in both groups. One week later, histological analysis demonstrated extensive neuronal damage in regions of the hippocampus, especially in the dentate gyrus and CA1 regions and less so in the CA3 region (P < 0.05), although total hippocampal damage was not different between groups. However, in the cortex, DIAB rats had significantly (2.3-fold) more dead neurons than CONT rats (P < 0.05). There was a strong correlation between neuronal damage and the occurrence of seizure-like activity (r(2) > 0.9). Separate studies conducted in groups of diabetic (n = 5) and nondiabetic (n = 5) rats not exposed to severe hypoglycemia showed no brain damage. In summary, under the conditions studied, severe hypoglycemia causes brain damage in the cortex and regions within the hippocampus, and the extent of damage is closely correlated to the presence of seizure-like activity in nonanesthetized rats. It is concluded that, in response to insulin-induced severe hypoglycemia, diabetes uniquely increases the vulnerability of specific brain areas to neuronal damage.

Imaging the effects of propofol on human cerebral glucose metabolism using positron emission tomography

The effects of propofol on glucose metabolism in different cerebral regions were observed, using positron emission tomography (PET) technology, to determine a possible cerebral target region. Seven healthy volunteers were injected with (18)F-fluorodeoxyglucose developing agent for PET scanning whilst awake (control group T1), during sedation (induced by 1.5 microg/ml propofol administered by target controlled injection [TCI], group T2) and when unconsciousness (induced by 2.5 microg/ml propofol administered by TCI, group T3). Whole brain glucose metabolism was reduced during propofol anaesthesia; this was initially observed in the cortical areas at the lower dose of propofol (group T2) but extended to the subcortical regions, especially the thalamus and hippocampus, at the higher dose (group T3). This suggests that these regions of the brain might be important targets that are susceptible to propofol.