Neuroplasticity induced by general anaesthesia: study protocol for a randomised cross-over clinical trial exploring the effects of sevoflurane and propofol on the brain - A 3-T magnetic resonance imaging study of healthy volunteers

Impact of Anesthesia on Brain Functional Networks in Moyamoya Disease and Spinal Lesions

AIMS

To analyze the effects of intravenous propofol combined with remifentanil on whole-brain functional networks in patients with ischemic moyamoya disease (IMMD) and intraspinal space-occupying lesions (SOLs) using resting-state functional magnetic resonance imaging (rs-fMRI).

METHODS

Ten patients with IMMD and 10 sex- and age-matched patients with lumbar SOL (normal cerebrovascular findings on preoperative MRI) were recruited. General anesthesia was administered using propofol and remifentanil. rs-fMRI imaging was performed in both awake and anesthetized states. Whole-brain functional network in different states was constructed based on graph theory tools.

RESULTS

In awake patients with IMMD, significant reductions in nodal strength (NS) were observed in the default mode network (DMN), sensorimotor network, and frontoparietal control network (FPN), compared to patients with SOL. Nodal efficiency (NE) showed further significant network declines. Under anesthesia, patients with IMMD: (1) exhibited disease-specific decreases in NS and NE across several networks, potentially reflecting underlying cerebral pathology. (2) Propofol's effects also contributed to significant NS and NE reductions in several brain regions. Changes before and after anesthesia in patients with IMMD were significantly decreased in specific regions (discussed in detail) per analysis of NS versus NE. DMN connectivity correlated moderately with Montreal Cognitive Assessment scores.

CONCLUSIONS

Reduced whole-brain functional connectivity in patients with IMMD before anesthesia was similar to the alterations caused by systemic intravenous drugs administered after anesthesia.

TRIAL REGISTRATION

ChiCTR2300075268.

Reproducibility of cerebral blood flow, oxygen metabolism, and lactate and N-acetyl-aspartate concentrations measured using magnetic resonance imaging and spectroscopy

In humans, resting cerebral perfusion, oxygen consumption and energy metabolism demonstrate large intersubject variation regardless of methodology. Whether a similar large variation is also present longitudinally in individual subjects is much less studied, but knowing the time variance in reproducibility is important when designing and interpreting longitudinal follow-up studies examining brain physiology. Therefore, we examined the reproducibility of cerebral blood flow (CBF), global cerebral metabolic rate of oxygen (CMRO2), global arteriovenous oxygen saturation difference (A-V.O2), and cerebral lactate and N-acetyl-aspartate (NAA) concentrations measured using magnetic resonance imaging (MRI) and spectroscopy (MRS) techniques through repeated measurements at 6 h, 24 h, 7 days and several weeks after initial baseline measurements in young healthy adults (N = 26, 13 females, age range 18-35 years). Using this setup, we calculated the correlation, limit of agreement (LoA) and within-subject coefficient of variation (CoVWS) between baseline values and the subsequent repeated measurements to examine the longitudinal variation in individual cerebral physiology. CBF and CMRO2 correlated significantly between baseline and all subsequent measurements. The strength of the correlations (R2) and reproducibility metrics (LoA and CoVWS) demonstrated the best reproducibility for the within-day measurements and generally declined with longer time between measurements. Cerebral lactate and NAA concentrations also correlated significantly for all measurements, except between baseline and the 7-day measurement for lactate. Similar to CBF and CMRO2, lactate and NAA demonstrated the best reproducibility for within-day repeated measurements. The gradual decline in reproducibility over time should be considered when designing and interpreting studies on brain physiology, for example, in the evaluation of treatment efficacy.

Effect of sevoflurane versus propofol on neutrophil-to-lymphocyte ratio in healthy individuals: a sub-study of a randomised crossover trial

Background

Sevoflurane and propofol are commonly used drugs in general anaesthesia. However, their effects on perioperative immune function are incompletely understood. We hypothesised that sevoflurane and propofol differentially affect immune function in healthy individuals. Therefore, we investigated the effect of sevoflurane and propofol on neutrophil-to-lymphocyte ratio before, during, and after general anaesthesia.

Methods

In this randomised crossover study, 19 healthy individuals underwent 2 h of general anaesthesia with either propofol or sevoflurane. After 4 weeks, anaesthesia was repeated using the other drug. Blood samples were obtained before, during, 1 h after, and 1 day after anaesthesia. The primary outcome was whole-blood neutrophil-to-lymphocyte ratio, and secondary outcomes were specific white blood cell differential counts. A linear mixed-effects model was used to estimate effect sizes.

Results

The neutrophil-to-lymphocyte ratio was higher in the propofol compared with the sevoflurane group during anaesthesia, 2.8 (confidence interval [CI]: 2.3-3.3) vs 1.6 (CI: 1.1-2.1), and 1 day after anaesthesia, 2.6 (CI: 2.1-3.1) vs 1.9 (CI: 1.4-2.4). In all patients, we observed transient lymphopaenia during propofol anaesthesia, 1.1 × 109 cells × L-1 (CI: 0.9-1.4), compared with sevoflurane anaesthesia, 1.9 × 109 cells × L-1 (CI: 1.7-2.1). In addition, neutrophil counts were higher 1 day after propofol anaesthesia, 4.4 × 109 cells × L-1 (CI: 4.0-4.9), compared with sevoflurane anaesthesia, 3.5 × 109 cells × L-1 (CI: 3.1-4.0). We observed no differences in the remaining white blood cell subgroups.

Conclusions

In healthy individuals undergoing general anaesthesia without surgery, the neutrophil-to-lymphocyte ratio was affected by the type of hypnotic used. Transient lymphopaenia was observed in all participants during propofol anaesthesia.