Gamma Aminobutyric Acid Transaminase Deficiency

Introduction: GABAergic synaptic transmigration in the anterior cingulate (ACC) cortex of hypothyroid rats has been demonstrated by electrophysiologic recordings. In this study, the investigators primary aim was to determine whether the dose requirement of propofol used under the guidance of bispectral index monitoring is correlated with thyroid hormone levels in patients undergoing surgery under total intravenous anaesthesia.The investigators secondary aim was to determine whether there is a difference in the amount of GABA metabolite in the midline posterior (mPCC) and midline anterior cingulate cortex (mACC) region in normal and thyroid dysfunction patients on magnetic resonance spectroscopic imaging.
Method: After ethics committee approval, the study included patients with ASA I-II status: Group 1 (Control group n=40) patients with regular thyroid function tests and Group 2 (Hypothyroid group n=40) patients with hypothyroidism history with Levothyroxine sodium treated. Patients were evaluated preoperatively with the Montreal assessment scale and Beck anxiety scale. Written informed consent was obtained from all the patients, andparticipants underwent a brain MRI examination one day before the operation. The possible increase of GABA, which is present in the imaging with NAA, Cr and Glx in the range of 2.2-2.4 ppm, was recorded as an elevated spectral curve in the MR spectroscopy spectrum and its numerical equivalent was determined as the amount of chemical shifting in the y-axis. To determine GABA, the investigators set the sequence with optimal parameters, for which the investigators set the radio frequency pulse-echo time (TE) as 20 msec.The investigators set the voxel size as 2*3*3 cm to obtain optimal results. Researchers determined single voxel imaging MR spectroscopy sampling area in the midline anterior and posterior to the cingulate gyrus in all patients. Patients with spectral voxels outside the specified area, dense ventricular contamination within the voxel, or with intra-voxel dense ventricular contamination or seminal contamination were excluded from the study.
Patients were operated on under total intravenous anaesthesia. Anesthesia Induction was performed with 2 mg/kg propofol, 0.5 mg/kg fentanyl and 0.5 mg/kg rocuronium. Maintenance was achieved by bispectral index monitoring with propofol infusion at a dose of 1-8 mg/kg/min and remifentanil infusion at a dose of 0.5-2 mcg/kg/min with values between 40-60.

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