The aim of this study is to determine the impact of ultrasound-guided bilateral intermediate cervical plexus block on the surgical stress response in patients undergoing total thyroidectomy, as measured by the concentration of stress and inflammatory biomarkers in the participants' saliva and serum.

The study will be conducted on 48 subjects divided into two groups of 24: a control group receiving total intravenous anesthesia (TIVA) and an experimental group receiving TIVA combined with a bilateral intermediate cervical plexus block.

Investigators hypothesized that a combination of bilateral intermediate cervical plexus block and total intravenous anesthesia (TIVA) would reduce the surgical stress response, as measured by salivary and blood biomarkers, compared to TIVA alone in patients undergoing total thyroidectomy.

Should the research confirm the hypothesis, it will provide an objective scientific argument for including the block in standard anesthetic protocols for total thyroidectomy surgeries, with the ultimate goal of reducing the surgical stress response and ensuring faster patient recovery.

The study will be conducted at the Dubrava University Hospital, within the Department of Anesthesiology, Resuscitation, and Intensive Care Medicine and the Department of Otorhinolaryngology and Head and Neck Surgery. The sample will consist of 48 patients scheduled for total thyroidectomy, divided into two groups of 24 subjects each:

Group C (Control): total intravenous anesthesia (TIVA) Group E (Experimental): TIVA + bilateral intermediate cervical plexus block with 0.25% levobupivacaine

The study will include patients of both sexes, aged 18 and older, with euthyroid status, classified as ASA I and ASA II, for whom total thyroidectomy is indicated and who have signed an informed consent form to participate in the study.

Exclusion criteria include patients who refuse to sign the informed consent, patients with an infection at the block injection site, hypersensitivity or contraindications to the drugs used in the study, presence of hypothyroidism or hyperthyroidism at the time of surgery, presence of substernal goiter, or additional surgical interventions during the procedure. Furthermore, patients with prior neck surgery or radiation, coagulopathy, uncontrolled respiratory disease, diabetes mellitus, autoimmune disease, patients on chronic corticosteroid therapy, smokers and pregnant women will be excluded.

The study is single-blinded; participants will only learn which group they were assigned to after the completion of the postoperative follow-up period.

The efficacy of the investigated protocols and their comparison will be assessed by laboratory determination of surgical stress response biomarkers in the participants' saliva and serum.

STUDY PLAN Participant randomization into the control or experimental group will be performed using a computer-generated list of random numbers with a 1:1 allocation ratio. The assignment sequence will be predetermined and sealed in numbered envelopes, which will be opened immediately before the induction of anesthesia.

Due to the circadian rhythm of cortisol and alpha-amylase, all study participants will undergo surgery at comparable times of day.Thirty minutes before the start of surgery, venous blood samples will be collected to determine baseline concentrations of cortisol, IL-6, CRP, glucose, alpha-amylase activity and total white blood cell count. Simultaneously, a non-stimulated saliva sample will be collected using a salivette to determine salivary concentrations of cortisol, IL-6, and alpha-amylase activity.

Premedication with midazolam (5 mg i.m.) will be administered on the ward 20 minutes before the surgical procedure.

For the induction of general anesthesia, sufentanil (0.15 mcg/kg), propofol (2 mg/kg), and rocuronium (0.6 mg/kg) will be used. Following endotracheal intubation, general anesthesia will be maintained with a continuous infusion of propofol. Anesthesia depth will be monitored using the Bispectral Index (BIS), with the propofol dose titrated to maintain BIS values between 40 and 60. Neuromuscular relaxation will be maintained by intermittent administration of 10 mg rocuronium every 30 minutes. After induction, 0.2 mg/kg of intravenous dexamethasone will be administered for anti-edematous prophylaxis. The dexamethasone dose is standardized in both groups, and its influence on inflammatory markers will be accounted for during data interpretation.

Following the induction of general anesthesia, the experimental group will receive a bilateral intermediate cervical plexus block Systolic, diastolic, and mean arterial pressure, heart rate, and SpO2 will be recorded upon entry into the operating room, after induction, after the surgical incision, and every 15 minutes during surgery as parameters of the hemodynamic response to surgical stress. End-tidal CO2 (EtCO2) and BIS values will also be recorded at 15-minute intervals after induction. In the event of an increase in heart rate or mean arterial pressure of 20% or more from baseline, a bolus of 0.1 mcg/kg sufentanil will be administered. During wound closure, 1 g of intravenous paracetamol will be administered. At the end of the surgery, reversal of neuromuscular blockade will be performed with sugammadex at a dose of 2 mg/kg.

After emergence, block success will be confirmed by the absence of pain during a pinprick test in the anesthetized area of the neck.

Postoperatively, heart rate, systolic, diastolic, and mean arterial pressure, SpO2 and respiratory rate will be recorded at 15 minutes, 30 minutes, and 1, 4, 12, and 24 hours after surgery. At the same time points, postoperative pain levels will be assessed using a Visual Analog Scale (VAS) from 0 to 10 at rest and during swallowing. For pain scores of VAS >4 , 100 mg of intravenous ketoprofen will be administered. If pain persists, an additional 1 mg/kg of tramadol will be given. The analgesic protocol is standardized for both groups. Total analgesic consumption during the first 24 hours and the time to first analgesic request will be recorded.

The degree of postoperative sedation will be assessed using the Richmond Agitation-Sedation Scale (RASS) at 15 minutes, 30 minutes, 1, and 4 hours postoperatively.

Saliva samples for cortisol, IL-6, and alpha-amylase will be collected 1 and 24 hours after surgery.

Venous blood samples for cortisol, IL-6, alpha-amylase, CRP, glucose, and total white blood cell count will be taken at 1, 24, and 48 hours postoperatively.

STATISTICAL ANALYSIS Based on previous research, to detect differences between the two groups with an effect size f = 0.40, a power of 0.80, and a significance level of 0.05, the minimum required sample size is 48 participants (24 per group). Categorical data will be presented as absolute and relative frequencies. Differences in categorical variables will be tested using the Chi-square test or, where appropriate, Fisher's exact test. Changes in categorical variables between measurements will be analyzed using the McNemar-Bowker test and the Marginal Homogeneity test.The normality of distribution for numerical variables will be assessed using the Shapiro-Wilk test. Continuous data will be described by the mean and standard deviation for normally distributed data; otherwise, data will be presented as the median and interquartile range (IQR).Differences in continuous variables between the control and experimental groups will be tested using the Student's t-test or the Mann-Whitney U test, depending on the normality of the distribution (with the reported difference and its associated 95% confidence interval).Differences in continuous variables between two time points will be tested using the paired t-test or the Wilcoxon signed-rank test (with the reported difference and 95% CI), depending on the distribution. For comparisons across more than two time points, repeated measures ANOVA or the Friedman test (with post hoc Conover test) will be used.The correlation between normally distributed continuous variables will be assessed using the Pearson correlation coefficient, while the Spearman correlation coefficient will be used for non-normally distributed data.All p-values will be two-sided. The level of significance will be set at alpha = 0.05.

The expected contribution of this research is based on evaluating the impact of bilateral intermediate cervical plexus block on the modulation of the surgical stress response during total thyroidectomy and the postoperative period. The study aims to determine whether the application of this method is associated with lower consumption of opioid and non-opioid analgesics and a more stable cardiovascular profile in patients. These results could provide a scientific foundation for integrating this regional technique into standard multimodal analgesia protocols, with the goal of optimizing perioperative care.

Inclusion Criteria:

• patienets of both sexes
• 18 years of age and older
• ASA I or ASA II
• euthyroid status
• signed informed consent

Exclusion Criteria:

• patients who refuse to sign the informed consent form
• infection at the block injection site
• hypersensitivity or contraindications to the medications used in the study
• hypothyroidism or hyperthyroidism at the time of surgery
• presence of substernal goiter
• additional surgical interventions during the procedure
• history of previous neck surgery or radiation
• coagulopathy
• uncontrolled respiratory disease
• diabetes mellitus
• autoimmune disease
• chronic corticosteroid therapy
• smokers
• pregnant women.