Postoperative nausea and vomiting is one of the most common postoperative complications second only to postoperative pain. Studies have reported that without any antiemetic prevention treatment, the overall incidence of PONV in surgical operations is up to 20-30%, and the incidence of PONV in high-risk patients such as thyroid surgery is even up to 70-80%. PONV not only increased discomfort and prolonged hospital stay; Severe cases can lead to wound dehysis, acid-base imbalance, water and electrolyte metabolism disorders, seriously affect the prognosis of patients. Although various prevention and treatment measures have been adopted in clinical practice, it still cannot be completely eliminated. Therefore, postoperative nausea and vomiting of thyroid is still a concern in clinical anesthesia work, so it is urgent to explore more simple and effective measures to prevent thyroid PONV. SGB is the injection of local anesthetics into loose connective tissue containing stellate ganglion. It has a clear effect on postoperative analgesia of thyroid surgery, and can play a certain role in preventing thyroid PONV by reducing the application of perioperative opioids. Few studies have reported that the incidence of PONV can be significantly reduced after the application of SGB in patients with thyroid surgery, which provides a certain basis for the prevention of thyroid PONV. Therefore, this study aims to explore the effect of right stellate ganglion block on preventing postoperative nausea and vomiting of thyroid, and to explore the possible mechanism of action.

Postoperative nausea and vomiting is one of the most common postoperative complications second only to postoperative pain. Studies have reported that without any antiemetic prevention treatment, the overall incidence of PONV in surgical operations is up to 20-30%, and the incidence of PONV in high-risk patients such as thyroid surgery is even up to 70-80%. The pathogenesis of postoperative nausea and vomiting is very complex, including central, peripheral receptors and multiple nerve pathways. When peripheral receptors are stimulated, the signal passes through the afferent nerve to the vomiting center, causing nausea and vomiting. The emetic chemical receptors are rich in many receptors, which can directly feel various toxins, metabolites or drugs in the blood and cerebrospinal fluid, project signals to the nerve center and then spread to the cerebral cortex, causing nausea and vertigo, or transmit signals along the vagus nerve, glossopharyngeal nerve, spinal nerve, etc. to the digestive tract, diaphragm and abdominal wall muscles, resulting in the opening of the sphincter in the upper esophagus and strong contraction of the diaphragm. Abdominal muscles contract, so that the stomach pressure increases, stomach contents through the digestive tract is expelled from the body, vomiting.

Thyroid, as the endocrine organ of human body, mainly secretes thyroid hormone and participates in human metabolism. With the progress of modern medical technology, although thyroid postoperative complications have decreased, due to the limited operating space of thyroid surgery, in order to fully exposed the surgical field of vision and facilitate the operation of surgeons, patients often take the cervical hyperextension position, that is, patients take the supine position with high shoulder pads. Tilt your head back so that your lower jaw, trachea, and sternum are at the same level, allowing the thyroid gland to protrate forward as much as possible. Although this position is easy for surgeons to operate, due to the complex anatomical structure around the thyroid gland, adjacent to important blood vessels and nerves, this position often causes thyroid surgical position syndrome in patients, that is, nausea and vomiting, dizziness, headache, tinnitus, neck radiation pain and other symptoms, which not only increases patients' pain, but also seriously reduces patients' medical experience.

Stellate ganglion block has been proved to be widely used in clinic and can play a positive role in multiple organs and systems of the whole body. In clinical work, stellate ganglion block is more widely used in the treatment of various pain, autonomic nerve disorders and other diseases. However, there are few clinical studies on whether stellate ganglion block can be used as an effective and feasible means to prevent postoperative nausea and vomiting and the related mechanisms to prevent the possible occurrence of nausea and vomiting. Therefore, this study will explore the preventive effect of stellate ganglion block on postoperative thyroid nausea and vomiting, and hope to explore its possible mechanism, so as to provide more effective and feasible methods for clinical prevention of postoperative nausea and vomiting and improve patients' medical comfort and satisfaction.

Inclusion Criteria:

1. Receiving thyroid surgery under general anesthesia
2. Age ≥18 years and ≤ 70 years
3. American Society of Anesthesiologists(ASA) physical status classification I-III.
4. Voluntary participation and ability to understand and sign the informed consent form.

Exclusion Criteria:

1. Patients with obesity(BMI>30 kg/m2)
2. contraindicated to stellate ganglion block
3. Patients who cannot cooperate with the study for any reason, or whom the investigator deems unsuitable for inclusion in this trial.

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