Background  Although studies have shown that blood flow of the vertebral arteries will decrease in the hyperextension position, no studies have been conducted to monitor the dynamic changes of carotid artery blood flow, record the real experience of patients in real time, and thus prove the association of the change in carotid artery blood flow with headache discomfort in the hyperextension position.

  Objective  To investigate the influence of the hyperextension position on carotid hemodynamics in patients undergoing thyroid surgery and the association of the change in carotid hemodynamics with postoperative headache discomfort.

  Methods  A total of 20 healthy volunteers, aged 20-30 years, were selected to simulate the hyperextension position during thyroid surgery in department of ultrasound in our hospital in May 2019. Doppler ultrasound was used to measure the changes in the blood flow of the common carotid artery and the vertebral artery in the supine position and the hyperextension position at 10, 20, 30, 40, and 50 minutes, and the time and symptoms of headache discomfort were recorded at the same time.

  Results  The mean blood flow velocity of both common carotid arteries and vertebral arteries in the hyperextension position was significantly lower than that in the supine position (P＜0.05), and the blood flow volume in the hyperextension position was also significantly lower than that in the supine position (P＜0.05). The peak systolic velocity of the common carotid artery in the hyperextension position was significantly lower than those in the supine position (P＜0.05). During the experiment, 13 volunteers developed varying degrees of dizziness, headache, and shoulder discomfort, and the incidence rate of headache discomfort was 65%. In the hyperextension position, the degree of headache discomfort was negatively correlated with the mean blood flow velocity, blood flow volume, and peak systolic velocity of the left vertebral artery, the blood flow volume of the right common carotid artery, and the peak systolic velocity of the right vertebral artery (P＜0.05).

  Conclusion  The hyperextension position has certain influence on carotid hemodynamics and may lead to postoperative headache discomfort in patients undergoing thyroid surgery.