The effect of head position on the optic nerve sheath diameter in patients undergoing thyroid surgery

Aim: In thyroidectomy surgery, the patient's head is placed in hyperextension and the patient is placed in a semi-sitting position to facilitate access to the surgical site. This position of the head causes a decrease in venous return or partial obstruction of venous return due to stretching of the neck veins. The aim of our study is to demonstrate the effect of surgical position on intracranial pressure by measuring the optic nerve sheath diameter (OSSD) using ultrasonography in patients undergoing thyroid surgery and to determine its correlation with post-operative headaches. Material And Method: Our study was conducted prospectively and randomly in patients undergoing elective total thyroidectomy. Patients aged 18-65 with an ASA score of 1-2 and an operation time of less than 4 hours were included in our study. Patients were positioned in the semi-Fowler position with a 30° extension of the head. Bilateral OSSD surgical positioning was applied, and after ensuring haemodynamic stability for 5 minutes and at the end of the operation, measurements were taken twice using ultrasound, and the average was recorded. The Visual Analogue Scale (VAS) was used to assess postoperative pain intensity. Headache was assessed and recorded at 15 minutes, 30 minutes, 1 hour, 24 hours, 3 days, and 7 days postoperatively. Results: At the end of surgery, the average optic nerve sheath diameter measured in both eyes (4.83±0.78 mm) showed a significant increase compared to the measurements taken after intubation (4.17±0.57 mm) (p<0.001). It was found that VAS values decreased over time in the postoperative period (p<0.05). No relationship was found between changes in optic nerve sheath diameter during surgery and postoperative pain scores (p>0.05). Conclusion: In our study, it was observed that neck extension position increased optic nerve sheath diameter in patients undergoing thyroid surgery, but it was not associated with postoperative headache. Keywords: Thyroidectomy, Headache, Optic Nerve Sheath Diameter Measurement, Head Hyperextension, Intracranial Pressure