Effect of Neck Rotation With Flexion on Ultrasonographic Optic Nerve Sheath Diameter in Patients Undergoing Elective Craniotomy

Background
Extreme neck positioning to facilitate craniotomy can result in impaired venous drainage from the brain and a subsequent rise in increased intracranial pressure (ICP). The effects of varied neck positioning intraoperatively on ultrasonographic optic nerve sheath diameter (USG-ONSD) are still unexplored. This study aims to quantify the angle of neck rotation and flexion that can cause a significant increase in USGONSD in patients undergoing elective craniotomy. Methods
A total of 100 patients were recruited in this non -randomized study and equally divided into two groups. In one group, patients with neck rotation <= 30 degrees and in another group, patients with neck rotation >30 degrees with varying degrees of neck flexion were included. The average of three USG-ONSD measurements in both eyes was obtained and compared in both groups at baseline, after positioning, and at the end of the surgery after making the neck neutral. Results
The results of 100 recruited patients were analyzed. All the patients had neck flexion in the range of 40(degrees) to 45(degrees), whereas the neck rotation ranged from 10(degrees) to 45(degrees) The USG-ONSD of both eyes changed significantly from baseline to post -positioning time point in patients with neck rotation >30(degrees) (right eye p=0.038, left eye p=0.04) when compared to neck rotation <= 30(degrees) There was no significant change in USG-ONSD from baseline to the postoperative time point after making the neck neutral (right eye p=0.245, left eye p=0.850) in both groups. Conclusions
This study demonstrates that USG-ONSD, a surrogate measure of ICP, increased significantly after neck flexion with rotation >30(degrees) in neurosurgical patients. However, USG-ONSD becomes comparable to baseline after putting the patient's neck in a neutral position after surgery.