The effects of tourniquet deflation on optic nerve sheath diameter in lower limb orthopaedic surgeries

Background: Pneumatic tourniquets are used in orthopedic surgeries to provide a bloodless surgical area and reduce blood loss. Tourniquet inflation causes metabolic changes, leading to cerebral vasodilatation and increased intracranial pressure (ICP). A new noninvasive method to measure optic nerve sheath diameter (ONSD) via ultrasonography to detect the raised ICP is reliable, inexpensive, and can be repeated many times. Materials and Methods: In this prospective observational study, 23 patients aged between 16 and 60 years, undergoing elective lower limb orthopedic surgeries under spinal anesthesia were included. After pre-anesthetic evaluation and obtaining informed written consent, an ocular ultrasound was performed to measure baseline ONSD in both eyes. Spinal anesthesia was administered and A pneumatic thigh tourniquet was applied as close as possible to the limb root and inflated to 150 mmHg–250 mmHg above the systolic blood pressure. A total of 5 measurements of ONSD were taken by the investigator (anesthetist): before giving spinal anesthesia, after giving spinal anesthesia, before tourniquet deflation, within 5 min, and after 10 min of tourniquet deflation. Results: In our study, the mean age of subjects was 34.57 ± 13.5 years. The majority were males (83%). The subjects showed an increase in ONSD after pneumatic tourniquet deflation in comparison with the baseline values, in the left eye [0.543 cm ± 0.021, P < 0.001] and the right eye [0.549 cm ± 0.021, P < 0.001], which were statistically significant. Conclusion: The impact of pneumatic tourniquet deflation on ONSD measurements recorded by ultrasound in lower limb orthopedic surgeries was significant and this change occurred with a simultaneous increase in end-tidal carbon dioxide (EtCO 2 ).