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

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.

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.

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.

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 (EtCO₂).