Effect of Spinal Needle Type on Optic Nerve Sheath Diameter

The optic nerve sheath is a continuation of the dura mater, extending along the subarachnoid space surrounding the optic nerve. Consequently, changes in intracranial pressure cause an augmentation or contraction in the diameter of the optic nerve sheath, which is coreleted with intracranial pressure. Participants undergoing lower extremity operations (ankle, distal tibia and fibula surgeries) using a tourniquet under spinal anesthesia will be investigated. Spinal anesthesia will be performed with a 25 G Whitacre, 25 G Quincke, or 27 G Quincke needle, depending on the study group. Optic nerve sheath diameter (ONSD) measurements will be performed before spinal anesthesia; and 5 minutes, 15 minutes,,24 hours after spinal block, respectively.The 4th measurement will be performed after tourniquet is opened. Measurements will be done with 15 MHz linear ultrasound (US) probe in B mode, 3 mm behind the posterior globe in the transverse plane from both eyes, on upper eyelid. Values will be recorded numerically. The impact of spinal anesthesia administered using various needle designs (Quincke and Whitacre) and sizes (25G-27G) on intracranial pressure will be investigated.

Optic nerve sheath diameter (ONSD) measured with US emerges as a standout intracranial pressure reflector among non-invasive modalities as a bed side assessment. Different types of needles used in spinal anesthesia cause different lesions in the dura. Lesions created by Quincke needles are small and clean-cut opening in the dural membrane, while those from Whitacre needles result in a more traumatic opening. Also it is known that CSF leakage increase when larger needles are used. As one of postspinal headache mechanism is decrease in the intracranial pressure, the investigators aim to investigate the ONSD changes reflecting intracranial pressure changes.

Participants undergoing lower extremity operations (ankle, distal tibia and fibula surgeries) using a tourniquet under spinal anesthesia will be investigated. Spinal anesthesia will be performed with a 25 G Whitacre, 25 G Quincke, or 27 G Quincke needle, depending on the study group. ONSD measurements will be performed before spinal anesthesia as baseline; and 5 minutes, 15 minutes, 24 hours after spinal block, respectively. Also a measurement will be performed after opening of the surgical tourniquet. Measurements will be done with 15 MHz linear ultrasound (US) probe in B mode, 3 mm behind the posterior globe in the transverse plane from both eyes. Values will be recorded numerically. The impact of spinal anesthesia administered using various needle designs (Quincke and Whitacre) and sizes (25G-27G) on intracranial pressure will be investigated.

Eligibility Criteria:
Inclusion Criteria:

* American Society of Anesthesiologists (ASA) I-II Risk Classification
* Elective orthopedic lower extremity surgery
* Using a tourniquet
* Spinal anesthesia

Exclusion Criteria:

* Bilateral tourniquet usage
* History of orbital trauma
* Optic nerve pathology
* Glaucoma
* Asthma
* Coronary obstructive or pulmonary disease
* Previous corneal or intraocular surgery
* Increased intracranial pressure
* Coagulopathy
* Local site infection
* Refusing to participate in the study