Upper Extremity Position and Intraocular Pressure During Spinal Anesthesia

Intraocular pressure (IOP) is influenced by aqueous humor dynamics as well as episcleral venous pressure, which may be affected by body and extremity positioning. Changes in venous return, intrathoracic pressure, and systemic hemodynamics during surgical positioning may lead to measurable alterations in IOP. Although the effects of head and body position on IOP have been investigated, the impact of different upper extremity positions during spinal anesthesia has not been clearly established. This prospective randomized controlled trial will be conducted at Elazığ Fethi Sekin City Hospital. Adult patients (18-80 years, ASA I-III) scheduled for elective open inguinal hernia repair under spinal anesthesia will be included. After written informed consent, participants will be randomly assigned using sealed opaque envelopes to one of three upper extremity positions: (1) arms adducted alongside the body, (2) arms positioned at 90° abduction, or (3) arms crossed over the chest. Intraocular pressure will be measured bilaterally using a Tono-Pen AVIA tonometer by the same ophthalmologist. Measurements will be performed at predefined time points: before spinal anesthesia (T0), 5 minutes after spinal anesthesia (T1), at surgical incision (T2), at 15 minutes (T3), at 30 minutes (T4), at skin closure (T5), and in the recovery unit (T6). Head and neck position will be maintained neutral throughout the procedure. Hemodynamic parameters including mean arterial pressure, heart rate, and oxygen saturation will be recorded simultaneously. The primary outcome is the change in IOP over time between the three groups. Secondary outcomes include hemodynamic changes and group-by-time interaction effects. Data will be analyzed using appropriate parametric or non-parametric tests according to distribution. Repeated measurements will be evaluated using linear mixed-effects models. A p-value \<0.05 will be considered statistically significant.