The aim of this study is to evaluate the effects of non-pharmacological factors-such as age, sex, body mass index, paraspinal muscle mass, vertebral canal anatomy, patient positioning, and injection technique-on the duration of sensory and motor block in patients undergoing spinal anesthesia, and to investigate the potential relationships between these factors and block duration.

It is well known that the level of sensory and motor block following spinal anesthesia varies among individuals. This variability is not only related to the dose of local anesthetic but has also been reported to be associated with patient-related non-pharmacological factors. In particular, a relationship has been demonstrated between body mass index (BMI) and both the level and duration of spinal block, with higher block levels and prolonged block duration observed in patients with increased BMI. This phenomenon is thought to be associated with epidural venous distension due to increased intra-abdominal pressure and a reduction in subarachnoid cerebrospinal fluid (CSF) volume. A decrease in CSF volume may facilitate greater cephalad spread of intrathecal local anesthetic agents, thereby prolonging block duration.

Paraspinal muscle mass is also an important anatomical parameter that may influence intra-abdominal pressure and epidural space compliance, and thus may play a determining role in the spread of spinal anesthesia. However, although several studies have investigated the relationship between BMI and body composition and spinal block characteristics, the number of clinical studies directly evaluating the association between ultrasonographically measured paraspinal muscle mass and spinal anesthesia block duration remains limited. Therefore, ultrasonographic measurement of paraspinal muscle thickness may serve as a potential predictor of spinal block duration.

Inclusion Criteria:

• Patients aged 18-80 years
• ASA physical status I-III
• Patients scheduled for elective lower abdominal surgery.

Exclusion Criteria:

• Patient refusal to participate
• Coagulopathy
• Use of medications or substances known to impair coagulation
• Pregnancy, sepsis
• Shock
• Severe aortic or mitral regurgitation
• Peripheral vascular disease
• Increased intracranial pressure
• Mental disorders
• Spinal column deformity
• History of previous spinal surgery.

Patients aged 18-80 years, male and female, classified as ASA physical status I-III, and scheduled for elective lower abdominal surgery.

All the statistical data will be shared if required