Effect of caudal block injection speed on optic nerve sheath diameter in pediatric surgeries: A prospective observational cohort study

Perioperative pain management in children is challenging due to limited communication and the risk of long-term psychological effects. Regional anesthesia, particularly the caudal block (CB), is frequently used in pediatric surgery for lower abdominal and urogenital procedures. However, the influence of injection speed during CB on intracranial and hemodynamic responses remains unclear. This prospective observational cohort study included 64 pediatric patients (American Society of Anesthesiologists I-II, aged 1-7 years) undergoing elective lower abdominal or urogenital surgery under general anesthesia. All patients received a CB with 0.8 mL/kg of 0.125% bupivacaine. Injection speed was not assigned by the study protocol but reflected routine clinical practice, and patients were categorized according to the injection speed used (0.25 mL/s or 0.5 mL/s). The primary outcome was the change in optic nerve sheath diameter (ONSD) over time and between injection-speed groups. Secondary outcomes included heart rate and mean arterial pressure, recorded at baseline and at predefined time points after the block. Baseline ONSD values were similar between groups. ONSD increased transiently after caudal injection in both groups, with a significantly greater increase in the fast-injection group immediately after the block. These differences were short-lived, and ONSD values returned toward baseline within 10 to 20 minutes, with no persistent intergroup differences. Heart rate and mean arterial pressure showed mild, transient reductions in both groups, which were slightly more pronounced in the fast-injection group but remained within physiological limits. Different caudal injection speeds were associated with distinct transient changes in ONSD and hemodynamic parameters. Slower injection was associated with more gradual physiological responses during the early postinjection period.