Predictive Performance Of Armitage And Takasaki Formulas In Estimating Local Anesthetic Volume For Pediatric Caudal Block In Lower Abdominal Surgery: A Prospective Comparative Study

Background: Caudal epidural anesthesia is a widely used technique for pediatric lower abdominal surgeries. However, there is no universal consensus on the optimal formula for estimating local anesthetic (LA) volume. The Armitage formula, though well-established, may lead to overestimation, while the Takasaki modification introduces age- and weight-adjusted dosing aimed at minimizing potential toxicity. This study evaluates the predictive performance of both formulas in pediatric caudal blocks. Methods: This prospective, randomized, comparative observational study was conducted over six months in the Department of Anaesthesiology at Karpaga Vinayaga Institute of Medical Sciences & Research Centre. Sixty children aged 6 months to 8 years undergoing elective lower abdominal surgeries were randomized into two groups of 30 each. Group A received LA volume as per the Armitage formula (1 mL/kg to T10), while Group T received volume calculated by the Takasaki formula (weight × [0.07 + 0.002 × age in months]). All blocks were administered with 0.25% bupivacaine following standard anesthesia protocols. Results: Demographic characteristics were comparable between the two groups (p > 0.05). Group A (Armitage) demonstrated significantly faster onset (6.4 ± 1.3 vs. 8.1 ± 1.5 min, p < 0.01), longer duration of analgesia (345 ± 32 vs. 290 ± 35 min, p < 0.01), and fewer patients requiring rescue analgesia (3/30 vs. 9/30, p = 0.04). However, Group T (Takasaki group) used significantly lower volumes of LA (8.5 ± 0.9 vs. 10.2 ± 1.1 mL, p < 0.001). Adverse effects were minimal and statistically insignificant in both groups. Conclusion: The Armitage formula yielded superior block characteristics, while the Takasaki method reduced anesthetic volume, potentially enhancing safety in younger children. Both methods were safe. Formula selection should be tailored to patient age, weight, and clinical context to balance efficacy and safety in pediatric caudal anesthesia