Pediatric anesthesia presents distinctive challenges, particularly concerning appropriate dosage administration of local anesthetics for spinal anesthesia (SA). Spinal anesthesia in infants has been linked to a lower incidence of hypotension, hypoxia, bradycardia, and postoperative apnea in comparison to general anesthesia (GA); ensuring a high level of cardiovascular and respiratory stability.

Additionally, SA has been linked to lower operating room time, post-anesthesia care unit, hospital length of stay, corticosteroid administration, narcotic requirements, postoperative emesis, and cardiopulmonary complications in comparison to GA.

A reduction in systemic blood pressure frequently accompanies neuraxial blocks in adults, necessitating intervention. Nevertheless, spinal, caudal, or epidural blocks administered to children under six years old are not associated with any substantial alterations in blood pressure. In children aged 6 to 10, there is a linear decrease in blood pressure that will reach a plateau at approximately a 30% decrease in those beyond the age of 10. Conversely, younger children require no additional precautions.

Bupivacaine, has a narrow therapeutic index in children, and its dosing requires careful consideration to strike a balance between effective anesthesia and the risk of toxicity. The traditional method of dosing bupivacaine in pediatric spinal anesthesia is based on the child's body weight. This weight-based dosing considers the assumption that children's drug clearance correlates with their body mass. However, this approach might not account for the maturational changes in drug handling by pediatric patients or the variability in spinal column length and cerebrospinal fluid volumes, not always proportional to weight but may evolve with age.

Emerging evidence suggests that age-based dosing may be more effective. It hypothesizes that developmental pharmacokinetics, including changes in body composition, organ function, and drug-receptor differences, can influence bupivacaine metabolism and action more significantly than body mass alone. By accounting for the age-related anatomical and physiological changes, age-based dosing could result in more precise and effective anesthesia with a decreased risk of adverse outcomes.

To the authors knowledge, there is no study comparing age-based and weight-based bupivacaine dosing for pediatric spinal anesthesia in children undergoing elective infra-umbilical surgery.

Inclusion Criteria:

• ASA I and II
• Both genders
• Elective infra-umbilical surgeries with anticipated duration ≤ 90 minutes.

Exclusion Criteria:

• Guardian refusal.
• Children with major congenital heart disease, including septal defects.
• Patients with neuromuscular disorders or high intracranial pressure.
• Children with spinal deformities or morbid obesity (BMI above the 99th percentile).
• Children with a history or family history of coagulation disorders.
• Children with local infection at the site of skin puncture for spinal anesthesia.
• Children with known allergy to bupivacaine.
• Surgeries requiring head down (Trendelenburg) or prone position.
• Unexpected prolongation of surgery > 90 minutes.