From the Guidelines
The Armitage formula for caudal anesthesia recommends a bupivacaine dose of 0.5-1.0 ml/kg of 0.25% bupivacaine, with a maximum volume of 20 ml, and a toxic dose limit of 2-2.5 mg/kg (or 3 mg/kg with epinephrine) in a single dose to avoid systemic toxicity, as supported by the most recent guidance from the European Society for Paediatric Anaesthesiology (1).
Key Considerations
- The recommended dose of bupivacaine for caudal anesthesia is 0.5-1.0 ml/kg of 0.25% bupivacaine, with a maximum volume of 20 ml, as stated in the most recent guidance (1).
- The toxic dose limit for bupivacaine is 2-2.5 mg/kg (or 3 mg/kg with epinephrine) in a single dose to avoid systemic toxicity, as highlighted in previous guidelines (1).
- It is essential to aspirate before injection to avoid intravascular administration, inject slowly, and monitor the patient closely for signs of toxicity, such as perioral numbness, tinnitus, seizures, arrhythmias, or cardiovascular collapse.
Administration and Monitoring
- The duration of action is typically 4-8 hours depending on the concentration used and whether epinephrine is added (which can prolong the effect by reducing vascular absorption) (1).
- Long-acting local anesthetics, such as bupivacaine, levo-bupivacaine, and ropivacaine, can be used for landmark-based and ultrasound-guided caudal block, with recommended doses of 1.0 ml/kg (1).
- Preservative-free clonidine or morphine can be added to the local anesthetic, but with careful monitoring and at recommended doses of 1 to 2 micrograms/kg or 30 to 50 micrograms/kg, respectively (1).
From the Research
Armitage Formula for Caudal and Toxic Dose of Bupivacaine
- The Armitage formula is used to calculate the dose of bupivacaine for caudal analgesia in pediatric patients 2, 3, 4.
- According to the formula, the dose of bupivacaine is calculated based on the patient's weight, with a recommended dose of 1 ml/kg of 0.25% bupivacaine 3.
- Studies have compared the Armitage formula with other formulas, such as the Spiegel and Takasaki formulas, and found that it provides effective analgesia with minimal toxicity 2.
- The formula has also been used in combination with other anesthetics, such as desflurane, to determine the optimal end-tidal concentration for removal of the laryngeal mask airway in anesthetized children 3.
- The toxicity of bupivacaine and other local anesthetics, such as ropivacaine and levobupivacaine, has been studied, and it has been found that ropivacaine has a greater margin of safety than levobupivacaine 5.
- The Armitage formula has been found to be useful for calculating the dose of ropivacaine for caudal analgesia in pediatric patients, with a recommended dose of 1 ml/kg of 0.2% ropivacaine 4.
- Levobupivacaine has been found to be an effective agent for caudal anesthesia in children, with a recommended dose of 2.5 mg/kg 6.