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INTRODUCTION

FOCUS POINTS

  1. Local anesthetics are the primary medication utilized in regional and neuraxial anesthesia or analgesia, with or without other adjuvants.

  2. The local anesthetics most commonly utilized are the amino-amides, bupivacaine, and lidocaine. However, given the decreased metabolism and clearance of amino-amides and resultant increased risk of local anesthetic toxicity in infants less than 6 months, chloroprocaine is preferred particularly for infusions administered for greater than 48 hours.

  3. Adjuvant analgesics are used in combination with local anesthetics to improve the quality of neuraxial analgesia and at the same time decrease the concentration of local anesthetic agent needed to achieve adequate analgesia.

  4. The single-shot caudal technique is the most commonly utilized neuraxial technique for ambulatory surgeries involving the truncal or lower extremity dermatomes.

  5. Spinal anesthesia can be particularly useful when used as the sole anesthestic in ex-premature and term infants in an attempt to avoid intubation and/or exposure to general anesthesia.

  6. Continuous epidural anesthesia/analgesia is primarily utilized for surgeries involving bilateral lower extremities, open thoracic surgeries, major intra-abdominal surgeries with visceral dissection, or spinal surgeries.

LOCAL ANESTHETICS AND DEVELOPMENTAL CONSIDERATIONS

Local anesthetics are the primary medication utilized in regional and neuraxial anesthesia or analgesia, with or without other adjuvants. The main mechanism of action regardless of chemical structure is the blockage of sodium channels with resultant blockade of neuronal impulse. As in adults, in order to prevent a neuronal impulse, three nodes of Ranvier must be blocked. The pharmacodynamic and pharmacokinetic differences in neonates and infants are imperative to understanding dosage administration. Local anesthetics largely exist in the ionized form and are therefore distributed to the extracellular body water compartment. In neonates and children, this space is nearly double that in adults and therefore results in lower peak plasma concentrations with initial bolus dosing due to the larger volume of distribution. However, due to synthetic liver function immaturity, infants under 6 months of age have decreased serum levels of both albumin and alpha-1-glycoprotein.1 The lower concentrations of these serum proteins allow for higher free or unbound local anesthetics, placing these patients at higher risk of local anesthetic systemic toxicity with repeated doses or continuous infusions. Luz et al. reported that free plasma bupivacaine concentrations were significantly higher in infants than in older children receiving continuous epidural anesthesia.2 Furthermore, the ability of the liver to clear and metabolize local anesthetics is greatly reduced in neonates, infants, and children under the age of 4.3 The amino-amide local anesthetics rely on the cytochrome p450 system in the liver for metabolism which is also not yet fully developed in the neonate and infant. The ability to conjugate is not reached until approximately 3 to 6 months of age.3 Due to the impaired hepatic clearance of the amino-amide local anesthetics, the elimination half-lives of these drugs are prolonged and the doses should be decreased for this group of patients.

The local anesthetics ...

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