15 General Overview
Interest in regional anesthesia procedures in pediatric anesthesia has increased significantly in recent years. Due in part to the spread of ultrasonography, peripheral regional anesthesia is increasingly performed in children. In principle, all peripheral regional procedures that are known in adult anesthesia are possible in pediatric patients. But the smaller the child, the higher are the requirements for handling, the material used, and knowledge of the specific physiological, anatomical, and pharmacological characteristics of these patients.
Local anesthetic toxicity.
In children up to the age of 6 months, there is an increased risk of toxic complications after administration of local anesthetics (Berde 1992). Local anesthetics of the amide type are weak bases and are bound mainly to proteins in plasma. There is more than 90% binding of bupivacaine, ropivacaine, and levobupivacaine to alpha 1-acid glycoprotein and albumin in the serum. The free, unbound fraction of the local anesthetic is responsible for the pharmacological, but also for the toxic effects on the heart and central nervous system. In children under 6 months, plasma concentrations of the abovementioned proteins are still low, so that higher levels of free local anesthetic may result in the serum.
Amino amide local anesthetics are metabolized by the hepatic cytochrome P450 system. But enzyme activity in children reaches the levels of adult patients only after the age of 1 year.
Due to the immaturity of the P450 system in infants, there is limited clearance of local anesthetics of the amide type with the risk of accumulation. In addition, due to their higher total body water, newborns and infants have a larger distribution volume and a longer elimination half-life than children and adults (Suresh and Wheeler 2002).
Continuous peripheral regional anesthesia offers great advantages in terms of effective postoperative pain management. Nevertheless, elevated plasma levels with dangerous accumulation of local anesthetics can occur due to the mechanisms described here.
Short duration of action.
Owing to the smaller diameter and the still incomplete myelination of the nerve fibers in children up to toddler age, lower local anesthetic concentrations than required for adults are sufficient for a successful block. However, the duration of the regional anesthesia is shorter than in adults due to higher cardiac output and the associated rapid systemic absorption.
The plasma concentrations of the local anesthetics that can lead to toxic reactions are largely unknown in children. For this reason especially in children, the recommended local anesthetic dosage limits should not be exceeded (Table 15.1). The maximum quantity of local anesthetic must be calculated based on the body weight of children, and only that amount should be drawn up into a syringe to prevent accidental overdose.
Main indication: postoperative analgesia.
The main indication for the use of regional anesthesia in children is postoperative analgesia. These procedures are therefore usually performed after induction of general anesthesia until about the age of 10 years. The use of peripheral regional anesthesia in children after general anesthesia is widely accepted and is even recommended (Dalens 2006, Taenzer et al 2014).
Without sedation or general anesthesia, children usually tolerate regional anesthesia inadequately or not at all. A movement at the “wrong time” can have devastating effects and provoke a faulty puncture or even a nerve lesion. On the other hand nerve blocks under sedation or general anesthesia involve the risk of undetected complications. Signs of puncture-induced nerve injury or intravascular injection are missing.