Pediatric Regional Anesthesia: Beyond the Caudal

Abstract

Pediatric regional anesthesia has gone through significant development in recent years with advances in safety information, pharmacology, and block techniques. There is an increasing interest in regional anesthesia in pediatrics beyond the common caudal, epidural, or spinal. With improvements in equipment that are specific to children and the addition of ropivacaine as a proven local anesthetic, pediatric regional anesthesia, and specifically peripheral nerve blockade, should continue to gain popularity. The last literature reviews in major anesthesia journals on pediatric regional anesthesia were published more than a decade ago (1,2). The popularity of regional anesthesia as a supplement to general anesthesia in children has grown out of recognition of its advantages beyond simple avoidance of general anesthesia. Suggested benefits include the decreased intraoperative requirement for general anesthetics, less of a need for the use of parenteral opioids thereby limiting the incidence of respiratory depression, and limitation of stress hormone responses (1,3,4). Improved postoperative analgesia and shortened recovery for outpatient surgery have provided further impetus for refinement of techniques that can be used safely in combination with general anesthesia in children. The goal of these techniques that specifically and peripherally target the location of the surgery is to minimize the undesirable side effects of central blocks such as urinary retention, hypotension, and muscle weakness in unaffected areas. Additionally, when compared with central regional blockade, peripheral nerve blocks may be associated with a decreased incidence of serious sequelae as demonstrated in a large-scale study by the French-Language Society of Pediatric Anesthesiologists, which led the authors to suggest that peripheral blocks be used more often in place of central blocks when appropriate (5). The following review will discuss the safety and the unique differences between adults and children that influence the anesthetics and techniques of peripheral nerve blockade in children. Safety A common misconception is that performing blocks on anesthetized patients, particularly in children, is not safe. The anesthesia literature that has provided safety data on pediatric regional anesthesia has concluded that, overall, these techniques have extremely small complication rates (5–11). The limitation to these reports is that they typically only include information on the central neuraxis blocks. An exception to this limitation was demonstrated by the report from the French-Language Society of Pediatric Anesthesiologists (5). This one-year study of 24,409 regional blocks in children revealed a complication rate of 1.5 per 1000 in the 60% of children receiving central blocks, and 0 per 1000 in the 38% of children who received peripheral nerve blocks. The authors concluded that these findings should renew the interest in peripheral techniques by anesthesiologists who have sufficient experience in their usage. A subsequent editorial showed the pitfalls with the French study, such as selection bias and lack of efficacy data on the peripheral nerve blocks (12). This same editorial, however, also reconfirmed the advantages of decreased urinary retention and increased duration of analgesia by using a peripheral nerve block. Certain inherent features of pediatric anatomy and physiology add an additional level of safety to regional anesthesia and specifically to peripheral nerve blockade. These features include a lack of hypotensive response from a sympathectomy produced by the local anesthetic, which is often seen in adults, but only rarely in children. This effect may be a result of either the immature sympathetic nervous system in children younger than five–eight years or a result of the relatively small intravascular volume in the lower extremities thereby limiting venous pooling (13). Although this is a phenomenon of central blockade, it is reassuring to know that severe hypotension should not occur as a result of accidental epidural spread from either a lumbar plexus or paravertebral block. The presence of loose perineurovascular sheaths offers another advantage to regional anesthesia in children by allowing a wider spread of local anesthetic for a large area of analgesia from a single injection site. This should theoretically decrease the chance of inadvertent local anesthetic overdose that may occur with multiple injections. Pharmacology and Physiology When performing regional techniques in pediatric patients, one should keep safety in mind and be aware of the differences between adults and children with regard to pharmacology, physiology, and appropriate dosing. Perhaps the most important difference between adult and pediatric pharmacology is the increased risk of toxicity when using local anesthetics in the younger age groups. Infants younger than two months are particularly at risk because of immature hepatic metabolism and decreased plasma proteins such as albumin and α-1-acid glycoprotein (14). This age-effect results in increased serum concentrations of the unbound amide local anesthetics, particularly bupivacaine and ropivacaine, which are normally 90% protein-bound (15). Infants also have decreased levels of plasma pseudocholinesterase that theoretically could increase the risk of toxicity with ester local anesthetics (16,17). This does not appear to be clinically relevant as the half-life of ester anesthetics such as chloroprocaine is still within the ranges of adult patients. All children may be at increased risk of local anesthetic toxicity because of the rapid increase in blood levels of local anesthetic that may occur as a result of the relatively higher cardiac output and regional blood flow that are present in this age group (18,19). Although the routine use of epinephrine for test dosing is controversial because of its lack of total reliability, the addition of epinephrine to the local anesthetic solution may be used to decrease the rapid vascular uptake that can occur at the site of injection. This effect was illustrated in a study that compared plain bupivacaine with bupivacaine and epinephrine 1:200,000 (5 μg/mL) for a fascia iliaca compartment block (20). The maximum plasma concentration in the plain bupivacaine group was 1.1 μg/mL and peaked at 20 minutes compared with a level of 0.35 μg/mL in the bupivacaine with epinephrine group, which peaked at 45 minutes. Also, because the vast majority of children receive regional blocks while under general anesthesia and are unable to describe the prodrome that occurs from intravascular injection of local anesthetic, epinephrine 1:200,000 may aid in detecting the inadvertent intravascular delivery of local anesthetic before neurologic or cardiac sequelae (21). In the presence of halothane, the use of epinephrine as a test dose has been shown to be most reliable when the patient has received atropine, 10 μg/kg, before the test (22). This addition of atropine may depress the parasympathetic tone and thus enhance the sympathetic accelerator effect of epinephrine. This effect of atropine was not present when tested in a similar fashion in the presence of sevoflurane (23). In both studies, an increase in heart rate of 10 bpm was found to be an indication of intravascular injection, whereas using the older criteria of 20 bpm would result in a large number of false negatives of intravascular injection. A 25% increase in T wave amplitude has been shown to be as reliable an indicator as heart rate increase (24). Whether or not epinephrine has been added to the local anesthetic, it is important to remember that there is no good substitute for meticulous attention to the electrocardiogram for ST-T wave changes and slow, incremental dosing (25). Aspiration of blood, although helpful if present, is not reliable, and it is unknown what the relationship between a negative aspiration and the possibility of a positive test response may be when performing a peripheral nerve block in children. Peripheral nerve blocks, with the exception of intercostal blockade, should decrease the risk of toxicity from increased uptake when compared with central neuraxis blocks. The following blocks are in order of increasing speed of absorption: 1. Peripheral nerve blocks of the lower extremity, 2. Peripheral nerve blocks of the upper extremity, 3. Caudal blocks, 4. Epidural blocks, 5. Intercostal nerve blocks, 6. Interpleural analgesia, and 7. Topical airway applications. To prevent the occurrence of neurologic and cardiac side effects, maximal dosing guidelines should be strictly followed. The maximum recommended doses of the amides most commonly used in children are presented in Table 1. Ropivacaine has yet to have appropriate pediatric dosing established, although it appears to be nearly equipotent to bupivacaine in central and peripheral blockade (26–29).Table 1: Maximal Allowable Doses of Amide Local AnestheticsInherent physiologic properties in children result in a decreased minimum anesthetic concentration required to block impulse conduction (30). In younger children, particularly infants, nerves have a thinner myelin sheath, a smaller fiber diameter, and a shorter internodal distance. For these reasons, it is possible to produce an adequate surgical block by using smaller concentrations of local anesthetics in children compared with adults. Although strict age criteria for achieving the adult minimum anesthetic concentration are yet to be established, clinical experience suggests that the smaller concentrations provide sufficient surgical block for children who are younger than the early school ages. The larger concentrations are required for adequate surgical analgesia in the older children and adolescents. Future study to determine the ages and concentration requirements would help to clarify this issue. Regardless of the local anesthetic chosen or the volume, acetaminophen or a nonsteroidal may be a useful adjunct to improve postoperative analgesia. For example, rectal acetaminophen 35–40 mg/kg or ketorolac 0.5–1 mg/kg will provide additional analgesia without sedating effects and will result in less postoperative nausea and vomiting (31–33). Specific guidelines and further recommendations on adjunctive therapy, although an important part of the overall regional anesthesia experience, are beyond the scope of this review. Equipment Despite the risks of increased toxicity in children, the use of the appropriate equipment should help decrease the risk of injury. Although not proven that a nerve stimulator decreases the risk of neuropathy in anesthetized children, we recommended the use of one to improve the success rate with peripheral nerve blocks. When used in combination with insulated needles, the ability to locate a peripheral nerve in children becomes more reliable despite the relatively small size and variability in anatomy, in our experience. A 1- or 2-inch insulated needle will suffice for the vast majority of peripheral nerve blocks in children, with the exception of sciatic block in older children that will require a 4-inch The nerve stimulator is at to if using and at for the nerve is as seen by muscle the response is is decreased to less than and the of the needle should be that adequate but not muscle response is still one that the muscle group with at less than the needle should be and on the chance that the is In anesthetized children, will not be one should for such as increased heart rate or muscle response at of the blocks in this review will require a nerve stimulator or an insulated needle for An may be to locate the sciatic nerve by using the by of With an of anatomy and pharmacology, and the appropriate pediatric anesthesiologists are to and peripheral nerve blocks in an A of peripheral nerve blocks will be presented with possible and The plexus is of and and that the and The nerve block may be used for such 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not to the to the sciatic and of were from local the should not to this block to the sciatic nerve that is popularity in pediatrics is the block. 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For example, a adult may receive 10 of ropivacaine in a peripheral nerve this is on a per for a the rate would be of This would to the which is the maximum of recommended for central blocks This example, of of adult data to pediatrics and ropivacaine data from bupivacaine experience with of local anesthetics in peripheral nerve in children have recommended a rate of of bupivacaine Although uptake of local anesthetic from peripheral nerve in children is not yet uptake is less from peripheral nerves when compared with central blocks, the of safety should be There to be in the area of postoperative using in children. Peripheral nerve blockade for in the and nerve blocks. nerve blocks have been shown to provide postoperative for and and for and with no lower weakness Additionally, blood levels of local anesthetics have been shown to be the in children with blocks for either or The and nerves both from the lumbar nerve and the before to the of the and upper of these nerves is by a and to the A or needle is to the of the and Local anesthetic is as the needle is to the and the needle the a is as the muscle is Local anesthetic is in a the of the muscle and and may be the the nerves can be anesthetized by local anesthetic the at the of the before often in combination with of the this is at the of the to of the anatomy, the intraoperative advantages of a regional anesthetic with general anesthesia. The block should be relatively of when used with attention to and to the nerve block is an side and has been blockade for on the nerve and anesthesia. The most common on the is are on without the of anesthesia have shown that the stress response of to is less when with of anesthesia and that block is more than either nerve block or of a of local anesthetic before For older children under general anesthesia, nerve block is as for postoperative as blockade with effects and blood levels of local anesthetic the nerve block has also been as an to general anesthesia in children age years block postoperative analgesia surgery and should result in a lower incidence of compared with techniques The of the is the two which are of the nerves from the The nerves the in the of fascia to the and the two of the of the The and nerves a small of the of the of the and are from the lumbar These nerves need not be for a simple techniques have been for the The most important are to vascular and the of a block is and is to a is by local anesthetic the of the a as the block is of local anesthetic is be to keep the needle to blood and to use local The duration of analgesia is on the local anesthetic may provide of analgesia or more Perhaps the most in regional anesthesia is the use of paravertebral nerve blocks This block has as an to general anesthesia in adults for of surgery and is also an adjunct with general anesthesia in children who surgery or requirements have been shown to be lower by using a when compared with a epidural in children surgery To a in children, it is important to review the of the paravertebral of the of size in children, one should not only be aware of the but also use a of to the than the location by The is in the The of the are at the levels that need to be for the Although the from the to of is in adults, a of in children is that the from the to the of should to the from one to There are also that are on The for from to paravertebral in and the for in A needle or needle with and may be The needle is to the on the side at the to and at the level of the The needle is the is The needle is the of the a is and a of to is used to the paravertebral the The of is similar but not as the of the when performing an block. is to the at the to the between of of the include vascular and hypotension The complication should rarely be seen in children because of a lack of sympathectomy response in younger than This was by as no hypotension was in the children in the study who received a To use this block in children, one may use a single injection of bupivacaine or ropivacaine with epinephrine at the using multiple levels in children, it is important not to the maximal A maximum of per level is more than local anesthetic in the when multiple levels are to be a in the paravertebral dosing has been by using an of bupivacaine with 1:200,000 epinephrine at a rate of Although regional anesthesia is commonly in adult patients, there in these to children. With in and refinement in these techniques can be to our patients. with adult patients, regional anesthetic techniques and peripheral nerve blockade can be used of general anesthesia, as an adjunct to general anesthesia as a of the surgical stress response and the use of or to provide postoperative analgesia. Additionally, the in regional blood flow peripheral nerve blockade can be used as a in specific there are of regional blood peripheral nerve blocks in children are particularly in that their duration when compared with central blocks should for a recovery with an increased duration of the The of local anesthetics should also increase the popularity of peripheral nerve blockade. appropriate clinical will be to our and experience.