Equipment

The sterile material necessary for performing a regional block is rather simple and not expensive: a non-reusable needle, a syringe, a local anesthetic, skin preparation solutions, and drapes. Different types of needles are available, and the anesthesiologist has to make a selection so that any regional block can be safely performed and sufficient experience gained with all the selected needles, especially with regard to the sensation felt during insertion. Recommended equipment is listed in Table 45-6 .

Location of nerve trunks and anatomic spaces has to be ascertained by physical means because most children cannot reliably cooperate or are under general anesthesia. Plexus and mixed nerves are best localized by using electrical stimulation to elicit muscle twitches. This requires a nerve stimulator delivering squared electrical impulses lasting 50 to 100 µsec at the rate of one to five impulses per second. The anode is connected to a skin electrode that is preferably fixed distal to the site of puncture, and the cathode is connected to the block needle.^{[116] [117]} To avoid traumatic nerve lesions, depolarization of motor fibers must occur before the needle contacts the nerve trunk and, at the same time, when it is close enough to it to allow a successful block. The key factor is the electrical intensity of the stimulus, which should range between 0.5 and 1 mA. With such current intensity, motor fibers are depolarized, and muscle twitches

TABLE 45-6 -- Recommended devices for most regional block procedures in children

Block Procedure	Recommended Device	Alternate Device
Intradermal wheals	Intradermal needles (25 gauge)	—
Infiltrations and field blocks	Standard intramuscular needles (21–23 gauge)	Intradermal needles (25 gauge)
Compartment blocks (fascia iliaca, ilioinguinal, penile, rectus sheath, pudendal)	Short (25–50 mm) and short-bevel (45–55 degrees) needles	Epidural needles (intercostal block); neonatal spinal needle
Peripheral mixed nerve blocks and plexus blocks	Insulated, 21–23 gauge, short-bevel needles of appropriate length connected to a nerve stimulator (0.5–1 mA); specific catheter for continuous techniques	Unsheathed needles with the same characteristics connected to a nerve stimulator (0.5–1 mA); epidural catheter for continuous techniques
Spinal anesthesia	Spinal needle (24–25 gauge; 30, 50, or 100 mm long; Quincke bevel) with stylet	Neonatal lumbar tap needle (22 gauge, 30–50 mm long), Whitacre spinal needle
Caudal anesthesia	Short (25–30 mm) and short-bevel (45 degrees) needle with stylet	Pediatric epidural (occasionally spinal) needle
Epidural anesthesia	Tuohy needle (22, 20, and 19/18 gauge); loss-of-resistance syringe and medium; epidural catheter	Crawford, Whitacre or Sprotte epidural needles appropriately sized; loss-of-resistance syringe and medium; epidural catheter

are elicited when the tip of the needle is approximately 0.5 to 1 mm away from the nerve. At this distance, provided twitches persist when the needle is temporarily released, the injection site is within the perineural fascial sheath and the bevel far enough away to avoid damaging the nerve fibers.^[118]

Location of the epidural space can be achieved by the hanging-drop method or the Macintosh balloon technique as in adults. However, the most common technique consists of seeking an LOR while exerting a continuous (with fluid) or intermittent (with gas) pressure on the plunger of an air-tight syringe that offers no resistance to movement while the needle is advanced, until the ligamentum flavum is pierced. The medium used to fill in the syringe has generated much controversy. Air has been used for decades because of its availability, simplicity of use, and suitability for precisely identifying the ligamentum flavum. However, severe complications may occur after its administration,^{[119] [120]} mainly in large amounts, and this medium should be avoided in all patients whenever possible. Saline can be used instead in older children as in adults, but the technique is not dependable enough in infants and young children, and carbon dioxide, which is available in any operating theater, is preferable.^[121] Nevertheless, when the technique is appropriately performed, the air-LOR technique cannot be considered detrimental.^[122]

The subarachnoid space is located by seeking CSF reflux. The diameter of the lumen of the needle and the position of the patient during the approach (which affects the hydrostatic pressure of the CSF) must be considered. It is recommended to approach the subarachnoid space while negative pressure is continuously exerted on the plunger of a syringe connected to the spinal needle (preferably with an extension line in between to ensure free movements of the needle).