Fig. 5.1
Pajunk® SonoLong Curl
2.
Stimulating Catheters
Although it is still unclear as to whether stimulating catheters are more effective than non-stimulating catheters at positioning the catheter tip in proximity to the nerve, stimulating catheters can aid in the verification of catheter tip localization. When motor response is present at a reasonable threshold (0.5 mA), this usually signifies the correct placement of a stimulating catheter. Some stimulating needle and catheter sets, for example, the StimuCath® (Arrow International, Reading, PA, USA) with a 5 mm bare tip, may need a higher stimulation current, such as 1 mA; it should also be noted that nerve stimulation is not sensitive enough to detect intraneural placement of the catheter. Therefore, it is our recommendation that the spread of local anesthetic through the catheter tip be observed with ultrasound. Ultrasound-guided perineural catheter insertion can be technically challenging and requires a sound knowledge of sonoanatomy, good hand-eye coordination, and a competent assistant. High success rates can be obtained once these skills are acquired.
Catheters that are used in continuous peripheral nerve blocks in children are similar to those used in adults. There are four commercial varieties of catheters available with different lengths of needles required for various blocks and to accommodate the child’s habitus/size. Several manufacturers now provide Tuohy needle/catheter sets specifically tailored for pediatric use.
Arrow® StimuCath (Arrow International, Reading, PA, USA)
The insulated needle is 17G and 18G Tuohy-tipped with centimeter markings available in 4 and 8 cm (Fig. 5.2).
Fig. 5.2
Arrow® StimuCath
The 60-cm-long catheter comes in 19G and 20G which is made more rigid by a steel stylet.
The catheter has a female adaptor to accommodate the stimulating cable from the nerve stimulator.
The catheter has a SnapLockTM adaptor.
The hub of the catheter is a stimulating cable that stimulates the catheter
The stylet has to be removed before liquid can be injected through the catheter as it is advanced for hydrodissection (see below).
The catheter can kink if resistance is encountered during insertion.
Pajunk® StimuLong Sono (Pajunk, Geisingen, Germany)
The insulated Tuohy needles are available in 50, 100, and 110 mm lengths.
The stimulating catheter has a gold-plated, atraumatic rounded tip with a high conductivity (Fig. 5.3).
Fig. 5.3
Stimulating catheter (Pajunk® StimuLong Sono) featuring a gold-plated, atraumatic rounded tip with a high conductivity
The catheter does not have a stylet, enabling fluid to be injected as the catheter is advanced.
The metal coil of the catheter provides radiopacity and prevents kinking of the catheter as it meets resistance.
Pajunk® StimuLong Sono-Tsui Set (Pajunk, Geisingen, Germany)
The insulated Tuohy needles have lengths of 50 and 100 mm (Fig. 5.4).
Fig. 5.4
Pajunk® StimuLong Sono-Tsui Set. Catheter tip with steel stylet to adjust stiffness. Stylet can be pushed forward or backward and can be locked in place with a valve
The catheter design incorporates the characteristics of the StimuLong Sono catheter with two distinct features:
The stiffness of the catheter tip can be regulated by pushing the steel stylet forward and backward and can be locked in place by tightening or loosening a valve. This ensures atraumatic manipulation of the catheter tip.
Similar to the StimuLong Sono catheters, fluid can be injected through the catheter during advancement for hydrodissection.
ContiStim® Catheters (B.Braun, Melsungen, Germany)
Life-Tech has incorporated smaller catheters (21G–24G; Prolong Micro) for pediatric use.
The 18G, 19G, and 20G insulated Tuohy needles are available in variable lengths of 50, 100, and 150 mm.
It has an atraumatic ball tip to reduce tissue damage and create a 360° oUTFlow pattern.
The catheters are said to be kink resistant.
The fluid path/giving set connector is attached to a port for stimulation of the catheter.
It features an EzTwistTM closure for the fluid path connector which indicates that the catheter has been securely connected.
3.
Catheter–over–needle assembly
There are a few variations on this design marketed by different brands:
Pajunk, whose feature design is its two components, the outer catheter sheath and the flexible, non-kinkable inner catheter (Figs. 5.5 and 5.6). This assembly was initially designed and modified by Dr. Ban Tsui. The inner catheter is introduced within the outer catheter and is Luer-locked in place for injection (Fig. 5.7).
Fig. 5.5
Pajunk® catheter-over-needle assembly
Fig. 5.6
Detail of Pajunk® catheter-over-needle components
Fig. 5.7
Luer-lock holding together the inner and outer catheter
B.Braun, with the catheter-over-needle as a sole component (Fig. 5.8)
Fig. 5.8
B.Braun® catheter-over-needle assembly
Arrow, with a catheter-over-needle with a blunt needle and a sharp injection needle for the initial puncture of the skin (Fig. 5.9).
Fig. 5.9
Blunt and sharp needles from Arrow® catheter-over-needle assembly
To position the distal end of the outer catheter in proximity to the target nerve, a 21G needle is inserted within the outer catheter with its distal end protruding for its electrically conductive property.
The insertion of this catheter/needle unit is under real-time ultrasound guidance and nerve stimulation. The latter is used mainly to monitor for the absence of motor response to prevent intraneural injection.
The distal end of the outer catheter is tapered and thin for smooth advancement within the tissue. The second component of the inner catheter is inserted into the outer catheter after the needle has been withdrawn.
The main difference between this catheter-over-needle assembly and the traditional catheter-through-needle assembly is the position of the needle in relation to the catheter. In the traditional assembly, the catheter is introduced within the Tuohy needle; therefore, upon removal of the Tuohy needle, a gap is left between the skin and the catheter. In contrast, the needle in the catheter-over-needle assembly is within the outer catheter which remains in situ at the end of the procedure. This enables a tight fit between the skin and the catheter. Moreover, the inner catheter literally replaces the needle, which was initially placed in proximity to the nerve before its withdrawal. This enables the tip of the inner catheter to be in proximity to the nerve.
Several advantages of this design include:
Simple to use with the insertion technique comparable to that of a single-shot nerve block
Less risk of leakage from the catheter insertion site, which is particularly important in shoulder surgery where the patient is in a sitting position with a potential for surgical field contamination
Less risk of dressing adhesive disruption
Less risk of dislodgement
Less cumbersome steps
Easy visualization of the catheter, especially the catheter tip
A preassembled peripheral catheter pack is an efficient way of bringing together all the essential equipment to perform a peripheral nerve catheter. If such a pack is not available, a cart/trolley with all the necessary equipment should be prepared. The equipment required includes:
Sterilizing solution.
Sponges/gauze.
Drapes.
Lidocaine in a small syringe and 23G hypodermic needle for skin infiltration if necessary.
Sterile ultrasound transducer cover, sterile gel, and elastic bands for transducer preparation (see below).
Appropriately sized (gauge and length) Tuohy needle and extension tubing, nerve block catheter, or catheter-over-needle.
5 % dextrose in water (D5W) and appropriate syringes for hydrodissection.
Micro-filter or giving set attachment for the injecting into the catheter.
Appropriate dressings.
Sterile gowns and gloves (it is recommended that full sterile procedure should be observed for peripheral catheter insertion, including a face mask, hat, sterile gown, and gloves).
Ultrasound machine with appropriate settings.
The nerve stimulator should be set up and ready to use for the initial placement of the needle and/or if a stimulating catheter is to be used.
5.2.2 Sterile Transducer Preparation
For peripheral nerve catheter insertion, it is important to have an appropriate sterile cover for the ultrasound transducer as well as for the cord so it does not contaminate the sterile field while scanning (see Chap. 4, Sect. 4.3). The following describes how to prepare a sterile transducer probe:
Open the sterile sheath by placing two thumbs inside the sheath, and roll the length of the sheath up so that the sheath bunches up in the hand.
Ensure plenty of sterile gel is applied on the inside of the sheath where the surface of the transducer is to be placed.
Cover the transducer inside the sheath, and push the length of the sheath to cover the cord of the transducer (take care to avoid desterilizing the gloves).
Pull an elastic band over the cord to hold the sheath on the cord.
Stretch the surface of the sheath covering the transducer to avoid any air bubbles or creases before pulling an elastic band over the transducer to hold it in place. This will also minimize any sliding between the sheath and the transducer while scanning.
5.2.3 Choice of Injectates
5.2.3.1 During Catheter Insertion
To facilitate advancement of the catheter, a solution is injected through the Tuohy needle to expand the perineural space; however, the use of local anesthetics or conducting solution, such as normal saline, will abolish the capacity to stimulate. This is particularly important when stimulating catheters are used.
Hydrodissection using D5W, a nonconducting fluid, is useful for “dissecting” or “opening” of the perineural space. This facilitates catheter advancement while maintaining the ability to stimulate and may enhance the contrast at the tissue interface, potentially allowing for better visibility of both the needle and the catheter under ultrasound. Overaggressive hydrodissection is not advised since it may hinder electrical stimulation of the nerve by creating a potential mechanical barrier.
Local Anesthetics
Unlike in adults, the dose of local anesthetics is weight dependent in infants and children. In pediatric patients, after an initial bolus, the dosage recommended for continuous infusion is 0.1–0.2 mL/kg/h of either bupivacaine or levobupivacaine (0.125–0.25 %) or ropivacaine (0.15–0.2 %). The lower rates are generally used for upper extremity catheters and the higher rates for lower extremity catheters. If necessary, the infusion rate may be adjusted up to a maximum of 0.2 mg/kg/h for infants of less than 6 months and 0.4 mg/kg/h in children of more than 6 months.
5.3 Technique
When inserting peripheral nerve catheters, aseptic technique should always be observed in order to reduce the risk of infection. All the equipment should be ready as described in Chap. 1.
The key practical techniques for insertion of peripheral nerve catheters are as follows:
An assistant who is trained in regional anesthesia with experience in monitoring pediatric patients under sedation or general anesthesia should be present. This is important not only for monitoring the child during catheter insertion but to assist with the nerve stimulator and the injectate.
Routine monitoring such as electrocardiography, noninvasive blood pressure, pulse oximetry, capnography, and end-tidal gas monitoring (especially for those in whom anesthesia is maintained on volatile agents) is applied.
Emergency drugs such as atropine, ephedrine, and succinylcholine are drawn up, and resuscitation drugs such as epinephrine and Intralipid are available if needed.Related posts:
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