Equipment and ultrasound

Needles, catheters, and syringes

Effective regional anesthesia requires comprehensive knowledge of equipment—that is, the needles, syringes, and catheters that allow the anesthetic to be injected into the desired area. In early years, regional anesthesia found many variations in the method of joining needle to syringe. Around the turn of the century, Schneider developed the first all-glass syringe for Hermann Wülfing-Luer. Luer is credited with the innovation of a simple conical tip for easy exchange of needle to syringe, but the “Luer-Lok” found in use on most syringes today is thought to have been designed by Dickenson in the mid-1920s. The Luer fitting became virtually universal, and both the Luer slip tip and the Luer-Lok were standardized in 1955.

In almost all disposable and reusable needles used in regional anesthesia, the bevel is cut on three planes. The design theoretically creates less tissue laceration and discomfort than the earlier styles did, and it limits tissue coring. Many needles that are to be used for deep injection during regional block incorporate a security bead in the shaft so that the needle can be easily retrieved on the rare occasions when the needle hub separates from the needle shaft. Fig. 3.1 contrasts a blunt-beveled, 25-gauge needle with a 25-gauge “hypodermic” needle. Traditional teaching holds that the short-beveled needle is less traumatic to neural structures. There is little clinical evidence that this is so, and experimental data about whether sharp or blunt needle tips minimize nerve injury are equivocal.

Fig. 3.2 shows various spinal needles. The key to their successful use is to find the size and bevel tip that allow one to cannulate the subarachnoid space easily without causing repeated unrecognized puncture. For equivalent needle size, rounded needle tips that spread the dural fibers are associated with a lesser incidence of headache than are those that cut fibers. The past interest in very-small-gauge spinal catheters to reduce the incidence of spinal headache, with controllability of a continuous technique, faded during the controversy over lidocaine neurotoxicity.

Fig. 3.3 depicts epidural needles. Needle tip design is often mandated by the decision to use a catheter with the epidural technique. Fig. 3.4 shows two catheters available for either subarachnoid or epidural use. Although each has advantages and disadvantages, a single–end-hole catheter appears to provide the highest level of certainty of catheter tip location at the time of injection, whereas a multiple–side-hole catheter may be preferred for continuous analgesia techniques.

Continuous Infusion Dosage With the advent of ultrasound and better training, more and more continuous nerve block catheters are performed to help patients. Current practice is to limit continuous infusion at 0.4/mg/kg/h (bupivacaine/ropivacaine). See Table 3.1 for specific block recommendations.