Ultrasonography and stimulating perineural catheters for nerve blocks: a review of the evidence.

PURPOSE This narrative review summarizes the evidence derived from randomized controlled trials (RCTs) offering blinded assessment and sample size justification, in order to determine the benefits associated with adjunctive ultrasonography (US) and stimulating perineural catheters for nerve blocks. SOURCE The literature search for this review was conducted during the second week of December 2007 using the MEDLINE (January 1950 to November 2007) and EMBASE (January 1980 to November 2007) databases. For US-guided peripheral and neuraxial blocks, the following medical subject heading (MeSH) terms were searched: "nerve block", "epidural anesthesia", "epidural analgesia", "epidural injection", "epidural space", "spinal anesthesia", and "spinal injection", the results were combined with "ultrasonography" (MeSH term) and "ultrasound" (key word). For stimulating perineural catheters, the following MeSH terms were cross referenced with the MeSH term, "nerve block": "peripheral catheterization", "indwelling catheterization", "catheterization", and keywords, "nerve catheter" and "continuous". Subsequently, the result of this search was combined to "stimulating" (key word). Fifteen RCTs, offering blinded assessment and sample size justification, were retained for analysis. PRINCIPAL FINDINGS For axillary blocks, US guidance yields a higher success rate than a double-injection, transarterial and a triple-injection, neurostimulation-guided technique. Compared to a quadruple-stimulation technique, no major differences can be found. The addition of nerve stimulation to US guidance offers no clear benefits for axillary blocks. For femoral blocks, compared to neurostimulation, echoguidance is associated with a local anesthetic (LA) sparing effect (up to 42%). In children, US guidance yields a LA sparing effect and a longer duration of action for lower extremity nerve blocks.Compared to their blind counterparts, stimulating catheters seem to offer limited clinical benefits. Despite providing a sparing effect on LA and opioid consumption, stimulating catheters are not associated with a decrease in side effects or analgesia-related expenditures. CONCLUSIONS Published reports of RCTs provide evidence to formulate limited recommendations regarding the use of adjunctive US and stimulating perineural catheters. Further well-designed and meticulously executed RCTs are warranted.