Ketamine has diverse effects that may be of relevance to chronic pain including: N-methyl-D-aspartic acid, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, kainate, gamma-aminobutyric acid(A) receptors; inhibition of voltage gated Na(+) and K(+) channels and serotonin, dopamine re-uptake. Ketamine has been in clinical practice for over 30 yr; however, there has been little formal research on the effectiveness of ketamine for chronic pain management. In this review we evaluate the available clinical data as a basis for defining the potential use of ketamine for chronic pain. Literature referenced in this review was obtained from a computer search of EMBASE and MEDLINE from 1966 through August, 2002. Search terms included ketamine, ketalar, pain, painful, analgesic, and analgesia. Abstracts were screened for relevance and publications relating to chronic pain use were obtained. Levels of evidence were stratified according to accepted guidelines (level I-IV). For central pain, there is level II and level IV evidence of efficacy for parenteral and oral ketamine. For complex regional pain syndromes, there is only level IV evidence of efficacy of epidural ketamine. For fibromyalgia, there is level II evidence of pain relief, reduced tenderness at trigger points, and increased endurance. For ischemic pain, a level II study reported a potent dose-dependent analgesic effect, but with a narrow therapeutic window. For nonspecific neuropathic pain, level II and level IV studies reported divergent results with questionable long-term effects on pain. For phantom limb pain and postherpetic neuralgia, level II and level II studies provided objective evidence of reduced hyperpathia and pain relief was usually substantial either after parenteral or oral ketamine. Acute on chronic episodes of severe neuropathic pain represented the most frequent use of ketamine as a "third line analgesic," often by IV or subcutaneous infusion (level IV). In conclusion, the evidence for efficacy of ketamine for treatment of chronic pain is moderate to weak. However, in situations where standard analgesic options have failed ketamine is a reasonable "third line" option. Further controlled studies are needed.

With the growth of ultrasound-guided regional anesthesia, so has the requirement for training tools to practice needle guidance skills and evaluate echogenic needles. Ethically, skills in ultrasound-guided needle placement should be gained in a phantom before performance of nerve blocks on patients in clinical practice. However, phantom technology is varied, and critical evaluation of the images is needed to understand their application to clinical use. Needle visibility depends on the echogenicity of the needle relative to the echogenicity of the tissue adjacent the needle. We demonstrate this point using images of echogenic and nonechogenic needles in 5 different phantoms at both shallow angles (20 degrees) and steep angles (45 degrees). The echogenicity of phantoms varies enormously, and this impacts on how needles are visualized. Water is anechoic, making all needles highly visible, but does not fix the needle to allow practice placement. Gelatin phantoms and Blue Phantoms provide tactile feedback but have very low background echogenicity, which greatly exaggerates needle visibility. This makes skill acquisition easier but can lead to false confidence in regard to clinical ability. Fresh-frozen cadavers retain much of the textural feel of live human tissue and are nearly as echogenic. Similar to clinical practice, this makes needles inserted at steep angles practically invisible, unless they are highly echogenic. This review describes the uses and pitfalls of phantoms that have been described or commercially produced.

Needle tip visualization is fundamental to the safety and efficacy of ultrasound-guided regional anesthesia (UGRA). It can be extremely challenging especially at steep insertion angles. We assessed whether an echogenic needle improved tip visibility during UGRA by anesthesiologists performing their normal in-plane technique. The visibility of the Pajunk Sonoplex (echogenic) and the Pajunk Uniplex (control) needle were compared during 60 nerve blocks (30 femoral, 30 sciatic) in this randomized controlled trial. All ultrasound imaging was recorded for analysis. The anesthesiologist subjectively estimated the percentage time they had visualized the needle tip (5-point scale: 1 [0%-20%], 2 [20%-40%], 3 [40%-60%], 4 [60%-80%], 5 [80%-100%]). The actual time the tip was in view, angle of needle insertion, target depth, and procedure time were subsequently measured objectively by a single investigator. The Sonoplex group had both subjectively and objectively better tip visibility (P=0.002), despite having larger mean body mass index (29.0 vs 25.0 kg/m(2), P=0.01) and steeper mean insertion angle (31 vs 22 degrees, P=0.03). Objective percentage tip visibility, during in-plane UGRA, reduced by 12% for every 10-degree increase in insertion angle with the control. Tip visibility with the Sonoplex was independent of insertion angle over the range studied (0-57 degrees, P=0.95). This finding occurred when nonexpert anesthesiologists performed their standard UGRA technique. A needle that is visible for a greater percentage of time has potential safety and efficacy implications.