Current perception threshold may be of value in determining subtle differences in onset and intensity of block with similar concentrations of different local anesthetics (Image source: Thinkstock)

Current perception threshold may be of value in determining subtle differences in onset and intensity of block with similar concentrations of different local anesthetics (Image source: Thinkstock)

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Regional anesthesia (RA) uses contrasting technologies. The latest ultrasound technology is used to guide the correct placement of the block, but simple subjective responses to stimuli such as cold and pinprick are used to assess the effectiveness of the sensory denervation. Surely there must be a better method of measuring the adequacy of sensory blockade? Current perception threshold (CPT) is a quantitative method and is essentially a nerve stimulator with a microprocessor-controlled constant stimulus that is applied to the skin to evoke a sensory response such as itching or burning. Occasional reports suggest that it be of value in RA, but its reliability has not been determined.

Dr. France Varin, Faculty of Pharmacy, Université de Montréal, Montreal, Canada and colleagues from the same faculty in addition to colleagues at the Department of Anesthesiology and the Department of Orthopedic Surgery, Maisonneuve-Rosemont Hospital, Montreal, Canada, studied current perception thresholds in volunteers and patients undergoing femoral nerve block for total knee arthroplasty. Their results are published in this month’s issue of Anesthesia and Analgesia and discussed in the article titled “The Reliability of the Current Perception Threshold in Volunteers and Its Applicability in a Clinical Setting.”

CPT was found to be a reliable method for measuring sensory perception in healthy volunteers. It was also able to quantify the onset and progression of a femoral nerve block, with the maximal sensory response to 20 mL of ropivacaine 0.5% occurring after 22 min of dosing.

The results suggest that CPT offers some progress in the quantitative measurement of sensory blockade. It may be of value in determining subtle differences in onset and intensity of block with similar concentrations of different local anesthetics. So far CPT has not found favor with anesthesiologists, but ice and a needle are so 19th century!