Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content ++ Ability to stimulate peripheral nerve or plexus depends on: ++Table Graphic Jump Location|Download (.pdf)|PrintElectrical Parameters of Peripheral Nerve StimulationVariableClinical significanceElectrical impedanceVaries with tissue compositionMost stimulators have constant current output generators that automatically compensate for impedance changesElectrode to nerve distanceAbility to stimulate nerve at low current flow (<0.5 mA) indicates close proximity tonerveTarget muscle twitch still present at <0.2 mA probably indicates intraneural tip positionIncreased current flow and pulse duration increase ability to stimulate nerve at a greater distance from stimulating electrodeCurrent flow (amperage)Presence of appropriate muscle twitch at current 0.23–0.5 mA generally results in safe, reliable blockPosition of electrodesCathode (negative electrode) is attached to insulated needle and anode (positive electrode) is attached to patient skin via an EKG electrodeInverting polarities requires four times current to achieve similar response ++ Insulated needle—insulated needle shaft ensures that current dispersion is concentrated at needle tip, allowing specificity of needle tip locationNerve stimulator device ++Table Graphic Jump Location|Download (.pdf)|PrintBasic Features of Nerve StimulatorsFeatureFunctionSettingsConstant current outputAutomatically compensates for changes in impedance of tissues, needles, connecting wires, and grounding electrodes during needle placement to ensure consistent delivery of set currentPresent in most modern stimulatorsCurrent meterDisplays the current being deliveredMake sure it displays in 0.01 mA increments for better accuracyPNS: 0.2–1.5 mATES: 5 mAPulse width/durationShort duration (0.05–0.1 ms) targets A-α motor fibers and avoids stimulation of pain fibers at longer durationPulse duration required to depolarize pain fibers: A-δ (0.17 ms) and C fibers (0.4 ms)PNS: 0.1 msDiabetic patients with neuropathy may require a longer pulse duration (0.3 or 1ms) to achieve target twitchTES: 0.2–0.3 ms to achieve motor response at greater distance from nerveStimulating frequencyDetermines how quickly pulses are delivered to elicit twitch (pulses/s)Older models with 1 Hz (1 pulse/s) frequency require slow needle manipulation to avoid missing target twitchUsual setting: 2 Hz allows for faster manipulation of needle tip ++ Identify landmarks, insertion site, direction, target muscle(s) to elicit response: Due to anatomical variance or large body habitus, the exact course of a nerve can be difficult to identify. In these cases consider doing a surface mapping of the nerve/plexus by transcutaneous electrical stimulation (TES, see below)Ensure cathode (negative electrode, black) is attached to insulated needle and anode (positive electrode, red) is attached to patientSet starting current to about 1.2–1.4 mA. Much higher current can result in patient discomfortInsert needle and advance while observing target muscle groupOnce target muscle twitch is elicited, slowly dial down current while adjusting needle position to optimize muscle responseIf twitch disappears at ≥0.5 mA, turn current up until twitch is again presentGoal: response present at current 0.2–0.4 mAHold needle securely to ensure it does not move ... Your Access profile is currently affiliated with [InstitutionA] and is in the process of switching affiliations to [InstitutionB]. Please select how you would like to proceed. Keep the current affiliation with [InstitutionA] and continue with the Access profile sign in process Switch affiliation to [InstitutionB] and continue with the Access profile sign in process Get Free Access Through Your Institution Learn how to see if your library subscribes to McGraw Hill Medical products. Subscribe: Institutional or Individual Sign In Error: Incorrect UserName or Password Username Error: Please enter User Name Password Error: Please enter Password Sign in Forgot Password? Forgot Username? Download the Access App: iOS | Android Sign in via OpenAthens Sign in via Shibboleth You already have access! Please proceed to your institution's subscription. Create a free profile for additional features.