Nearly all studies reported the total local anesthetic dose reduced with bolus-only dosing.įIGURE 1. Sensory and motor effects are similar when comparing repeated, scheduled hourly bolus doses to a continuous basal infusion of the same hourly volume and dose.
Findings of RCTs at the femoral or fascia iliaca location have not demonstrated an overwhelming preference for a specific regimen. In the lower extremity, some differences in dosing effects have been found in randomized controlled trials (RCTs) examining femoral versus popliteal sciatic locations. At the infraclavicular location, utilizing a basal infusion with bolus (in comparison to basal only or bolus only) also has been found to provide improved analgesia with decreased severity and incidence of breakthrough pain, sleep disturbances, as well as higher patient satisfaction. One study involving interscalene catheters suggested that a relatively large basal rate with small-volume bolus doses (8 mL/h basal, 2-mL bolus, 60-minute lockout) provides improved analgesia and functioning, but with higher overall local anesthetic consumption compared with a slower basal rate and larger bolus doses. Regarding specific basal infusion rates, the evidence is mixed, with many studies reporting few differences among various rates. For example, in the upper extremity, an interscalene infusion that includes a basal infusion has been found superior to a bolus-only regimen. Adding a patient-controlled bolus usually decreases the required basal infusion rate incidence of an insensate extremity, and local anesthetic consumption, the last allowing for a longer infusion duration in the ambulatory setting. In many cases, providing a basal infusion minimizes breakthrough pain and supplemental analgesic requirements. No single delivery regimen has proven ideal for all anatomic locations and clinical situations. The delivery regimen should minimize total local anesthetic consumption, supplemental opioid requirements, and disturbance of daily functioning/sleep.
Regimens are often reported as basal rate (mL/hour)/bolus volume (mL)/bolus lockout time (minutes). Infusates are typically delivered using an infusion pump with a basal infusion, bolus dose, or combination of the two modalities. Commonly described concentrations include ropivacaine 0.1%–0.4%, bupivacaine 0.125%–0.15%, and levobupivacaine 0.1%–0.125%.Īn infusion with ropivacaine 0.1%–0.2% is easier to titrate due to faster resolution of an insensate extremity but bupivacaine 0.1%–0.125% provides the same degree of analgesia and costs less in most regions and hospitals. Therefore, at this time it remains unknown if there is an “optimal” concentration of local anesthetic. While the evidence suggests that for infusions involving the femoral nerve, local anesthetic concentration is of minimal importance compared with total dose, data for the sciatic nerve are lacking, and the brachial plexus information is conflicting. It is currently unclear if local anesthetic concentration-or simply the total delivered dose-influences continuous block effects. Studies have suggested that sensory-and-motor block regresses faster with ropivacaine than with bupivacaine. At the termination of an infusion, it is desirable for sensory and motor block to resolve quickly and predictably. These long-acting agents provide a favorable differential sensory-to-motor block. Intermediate-duration local anesthetics such as mepivacaine have been used, but long-acting local anesthetics such as ropivacaine, bupivacaine, and levobupivacaine are most frequently described. Local anesthetics were described in continuous perineural infusions as early as 1946. INFUSATES AND LOCAL ANESTHETIC CONCENTRATION
Considerations include the indication for perineural catheter placement, the number and location of catheters, patient weight, and ambulatory versus inpatient status. The optimal infusion strategy may be modified for the large number of clinical scenarios that the regional anesthesiologist will encounter in daily practice. In addition, desirable attributes include a favorable toxicity profile and costefficacy. An ideal perineural local anesthetic solution would provide analgesia while minimizing sensory, motor, and proprioception deficits. Overwhelming plethora of options are available for nearly every aspect of continuous infusion administration, from the choice of infusate to choice of infusion rate and bolus regimen, to infusion pump selection. Ilfeld INTRODUCTIONĬontinuous peripheral nerve blocks are accomplished by infusion or intermittent boluses of local anesthetic solutions. Table of Contents Continuous Peripheral Nerve Blocks: Local Anesthetic Solutions and Infusion StrategiesĪmanda M.
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