• Elizabeth M. Renehan, MD
• F. Kayser Enneking, MD

        INTRODUCTION

Over 40% of ambulatory patients experience moderate- to-severe postoperative pain at home following orthopedic procedures.¹ Single-injection peripheral nerve blocks with long-acting local anesthetics can provide excellent postoperative analgesia. However, the analgesic benefit of singleinjection blocks is typically limited to the duration of the blockade and, subsequently, patients must usually rely on oral opioids to control pain. Unfortunately, opioids are associated with undesirable side effects, such as pruritus, nausea and vomiting, sedation, and constipation. To improve postoperative analgesia following ambulatory surgery, increasing interest has focused on providing perineural local anesthetic infusions, also called, continuous peripheral nerve blocks, to outpatients. This technique involves a percutaneous insertion of a catheter directly adjacent to the peripheral nerve(s) supplying the surgical site. Local anesthetic is then infused via the catheter, providing prolonged, site-specific analgesia.

        HISTORY

In 1946, Ansbro first described continuous regional blockade using a cork to stabilize a needle placed adjacent to the brachial plexus divisions to provide a continuous supraclavicular block.² However, for decades, patients were required to remain hospitalized because the available pumps used to infuse local anesthetic were large, heavy, and technically sophisticated. It was not until 52 years later that outpatient perineural infusion using a percutaneous catheter and a small, lightweight, portable infusion pump was described.³

        ADVANTAGES & EVIDENCE

The first report of continuous infusion of local anesthetics at home was reported by Rawal and colleagues.³ Shortly thereafter, numerous reports or series of ambulatory perineural infusions were published, which described the use of catheters in various anatomic locations, including paravertebral,⁴ interscalene,^5–7 intersternocleidomastoid,⁸ infraclavicular,⁶ axillary,⁹ psoas compartment,^9,10 femoral,^9,11 fascia iliaca,⁵ sciatic,^9,10 popliteal,^6,12 and tibial nerve.⁶ Ambulatory continuous peripheral nerve blocks in pediatric patients also were reported.¹³

        Klein and colleagues were first to study and quantify the benefits of perineural infusion of local anesthetic.¹⁴ In their randomized, double-blind, placebo-controlled investigation, patients undergoing open rotator cuff repair who received an interscalene block and perineural catheter preoperatively, were randomized to receive either perineural ropivacaine 0.2% or normal saline postoperatively (10 mL/h). Patients receiving perineural placebo averaged a 3 on a 0-10 visual analog pain scale (VAS), compared with a 1 for subjects receiving ropivacaine. Although a portable pump was used, patients remained hospitalized during local anesthetic infusion of less than 24 h, and catheters were removed by the investigators prior to home discharge.¹⁴ Consequently, while these data suggested that perineural infusion may improve postoperative analgesia following hospital discharge, the actual advantages of continuous nerve blocks for patients at home remained unknown.

        Data from perineural infusion in outpatients subsequently were provided in four randomized, double-blind, placebo-controlled studies.^15–18 Patients receiving perineural local anesthetic achieved significantly lower resting and breakthrough pain scores than did those using exclusively oral opioids for analgesia (Figure 64-1). In addition, they required significantly fewer oral analgesics to achieve their improved level of analgesia (see Figure 64-1). Preoperatively, patients scheduled for moderately painful procedures had a perineural catheter placed: an infraclavicular catheter for hand/forearm procedures,¹⁵ a popliteal catheter for foot/ankle surgeries,^16,18 or an interscalene catheter for shoulder procedures.¹⁷ Postoperatively, patients received either perineural local anesthetic or normal saline and were followed at home for up to 60 h. All patients were instructed to use a bolus from their infusion pump for breakthrough pain, and oral analgesics if this maneuver failed. In patients with an interscalene catheter following shoulder surgery, the local anesthetic infusion provided analgesia so effective that 80% of patients receiving ropivacaine required one or fewer opioid tablets per day during their infusion and reported average resting pain as less than 1. 5 on a scale of 0 to 10.¹⁷ This compares with all patients receiving placebo, who required four or more opioid tablets per day, beginning the evening of surgery. These patients reported average resting pain scores between 3 and 4. For breakthrough pain, the differences between treatment groups were even more pronounced in all of these four placebo-controlled studies (see Figure 64-1).

        Improved analgesia provided several additional benefits in patients who received perineural local anesthetic. Of patients receiving perineural ropivacaine, 0 to 30% reported insomnia due to pain, compared with 60% to 70% of patients receiving placebo.¹⁵”¹⁷ Additionally, awakenings from sleep because of pain averaged 0.0 to 0.2 times on the first postoperative night, compared with 2.0 to 2.3 times for patients using only oral opioids.^15–17 Lower doses of oral opioid intake translated into a lower rate of nausea, vomiting, pruritus, and sedation.^15–18 Satisfaction with postoperative analgesia was both clinically and statistically higher for patients receiving local anesthetic.¹⁵”¹⁸ Finally, patients with popliteal local anesthetic infusion rated their quality of recovery significantly higher than patients receiving placebo.¹⁸ Whether these demonstrated benefits resulted in a tangible improvement in patients’ health-related quality of life remains unanswered.¹⁹ Additionally, more work is required to determine the optimal location of catheter placement for common surgical procedures (eg, axillary vs infraclavicular for hand surgery).

        Additional possible advantages of using outpatient perineural infusion to allow earlier discharge of patients who require potent analgesia may include other benefits of a shorter hospitalization, such as decreases in nosocomial infection,^20,21 harmful medical error,²²,²³ and increases in health-related quality of life.¹⁹ Societal benefits include tangible cost savings^24–26 arising from the ability to discharge patients home directly from the recovery room after surgeries such as total elbow and shoulder replacement²⁷ and on the first postoperative day following total hip and knee replacement.²⁸ Additional data are required to define the appropriate subset of patients and assess the benefits and incidence of complications associated with this practice.

        PATIENT SELECTION

Clinical Pearls

        Most investigators limit the use of ambulatory infusion to patients who are expected to have moderate or severe postoperative pain of a duration greater than 24 h that is not easily managed with oral opioids. This practice attempts to balance the potential benefits of this technique with the potential risks,^29,30 financial cost, and patient inconvenience of carrying an infusion pump with local anesthetic.²⁷ However, outpatient infusion can be used judicially in patients having less invasive procedures to decrease opioid requirements and opioid-related side effects.^3,31 Appropriate patient selection is crucial for safe outpatient infusion because not all patients desire, or are capable of accepting, the extra responsibility that comes with the use of the catheter and pump system. For instance, because some degree of postoperative cognitive dysfunction is common following surgery,³² patients are often required to have a caretaker during infusion.^{15”17,33”36} Whether a caretaker is necessary for one night or for the entire duration of infusion remains unresolved.³⁷ If removal of the catheter is expected to occur at home, then a caretaker willing to perform this procedure must be available at the infusion conclusion if the patient is unwilling or unable to do this (eg, psoas compartment catheter).

Figure 64-1.Effects of interscalene and sciatic/popliteal perineural infusion of either ropivacaine or placebo on average pain at rest (A and D), worst pain overall (B and £), and opiate use (C and F) following moderately painful shoulder or lower extremity surgery (scale: 0-10). Each opiate tablet consisted of oxycodone, 5 mg. Note: The infusion was discontinued after postoperative day 2, as indicated by the horizontal lines. Data are expressed as median (horizontal bar) with twenty-fifth to seventy-fifth (box) and tenth to ninetieth (whiskers) percentiles for patients randomly assigned to receive either 0.2% ropivacaine or 0.9% saline placebo. For tightly clustered data (eg, panel A, postoperative days 0 and 1, ropivacaine group), the median approximated the tenth and twenty-fifth percentile values. In this case, the median is 0 and only the seventy-fifth and ninetieth percentiles are clearly noted (p < 0.05: *, compared to saline for a given postoperative day. (Adapted, with permission, from llfeld BM, Morey TE, Wang RD, et al: Continuous popliteal sciatic nerve blockfor postoperative pain control at home: A randomized, double-blinded, placebo-controlled study. Anesthesiology 2002;97:959-965; llfeld BM, Morey TE, Wright TW, et al: Continuous interscalene brachial plexus block for postoperative pain control at home: A randomized, double-blinded, placebo-controlled study. Anesth Analg 2003;96:1089-1095.)

        In medically unsupervised outpatients, complications may take longer to identify orbe more difficult to manage than in hospitalized patients. Therefore, hepatic or renal insufficiency is a relative contraindication to outpatient infusion in an effort to avoid local anesthetic toxicity.³⁸ For infusions that may affect the phrenic nerve and ipsilateral diaphragm function (eg, interscalene or cervical paravertebral catheters), patients with lung disease (eg, reactive airway disease, chronic obstructive pulmonary disease) are often excluded because continuous interscalene local anesthetic infusions can result in ipsilateral diaphragm paralysis.³⁹ Consequently, conservative application of continuous interscalene block is suggested until additional investigation of hospitalized, medically supervised patients documents its safety,^40,41 although the effect on overall pulmonary function may be minimal for relatively healthy patients.⁴²

        SELECTION OF INSERTION TECHNIQUE

Clinical Pearls

In a substantial number of cases—as high as 40% in some reports⁴³—inaccurate catheter placement may occur.^17,44,45 This issue is of critical importance for outpatients because catheter replacement is not an option after leaving the medical facility. Many techniques and types of equipment have been described for catheter insertion. Using one common technique, the initial local anesthetic bolus is given via the needle, followed by catheter placement. Using this method, it is possible to provide a successful surgical block, but inaccurate catheter placement cannot be ruled out.¹⁷ For ambulatory patients, inadequate perineural infusion often will not be detected until after surgical block resolution following home discharge.¹⁷ Using another technique, investigators first inserted the catheter and then administered a bolus of local anesthetic via the catheter, with a reported failure rate of 1% to 8%.^46,47

        In an attempt to further improve catheter placement success rates, stimulating catheters were developed. These devices deliver electric current to the tip of the catheter.⁴⁸ The design provides feedback on the positional relationship of the catheter tip to the target nerve(s) prior to administering local anesthetics.^33,34 There is some evidence that confirming the placement of the catheter via stimulation through the catheter may improve the accuracy of catheter placement.⁴⁹ However, the optimal placement techniques and equipment for ambulatory perineural infusion have not been determined and require further investigation.³⁰ A negative aspiration test for blood and administration of epinephrine-containing local anesthetic ( test dose) via the catheter is suggested to rule out intrathecal,⁵¹ epidural,⁵² or intravascular⁵³ placement prior to initiating infusion of local anesthetics, regardless of the equipment or technique used.

        For patients at home, daily inspection of the catheter insertion site and reinforcement, when needed, may not be possible without home nursing care. Therefore, in an effort to minimize the risk of accidental dislodgement, every effort to optimally secure the catheter must be made prior to discharge. Such maneuvers include the use of sterile liquid adhesive (eg, benzoin), sterile tape (eg, Steri-Strips), securing of the catheter-hub connection with either tape or specifically designed devices (eg, StatLock), subcutaneous tunneling of the catheter,^48,54 and the use of 2-octyl cyanoacrylate glue.⁵⁵ Using a combination of these techniques, investigators have reported a catheter retention rate of 95% to 100% for over 60 h^33,34,36 and 85% for up to 7 days²⁷ in ambulatory patients.

        LOCAL ANESTHETIC & ADJUVANT SELECTION

Clinical Pearls

        Although perineural infusions of levobupivacaine⁵’¹ and shorter acting agents have been reported,^57–59 the majority of publications involve techniques using ropivacaine 0. 2% or bupivacaine 0.125% to 0.25%. Currently, there is insufficient information to determine if there is an optimal local anesthetic (or concentration) for ambulatory infusions.^31,56,60 Although higher concentrations of local anesthetic provide additional analgesia, they also increase the risk of local anesthetic toxicity, undesirable motor blockade, and the incidence of a completely insensate extremity, and they may mask possible subsequent nerve compression injury.^16,18,36,59 In ambulatory patients, the degree of motor block provided by the infusion is an important consideration. The optimal concentration and infusion rate for a particular catheter site in relationship to the degree of motor block are not established. The only studies investigating local anesthetics and motor block involved patients with an interscalene catheter, and results suggested that 0.2% ropivacaine and 0.15% bupivacaine are associated with a low incidence of motor block and complete sensory block.^60,61 However, practitioners should note that even when using a low concentration of local anesthetic, complete motor and sensory block can occur.

        Clonidine has been added to long-acting local anesthetic (1-2 mcg/mL) for continuous perineural femoral,⁶² anterior lumbar plexus,^63–65 interscalene,⁶⁶ and popliteal⁶⁷ inpatient infusions. Although clonidine added to intermediate-acting local anesthetics increases the duration of single-injection nerve blocks,⁶⁸ the only available controlled investigations of adding clonidine to a continuous ropivacaine infusion (1 or 2 mcg/mL) do not reveal any clinically relevant benefits in outpatients.^35,69 Currently, there is little data to suggest any benefits from the addition of opioids and epinephrine to local anesthetic infusions.

Patient-Controlled Regional Analgesia

Clinical Pearls

        Available inpatient and outpatient data suggest that following procedures producing moderate-to-severe pain, providing patients with the ability to self-administer local anesthetic doses (patient-controlled regional analgesia [PCRA]) increases perioperative benefits or decreases local anesthetic consumption (or both).^{33–36,63,65,66} However, no information is available to base recommendations on the optimal basal rate, bolus volume, or lockout period, other than for interscalene catheters.³³ In all probability, these factors will also be influenced by the variables noted previously, such as surgical pain intensity and choice of local anesthetic infusion. Until recommendations based on prospectively collected data are published, practitioners should be aware that investigators have reported successful analgesia using the following with long-acting local anesthetics: basal rate of 5 to 10 mL/h, bolus volume of 2 to 5 mL, and lockout duration of 20 to 60 min. The maximum safe doses for the long-acting local anesthetics remain unknown. However, multiple investigations involving patients free of renal or hepatic disease reported blood concentrations within acceptable limits following up to 5 days of perineural infusion with similar dosing schedules.^38,70–72 Extrapolating from data from patients receiving epidural bupivacaine infusion, a maximum infusion rate of 0.5 mg/kg/h of bupivacaine may be considered.³⁸

        Following ambulatory shoulder surgery with an interscalene catheter, infusion duration may be increased and similar baseline analgesia can be provided by decreasing the basal rate from 8 to 4 mL/h when patients supplement their block with large bolus doses (6 mL).³³ However, patients experience an increase in breakthrough pain incidence and intensity and sleep disturbances and a decrease in satisfaction with their analgesia. Therefore, if ambulatory patients do not return for additional local anesthetic, practitioners are left with the dilemma of superior analgesia for a shorter duration versus a lesser degree of analgesia for a longer period of time. Of note, the infusion duration can be increased by progressively decreasing the basal infusion rate with a reprogrammable infusion pump, thus theoretically maximizing postoperative analgesia.⁷

        Studies that investigated the optimal dosing regimen for outpatients involved surgical procedures producing moderate postoperative pain. For procedures resulting in relatively mild postoperative pain, it is possible—even probable—that adequate analgesia would be adequately achieved with a bolus-only dosing regimen.³¹ It is possible that the optimal dosing regimens, basal rates, and bolus doses may vary among different catheter types.⁴⁹ More data are necessary, however, before any such recommendations can be made.

Clinical Pearls

Related posts:

Regional Anesthesia in the Patient with Preexisting Neurologic Disease. The History of Local Anesthesia. Stimulating Catheters. Ultrasound-Assisted Nerve Blocks in Adults. Cutaneous Blocks for the Upper Extremity. Cervical Plexus Block.

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