Postoperative Pain Control
- Regional Anesthesia
A variety of regional techniques exist that can be used to promote
postoperative pain relief. These techniques can be categorized as
neuraxial local and narcotics, peripheral nerve blocks, and wound
infiltration.
Intrathecal analgesia Intrathecal (IT) narcotics can offer effective postoperative analgesia. These agents bind with opioid receptor sites in the dorsal horn of the spinal cord, resulting in modulation of pain signals at the cord level. IT narcotics can be administered as an adjunct to general anesthesia (eg, scoliosis surgery) or mixed with local anesthetics and administered during a spinal anesthetic (eg, THA). For IT morphine, the onset of analgesia is 30-60 minutes, and the duration of analgesia is 18-24 hours, depending on the dose used. Adverse effects include nausea, pruritus, urinary retention, and respiratory depression. Respiratory depression from IT morphine peaks at approximately 7-9 hours after surgery and is dose dependent. The incidence of respiratory depression in one retrospective study was 0.36% but is probably lower now since smaller doses are used currently. The incidence of nausea and vomiting is approximately 20% and peaks at approximately 4 hours postinjection. The onset of pruritus is 3-5 hours postinjection and occurs in approximately 40% of patients. Severe pruritus requiring treatment occurs in approximately 9% of patients. The incidence of urinary retention is hard to estimate because many patients receive prophylactic catheterization. Catheterization appears to be required in 10-40% of patients. This is a very simple analgesic method to use, especially if spinal anesthesia is already planned. The advantages of this technique include simple technique, no catheter care or pumps required, low cost, and easy supplementation with low-dose patient-controlled analgesia (PCA) narcotics as needed. The main disadvantages are limited duration of action (in comparison to catheter techniques) and the adverse effects discussed above. When higher doses are used, frequent monitoring of respirations is mandated. Contraindications to this technique include heparinization or other coagulopathy, local or systemic infection, and morphine allergy. Dosing is as follows:
Epidural analgesiaEpidural analgesia is accomplished by means of epidural narcotics, local anesthetics, or their combination. Narcotics can be administered by bolus or infusion. Adverse effects are the same as those of IT narcotics. Epidural local anesthetics, typically dilute solutions of bupivacaine or ropivacaine, are administered by infusion. Epidural local anesthetic adverse effects include urinary retention, motor block, and sympathectomy-induced decrease in blood pressure. Epidural local anesthetics and narcotics frequently are combined in lower dosages in an effort to provide analgesia with a lower risk of the associated adverse effects of each drug. The duration of epidural infusion depends on several factors. Catheters must be removed prior to the advent of significant anticoagulation from heparin, low molecular weight heparins (LMWH), or Coumadin. The authors tend to remove epidural catheters by 72 hours to reduce the risk of epidural site bacterial colonization. A wide variety of dosing regimens are in use. Narcotic and local anesthetic drugs can be combined in the same infusion and run at a lower rate. Intravenous PCA narcotics can be administered as an adjunct to local anesthetic infusions. Typical epidural infusions include the following:
Treatment of epidural or IT narcotic adverse effects is as follows:
As an alternative to boluses, naloxone can be administered by infusion at 0.2-0.3 mg/h. Neuraxial blocks and anticoagulation The American Society of Regional Anesthesia has made the following recommendations regarding neuraxial blocks. When any anticoagulant is administered perioperatively with a neuraxial catheter in place, close neurologic monitoring of the lower extremities is mandated as follows:
Peripheral nerve blocks can provide significant pain relief. Nerve blocks can be either combined with general anesthesia or used as the sole anesthetic. Long-acting local anesthetics, such as bupivacaine or ropivacaine, provide block duration of approximately 12 hours. However, longer duration can be achieved by placement of catheters perineurally, which are then infused continuously or boluses are given as needed. Serious adverse effects of peripheral nerve blocks are rare. Adverse effects can be categorized as due to either local anesthetic toxicity, complications of needle placement, or spill over of local anesthetic to surrounding neural structures. Local anesthetic toxicity can occur because of unplanned intravascular injection or slow absorption from the site of injection. This can be manifested by reactions ranging from tinnitus and dizziness to convulsions and cardiac arrest. Complications of needle placement can include hematomas, dysesthesias (0.2%), and other problems related to the specific block. Spillover adverse effects are manifested mainly in interscalene and supraclavicular blocks. Peripheral blocks have the advantages of no sympathectomy-induced decrease in blood pressure and no narcotic-related adverse effects such as urinary retention, nausea, or itching. However, some degree of motor block is observed with the sensory block. This may limit the usefulness of some blocks in some situations. For example, prolonged femoral blocks are a good choice for pain control in anterior cruciate ligament (ACL) reconstructions but are not a good choice in knee arthroscopy because the quadriceps motor block would prevent safe ambulation. Successful use of nerve blocks depends not only on knowledge of innervation of site of incision but also of innervation of underlying bone and muscular tissue. Brachial plexus blocks The brachial plexus can be anesthetized at sites above the clavicle (interscalene and supraclavicular approaches) or below the clavicle (infraclavicular and axillary approaches). The interscalene approach is used for shoulder and upper arm surgery, since the roots of both the brachial and cervical plexus are anesthetized. It is in general not a good approach for lower arm or hand surgery because the C8 and T1 nerve roots frequently are anesthetized inadequately. The supraclavicular approach can result in good block of the arm and hand. The infraclavicular or axillary approaches are used for surgery of the elbow, lower arm, and hand. Interscalene and supraclavicular blocks, although safely performed in most patients, have more adverse effects and risks associated with them. Phrenic nerve dysfunction occurs in 100% of interscalene blocks and 25-50% of supraclavicular blocks. Thus, these blocks may not be well tolerated in patients with preexisting respiratory compromise. Case reports exist of epidural or IT injections with interscalene blocks. Pneumothorax has been reported in 1% of supraclavicular blocks. Horner syndrome (sympathetic chain) and hoarseness (recurrent laryngeal nerve) commonly occur from spread of local to surrounding nerves. For hand surgeries, more distal blocks also can be performed to provide analgesia. Block of the radial, median, and ulnar nerves at the wrist or block of the digital nerves of the fingers can be performed. Leg blocks The knee joint is innervated by femoral (anteriorly), sciatic (posteriorly), obturator (medially), and lateral femoral cutaneous nerves (laterally). Femoral blocks frequently are used for analgesia after knee surgery; however, the degree of analgesia depends on the amount of surgical trespass into other nerve distributions. Thus, patients having arthroscopic ACL and patellar surgery obtain excellent pain relief after femoral block, while patients having knee replacement surgery frequently have severe posterior pain of sciatic origin. Unless the knee is properly braced, weightbearing and ambulation may need to be restricted until quadriceps function recovers in patients with femoral nerve blocks. Sciatic or popliteal fossa blocks are performed to provide analgesia after foot surgery. The popliteal fossa block is a block of the sciatic nerve in the popliteal fossa in the vicinity of its division into tibial and common peroneal nerves. The advantage of popliteal fossa block over standard sciatic block is that hamstring function is maintained. A saphenous block can be added if the site of surgery includes medial malleolus. For some foot or toe surgeries, more distal blocks also can be performed to provide analgesia. Block of the deep peroneal, superficial peroneal, tibial, sural, and saphenous nerves can be performed at the ankle level, or block of the digital nerves of the toes can be used. WOUND INFILTRATION Infiltration of wounds with local anesthetics, besides providing analgesia, appears to reduce the local inflammatory response to trauma or surgery. Thus, local infiltration may help reduce the upregulation of peripheral nociceptors that manifests as hypersensitivity to stimulus. Local anesthetic can be administered in skin incision sites, intra-articularly (knee and shoulder), or on bone wounds (iliac crest graft sites). Bupivacaine or ropivacaine provide approximately 6 hours of analgesia. Alternatively, catheters can be placed at these locations and either infused continuously or boluses can be administered with patient-controlled pumps. With the advent of disposable infusion pumps, home discharge with catheter and pump in place is now possible. Details regarding patient selection and safety of this practice are being investigated. Peripherally located opioid receptors have been discovered in animals. Animal studies suggest that intraarticular inflammation induces the development of synovial opioid binding sites. In addition, intraarticular opioid administration appears to have an anti-inflammatory effect. Based on these observations, intraarticular narcotics are being administered in knee and shoulder surgery. The effect of intraarticular morphine in knee arthroscopy has been examined in multiple studies. A recent metaanalysis concluded that a mild analgesic effect is observed, but a systemic effect cannot be excluded completely. Whether a dose response effect is observed, and what the optimal dose is, are still in question. Morphine doses of 1-5 mg have been used. Regarding shoulder surgery, in a study of patients undergoing open rotator cuff repairs, patients receiving a combination of 1 mg of morphine with 20 mL of 0.25% bupivacaine had better postoperative pain relief than those patients receiving bupivacaine alone. In another interesting study of patients with cervical diskectomy, 5 mg of morphine infiltrated into the iliac crest donor site produced better short-term analgesia and resulted in less chronic pain in the months after surgery.
For any specific surgery type, several regional anesthetic pain management options may be present. The choices may include the above-mentioned wound infiltration, neuraxial, or peripheral nerve block techniques. In addition, techniques may be combined. Techniques are selected based on the surgical trauma, goals for physical therapy, expected length of hospital stay, and avoidance of adverse effects. Spine IT morphine has been used as an adjunct in complex spine surgery, such as scoliosis surgery. Iliac crest harvest site infiltration with morphine and local anesthetic is an option. Shoulder/arm/hand Shoulder surgery can be performed under interscalene block or combination general/block. Complete pain relief can be achieved (for the duration of the block) unless the incision extends to close to the axilla. Interscalene catheters can be placed and infused for more prolonged analgesia. Options include subacromial or intraarticular morphine and local anesthetic. Interscalene, axillary, and infraclavicular catheters can be placed for prolonged pain relief or arm surgery. Besides pain relief, the arm sympathectomy may be of value in certain operations involving vascular repairs. Hip IT morphine is very effective for pain control in the first 12-24 hours. Epidural local anesthetic and narcotic can be infused. Duration of infusion is limited by perioperative anticoagulation for DVT prophylaxis, and by the need to terminate motor block so that physical therapy can by performed. Thus, at the authors? institution, epidural catheters typically are removed on the morning of postoperative day 1. Knee arthroplasty IT morphine can be used for pain control in the first 12-24 hours. Epidural local anesthetic and narcotic can be infused. Duration of infusion is limited by perioperative anticoagulation for DVT prophylaxis and by the need to terminate motor block so that physical therapy can by performed. Thus, at the authors? institution, epidural catheters typically are removed on the morning of postoperative day 1. Femoral and sciatic blocks can be used. Femoral blocks alone are usually not adequate because of posterior capsular pain that is of sciatic innervation. Continuous femoral nerve block with single shot sciatic nerve block has been described to be effective. Knee arthroscopic procedures Epidural anesthesia is an effective technique for performing arthroscopic ACL repair. However, as this procedure has evolved to an outpatient or 23-hour stay procedure, epidural adverse effects such as urinary retention and motor block make this an unsuitable technique for postoperative use. Instead, femoral block is used frequently and provides very effective pain relief. At the authors? institution, femoral nerve block typically is used with intraarticular bupivacaine/morphine. For arthroscopy/meniscectomy, intraarticular local and morphine is used routinely. Long-acting femoral blocks are avoided so that ambulation in not impeded. Foot Foot and ankle pain can be controlled with popliteal fossa block. The saphenous nerve also may need to be blocked if the surgical incision is on the medial aspect of the foot or ankle.
Peripheral nerve blocks can provide excellent pain relief but have the problem of limited duration. An example of this scenario is the rotator cuff operation performed with interscalene block with bupivacaine. The sudden return of pain 12-18 hours after the block can be very distressing to the patient and result in the need for large doses of narcotics to get pain under control. Strategies to manage this include the following: Perioperative narcotics It is a good strategy for the patient to receive a dose of narcotic prior to the expected time of block resolution. The authors typically have narcotic intravenous PCA pumps attached to patients prior to removal of epidural catheters. OxyContin has been demonstrated to be an effective analgesic for orthopedic procedures. As an example, the first dose can be administered 10-12 hours after the placement of a bupivacaine interscalene block for shoulder surgery. PRN narcotics should always be available for pain control once the block has terminated. Perioperative nonsteroidal anti-inflammatory drugs NSAIDs can be used as a supplement to narcotics. Intravenous ketorolac (Toradol) is a very effective pain reliever of orthopedic pain. Ketorolac 15-30 mg IV every 6 hours can be administered as a background analgesic without respiratory depressant effects while a block is in effect. Concerns about the use of NSAIDs include platelet dysfunction, renal dysfunction, gastric ulceration (especially in patients receiving oral anticoagulants), and potentially decreased bone growth and healing, which might impact on fusion success rates following spinal surgery or implant osteointegration following cementless total joint replacement. Intravenous cyclooxygenase-2 (COX-2) inhibitors will be available soon and appear to reduce many of these risks. Catheter techniques Catheter techniques can be used to prolong the duration of peripheral nerve blocks. Both continuous infusion and PCA techniques have been used. Blocks amenable to catheter placement include interscalene, infraclavicular, axillary, femoral, and popliteal fossa. Intrabursal, intraarticular, and intrawound catheter placement is also possible. The local anesthetic chosen for infusion is typically either bupivacaine (0.125-0.25%) or ropivacaine (0.1-0.2%). Potential problems include technical failure, dislodgment of catheter, and bacterial colonization of catheter site. Recently, authors have described the use of disposable ambulatory infusion pumps that allow discharge of patients with catheters in place and being infused. Questions regarding patient selection and safety are under investigation. Investigatory more prolonged effect drugs Drugs with more prolonged effect are under investigation. Liposome encapsulated local anesthetics and narcotics, with slow release, are under investigation. In some studies, local anesthetic additives, such as clonidine and buprenorphine, have demonstrated promise as ways to prolong postoperative pain relief. REFERENCES:
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