Better Techniques Aid

Acute Pain Management

By Daniel J. McFarland, M.D.

The last three decades have seen a significant resurgence in the application of regional anesthetic techniques to the treatment of acute and chronic pain. After discovery of CNS opiate receptors in the 1970s, neuraxial administration of analgesics via catheter into the epidural space or the CSF became commonplace for the management of thoracic-, abdominal-, pelvic-, and lower-extremity pain, particularly after surgery. More recently, the development of novel catheter technology and improved techniques of accurate catheter placement have made possible the reliable and effective application of continuous local anesthetic analgesia for the treatment of shoulder-, arm-, and lower-extremity pain.

Traditional, “single shot” peripheral nerve blocks can provide both excellent surgical anesthesia as well as postoperative analgesia, but the duration of the latter is limited to approximately 24 hours with the longest-acting local anesthetics currently available. Successful attempts to prolong pain relief by placing catheters close to peripheral nerves for local anesthetic administration (at first by repeated drug boluses and more recently by continuous infusion) were first reported in the 1940s. Two major problems prevented earlier and widespread use of peripheral nerve catheters. First, they were very difficult to accurately place near enough to peripheral nerves to reliably deliver local anesthetic and maintain analgesia. Second, even an accurately placed peripheral nerve block catheter was often subsequently displaced enough that local anesthetic delivery via the catheter became ineffective.

The explosive growth of the volume and complexity of outpatient surgery and the introduction of low molecular weight heparin therapy for deep veinous thrombophlebitis prophylaxis both provided strong incentives to overcome these largely technical problems, and it was recognized that both high patient satisfaction and improved clinical outcomes in acute pain management were associated with the use of peripheral regional anesthesia. Continuous nerve block via catheter has a number of advantages over alternative analgesic strategies. Side effects associated with opiate analgesia (such as nausea, vomiting, respiratory depression, itching, urinary retention, constipation, excessive sedation, and mental status changes) are virtually eliminated. Compared with neuraxial (epidural or spinal) analgesia, continuous peripheral nerve block with local anesthetic provides superior hemodynamic stability, better ability to participate in physical therapy, and less need for bladder catheterization (and its complications). Most important, the serious complications of neuraxial catheters such as meningitis, spinal abscess, and heparin therapy-related epidural hematoma can be avoided altogether.

By the 1980s many anesthesiologists routinely employed battery-powered peripheral nerve stimulators attached to insulated nerve block needles to perform peripheral nerve blocks as an alternative to traditional methods that relied on eliciting (often painful) nerve paresthesias with a nerve block needle. Nerve stimulation lets the anesthesiologist provoke a motor response appropriate to the nerve or plexus of interest, use that response to precisely (and more comfortably) position a nerve block needle closely adjacent (within mm’s) to the neural target, and deposit local anesthetic close enough to reliably result in clinical neural blockade. It was not long before academic regional anesthesia specialists began to report some reasonable success at placing standard 20-gauge epidural catheters through such precisely placed insulated needles and providing highly effective continuous local anesthetic analgesia for several days postoperatively. Anesthesia faculty members at Duke University Medical Center were pioneers in these efforts. However, a significant problem remained with this approach: An initial nerve block administered through a needle was highly likely to be effective. However, the “blind” placement of a percutaneous nerve block catheter, after the initial block dose of local anesthetic given through the needle, too often resulted in the catheter deflecting far enough away from the target nerve (only mm’s!) to result in inadequate continuous analgesia when additional local anesthetic was administered via the catheter. In addition, it was only after the initial nerve block started to resolve, hours after surgery, that the catheter malposition could be discerned.

The solution to this problem was the development (by Andre Boezaart, M.D., Ph.D., now at the University of Iowa School of Medicine) of a stimulating peripheral nerve catheter (Arrow Stimucath; Arrow International, Reading, PA.). This device is a Teflon-coated, hollow, flexible-wire catheter designed to be advanced under peripheral nerve stimulator guidance. The stimulating catheter can thus be directed closely adjacent to a nerve or nerve plexus, and its position relative to the target confirmed by observing the correct, expected motor response to appropriately low-voltage electrical stimulation. Stimulating catheters are placed via insulated nerve block needles before the administration of any local anesthetic to the target nerve. After satisfactory positioning, the catheter is aspirated to check for inadvertent vascular placement, and several cc’s of local anesthetic with epinephrine are injected as a “test dose” via the catheter to further assess for possible unintended intravascular local anesthetic administration. Supplying electrical stimulation to the catheter tip while injecting this small preliminary dose of local anesthetic is a further means of assuring its correct position: A fraction of a cc of local anesthetic exiting the tip of a properly positioned nerve block catheter will result in immediate cessation of the motor response to stimulation obtained before drug administration (the Raj test). A properly positioned stimulating catheter lets the anesthesiologist administer increments of local anesthetic via the catheter, slowly and safely, to establish initial analgesia. A continuous infusion provided by a portable electronic, or simple elastomeric pump, can maintain analgesia for several days if necessary. Displacement of stimulating peripheral nerve catheters has not been a major problem since simple subcutaneous tunneling techniques to secure them were introduced (also by Dr. Boezaart).

Placement of catheters adjacent to the brachial plexus in the neck allows for particularly effective analgesia following surgery on the shoulder and proximal upper extremity. These so-called “continuous interscalene brachial plexus blocks” require the infusion of surprisingly small volumes of dilute local anesthetic. Continuous blockade of the brachial plexus more distally is also highly effective and several different anatomic approaches for catheter placement have been described. Catheters for nerve block may be inserted paraspinally at several different levels to achieve unilateral, localized regional neural blockade. For example, in the lumbar area, catheters placed in the paraspinal psoas compartment allow continuous blockade of the lumbar plexus, providing analgesia after hip injury or surgery. In the lower extremity, stimulating catheters facilitate reliable continuous analgesia in the sensory distributions of either the femoral or sciatic nerves.

As with any invasive technique, continuous nerve block analgesia with stimulating catheters requires detailed knowledge of relevant anatomy, strict attention to the details of sterile technique, and proper patient selection. Skin lesions in the area of intended catheter placement, sepsis, lack of informed consent, neurologic deficits in the distribution of the intended block, and mental status problems likely to interfere with the patient’s ability to cooperate with catheter placement are all strong contraindications to the procedure. Most continuous peripheral nerve blocks may be safely performed in the presence of anticoagulation. If continuous peripheral nerve block analgesia is contemplated for use in an outpatient setting, instructions must be communicated to the patients and their caregivers about protecting the body part affected by local anesthesia, how to detect potential problems with their infusion device, and how to contact a physician responsible for their care if problems arise. Ordinarily, peripheral nerve catheters are removed on the second to fourth postoperative day by a physician, although in some areas with large volumes of patients receiving these catheters, the devices are removed by specially trained nurses, or even by the patients themselves in some cases.

Continuous peripheral nerve block analgesia via stimulating catheters represents an area of special growth within the specialty of anesthesiology in the last decade. Driven by the ever-increasing rise in the number and complexity of outpatient surgeries, and the demand by patients for effective analgesia with minimal side effects, nerve block analgesia is likely to be utilized in increasing numbers of patients in the future. Further development of new medications, medical devices, and techniques will likely contribute to wider use of nerve blocks as well. 

Dr. McFarland is an anesthesiologist at Sequoia Hospital, Redwood City, and a neurologist.