Methadone and Interscalene Block for Shoulder Surgery

Shoulder surgery is one of the most common orthopedic operations, with 1.4 million procedures performed worldwide. Advances in surgical technology now allow the majority of these procedures to be performed arthroscopically. A growing number of shoulder arthroscopic procedures are now conducted on an outpatient basis. Effective pain control is therefore essential if a patient is to be sent home on the same day as the operation. This management strategy presents an important challenge to anesthesiologists, surgeons, and postanesthesia care unit (PACU) nurses. The pain of a shoulder arthroscopic procedure is equivalent to an open procedure during the first 24-48 hours, and up to 30% of patients report pain of a severe intensity on the first postoperative day. Poor pain control after surgery is associated with lower patient satisfaction scores, adverse events, and the development of chronic postsurgical pain. A variety of therapeutic strategies have been developed to more effectively control this early postoperative pain. However, there are a number of important limitations to each of these approaches.

There are three general approaches that anesthesiologists use to provide anesthesia and analgesia for shoulder arthroscopic surgery. Traditionally, shoulder surgery has been performed with a general anesthetic and a breathing tube (oral endotracheal intubation). Although this provides effective analgesia for the duration of the operation, the patient will experience pain once the intraoperative anesthetic has worn off. In this setting, the anesthesia care provider administers an opioid through the intravenous line so that the patient will awaken in less pain. In the PACU, the nursing staff continues to administer an intravenous opioid until pain is effectively controlled. There are important limitations to this anesthetic management strategy. Anesthesia care providers must estimate the amount of opioid to administer intraoperatively. Since the individual responses to opioids may vary widely, it is possible that patients may awaken in pain or may difficult to extubate (remove the breathing tube) due opioid-induced respiratory depression. Once admitted to the PACU, the patients' pain can be effectively controlled by the careful titration of opioids by nursing staff (pain of less than 3 on a scale of 0 to 10). However, the duration of the effectiveness of commonly-used opioids is only 3-4 hours. Therefore, the patient may have little pain at the time of hospital discharge, but may experience severe pain several hours later. Oral analgesic agents are used to control pain in the home setting. The use of oral opioids results in variability in the level of pain that each patient experiences. This variability is related to the slow onset time and short duration of effect of these oral agents (results in "peaks and troughs" of postoperative pain).

A second anesthetic technique involves the use of a general anesthetic with an interscalene nerve block (ISB). Over 40 years ago, Winnie et al. described the use of a single interscalene brachial plexus block to provide analgesia following shoulder surgery. This practice involves the injection of a large volume of local anesthetic agent near the nerves of the brachial plexus. An ISB or brachial plexus block is a regional anesthetic technique that blocks the nerves that supply the shoulder, arm, and forearm. The block is typically administered in the preoperative holding area before a general anesthetic is performed. When the patient awakens from the general anesthetic and arrives in the PACU, the nerve block provides pain relief which persists for several hours. The risk of nausea and vomiting is also reduced with an ISB block. In addition, most studies have demonstrated that patients randomized to receive an ISB have shorter PACU and hospital length of stays. The advantages of the ISB block have prompted many clinicians to introduce this regional anesthesia technique into their clinical practices. Although an ISB is a very effective postoperative pain management technique, there are several important limitations. The block is usually performed before entering the operating room and may delay the start of the case. In addition, the needle placement for the block is in the neck, and improper placement may result in a pneumothorax (lung collapse). Approximately 5% of ISBs fail, even in experienced hands. Block failure necessitates the use of opioids to control pain. Temporary phrenic nerve palsy or diaphragm paralysis is common after the ISB is performed. This results in a significant decrement in pulmonary function in many patients, including those with normal baseline respiratory muscle strength. Most importantly, clinical investigations, cadaveric studies, and retrospective reviews have suggested that the nerve roots of the brachial plexus may be particularly susceptible to nerve injury from the local anesthetic used for the nerve block. Studies have demonstrated that the ISB is associated with a higher risk of transient and long-term neurologic complications when compared to other peripheral nerve blocks. Furthermore, it is now recognized that the ISB may result in delayed onset phrenic nerve damage and permanent unilateral diaphragmatic paralysis. Finally, the analgesic effects of the ISB may resolve abruptly, resulting in the sudden perception of severe pain. In light of these risks, some experts have questioned the routine use of ISBs for shoulder surgery.

The third strategy for anesthetic and postoperative pain management involves the use an ISB not only as a postoperative analgesic but also as a primary anesthetic. With this approach, an ISB is performed in the preoperative holding area. Once clinicians are assured that the block is functioning, the patient is transported to the operating room, sedation is administered, and the shoulder surgery performed with a combination of sedation and the regional block. Advantages of this technique include the avoidance of general anesthesia (and associated complications), and a better maintenance of blood flow to the brain. A disadvantage of the technique is that a profound nerve block must be present in order for the procedure to be completed successfully. Careful patient selection is also essential when performing shoulder surgery in a sedated patient in the sitting position (anesthesiologists do not have easy access to the patients' airway). Finally, the patient is at risk for all of the complications of ISB listed previously.

When deciding on the appropriate anesthetic for the patient undergoing arthroscopic shoulder surgery, clinicians must weigh the risks and benefits of each technique. As noted above, each anesthetic approach has important limitations. At Evanston hospital, approximately 75% of shoulder surgery patients have an ISB for their procedure. There is a higher utilization of this block at Glenbrook Hospital and at the orthopedic surgery center.