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.

The most important benefit of the ISB is that it provides long-lasting pain relief in the
postoperative period. Previous studies have suggested that the analgesic effect of the ISB
lasts up to 12 to 24 hours. However, other clinical trials have demonstrated that an ISB
provides pain relief for approximately 6 hours, and that pain may be worse after the block
has resolved (compared to intravenous opioids). Recently, Abdallah et al. performed a
meta-analysis of 23 randomized trials examining 1090 patients to assess the effect of ISBs on
pain after shoulder surgery (compared to those not given a block). The authors observed that
the duration of pain relief for patients in the ISB group was only 8 hours at rest and 6
hours with movement. There was no further benefit beyond this time. Pain was actually worse
at 24 hours in patients given an ISB. These important findings suggest that the effects of
the ISB last for a much shorter period of time than estimated by most clinicians, and may
impact the evaluation of the risk / benefit ratio of the ISB.

As described previously, an important limitation of the intravenous and oral opioid approach
to pain management is that the duration of effect of these agents is only typically 3 to 4
hours. This results in periods of effective pain relief, followed by periods of
moderate-to-severe pain in the postoperative period. An alternative strategy for opioid
utilization may involve the administration of a very long-acting opioid in the operating room
that would provide effective analgesia for the first 24 postoperative hours (which
corresponds with the period of the most severe pain after surgery). At the present time,
intravenous methadone is the only long-acting opioid available to clinicians. Methadone was
developed in 1939 and approved by the FDA for clinical use in 1947. A primary advantage of
methadone is its long half-life, which ranges from 25-52 hours when given intravenously in
larger doses. This unique property of methadone means that single daily doses can often be
used in patients with moderate-to-severe acute or chronic pain. A number of recent
investigations have demonstrated that methadone is effective in treating a variety of acute
and chronic pain conditions. Although it is best known as a drug used to treat narcotic
addiction, methadone is also being used with increasing frequency as an analgesic agent in
the operating room to provide prolonged postoperative analgesia. A calculated half-life of 35
hours was observed when methadone was administered intravenously to surgical patients,
resulting in a median duration of analgesia lasting 26 hours. In patients undergoing
abdominal, orthopedic, cardiac, or gynecologic surgery, the use of a single dose of methadone
(20 mg or 0.2-0.3 mg/kg) at induction of anesthesia resulted in improved analgesia for the
first 24 hours after surgery, when compared to other intraoperative opioids. In these
investigations, patients in the methadone groups required significantly less postoperative
pain medication and reported lower pain scores during the first postoperative day. Up to 39%
of patients required no additional pain medications, despite undergoing major surgery
associated with moderate-to- severe levels of postoperative pain. In a randomized,
double-blinded investigation in cardiac surgical patients completed at Evanston Hospital,
subjects randomized to the methadone group reported less pain, required reduced postoperative
pain medications, and described increased satisfaction with overall pain management when
compared to subjects administered a standard opioid (fentanyl). No adverse events directly
attributable to methadone were reported in any of these clinical trials.

The use of methadone may be advantageous in the setting of shoulder arthroscopic surgery. The
investigators hypothesize that a single dose administered at the start of surgery may provide
pain relief throughout the procedure and PACU recovery and for the first 24 hours (or more)
after hospital discharge to home. The aim of this clinical trial is to compare analgesia
provided by an ISB to that from a pain management strategy using intravenous methadone. Pain
scores will be collected from both groups for the first 72 hours after surgery. The
requirements for pain medications will also be recorded. Overall satisfaction with pain
management will be assessed, and all postoperative complications noted.

Inclusion Criteria:

- All patients presenting for elective shoulder arthroscopic procedures will be eligible
for enrollment.

Exclusion Criteria:

- Preoperative renal failure requiring dialysis

- Poorly controlled pulmonary disease (severe asthma or COPD) -Contraindication to
regional anesthesia (recent anticoagulant use)

- Sleep apnea or morbid obesity with possible sleep apnea

- Allergy to methadone

- Significant preoperative pain requiring treatment with high doses of opioids (more
than 6-8 Norco tablets or equivalence per day) or recent history of opioid abuse