General Considerations for Continuous Nerve Blocks

In the past few years, continuous nerve blocks have
enjoyed a significant surge of interest, especially for acute
postoperative pain management following major orthopedic procedures
(both inpatient and outpatient) in adults as well as in children. The
present interest is based in part on several encouraging reports about
the beneficial effects of these techniques on functional outcome and
hospital length of stay. Furthermore, interest has been fueled by the
increased number of indications for continuous lumbar plexus and
femoral block, the development of new approaches related to the
placement of sciatic perineural catheters (posterior popliteal,
lateral, and gluteal approaches), the recent introductions of the
insulated Tuohy needle, and new pumps especially designed for
outpatient surgery. These techniques are very effective and provide a
pain-free environment, especially when incorporated into a multimodal
and multidisciplinary approach to postoperative pain management. To
maximize functional outcome and shorter recovery, it is necessary to
start prior to surgery and combine peripheral nerve blocks with
cyclooxygenase (COX)-2 inhibitors, opioids, cryotherapy, appropriate
immobilization, the least traumatic surgical techniques, and optimal
sleep and nutrition after surgery.

The indications for continuous blocks for major
inpatient orthopedic surgeries (which in the United States represent an
average of 2 to 4 days of hospitalization), include major shoulder
surgery; upper and lower extremity trauma; upper and lower extremity
reimplantation; shoulder, elbow, hip, knee, and ankle arthroplasty; as
well as prolonged upper and lower physical therapy.

The techniques applied vary with the indications. For
major shoulder surgeries, most authors favor the use of continuous
interscalene and (less frequently) supraclavicular continuous blocks.
For major surgeries below the shoulder, infraclavicular, and axillary
(including the Raj approach) continuous techniques have been
demonstrated to be safe and effective. For major lower extremity
surgeries, the techniques also vary according to the indications and
the most prevalent nerve(s) involved in the postoperative pain. Thus,
psoas compartment or lumbar plexus continuous blocks have been reported
to be effective in patients undergoing hip surgery, whereas the use of
continuous femoral blocks seems to be preferred for major knee surgery.
Furthermore, for major ankle and foot surgeries, continuous sciatic
nerve blocks using a subgluteal, lateral, and posterior popliteal
approach are indicated.

Although several local anesthetic solutions have been
advocated (including 1% procaine, 1% lidocaine, and 0.1%, 0.2%, 0.25%,
and even 0.5% bupivacaine), it seems that 0.2% ropivacaine is becoming
the local anesthetic of choice for these techniques. Compared with
bupivacaine, ropivacaine is less toxic and provides a more preferential
sensory block with less paresthesia. In addition, residual motor blocks
may represent an important limitation to an optimum active mobilization
and have been shown to be more frequent with bupivacaine than with
ropivacaine. In the past few years, local anesthetic mixtures used for
continuous nerve blocks have also included opioids such as morphine
(0.03 mg/mL), fentanyl (2 mg/mL), diamorphine (0.02 mg/mL), sufentanil
(0.1 mg/mL), and clonidine (1 mg/mL), but none of these drugs have been
proven to be beneficial.

Until the introduction of electronic infusion pumps,
continuous nerve blockades were performed using discontinuous
perineural injections of various types of local anesthetic solutions in
various concentrations and volumes. In the late 1970s, continuous
infusion techniques were introduced and have now become the techniques
of choice. In the past few years, however, the use of select
patient-controlled techniques has generated particular attention. It
has been shown that a patient-controlled bolus of 5 mL with a lockout
period of 30 minutes or 5 mL/hour plus a 2 to 3 mL bolus and a lockout
period of 20 to 30 minutes is as effective as 10 mL/hour after
inpatient shoulder and knee surgery.

The constant search for increased efficiency and earlier
discharge from the hospital coupled with present health care
reimbursement issues led to a continuing increase in the number of
orthopedic procedures being performed on an outpatient basis. In this
environment, several authors have demonstrated that pain is the first
cause of unscheduled rehospitalization and delayed discharge after
ambulatory surgery, and that a significant number of patients
experienced moderate to severe pain, despite the prescription of oral
medication including opioids after surgery while being at home.
Although the reasons for this situation are multifactorial, it is clear
that ineffective or short-lasting pain treatment (including single
peripheral nerve blocks and intraarticular injections of opioids or
local anesthetics) represents an important contributing factor. To
provide better postoperative pain control in an ambulatory environment,
continuous perineural infusions of 0.2% ropivacaine have been used for
several indications, including rotator cuff repair (interscalene
continuous blocks) and hand surgery (axillary continuous blocks),
anterior cruciate ligament (ACL) and patella repair (femoral continuous
blocks), and major foot surgery (popliteal and lateral continuous
sciatic blocks). In the past 2 years, several investigators have also
reported the effectiveness and safety of continuous nerve blocks and
subacromial infusion after ambulatory orthopedic surgery.