Anesthesia Student Survival Guide
Jesse Ehrenfeld, Richard Urman, and Scott Segal, editors
© 2010 Springer Science and Business Media
CASE STUDY
Chapter 13: Anesthetic Technique: Regional
A 58 year old man is to undergo right total knee replacement (TKR). After a thorough
H&P and consultation, he elects to have the procedure under regional anesthesia. He
is otherwise healthy, though he smokes a pack of cigarettes a day and does not
exercise regularly due to his arthritic knee. He takes a NSAID daily for pain and
lately has been taking oxycodone and acetaminophen for worsening pain.
Which dermatomes or nerves will you need to block to perform a total knee replacement
comfortably?
The anterior portion of the thigh and leg are innervated by the L3, L4, and L5
dermatomes. The back of the knee, though not in the incision, is stimulated nonetheless
in TKR, and is innervated by S2. In addition, a thigh tourniquet is usually employed to
prevent blood loss, so L2 and possibly L1 should be blocked. In practice, the femoral,
lateral femoral cutaneous, obturator, and portions of the sciatic nerve need to be
blocked.
Which regional anesthetic techniques are suitable for total knee replacement? Which will you
choose?
In theory, several techniques are possible. Spinal anesthesia will reliably block all the
involved nerve roots, whether a plain solution or hyperbaric solution containing
glucose are used. Hyperbaric solutions produce higher levels than are necessary, so
plain solutions may be favored for the lower incidence of hypotension. Epidural
anesthesia is commonly used for TKR and allows titration of local anesthetic to the
desired level. Disadvantages include a 5-10% incidence of failed or inadequate block
(asymmetric anesthesia or incomplete sacral nerve blockade). An additional advantage
is the ability to extend the block for either prolonged surgery or for postoperative
analgesia. Peripheral nerve blocks may also be used. Individual nerve blocks can
provide surgical anesthesia. It is more practical to perform a lumbar plexus or three-inone block (which will cover the femoral, lateral femoral cutaneous, and obturator
nerves with a single injection or catheter). A separate sciatic block, or a spinal or general
anesthetic is then added to complete the anesthetic.
If you choose epidural analgesia, how will you locate the epidural space? What precautions will
you take to avoid toxicity?
Standard monitors are placed and an IV is inserted. The patient can be seated or lying
on his side; many find the sitting position easier to locate the midline. The back is
Anesthesia Student Survival Guide
Jesse Ehrenfeld, Richard Urman, and Scott Segal, editors
© 2010 Springer Science and Business Media
sterilely prepped and draped and local anesthetic is infiltrated in a lumbar interspace,
typically L3-4 or L2-3. The epidural needle is advanced until it is seated in ligament.
Then a loss-of-resistance syringe is attached, containing either air or saline. The epidural
needle is advanced in slow increments, checking for resistance to injection, indicating
the tip is still in ligament. When the needle enters the epidural space, a loss of resistance
to injection will be felt. The epidural catheter is then inserted 3-5 cm and the needle
withdrawn. To avoid toxicity, it is important to exclude intravascular or intrathecal
(spinal) placement. A test dose of lidocaine with epinephrine is given (typically 3-5 mL
of a 2% concentration) and signs and symptoms of intravascular injection are sought.
The heart rate will increase if epinephrine is injected IV, and the patient may experience
symptoms such as tinnitus, perioral numbness, or metallic taste. If 60-100 mg of
lidocaine were injected intrathecally, an immediate spinal anesthetic would be obtained.
After verifying proper position of the epidural catheter, what drugs will you use?
Assuming neither intravascular nor intrathecal placement is detected, an additional 1015 mL of lidocaine can be injected in divided doses to obtain a low thoracic dermatomal
level and motor blockade of the legs. Care should be taken not to inject too much drug
without ensuring that the block is symmetrical (or at least that the operative site is
numb). The case can be continued with lidocaine, or a longer-acting local anesthetic
such as bupivacaine (0.5 or 0.75%) or ropivicaine (1%) can be given to ensure a dense
block for surgery.
Will you continue to use your epidural after the procedure?
Although no one technique has been shown to be better than others, use of regional
analgesia in the immediate postoperative period and for 1-3 days following surgery can
help facilitate active rehabilitation efforts and improve joint mobility. If you use the
epidural postop, you will reduce the concentration of local anesthetic, so that you are
providing analgesia rather than surgical anesthesia. Bupivacaine or ropivacaine, 0.1250.2%, often with an opioid such as fentanyl or hydromorphone, are common choices.