Understanding Anesthesiology - The Global Regional Anesthesia ...

area of non-inked skin just slightly off midline, which
provides satisfactory access for catheter insertion. The
second challenge is performing a technical procedure
in a patient who is in active labour. In this case, the anesthesiologist
pauses while the patient is having contractions.
The patient is able to do an excellent job of remaining
still, which is quite important during this delicate
procedure. As you are watching the video, watch
carefully for the moment of the “loss of resistance”,
when the gentle pressure on the hub of the syringe finally
gives way, as the needle has entered the “potential”
space that is the epidural space.
Once the catheter is in place, the anesthesiologist
“tests” the catheter to ensure that neither blood nor
cerebral spinal fluid (CSF) can be aspirated. While delivering
LA in small (3 ml) aliquots, the anesthesiologist
observes for symptoms or signs of incorrect catheter
placement. If the catheter is situated in one of the veins
of the epidural plexus then the patient may experience
symptoms of local anesthetic toxicity: tinnitus, perioral
numbness, metallic taste in the mouth and dizziness.
If the catheter is situated in the intrathecal space,
then the patient will develop a sensory/motor block
rapidly after the administration of only a small amount
of LA.
In the absence of any signs or symptoms of incorrect
catheter placement, the full dose of LA is delivered
over 10-20 minutes. Some LA’s, such as lidocaine, have
a relatively rapid onset of effect but also have a relatively
shorter duration of action. Bupivacaine, while
possessing a slower onset of effect, has a longer duration
of action. The dermatomal level of block is tested
by pinprick or ice cube (Figure 14). It generally takes
20-30 minutes for an adequate epidural block to take
effect.The required dose is determined by the range of
segments which must be blocked. The higher the surgical
site is, the higher the block must be. Table 10 describes
the dermatomal level of block required for some
of the more common surgical procedures which apply
to both spinal and epidural anesthesia. Many other factors
influence the amount of local anesthetic required.
For example, in pregnancy, there is a significant reduc-
Table 10 Required dermatomal levels for various surgical procedures
SURGICAL
PROCEDURE
Caesarian section
inguinal hernia repair
repair fractured hip
total knee arthroplasty (with
tourniquet)
hemorrhoidectomy
REQUIRED LEVEL
OF BLOCK
T4
T10
L1
L2
S4
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