Understanding Anesthesiology - The Global Regional Anesthesia ...

Figure 12 Insertion of Tuohy needle into epidural
space
Reproduced with permission from Astra Pharma Inc.
Figure 13 Insertion of epidural catheter
Reproduced with permission from Astra Pharma Inc.
and cauda equina. The volume of anesthetic delivered
and the site of the catheter determine the level or
“height” of the block. The presence of an indwelling
catheter allows the block to be extended in height or duration
as required.
Insertion of an epidural catheter is done in a strictly
sterile fashion. After local infiltration, a specially designed
17 or 18 gauge epidural needle (common trade
names Tuohy® or Hustead®) is inserted into the
spinous interspace. A special syringe, filled with air or
saline is attached to the hub of the needle. While advancing
the needle, the anesthesiologist maintains pressure
on the syringe in order to sense the resistance of
the tissue being traversed (Figure 12). The epidural
space is a “potential space” such that when it is entered
with the needle, a sudden loss of resistance is detected.
The syringe is then removed so that a catheter can be
threaded through the needle into the epidural space
(Figure 13), after which the needle is removed. A labour
epidural insertion can be viewed in Movie 3.1.
This movie demonstrates two frequent challenges faced
by the anesthesiologist. The first is the difficulty of inserting
an epidural in the presence of a dermal tattoo.
Inserting an epidural through tattooed skin is undesirable
as it may bring a plug of ink into the epidural
space, the consequences of which are not known. In
this case, the anesthesiologist is able to locate a small
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