Understanding Anesthesiology - The Global Regional Anesthesia ...

Figure 16 Anatomy relevant to spinal anesthesia
From “Introduction to Regional Anaesthesia” by D. Bruce Scott
(1989). Used with permission from his wife, Joan and son, Nicholas
B. Scott.
esthesia. The choice of LA used is based primarily on
the anticipated length of procedure. Spinal lidocaine
provides surgical anesthesia for procedures lasting up
to 75 minutes however its use has been limited by the
associated increased incidence of postoperative radiculopathies.
Spinal bupivacaine will provide up to 3.5
hours of anesthesia and is considered to be safe. The addition
of opioids (e.g. fentanyl) to the local anesthetic
solution can extend the duration of block. However, if
the block dissipates prior to the end of the procedure
there is no way to extend the block at that point. Spinal
anesthesia is performed under strict asepsis. The patient
may be sitting or curled in the lateral position. A
special small-bore “spinal needle” is used (22-27
gauge). The needle is inserted at a lower lumber interspace
and is advanced through the dura. Because the
dura is a tough membrane, a definite “pop” is often felt
as the needle passes through into the intrathecal space.
The stylet of the needle is removed and cerebrospinal
fluid (CSF) is observed in the lumen of the needle. The
local anesthetic is then injected and the needle removed.
The height of the required block depends on
the surgical procedure (Table 10). The height of the
block achieved is determined by many factors including
the mass and volume of LA administered, the position
of the patient and the baricity or “heaviness” of
the LA relative to CSF.
The complications of spinal anesthesia are similar to
those of epidural anesthesia with a few exceptions. Because
of the small dose of LA required, LA toxicity is
not an issue even if intravascular injection occurs.
Dural puncture is required for spinal anesthesia therefore
“spinal headache” is always a risk, especially in
young adult patients. The use of needles which are
smaller-bore and have a “pencil-point” tip helps to decrease
the incidence of post-dural puncture headache.
The contraindications to spinal anesthesia are listed in
Table 11.
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