Understanding Anesthesiology - The Global Regional Anesthesia ...

There is good evidence that a labour epidural is associated with a
prolongation of the second stage of labour, due to the associated
motor block. Whether it also leads to an increased incidence of operative
delivery remains controversial. The degree of motor block
can be minimized by using lower concentrations of local anesthetics
along with opioid adjunct. The use of a local anesthetic infusion
(as opposed to boluses or “top-ups”) may give a more consistent
level of block, lower total dose of local anesthetic, less motor block
and less risk of drug toxicity.
Anesthesia for Operative Delivery
The major causes of anesthetic morbidity and mortality in the pregnant
patient are those related to the respiratory system. Because of
the risks of aspiration and failed intubation, and the depressant effects
of anesthetic agents on the fetus, general anesthesia is
avoided (where possible) in the parturient undergoing Caesarian
section. Regional anesthesia is the preferred technique and can be
provided by administering spinal anesthesia or by extending the
depth and height of an existing epidural block.
There are two situations where a regional technique would not be
chosen for Caesarian section. The first would be in the presence of
an absolute contraindication to regional anesthesia (Table 11).
These include coagulopathy, hypovolemia, infection, certain cardiovascular
conditions and patient refusal.
The second situation where a regional technique may not be appropriate
is in the setting of severe fetal distress. In this setting, general
anesthesia almost always allows the most rapid delivery of the
compromised fetus. If the fetal heart rate is very low and the maternal
airway appears favourable, then general anesthesia will be
quickly induced.
General anesthesia in the parturient is unique in several respects
which reflects the many physiologic changes in this patient population.
The pregnant patient has a lower anesthetic requirement
(MAC) and yet, paradoxically, is at higher risk of experiencing
awareness under anesthesia. Other important considerations are
the risk of aspiration, rapid desaturation and the need to avoid
both neonatal depression and uterine atony.
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