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Caesarean section is the commonest major operation in many
areas of the developing world. Most cases present as emergencies
in labour. Management of emergency caesarean section is
the everyday activity of all anaesthetists.
Mothers may present in extremis in obstructed labour or with
ruptured uterus, haemorrhage, sepsis or anaemia of several
days’ duration.
The primary reason for performing caesarean section in these
circumstances is to save a mother’s life. Both general
and spinal anaesthesia can be used. Epidural is less common owing
to the time, expense and expertise required for use of the
technique.
Several changes occurring in pregnancy are relevant for anaesthesia:
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Blood
volume begins to rise |
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Cardiac
output begins to rise |
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There
is less increase in the number of red cells, so the haemoglobin concentration
falls |
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As
the uterus enlarges, respiration comes to depend more
on thoracic than diaphragmatic movement |
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Gastric
emptying becomes less efficient. |
In
late pregnancy:
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The
uterus presses back on the inferior vena cava when the
patient lies on her back, causing a fall in cardiac output |
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There
may also be a severe fall in blood pressure – the “supine
hypotensive syndrome” – but most non-anaesthetized
patients are able to maintain their blood pressure by
widespread vasoconstriction |
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During
general or spinal anaesthesia, the capacity for vasoconstriction
is lost; this is likely to result in a severe fall in
blood pressure to levels that are dangerous for both mother
and baby. |
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As
the uterus enlarges, respiration comes to depend more
on thoracic than diaphragmatic movement |
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Gastric
emptying becomes less efficient. |
Supine hypotension can be prevented merely by ensuring that the mother is never
fully supine.
A pillow or sandbag must always be placed under one hip to tilt the uterus slightly
to one side; this is perfectly simple to do even with the patient in the
lithotomy position. This simple precaution must always be carried out in obstetric patients
receiving either general or spinal/epidural anaesthesia.
When you anaesthetize a pregnant woman for delivery, there are two patients
to deal with: mother and child. Most drugs cross the placenta quickly. This
is a problem, since the aim is to anaesthetize the mother, but to allow the
baby
to be born without any drug-induced depression of body functions, especially
of respiration. For this reason, drugs that can cause depression of the fetus, such
as sedative premedication, should not be given.
Don’t be so concerned about the baby that
you fail to give the mother a sufficient dose of anaesthetic.
A suitable general anaesthetic technique is outlined below. Spinal anaesthesia is
often as good or better, and is described on pages 14–23 to 14–25.
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Before
inducing anaesthesia, give a 30 ml dose of a liquid antacid,
such as sodium citrate 0.3 mol/litre (77.4 g/litre), to
neutralize excess gastric acid. |
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Insert
a wedge or cushion under one hip to tilt the uterus off
the inferior vena cava:
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Never
induce anaesthesia with the patient in the lithotomy
position |
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If
she is already in that position, her legs must
be lowered for induction
to avoid regurgitation of gastric contents. |
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Set
up a fast-flowing infusion of an appropriate fluid into
a large vein and
preoxygenate the patient. |
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Induce
anaesthesia as for an emergency:
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Preoxygenate |
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Apply
cricoid pressure |
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Administer
a previously calculated dose of thiopental or ketamine |
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Intubate
the patient after giving suxamethonium |
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Give
IPPV. |
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For
a full account of managing the full stomach, see page 13 –32.
Laryngoscopy
in the pregnant woman is sometimes more difficult than usual.
Always prepare a spare tube of a small size (5–6 mm)
in case the patient has laryngeal oedema secondary to pre-eclampsia.
Avoid high concentrations of ether or halothane, as these will
reduce the uterine tone and increase bleeding. However, in a
spontaneously breathing
patient, you will not be able to maintain adequate anaesthesia
(the mother will push) at ether concentrations below about
8–10%
or halothane below 1.5%. You may give opiates intravenously
once the umbilical cord is clamped and then reduce the concentration
of the volatile agent.
Be prepared to give an oxytocic drug intravenously when requested
by the surgeon, but never give ergometrine to a woman with
pre-eclampsia as it may cause a hypertensive crisis. Syntocinon
causes hypotension and should be given in two divided doses
of 5 mg IV.
The average blood loss from caesarean section is 600–700
ml, so make sure that you give enough fluid replacement. You
may need to transfuse blood.
In additi
on
to looking after the mother, you may have to resuscitate
the baby, so be prepared with infant resuscitation equipment
and a separate oxygen supply.
If mother and child are both critically ill, it is your clear
duty to attend to the mother first.
Always try to have a trained assistant with you for these
cases. At the end of anaesthesia, remember that the mother
still has a full stomach; remove the tracheal tube with her
in the lateral position.
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