Download Introductory Lecture Series: The Anesthesia Machine

Obstetrics Anesthesia
By Dr. Mahmoud Abdelkhalek
Physiological changes of pregnancy
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Physiologic and anatomic changes develop across many organ
systems during pregnancy and the postpartum period
The Metabolic, hormonal and physical changes all have impact on
anesthetic management
To the anesthesiologist, the most important changes are those that
affect the respiratory and circulatory systems.
Respiratory system
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There is an increased risk of difficult or failed intubation in the
parturient.
This is primarily due mucosal vascular engorgement which leads to
airway edema and friability.
Laryngoscopy can be further impeded by the presence of large
breasts.
Increased risk of pulmonary aspiration of stomach contents due to:
– Upward displacement of the stomach
– Decreased gastric motility and increased gastric
secretions
– Incompetent gastro-esophageal junction
Respiratory system
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In fact, airway complications (difficult intubation, aspiration) are the
most common anesthetic cause of maternal mortality
The best means of avoiding this outcome is to avoid general
anesthesia (by using a regional technique)
If a general anesthetic is required, NPO status for eight hours is
preferred although not achievable in an emergency situation
Pretreatment of all parturients with a non-particulate antacid (30 cc
sodium citrate p.o.) as well as with a histamine blocker (ranitidine 50
mg IV) is important.
Finally, a rapid sequence induction with cricoid pressure is mandatory
Respiratory system
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With the apnea that occurs at induction of anesthesia, the parturient
becomes hypoxic much more rapidly than the non-pregnant patient
due to 2 main reasons:
– Oxygen requirement has increased by 20% by term
– Decrease of FRC, which serves as an “oxygen reserve” by 20%
due to upward displacement of the diaphragm
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Minute ventilation increases to 150% of baseline leading to a
decrease in PaCO2 (32 mmHg)
The concomitant rightward shift in the oxyhemoglobin dissociation
curve allows increased fetal transfer of O2
CVS
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Blood volume increases by 40% during pregnancy in preparation for
the anticipated 500-1000 cc average blood loss during vaginal or
Caesarian delivery, respectively. The increase of intravascular volume
may not be tolerated by parturients with concomitant cardiovascular
disease, such as mitral stenosis
When the pregnant patient is in the supine position, the heavy gravid
uterus compresses the major vessels in the abdomen leading to
maternal hypotension and fetal distress (supine hypotensive
syndrome)
Left lateral tilt, usually achieved with a pillow under the woman’s
right hip, is an important positioning maneuver
Stages of normal labour
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The 1st stage of labour
– Cervix effaces then cervical dilatation begins
– Rate of cervical dilatation:
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Primigravida: 1 cm/ hour
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Multigravida: 2 cm/ hour
– Routine observations:
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Fetal HR every 15 minutes
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Maternal pulse and BP every 30 minutes
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Temperature 4-hourly
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Urine analysis at each emptying of bladder
Stages of normal labour
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The 2nd stage of labour
– Commences at full dilatation of the cervix and terminates at the
delivery of the baby
– If prolonged more than 1 hour the fetus may become acidotic
– At the delivery of anterior shoulder, IM oxytocin is given to hasten
the delivery of the placenta and to stimulate the uterine
contraction
Stages of normal labour
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The 3rd stage of labour
– The complete delivery of the placenta& membranes& contraction
of the uterus
– Placental blood flow (15% of CO) redistribute to maternal
circulation and may precipitate heart failure immediately
postpartum in women with cardiac disease
Analgesia for labour
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The three most commonly used types of analgesic agents in labour
are:
1. Inhaled N2O
2. Opioids
3. Regional techniques
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N2O/O2 (Entonox®) is the most commonly used inhalational agent
and may be slightly more efficacious than pethidine, but complete
analgesia is never attained
Analgesia for labour
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Worldwide, pethidine remains one of the most popular opioids for
labour analgesia
Drawbacks:
– Has a long half-life in the fetus (18–23hr)
– Known to reduce fetal heart rate variability in labour
– Associated with changes in neonatal neurobehaviour, including an
effect on breastfeeding
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When regional analgesia is contraindicated, fentanyl or remifentanil
PCA may be more Beneficial
Diamorphine has also been advocated, although it may prolong
labour by >1hr
Analgesia for labour
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Uterine pain is transmitted in sensory
fibres, which accompany sympathetic
nerves and end in the dorsal horns of
T10–L1
Vaginal pain is transmitted via the
S2–S4 nerve roots (the pudendal
nerve)
Neuraxial techniques; spinal,
combined spinal/epidural (CSE)&
epidural; can be expected to provide
effective analgesia in over 85% of
women
Remember that acceptable analgesia
for women in labour does not mean a
complete absence of sensation
Analgesia for labour
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However, neuraxial analgesia was associated with:
– Hypotension
– Increased oxytocin use
– An increased incidence of maternal pyrexia
– A 40% increase in the incidence of instrumental deliveries,
although techniques, such as using low concentrations of LA, can
reduce this effect
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Fetal umbilical pH was marginally improved with epidural analgesia
Regional labour analgesia
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Indications
– Maternal request.
– Expectation of operative delivery (e.g. multiple pregnancy,
malpresentation)
– Obstetric disease (e.g. pre-eclampsia)
– Maternal disease: in particular, conditions in which sympathetic
stimulation may cause deterioration in maternal or fetal condition
– Specific CVS disease (e.g. regurgitant valvular lesions)
– Severe respiratory disease (e.g. cystic fibrosis)
– Specific neurological disease (intracranial A–V malformations, spinal cord
injury etc.)
– Conditions in which GA may be life-threatening (e.g. morbid obesity)
Regional labour analgesia
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Contraindications
– Allergy (true allergy to amide LAs is rare)
– Local infection
– Uncorrected hypovolemia
– Raised ICP
– Coagulopathy:
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Spinal analgesia is probably safer than epidural analgesia
Tests of coagulation and the platelet count should be within 6hr of
the time of the procedure, but, especially with pre-eclampsia, it is
also important to consider the rate at which the platelet count is
falling
Relative contraindications
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Expectation of significant hemorrhage
Untreated systemic infection (risk of ‘seeding’ infection into the
epidural space)
Specific cardiac disease (e.g. severe valvular stenosis, Eisenmenger’s
syndrome, peripartum cardiomyopathy (rapid changes in BP, preload,
and afterload of the heart)
‘Bad backs’ and previous back surgery do not contraindicate regional
analgesia/anesthesia, but scarring of the epidural space may limit the
effectiveness of epidural analgesia and increase the risk of
inadvertent dural puncture. Intrathecal techniques can be expected
to work normally
Consent
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Most UK anesthetists do not take written consent before inserting an
epidural for labour analgesia, but ‘appropriate’ explanation must be
given
The Obstetric Anesthetists’ Association has produced an information
leaflet for mothers which includes a quantitative estimate of the
incidence of a variety of potential complications, including
neurological injury
The explanation and, in particular, the possible hazards discussed
must be documented, as many women do not accurately recall
information given in labour
Information about labour analgesia should always be available
antenatally
Epidural analgesia for labour
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Competent assistant should be available
Scrupulous attention to sterile technique is required. A mask, hat,
gown, and gloves should be worn
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Establish IV access
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Fluid preload may help with subsequent hypotension
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Position in either a full lateral or sitting position
– Finding the midline in the obese may be easier in the sitting position
– Accidental dural puncture may be slightly lower in the lateral position
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Fetal HR should be recorded before and during the establishment of
analgesia
Epidural analgesia for labour
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Skin sterilization with 0.5% chlorhexidine is common in the UK:
– most sterilizing solutions, including chlorhexidine, are neurotoxic, so
great care must be taken to avoid contamination of the neuraxial
equipment or the anesthetist’s gloves
– It is recommended that chlorhexidine is never on the sterile work
surface, and it is sensible to complete skin sterilization before the
neuraxial equipment is unwrapped
– Chlorhexidine must be allowed to dry before the skin is touched
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Locate the epidural space:
– Loss of resistance to saline may have slight advantages in both the
reduced incidence of accidental dural puncture and reduced incidence of
‘missed segments’, compared with loss of resistance to air).
– The incidence of puncturing a blood vessel with the epidural catheter is
reduced if 10mL of saline is flushed into the epidural space before the
catheter is inserted
Epidural analgesia for labour
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Always insert the catheter as gently as possible
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Introduce 4–5cm of the catheter into the epidural space:
– Longer has an increased incidence of unilateral block, and shorter
increases the chance that the catheter pulls out of the space
– Multihole catheters have a lower incidence of unsatisfactory blocks
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Check for blood/CSF:
– If blood is aspirated, see if the catheter can be withdrawn further (leave
a minimum of 3cm in the space)
– If blood is still present, remove the catheter, and reinsert
Epidural analgesia for labour
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Give an appropriate test dose
– An ‘appropriate’ test remains controversial
– Using 0.5% bupivacaine significantly increases motor block
– Using 1:200 000 adrenaline to detect IV placement of a catheter has
both high false positive and false negative rates
– Many anesthetists will use 8–15mL of 0.1% bupivacaine with a dilute
opioid (2 micrograms/mL fentanyl) as both the test and main doses
– This will exclude intrathecal placement but may not exclude intravascular
placement
– However, the complete absence of a detectable block after a normal
labour analgesia loading dose is a warning sign of possible IV cannulation
– Remember every dose is a ‘test dose’!
Epidural analgesia for labour
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If required, give further LA to establish analgesia:
– There should be no need to use concentrations >0.25% bupivacaine
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Measure maternal BP every 5min for at least 20min after every bolus
dose of LA
Once the epidural is functioning, it can be maintained by one of three
methods:
1. Intermittent top-ups of LA administered by a PCEA:
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In general, larger volumes of low-concentration bupivacaine
with opioid produce more effective analgesia
A common regimen would be 5–10mL boluses of 0.0625–
0.1% bupivacaine with 2 micrograms/mL fentanyl and a 15–
20min lockout period
Epidural analgesia for labour
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A continuous infusion of LA (5–12mL/hr of 0.0625–0.1%
bupivacaine with 2 micrograms/mL fentanyl)
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Intermittent top-ups of LA administered by midwives:
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this is now rare in the UK
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Historically, boluses of 5–10mL of 0.25% bupivacaine were used,
but a more modern approach would be to use a larger volume of
a lower concentration such as 10–15mL of 0.1% bupivacaine
with 2 micrograms/mL fentanyl
Combined spinal/epidural analgesia for labour
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A combination of low-dose subarachnoid LA and/or opioid, together
with subsequent top-ups of weak epidural LA, produces a rapid onset
of analgesia with minimal motor block
An epidural technique alone can produce a similar degree of
analgesia and motor block but may take 10–15min longer to establish
Indications for CSEs include establishing rapid analgesia in women
who are unable to cope with labour pain, re-establishing analgesia for
women who have had a failed epidural, and preservation of leg
strength for women who want to walk in labour
In some centres, CSEs are used routinely because of the rapid speed
of onset, the reliable initial analgesia, together with some evidence of
improved epidural analgesia after the initial spinal analgesia has
receded
Combined spinal/epidural analgesia for labour
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CSE can be performed as a needle-through-needle technique or as
separate injections in the same, or in different, intervertebral spaces:
Either:
– Locate the epidural space at the L3/4 interspace or below with a Tuohy
needle (The level of the iliac crests usually corresponds to the spinous
process of L4 (Tuffier’s line), although there is variation between
individuals)
– Pass a 25–27G pencil-point needle through the Tuohy needle to locate
the subarachnoid space
– Inject the subarachnoid solution (e.g. 0.5–1.0mL of 0.25% bupivacaine
– with 5–25 micrograms of fentanyl or the equivalent dose in mg)
– Without rotating the epidural needle, insert an epidural catheter
Combined spinal/epidural analgesia for labour
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Or:
– Perform the spinal at L3/4 or below with a 25–27G pencil-point needle
– Inject the spinal solution
– Insert an epidural catheter at a different interspace
– This technique is particularly helpful when women are unable to stay still
because of pain
– The spinal is usually quick and relatively easy, and, once analgesia has
been established, an epidural can be performed with a more cooperative
patient
– After 15min, once the analgesia from the spinal solution is established,
– check the degree of motor and sensory block, and then administer an
epidural test dose. If this dose is given accidentally intrathecally, the
block would be expected to change significantly within 5min
– Further management of the epidural is the same as for epidural analgesia
alone.
‘Walking’ epidurals
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Effective analgesia with minimal motor block of the lower limbs can be
readily produced with low doses of an epidural or intrathecal LA, usually in
combination with an opioid, e.g. subarachnoid injection of 1–2.5mg of
bupivacaine with 10–25micrograms of fentanyl or an epidural bolus of 15–
20mL of 0.1% bupivacaine with 2 micrograms/mL fentanyl, and subsequent
epidural
top-ups of 15mL of the same solution, as required.
In some centres, women with minimal motor blockade are encouraged to
mobilize
The possible advantages of these techniques include:
– Minimal motor block associated with these techniques increases maternal
satisfaction scores
– Intrathecal, as opposed to epidural, techniques produce a more rapid
onset of analgesia
Mobilization
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Mobilization has been criticized, because:
– Leg strength may be compromised, and this becomes increasingly likely
with repeated doses of epidural LA
– Impaired proprioception may make walking dangerous, even when leg
strength has been maintained. While dynamic posturography suggests
that, following an initial intrathecal dose of 2.5mg of bupivacaine and 10
micrograms of fentanyl, proprioception is adequate for safe walking, this
may no longer be true after repeated epidural top-ups
– Intrathecal opioid may cause temporary fetal bradycardia, probably by
altering uterine blood flow through a change in maternal spinal reflexes
– Assessing the fetal condition is difficult when the mother is mobile
– In practice, even when a technique is used that could allow
walking, only ~50% of women actually choose to do so. Despite
this, most women prefer the added sense of control engendered
by retaining leg strength
Mobilization
– If women are to be allowed to walk, always wait at least 30min from the
initiation of the block before attempting mobilization
– Then:
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Check the strength of straight leg-raising in bed
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Ask the woman if she feels able to stand
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When the woman first stands, have two assistants ready to offer
support, if required
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Perform a knee bend
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Ask the woman if she feels safe
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Allow full mobilization
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After each top-up, the same sequence must be repeated
The poorly functioning epidural
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Look for the pattern of failure (Table 33.3)
Remember that a full bladder may cause breakthrough pain, ask the
midwife if a full bladder is likely
Carefully assess the spread of the block
It is important to be confident that the epidural could be topped up
for a Caesarean section, if required
Therefore, if in doubt, re-site the epidural
The poorly functioning epidural
Complications of epidural analgesia
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Hypotension:
– In the absence of fetal distress, a fall in systolic BP of 20% or to
100mmHg (whichever is higher) is acceptable
– However, uterine blood flow is not autoregulated, and prolonged
or severe hypotension will cause fetal compromise
– IV fluid loading is not routinely required when using low doses of
LA, but patients should not be hypovolemic before instituting
regional analgesia
– When hypotension or fetal distress is detected, it should be
treated quickly
– Avoid aortocaval occlusion—make sure that the patient is in the
full lateral position. (Remember that, in the lateral position, BP
should be measured in the dependent arm—there is often a
10mmHg difference between the upper and lower limbs)
Complications of epidural analgesia
– Give an IV fluid bolus of crystalloid solution and, if the fetus is
distressed, mask O2 supplementation
– Give 6mg IV ephedrine, and repeat as necessary
– If the fetus is distressed, call the obstetricians
– Remember that brachial artery pressure may not reflect uterine
artery blood flow
– If fetal distress is detected and is chronologically related to a
regional anesthetic procedure, treat as above, even in the
absence of overt hypotension
Subdural block
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Subdural block occurs when the epidural catheter is misplaced
between the dura mater and arachnoid mater
In obstetric practice, the incidence of clinically recognized subdural
block is <1:1000 epidurals
However, subdural blocks may be clinically indistinguishable from
epidural blocks
Definitive diagnosis is radiological
Subdural block
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The classical characteristics of a subdural block are:
– A slow onset (20–30min) of a block that is inappropriately
extensive for the volume of LA injected
– The block may extend to the cervical dermatomes, and Horner’s
syndrome may develop
– The block is often patchy and asymmetrical
– Sparing of motor fibres to the lower limbs may occur
– A total spinal may occur with top-up doses. This is probably due
to an increase in volume, causing the arachnoid mater to rupture
– If a subdural is suspected, re-site the epidural catheter
Total spinal
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The incidence of unexpected high or total spinal is variously reported
to be 1:1500 to 1:4500 epidurals
Usually the onset is rapid, although delays of 30min or more have
been reported
Delayed onset may be related to a change in the maternal position or
a subdural catheter placement
Symptoms are of a rapidly rising block
Initially, difficulty in coughing may be noted (which is commonly seen
during regional anesthesia for a Caesarean section), then loss of
hand and arm strength, followed by difficulty with talking, breathing,
and swallowing
If the block is rising to a concerning height, think about the likely
cause
Total spinal
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If the block is likely to be due to a correctly sited epidural LA, but
excess dose, position the patient head-up
If the block is due to subarachnoid plain LA (which is hypobaric,
compared to CSF), a head-up position may actually encourage the
block to spread further
So gently position the mother in a left lateral position, which should
minimize dural compression through epidural vein engorgement
(which occurs with caval occlusion), and observe very closely
Sudden movements may cause CSF to move further
Make sure that the equipment for ventilatory and CVS support are
immediately available
Respiratory paralysis, CVS depression, unconsciousness, and finally
fixed dilated pupils may ensue
Total spinal
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Unsurprisingly, total spinals are reported more often after epidural
anesthesia than epidural analgesia, as larger doses of LA are
employed
Management of total spinal
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Maintain airway and ventilation; avoid aortocaval compression, and
provide CVS support
Even if consciousness is not lost, intubation may be required to
protect the airway
Careful maternal and fetal monitoring is essential and, if appropriate,
delivery of the fetus
In the absence of fetal distress, a Caesarean section is not an
immediate requirement
Ventilation is usually necessary for 1–2hr
Accidental intravenous injection of local anesthetic
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‘Every dose is a test dose.’ The maxim is to avoid injecting any single
large bolus of LA IV
The risk can be minimized by:
– Meticulous attention to the technique during placement
– Always check for blood in the catheter
– Always being alert to symptoms of IV injection with every dose of LA,
even when previous doses have been uncomplicated
– Dividing all large doses of LA into aliquots
– Using appropriate Las
– If neurological or cardiovascular symptoms occur
– Stop injecting the LA
– Treat according to BLS and ALS protocols.
– Administer 20% lipid emulsion
Neurological damage
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Neurological damage does occur after childbirth, but establishing
cause and effect is difficult
Neurological sequelae following delivery under GA is as common as
delivery under regional anesthesia, suggesting that obstetric causes
of neurological problems are probably commoner than any effects
from the regional technique
Prolonged neurological deficit after epidural anesthesia occurs in
~1:10 000 to 1:15 000
Major neurological damage probably occurs in <1:80 000 neuraxial
procedures in the obstetric population, and this group of patients
probably has the lowest risk of any patient population
Dural puncture
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When loss of CSF is greater than production, as might occur through
a dural tear, CSF pressure falls, and the brain sinks, stretching the
meninges
This stretching is thought to cause headache
Compensatory vasodilatation of intracranial vessels may further
worsen symptoms
The incidence of dural puncture should be <1% of epidurals
All midwives, as well as obstetric and anesthetic staff, should be alert
to the signs of PDPH, as symptoms may not develop for several days
If untreated, headaches are not only unpleasant, but also can very
rarely be life-threatening, usually as a result of intracranial
hemorrhage or coning of the brainstem
Management of an accidental dural puncture can be divided into
immediate and late
Management of dural puncture:
Immediate management
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Management of an accidental dural puncture can be divided into
immediate and late
Immediate management:
– The initial aim is to achieve effective analgesia without causing further
complication
– Either:
– If a dural puncture occurs, pass the ‘epidural’ catheter into the
subarachnoid space
– Label the catheter clearly as an intrathecal catheter, and only allow
anesthetists to perform top-ups
– Give intermittent top-ups through the catheter (1.0–2.5mg of
bupivacaine ± 5–25 micrograms of fentanyl
– Tachyphylaxis may occur with prolonged labour
Management of dural puncture
– Advantages:
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The analgesia produced is likely to be excellent
There is no possibility of performing another dural puncture on reinsertion of
the epidural
The unpredictable spread of the epidural solution through the dural tear is
eliminated
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The need for an epidural blood patch (although not the incidence of
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PDPH) may be reduced
– Disadvantages:
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There is a theoretical risk of introducing infection
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The catheter may be mistaken for an epidural catheter
Management of dural puncture
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Or:
– Remove the epidural catheter
– Reinsert the epidural at a different interspace—usually one interspace
higher
– If the reason for the dural puncture was difficult anatomy, a senior
colleague should take over
– Run the epidural as normal, but beware of intrathecal spread of LA
– Be particularly cautious if the epidural catheter is topped up with a large
dose of anesthetic for a Caesarean section
– All top-ups should be given by an anesthetist
– With either technique, the patient should be informed, at the earliest
opportunity, that a dural puncture has occurred and of the likely sequelae
– Labour itself may be allowed to continue normally. Arrange daily postnatal follow-up.
Management of dural puncture:
Late management
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Following a dural puncture with a 16G Tuohy needle, the incidence of
PDPH is ~90%
In only 40% of dural punctures CSF is recognized flowing from the
Tuohy needle
In >30% of individuals who develop PDPH, a dural puncture was not
recognized in labour
Headaches in the post-natal period are common
The key differentiating factor between a ‘normal’ post-natal headache
and PDPH is the positional nature of the latter
Management of dural puncture
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Common features of PDPH include:
– Typically, the onset is 24–48hr post-dural puncture, if untreated,
they are said to last 7–10d, but the evidence is poor
– Characteristically, PDPH is worse on standing. Headache is often
absent after overnight bed rest but returns after mobilizing
– The headache is usually fronto-occipital and may be associated
with neck stiffness
– The headache may be relieved by tight abdominal compression—
while abdominal binders are no longer used as a treatment, this
can be a useful diagnostic tool
Management of dural puncture
– Photophobia and difficulty in accommodation are common
– Hearing loss, tinnitus, and 6th nerve palsy with diplopia are
possible
– If these signs develop, women should be encouraged to have a
blood patch sooner rather than later, as these signs are an
indication of a more severe headache, and the risk of more
serious complications—seizures, subdural hematoma, and cerebral
herniation—may be increased
– Nausea in up to 60% of women
 Treatment is either to alleviate symptoms, while waiting for the dural tear
to heal itself, or to seal the puncture
 Epidural blood patching is the only commonly used method of sealing dural
tears, although neurosurgical closure has been reported
Management of dural puncture:
Prophylactic treatment
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There is a high incidence of bacteremia shortly after delivery
This, combined with the poor efficacy of prophylactic blood patching,
means that the use of prophylactic blood patching has fallen out of
favour
Although bed rest alleviates symptoms, the incidence of PDPH after
48hr is the same for those cases that mobilized throughout. Because
of the risk of thromboembolism, bed rest should not be routinely
encouraged in asymptomatic women
Management of dural puncture:
Symptomatic treatment
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Although there is no well-established mechanism for preventing
PDPH, once a dural puncture has occurred, various treatments have
been proposed to alleviate symptoms, while waiting for the dural
puncture to seal itself
Simple analgesics (paracetamol and NSAIDs) are the mainstays of
symptomatic treatment. They should always be offered, even though
they are unlikely to completely relieve severe PDPH
Adequate fluid intake should be encouraged, although there is no
evidence that hydration reduces the incidence of PDPH
Caffeine/ theophyllines act by reducing intracranial vasodilatation,
which is partially responsible for the headache. IV aminophylline has
been shown to reduce the incidence of headache. However, concern
has been expressed that the incidence of seizures following dural
puncture may be increased in the presence of caffeine
Management of dural puncture:
Symptomatic treatment
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Epidural infusion of saline is no longer recommended. Although
compression of the dural sac with epidural saline can alleviate
symptoms, after 24hr of continuous infusion, the incidence of PDPH is
only marginally reduced. However, radicular pain in the lower limbs
may occur, and patients are immobilized
In relatively small RCT studies, ACTH analogues reduced the
incidence of headache after a known dural puncture, while IV
dexamethasone increased the incidence. However, the studies are
small, and the results need to be treated with caution.12,13
A number of case series have also supported the use of gabapentin
or pregabalin. However, again the numbers are small, and the results
need to be treated with caution
Definitive treatment is with epidural blood patching
Management of dural puncture:
Epidural blood patch
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Epidural blood patch performed around 48hr post-partum has a 60–
90% cure rate at the 1st attempt (with a lower success rate if
performed between 24 and 48hr post-partum, and lower still if
performed at <24hr post-partum). The proposed mechanism of
action is 2-fold:
– Blood injected into the epidural space compresses the dural sac
and raises the ICP. This produces an almost instantaneous
improvement in pain
– The injected blood forms a clot over the site of the dural tear, and
this seals the CSF leak
Management of dural puncture:
Epidural blood patch
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Blood injected into the epidural space predominantly spreads
cephalad, so blood patches should be performed at the same or lower
interspace as the dural puncture
Consent must be obtained. The patient should be apyrexial and not
have a raised WCC
Two operators are required. One should be an experienced
‘epiduralist’; the other is required to take blood in a sterile manner
The patient should have a period of bed rest before performing the
patch to reduce the CSF volume in the epidural space
Aseptic technique must be meticulous both at the epidural site and
the site of blood letting (usually the antecubital fossa)
Management of dural puncture:
Epidural blood patch




An epidural should be performed at the same or a lower vertebral
interspace as the dural puncture, with the woman in the lateral
position to minimize CSF pressure in the lumbar dural sac
Once the epidural space has been identified, 20mL of blood is
obtained
Inject the blood slowly through the epidural needle, until either a
maximum of 20mL has been given or pain develops (commonly in the
back or legs). If pain occurs, pause, and, if the pain resolves, try
continuing with a slow injection. If the pain does not resolve or
recurs, then stop
To allow the clot to form, maintain bed rest for at least 2hr, and then
allow slow mobilization
Management of dural puncture:
Epidural blood patch


As far as possible, the patient should avoid straining, lifting, or
excessive bending for 48hr, although there are obvious limitations
when a woman has a newborn infant to care for
Follow-up is still required. Every woman should have clear
instructions to contact the anesthetists again if symptoms recur, even
after discharge home
 Serious complications of blood patching are rare. However, backache
is common, with 35% of women experiencing some discomfort 48hr
post-epidural blood patch and 16% of women having prolonged backache
(mean duration 27d)
Other reported complications include repeated dural puncture, neurological
deficits, epileptiform fits, and cranial nerve damage
Suggestions that labour epidurals after blood patching may be less effective
have not been confirmed
Remifentanil for labour analgesia




Remifentanil is an ultrashort-acting mu-agonist opioid, which is
broken down by tissue and plasma esterases
It has an analgesia half-life of about 6min and a rapid onset time of
30–60s. Although remifentanil readily crosses the placenta, it is also
rapidly metabolized in the fetus
These features make remifentanil a potentially useful analgesic agent
in labour
Like all opioids, it does not produce complete analgesia but appears
to be more effective than IM pethidine. When compared with a
fentanyl PCA, the analgesic effect may be little different, but, as
might be expected, remifentanil is associated with less need for fetal
resuscitation, which is good, and an increased incidence of maternal
respiratory depression, which is potentially worrying
Remifentanil for labour analgesia



Up to 40% of women who use remifentanil PCA for pain relief in
labour will develop respiratory depression. So remifentanil must only
be used with direct (in the room) supervision and careful training of
all the staff involved in its administration. There have been numerous
case reports of maternal respiratory arrests with remifentanil
The ideal PCA regimen has not been established. Many proposed
techniques are based on body weight, but the technique below is
based on a fixed dose which has the advantage of simplicity
The addition of N2O may improve analgesia further but may increase
the risk of hypoxemia
Remifentanil for labour analgesia


Technique:
Of critical importance is establishing one-to-one care with a trained
individual (midwife) who must be continuously present in the labour
room

No opioid should have been used in the previous 4hr

Establish dedicated IV access

PCA bolus dose of 20–40 micrograms and lockout of 2min

Monitor with continuous pulse oximetry

Give O2 if SpO2 <94% on air

Thirty-minute observations of respiratory rate, sedation score, and
pain scores
Remifentanil for labour analgesia

Always flush the cannula when PCA is discontinued

Call the anesthetist if:
– The patient is not rousable to voice
– Respiratory rate <8 breaths/min
– SpO2 <94% despite O2 supplementation
Cesarean section (CS)

With all Caesarean sections, it is vital that the obstetrician clearly
communicates the degree of urgency to all staff. The four-point
classification17 in Table is a modification of a system originally
proposed by Lucas
Cesarean section (CS)




For all emergency Cesarean sections, the patient must be transferred
to theatre as rapidly as possible. Fetal monitoring should be
continued until abdominal skin preparation starts
For category 1 (emergency) sections, the objective should be to
deliver the fetus as quickly as possible, while not compromising
maternal safety
It is the obstetrician’s responsibility to call the urgency of the
Cesarean section, but it is the anesthetist’s responsibility to choose a
method of anesthesia that is safe
While, in many centres, GA is commonly used for category 1 sections,
do not be pressured into choosing a form of anesthetic that is
inappropriate for the mother
Regional anesthesia for Cesarean section




Categories 2–4 Caesarean sections are usually performed under
regional anesthesia
Remember that the classification of urgency should be continuously
reviewed. Category 1 sections can become category 2, and vice versa
Regional anesthesia for Caesarean section was initially driven by
maternal preference
It was subsequently found that regional anesthesia is also safer than
GA, although, with good-quality training, and modern anesthetic
standards and equipment, the difference in maternal mortality
appears to be less than it was in the past
Regional anesthesia for Cesarean section:
Advantages of regional anesthesia


Minimal risk of aspiration and lower risk of anaphylaxis
The neonate is more alert, which promotes early bonding and
breastfeeding

Fewer drugs are administered, with less ‘hangover’ than after GA

Better post-operative analgesia and earlier mobilization
 Mothers who are nervous about having a Cesarean section under regional
anesthesia should be given a clear explanation of the advantages and
disadvantages of regional anesthesia and GA but should never be coerced into
having a regional technique
Regional anesthesia for Cesarean section




There are three techniques for neuraxial anesthesia—epidural, spinal,
and CSE
Epidural anesthesia is most commonly used for women who already
have labour epidural analgesia. Spinal anesthesia is the most popular
technique for an elective Caesarean section, although, in some
centres, CSEs are preferred
The speed of onset of sympathectomy that occurs with spinal
anesthesia (as opposed to epidural) results in a greater fall in
maternal cardiac output and BP and may be associated with a more
acidotic neonate at delivery
This can be minimized by using a prophylactic phenylephrine infusion
and careful positioning of the mother
Regional anesthesia for Cesarean section



When there is particular concern about the speed of onset of a block,
a CSE approach can be used, injecting only a small dose of
intrathecal LA and extending the block, if required, using the epidural
catheter
Spinal anesthesia generally provides a better quality of analgesia than
epidural anesthesia
Whatever technique is chosen, a careful history and an appropriate
examination should be performed. This should include checking:
– Blood group and antibody screen. Routine cross-matching of blood is not
required, unless hemorrhage is expected or if antibodies that interfere
with cross-matching are present.
– Ultrasound reports to establish the position of the placenta. A low-lying
anterior placenta puts a woman at risk of major hemorrhage, particularly
if associated with a scar from a previous Caesarean section
Regional anesthesia for Cesarean section




An explanation of the technique must be offered. Although a
Cesarean section under regional anesthesia becomes routine for the
anesthetist, it can be an intimidating prospect for the mother.
Reassurance and support are important. However, the possibility of
complications must also be mentioned, including the possibility of
intraoperative discomfort and its management
Pain during regional anesthesia remains a leading obstetric anesthetic
cause of maternal litigation
Document all complications that are discussed
Cesarean section: epidural

Indications for a Caesarean section under epidural anesthesia
include:
– Women who already have epidural analgesia established for
labour
– Specific maternal disease (e.g. cardiac disease) where rapid
changes in SVR might be problematic, although, more commonly,
these individuals will have a careful CSE
Cesarean section: epidural

Table shows advantages and disadvantages of epidural for CS
Cesarean section: epidural technique







History/examination/explanation and
consent.
Ensure that antacid prophylaxis has been
given


Establish 16G or larger IV access. Start
crystalloid co-load
Insert epidural catheter at the L2/3 or L3/4
vertebral interspace.
Position the patient in the supine position
with a left lateral tilt or wedge
Give supplemental O2 by face mask if SpO2
<95% on air. (This is very important in
obese patients, who may become hypoxic
when supine, and may also be beneficial for
a compromised fetus)
Test the dose, then incrementally top up the
epidural with LA and opioid:


Five to 8mL boluses of 2% lidocaine with
1:200 000 adrenaline every2–3min, up to a
maximum of 7mg/kg (~20mL), or
Five mL of 0.5%
bupivacaine/levobupivacaine/ ropivacaine
every 4–5min, up to a maximum of 2mg/kg
in any 4hr period. (The single-enantiomer
LAs may offer some safety advantage;
however, lidocaine is still safer than either
ropivacaine or levobupivacaine.)
Opioid (e.g. 100 micrograms of
fentanyl or 2.5mg of diamorphine)
improves the quality of the analgesia,
and a slightly lower dermatomal block
height may be accepted before starting
surgery (i.e. T6 to light touch)
Establish an S4–T4 block (nipple level).
Always check the sacral dermatomes,
as epidural LA occasionally does not
spread caudally
Cesarean section: epidural technique






Anesthesia to light touch is more reliable at
predicting adequacy of block than loss of
cold sensation

Document the level of block obtained and
the adequacy of perioperative analgesia
Hypotension is much less common than with
intrathecal techniques. However, if
hypotension does occur, treat hypotension
with:
Boluses of 500 mL of crystalloid
Fifty to 100 micrograms of phenylephrine IV bolus
(expect a reflex bradycardia) or 6mg of ephedrine
IV. α-agonists may be more effective and may be
associated with less fetal acidosis than ephedrine
Increasing the left uterine displacement


At delivery, give 2–5IU of oxytocin as a
slow IV bolus. If tachycardia must be
avoided, then an IV infusion of 30–
50IU of oxytocin in 500mL of
crystalloid, given over 4hr, is an
acceptable alternative
At the end of the procedure, give
NSAID, unless contraindicated (100mg
of diclofenac PR)
Epidural diamorphine given at the time
of surgery improves post-operative
analgesia, while epidural fentanyl has
little post-operative analgesic benefit
Cesarean section: spinal



Spinal anesthesia is the most commonly used technique for elective
Cesarean sections
It is rapid in onset, produces a dense block, and, with intrathecal
opioids, can produce long-acting post-operative analgesia.
However, hypotension is much commoner than with epidural
anesthesia
Cesarean section: spinal technique




History/examination/explanation and
consent

Ensure that antacid prophylaxis has been
given
Establish 16G or larger IV access. Start
crystalloid co-load
Position the patient. A sitting position
usually makes finding the midline easier,
which may be helpful with obese patients,
and may be associated with a faster onset,
although the height of block is less
predictable. A lateral position is associated
with a slower onset of block, particularly if a
full lateral position is maintained until the
block has fully developed. The block height
may be slightly more consistent, and the
women may sometimes find it more
comfortable than sitting if the fetal head is
very low

Perform spinal anesthetic at L3/4
interspace, using a 25G or smaller
pencil-point needle. (The level of the
iliac crests usually corresponds to the
spinous process of L4 (Tuffier’s line),
although there is variation between
individuals)
With the orifice pointing cephalad,
inject the anesthetic solution, e.g.
2.5mL of 0.5% hyperbaric bupivacaine
with 300 micrograms of diamorphine or
15 micrograms of fentanyl. Intrathecal
diamorphine improves post-operative
analgesia, while intrathecal fentanyl
has little post-operative analgesic
benefit. (A total of 100 micrograms of
preservative-free morphine is also used
and can produce prolonged postoperative analgesia. However, there is
a high incidence of PONV and an
increased risk of late respiratory
depression)
Cesarean section: spinal technique



After injection of the solution, move the
woman to a supine position with a left
lateral tilt or wedge. When hyperbaric LA
solutions are used, it is important that the
cervical spine is kept elevated (pillow) to
prevent LA from spreading to the cervical
dermatomes. If supine hypotension occurs,
increase the tilt, or, if severe, temporarily
move the woman to a full lateral position
Start pressor infusion. Hypotension is
commoner with spinal anesthesia than
epidural anesthesia. Try to prevent
hypotension, rather than treat it after it has
occurred. When possible, a continuous
infusion of the pressor agent should be
started at the time of the injection of spinal
LA
Continue as for epidural anesthesia for
Caesarean section
Cesarean section: combined
spinal/epidural

To be completed in a later time
Inadequate anesthesia

To be completed in a later time
Hypotension


Preventing maternal hypotension, rather than treating BP after
hypotension has occurred, is associated with better fetal outcome
and less maternal nausea
There are two principal methods of treating hypotension—pressor
agents and fluid
Hypotension: Pressor agents
Using prophylactic pressor agents is beneficial for both mother and fetus. Ephedrine was
used to treat hypotension in obstetric neuraxial anesthesia for many years. However, in
the last decade, it has been established that treatment to normotension with
phenylephrine is associated with better fetal umbilical pH than when ephedrine is used,
although the difference is marginal. If phenylephrine is used, bolus doses of 50–100
micrograms can cause profound reflex bradycardias, so, if possible, use a phenylephrine
infusion instead

A simple regime is to use a syringe driver with a solution of 100 micrograms/mL of
phenylephrine (i.e. make up 10mg in 100mL of saline, and decant 20mL into a syringe)

Start infusing at 30mL/hr, as the spinal solution is injected

Titrate to response, adjusting the rate of infusion up or down in increments of 10mL/hr

During the infusion, expect the HR to gradually slow, so give anticholinergic agents, as
required

Reduce and stop the infusion post-delivery

Be careful with this technique in hypertensive individuals. Start at a lower infusion rate.

Metaraminol can be used as an alternative to phenylephrine.
Hypotension: Fluid
A fluid preload was a traditional part of the anesthetic technique for regional anesthesia.
It had two functions:
 To maintain the intravascular volume in a patient who is likely to lose 500–1000mL of
blood
 To reduce the incidence of hypotension associated with regional anesthesia




However, crystalloid preloading is very ineffective at preventing
hypotension
In addition, in women with severe pre-eclampsia, large preloads are
harmful, as the rise in filling pressures and the reduced colloid
osmotic pressure will predispose to pulmonary edema
Using colloids as a preload is more effective, but colloids may be
associated with significant problems such as anaphylaxis
There is evidence that co-loading with crystalloid (giving fluid as the
block is establishing) is more effective than preloading.
Hypotension: Fluid

A co-load should be:
– Timely (given immediately before or during the onset of the
regional technique to minimize redistribution)
– Limited to 10–15mL/kg of crystalloid. Larger volumes should be
avoided, as they offer little advantage and may be harmful
– More fluid should only be given as clinically indicated
– Emergency Caesarean section should not be delayed to allow a
fluid preload to be administered
Cesarean section: general anesthesia
Elective GA is now uncommon in the UK, limiting opportunities for training.
The majority of complications relate to the airway. Failed intubation
is much more frequent in obstetric than non-obstetric anesthesia. All obstetric theatres
should have equipment to help with the difficult airway, and all obstetric anesthetists
should be familiar with a failed intubation drill
Indications for GA include:



Maternal request
Urgent surgery (in experienced hands and with a team that is familiar
with rapid regional anesthesia, a spinal or epidural top-up can be
performed almost as rapidly as a GA)
Regional anesthesia contraindicated (e.g. coagulopathy, maternal
hypovolemia)

Failed regional anesthesia

Additional surgery planned at the same time as a Caesarean section
Cesarean section: GA technique





History and examination. In particular,
assess the maternal airway—mouth
opening, Mallampati score, thyromental
distance, neck mobility


Antacid prophylaxis, including 30mL of 0.3M
sodium citrate
Start appropriate monitoring

Position supine with a left lateral tilt or
wedge
Preoxygenate for 3–5min or, in an
emergency, with 4–8 VC breaths with a high
flow through the circuit. Ensure a seal with
the face mask. At term, women have a
reduced FRC and a higher respiratory rate
and O2 consumption. This reduces the time
required for denitrogenation, but also
reduces the time from apnea to arterial O2
desaturation

Perform RSI with an adequate dose of
induction agent (e.g. 5–7mg/ kg of
thiopental)
A 7.0mm ETT is adequate for
ventilation and may make intubation
easier
Propofol has also been used for
Cesarean section, without any major
reported complications, although, at
present, thiopental is still the most
commonly used agent in the UK
Use ‘overpressure’ of the inhalational
agent to rapidly increase the end-tidal
concentration of the anesthetic agent
to at least 0.75 MAC (e.g. 2%
isoflurane for 5min, then reduce to
1.5% for a further 5min)
Cesarean section: GA technique

At delivery:
– Give 2–5IU of oxytocin IV bolus. If
tachycardia must be avoided, then an
IV infusion of 30–50IU of oxytocin in
500mL of crystalloid, infused over 4hr,
is effective
– Administer opioid (e.g. 10–15mg of
morphine ± 100 micrograms of
fentanyl), IV paracetamol, and IV
diclofenac (unless contraindicated)
– Ventilate with 35% inspired O2
concentration in N2O. The inhalational
agent can be reduced to 0.75 MAC to
reduce uterine relaxation

At the end of the procedure, consider
performing bilateral ilioinguinal nerve
blocks, rectus sheath, or TAP blocks which
can all improve post-operative analgesia




If a woman has eaten shortly before
surgery, consider passing a large-bore
orogastric tube to empty the stomach
before extubation
Extubate awake. Be aware that
extubation is a high-risk time.
Give additional IV analgesia, as
required
Recovery: Be aware that recovery units
are potentially dangerous places for
mothers after GAs, particularly if the
recovery is staffed by midwives who
may be less familiar with airway care.
The same standard of recovery staff
should be available to women on
labour wards as in a normal theatre
recovery unit
Effect of general anesthesia on the fetus





Lower fetal 1min and 5min Apgar scores are commoner when GA is
used for Cesarean section
Most anesthetic agents, except for muscle relaxants, rapidly cross the
placenta
Opioids administered before delivery may cause fetal depression.
Which can be rapidly reversed with naloxone (e.g. 200 micrograms
IM or 10 micrograms/kg IV)
If there is a specific indication for opioids before delivery, they should
be given, and the neonatologist informed
Hypotension, hypoxia, hypocapnia, and excessive maternal
catecholamine secretion may all be harmful to the fetus
Failed intubation



Failed intubation is ten times commoner in the obstetric population
(~1:300, compared to 1:3000)
Causes of failed intubation include obesity, increased fatty tissue,
pharyngeal/laryngeal edema, large tongue, large breasts, incorrect
cricoid pressure, complete dentition, and the experience and training
of anesthetic staff
When intubation fails, but mask ventilation succeeds, a decision on
whether to continue with the Caesarean section must be made. A
suggested grading system is shown in Box
Failed intubation




For grade 1 cases, surgery should continue, and for grade 5 the
mother should be woken. The action between these extremes must
take account of additional factors, including the ease of maintaining
the airway, the likely difficulty of performing a regional anesthetic,
and the experience of the anesthetist
Once a failed intubation has occurred and an airway has been
established, while waiting for the muscle relaxant to wear off, reapply
fetal monitoring as this may give useful additional information to
guide management
If the surgery continues, decisions will have to be made on whether
to use 1st- or 2nd-generation laryngeal masks and whether to use
muscle paralysis (if yes, then rocuronium with an availability of
sugammadex may be useful)
Ask the obstetricians to avoid fundal pressure at delivery, if possible,
because fundal pressure can increase intragastric pressure to >70
mmHg
Antacid prophylaxis
Aspiration of particulate matter, blood, or bile is associated with worse
outcome than aspiration of gastric fluid. Fluid aspiration is commonly
associated with chemical pneumonitis, and the severity of this is, in turn,
dependent on the volume and acidity of the aspirated fluid. Use of antacids
and prokinetic agents can elevate the gastric pH and reduce the intragastric
volume. A suggested regime is as follows
Elective surgery
• Ranitidine 150mg orally, 2hr and 12hr before surgery
• Metoclopramide 10mg orally, 2hr before surgery
• A total of 30mL of 0.3M sodium citrate immediately before induction of GA. (Gastric pH
>2.5 is maintained for only 30min after 30mL of 0.3M sodium citrate. If a GA is required
after this, a further dose of citrate is required)
Emergency surgery (if prophylaxis has not already been given)
• Ranitidine 50mg by slow IV injection immediately before surgery (PPIs
are an alternative). Remember this will not alter the risk of aspiration during induction
but may offer benefit by the time of extubation
• Metoclopramide 10mg IV injection immediately before surgery
• A total of 30mL of 0.3M sodium citrate orally immediately before induction of GA
Thank you