Obstetrical Anesthesia
Dr Lindsey Patterson
Objectives
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Overview of maternal physiology
Analgesia for labor and delivery
Regional anesthesia
Anesthesia concerns in the parturient
Study MCQs with explanations
Physiological ChangesCVS
Almost all the changes seen are due to high
levels of progesterone and include:
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35%  Total Blood Volume
 heart rate 15 beats/min
40%  CO
30%  SV
15%  SVR
500ml/min  blood flow to uterus
 venous return from legs
AORTOCAVAL COMPRESSION (mechanical)
Impact of CVS changes
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Patients with pre-existing cardiac
disease may decompensate either
during labor or immediately post
delivery. This corresponds to the time
of maximal CO
Approx 400 – 600ml blood loss occurs
at delivery
Supine hypotensive syndrome
Aortocaval Compression
Physiological Changes Resp
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 oxygen consumption ~ 20% (100%
in labor) due to increased metabolic
rate
 minute ventilation ~ 50% (due to
increased tidal volume)
 arterial pCO2
 FRC causing a decrease in oxygen
reserves
Impact of Resp. changes
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Uptake of inhalational agents is faster
Decreased FRC and increased oxygen
consumption increase the risk of
hyoxia with apnea
Preoxygenation prior to GA less
effective
Physiological ChangesAirway
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Venous engorgement of airway
mucosa
Edema of airway mucosa
Worsening of Mallampati score in labor
Impact of Airway
Changes
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Trauma to upper airway with
suctioning, intubation
Increased incidence of difficult/failed
intubation x10
Require smaller ETT
Physiological ChangesCNS
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Decrease in MAC by 25 – 40%
Decreased dose of Local Anesthetic
requirement for regional techniques
More rapid onset of neural blockade
Impact of CNS Changes
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Decreased inhalation anesthetic agent
requirements
Decreased dose of local anesthetic for
same effect
Increased risk of local anesthetic
toxicity
Physiological Changes GIT
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Increased gastric fluid volume
Increased gastric fluid acidity
Decreased competency of lower
esophageal sphincter
Impact of GIT Changes
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Increased risk of aspiration
All parturients are a “full stomach”
Aspiration prophylaxis recommended
for C/S
– 0.3M Sodium citrate 30 mls po
– Ranitidine 50mg iv
– Metoclopramide 10mg iv
Analgesia for labor and
delivery
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Where is the pain coming from?
Is pain bad in labor?
Analgesic options
Pain of childbirth
Nociceptive pathways
involved
T10 – L1 during
labor
plus
S2-S4 for delivery
Is pain bad in labor?
Psychological stress can cause:
increased levels of catecholamines
hyperventilation
These may result in decreased uterine
blood flow leading to hypoxia and
acidosis in the fetus
Factors affecting pain
perception in labor
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Mental preparation
Family support
Medical support
Cultural expectations
Underlying mental status
Parity
Size and presentation of the fetus
Maternal pelvic anatomy
Duration of labor
Medications
Analgesia for labor and
delivery
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Non-medication
Inhalational
Parenteral
Regional
Analgesia- Non
medication options
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Breathing exercises
Autohypnosis
Acupuncture
White Noise/ Music
Massage/ walking
TENS
Water bath
Inhalation Medications
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Nitronox: 50:50 mixture of oxygen and
nitrous oxide
Low dose Isoflurane in oxygen
Advantages: on demand delivery, relatively
safe
Disadvantages: variable efficacy, nausea,
drowsiness, neonatal depression
Parenteral Medications
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Narcotics: meperidine, morphine fentanyl
Advantages: relatively good analgesia
Disadvantages: nausea, vomiting, sedation,
neonatal depression (max. 2 hours after
meperidine dose), short duration of action
Regional techniques
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Epidural, spinal, combined spinal-epidural
Advantages: excellent pain control, minimal
impact on progress of labor with low doses,
less drug transfer to fetus, improved uterine
blood flow, decrease in birth trauma e.g.
use of forceps, minimal neonatal depression
Disadvantages: invasive technique, side
effects (hypotension, headache, itching,
nausea, urinary retention, limited mobility),
nerve damage, infection
Anesthesia in the
parturient
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General considerations of the
parturient undergoing surgery
Obstetric surgery
General considerations
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Altered physiology as mentioned
Risks to the fetus:
– Effect of the disease process/therapies
– Possible teratogenicity of anesthetic
agents
– Intraoperative effects on uteroplacental
blood flow
– Increased risk of preterm labor/ risk of
abortion
Maternal considerations
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Altered physiology
Altered response to anesthesia
– Decrease in MAC
– Increased sensitivity to neuraxial agents
– Decreased plasma cholinesterase
– Decreased protein binding (more free
drug)
– Limited drug information in parturients
Fetal Considerations
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Teratogenicity:
– Limited information due to impracticality
of conducting trials with sufficient power
– Guidelines based on a) effects on
reproduction in animals; b)
epidemiological surveys of OR personnel;
c) studies of pregnancy outcomes in
parturient undergoing ante partum
surgery
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Nitrous oxide has been shown to have a
teratogenic effect in rats during the first
trimester
No anesthetic agent is a proven teratogen in
humans
Anesthetic agents deemed safe include:
thiopental,morphine, meperidine,fentanyl,
succinylcholine, NDMRs
Limiting nitrous oxide use but only if
hypotension secondary to volatiles can be
avoided
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Anesthetic management in the
parturient should be directed to:
– Avoidance of hypoxemia
– Avoidance of hypotension
– Avoidance of acidosis
– Maintain PaCO2 in the normal range for
the parturient
– Minimize effects of aortocaval
compression
Anesthesia for Caesarean
Section
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Preparation
Preventing complications
Choice of Anesthetic technique
Effects on the fetus
Preparation
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Premeds: antacid (sodium citrate)
IV access and fluid bolus within 30 minutes
of operating (avoid glucose containing
fluids)
Left lateral tilt with wedge under right pelvis
Routine Monitors: ECG, NIBP, pulse
oximeter, fetal monitoring
Additional monitors for GAs: ETCO2, nerve
stimulator, temp probe
Preventing complications
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Aspiration prophylaxis
Detailed airway assessment
Fluid resuscitation/left lateral tilt to
prevent hypotension
Safe practice for placement of
neuraxial blocks
Anesthetic techniques
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Local infiltration by surgeon
Regional anesthesia: spinal, epidural,
combined spinal-epidural
General anesthesia
Local Infiltration
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Rarely performed
Patient usually in extremis
Surgery must be done via midline
incision, gentle retraction, no
exteriorization of the uterus
Usually done to supplement a regional
technique if local anesthetic toxicity
not a concern
Regional: Spinal
Anesthesia
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Simple to perform
Rapid onset
Single shot technique
Profound neural block
Technique of choice for uncomplicated
elective caesarean sections and in many
emergency caesarean sections
Spinal Anesthesia
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Potential Complications:
– Hypotension
– Headache (rare ~1:100)
– Backache (temporary ~24hrs)
– Nausea/vomiting (secondary to BP,
narcotics)
– Neurological damage (very rare)
– Anaphylaxis (very rare)
Regional: Epidural
Anesthesia
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More technically challenging
Slower onset
Used when already placed for labor
analgesia
Useful in parturient where a slow,
controlled onset of block is needed
Allows prolongation of block should
surgery be complicated
Epidural Anesthesia
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Potential Complications:
– Hypotension
– Headache (approx 1:100)
– Transient backache ~24hrs
– Urinary retention
– Unintentional spinal injection
– Intravascular injection of local anesthetic
– Neurological damage
– Infection
Regional: Combined
spinal-epidural
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Used when require the speed and
density of a spinal anesthetic with the
flexibility of prolonging the block by
supplemental increments of local
anesthesia via the epidural catheter
Complications: as mentioned for
spinals and epidurals
General Anesthesia
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Used when
– Patient refuses regional technique
– Regional technique is contraindicated
– Emergency C/S when there is
inadequate/absent regional analgesia
and to delay will cause undue risk to the
fetus / mother
General Anesthesia
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Complications:
– Failed intubation
– Failed ventilation causing death or
neurological injury
– Awareness
– Aspiration pneumonia
Anesthesia: Effects on the
fetus
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Avoid hypotension, hypoxia, acidosis,
hyperventilation
Limit time between uterine incision and
delivery to less than 3 minutes
Infants exposed to GA have lower Apgar at
one minute but no difference at 5 mins
No significant alteration in neurobehavioral
scores with regional techniques
MCQ 1. Epidural Anesthesia in
Obstetric Practice. Which of the
following is false.
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A. Commonly causes itching
B. Can be used to control blood
pressure in pre-eclampsia
C. Causes uterine relaxation
D. Causes urinary retention
E. Contributes to the effects of
aortocaval compression
MCQ 1. Epidural Anesthesia in
Obstetric Practice…
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A. Commonly causes itching
B. Can be used to control blood
pressure in pre-eclampsia
C. Causes uterine relaxation
D. Causes urinary retention
E. Contributes to the effects of
aortocaval compression
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Itching is one of the most common
side-effects of opioids when delivered
in the epidural space. Their use allows
for a decreased concentration of local
anesthetic whilst maintaining excellent
analgesia. Patients have better motor
function and retain the ability to push.
MCQ 2. All of the following are false
concerning general anesthesia in
the parturient, EXCEPT:
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A. General anesthesia reduces gastric
pH
B. MAC is decreased
C. It is contra-indicated in patients
with a bleeding diathesis
D. Is a major cause of overall maternal
mortality
E. Succinylcholine crosses the placenta
MCQ 2. All of the following are false
concerning general anesthesia in
the parturient, EXCEPT:
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A. General anesthesia reduces gastric
pH
B. MAC is decreased
C. It is contra-indicated in patients
with a bleeding diathesis
D. Is a major cause of overall maternal
mortality
E. Succinylcholine crosses the placenta
General anesthetics have no effect on
gastric pH.
It is the method of choice in patients
with a bleeding diathesis since
regional anesthesia is contra-indicated.
Although of concern to Anesthesiologists
general anesthesia is not a major
cause of maternal mortality.
Succinylcholine is unable to cross the
placenta and effect the fetus.
MCQ 3. The following are all true
concerning the nerve supply of the
uterus , EXCEPT:
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A. Sensation from the upper segment
travels with the sympathetic nerves to T11T12
B. Sensation from the birth canal is via the
pudendal nerve
C. Lower segment innervation is via S2-4
D. Motor function occurs via sympathetic
and parasympathetic nerves
E. An intact nerve supply is essential to
initiate normal labor
MCQ 3. The following are all true
concerning the nerve supply of the
uterus , EXCEPT:
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A. Sensation from the upper segment
travels with the sympathetic nerves to T11T12
B. Sensation from the birth canal is via the
pudendal nerve
C. Lower segment innervation is via S2-4
D. Motor function occurs via sympathetic
and parasympathetic nerves
E. An intact nerve supply is essential to
initiate normal labor
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Normal labor occurs in patients with a
transected spinal cord.
MCQ 4: Physiological changes seen
in the last trimester include all
EXCEPT
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A. Resting PaCO2 is decreased
B. Hematocrit is decreased
C. Blood volume is increased
D. Gastric secretion is increased
E. Total peripheral resistance is
decreased
MCQ 4: Physiological changes seen
in the last trimester include all
EXCEPT
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A. Resting PaCO2 is decreased
B. Hematocrit is decreased
C. Blood volume is increased
D. Gastric secretion is increased
E. Total peripheral resistance is
decreased
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Gastric acid production does not
increase. There is an increased risk of
aspiration due to delayed gastric
emptying and a decrease in lower
esophageal sphincter tone.
MCQ 5: All of the following are
suitable for aspiration prophylaxis
prior to caesarean section, EXCEPT:
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A. Metoclopramide
B. Glycopyrollate
C. Sodium citrate
D. Clear fluids 4 hours pre-op
E. Ranitidine
MCQ 5: All of the following are
suitable for aspiration prophylaxis
prior to caesarean section, EXCEPT:
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A. Metoclopramide
B. Glycopyrollate
C. Sodium citrate
D. Clear fluids 4 hours pre-op
E. Ranitidine
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Metoclopramide acts as a pro-kinetic to
empty the stomach of any gastric contents.
Sodium citrate is a non-particulate antacid
used to neutralize gastric contents.
Ranitidine is an H2 antagonist used to
prevent gastric acid secretion.
Allowing clear fluids up to 4 hours prior to
suregry has been shown to decrease the
gastric content volume so decreasing the
risk of aspiration.
Glycopyrollate is an anti-sialogogue used for
preoperative preparation when an awake
intubation is anticipated.
MCQ 6: All are suitable techniques
for pain relief in labor EXCEPT:
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A. Transcutaneous electrical nerve
stimulation
B. White noise
C. Epidural bupivacaine
D. Intrathecal narcotics
E. 70% Nitrous oxide in Oxygen
MCQ 6: All are suitable techniques
for pain relief in labor EXCEPT:
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A. Transcutaneous electrical nerve
stimulation
B. White noise
C. Epidural bupivacaine
D. Intrathecal narcotics
E. 70% Nitrous oxide in Oxygen
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The concentration of nitrous oxide in
oxygen when used for analgesia is
50%. Higher concentrations can result
in loss of consciousness.
MCQ 7: Which of the following is a
contraindication to epidural
analgesia in labor:
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A. Previous caesarean section
B. Fetal distress
C. INR 1.6
D. Maternal exhaustion
E. Maternal multiple sclerosis
MCQ 7: Which of the following is a
contraindication to epidural
analgesia in labor:
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A. Previous caesarean section
B. Fetal distress
C. INR 1.6
D. Maternal exhaustion
E. Maternal multiple sclerosis
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Epidural analgesia is not contraindicated in
patients who have had a prior C/S. The pain
caused as a result of uterine rupture is not
effectively masked by epidural analgesia.
Fetal distress can be reduced by epidural
analgesia so long as hypotension is avoided
Maternal exhaustion is an indication for
epidural analgesia.
Maternal multiple sclerosis is not a
contraindication to epidural analgesia as
long as the concentration of local anesthetic
is reduced
Coagulopathy is an absolute
contraindication to epidural analgesia
MCQ 8 : Likely complications of
epidural opioids include all of the
following, EXCEPT:
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A. Itching
B. Urinary retention
C. Hypotension
D. Respiratory depression
E. Nausea
MCQ 8 : Likely complications of
epidural opioids include all of the
following, EXCEPT:
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A. Itching
B. Urinary retention
C. Hypotension
D. Respiratory depression
E. Nausea