anesthesia in obstetrics

1. OBSTETRIC
ANESTHESIA
D E V O R A A B R E H A M
N O V 2 5 , 2 0 2 2
M O D E R A T O R : D R . K I N F U
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2. Physiologic changes of pregnancy
 Respiratory system
- Mucosal vascular engorgement which leads to airway
edema and friability.
- Presence of large breasts.
- Increased risk of pulmonary aspiration of stomach
contents due to upward displacement of the stomach.
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3.  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. If a general anesthetic is required,
NPO status for eight hours is preferred
 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 is mandatory
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4.  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
- 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
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5.  Cardiovascular system
- Blood volume increases by 40% during pregnancy in
preparation for the anticipated average blood loss during
vaginal or Caesarian.
- 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)
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7. Medications that cause uterine contraction
- Vasopressors: large doses of α-adrenergic agents, such as
phenylephrine, in addition to causing uterine arterial
constriction, can produce tetanic uterine contractions
- Ergot Alkaloids- cause intense and prolonged uterine
contractions. It is therefore given only postpartum (single
0.2 mg dose intramuscularly or in dilute form as an
intravenous infusion over 10 minutes) to treat uterine atony.
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8. - Oxytocin (Pitocin): is usually administered intravenously
to induce or augment uterine contractions or to maintain
uterine tone postpartum.
- It has a half-life of 3–5 min.
- Induction doses for labor are 0.5–8 mU/min
- Prostaglandins: given for PPH
- An initial dose of 0.25 mg intramuscularly may be
repeated every 15–90 min to a maximum of 2 mg
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9. Analgesia during labour
 Inhaled N2O (Entonox®)
 Opioids
 N2O/O2 (Entonox®)
 Pethidine - Has a long half-life in the fetus (18–23hr)
- Reduces fetal heart rate variability in labour
- Associated with changes in neonatal
neurobehaviour, including an effect on breastfeeding
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10. - 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
- Neuraxial techniques; spinal, combined spinal/epidural (CSE)&
epidural; can be expected to provide effective analgesia in over
85% of women
 However, neuraxial analgesia was associated with:
- Hypotension
- Increased oxytocin use
- An increased incidence of maternal pyrexia
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11. Regional labour analgesia
 Indications
- Maternal request
- Expectation of operative delivery
- Obstetric disease
- Maternal disease: in particular, conditions in which
sympathetic stimulation may cause deterioration in maternal
or fetal condition
- Specific CVS disease
- Severe respiratory disease
- Conditions in which GA may be life-threatening
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12. Regional labor analgesia cont.
Contraindications
- Allergy
- Local infection
- Uncorrected hypovolemia
- Raised ICP
- Untreated systemic infection (risk of ‘seeding’ infection
into the epidural space)
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13. Epidural analgesia for labour
Skin sterilization with 0.5% chlorhexidine
Chlorhexidine must be allowed to dry before the skin is
touched
Locate the epidural space
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
Introduce 4–5cm of the catheter into the epidural space
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14. Epidural analgesia cont.
 Give an appropriate test dose
 Using 0.5% bupivacaine significantly increases motor block.
- There should be no need to use concentrations >0.25%
bupivacaine.
 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.
 If required, give further LA to establish analgesia
 Once the epidural is functioning, it can be maintained by:
- Intermittent top-ups of LA or continuous infusion of LA
(5–12mL/hr of –0.1% bupivacaine with 2 micrograms/mL
fentanyl)
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15. Epidural analgesia cont.
 Main complication
- Hypotension: prolonged or severe hypotension will
cause fetal compromise.
*Give an IV fluid bolus of crystalloid solution, if the
fetus is distressed, mask O2 supplementation.
*Give 6mg IV ephedrine, and repeat as necessary
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16. Combined spinal/epidural analgesia for
labour
 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.
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17. Combined..
 Indications
- Establishing rapid analgesia in women who are unable to
cope with labour pain.
- Re-establishing analgesia for women who have had a
failed epidural.
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18. Combined..
Perform the spinal at L3/4 or below.
Inject the spinal solution
Insert an epidural catheter at a different interspace.
Check the degree of motor and sensory block, and then
administer an epidural test dose
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19. Total spinal analgesia for labour
• Symptoms are of a rapidly rising block
• Difficulty in coughing may be noted (which is commonly
seen during regional anesthesia for a Caesarean section) -
>loss of hand and arm strength -> difficulty with talking,
breathing, and swallowing.
* Make sure that the equipment for ventilatory and CVS
support are immediately available
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20. C- section
 For category 1 (emergency) sections, the objective should
be to deliver the fetus as quickly as possible, while not
compromising maternal safety.
 General anesthesia is commonly used for category 1
sections.
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21. Regional anesthesia for Cesarean section
 Advantages of regional anesthesia
- Minimal risk of aspiration
- 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
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22. Cesarean section: epidural
 Indications
Women who already have epidural analgesia established
for labour.
Specific maternal disease (e.g. cardiac disease) where
rapid changes in SVR might be problematic.
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23. Cesarean section: spinal
 Spinal anesthesia is the most commonly used technique
for elective Cesarean sections.
 Rapid in onset
 Produces a dense block, and, with intrathecal opioids, can
produce long-acting post-operative analgesia.
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24. Spinal cont.
 However, hypotension is much more common than with
epidural anesthesia.
* Use a phenylephrine infusion.
- A simple regime is to use a syringe driver with a
solution of 100 micrograms/mL of phenylephrine.
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25. General anesthesia
 Indications
 Maternal request
Urgent surgery
Regional anesthesia contraindicated (e.g. coagulopathy,
maternal hypovolemia)
Failed regional anesthesia
Additional surgery planned at the same time as a
Caesarean section
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26. Effect of general anesthesia on the fetus
 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)
 Hypotension, hypoxia, hypocapnia, and excessive
maternal catecholamine secretion may all be harmful to
the fetus
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27.  Difficulties
- Failed intubation
* When intubation fails, but mask ventilation succeeds, a
decision on whether to continue with the Caesarean section
must be made.
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28.  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 may be useful)
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29.  Antacid prophylaxis
- Fluid aspiration is commonly associated with chemical
pneumonitis, and the severity of this is 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 ( e.g
Metoclopramide, Ranitidine and Sodium citrate)
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30.  Citations:http://horizon.hsc.edu.kw/Library/publications/
pdf/Morgan.pdf
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