Obstetric Analgesia and Anesthesia

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Obstetric Analgesia and Anesthesia

• By Abdulaziz Al Gain

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History

• The first anesthetic used in obstetrics was
  chloroform and ether in 1848
• 1902- Morphine and Scopolamine were used to
  induce a twilight sleep.
• 1924 Barbituates were added for sedation
• 1940 Dr. Lamaze and Read advocated natural child
  birth

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Factors associated with pain in Labor

• Anxiety (reduce fear and reduce pain)
• Hx of severe menstrual pain
• Age ( negative correlation)
• Socio-economic status (negative correlation)
• Education

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Systemic Analgesics

• All narcotics used for pain relief in labor can
  have adverse effects on the mother and the fetus
  or neonate.
• Maternal adverse effects- cardiac, respiratory,
  allergic, GI, neurologic
• Fetal adverse - same

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Factors that effect the transfer of a drug to the
fetus

• Amount of drug
• Site of administration
• Drug distribution in maternal tissue
• Maternal metabolism
• Renal or liver excretion of the drugs and their
  metabolites
• Lipid solubility and protein binding

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Factors that effect the transfer of a drug to the
fetus

• Spatial configuration
• Molecule size
• Acid base status of the fetus (all narcotics are
  weak bases and will become concentrated in an
  acidotic fetus, or if the mother is alkalotic the
  narcotics will be concentrated in the fetus

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Factors that effect the transfer of drugs to the
fetus

• Uteroplacental blood flow ( if diminished then
  less drug is delivered i.e.. PIH, DM as well as
  hypovolemia

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Narcotics and the fetus

• Fetal metabolism is slower to metabolize
  narcotics because of the immature liver, also the
  blood brain barrier is very permeable so the
  fetuses are more susceptible to depression from
  narcotics.
• Narcotics can be given IV, IM. Continuous
  infusion

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Narcotics and the fetus

• IM injections result in a significant delay in
  analgesic effect
• IM injections can have unpredictable blood
  concentrations
• IM absorbtion is highly variable from patient to
  patient

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Narcotics and the fetus

• IV administration has advantages over IM
  injections. There is less variability in plasma
  levels, quicker onset of action and less
  medication is given per injection and it is
  easier to titrate dose.
• Observe patients for 15-20 min after IV narcotic
  injection

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Narcotics and the fetus

• IV dose can accumulate over time and cause
  respiratory depression
• Continuous IV infusion or PCA better pain control
  less placental transfer

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Narcotics and labor

• Narcotics may decrease the progress of labor by
  reducing the force or rate of contractions ( this
  is dose dependant as well as dependant on the
  timing of the doses
• Biggest effect is in the latent phase
• In the active phase of labor narcotics my speed
  up the progress of labor by decreasing anxiety
  and decreasing catecholamines.

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Narcotics in labor

• Narcotics cause a decrease in long and short term
  variability
• Occasionally a sinusoidal pattern is observed
  after narcotic administration (severe anemia and
  hypoxia can cause this)

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Maternal side effects of Narcotic Analgesics

• Nausea and vomiting (increased smooth muscle
  tone, decreased peristalsis, pyloric sphincter
  spasm and delayed gastric emptying
• Respiratory depression (decreased minute volume,
  lower oxygen saturation and a shift to the right
  of the co2 curve causing hypoxia or hypercarbia,
  aspiration

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Maternal side effects of narcotic analgesics

• Arterial and venous dilation because of histamine
  release and interference with baroreceptors
• Orthostatic hypotension can develop
• Usually cardiovascular effects are minimal unless
  the pt is hypovolemic or conduction anesthesia is
  used

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Neonatal side effects of narcotic analgesia

• Respiratory depression (decreased minute volume
  and oxygen saturation causing a shift of the CO2
  dissociation curve to the right
• Neonates tolerate this much less than the mother
  so hypoxia and acidosis can occur rapidly

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Neonatal side effects of narcotic analgesics

• The maximal depressive effect from IM narcotics
  is 2-3 hours
• Certain narcotics such as Morphine or
  Alaphaprodine have 10 times the respiratory
  depressant actions when compare to meperidine.

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Neuro-behavioral effects of narcotics

• Apgar scores will reflect major depressant
  effects but there are specific tests to assess
  neural behavior of infants who were given
  narcotics in labor
• Evaluation consists of neonatal muscle tone,
  ability to alter their state of arousal,
  reflexes, and reactions to repetitive stimuli

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Neonatal effects of narcotic analgesics

• Some studies have shown behavior changes up to 4
  days post delivery
• Suck less effectively
• Depressed visual and auditory attention
• Decrease reflexes
• Take longer to habituate to noise
• Decrease social responsiveness

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Management of Depressed neonate

• Narcan 0.2cc IM to the fetus (not the mother)
  (0.01-0.02mg/kg
• Repeat in 3-5 minutes
• Narcan competitively displaces the narcotic
  molecule from its receptor
• Watch infant for 1 hour after narcan is given

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Meperidine (Demerol)

• Most common analgesic in North America and
  Europe
• IM up to 100mg-onset 40-50 min
• IV up to 50mg-onset5-10 min
• Quick placental transfer
• ½ life 3 hours in mother (up to23 in fetus)
• Metabolized to normeperidine

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Morphine

• IV 20min onset time
• Last 4-6 hours
• Very high likelihood on neonatal depression
• Not used for pain in Labor
• Used for sedation in latent phase
• 10-15mg IM

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Fentanyl (Sublimaze)

• Synthetic opoid 1000 times more potent than
  meperidine
• Rapid onset
• Brief duration
• Repeated doses result in drug accumulation and
  long duration of action
• Dose 50-100micrograms IV

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Fentanyl cont

• Not used in labor
• Causes sudden and profound respiratory depression

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Local anesthetics

• Cocaine was the 1st local anesthetic later
  procaine was synthesized
• All local anesthetics cross the placenta quickly
• All local anesthetics are vasodilators except
  cocaine and mepivacaine (carbocaine)

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Esters

• Broken down by pseudocholinesterase to
  para-aminobenzoic acid which does not cause fetal
  depression
• Procaine
• Chlorprocaine
• Tetracaine
• Potential for allergic reactions
• All others are Amides

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Amides

• This class of anesthetics is almost free of
  allergic reactions
• Lidocaine (Xylocaine)
• Mepivicaine (Carbocaine)
• Prilocaine (Citanest)
• Bupivacaine (Marcaine and Sensorcaine)
• Etidocaine (Duranest)

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Local anesthetics

• Ionization, PH, Protein binding, lipid solubility
  all effect the duration to onset and duration of
  action, and the quickness of onset
• Some will have epinephrine added to increase the
  length of time it will be effective

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Local anesthetics

• Some local anesthetics will be found in the
  maternal and fetal blood stream from epidural and
  Para cervical anesthesia

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Regional anesthesia

• Spinal
• Epidural (5-8ml of local)
• The pain of uterine contractions and cervical
  dilation can be alleviated by blocking T11 and
  T12 in the early 1st stage of labor and T10 and
  L1 later in the 1st stage

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Regional anesthesia

• During the 2nd stage of labor pain comes from the
  stretching of the perineum S2,3,4 this can be
  blocked by an epidural block but may inhibit the
  pushing effort
• Bupivicaine and Chlorprocaine have become the
  agents of choice for epidural anesthesia (IV of
  either can cause cardiac collapse and death

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Epidural anesthesia

• Need prior IV hydration
• Continuous monitoring of the FHR and contractions
• Used in SVDs
• 20 min of close BP monitoring after 1st dose and
  after top off doses for 10min
• Placed at L2-3 or L3-4

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Epidural anesthesia

• Test dose is given
• Slow injection of the dose to give a more even
  anesthetic
• Continuous infusion better than boluses
• If BP drops treat with ephedrine 5-10mg each dose
  and IV fluid bolus

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Epidural anesthesia

• Continuous epidural use 1/3 less anesthetic
• Gives better pain relief
• 15mg/hr Bupivicaine
• 200mg/hr Chlorprocaine
• Requires IV pump but pump can be adjusted, has
  battery back up, is under positive pressure and
  has auto shut off

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Epidural

• Bolus epidural have been known to slow the
  progress of labor as well as decrease the pushing
  urge. Avoid boluses near delivery. Some authors
  do not like to discontinue the epidural until
  after delivery
• Increased risk of assisted delivery with bolus
  epidural and not with continuous

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Epidurals

• Best anesthesia for PIH
• OK for VBACs
• Complications include incomplete block,
  Unilateral block, Maternal hypotension,
  intravascular injection
• Can give test dose with epinephrine it will cause
  the maternal heart rate to increase by 30
  beats/min for 1min

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Epidurals

• Other complications include accidental dural
  puncture 50 get headache because of large bore
  needle (incidence 0.5-1)
• Treatment is abdominal binder, IV
  hydration(3000cc), analgesics, caffeine, last
  resort is blood patch with10-15cc of pt blood

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Epidural complications

• Accidental Sub arachnoid injection- usually a
  complete spinal block occurs, leave pt supine
  elevating head can cause hypotension

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Contraindications to Epidural anesthesia-

• Patient refusal
• If continuous monitoring of the pt is not
  available
• Infection at or near the epidural site, or
  septicemia
• Coagulation abnormalities
• Anatomical abnormalities (Spina bifida etc)

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Relative contraindications of epidural anesthesia

• Anatomic difficulty
• Late in labor close to delivery
• Very early in labor
• Uncooperative pt
• Uncontrolled PIH or ecclampsia
• Uncorrected hypovolemia
• Chronic low back pain

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Relative contraindications of epidurals

• Recurrent neurologic disease such as MS
• Cardiovascular disease with a left to right shunt
  unless you have appropriate hemodynamic monitoring

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Para cervical block

• Good for the pain of cervical dilation phase but
  no help for the perineum
• Given at 400 and 800 as the cervix reflects
  onto the vaginal fornices
• 3-5cc in each site( always aspirate 1st)
• Complications are lacerations, intravascular
  injection, Parametrial hematoma, abscess, and
  hypotension

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Fetal complications of para cervical block

• Up to 70 get bradycardic (last 2-10min)

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Pudendal block

• Transvaginally or transperineal
• Use a needle guide (Iowa trumpet)
• Medial and inferior to the sacrospinous ligament
  and ischial spine (aspirate 1st)
• 7-10cc each side of lidocaine1 or chlorprocaine
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• For pelvic outlet manipulations(2nd stage)

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Perineal infiltration

• Most common anesthetic
• Best choices are lidocaine or chlorprocaine
• For episiotomy and repair of perineal lacerations

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Complications of Pudendal blocks

• Systemic toxicity(IV)
• Vaginal laceration
• Vaginal or ischiorectal hematoma
• Retro psoas or sub gluteal abscess

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Spinal Analgesia

• Administered in the subdural space
• Very effective and requires a single injection
• Last 1-2 hrs, may cause profound hypotension
• Good for caesarian section

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