Download Obstetric Analgesia and Anesthesia

Obstetric Analgesia and
Anesthesia
By Abdulaziz Al Gain
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”
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
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
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
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
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
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
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
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
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
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.
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)
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
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
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
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.
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
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
Management of Depressed
neonate
 Narcan 0.2cc IM to the fetus (not the mother) (0.010.02mg/kg
 Repeat in 3-5 minutes
 Narcan competitively displaces the narcotic molecule
from its receptor
 Watch infant for 1 hour after narcan is given
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
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
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
Fentanyl cont
 Not used in labor
 Causes sudden and profound respiratory depression
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)
Esters
 Broken down by pseudocholinesterase to paraaminobenzoic acid which does not cause fetal
depression
 Procaine
 Chlorprocaine
 Tetracaine
 Potential for allergic reactions
 All others are Amides
Amides
 This class of anesthetics is almost free of allergic
reactions
 Lidocaine (Xylocaine)
 Mepivicaine (Carbocaine)
 Prilocaine (Citanest)
 Bupivacaine (Marcaine and Sensorcaine)
 Etidocaine (Duranest)
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
Local anesthetics
 Some local anesthetics will be found in the maternal
and fetal blood stream from epidural and Para cervical
anesthesia
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
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
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
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
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
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
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
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 with1015cc of pt blood
Epidural complications
 Accidental Sub arachnoid injection- usually a complete
spinal block occurs, leave pt supine elevating head can
cause hypotension
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)
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
Relative contraindications of
epidurals
 Recurrent neurologic disease such as MS
 Cardiovascular disease with a left to right shunt unless
you have appropriate hemodynamic monitoring
Para cervical block
 Good for the pain of cervical dilation phase but no help
for the perineum
 Given at 4:00 and 8:00 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
Fetal complications of para
cervical block
 Up to 70% get bradycardic (last 2-10min)
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 2%
 For pelvic outlet manipulations(2nd stage)
Perineal infiltration
 Most common anesthetic
 Best choices are lidocaine or chlorprocaine
 For episiotomy and repair of perineal lacerations
Complications of Pudendal
blocks
 Systemic toxicity(IV)
 Vaginal laceration
 Vaginal or ischiorectal hematoma
 Retro psoas or sub gluteal abscess
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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