Obstetric Analgesia and Anesthesia

Flint Women’s Clinic

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 menstral 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 there 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 (unsure if this is CNS or cardiac)

• Occasionally a sinusoidal pattern is observed after narcotic administration (severe anemia and hypoxia can cause this)

• There is no way to distinguish the two

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 benous 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) (0.01-0.02mg/kg

• Repeat in 3-5 minutes

• Narcan competitively displaces the narcotic molecule from its receptor

• Watch infant for 1 hour after narcan is given

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

Pentazocine (Talwin)

• No advantage over other narcotics

• Respiratory depression

• Weak opiate antagonist, strong opiate agonist

Butorphanol (Stadol)

• Synthetic analgesic like pentazocine (mixed agonist/antagonist

• 5 times more potent than morphine (40X more than Demerol)

• Dose 1-2 mg

• IM 10min onset, IV 1-2min onset

• Duration 2-4 hours

Butorphanol cont.

• Metabolites are inactive

• Less nausea and vomiting

• Causes drowsiness

• Don’t give after Demerol

Alphaprodine (Nisentil)

• Rapid onset of action 5-10 min sub Q, 1-2min IV (IM absorbtion is unpredictable)

• Short duration 1-2 hours

• Repeated doses result in long duration of action because it is accumulated in tissue and slowly released

Alphaprodine cont

• Maternal respiratory depression is common

• Dose 10-20mg IV

• Dose 30mg sub Q

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 para-aminobenzoic 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

• LL displacement of the uterus

• 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

• Catheter is indwelling

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 with10-15cc 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 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)

• Use chlorprocaine 2%

• Rarely used

Pudendal block

• Can be done transvaginally or transperineal• Use a needle guide (Iowa trumpet) Left

hand to Left side and Right hand to Right side

• Medial and inferior to the sacrospinous ligament and ischial spine (aspirate 1st)

• 7-10cc each side of lidocaine1% or chlorprocaine 2%

Perineal infiltration

• Most common anesthetic

• Best choices are lidocaine or chlorprocaine

Complications of Pudendal blocks

• Systemic toxicity(IV)

• Vaginal laceration

• Vaginal or ischiorectal hematoma

• Retro psoas or sub gluteal abscess