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) (0.01-0.02mg/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

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

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 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 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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