Analgesia & Anesthesia

Chapter 15. Analgesia & Anesthesia

May 3, 1999

1st year resident  Ji-soo Lee

 1. General Principles

  A. Obstetrical Anesthesia Services

   - Anesthetic risk factor

   - marked obesity

      - severe edema or anatomical anomalies of face & neck

      - protuberant teeth or difficulty in opening the mouth

      - short stature or short neck

      - Asthma or other serious medical or obstetrical complications

      - previous history of anesthetic complications

   B. Principles of pain relief

      - simplicity, safety, preservation of fetal homeostasis

      - with respect to the preservation of fetal homeostasis

   - the most important factor : transfer of oxygen (concentration of inhaled oxygen, uterine blood flow, oxygen gradient across the placenta)

      - impairment fetal oxygenation : compression of the umblical cord, or prolonged or repeated decrease in placental perfusion

   - cause of reduced placental perfusion - hypertonic uterine contraction

- severe preeclampsia

- maternal or fetal hemorrhage

- premature separation of the placenta

- hypotension from spinal or epidural analgesia

   C. Nonpharmacologic Methods of pain control

       - Pain can be  minimized by appropriate training in breathing &
appropriate training in breathing & appropriate pshycological support

 2. Analgesia & Sedation during labor

     - Pain relief with a narcotic such as meperidine, plus one of the tranquilizer drugs such as promethazine

     A. Meperidine & Promethazine

- meperidine 50 - 100mg with Promethazine 25mg IM q 3 to 4hours

( peak effect is achieved 45minutes after IM )

- no convincing evidence that Meperidine prolongs labor

- slightly increase in uterine activity (- epinephrine & other catecholamines )

     B. Other drugs

      - Butolphanol

¨c synthetic narcotic

- 1-2mg doses compares with 40 - 60 mg of Meperidine

- neonatal respiratory depression : less than with meperidine

- antagonizes the narcotic effect of Meperidine

- sinusoidal fetal heart rate pattern

     - Fentanyl (50-100§¶/hr as needed) & Butorphanol (1-2mg/hr
as needed)

- safe & without effect on the active phase of labor

     C. Narcotic antagonist

     - Naloxone

       - displacing the narcotic form specific receptors in the CNS

       - reversing respiratory depression induced by opioid narcotics

       - newborn respiratory depression -> 0.1mg/kg of body weight injected into the umblical v.

-> acts within 2minutes with an effective duration of at least 30 min

-> repeat in three to five minutes if no response

- no adverse effect on the newborn

 3. General Anesthesia

    - All anesthetic agents - cross the placenta & depress the fetal CNS

    - Aspiration
of gastric contents - obstruct airways & lead pneumonitis, pulmonary edema, death


 A. Inhalation Anesthesia

    - Gas anesthetics

       - N2O
- only anesthetic gas in use for intrapartum

- not prolong labor or interfere with uterine contractions

- 50% mixture with 50% oxygen  -> excellent pain relief during the second stage of labor

- commonly used as part of a balanced general anesthesia for C/S

    - Volatile Anesthetics

       -Isoflurane - most commonly used

       - can be used for internal podalic version of 2nd twin

breech decomposition

replacement of acutely inverted uterus

       - S/E

- unconsciousness -> aspiration pneumonia

- cardiodepressant & hypotension

- hepatitis & hepatic necrosis

   - Anesthetic gas exposure & Pregnancy outcome

¡¤not a substantial risk for either pregnancy loss or congenital anomalies (cohen.1994)

   - IV drugs during anesthesia


* advantage - ¨c ease & extreme rapidity of induction

¨e ready controllability

¨e prompt recovery with minimal risk of vomiting

* poor analgesic agents

- sufficient drug dose -> newborn depression

- not used as the sole anesthetic agent

- given along with a muscle relaxant

    - Aspiration during general anesthesia


- fasting for at least 6 & preferably 12hrs before anesthesia

- use of agents to reduce gastric acidity during the induction and maintenance
of general anesthesia

: sodium citrate with citric acid (Bicitra), cimetidine, ranitidine

- skillful tracheal intubation-stelick maneuver

- after intubation & during the surgery, passage of a nasogastric tube
to empty the stomach

- awake extubation with protective airway reflexes intact

- use of regional analgesia

       - Pathophysiology

- fluid PH < 2.5 -> chemical pneumonitis


- aspiration of large amount of solid material : obvious signs of airway

- smaller particles without acidic liquid : patchy atelectasis & later to bronchopneumonia

- highly acidic liquid : decreased SpO2, tachypnea, bronchospasm, ronchi, rales, atelectasis, cyanosis, tachycardia, hypotension

      - Treatment

- Suction & bronchoscopy

- oxygen ventilation : primary goal -  SaO2 >= 90% with the least amount of oxygen & ventilator pressure

- antimicrobials : not recommended prophylactically

 4. Regional Analgesia

    1. Sensory innervation of genital tract

¨c uterine innervation

- pain in the 1st stage of labor : from uterus

- Frankenhauser ganglion : just lateral to the cervix->into the pelvic plexus->to the middle & superior internal iliac plexus

: visceral sensory fibers  from the uterus, vagina, cervix transverse through this ganglion

- motor pathway : 7th & 8th thoracic v.

¨e lower genital tract innervation

- pain in the second stage of labor : from the lower genital tract

- pudendal nerve : sensory innervation to the peritoneum, anus, the more medial & inferior parts of the vulva,

& clitoris(2nd,3th,4th sacral n.)

    2. Anesthetic Agents

¨c some local anesthetic agents used in obstetrics

¨e central nervous system toxicity

- depression

- symptoms : light-headness, dizziness, tinnitus, bizarre behavior, slurred
speech, metallic  taste, numbness of the tongue & mouth,

muscle fasciculation & excitation, generalized convulsion & loss of consciousness

¨e cardiovascular toxicity

- in general, it develops later than cerebral toxicity (at higher blood level)

- hypertension & tachycardia followed by hypotension & arrhythmia

-> turning the women & crystalloid solution IV rapidly with IV Epedrine

->if maternal V/S is not restored within 5minutes, emergency C/S !

     3. Local infiltration

- before episiotomy & delivery

- after delivery into the site of lacerations to be repaired

- around the episiotomy wound, if inadequate analgesia

4. Pudendal block

       a. local infiltration of the pudendal nerve


    b. within 3-4mins
-> successful pudendal block

    c. complication

      - IV injection->
stimulation of the cerebral cortex -> convulsion

      - troublesome

      - rarely
severe infection

   5. Paracervical

     * relief the pain
of uterine contraction, additional analgesia is required for delivery

     * 3 & 9 o

     * complications

- fetal bradycardia : transplacental transfer -> depressant effect on the heart

- consequence of drug-induced uterine artery vasoconstriction & myometrial

    6. Spinal(subarachnoid) block

      * Pregnancy -> engorgement of the internal vertebral venous plexus

-> smaller subarachnoid space

-> much higher blockade with same volume of solution

      a. vaginal delivery

- low spinal block : the level extends to the 10th thoracic dermatome, the umblicus

- lidocaine : excellent spinal analgesia

: relatively short duration

- Tetracaine : 4-6mg in 6% solution of dextrose in water

: satisfactory anesthesia in te lower vaginal and the perineum for about an hour

: neither is administered for vaginal delivery until the cervix is full dilated & all other criteria for safe forceps delivery

have been fulfilled

: preanalgesic IV hydration for preventing of hypotension

       b. cesarean delivery

- level of the eighth thoracic dermatome

: just below the xyphoid process of the sternum

- 8 to 10mg of tetracaine

12mg of Bupivacaine

50-75mg of Lidocaine

- additional of 0.2 mg of morphine

       c. complications with spinal analgesia

* hypotension

¡¤uterine displacement

¡¤hydration with 500 to 1000mg salt solution

¡¤Ephedrine : 5-10mg IV if hypotension persists

* total spinal blockade

¡¤Tx.- Treat associated hypotension

- tracheal intubation & effective ventilation

- IV fluid

- Ephedrine for increasement of BP

* spinal (post puncture ) headache

¡¤due to leakage of CSF

¡¤reduced by using a small-guage spinal needle & avoiding multiple puncture

* convulsion

* bladder dysfunction

* Oxytocins¡¤& hypertension - injection following delivery

* Arachnoiditis & meningitis

      d. contraindication to spinal analgesia

* maternal hypovolemia & hypotension

* severe preeclampsia

* disorders of coagulation and defective hemostasis

* spread of the epidurally injected anesthetic agent depends on

: the location of the catheter tip

dose, concentration, volume of anesthetic agent used patient position

-> head-down, horizontal, head-up

unique to each epidural space

  7. Epidural analgesia

       : epidural or peridural space

- contains areolar tissue, fat, lymphatics & the internal venous plexus

     1) continuous lumbar epidural block

- vaginal delivery : block from the 10th thoracic to 5th sacral dermatome

- abdominal delivery : block at 8th thoracic level and extending to the first sacral dermatome

- spread of the epidurallly injected anesthetic agent depends upon

: the location of the catheter tip

dose, concentration

volume of anesthetic agent used

patient position

      2) technique


3) complication


       4) effect on labor


      5) maternal pyrexia

       : mean temperature -> higher after 6hours of labor

       : not attributed to infection

      6) Contraindications

      : actual or anticipated serious maternal hemorrhage

      : infection at or near the sites for puncture

      : suspicion of neurological disease

      7) epidural opiate analgesia

      : advantages of using a combination of oppiates and local anesthetics

- rapid onset of pain relief

- decrease in shivering

- absence of motor blockade from the smaller doses of bupivacaine required

      : side effects

- pruritus(80%)

- urinary retention(55%)

- nausea and vomiting(45%)

- headaches(10%)

- immediate or delayed respiratory depression

- fetal sinusoidal heart rate pattern