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
¡¤Thiopental
* 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
¡¤prophylaxis
- 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
- RLL
- aspiration of large amount of solid material : obvious signs of airway
obstruction
- 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
hematoma
- rarely
severe infection
5. Paracervical
block
* relief the pain
of uterine contraction, additional analgesia is required for delivery
* 3 & 9 o
clock
* complications
- fetal bradycardia : transplacental transfer -> depressant effect on the heart
- consequence of drug-induced uterine artery vasoconstriction & myometrial
hypertonus
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