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

       
¡¤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