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Analgesia and anaesthyesia

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  • 1. Chapter 15 ANALGESICA AND ANESTHESIA 2004-11-29 R3 길민경
  • 2.
    •   Pain relief in labor : unique problems
    • Host of disorders unique to pregnancy (preeclampsia, pl abruption, chorioamnionitis, unique physiological adaptations of pregnancy) : directly affected by the choice of analgesia and anesthesia selected
    • 3.8% of total 4097 preg-related deaths
    • Most important single factor associated with anesthesia-related maternal mortality : experience of the anesthetist
  • 3. GENERAL PRINCIPLES
  • 4. OBSTETRICAL ANESTHESIA SERVICES
    • Certain risk factors should be communicated to the anesthesia-care provider in advance of delivery
      • 1. Marked obesity
      • 2.   severe edema or anatomical anomalies of the face and neck
      • 3. protuberant teeth, small mandible, or difficulty in opening the mouth
      • 4. short stature, short neck, or arthritis of the neck
      • 5.   large thyroid
      • 6.   asthma, chronic pul dis, or cardiac dis
      • 7.   bleeding disorders
      • 8.   severe preeclampsia-ecalmpsia
      • 9.   prev history of anesthetic Cx
      • 10.other significant medical or obstetrical Cx
  • 5. PRINCIPLES OF PAIN RELIEF
    • Simplicity
    • Safety
    • Preservation of fetal homeostasis
  • 6. ANALGESIA AND SEDATION DURING LABOR
  • 7. MEPERIDINE AND PROMETHAZINE
    • Meperidine(50~100mg) + promethazine(25mg) : IM/2-4hrs
    • More rapid effect – meperidine(25~50mg) IV/1-2hrs
    • Depressant effect in the fetus : closely behind the peak analgesic effect in the mother
    • Meperidine : readily crosses the pl, half-life- 2 1/2hrs in mother, 13hrs in newborn
  • 8. OTHER DRUGS
    • Butorphanol (synthetic narcotics) : 1~2mg – compares favorably with 40~60mg meperidine
      • Neonatal respiratory depression ↓
      • Not given with meperidine (antagonizes the narcotic effects of meperidine)
    • Nalbuphine
    • Fentanyl
      • short acting, very potent synthetic opoid
      • 50~100ug IV/hr, if needed
  • 9. NARCOTIC ANTAGONISTS
    • May cause newborn respiratory depression, 2~3hrs after meperidine administration
    • Naloxone(narcotic antagonist) : 0.1mg/kg injected into the umbilical vein
      • Acts within 2min with an effective duration of at least 30min
      • Repeated in 3~5min
      • exhibits no adverse effects in the newborn
  • 10. GENERAL ANESTHESIA
  • 11.
    • Without exception, all anesthetic agents that depress the maternal CNS cross the pl and depress the fetal CNS
    • Aspiration of gastric contents and particulate matter
  • 12. INHALATION ANESTHESIA
    • GAS ANESTHETICS
      • Nitrous oxide(N2O) : provide pain relief during labor as well as at delivery
        • Produces analgesia and altered consciousness
        • Does not provide true anesthesia
        • Does not prolong labor or interfere with Ut contractions
        • N20 50% mixture with 50% oxygen (Nitronox) : excellent pain relief during the 2 nd stage of labor
        • Used as part of a balanced GA for c/sec and some forceps deliveries
  • 13. INHALATION ANESTHESIA
    • VOLATILE ANESTHETICS
      • Cause unconsciousness, potential for aspiration with an unprotected airway
      • Cross pl : producing narcosis in the fetus
      • Isoflurane, Halothane
        • Potent, nonexplosive agents that produce remarkable Ut relaxation when given in high inhaled concentrations
        • Used for Int podalic version of 2 nd twin, breech decomposition, replacement of acutely inverted Ut
        • Maneuver has been completed, anesthetic administration should be stopped and immediate efforts made to promote myometrial contraction to minimize hemorrhage
  • 14. INHALATION ANESTHESIA
    • BALANCED GENERAL ANESTESIA
      • Nitronox given for balanced general nesthesia : some degree of maternal awareness
      • Able to increase the inspired concentration of oxygen
      • 50% N20 + 100% oxygen + halogenated agents(1%↓)
  • 15. INHALATION ANESTHESIA
    • ANESTHETIC GAS EXPOSURE AND PREGNANCY OUTCOME
      • Although exact fetal risk of chronic maternal exposure to waste anesthetic gas is unknown, available data suggest that there is not a substantial risk for either preg loss or congenital anomalies
  • 16. INTRAVENOUS DRUGS DURING ANESTHESIA
    • THIOPENTAL
      • Thiobarbituate, IV : widely used in conjunction with other agents for GA
      • Advantages : ease and extreme rapidity of induction, ready controllability, prompt recovery with minimal risk of vomiting
      • Poor analgesic agents : not used as the sole anesthetic agent
  • 17. INTRAVENOUS DRUGS DURING ANESTHESIA
    • KETAMINE
      • IV in low doses of 0.2~0.3mg/kg : analgesia and sedation just prior to delivery
      • 1mg/kg : induce GA
      • useful in women with acute hemorrhage ← not associated with hypotension
      • avoided in women already hypertensive
      • unpleasant delirium and hallucinations
  • 18. ASPIRATION DURING GENERAL ANESTHESIA
    • pneumonitis from inhalation of gastric contents : m/c cause of anesthetic deaths in obstetrics
  • 19. ASPIRATION DURING GENERAL ANESTHESIA
    • PROPHYLAXIS
    • Fasting from solids for at least 8 hrs and preferably longer before anesthesia
    • Use of agents to reduce gastric acidity during the induction and maintenace of GA
    • Skillful tracheal intubation
    • After intubation, and during the surgery, passage of a N-G tube to empty the stomach of all contents
    • Awake extubation with protective airway reflexes
    • Use of regional analgesia techniques when appropriate
  • 20. ASPIRATION DURING GENERAL ANESTHESIA
    • PATHOPHYSIOLOGY
      • Rt mainstem bronchus usually offers simplest pathway for aspirated material to reach the lung paraenchyma
      • Highly acidic liquid is inspired : O2 sat↓ c tachypnea, bornchospasm, rhonchi, rales, atelectasis, cyanosis, tachycardia, hypotension
  • 21. ASPIRATION DURING GENERAL ANESTHESIA
    • TREAMENT
      • Close monitoring : attention to RR, O2 sat – most sensitive and earliest indicators of injury
      • As much as possible of the inhalated fluid should be immediately wiped out of the mouth and removed from the pharynx and trachea by suction
      • Saline lavage : not recommended (disseminated the acid throughout the lung)
      • No convincing clinical or experimental evidence that corticosteroid therapy or prophylatic antimicrobial administration is beneficial
  • 22. FAILED INTUBATION
    • Uncommon, often associated with aspiration – major cause of anesthetic-related maternal mortality
  • 23. REGIONAL ANALGESIA
  • 24. SENSORY INNERVATION OF THE GENITAL TRACT
    • UTERINE INNERVATION
      • Pain in the 1 st stage of labor is generated largely from the Ut
      • Visceral sensory fibers from the Ut, Cx, upper vagina -> frankenhauser ganglion(lies just lat to Cx) -> pelvic plexus -> mid & sup int iliac plexuses -> 10 th , 11 th , 12 th thoracic & 1 st lumbar nerves
    • LOWER GENITAL TRACT INNERVATION
      • Pain with vag del : arises from stimuli from the lower genital tract
      • Pudendal nerve(peripheral braches of which provide sensory innervation to the perineum, anus, more medial and inf parts of the vulva & clitoris) -> 2 nd , 3 rd & 4 th sacral nerves
  • 25. ANESTHETIC AGENTS
    • Most often, serious toxicity follows injection of an anesthetic into a blood vessel, but it may also be induced by administration of excessive amounts
    • Two manifestations of systemic toxicity : CNS & cardiovascular system(CVS)
  • 26. ANESTHETIC AGENTS
    • CENTRAL NERVOUS SYSTEM TOXICITY
      • Sx : light-headedness, dizziness, tinnitus, bizarre behavior, slurred speech, metallic taste, numbness of the tongue and mouth, muscle fasciculation and excitation, generalized convulsions, loss of consciousness
      • Convulsions should be controlled, an airway established, oxygen delivered
      • Abnormal FHR pattern (late decelerations, persistent bradycardia) : may develop from maternal hypoxia and lactic acidosis induced by convulsions
      • Fetus likely will recover more quickly in utero than following immediate c/sec
  • 27. ANESTHETIC AGENTS
    • CARDIOVASCULAR TOXICITY
      • Do not always follow CNS involvement
      • Develop later than those from cerebral toxicity ← induced by higher blood levels of drug
      • Characterized first by stimulation and then depression
        • Hypertension & tachycardia -> hypotension & cardiac arrhythmias
      • Impaired U-P perfusion & fetal distress
      • Turning the woman onto either side to avoid aortocaval compression
      • Crystalloid solution : infused rapidly, IV ephedrine
      • Emergency c/sec : maternal vital signs have not been restored within 5 min of cardiac arrest
  • 28. LOCAL INFLITRATION
    • Before episiotomy and delivery
    • After delivery into the site of lacerations to be repaired
  • 29. PUDENDAL BLOCK
  • 30. PUDENDAL BLOCK
    • Lower vagina & post vulva
    • Works well and is an extremely safe and relatively simple method of providing analgesia for spontaneous delivery
  • 31. PUDENDAL BLOCK
    • COMPLICATIONS
      • IV injection of a local anesthetic agent : serious systemic toxicity (stimulation of cerebral cortex leading to convulsions)
      • Hematoma
      • Severe infection at the injection site (rare)
  • 32. PARACERVICAL BLOCK
    • Excellent pain relief during the 1 st stage of labor
    • Additional analgesia is required for delivery
  • 33. PARACERVICAL BLOCK
    • COMPLICAITONS
      • Fetal bradycarida : 10~70%
        • Within 10 min, last up to 30min
        • Not a sign of fetal asphyxia ← usually transient and newborns are in most instances vigorous at birth
        • Result form decreased pl perfusion (drug-induced Ut a. vasoconstriction & myometrial hypertonus)
      • Should not be used in situations of potential fetal compromise
  • 34. SPINAL (SUBARACHNOID) BLOCK
    • VAGINAL DELIVERY
      • Low spinal block : popular form a analgesia for forceps or vacuum delivery
      • Level of analgesia : 10 th thoracic – corresponds to level of umbilicus
      • Excellent relief from the pain of Ut contraction
  • 35. SPINAL (SUBARACHNOID) BLOCK
    • CESAREAN DELIVERY
      • Level of analgesia : extend at least 8 th thoracic – just below xiphoid process
    • COMPLICATIONS
      • HYPOTENSION
        • Develop very soon after injection of local anesthetic agent
        • Definition : 20% decrease from baseline
  • 36. SPINAL (SUBARACHNOID) BLOCK
        • Vasodilatation from sympathetic blockade + obstructed venous return from Ut compression of the vena cava & adjacent large veins
        • Supine position : absence of maternal hypotension measured in brachial a. -> pl blood flow may still be significantly reduced
        • Prevention : 1000ml Ringer lactate infused over 20min before spinal injection and 5mg bolus of ephedrine as needed to maintain blood pressure
  • 37. SPINAL (SUBARACHNOID) BLOCK
      • TOTAL SPINAL BOLCKADE
        • Excessive dose of analgesic agent
        • Hypotension & apnea -> immediately treated to prevent cardiac arrest
      • SPINAL (POSTPUNCUTRE) HEADACHE
        • 22 or 24 gauage needles : 1.5% develop postdural puncture headaches
        • reduced by using a small-gauge spinal needle and avoiding multiple punctures
  • 38. SPINAL (SUBARACHNOID) BLOCK
        • no good evidence that placing the woman absolutely flat on her back for several hours is very effective in preventing headache
        • vigorous hydration may be of value, also without compelling evidence to support its use
        • remarkably improved by the 3 rd day and absent by the 5 th
        • severe cases, a blood patch is effective
  • 39. SPINAL (SUBARACHNOID) BLOCK
      • CONVULSIONS
      • BLADDER DYSFUNCTION
      • OXYTOCICS AND HYPERTENSION
      • ARACHNOIDITIS AND MENINGITIS
  • 40. SPINAL (SUBARACHNOID) BLOCK
    • CONTRAINDICATIONS TO SPINAL ANALGESIA
      • m/c serious Cx from spinal block : hypotension
      • Obstetrical Cx that are associated with maternal hypovolemia and hypotension
      • Severe preeclampsia ?
      • Disorders of coagulation and defective hemostasis
      • Skin or underlying tissue at the site of needle entry is infected
      • Neurological disorders
  • 41. EPIDURAL ANALGESIA
    • CONTINUOUS LUMBAR EPIDURAL BLOCK
      • Complete analgesia for the pain of labor and vaginal delivery ← block from 10 th thoracic to 5 th sacral dermatomes
      • Abdominal delivery : block 8 th thoracic level ~ 1 st sacral dermatome
  • 42. EPIDURAL ANALGESIA
    • COMPLICATIONS
      • TOTAL SPINAL BLOCKADE
        • Dural puncture with inadvertent subarachnoid injection
      • HYPOTENSION
        • Normal preg women hypotension can be prevented by rapid infusion of 500-1000ml of crystalloid solution
  • 43. EPIDURAL ANALGESIA
      • CENTRAL NERVOUS STIMULATION
      • MATERNAL PYREXIA
        • Mean temperature ↑
        • Significantly associated with neonatal sepsis evaluation and antibiotic therapy
        • Presence of pl inflammation
        • ⇒ due to infection rather than the analgesia itself
        • Pyrexia : associated with a higher incidence of IU infection from longer 1 st stage labor
      • BACK PAIN
  • 44. EPIDURAL ANALGESIA
    • EFFECT ON LABOR
      • Epidural analgesia usually prolongs the 1 st stage of labor, increases the need for labor stimulation with oxytocin
  • 45. EPIDURAL ANALGESIA
    • Did not significantly increase cesarean deliveries in either nulliparous or parous women in any individual trial or in their aggregate
  • 46. EPIDURAL ANALGESIA
    • TIMING OF EPIDURAL PALCEMENT
      • No increase in either operative vaginal delivery or cesarean delivery with early (≤3cm dilatation) administration of epidural analgesia compared with later administration
      • Parkland Hospital : not begun prior to 3-5cm Cx dilatation
  • 47. EPIDURAL ANALGESIA
    • SAFETY
      • 1968-1985, 26000 women : no maternal deaths
    • CONTRAINDICATIONS
      • actual or anticipated serious maternal hemorrhage, infection at or near the sites for puncture, suspicion of neurological disease
  • 48. EPIDURAL ANALGESIA
      • SEVERE PREECLAMPSIA-ECLAMPSIA
        • Ideal labor analgesia for women with severe preeclampsia : controversial
        • Past two to three decades, most obstetrical anesthesiologists : favor epidural blockade for labor and delivery in women with severe preecalmpsia
        • 1995, Wallace and colleagues : GA and RA are equally acceptable for cesarean delivery in women with severe preecalmpsia
  • 49. EPIDURAL ANALGESIA
    • INTRAVENOUS FLUID PRELOADING
      • Most authorities recommend prehydration, usually with 500~1000ml of crystalloid solution
      • Aggressive volume replacement in severe preeclampsia women increases their risk for pul edema, especially in the first 72 hrs postpartum
      • No instances of pul edema in 738 women in whom crystalloid preload was limited to 500ml
  • 50. EPIDURAL ANALGESIA
    • EPIDURAL OPIATE ANALGESIA
      • Injection of opiates into the epidural space to relieve pain from labor become popular -> rapid onset of pain relief, decrease in shevering, less dense motor blockade
      • Side effect : pruritus(80%), urinary retention(55%), N/V(45%), headaches(10%)
  • 51. EPIDURAL ANALGESIA
    • COMBINED SPINAL-EPIDURAL TECHNIQUES
      • No consensus regarding maternal Cx when comparing spinal or epidural analgesia with combined techniques
  • 52. EPIDURAL ANALGESIA
      • Parkland Hospital : 1223 women with uncomplicated term preg(combine Vs IV meperidine)
        • Emergency c/sec for profound fetal tachycardia
        • Fetal bardycardia occurred within 30min
        • None of the cases responded to conservative measures
        • ⇒ avoid the combined spinal-epidural technique

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