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Chapter 15 ANALGESICA AND ANESTHESIA

Chapter 15 ANALGESICA AND ANESTHESIA. 2004-11-29 R3 길민경. Pain relief in labor : unique problems

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Chapter 15 ANALGESICA AND ANESTHESIA

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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 2nd 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 2nd 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 1st 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 → 10th, 11th, 12th thoracic & 1st 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) → 2nd, 3rd & 4th 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 1st 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 : 10th 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 8th 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 3rd day and absent by the 5th • 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 10th thoracic to 5th sacral dermatomes • Abdominal delivery : block 8th thoracic level ~ 1st 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 1st stage labor • BACK PAIN

  44. EFFECT ON LABOR Epidural analgesia usually prolongs the 1st stage of labor, increases the need for labor stimulation with oxytocin EPIDURAL ANALGESIA

  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%)

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