Analgesia for Labor and Vaginal Delivery

2. Analgesia for Labor andVaginal Delivery Hirmanpour A . MD

3. Pain perception by the parturient is a dynamic process that involves both peripheral and central mechanisms. • On the McGill pain questionnaire, labor pain is one of the most intense pains that a woman can experience, and it is typically worse than a toothache, backpain, and pain associated with a deep laceration.

5. Labor analgesia options are: • Psychoprophylaxis • Transcutaneous electrical nerve stimulation(TENS) • Systemic medication • Inhalational techniques • Neuraxial blocks • Lumbar sympathic block • Paracervical and pudendal block(infrequently)

6. Psychoprophylaxis • “Natural childbirth” stems from a phrase coined by Grantley Dick-Read in 1933; • He believed that childbirth was a painless process that did not need medical intervention. • He opined that the pain of childbirth results from a ‘‘fear-tension-pain-syndrome.’’

7. Fernand Lamaze introduced the Western world to psychoprophylaxis. • “natural childbirth” was popularized after Marjorie Karmel described and published her childbirth experience under the care of Dr. Lamaze. (Lamaze method) • American society for Psychoprophylaxis was born. Karmel M. Thank You, Dr. Lamaze: A Mother’s Experiences in Painless Childbirth. 2nd edition. New York, Harper & Row, 1981.

10. Labor analgesia options are: • Psychoprophylaxis • Transcutaneous electrical nerve stimulation(TENS) • Systemic medication • Inhalational techniques • Neuraxial blocks • Lumbar sympathic block • Paracervical and pudendal block(infrequently)

12. Transcutaneous Electrical Nerve Stimulation • TENS is thought to reduce pain by nociceptive inhibition at a presynaptic level in the dorsal horn by limiting central transmission. • TENS involves the transmission of low-voltage electrical current to the skin via surface electrodes. • It is most widely used for childbirth in Scandinavia and the United Kingdom.

13. Transcutaneous Electrical Nerve Stimulation • A systematic review of eight trials in more than 700 women concluded that evidence for TENS-mediated reduction in pain during labor is weak. Carroll D, Tramer M, McQuay H, et al. Transcutaneous electrical nerve stimulation in labour pain: A systematic review. Br J ObstetGynaecol 1997; 104:169-75.

14. Transcutaneous Electrical Nerve Stimulation • Electrical stimulation activates low-threshold myelinatednerves. • Inhibit unmyelinated small c fibers by blocking impulses to target cells in the substantiagelatinosa of the dorsal horn. • TENS is also thought to enhance release of endorphins and dynorphins centrally. • Placement of electrodepads over the lower back region in the distribution of T10-L1 may provide some analgesia for parturients in early labor.

16. Labor analgesia options are: • Psychoprophylaxis • Transcutaneous electrical nerve stimulation(TENS) • Systemic medication • Inhalational techniques • Neuraxial blocks • Lumbar sympathic block • Paracervical and pudendal block(infrequently)

17. Systemic Medication • Opioids are the most commonly used class of drugs • Sedative – transqualizer

18. Meperidine • Meperidine is the most commonly used parenteralopioid analgesic during labor. • IM : 50 to 100 mg( peak onset of effect at 40 to 50 minutes); • IV : 25 to 50 mg ( 5 to 10 minutes). • The analgesic effect lasts up to 3 to 4 hours. • Fetal exposure to meperidine is highest between 2 and 3 hours after maternal administration.

20. Meperidine • Cause less respiratory depression in the neonate than morphine does; So, it is more commonly used. • It may cause loss of beat-to-beat variability of FHR tracings.

21. A meta-analysis failed to prove that other opioids(tramadol, meptazinol, diamorphine, pentazocine, nalbuphine,andbutorphanol) were superior to meperidine for labor analgesia. • Some investigators have proposed fentanyl and remifentanil as superior choices.

22. Meperidine • Metabolized in the liver to produce normeperidine, Normeperidine • Pharmacologically active metabolite • A potent respiratory depressant • Crosses the placenta. • Half-life of 60 hours in the neonate.

23. Fentanyl • An alternative analgesic option • For patients in whom neuraxial anesthesia is contraindicated. • Its short half-life makes it suitable for prolonged use in labor, • Use as an IV bolus or as an analgesic administered by means of a PCA delivery system. • Provides reasonable levels of analgesia with minimal neonatal depression.

24. Fentanyl • The usual dose : 25 to 50 µg (IV). • The peak effect occurs within 3 to 5 minutes and has a duration of 30 to 60. • Eisele found IV fentanyl 1 µg/kg provided good analgesia with no appreciable hemodynamic effect and no adverse effects on Apgar scores, fetal acid-base status, or neurobehavioral scores at 2 and 24 hours.

25. Fentanyl Another advantage: • Can be administered in non parenteralmodalities, • Subcutaneously-Orally- Patch. • These uses, have not been adequately evaluated in laboring patients.

26. Butorphanol and Nalbuphine • Opioid agonist-antagonists • Structurally related to oxymorphone and naloxone. • The potential advantages of producing less nausea and vomiting

27. Butorphanol • Is a κ-agonist and a µ-antagonist • Minimal affinity for σ-receptors. • Dose : 1 to 2 mg IM or IV • Duration of action up to 4 hours.

28. Nalbuphine • Is a partial κ-agonist and a potent µ-antagonist • Minimal σ-receptor activity. • A dose of 10 mg IM or IV is equivalent to 10 mg of morphine • IV : Onset 2 to 3 minutes • IM: Onset 10 to 15 minutes • It can offer analgesia for up to 6 hours.

29. One advantage of these agents over µ-agonists • They demonstrate a “ceiling effect” • By increasing doses do not produce further respiratory depression. Unfortunately, • The use of these drugs is limited in clinical practice • Because of rapidly transferred across the placenta and have produced ominous sinusoidal FHR patterns.

30. The use of antagonists or agonist-antagonists may precipitate acute withdrawal syndrome in the mother and the newborn of an opioid-dependent parturient. • This syndrome has been reported after parenteralor neuraxial routes of administration.

31. Naloxone • There is no neonatal benefit to the maternal administration of naloxone during labor or just before delivery. • Naloxone reverses opioid depression of newborn minute ventilation and increases the slope of the CO2-response curve in infants affected by the maternal administration of an opioid. • The recommended dose is 0.1 mg/kg of a 1 mg/mL or 0.4 mg/mL solution. • Not recommended during the primary steps of neonatal resuscitation,

32. Naloxone • Only use if respiratory depression continues and after PPV, normal heart rate and color of neonate appears (In mother received an opioid within the previous 4 hours). • Preferred route of administration is intravenous. • If IV access is not available, IM administration is acceptable, although absorption may be delayed. • Endotracheal administration of naloxone is not recommended.

33. Remifentanil • A potent, short-acting µ-opioid receptor agonist • Approved for clinical use in the US since1996. • Contains an ester linkage that allows metabolism by nonspecific esterasesthroughout the blood and muscles. • This metabolism gives it a unique pharmacologic profile in comparison to other opioids. • Remifentanil has an extremely rapid plasma clearance and offset of action. • Half life : 1.3 mins

34. Remifentanil • Prolonged administration does not cause accumulation of this drug. • UV/M= 0.88. • Fetal exposure to the drug is minimized because of its rapid metabolism or redistribution, or both. • An attractive alternative systemic analgesic in parturients in whom regional anesthesia is contraindicated.

35. Remifentanil PCA with IV remifentanil : • Bolus dose of 0.4 µg/kg with a lockout time of 1 minute • Continuous infusion of remifentanil at 0.05 µg/kg/min with a bolus of 25 µg and a lockout time of 5 minutes provides satisfactory labor analgesia.

36. Systemic Medication • Opioids are the most commonly used class of drugs • Sedative – transqualizer

37. Sedative-Tranquilizers used for sedation,anxiolysis, or both during early labor and before cesarean delivery. • Barbiturates • Phenothiazines • Hydroxyzine • Benzodiazepines • Secobarbitalwere once popular, they are currently unfashionable because of antianalgesic effects in the mother and prolonged depressant effects inthe neonate.

38. Even with small doses of barbiturates that result in no depression of the Apgar score, the newborn’s attention span may be depressed for more than 4 days.

39. Promethazine • The most commonly phenothiazine used in obstetrics. • Used with meperidine • Doses : 25 to 50 mg to prevent emesis. • Promethazine appears in fetal blood within 1 to 2 minutes after IV injection in the mother and reaches equilibrium within 15minutes.

40. Ketamine • N-methyl-d-aspartate (NMDA) receptor antagonist • Produces dissociative anesthesia • Its mechanism: With phencyclidine receptors located in the limbic and corticothalamic areas of the brain. • Subanesthetic doses: 0.5 to 1 mg/kg or 10 mg every 2 to 5 minutes to a total of 1 mg/kg in 30 minutes during labor.

41. ketamine In addition to its use in labor….. • Ketamine in dose of 25 to 50 mg can be used to supplement an incomplete neuraxial blockade for C/S. • Its main disadvantages are the potential for hypertension and emergence reactions. • High doses (>2 mg/kg)can produce psychomimetic effects and increased uterine tone, which may cause low Apgar scores and abnormalities in neonatal muscle tone.

42. Benzodiazepines can be used as sedatives and anxiolytics in labor. • Diazepam (Valium), • Lorazepam(Ativan), • Midazolam (Versed), • Disadvantages: cross the placenta, with elimination half-lives as long as 48 hours for diazepam and upward of 120 hours for its main metabolite N-desmethyldiazepam. • Exposure to BNZ early in uteromay result in malformations such as cleft lip.

43. Benzodiazepines • Use of BNZ during labor no effect on fetal malformations, • But may be with other problems in the neonate: • Sedation • Hypotonia • Cyanosis • Impaired metabolic responses to stress. • BNZ are potent amnestic agents, a parturient may not be able to remember her birthing experience. • Many of the adverse effects can be reversed by flumazenil, which is a competitive benzodiazepine receptor antagonist.

44. Labor analgesia options are: • Psychoprophylaxis • Transcutaneous electrical nerve stimulation(TENS) • Systemic medication • Inhalational techniques • Neuraxial blocks • Lumbar sympathic block • Paracervical and pudendal block(infrequently)

45. Inhalational techniques • Definition : administration of subanesthetic concentrations of inhaled anesthetics to relieve pain during labor. • This pain relief technique should not be confused with inhaled anesthesia that produces unconsciousness and loss of protective laryngeal reflexes. • Although inhaled analgesia provides a limited amount of pain relief, it is not adequate to provide sufficient pain relief for most mothers.

46. Inhalational techniques • Inhaled analgesics can be administered either intermittently (during contractions) or continuously. • They can be self-administered, but the patient should have a health care provider present to ensure an adequate level of consciousness and proper use of the equipment.

47. Inhalational techniques • Entonox (50 : 50 N2O/O2 mixture) has been used for many years as both a sole analgesic and an adjuvant to systemic and regional techniques for labor. • Side effects include dizziness, nausea, dysphoria, and lack of cooperation. • The maximum analgesic effect : after 45 to 60 seconds, • Should use in early onset of contractions and discontinue its use after the peak of the contraction.

48. Entonox

49. Inhalational techniques

50. Inhalational techniques • The lack of scavenging systems in labor may theoretically put staff at risk of exposure to excessive levels in prolonged period. • The administration of N2O and O2 in a 50 : 50 combination appears to have no effect on hepatic, renal, cardiac, or pulmonary functions. • A recent meta-analysis by Kronberg and Thompson concludes that inhaled N2O relieves labor pain to a significant degree in most patients but does not provide complete analgesia for many. • The analgesic effect of N2O is dose dependent, which supports its analgesic efficacy during labor.