Obstetrical Anesthesia

1. Obstetrical Anesthesia Dr Lindsey Patterson

2. Objectives • Overview of maternal physiology • Analgesia for labor and delivery • Regional anesthesia • Anesthesia concerns in the parturient • Study MCQs with explanations

3. Physiological Changes-CVS Almost all the changes seen are due to high levels of progesterone and include: • 35%  Total Blood Volume •  heart rate 15 beats/min • 40%  CO • 30%  SV • 15%  SVR • 500ml/min  blood flow to uterus •  venous return from legs • AORTOCAVAL COMPRESSION (mechanical)

4. Impact of CVS changes • Patients with pre-existing cardiac disease may decompensate either during labor or immediately post delivery. This corresponds to the time of maximal CO • Approx 400 – 600ml blood loss occurs at delivery • Supine hypotensive syndrome

5. Aortocaval Compression

6. Physiological Changes - Resp •  oxygen consumption ~ 20% (100% in labor) due to increased metabolic rate •  minute ventilation ~ 50% (due to increased tidal volume) •  arterial pCO2 •  FRC causing a decrease in oxygen reserves

7. Impact of Resp. changes • Uptake of inhalational agents is faster • Decreased FRC and increased oxygen consumption increase the risk of hyoxia with apnea • Preoxygenation prior to GA less effective

8. Physiological Changes- Airway • Venous engorgement of airway mucosa • Edema of airway mucosa • Worsening of Mallampati score in labor

9. Impact of Airway Changes • Trauma to upper airway with suctioning, intubation • Increased incidence of difficult/failed intubation x10 • Require smaller ETT

10. Physiological Changes-CNS • Decrease in MAC by 25 – 40% • Decreased dose of Local Anesthetic requirement for regional techniques • More rapid onset of neural blockade

11. Impact of CNS Changes • Decreased inhalation anesthetic agent requirements • Decreased dose of local anesthetic for same effect • Increased risk of local anesthetic toxicity

12. Physiological Changes - GIT • Increased gastric fluid volume • Increased gastric fluid acidity • Decreased competency of lower esophageal sphincter

13. Impact of GIT Changes • Increased risk of aspiration • All parturients are a “full stomach” • Aspiration prophylaxis recommended for C/S • 0.3M Sodium citrate 30 mls po • Ranitidine 50mg iv • Metoclopramide 10mg iv

14. Analgesia for labor and delivery • Where is the pain coming from? • Is pain bad in labor? • Analgesic options

15. Nociceptive pathways involved T10 – L1 during labor plus S2-S4 for delivery Pain of childbirth

16. Is pain bad in labor? Psychological stress can cause: increased levels of catecholamines hyperventilation These may result in decreased uterine blood flow leading to hypoxia and acidosis in the fetus

17. Factors affecting pain perception in labor • Mental preparation • Family support • Medical support • Cultural expectations • Underlying mental status • Parity • Size and presentation of the fetus • Maternal pelvic anatomy • Duration of labor • Medications

18. Analgesia for labor and delivery • Non-medication • Inhalational • Parenteral • Regional

19. Analgesia- Non medication options • Breathing exercises • Autohypnosis • Acupuncture • White Noise/ Music • Massage/ walking • TENS • Water bath

20. Inhalation Medications • Nitronox: 50:50 mixture of oxygen and nitrous oxide • Low dose Isoflurane in oxygen Advantages: on demand delivery, relatively safe Disadvantages: variable efficacy, nausea, drowsiness, neonatal depression

21. Parenteral Medications • Narcotics: meperidine, morphine fentanyl Advantages: relatively good analgesia Disadvantages: nausea, vomiting, sedation, neonatal depression (max. 2 hours after meperidine dose), short duration of action

22. Regional techniques • Epidural, spinal, combined spinal-epidural Advantages: excellent pain control, minimal impact on progress of labor with low doses, less drug transfer to fetus, improved uterine blood flow, decrease in birth trauma e.g. use of forceps, minimal neonatal depression Disadvantages: invasive technique, side effects (hypotension, headache, itching, nausea, urinary retention, limited mobility), nerve damage, infection

23. Anesthesia in the parturient • General considerations of the parturient undergoing surgery • Obstetric surgery

24. General considerations • Altered physiology as mentioned • Risks to the fetus: • Effect of the disease process/therapies • Possible teratogenicity of anesthetic agents • Intraoperative effects on uteroplacental blood flow • Increased risk of preterm labor/ risk of abortion

25. Maternal considerations • Altered physiology • Altered response to anesthesia • Decrease in MAC • Increased sensitivity to neuraxial agents • Decreased plasma cholinesterase • Decreased protein binding (more free drug) • Limited drug information in parturients

26. Fetal Considerations • Teratogenicity: • Limited information due to impracticality of conducting trials with sufficient power • Guidelines based on a) effects on reproduction in animals; b) epidemiological surveys of OR personnel; c) studies of pregnancy outcomes in parturient undergoing ante partum surgery

27. Nitrous oxide has been shown to have a teratogenic effect in rats during the first trimester • No anesthetic agent is a proven teratogen in humans • Anesthetic agents deemed safe include: thiopental,morphine, meperidine,fentanyl, succinylcholine, NDMRs • Limiting nitrous oxide use but only if hypotension secondary to volatiles can be avoided

28. Anesthetic management in the parturient should be directed to: • Avoidance of hypoxemia • Avoidance of hypotension • Avoidance of acidosis • Maintain PaCO2 in the normal range for the parturient • Minimize effects of aortocaval compression

29. Anesthesia for Caesarean Section • Preparation • Preventing complications • Choice of Anesthetic technique • Effects on the fetus

30. Preparation • Premeds: antacid (sodium citrate) • IV access and fluid bolus within 30 minutes of operating (avoid glucose containing fluids) • Left lateral tilt with wedge under right pelvis • Routine Monitors: ECG, NIBP, pulse oximeter, fetal monitoring • Additional monitors for GAs: ETCO2, nerve stimulator, temp probe

31. Preventing complications • Aspiration prophylaxis • Detailed airway assessment • Fluid resuscitation/left lateral tilt to prevent hypotension • Safe practice for placement of neuraxial blocks

32. Anesthetic techniques • Local infiltration by surgeon • Regional anesthesia: spinal, epidural, combined spinal-epidural • General anesthesia

33. Local Infiltration • Rarely performed • Patient usually in extremis • Surgery must be done via midline incision, gentle retraction, no exteriorization of the uterus • Usually done to supplement a regional technique if local anesthetic toxicity not a concern

34. Regional: Spinal Anesthesia • Simple to perform • Rapid onset • Single shot technique • Profound neural block • Technique of choice for uncomplicated elective caesarean sections and in many emergency caesarean sections

35. Spinal Anesthesia • Potential Complications: • Hypotension • Headache (rare ~1:100) • Backache (temporary ~24hrs) • Nausea/vomiting (secondary to BP, narcotics) • Neurological damage (very rare) • Anaphylaxis (very rare)

36. Regional: Epidural Anesthesia • More technically challenging • Slower onset • Used when already placed for labor analgesia • Useful in parturient where a slow, controlled onset of block is needed • Allows prolongation of block should surgery be complicated

37. Epidural Anesthesia • Potential Complications: • Hypotension • Headache (approx 1:100) • Transient backache ~24hrs • Urinary retention • Unintentional spinal injection • Intravascular injection of local anesthetic • Neurological damage • Infection

38. Regional: Combined spinal-epidural • Used when require the speed and density of a spinal anesthetic with the flexibility of prolonging the block by supplemental increments of local anesthesia via the epidural catheter • Complications: as mentioned for spinals and epidurals

39. General Anesthesia • Used when • Patient refuses regional technique • Regional technique is contraindicated • Emergency C/S when there is inadequate/absent regional analgesia and to delay will cause undue risk to the fetus / mother

40. General Anesthesia • Complications: • Failed intubation • Failed ventilation causing death or neurological injury • Awareness • Aspiration pneumonia

41. Anesthesia: Effects on the fetus • Avoid hypotension, hypoxia, acidosis, hyperventilation • Limit time between uterine incision and delivery to less than 3 minutes • Infants exposed to GA have lower Apgar at one minute but no difference at 5 mins • No significant alteration in neurobehavioral scores with regional techniques

42. MCQ 1. Epidural Anesthesia in Obstetric Practice. Which of the following is false. • A. Commonly causes itching • B. Can be used to control blood pressure in pre-eclampsia • C. Causes uterine relaxation • D. Causes urinary retention • E. Contributes to the effects of aortocaval compression

43. MCQ 1. Epidural Anesthesia in Obstetric Practice… • A. Commonly causes itching • B. Can be used to control blood pressure in pre-eclampsia • C. Causes uterine relaxation • D. Causes urinary retention • E. Contributes to the effects of aortocaval compression

44. Itching is one of the most common side-effects of opioids when delivered in the epidural space. Their use allows for a decreased concentration of local anesthetic whilst maintaining excellent analgesia. Patients have better motor function and retain the ability to push.

45. MCQ 2. All of the following are false concerning general anesthesia in the parturient, EXCEPT: • A. General anesthesia reduces gastric pH • B. MAC is decreased • C. It is contra-indicated in patients with a bleeding diathesis • D. Is a major cause of overall maternal mortality • E. Succinylcholine crosses the placenta

46. MCQ 2. All of the following are false concerning general anesthesia in the parturient, EXCEPT: • A. General anesthesia reduces gastric pH • B. MAC is decreased • C. It is contra-indicated in patients with a bleeding diathesis • D. Is a major cause of overall maternal mortality • E. Succinylcholine crosses the placenta

47. General anesthetics have no effect on gastric pH. It is the method of choice in patients with a bleeding diathesis since regional anesthesia is contra-indicated. Although of concern to Anesthesiologists general anesthesia is not a major cause of maternal mortality. Succinylcholine is unable to cross the placenta and effect the fetus.

48. MCQ 3. The following are all true concerning the nerve supply of the uterus , EXCEPT: • A. Sensation from the upper segment travels with the sympathetic nerves to T11-T12 • B. Sensation from the birth canal is via the pudendal nerve • C. Lower segment innervation is via S2-4 • D. Motor function occurs via sympathetic and parasympathetic nerves • E. An intact nerve supply is essential to initiate normal labor

49. MCQ 3. The following are all true concerning the nerve supply of the uterus , EXCEPT: • A. Sensation from the upper segment travels with the sympathetic nerves to T11-T12 • B. Sensation from the birth canal is via the pudendal nerve • C. Lower segment innervation is via S2-4 • D. Motor function occurs via sympathetic and parasympathetic nerves • E. An intact nerve supply is essential to initiate normal labor

50. Normal labor occurs in patients with a transected spinal cord.