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

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
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.

51. MCQ 4: Physiological changes seen in the last trimester include all EXCEPT
A. Resting PaCO2 is decreased
B. Hematocrit is decreased
C. Blood volume is increased
D. Gastric secretion is increased
E. Total peripheral resistance is decreased

52. MCQ 4: Physiological changes seen in the last trimester include all EXCEPT
A. Resting PaCO2 is decreased
B. Hematocrit is decreased
C. Blood volume is increased
D. Gastric secretion is increased
E. Total peripheral resistance is decreased

53. Gastric acid production does not increase
Gastric acid production does not increase. There is an increased risk of aspiration due to delayed gastric emptying and a decrease in lower esophageal sphincter tone.

54. MCQ 5: All of the following are suitable for aspiration prophylaxis prior to caesarean section, EXCEPT:
A. Metoclopramide
B. Glycopyrollate
C. Sodium citrate
D. Clear fluids 4 hours pre-op
E. Ranitidine

55. MCQ 5: All of the following are suitable for aspiration prophylaxis prior to caesarean section, EXCEPT:
A. Metoclopramide
B. Glycopyrollate
C. Sodium citrate
D. Clear fluids 4 hours pre-op
E. Ranitidine

56. Metoclopramide acts as a pro-kinetic to empty the stomach of any gastric contents.
Sodium citrate is a non-particulate antacid used to neutralize gastric contents.
Ranitidine is an H2 antagonist used to prevent gastric acid secretion.
Allowing clear fluids up to 4 hours prior to suregry has been shown to decrease the gastric content volume so decreasing the risk of aspiration.
Glycopyrollate is an anti-sialogogue used for preoperative preparation when an awake intubation is anticipated.

57. MCQ 6: All are suitable techniques for pain relief in labor EXCEPT:
A. Transcutaneous electrical nerve stimulation
B. White noise
C. Epidural bupivacaine
D. Intrathecal narcotics
E. 70% Nitrous oxide in Oxygen

58. MCQ 6: All are suitable techniques for pain relief in labor EXCEPT:
A. Transcutaneous electrical nerve stimulation
B. White noise
C. Epidural bupivacaine
D. Intrathecal narcotics
E. 70% Nitrous oxide in Oxygen

59. The concentration of nitrous oxide in oxygen when used for analgesia is 50%. Higher concentrations can result in loss of consciousness.

60. MCQ 7: Which of the following is a contraindication to epidural analgesia in labor:
A. Previous caesarean section
B. Fetal distress
C. INR 1.6
D. Maternal exhaustion
E. Maternal multiple sclerosis

61. MCQ 7: Which of the following is a contraindication to epidural analgesia in labor:
A. Previous caesarean section
B. Fetal distress
C. INR 1.6
D. Maternal exhaustion
E. Maternal multiple sclerosis

62. Epidural analgesia is not contraindicated in patients who have had a prior C/S. The pain caused as a result of uterine rupture is not effectively masked by epidural analgesia.
Fetal distress can be reduced by epidural analgesia so long as hypotension is avoided
Maternal exhaustion is an indication for epidural analgesia.
Maternal multiple sclerosis is not a contraindication to epidural analgesia as long as the concentration of local anesthetic is reduced
Coagulopathy is an absolute contraindication to epidural analgesia

63. MCQ 8 : Likely complications of epidural opioids include all of the following, EXCEPT:
A. Itching
B. Urinary retention
C. Hypotension
D. Respiratory depression
E. Nausea

64. MCQ 8 : Likely complications of epidural opioids include all of the following, EXCEPT:
A. Itching
B. Urinary retention
C. Hypotension
D. Respiratory depression
E. Nausea