anaesthetic management in obstetric patients

1. OBSTETRIC
ANESTHESIA
PROF DR RANJITA ACHARYA

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

4. CONT.…
• 15%  SVR
• 500ml/min  blood flow to uterus
•  venous return from legs
• AORTOCAVAL COMPRESSION (mechanical)

5. 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

6. AORTOCAVAL COMPRESSION

7. 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

8. IMPACT OF RESP. CHANGES
• Uptake of inhalational agents is faster
• Decreased FRC and increased oxygen consumption increase the
risk of hypoxia with apnea
• Preoxygenation prior to GA less effective

9. PHYSIOLOGICAL CHANGES- AIRWAY
• Venous engorgement of airway mucosa
• Edema of airway mucosa
• Worsening of Mallampati score in labor

10. IMPACT OF AIRWAY CHANGES
• Trauma to upper airway with suctioning, intubation
• Increased incidence of difficult/failed intubation
• Require smaller ETT

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

12. IMPACT OF CNS CHANGES
• Decreased inhalation anesthetic agent requirements
• Decreased dose of local anesthetic for same effect
• Increased risk of local anesthetic toxicity

13. PHYSIOLOGICAL CHANGES - GIT
• Increased gastric fluid volume
• Increased gastric fluid acidity
• Decreased competency of lower esophageal sphincter

14. IMPACT OF GIT CHANGES
• Increased risk of aspiration
Mendelson syndrome was initially described as aspiration of gastric
contents causing a chemical pneumonitis characterized by fever, cyanosis,
hypoxia, pulmonary edema, and potential death.
Chemical pneumonitis is more likely following the aspiration of
gastric contents if pH is less than 2.5 and volume is at least 0.3 mL/kg
body weight.

15. • All parturient are a “full stomach”
• Aspiration prophylaxis recommended for C/S
• 0.3M Sodium citrate 30 ml po
• Ranitidine 50mg iv
• Metoclopramide 10mg iv

16. ANALGESIA FOR LABOR AND DELIVERY
•Where is the pain coming from?
•Analgesic options

17. PAIN OF CHILD BIRTH
Nociceptive pathways
involved
T10 – L1 during labor
plus
S2-S4 for delivery

18. 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

19. ANALGESIA FOR LABOR AND DELIVERY
• Non-medication
• Inhalational
• Parenteral
• Regional

20. ANALGESIA- NON MEDICATION OPTIONS
• Breathing exercises
• Acupuncture
• Music
• Massage/ walking
• TENS
• Water bath

21. INHALATION MEDICATIONS
• ENTONOX: 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

22. PARENTERAL MEDICATIONS
• Narcotics: meperidine, morphine, fentanyl
Advantages: relatively good analgesia
Disadvantages: nausea, vomiting, sedation, neonatal depression,
short duration of action

23. REGIONAL TECHNIQUES
• Epidural, spinal, combined spinal-epidural
Advantages:
1. excellent pain control,
2. minimal impact on progress of labor with low
doses,
3. less drug transfer to fetus,
4. improved uterine blood flow,
5. decrease in birth trauma e.g. use of forceps,
minimal neonatal depression

24. • Disadvantages:
• invasive technique,
• side effects (hypotension, headache, itching, nausea, urinary
retention, limited mobility),
• nerve damage,
• infection

25. ANESTHESIA IN THE PARTURIENT
• General considerations of the parturient undergoing surgery
• Obstetric surgery

26. 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

27. 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 parturient

28. 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

29. • 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

30. • 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

31. ANESTHESIA FOR CAESAREAN SECTION
• Preparation
• Preventing complications
• Choice of Anesthetic technique
• Effects on the fetus

32. 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

33. PREVENTING COMPLICATIONS
• Aspiration prophylaxis
• Detailed airway assessment
• Fluid resuscitation/left lateral tilt to prevent hypotension
• Safe practice for placement of neuraxial blocks

34. ANESTHETIC TECHNIQUES
• Local infiltration by surgeon
• Regional anesthesia: spinal, epidural, combined spinal-epidural
• General anesthesia

35. 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

36. REGIONAL: SPINALANESTHESIA
 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

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

38. REGIONAL: EPIDURALANESTHESIA
• 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

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

40. 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

41. GENERALANESTHESIA
• 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

42. GENERALANESTHESIA
• Complications:
• Failed intubation
• Failed ventilation
• Awareness
• Aspiration pneumonia

43. 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

44. 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

45. MCQ 1. EPIDURALANESTHESIA 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

46. • 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.

47. MCQ 2. ALL OF THE FOLLOWING ARE FALSE CONCERNING
GENERALANESTHESIA 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

48. MCQ 2. ALL OF THE FOLLOWING ARE FALSE CONCERNING
GENERALANESTHESIA 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

49. • 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.

50. MCQ 3: 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

51. MCQ 3: 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. • 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.

53. MCQ 4: 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

54. MCQ 4: 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. • 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.

56. • Allowing clear fluids up to 4 hours prior to surgery has been shown to
decrease the gastric content volume so decreasing the risk of aspiration.
• Glycopyrrolate is an anti-sialogogue used for preoperative preparation
when an awake intubation is anticipated.

57. MCQ 5: ALLARE 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 5: ALLARE 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 6: 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 6: 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. • 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. • 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

64. MCQ 7 : LIKELY COMPLICATIONS OF EPIDURAL
OPIOIDS INCLUDE ALL OF THE FOLLOWING,
EXCEPT:
• A. Itching
• B. Urinary retention
• C. Hypotension
• D. Respiratory depression
• E. Nausea

65. MCQ 7 : LIKELY COMPLICATIONS OF EPIDURAL
OPIOIDS INCLUDE ALL OF THE FOLLOWING,
EXCEPT:
• A. Itching
• B. Urinary retention
• C. Hypotension
• D. Respiratory depression
• E. Nausea

66. THANK YOU