Anesthesia for Cesarean Section

1. Anesthesia for Cesarean Section Michelle Gros, FRCPC Feb 13, 2008

2. Cesarean Section Cesarean section rate in Canada in 2005 was 23.7% (CIH) Cesarean section rate in US now exceeds 24% Incidence of anesthesia-related maternal mortality is declining Anesthesia remains responsible for ~ 3-12% of all maternal deaths Majority during general anesthesia (failed intubation, failed ventilation and oxygenation, and or aspiration) Associated factors include obesity, hypertensive disorders of pregnancy, and emergently performed procedures

4. Cesarean Section Review of anesthetic technique used for all c-sections performed at Brigham and Women�s hospital between 1990 and 1995 GA ? from 7.2% in 1990 to 3.6% in 1995 Are we getting enough experience in GA�s for c-sections?

5. Preparation for Anesthesia - Meds Minimize drugs prior to delivery of infant If necessary, midazolam 0.5 � 1 mg or fentanyl 25-50 ug IV Small doses � minimal fetal and neonatal depression Disadvantage of benzos � ? Anticholinergics � decreases secretions Atropine � crosses placenta - ? FHR and ? variability Glycopyrrolate � does not cross placenta Aspiration prophylaxis

6. Preparation for Anesthesia - Meds CJA 2006; 53(1): 79-85. RCT of 60 women Either 1 ug/kg fent and 0.02 mg/kg midaz IV, OR an equal volume IV NS at time of skin prep for spinal No between group differences of neonatal outcome variables (Apgar, neurobehavioural scores, continuous oxygen saturation) Mothers had no difference in recall of the birth

7. Preparation for Anesthesia � IV Fluids Prior to regional � 15-20 mL/kg RL or NS 30 mins prior Rout et al. 1993 � incidence of hypotension ? from 71% to 55% if prehydrated Message: Additional means are necessary In urgent situation � not necessary to wait for fluid bolus ? hypotension � means improved uteroplacental perfusion ?crystalloid vs. colloid

8. Preparation for Anesthesia � IV Fluids CJA 2000; 47: 607-610. Crystalloid preload no longer magic bullet Study found 1 L crystalloid preload was of no value in preventing hypotension Both speed and volume of preloading unimportant Still reasonable to give modest preload prior to spinal Patients are often relatively dehydrated BUT � no need to delay emergency surgery in order to preload

9. Preparation for Anesthesia � IV Fluids Siddik showed 500 mL pentaspan more effective than 1 L NS in reducing hypotension (40% vs. 80%) N+V also reduced in colloid group Neonatal outcome unaffected Riley et al showed less hypotension in colloid group (45% vs. 85%) but no difference in nausea scores or neonatal outcome

10. Preparation for Anesthesia � IV Fluids French et al showed less hypotension in colloid group (12.5% vs. 47.5%), again no differences in neonatal outcome Karinen et al failed to find any differences in hypotension when colloid was used

11. Preparation for Anesthesia � IV Fluids Disadvantages to Colloid? Expensive Anaphylactoid reactions Coagulation effects

12. Preparation for Anesthesia � IV Fluids Is type, amount, timing of fluids that important? Also consider: Effective LUD - 15? often not enough Aggressive use of vasopressors Low dose spinal anesthesia

13. Preparation for Anesthesia � Maternal Position Avoid aortocaval compression Results in ? uteroplacental perfusion by 3 mechanisms: ? venous return ? ? C.O. and BP Obstruction of uterine venous drainage ?�s uterine venous pressure and ? uterine artery perfusion pressure Compression of aorta or common iliac arteries ? ? uterine artery perfusion pressure

14. Preparation for Anesthesia � Monitors Standard monitors +/- art, CVP FHR Before, during, after administration of anesthesia Evaluates effects of maternal position, anesthesia, hypotension, and other drugs on the fetus

15. General Considerations ? Support person ? Oxygen

16. General Considerations - Oxygen For elective c-section, current evidence suggests that supplementary oxygen is unnecessary For emergency section � further data are required Improvement of fetal oxygenation should be primary objective � this achieved in short-term by using very high FiO2 BUT, possibility of reperfusion injury with free radicals

17. Prevention of Maternal Complications - Aspiration ALL patients should receive aspiration prophylaxis, regardless of planned anesthetic for c-section Large survey from Sweden Incidence of aspiration ~ 15 per 10,000 cases of GA for c-sxn 3X greater than in nonobstetric surgery

18. Preventing Aspiration � Pharmacologic Tx Non-particulate antacid eg. 0.3 M sodium citrate H2-receptor antagonist ? gastric pH, BUT does NOT alter pH of existing gastric contents Rout et al 1993� IV ranitidine 50 mg + po Na citrate ? resulted in greater ? in gastric pH than Na citrate alone (provided >30 mins from time of administration to intubation)

19. Preventing Aspiration � Pharmacologic Tx Proton pump inhibitor eg. losec ? gastric acidity One study found it less effective than ranitidine Metoclopramide Accelerates gastric emptying ? Reliability of emptying stomach before c-sxn ? lower esophageal sphincter tone Antiemetic effect

20. Prevention of Maternal Complications - Hypotension In obstetric patients - ? in SBP > 25% OR, any SBP < 100 mmHg Measures of prevention: Fluids LUD Prophylactic vasopressors (ephedrine, phenylephrine)

22. Prevention of Maternal Complications - Hypotension Lee et al., CJA 2002 � systematic review of RCT�s of ephedrine vs. phenylephrine for tx of hypotension during spinal for c-sxn No difference for prevention and treatment of maternal hypotension Maternal bradycardia more likely to occur with phenylephrine than with ephedrine No difference in the incidence of fetal acidosis (umbilical artery pH < 7.2)

23. Prevention of Maternal Complications - Hypotension Chestnut says: They still mostly use ephedrine Phenylephrine preferred in patients who may not tolerate tachycardia eg. MS

24. Prevention of Maternal Complications - Hypotension Varying reports of efficacy of prophylactic ephedrine Some advocate 25 � 50 mg IM before spinal, or 5-10 mg IV immediately after intrathecal injection Chestnut � don�t give prophylactic ephedrine unless pt has a low baseline BP (ie. SBP <105 mmHg before spinal)

25. Prevention of Maternal Complications - Failures Failed spinal ~ 1% of cases

26. Prevention of Maternal Complications - Failures Failed spinal ~ 1% of cases If delivery not urgent � 2nd spinal

27. Prevention of Maternal Complications - Failures Failed spinal ~ 1% of cases If delivery not urgent � 2nd spinal Failed epidural ~ 2-6% of cases

28. Prevention of Maternal Complications - Failures Failed spinal ~ 1% of cases If delivery not urgent � 2nd spinal Failed epidural ~ 2-6% of cases Repeat epidural Watch for local toxicity Pt impatient

29. Prevention of Maternal Complications - Failures Failed spinal ~ 1% of cases If delivery not urgent � 2nd spinal Failed epidural ~ 2-6% of cases Repeat epidural Watch for local toxicity Pt impatient Spinal Collection of local � falsely think this is CSF High spinal

30. Prevention of Maternal Complications - Failures Chestnut: ~ 5% planned epidurals converted to spinals High spinals in 3 of 27 (11%)

31. Indications for Cesarean Section Repeat Scheduled Failed attempt at vaginal delivery Dystocia Abnormal presentation Transverse lie Breech Multiple gestation Fetal stress/distress Deteriorating maternal medical illness Preeclampsia Heart disease Pulmonary disease Hemorrhage Placenta previa Placental abruption

32. Choice of Technique

33. Choice of Technique Indication for c-sxn Urgency of procedure Health of mother and fetus Desires of mother

34. Spinal Pros: Simple Rapid onset Dense blockade Negligible maternal risk of systemic local toxicity Minimal transfer of drug to infant Negligible risk of local anesthetic depression of infant

35. Spinal Cons: Rapid onset of sympathetic blockade � abrupt, severe hypotension Limited duration Recovery time may be prolonged (if procedure shorter than anticipated)

36. Epidural Popularity increasing LA ? nerve roots (dural cuffs) by absorption through arachnoid villi that penetrate dura ? spread of anesthesia is volume dependent

37. Epidural Pros: Titrated dosing and slower onset ? ? risk of severe hypotension and reduced uteroplacental perfusion Duration of surgery not an issue Less intense motor blockade ? good for pts with multiple gestation or pulmonary disease Lower extremity �muscle pump� may remain intact ? may ? incidence of thromboembolic disease

38. Epidural Cons: Slower onset Risk of systemic local toxicity Greater placental transfer of drug than with spinal BUT � does not affect neonatal neurobehaviour and of little clinical significance when appropriate doses used Risk of high spinal

39. Combined Spinal � Epidural (CSE) Initially described in 1981 (epidural catheter at L1-2 and spinal at L3-4)

40. Combined Spinal � Epidural (CSE) Pros: Rapid onset and density of spinal anesthesia combined with versatility of epidural anesthesia Cons: Potential for high spinal Inability to test epidural catheter Only 1 published report of presumed unintentional insertion of epidural catheter through dural puncture site

41. Spinal Anesthesia for C - Section Metoclopramide 10 mg IV Clear antacid orally Intravascular volume expansion with RL or NS (15-20 mL/kg) Application of monitors Supplemental oxygen by face mask or nasal prongs Prophylactic intramuscular ephedrine (25-50 mg) in patients with a baseline SBP < 105 mmHg

42. Spinal Anesthesia for C - Section Lumbar puncture at L3-4 Right lateral or sitting position 25-gauge Sprotte or Whitacre needle Bupivacaine 12 mg (heavy) Morphine 0.1-0.25 mg for postoperative analgesia Left uterine displacement Aggressive treatment of hypotension Exaggerated LUD IV fluids Ephedrine and/or low dose phenylephrine

43. Drugs Used for Spinal Anesthesia for Cesarean Section

44. Epidural Anesthesia for C-Section Maxeran 10 mg IV Clear antacid po IV expansion with RL or NS (15-20 mL/kg) Application of monitors Supplemental oxygen Epidural catheter at L2-3 or L3-4 LUD Test dose Therapeutic dose 5 ml boluses of 2% lido with epi 5ml boluses of 0.5% bupivacaine, 0.5% ropivacaine, or 3% 2-chloroprocaine (lidocaine or 2-chloroprocaine q 1-2 mins, bupiv or ropiv q 2-5 mins) Aggressive tx of hypotension

45. Drugs Used for Epidural Anesthesia for Cesarean Section

46. Aids with Regional 40-50% N2O Low-dose ketamine (0.25 mg/kg) Fentanyl 50-100 ug IV Remifentanil Metoclopramide, ondansetron, or droperidol may be given to treat nausea Small dose of a benzodiazepine to treat anxiety and/or restlessness

47. Local Anesthetic? Int. J Ob Anesth. 2006; 15: 106-114. Prospective, single blind study Compared plain 0.5% bupivacaine (20 mL) with 2% lidocaine (20 mL) + 100 ug epi + 100 ug fentanyl for extending previous low-dose epidural analgesia for emergency c-sxn in 68 pts

48. Local Anesthetic? Sig. longer prep time for mixture (3.0 vs. 1.25 min) Median onset time for block to T7 was 13.8 min for mixture and 17.5 min for plain bupivacaine Difference not statistically different, and was offset by the longer prep time Need for other intra-op supplementation was not significantly different between the groups Lidocaine is cheaper and less toxic than alternatives

49. Local Dose � How Low Can We Go? Int J Ob Anesth, 2006; 15: 273-278. Randomized to receive either intrathecal hyperbaric bupivacaine 3.75 mg or 9 mg, plus 25 ug fentanyl, 100 ug morphine, and 1.5% lidocaine epidurally 3 mL Max sensory block achieved in low-dose group was significantly lower than that in conventional group (T4 vs. T2) Longer time to reach maximum sensory level in low dose group (8.6 min vs. 6.8 min)

50. Local Dose � How Low Can We Go? Low-dose group had less motor block, faster sensory regression to T10 and faster motor recovery No significant difference in need for epidural supplementation before or after delivery of baby Low-dose group � less hypotension (14% vs. 73%) with less ephedrine usage

51. Spinal Bupivacaine Dosed According to Patient Height Barash p 1149 Spinal bupivacaine 0.75% dosed according to patient height: 150-160 cm � 8 mg 160-182 cm � 10 mg >182 cm � 12 mg Onset of action: 2-4 mins Duration of action: 120-180 mins

52. Addition of Fentanyl to Spinal Acta Anesth Scand, 2006; 50: 364-367. Tested effect of intrathecal fentanyl added to hyperbaric bupivacaine on maternal spirometry in 40 pts 2 groups: 2 mL hyperbaric bupivacaine 0.5% + 0.4 mL saline 2 mL hyperbaric bupivacaine 0.5% + 0.4 mL fentanyl (20 ug) Performed spirometry on arrival to OR and 15 mins after subarachnoid blockade

53. Addition of Fentanyl to Spinal Subarachnoid block with bupivacaine � significantly ? peak expiratory flow rates No changes in VC or FVC Addition of intrathecal fentanyl: Improved quality of blockade (T1.5 vs. T4) Did not lead to a deterioration in resp function compared with intrathecal bupivacaine alone

54. Addition of Fentanyl to Spinal Int. J Ob. Anesth. 1997; 6: 43-48. Double-blind placebo-controlled study Compared periop pain relief with fentanyl, morphine, or combination In addition to bupivacaine � group A received 1 mL NS, group B � 25 ug fent, group C � 100 ug morph, group D � 25 ug fent + 100 ug morph Quality of intraop analgesia similar in all groups receiving opioid Opioid use increased side effects Postop analgesia with fentanyl inferior to morphine

55. Dose of Intrathecal Morphine? No good conclusive study Many varied practices Anesth 1999; 90: 437-44. Dose-finding study for intrathecal morphine No difference in PCA morphine use between 0.1 and 0.5 mg groups Pruritis ? in direct proportion to dose No difference in N+V between groups Conclusion: no need to use more than 0.1 mg

56. Epidural Morphine for Post-op Pain Control Anesth Analg. 2007; 105(1): 176-83. Compared 4 mg epidural morphine with 10 mg extended release epidural morphine Found superior and prolonged post-c-section analgesia (especially 24-48 hours post-op)

57. Risk Factors for Failure of Epidural Analgesia for C-Section Acta Anesth Scand, 2006; 50: 1014-1018. Prospectively studied women undergoing c-sxn with a functioning epidural in place All pts received same epidural protocol 16 mL 2% lido, 1 mL bicarb, and 100 ug fentanyl given for c-sxn Failed epidural analgesia was defined as need to convert to GA

58. Risk Factors for Failure of Epidural Analgesia for C-Section Of 101 pts, 20 (19.8%) required conversion to GA Failed epidural inversely correlated with pt�s age Directly correlated with: Pre-pregnancy weight Weight at end of pregnancy BMI Gestational week Number of top-ups VAS 2 hour before c-sxn

59. Risk Factors for Failure of Epidural Analgesia for C-Section Therefore, younger, more obese pts at a higher gestational week, requiring more top-ups during labour, having a higher VAS in the 2 hours before c-sxn � are at risk of inability to extend labour epidural analgesia to epidural analgesia for c-sxn

60. Indications for General Anesthesia for Cesarean Section

61. Indications for General Anesthesia for Cesarean Section Dire fetal distress in absence of pre-existing epidural Acute maternal hypovolemia Significant coagulopathy Inadequate regional anesthesia Maternal refusal of regional anesthesia

62. General Anesthesia for Cesarean Section Ranitidine and/or metoclopramide IV Clear antacid po LUD Application of monitors Denitrogenation (100% O2) Cricoid pressure IV induction Pentothal, propofol, ketamine, or etomidate Succinylcholine (roc if sux contraindicated)

63. General Anesthesia for Cesarean Section Intubation with 6.0-7.0 mm cuffed ETT 30-50% N2O in O2, and low conc of volatile (0.5 MAC) After delivery: Increased conc of N2O with low conc. Volatile Opioid IV hypnotic agent (eg. benzo, barbiturate, propofol) if needed Muscle relaxant (sux boluses or infusion, roc, cisatracurium) Extubation awake with intact airway reflexes

64. General Anesthesia � Traditional RSI Necessary? Int. J Ob Anesth. 2006; 15: 227-232 The effects on the fetus of anesthetics and opioid analgesics are �innocuous and reversible� Dose-dependent neonatal respiratory depression is predictable and readily treatable by a neonatal pediatrician Choice of drug regimen for pt with cardiac or cerebrovascular disease should not be restricted on account of concern for the fetus Opioids should not be withheld in hypertensive disorders, when prevention of a dangerous hypertensive response to laryngoscopy and tracheal intubation is paramount

65. General Anesthesia Adequate denitrogenation: ? FRC ? O2 consumption Baraka � compared head-up and supine positions for denitrogenation in pregnant and non-pregnant pts Head-up position prolonged interval between onset of apnea and desaturation (SpO2<95%) in non-pregnant pts, BUT NOT in pregnant pts

66. General Anesthesia � Induction Agents Goals: Preserve maternal BP, CO, and uterine blood flow Minimize fetal and neonatal depression Ensure maternal hypnosis and amnesia

67. General Anesthesia � Induction Agents Thiopental Extensive published data Safe in obstetric pts 4 mg/kg Rapidly crosses placenta Detected in umbilical venous blood within 30 secs Equilibration in fetus rapid and occurs by time of delivery With doses 4 mg/kg � peak concs in fetal brain rarely exceed threshold for depression

68. General Anesthesia � Unconscious mother and awake neonate? Preferential uptake by fetal liver (1st organ perfused by blood from umbilical vein) Higher relative water content of fetal brain Rapid redistribution of drug into maternal tissues ? rapid reduction in maternal � fetal conc gradient Non-homogeneity of blood flow to intervillous space Progressive dilution in fetal circulation

69. General Anesthesia � Propofol Rapid, smooth induction of anesthesia Attenuates cardiovascular response to laryngoscopy and intubation more effectively than pentothal Does not adversely affect umbilical cord blood gas measurements at delivery Rapidly crosses placenta Rapidly cleared from neonatal circulation Detected low concs in breast milk Propofol and pentothol ? similar Apgar and neurobehavioural scores

70. General Anesthesia � Ketamine 1 mg/kg Rapid onset Analgesia, hypnosis, and reliably provides amnesia Good in asthma or modest hypovolemia 1 mg/kg does NOT ? uterine tone (larger doses do) Rapidly crosses placenta Similar umbilical cord blood gas and Apgar scores with ketamine or pentothal

71. General Anesthesia � Succinylcholine 1-1.5 mg/kg Muscle relaxant of choice for most patients Highly ionized and water soluble, ? only small amounts cross placenta Maternal administration rarely affects neonatal neuromuscular function One study � only doses > 300 mg result in significant placental transfer Pseudocholinesterase activity ? 30% in pregnancy, BUT recovery is not prolonged ? volume of distribution offsets the effect of ? activity

72. General Anesthesia � Rocuronium 1 mg/kg Only very small amounts cross placenta Apgar and neurobehavioural scores not affected

73. General Anesthesia � Maternal Awareness Desire to minimize neonatal depression must be balanced against risk of awareness If another agent not given ? incidence of awareness ? in direct proportion to I-D interval 50% N2O/O2 alone ? 12-26% awareness Awareness ? ? catecholamines ? uterine artery vasoconstriction and ? oxygen delivery to fetus

74. General Anesthesia � Maternal Awareness Common Approaches: 50/50 N2O/O2 with 0.5 MAC inhalational agent ? awareness to <1% Pregnancy ? anesthetic requirements by 30-40% No adverse affect on neonatal condition No ? maternal blood loss Discontinue volatile only if there is uterine atony that is unresponsive to oxytocin

75. General Anesthesia � Oxygen Piggott et al, BJA 1990 � 100% O2 ? higher umbilical venous blood pO2 and higher 1 minute Apgar scores, compared to 50% O2 100% O2 ? higher conc of iso, without maternal awareness or excessive bleeding Supports 100% O2 and higher volatile in cases of fetal distress Lawes et al, BJA 1988 � elective c-sxn � no difference in neonatal oxygenation or outcome between 33% and 50% O2

76. Cesarean Section Under Local Potential indications: patient with severe coagulopathy, known difficult airway and requires emergency c-sxn No anesthesia provider immediately available and severe fetal distress Can begin surgery and deliver infant Temporary hemostasis achieved until anesthetist arrives, then induce GA to complete the surgery

77. Cesarean Section Under Local Need: Midline abdominal incision Minimal use of retractors Do not exteriorize the uterus

78. Local Infiltration Anesthesia for Cesarean Section Professional support person with patient Infiltration with lidocaine 0.5% (total dose < 500mg) Intracutaneous injection in midline from umbilicus to symphysis pubis Subcutaneous injection Incision down to rectus fascia Rectus fascia blockade Parietal peritoneum infiltration and incision Visceral peritoneum infiltration and incision Paracervical injection Uterine incision and delivery GA with ETT for uterine repair and closure, if needed

79. Cesarean Section Under Local Disadvantages: Patient discomfort Potential for systemic toxicity and anesthesia may not be available to assist with resuscitation Requires time Does not provide satisfactory operating conditions for complications, eg. uterine atony, uterine laceration

80. Once Infant Delivered Once umbilical cord clamped � oxytocin given 10-20 U oxytocin in 1000 mL crystalloid and run at 40-80 mU/min Bolus IV oxytocin may cause maternal hypotension and tachycardia and should be avoided

81. Once Infant Delivered If atony does not repond to oxytocin: Methylergonovine 0.2 mg IM 15-methylprostaglandin F2-alpha 250 ug IM or IMM Ergots: Severe hypertension PGF2a: N+V, diarrhea, fever, tachypnea, tachycardia, hypertension, bronchoconstriction Avoid in asthmatics

82. Once Infant Delivered Exteriorize Uterus � What to watch for: Pain Nausea Hemodynamic changes Risk of VAE

83. Effects of Anesthesia on Fetus and Neonate No significant difference in umbilical cord blood gas between general or regional anesthesia for elective or emergency c-sxn Goals: Effective LUD Ensure adequate maternal oxygenation Avoid maternal hyperventilation Avoid excessive doses of anesthetic agents Treat hypotension promptly

84. Effects of Anesthesia on Fetus and Neonate Crawford � found uterine incision to delivery (U-D) interval is more important than I-D interval A U-D interval >3 mins associated with ? incidence of low umbilical cord blood pH and Apgar scores, regardless of anesthetic technique