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Anesthesia for Cesarean Section

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

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Anesthesia for Cesarean Section

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  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

  3. 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?

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. Preparation for Anesthesia – IV Fluids • Disadvantages to Colloid? • Expensive • Anaphylactoid reactions • Coagulation effects

  11. 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

  12. 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

  13. 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

  14. General Considerations • ? Support person • ? Oxygen

  15. 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

  16. 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

  17. 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)

  18. 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

  19. 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)

  20. 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)

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

  22. 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)

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

  24. Prevention of Maternal Complications - Failures • Failed spinal • ~ 1% of cases • If delivery not urgent – 2nd spinal

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

  26. 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

  27. 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

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

  29. 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 Indications for Cesarean Section

  30. Choice of Technique

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

  32. 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

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

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

  35. 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

  36. 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

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

  38. 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

  39. 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

  40. 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

  41. Drugs Used for Spinal Anesthesia for Cesarean Section

  42. 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 Epidural Anesthesia for C-Section

  43. Drugs Used for Epidural Anesthesia for Cesarean Section

  44. 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

  45. 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

  46. 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

  47. 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)

  48. 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

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