Anesthesia for Cesarean Section：麻醉对剖宫产.ppt

Anesthesia for Cesarean Section Michelle Gros, FRCPC Feb 13, 2008 Cesarean Section l Cesarean section rate in Canada in 2005 was 23.7% (CIH) l Cesarean section rate in US now exceeds 24% l Incidence of anesthesia-related maternal mortality is declining l Anesthesia remains responsible for 3-12% of all maternal deaths l Majority during general anesthesia (failed intubation, failed ventilation and oxygenation, and or aspiration) l Associated factors include obesity, hypertensive disorders of pregnancy, and emergently performed procedures Cesarean Section l Review of anesthetic technique used for all c-sections performed at Brigham and Womens hospital between 1990 and 1995 l GA from 7.2% in 1990 to 3.6% in 1995 l Are we getting enough experience in GAs for c- sections? Preparation for Anesthesia - Meds l Minimize drugs prior to delivery of infant l If necessary, midazolam 0.5 1 mg or fentanyl 25-50 ug IV l Small doses minimal fetal and neonatal depression l Disadvantage of benzos ? l Anticholinergics decreases secretions nAtropine crosses placenta - FHR and variability nGlycopyrrolate does not cross placenta l Aspiration prophylaxis Preparation for Anesthesia - Meds l CJA 2006; 53(1): 79-85. l RCT of 60 women l 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 l No between group differences of neonatal outcome variables (Apgar, neurobehavioural scores, continuous oxygen saturation) l Mothers had no difference in recall of the birth Preparation for Anesthesia IV Fluids l Prior to regional 15-20 mL/kg RL or NS l 30 mins prior l Rout et al. 1993 incidence of hypotension from 71% to 55% if prehydrated l Message: nAdditional means are necessary nIn urgent situation not necessary to wait for fluid bolus l hypotension means improved uteroplacental perfusion l ?crystalloid vs. colloid Preparation for Anesthesia IV Fluids l CJA 2000; 47: 607-610. l Crystalloid preload no longer magic bullet l Study found 1 L crystalloid preload was of no value in preventing hypotension l Both speed and volume of preloading unimportant l Still reasonable to give modest preload prior to spinal l Patients are often relatively dehydrated l BUT no need to delay emergency surgery in order to preload Preparation for Anesthesia IV Fluids l Siddik showed 500 mL pentaspan more effective than 1 L NS in reducing hypotension (40% vs. 80%) l N+V also reduced in colloid group l Neonatal outcome unaffected l Riley et al showed less hypotension in colloid group (45% vs. 85%) but no difference in nausea scores or neonatal outcome Preparation for Anesthesia IV Fluids l French et al showed less hypotension in colloid group (12.5% vs. 47.5%), again no differences in neonatal outcome l Karinen et al failed to find any differences in hypotension when colloid was used Preparation for Anesthesia IV Fluids l Disadvantages to Colloid? nExpensive nAnaphylactoid reactions nCoagulation effects Preparation for Anesthesia IV Fluids l Is type, amount, timing of fluids that important? l Also consider: nEffective LUD - 15 often not enough nAggressive use of vasopressors nLow dose spinal anesthesia Preparation for Anesthesia Maternal Position l Avoid aortocaval compression l 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 Preparation for Anesthesia Monitors l Standard monitors l +/- art, CVP l FHR nBefore, during, after administration of anesthesia nEvaluates effects of maternal position, anesthesia, hypotension, and other drugs on the fetus General Considerations ? Support person ? Oxygen 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 Prevention of Maternal Complications - Aspiration l ALL patients should receive aspiration prophylaxis, regardless of planned anesthetic for c-section l Large survey from Sweden nIncidence of aspiration 15 per 10,000 cases of GA for c-sxn n3X greater than in nonobstetric surgery 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) 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 Prevention of Maternal Complications - Hypotension l In obstetric patients - in SBP 25% OR, any SBP 182 cm 12 mg l Onset of action: 2-4 mins l Duration of action: 120-180 mins Addition of Fentanyl to Spinal l Acta Anesth Scand, 2006; 50: 364-367. l Tested effect of intrathecal fentanyl added to hyperbaric bupivacaine on maternal spirometry in 40 pts l 2 groups: 2 mL hyperbaric bupivacaine 0.5% + 0.4 mL saline 2 mL hyperbaric bupivacaine 0.5% + 0.4 mL fentanyl (20 ug) l Performed spirometry on arrival to OR and 15 mins after subarachnoid blockade Addition of Fentanyl to Spinal l Subarachnoid block with bupivacaine significantly peak expiratory flow rates l No changes in VC or FVC l Addition of intrathecal fentanyl: nImproved quality of blockade (T1.5 vs. T4) nDid not lead to a deterioration in resp function compared with intrathecal bupivacaine alone Addition of Fentanyl to Spinal l Int. J Ob. Anesth. 1997; 6: 43-48. l Double-blind placebo-controlled study l Compared periop pain relief with fentanyl, morphine, or combination l 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 l Quality of intraop analgesia similar in all groups receiving opioid l Opioid use increased side effects l Postop analgesia with fentanyl inferior to morphine Dose of Intrathecal Morphine? l No good conclusive study l Many varied practices l Anesth 1999; 90: 437-44. l Dose-finding study for intrathecal morphine l No difference in PCA morphine use between 0.1 and 0.5 mg groups l Pruritis in direct proportion to dose l No difference in N+V between groups l Conclusion: no need to use more than 0.1 mg Epidural Morphine for Post-op Pain Control l Anesth Analg. 2007; 105(1): 176-83. l Compared 4 mg epidural morphine with 10 mg extended release epidural morphine l Found superior and prolonged post-c-section analgesia (especially 24-48 hours post-op) Risk Factors for Failure of Epidural Analgesia for C-Section l Acta Anesth Scand, 2006; 50: 1014-1018. l Prospectively studied women undergoing c-sxn with a functioning epidural in place l All pts received same epidural protocol l 16 mL 2% lido, 1 mL bicarb, and 100 ug fentanyl given for c-sxn l Failed epidural analgesia was defined as need to convert to GA Risk Factors for Failure of Epidural Analgesia for C-Section l Of 101 pts, 20 (19.8%) required conversion to GA l Failed epidural inversely correlated with pts age l Directly correlated with: nPre-pregnancy weight nWeight at end of pregnancy nBMI nGestational week nNumber of top-ups nVAS 2 hour before c-sxn 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 Indications for General Anesthesia for Cesarean Section Indications for General Anesthesia for Cesarean Section l Dire fetal distress in absence of pre-existing epidural l Acute maternal hypovolemia l Significant coagulopathy l Inadequate regional anesthesia l Maternal refusal of regional anesthesia General Anesthesia for Cesarean Section l Ranitidine and/or metoclopramide IV l Clear antacid po l LUD l Application of monitors l Denitrogenation (100% O2) l Cricoid pressure l IV induction nPentothal, propofol, ketamine, or etomidate nSuccinylcholine (roc if sux contraindicated) General Anesthesia for Cesarean Section l Intubation with 6.0-7.0 mm cuffed ETT l 30-50% N2O in O2, and low conc of volatile (0.5 MAC) l After delivery: nIncreased conc of N2O with low conc. Volatile nOpioid nIV hypnotic agent (eg. benzo, barbiturate, propofol) if needed nMuscle relaxant (sux boluses or infusion, roc, cisatracurium) l Extubation awake with intact airway reflexes General Anesthesia Traditional RSI Necessary? l Int. J Ob Anesth. 2006; 15: 227-232 l The effects on the fetus of anesthetics and opioid analgesics are “innocuous and reversible” l Dose-dependent neonatal respiratory depression is predictable and readily treatable by a neonatal pediatrician l Choice of drug regimen for pt with cardiac or cerebrovascular disease should not be restricted on account of concern for the fetus l Opioids should not be withheld in hypertensive disorders, when prevention of a dangerous hypertensive response to laryngoscopy and tracheal intubation is paramount General Anesthesia l Adequate denitrogenation: n FRC n O2 consumption l Baraka