81687031 Anesthesia for Cesarean Section

Anesthesia for Cesarean SectionMichelle Gros, FRCPC Feb 13, 2008

Cesarean SectionCesarean 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

Cesarean SectionReview of anesthetic technique used for all c-sections performed at Brigham and Womens hospital between 1990 and 1995 GA from 7.2% in 1990 to 3.6% in 1995 Are we getting enough experience in GAs for csections?

Preparation for Anesthesia - MedsMinimize 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

Preparation for Anesthesia - MedsCJA 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

Preparation for Anesthesia IV FluidsPrior 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

Preparation for Anesthesia IV FluidsCJA 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

Preparation for Anesthesia IV FluidsSiddik 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 unaffectedRiley et al showed less hypotension in colloid group (45% vs. 85%) but no difference in nausea scores or neonatal outcome

Preparation for Anesthesia IV FluidsFrench 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

Preparation for Anesthesia IV FluidsDisadvantages to Colloid?

Expensive Anaphylactoid reactions Coagulation effects

Preparation for Anesthesia IV FluidsIs type, amount, timing of fluids that important? Also consider:

Effective LUD - 15 often not enough Aggressive use of vasopressors Low dose spinal anesthesia

Preparation for Anesthesia Maternal PositionAvoid aortocaval compression Results in uteroplacental perfusion by 3 mechanisms:1)

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

2)

3)

Preparation for Anesthesia MonitorsStandard monitors +/- art, CVP

FHR

Before, during, after administration of anesthesia Evaluates 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 AspirationALL 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

Preventing Aspiration Pharmacologic Tx1) 2)1)

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)

2)

Preventing Aspiration Pharmacologic Tx3)1) 2)

Proton pump inhibitor eg. losec gastric acidity One study found it less effective than ranitidine

4)1)2) 3) 4)

MetoclopramideAccelerates gastric emptying ? Reliability of emptying stomach before c-sxn lower esophageal sphincter tone Antiemetic effect

Prevention of Maternal Complications HypotensionIn obstetric patients - in SBP > 25% OR, any SBP < 100 mmHg Measures of prevention:1) 2) 3)

Fluids LUD Prophylactic vasopressors (ephedrine, phenylephrine)

Prevention of Maternal Complications HypotensionLee et al., CJA 2002 systematic review of RCTs 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)

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

Prevention of Maternal Complications HypotensionVarying reports of efficacy of prophylactic ephedrine Some advocate 25 50 mg IM before spinal, or 5-10 mg IV immediately after intrathecal injection Chestnut dont give prophylactic ephedrine unless pt has a low baseline BP (ie. SBP 182 cm 12 mg

Onset of action: 2-4 mins Duration of action: 120-180 mins

Addition of Fentanyl to SpinalActa Anesth Scand, 2006; 50: 364-367. Tested effect of intrathecal fentanyl added to hyperbaric bupivacaine on maternal spirometry in 40 pts 2 groups:1) 2) 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

Addition of Fentanyl to SpinalSubarachnoid 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

Addition of Fentanyl to SpinalInt. 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

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

Epidural Morphine for Post-op Pain ControlAnesth 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)

Risk Factors for Failure of Epidural Analgesia for C-SectionActa 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

Risk Factors for Failure of Epidural Analgesia for C-SectionOf 101 pts, 20 (19.8%) required conversion to GA Failed epidural inversely correlated with pts 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

Risk Factors for Failure of Epidural Analgesia for C-SectionTherefore, younger, more obese pts at a higher gestational week, requiring more top-ups during labour, having a higher VAS in the 2 hours before csxn 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 SectionDire fetal distress in absence of pre-existing epidural Acute maternal hypovolemia Significant coagulopathy Inadequate regional anesthesia Maternal refusal of regional anesthesia

General Anesthesia for Cesarean SectionRanitidine 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)

General Anesthesia for Cesarean SectionIntubation 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

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 reversibleDose-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

General AnesthesiaAdequate 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 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

General Anesthesia Rocuronium1 mg/kg Only very small amounts cross placenta Apgar and neurobehavioural scores not affected

General Anesthesia Maternal AwarenessDesire 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

General Anesthesia Maternal AwarenessCommon Approaches: 50/50 N2O/O2 with 0.5 MAC inhalational agent awareness to 3 mins associated with incidence of low umbilical cord blood pH and Apgar scores, regardless of anesthetic technique