Obstetric Anesthesia Overview for Family Medicine Maternal

and Child Health Éva Szabó, M.D.

June 3, 2015

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Learning Objectives

Upon completion of the learning activity, participants should be able to:

1. Discuss the potential effects of labor analgesia on obstetric outcome

2. Compare the advantages and disadvantages of the most common neuraxial labor analgesia techniques

3. Identify those parturients who are at increased risk for anesthetic complications

4. Formulate a labor management plan for morbidly obese parturients to include early initiation of labor analgesia

Explain the risks and benefits of neuraxial morphine administration for postcesarean analgesia

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Topics Covered Today

1. Epidural analgesia and obstetric outcomes: progress of labor and method of delivery

2. Labor analgesia in the obese (especially the morbidly obese) parturient

3. Neuraxial opioid for postcesarean analgesia

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Pain Pathways of Labor

During first stage, pain results from uterine contractions and distention of lower uterine segment and cervixVisceral afferent nerve fibers travel with sympathetic

nerves

Visceral pain impulses entering the spinal cord at T10 –L1

must be blocked

Late first stage and second stage: stretching of vagina, pelvic floor, and perineumPain impulses travel via pudendal nerve

Somatic impulses entering the spinal cord at S2-4 must also be blocked

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Neuraxial Labor Analgesia

Most effective method of intrapartum pain relief

Only form of analgesia to provide complete analgesia for both stages

Additional benefits: reduced maternal catecholamine analgesia blunts hyperventilation-hypoventilation cyclecatheter allows rapid conversion of analgesia to surgical

anesthesia: safer than general anesthesia for emergency cesarean section

Concerns about epidural’s effect on the progress of labor

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Indications of Neuraxial Analgesia – Patient Selection

Maternal request is sufficient indication

For patients at risk of operative delivery (maternal or fetal)

Early (prophylactic) insertion should be considered in high-risk patients for either obstetric or anesthetic indications to reduce the need for GAPreeclampsiaTwinsDifficult airwayObesity

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Contraindications to Neuraxial Analgesia

AbsolutePatient refusal or inability to cooperate Infection at the site of needle insertionCoagulopathySevere hypovolemiaSepsis

RelativeSystemic infection Neurologic diseaseBack pathology or surgery

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Effects on Labor

Concern about side-effects on the progress of labor Increased Cesarean rate?? Increased rate of instrumental delivery??Prolongation of labor??

Difficult to studyObservational studies – not considered in systematic

reviewsNo studies where patients were randomly assigned to

receive epidural analgesia vs. no analgesiaRandomized controlled trials: epidural vs. systemic opioid

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Cesarean Section Rate

Early (1989) retrospective study of 711 consecutive nulliparous women with a spontaneous onset of labor showed 10% C-section rate for dystocia in the epidural group vs. 4% in the non-epidural group

Another retrospective study by same author in 1991: even greater difference

Retrospective studies suffer from selection biasPatients choose their analgesia Women with more pain/dysfunctional labor request epidural Greater labor pain in early labor may be a marker for increased

risk for obstetric complication and operative delivery

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Cesarean Section Rate: Prospective Randomized Trials

First prospective, randomized trial of 93 women in 1993 [1]

C/S: 12 of the 48 in the epidural group and1 in 45 in the meperidine group Increased risk of C-section was limited to dilation<5cm Primary investigators made decisions regarding mode of delivery

More randomized controlled trials Meta-analysis of 18 prospective randomized trials, 2004 [2]

6701 patients No difference in the cesarean delivery rate Increased incidence (13% vs. 7%) of instrumental vaginal delivery Prolongation of first and second stage

Limitations of randomized trials Cannot allocate patients to no analgesia: epidural compared to systemic Blinding is impossible Crossover is common

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Operative Vaginal Delivery Early retrospective studies reported association between epidural

analgesia and instrumental vaginal delivery

Retrospective studies suffer from selection bias

Studies in teaching institutions

Series of randomized controlled trials 1987-90, Chestnut

Dilute local anesthetic did not increase the incidence of instrumental vaginal delivery

Dilute local anesthetic did not provide satisfactory second stage analgesia

Maintenance of a dense block until delivery provided good analgesia but lead to more instrumental vaginal deliveries

Effective neuraxial analgesia also resulted in prolongation of the second stage

Dilute local anesthetic with opioid provided acceptable analgesia with less intense motor block and did not significantly increase the incidence of instrumental vaginal delivery

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Timing of Labor Epidural

ACOG guideline 2002: delay until 4-5 cm (to reduce the risk of C-section)

2005 NEJM article by Wong (728 women) [3]

Early CSE (2cm!) vs. IV/IM opioid followed by epidural later (4 cm)

No significant difference between the groups in the rate of Cesarean delivery and instrumental vaginal delivery

Shorter first stage in the early group

Meta-analyses Early epidural not associated with increased risk of C-section or

instrumental vaginal delivery Early systemic opioid associated with non-reassuring fetal status Early systemic opioid associated with lower umbilical artery pH

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Key PointsAdministered with modern protocols, neuraxial labor

analgesia does not increase the risk of cesarean delivery when compared with systemic opioid

Early initiation does not increase the cesarean rate

Severe pain in early labor may signal a higher risk for operative delivery

Early initiation does not prolong the first stage

Effective analgesia does prolong the second stage

Dense block increases the rate of instrumental vaginal delivery

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Epidural Technique

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Types of Neuraxial Analgesia

Epidural

Caudal

SpinalSingle shotcontinuous

Combined spinal-epidural

Dural puncture epidural analgesia (DPEA)

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Continuous Lumbar Epidural Analgesia

Most common technique

Analgesia is initiated with bolus injection after test dose

Analgesia can be maintained until after delivery Intermittent bolus, infusion, PCEA, programmable pumps

Allows conversion to epidural anesthesia

Local anesthetic spreads both cephalad and caudad

T10-L1 has to be blocked during 1st stage

S2-S4 added for 2nd stage

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Caudal Epidural Analgesia

Approach through sacro-coccygeal ligament

Older technique

Technically more difficult

Requires large volumes of LA solution

Risk of fetal injury

Double catheter technique

Remains an option for patients with L-spine pathology, surgery etc.

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Spinal Analgesia

Single shot if delivery is imminent (or if no epidural service available)

Continuous spinalNo FDA approved microcatheterEpidural catheter requires large-gauge introducer needle

(epidural needle, 18 or 17 gauge)High incidence of headacheOption after “wet tap” (preferred option at UNM) Intentional spinal catheter controversialGreatest advantage: easily converted to spinal

anesthesia if necessary

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Combined Spinal-Epidural

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Combined Spinal-EpiduralThe needle-through-needle technique

1. Epidural space is identified with the LOR technique 2. Spinal needle through epidural needle; dural puncture3. Intrathecal dose administered; spinal needle removed

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Combined Spinal-Epidural

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Combined Spinal-Epidural

Increasing popularity

Fast onset

Complete analgesia in early labor with IT opioid ± LA

“Walking epidural” – no motor block

Higher success rate of epidural

Optimal midline placement

Increased incidence of fetal bradycardia

Cannot initially confirm correct catheter placement

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Dural Puncture Epidural

Needle-through-needle

Without injecting anything into the intrathecal space

Additional confirmation of epidural space

Allows for testing the epidural catheter

Hypothesis: transfer of medication across the dural puncture hole

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Obesity: Definition

Excessive body fat with adverse health implicationsMetabolic disease

Ideal body weight: lowest mortality rate for given height and genderBroca index: height(cm)-100, height(cm)-105 (women)

BMI: weight/height2 (kg/m2)18-25 normal25-30 overweight>30 obesity (class I, II)>40 morbid obesity (class III)>50 (55) super obesity

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The Obesity Epidemic

2011-12 National Health and Nutrition Examination Survey: 35% of adults were obese (BMI>30)

8% of reproductive-aged women are morbidly obese Certain ethnic groups have higher incidence

The prevalence of childhood obesity is 2.5 times higher in offspring of obese womenMajority of LGA babies are born to obese mothers Insulin resistance shunts nutrient excess to the fetusMetabolic disease is programmed in utero

Increases risk for chronic diseases: OSA, HTN, CAD, DM, gall bladder disease, DJD, DVT

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Respiratory Function in Obesity

Increasing weight increased O2 consumption, CO2 production

Increased minute ventilation

Decreased chest wall compliance (weight)

Decreased FRC

Increased work of breathing (rapid, shallow – more efficient breathing pattern)

Obstructive sleep apnea (OSA)Desaturation during sleep, snoring, daytime fatigue, chronic

hypoxemia, pulmonary HTN, RV failure

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Respiratory Function in Pregnancy

Respiratory changes start early in pregnancyProgesteron is a respiratory stimulant

Increased O2 consumption, CO2 production

Increased minute ventilation Increased respiratory rate and tidal volumeDecreased airway resistance Increased work of breathingHyperventilation results in mild respiratory alkalosis

Arterial CO2 decreases from 40 to 30 mmHg

Arterial O2 increases (less increase in obese women)

At 20 weeks, mechanical effects of the uterus Decreased FRC

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Cardiovascular System Obesity Increases the Demands on the CV System

Excess tissue needs additional oxygen

Increased blood volume, increased cardiac output

Increased incidence of mild to moderate HTN

Arrhythmias: fatty infiltration of myocardium and conduction system

Left ventricular dilation, hypertrophy, dysfunction

Patients may be asymptomatic despite CV disease due to minimal physical activity, limited mobility

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Cardiovascular Changes in the Obese Pregnant woman

Physiologic effects of pregnancy and obesity are additive Blood volume and CO increases during pregnancy Obesity independently increases blood volume and CO Additional elevation of CO during labor, and postpartum; obese

parturients are at risk in the peripartum period

BP is maintained during normal pregnancy

Obesity increases risk of HTN, preeclampsia

Risk of cardiomyopathy

Supine hypotension syndrome more pronounced; may be impossible to position properly on OR table

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Cardiovascular Changes in Pregnancy and Obesity [6]

Pregnancy Obesity Combined

Blood volume

Cardiac output

Blood pressure

HR

Supine hypotension

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Anesthetic Implications of Morbid Obesity

Providing anesthesia presents unique challenges

Comorbidities increase anesthetic risk (ASA 3, severe systemic disease

Difficult access, line placement

Difficulty moving and positioning the patient

Difficulty monitoring (BP cuff may not fit)

Technical difficulties when placing neuraxial block

Potentially difficult airway management Neck circumference best predictor of difficult intubation

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Anesthetic Implications of Obesity in Pregnancy

Obesity increases maternal morbidity and mortalityComorbidities: HTN, preeclampsia, DMLong , difficult labor, induction, failed induction

Obesity increases perioperative riskCesarean deliverySurgical and anesthesia-related complications,

postoperative complications

Care of the morbidly obese parturient is challenging for everybody involved and requires planning and good communication

Obesity = high-risk pregnancy

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ACOG recommendation [4]:

“Because these patients are at increased risk of emergent cesarean delivery and anesthetic complications, anesthesiology consultation early in labor should be considered”

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Why do we worry?

Anesthesia-related complications are the seventh leading cause of maternal mortality

Maternal obesity increases the risk of maternal death

Incidence of failed intubation 1:2200 in general surgical population, 1:300 in obstetric patients, even higher in obese patients

Most morbidly obese parturients will require some sort of anesthetic intervention

General anesthesia carries higher risk in these patients

Anesthesia consult allows for planning and decreases the risk

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Obesity, obstetric complications and cesarean delivery rate – A population-based screening study, Weiss et al., Am J Obstet Gynecol 2004; 190:1091

Question: is obesity associated with obstetric complications?

Prospective multicenter review of 16,102 patients

13,752 control (BMI<30)

1,473 obese (BMI 30-35)

877 morbidly obese (BMI >35)

Result: obesity had a statistically significant association with GHTN, preeclampsia, GDM, macrosomia (OR 2.4 – 4)

Cesarean rate 33.8% for obese, 47.4% morbidly obese (control 20.7%) (nulliparous)

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Maternal superobesity and perinatal outcomes, Marshall et al., Am J Obstet Gynecol 2012;206:417.e1-6

Question: is there an increased risk of maternal and fetal complications in maternal superobesity when compared with maternal obesity and morbid obesity

Retrospective cohort-study

64,272 women with BMI≥30 82.5% obese, 15.6% morbidly obese, 1.8% superobese

Result: Increasing BMI was associated with increased risk of cesarean delivery (49% in the superobese)

Dose-response relationship between worsening obesity and Cesarean delivery, macrosomia, neonatal hypoglycemia, preeclampsia

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Anesthetic Management of Labor

Obese parturients need good analgesia

Effective pain relief improves respiratory function, decreases O2 consumption

Effective pain relief attenuates cardiovascular response to contraction pain (BP, HR, CO)

Higher incidence of macrosomia, complicated labor, pain

Higher incidence of induction, failed induction

Cesarean rate increases with BMI

Need a flexible plan for labor analgesia for vaginal delivery or labor analgesia ending in Cesarean delivery

Continuous technique can be extended for cesarean delivery

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Continuous Neuraxial Analgesia & Anesthesia Techniques

Can be extended when cesarean delivery becomes necessary Lumbar epidural labor analgesia Combined spinal-epidural analgesia Continuous spinal analgesia

All of the above can be very challenging in obese patients Obscured landmarks Distance to epidural space - long needle available

All require proper positioning and take time

Nothing can be done STAT in a morbidly obese parturient/patient [6]

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Technical Difficulties

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Continuous Lumbar Epidural AnalgesiaPlacement can be difficult in the morbidly obese (multiple

attempts)

Obscured landmarks; identification of midline may be difficult

Ultrasound imaging also difficult

Distance to epidural space correlates with BMI

High failure rate due to catheter migration during labor

Block has to be PERFECT!

If any doubt, epidural catheter has to be replaced [7]

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Tuohy Needles: 9 cm and 15 cm

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Cesarean Section in the Morbidly Obese Parturient with Good Labor Analgesia

Moving the patient to the operating room (heavy bed+ IV pole with pumps) – need moving help

Transfer to OR tableTwo pairs of extendersCareful attention to IV, epidural

Left uterine displacement as soon as possible

Long safety straps, monitors (consider A-line)

Start dosing epidural

Leave FHR monitor on as long as possible

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Case33-y-o G1 P0, EGA 39 weeks, 129kg, 163 cm (5’4”),

BMI 48.5 admitted for induction of labor

Type II diabetes, macrosomia

Saturday evening induction started; anesthesia consult on Sunday

Pt. requested epidural Monday morning; cervix 2 cm

Epidural placement; loss of resistance at 9 cm

20 hours later: no change in the last 6 hours

Chorioamnionitis

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Case continued

Patient consented for C-section (Tuesday morning)

Anesthetic plan discussed :Excellent labor analgesia plan epidural anesthesia

Pt. taken to OR at 0858

Pt. moved herself (with some help) to OR table (7 minutes)

IV, epidural catheter intact

Left uterine displacement

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Left Uterine Displacement

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Left Uterine Displacement

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Lidocaine 2% injected to establish surgical anesthesia.0920 (22 minutes later): sensory level adequate to retract the pannus.

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Case continued

Incision at 0940

Uterine incision 0951

Delivery at 0953 (almost 1 hour after we started moving the patient from her room to the operating room)

Apgars 9, 9, 4155g.

Total operating time 1 hour 11 minutes, EBL 600 ml

Discharged home on POD #4

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General Anesthesia for Cesarean Delivery

GA is riskier than regional in the obstetric patient (relative risk 1.7). Why? Intubation is more difficult in the obstetric patient GA is often chosen in emergencies GA is most commonly used in highest risk patients

Combination of morbid obesity and pregnancy increases the risk of GA

GA cannot be avoided if it is an emergency and: The patient does not have an epidural catheter If there is no time for spinal anesthesia If there is a contraindication to any neuraxial technique

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Emergency Cesarean Section under General Anesthesia in the Morbidly Obese Parturient

Added complexity of providing careAdditional staff to help move the patientAll components are more time consumingRisk of losing IV access

Technical issues to safely manage the morbidly obese parturientAppropriate table, extenders, safety strapsRamp or wedge to position for intubation Safe positioning to avoid fallSafe positioning to avoid aortocaval compression

All of the above are difficult to achieve in an emergency situation

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Summary: How to Avoid a CatastropheCommunication!

Identify morbidly obese patients in prenatal clinic refer to a center where epidural analgesia is available

Refer them to anesthesia preoperative evaluation

Aggressive approach: recommend early epidural placement

Technical issues: OR table, extenders, ramp/wedge ready

Proper positioning for intubation if GA required

Full preoxygenation takes minutes but is extremely important

Nothing can be done STAT in a morbidly obese patient

Anticipate problems to avoid a crash section

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Other Medical Conditions Requiring Pre-delivery Anesthesia Evaluation

Severe cardiac or pulmonary disease

Coagulopathy or anticoagulation

Prior anesthesia-related complication or family history

Contraindication to regional anesthesia

Back surgery/back pathology

Spinal cord disease

Facial deformity or limitation of neck mobility

Neurologic/ neuromuscular disorders

Placenta accreta/increta/percreta

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“Duramorph”

Preservative-free morphine for neuraxial administration: Subarachnoid (spinal, intrathecal): very small dose

required Epidural: dose similar to single IV dose (small fraction

crosses the dura) Opioid receptors in the spinal cord Intrathecal opioids do not cause motor block Mean duration of analgesia 20-23 hours Analgesic potency of morphine:

IV 1 Epidural 10 Intrathecal 200

Benefits and Problems

Better pain control facilitates:Early ambulation (less DVT)Early maternal-infant bonding

Lower doses: 0.1-0.2 mg IT, 2-3 mg epidurally

Lower plasma (breast milk) opioid levels

Better maternal satisfaction

Side effectsPruritusNausea and vomitingRespiratory depressionHerpes labialis (HSV-1) reactivation may be more likely 54

Pruritus

Incidence 40-80%

Most frequent cause of dissatisfaction

Most severe at 3-6 hours after IT Morphine

Treatment:Nalbuphine 2.5-5 mg IV q 4hNaloxone (0.4 mg/mL) 0.04-0.08 mg IVDiphenhydramine 25-50 mg IV q 4hOndansetronPropofol

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Nausea/Vomiting

Incidence 10-60%

Treatment:Nalbuphine 5-10 mg IV q 4 hoursOndansetron 4 mg IV q 6 hoursMetoclopramide 10 mg IV Intractable nausea: Naloxone 0.04-0.08 mg IV bolus then

0.05-0.1 mg/h infusion

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Respiratory Depression

Definition?Failure to respond to PaO2<60 or PaCO2>50Not synonymous with RR

Peak 3.5 - 12 hours after injection

Always preceded by sedation

Exacerbated by sedatives, morbid obesity

Risk is very low with currently used doses

Treatment: naloxone, O2

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Breakthrough Pain

Should not be treated with opioids in the first 24 hours without prior discussion with the anesthesia team

“Anesthesia spinal morphine” order set allows for oxycodone if pain not controlled or small doses of IV morphine if pain not controlled with oxycodone

Risk for of respiratory depression, hypoxemia

Ketorolac and ibuprofen preferred; multimodal analgesia

Morphine PCA rarely needed Small doses 0.5-1 mg No basal rate

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References

1. Thorp et al. The effect of intrapartum epidural analgesia on nulliparous labor: a randomized, controlled, prospective trial. Am J Obstet Gynecol 1993;169:851-8

2. Leighton et al. Epidural analgesia and the progress of labor. In Evidence-Based Obstetric Anesthesia 2005. p 10-22

3. Wong et al. The risk of cesarean delivery with neuraxial analgesia given early vs. late in labor. NEJM 2005;352:655-665

4. ACOG Committee Opinion Obesity in Pregnancy 2013

5. Soens et al. Obstetric anesthesia for the obese and morbidly obese patient: an ounce of prevention is worth more than a pound of treatment. Acta Anaesthesiol Scand 2008; 52: 6-19

6. Lucas. The 30 minute decision to delivery time is unrealistic in morbidly obese women. Int J Obstet Anesth 2010; 19: 431-7

7. Roofthooft. Anesthesia for the morbidly obese parturient. Curr Opin Anaesthesiol 2009; 22:341-346