THE OBESE PARTURIENT

HARRY SINGH, MDDEPT. OF ANESTHESIOLOGYUTMB

INDICES OF OBESITY AND THEIR PARAMETERS

Index Definition Values_______________________________________________________________

Overweight 20% > idealObesity > 20% over idealMorbid obesity Ideal weight x 2Broca index Ideal female weight Ht (cm) – 105

Body Mass Wt (kg) Normal = 25, obese > 30 (Quetelet) index Ht (m)2

3 Ht (in)Ponderal index √ Wt (lb) Obese < 11.6

______________________________________________________________

From Dewan DM, The obese parturient. In James FM, Wheeler AS, Dewan DM, editors.

Obsteric Anesthesia: The Complicated Patient, 2nd ed. Philadelphia, FA Davis, 1988:468.

DEFINITIONS AND INCIDENCE

Normal BMI: 25 Overweight –up to 20% more than

ideal body weight or BMI 25-29 Obesity : BMI > 30 Morbid Obesity : twice the ideal body

weight or BMI > 40 Recent data from National Center for

Health Statistics suggests 54% Americans overweight and 21% obese

6%-10% parturients morbidly obese

TYPES OF OBESITY

Android Obesity: Truncal distribution of fat

Associated with high incidence of cardiovascular disorders

Gynecoid Obesity: Fat distributed to thighs and buttocks

Associated with pregnancy

PATHOPHYSIOLOGIC CHANGES PULMONARY: ↑ O2 consumption and ↑ CO2 production: Secondary to metabolic activity of adipose tissue ↑ Minute Ventilation Reduced chest wall compliance (Restrictive

defect) ↓ Functional Residual Capacity and Residual

Volume FRC may be less than closing capacity→airway

closure during tidal ventilation→V/Q mismatch and shunting

Accentuated in supine, trendelenberg or lithotomy position

EFFECT OF POSITION ON LUNG VOLUMES

In obesity, decreased chest wall compliance results in a functional residual capacity (FRC) that decreases at the expense of expiratory reserve volume (ERV). Closing capacity (CC) stays normal. (From Vaughan RW. Pulmonary and cardiovascular derangements in the obese patient. In Brown BR, editor. Anesthesia and the Obese Patient. Philadelphia, FA Davis 1082:26.)

PICKWICKIAN SYNDROME OR OHS

8% of obese patients Alveolar hypoventilation, somnolence

and morbid obesity ↑ Soft tissue mass of oropharynx

→Intermittent obstruction of airway during sleep

Hypoxemia, hypercarbia Polycythemia, pulmonary hypertension

and right ventricular failure Pulmonary embolism and pneumonia

PATHOPHYSIOLOGIC CHANGES CARDIOVASCULAR: ↑ Blood Volume and ↑Cardiac Output (↑ Stroke

volume) Blood flow through adipose tissue-2 -3 ml/min/100 g Morbid obesity: 50% mild HTN, 5-10% severe HTN Doubling of incidence of CAD ↑ Afterload and preload (↑BP and ↑Blood Volume) ↑ Left ventricular end diastolic pressure and LV

hypertrophy More vulnerable to pulmonary hypertension Airway obstruction or hypoxemia→ ↑ PAP or PAOP

PATHOPHYSIOLOGIC CHANGES ENDOCRINE AND METABOLIC: ↑ Incidence of adult onset diabetes Impaired glucose tolerance Resistance to insulin Hypertrophy of Islets of Langerhans High serum triglycerides High serum cholesterol ↑ Incidence of IHD

PATHOPHYSIOLOGIC CHANGES GASTROINTESTINAL: ↑ Intragastric and intrabdominal pressures ↓ Lower esophageal sphincter tone ↑ Hiatus Hernia Strong correlation between BMI and reflux

symptoms (Odds ratio 6.3 for women with BMI>35)

80% obese patients have gastric pH < 2.5 86% obese patients have gastric

volume>25mL 75% patients at risk of aspiration

pneumonitis Combination of pregnancy and obesity

increases the risk of aspiration pneumonitis

CHANGES IN THE AIRWAY Short neck, ↓ chin to chest distance Limited flexion of cervical spine Nonexistent atlantooccipital gap Limited atlantooccipital extension and

bowing of cervical spine and forward displacement of larynx

Adiposity of the face, shoulders, neck and breasts

Narrow pharyngeal opening due to enlarged tongue and fleshy pharyngeal and supralaryngeal tissues

↑ Incidence of failed or difficult intubation 33% incidence of difficult intubation in

obese parturients Percutaneous cricothyrotomy may be

difficult due to difficulty to palpate landmarks

MATERNAL MORTALITY Obesity risk factor in 12 of 15 anesthesia

related deaths in Michigan between 1972 to 1984: Failed intubation leading cause of death

4 of 7 maternal deaths in Chicago Maternity Hospital in women > 200 lbs

12% of all maternal deaths in obese women between 1963 and 1997 in Minnesota: Pulmonary embolus leading cause of death

Anesthesia, surgery and pregnancy additively increase the mortality and morbidity in these patients.

MATERNAL COMPLICATIONS 47% of obese parturients have antenatal

disease Gestational diabetes (Odds ratio: 4.00) Gestational hypertension (Odds ratio: 3.20) Preeclampsia (Odds ratio:8.20) Incidence of cesarean delivery (Odds

ratio:2.69) Shoulder dystocia (Odds ratio:3.14): most

common indication for emergency CS in these patients

In one study of 117 patients, 62% CS rate in women > 300 lbs

Another study of 107 patients found 58% CS rate in women 200-504 lbs

Blood loss >1000 ml for cesarean delivery Prolonged duration of surgery Increased incidence of postpartum hemorrhage

OBSTETRIC COMPLICATIONS Fetal macrosomia (Odds ratio:3.82):

Maternal obesity, diabetes and increased gestational age contributory factors

Meconium aspiration (Odds ratio:2.85) Late decelerations (Odds ratio:2.52) Prolonged gestation Dysfunctional labor patterns Twins/breech presentation Fetal umbilical cord accidents Increased incidence of induction of labor

due to prolonged gestation High incidence of failed inductions Increased incidence of FTP and prolonged

second stage of labor

PERINATAL OUTCOME Birth asphyxia and trauma due to

shoulder dystocia Instrumental delivery (Odds ratio:1.34) Neonatal death (Odds ratio:3.41) Intrauterine fetal demise (Odds

ratio:2.79) Higher pregnancy weight associated with increased risk of late fetal death Increased neural tube defects and other

congenital malformations Neonatal hypoglycemia more frequent Increased frequency of neonatal intensive

care admissions

EPIDURAL ANALGESIA (KEY POINTS) Early insertion of epidural desirable in obese

parturients undergoing trial of labor Landmarks invariably difficult to palpate May consider ultrasound guidance for midline

bony structures with assistance from obstetrician

Small directional errors exaggerated with increasing depth of epidural space

Patient can help guide to the midline by telling if she senses pressure from needle advancement to right or left

Have extra long needles available if necessary Non functioning epidural should be replaced

immediately Catheter should be inserted at least 5 cm in

epidural space as risk of catheter displacement high in obese parturients

EPIDURAL ANALGESIA (KEY POINTS) Higher incidence of failed epidural, unilateral block and

more attempts to identify the space in morbidly obese 94% of obese parturients (>300 lbs) achieved

successful analgesia in one study Catheter had to be replaced once in 46% of these

patients Two or more times in 21% of these patients May consider a planned wet tap with your epidural

needle If one occurs unexpectedly, consider converting to a

continuous spinal with dilute local anesthetic and opioid for labor analgesia (usually 2ml/hr of 0.125% bupivacaine with fentanyl optimal)

More concentrated local anesthetic for cesarean delivery (1-2 ml of 0.75% bupivacaine with fentanyl and durmaorph)

Postdural puncture headache rare in morbidly obese patients

EPIDURAL ANALGESIA (KEY POINTS) Lateral sitting or semi recumbent position to

minimize airway closure and aortocaval compression O2 administration throughout labor to prevent

hypoxemia Epidural decreases O2 consumption and improves

oxygenation and prevents increases in cardiac output by inhibiting catecholamine release during labor

Optimal titration of local anesthetic can prevent hypotension and excess motor block

Epidural advantageous due to frequent need for operative vaginal or cesarean delivery in these patients

Can also be used for postoperative pain management CSE not the technique of choice for labor analgesia in

obese parturients due to delayed assessment of functionality of the epidural

SPINAL ANESTHESIA (KEY POINTS) Negative correlation between the degree of

obesity and dose requirement of local anesthetic Higher block may be due to decreased CSF

volume (engorged epidural venous plexus), exaggerated curvature of lumbar spine, pelvic fat and hormonal changes of pregnancy

High incidence of hypotension following spinal due to higher and variable extension of autonomic blockade in obese patients

High block may exaggerate hypoxemia in these patients

Single shot spinal disadvantageous due to prolonged surgery in these patients

Continuous spinal with epidural catheter may be advantageous in patients for emergent/urgent CS with anticipated difficult airway

CSE technique of choice for scheduled/elective CS CSE set with Gertie Marx spinal needle (12.4 cm)

may be necessary for some these patients

GENERAL ANESTHESIA (KEY POINTS) Increased incidence of complications with GETA The operating room should be prepared with a bed of

appropriate width and strength, and wider arm supports and pads

Most operating room beds only rated for weights up to 300 lbs

The patient should be interviewed early in course of labor or preferably during antepartum visit

Consider additional tests during preop visit like CXR, EKG and PFT with ABGs

Thorough airway evaluation mandatory Considerable proportion of maternal mortality

associated with GETA during cesarean delivery GETA should only be confined to cases where it is

indispensable to save mother or fetus Safety of mother of paramount importance and

overrides fetal considerations

GENERAL ANESTHESIA(KEY POINTS) Consider multimodal aspiration prophylaxis Difficult mask ventilation, laryngoscopy and intubation

should be anticipated; however, obesity alone doesn’t predict difficult airway

13% obese patients pose difficulty with intubation 30% obese parturients pose difficulty with intubation Landmarks for block obscure, therefore, consider

topical anesthesia of airway with 4% lidocaine Direct laryngoscopy following topical anesthesia can

be considered for anticipated difficult airway Obesity+MP IV: Consider fiberoptic intubation Positioning for airway important: the head, neck and

shoulder should be raised, there should be straight line between sternal notch and the external auditory meatus and patient should be in reverse trendelenberg position

GENERAL ANESTHESIA (KEY POINTS)

Rapid sequence induction should not be performed in obese parturients with anticipated difficult airway

Patient should be fully denitrogenated with 100% O2 for 3-5 min before rapid sequence induction

Additional experienced hands must be available for assistance during administration of GETA

Have ancillary airway equipment such as fiberoptic bronchoscope, short handle laryngoscope and an assortment of laryngeal mask airways available

Higher FiO2, tidal volumes and PEEP may be required to maintain adequate SaO2

Effect of muscle relaxant during surgery may be overestimated, whereas, reversal effect may be underestimated

GENERAL ANESTHESIA (KEY POINTS) Drug doses may be based on actual or ideal body weight Highly lipophilic drugs (barbiturates, benzodiazepines)

have considerably increased volume of distribution with higher doses and longer elimination half-lives

Non-lipophilic or weakly lipophilic drugs administered based on lean body mass

Emergence faster after desflurane than sevoflurane or isoflurane anesthesia and their O2 saturations higher with desflurane in PACU

Extubate conservatively and in reverse trendelenburg position

The incidence of dangerous postextubation obstruction is ≈5% in patients with OSA, so extubate with oral or nasal airway in place.

If concerned about possible re-intubation, extubate over an airway exchanger

POSTOPERATIVE MANAGEMENT Patient should be kept in semi-recumbent or reverse

trendelenberg position Continue monitoring for hypoxia and hypoventilation and

consider CPAP mask if OSA a problem A monitored or step down bed may be more appropriate

location for recovery in the L&D Hospitalization often prolonged Wound dehiscence and infection more common Increased incidence of postoperative pulmonary complications

including hypoxemia, atelectasis and pneumonia Vertical abdominal incision more likely to cause hypoxemia Increased risk of deep venous thrombosis and pulmonary

thromboembolism-consider anticoagulation soon after surgery with LMWH or unfractionated heparin

Adequate postoperative analgesia essential to promote early ambulation and to decrease risk of pulmonary complications

CONCLUSIONS Obesity increases the risk of anesthesia related

maternal mortality. Airway complications represent the most common cause of anesthesia-related maternal mortality

Unlike most parturients, associated co-morbidities complicate management of morbidly obese parturients

The obese parturient is at increased risk for fetal macrosomia, shoulder dystocia and cesarean section

Early administration of epidural is advisable in obese parturients undergoing trial of labor; a non-functioning epidural should be replaced immediately

The anesthetic management requires patience, planning and close collaboration amongst involved physicians

SUGGESTED READINGS D’Angelo R, Dewan DD. Obesity in Principles

and Practice of Anesthesia, Editor David H Chestnut, Elsevier Mosby, PA.

Hawkins JL. Labor and Delivery Management of the Morbidly Obese Parturient. 2005 IARS Meeting Review Course Lectures.

Endler GC, Mariona FG, Solok RJ, Stevenson LB. Anesthesia related maternal mortality in Michigan. Am J Obstet Gynecol 1988; 159:187-93.

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