Obstetric Anesthesia Update

Educational Objectives

The goals of this program are to improve management of analgesia after cesarean delivery and to improve manage­ment of anesthesia for the obese obstetric patient. After hearing and assimilating this program, the clinician will be better able to:

1.   Recognize the relationship between postcesarean analgesia and chronic pain.

2.   Discuss various modalities of postcesarean analgesia and regimens that combine their use.

3.   List the risks associated with obesity duringpregnancy.

4.   Describe techniques and precautions that improve maternal and fetal outcomes in obese obstetric patients.

5.   Optimize postoperative pain control and respiratory recovery in the obese obstetric patient.

Faculty Disclosure

In adherence to ACCME Standards for Commercial Support, Audio-Digest requires all faculty and members of the planning committee to disclose relevant financial relationships within the past 12 months that might create any personal conflicts of in­terest. Any identified conflicts were resolved to ensure that this educational activity promotes quality in health care and not a proprietary business or commercial interest. For this program, the faculty and planning committee reported nothing to disclose.

Acknowledgments

Dr. Cummings spoke at Survey of Current Issues in Surgical Anesthesia, held October 31 to November 4, 2009, in Naples, FL, and sponsored by the Cleveland Clinic Anesthesiology Institute. Dr. Hawkins was recorded at Scottsdale Anesthesia, held November 1-5, 2009, in Scottsdale, AZ, and presented by Holiday Seminars. The Audio-Digest Foundation thanks the speakers and the spon­sors for their cooperation in the production of this program.

Optimizing Postcesarean Analgesia

Kenneth Cummings, MD, Assistant Professor of Anesthesiology, Cleveland Clinic, Cleveland, OH, and Staff Anesthesiologist, Hillcrest Hospital, Department of Regional Practice Anesthesiology, Mayfield Heights, OH

Background: rate of cesarean delivery rising in recent years; patients want to be ambulatory as soon as possible after delivery, and often want to breastfeed; evidence suggests that good postcesarean analgesia improves mother’s func­tional capabilities and interaction with newborn, especially while breastfeeding; several studies show moderate to severe chronic pain persists 1 to 2 yr after cesarean delivery (Pfannenstiel incision) in some patients; better analge­sia for acute pain correlates with reduced risk for chronic pain

Systemic narcotics: intravenous (IV) patient-controlled analgesia (PCA) best option; less effective than epidural an­algesia, but similar maternal satisfaction (possibly due to increased sense of control over administration); avoid me­peridine (associated with more maternal sedation and dysphoria; metabolites accumulate in breast milk); American Academy of Pediatrics (AAP) considers codeine, fentanyl, methadone, and morphine compatible with breastfeed­ing; drawbacks  —  need for IV line; possibility of pump programming errors; patient movement limited by IV pole; transdermal fentanyl PCA system  —  iontophoretic system delivers acute doses of fentanyl; not inferior to PCA morphine; requires replacement after 24 hr

Neuraxial access (spinal or epidural): single long-acting dose of opioid lacks motor effects; morphine used most often in United States; one spinal dose provides 12 to 24 hr of analgesia; dissolves in and circulates with cerebro­spinal fluid (CSF), and therefore affects brainstem (ie, can cause nausea and sedation as well as itching); maxi­mum recommended dose 100 to 150 µg (analgesic ceiling); epidural morphine  —  kinetics and duration similar to those of spinal morphine; ceiling reached at 3 mg; respiratory depression rare due to protective effect of preg­nancy hormones; 24-hr monitoring nevertheless recommended; fentanyl and sufentanil useful for intraoperative augmentation of block

Prolonged-release morphine: incorporated into lipid foam; provides up to 48 hr of analgesia; side effects similar to but longer-lasting than those of other morphine preparations; also requires access to epidural space and place­ment of dedicated catheter; patients require longer monitoring; expensive

Continuous epidural infusion: provides good analgesia with limited systemic drug exposure; can use dilute solu­tions of bupivacaine or ropivacaine plus narcotic, or pure opioid alone; requires patient monitoring

Multimodal therapy: opioids  —  effective for somatic pain from skin incision; less effective for visceral pain; adding nonsteroidal anti-inflammatory drugs (NSAIDs) reduces visceral pain and postoperative opioid requirements; NSAIDs permissible for breastfeeding mothers, but no data on effect (if any) of cyclooxygenase (COX)-2 inhibi­tors on breastfed infants; acetaminophen acceptable

Wound infusion catheters: placed subcutaneously near wound or subfascially; reduce opioid requirements; good an­algesia shown in some studies, even with infusion of NSAIDs (better analgesia than with systemic NSAID admin­istration); blocks somatic pain from incision only (does not provide optimal analgesia); effect on chronic pain unknown

Single-shot peripheral nerve blocks: ileoinguinal and hypogastric blocks studied most; results mixed; may be indi­cated for patients who require minimal opioid use; technique can be difficult

New approaches

Transversis abdominis plane (TAP) block: applied correctly, provides good analgesia from T11 to L1; bilateral TAP blocks effective in prostatectomy, other urologic procedures, and cesarean delivery; treats only abdominal wall pain

Analgesic adjuvants: ketamine  —  single dose shown to relieve pain for 24 hr; dose too small to elicit psychiatric ef­fects; anticonvulsants  —  relieve neuropathic pain and may inhibit development of chronic pain

Conclusions: use of multimodal analgesia for acute pain current trend; combination of drugs and administration routes allows maximization of pain control and minimization of toxicity; many combinations possible to confer pain relief along multiple pathways; aggressive analgesia may reduce incidence of chronic pain

Management of Labor And Delivery in
the Morbidly Obese Parturient

Joy L. Hawkins, MD, Professor of Anesthesiology and Associate Chair for Academic Affairs, University of Col­orado School of Medicine, and Director of Obstetric Anesthesia, University of Colorado Hospital, Denver

Obstetric outcomes for obese vs thin women: 4 times more likely to develop gestational diabetes; >3 times more likely to develop preeclampsia or gestational hypertension; 2.5 times more likely to deliver child weighing >11 lb; twice as likely to need cesarean delivery; similar increases in risk for women who gain excessive weight dur­ing pregnancy; according to recent meta-analysis, being overweight (body mass index [BMI] of 25 to 30) in­creases risk for cesarean delivery by factor of 1.5; risk doubles with BMI >30 (defines obesity); nearly triples with BMI >40 (defines morbid obesity); also lowers chances of successful vaginal birth after cesarean delivery (VBAC); risk for failure of trial of labor increases as BMI increases, and 6-fold increase in morbidity associated with failure of labor; in one study, prolonged labor among obese women associated with doubling of risk for uterine rupture or dehiscence; rates of fetal as well as maternal injury increased among women with failed VBAC; speaker therefore advises against trial of labor in obese and morbidly obese women (ie, recommends scheduled cesarean delivery); obesity also associated with higher rate of stillbirth, especially among black women; utilization of health care services  —  good predictor of cost; in recent study, pregnant women with BMI >35 required longer hospital stays and needed more prenatal fetal testing and ultrasonography; received more medications; required more physician contact; more likely to see obstetrician rather than nurse practitioner for routine antepartum clinic appointments

New guidelines for weight gain during pregnancy: 30 lb for patient of normal weight (BMI <25); 0 to 20 lb for obese women

Physiologic changes in obese pregnant women: respiratory  —more cells requiring oxygen; elevated carbon dioxide production; difficulty breathing; lower functional residual capacity (FRC); decreased tolerance for apnea; normal-weight gravida has PO₂ >100 mm Hg (much lower among obese gravidae); risk for sleep-disordered breathing (in­creases likelihood of preeclampsia) higher during pregnancy, even among women of normal weight; in one study, obese gravidae more likely to become desaturated, have more apneic events, and snore than women of normal weight; cardiac  —  chronic hypoxemia increases risk for pulmonary hypertension and right ventricular dysfunction; in obese women, panniculus on top of fetus and uterus increases aortocaval compression and risk for supine hypo­tension; gastroesophageal reflux  —  obesity increases risk

Anesthesia for obese pregnant women: clear liquids permissible during labor (gastric emptying unaffected); water in stomach may dilute acid and protect against reflux; history of bariatric surgery  —  in 2004 study, no adverse outcomes related to pregnancy other than higher likelihood of cesarean delivery; 2008 study found evidence of improved fertility and lower risk for complications in mother and child

Physical plant: determine availability of appropriate operating room (OR) table (limit of standard tables 350 lb); make special arrangements if necessary; provide sufficient arm support; may need more powerful ventilator for obese patients; have equipment necessary for regional anesthesia (longer needles; ultrasonography machine, and equipment for managing difficult airways)

Labor and delivery: emphasize importance of consultation with anesthesiologist before delivery; assess airway, take history, and discuss risks; at delivery, offer assistance to nurses with placement of IV line; consider placing arterial line; consider providing supplemental oxygen or monitoring patient with pulse oximetry to determine po­tential need; start aspiration prophylaxis immediately; have back-up help available; emphasize to obstetrician need to be apprised of any changes in management as early as possible so that anesthesia management can be changed appropriately; keep anesthesia plan flexible

Neuraxial blocks: place catheter early in labor; have patient in sitting position; palpation may be difficult, but loca­tion of C7 possible; have patient sit flat, and insert catheter between buttocks crease and C7; make wide skin wheal; patient can offer guidance to midline (no nerve fibers in ligament at midline, but patient will experience pain if penetrating heavily enervated paraspinous muscles to right or left); ultrasonography shown to improve success rate; place catheter ³5 cm into epidural space; have patient sit up very straight or lie down on side during taping to prevent dislodging of catheter; administer test doses incrementally; expect hypotension when patient re­turns to reclining position due to aortocaval compression by panniculus; anticipate need for catheter replacement (include in consent that patient may require multiple replacements); “wet tap”  —  occurs when epidural needle enters CSF; incidence of postdural puncture headaches <10% in patients who weigh >300 lb (reasonable risk for planned wet tap); once in CSF, consider threading catheter in and converting to continuous spinal anesthesia; easy to determine when catheter dislodged; use doses similar to those for combined spinal-epidural (CSE); 5 µg sufentanil good loading dose for obese patient (does not cause motor block); 0.5 mL fentanyl plus 0.5 mL 0.25% bupivacaine provides good analgesia (also with little motor blockade); use 2 to 4 mL/hr of standard agent for maintenance infusion; add 5 µg sufentanil or 25 µg fentanyl for breakthrough pain; goal is good analgesia with no motor block

Cesarean delivery: dosing requirements unpredictable in obese patients; catheter placement allows incremental buildup; position patient on table before drug administration and initiation of motor block; pad table well to avoid peripheral nerve injury (procedure likely to be lengthy); monitor respiratory parameters with capnography; do not allow case to proceed until perfect surgical block achieved; high spinal block  —  associated with respira­tory compromise in patients with BMI >30; drugs for continuous spinal catheter  —  0.5% bupivacaine adminis­tered in increments of 1 mL (5 mg bupivacaine); speaker adds 25 µg fentanyl with first 5 mg bupivacaine; give second dose of bupivacaine (usually necessary) with intrathecal morphine for postoperative pain management

General anesthesia: “BMI, in and of itself, tells us nothing about airway management”; neck circumference and Mallampati score best predictors of airway problems; ramp patient for best alignment for tube placement (moves breasts down to facilitate placement of laryngoscope); make horizontal line between sternal notch and external au­ditory meatus; administer drying agent before anesthesia (due to probability of multiple laryngoscopies); have pa­tient go to sleep in reverse Trendelenburg position; awake intubation  —caution required with sedation if baby in distress (drug may cross placenta); narcotics acceptable; mucosa friable during pregnancy (awake oral intubation favored over nasal); airway block may be difficult if patient has thick neck; asleep intubation  —  consider patient’s limited FRC and compromised respiratory parameters; apply mask tightly for 5 min with patient in reverse Tren­delenburg position; unknown whether to use ideal or actual body weight when calculating doses for most drugs (ex­cept with succinylcholine; administer highest acceptable dose to establish optimal intubating conditions as rapidly as possible); capnography mandatory (cannot hear breath sounds); study showed induction with ketamine allows use of 100% oxygen for 10 to 15 min without risk for awareness; no significant difference in Apgar scores of in­fants between groups of mothers induced with ketamine vs thiopental, but ketamine associated with higher neonatal pH; ketamine not associated with higher rate of maternal dysphoria or unpleasant dreams, and resulted in better postoperative pain control; reverse Trendelenburg position recommended for induction and extubation; maintain during case if possible (increases compliance on ventilator; associated with better FRC, better return of alveolar-ar­terial gradient to baseline, and improved oxygenation, compared to positive end-expiratory pressure or large tidal volume); maintenance  —  propofol infusion, propofol plus ketamine, or opioids; plan ahead; consider using nonde­polarizing relaxants; muscle relaxation prolonged if dosage calculated according to actual body weight (calculate based on ideal body weight; use nerve stimulator to determine if redosing necessary); desflurane good choice of volatile anesthetic; emergence and extubation  —  high risk for airway obstruction (insert nasal airways before extu­bation); extubate over exchange catheter in difficult cases; have nasal continuous or bi-level positive airway pres­sure available; have patient recover in main postanesthesia care unit, if possible (nurses more familiar with obstructed airways); keep patient in semisitting position after extubation; pain control  —  if block in place, neurax­ial best; preservative-free epidural or intrathecal morphine recommended; if PCA used, additional monitoring nec­essary (basal dosing not recommended; have dose limits and frequent nursing assessments); consider putting patient in step-down or intensive care unit, depending on experience level of labor and delivery nurses; combine an­algesics with NSAIDs; consider 24-hr supplementation with ketorolac (eg, Toradol); then switch to combination of oral opioid plus NSAID; for patients with history of obstructive sleep apnea, monitor with pulse oximetry; start in­centive spirometry immediately; administer sufficient pain control to allow ambulation as soon as possible (due to high risk for pulmonary complications and thromboembolism); prescribe heparin for thromboembolism prophy­laxis

Editor’s Note

The next “Survey of Current Issues in Surgical Anesthesia” will take place December 1-5, 2010, also in Naples, FL.
For more information, go to: www.ccfcme.org/Surg/Anes10.

Suggested Reading

American Society of Anesthesiologists Task Force on Obstetric Anesthesia: Practice guidelines for obstetric anesthesia: an up­dated report by the American Society of Anesthesiologists Task Force on Obstetric Anesthesia. Anesthesiology 106:843, 2007; Balki M et al: Ultrasound imaging of the lumbar spine in the transverse plane: the correlation between estimated and actual depth to the epidural space in obese parturients. Anesth Analg 108:1876, 2009; Baron CM et al: Obstetrical and neonatal outcomes in obese par­turients. J Matern Fetal Neonatal Med 2009, Nov 9 [Epub ahead of print]; Horlocker T et al: Practice guidelines for the prevention, detection, and management of respiratory depression associated with neuraxial opioid administration Anesthesiology 110:218, 2009; Kopp SL, Horlocker TT: Anticoagulation in pregnancy and neuraxial blocks. Anesthesiol Clin 26:1, 2008; Loos MJ et al: The Pfannenstiel incision as a source of chronic pain. Obstet Gynecol 111:839, 2008; McDonnell JG et al: The analgesic efficacy of transversus abdominis plane block after cesarean delivery: a randomized controlled trial. Anesth Analg 106:186, 2008; McDonnell NJ et al: Management of a super-morbidly obese parturient requiring cesarean delivery (again!). Anaesth Intensive Care 36:751, 2008; Patil S et al: Successful delivery in a morbidly obese patient after failed intubation and regional technique. Br J Anaesth 99:919, 2007; Roofthooft E: Anesthesia for the morbidly obese parturient. Curr Opin Anesthesiol 22:341, 2009; Stotland NE: Obe­sity and pregnancy. BMJ 337:a2450. doi: 10.1136/bmj.a2450, 2008; Wilkins KK et al: A survey of obstetric perianesthesia care unit standards. Anesth Analg 108:1869, 2009.