In 2008, the prevalence of obesity in adult American women was 35.5%.1 In 2005, approximately 1 in 5 pregnant patients self-reported a prepregnancy body mass index (BMI) of >30 kg/m2.2 In some states the incidence of obesity approached 1 in 3 in certain maternal populations, particularly non-Hispanic African-American women and Medicaid populations.2 This focused review discusses the challenges of providing neuraxial labor analgesia in obese parturients, and suggests potential methods for increasing labor analgesia success in this population.
Risks and Complications of Obesity
Obese parturients have a higher likelihood of coexisting disease and diseases of pregnancy, especially hypertension, diabetes, and preeclampsia.3,4 These diseases, in addition to an increased risk of shoulder dystocia and large-for-gestational-age infants, lead to higher rates of induction of labor in comparison with nonobese parturients.5,6 Labor management is complicated by technical difficulties with fetal monitoring. Operative vaginal and intrapartum cesarean delivery (nulliparas) is more common (33% in obese women in comparison with 20% in nonobese women; and nearly 50% in superobese women; BMI >40 kg/m2).4
Obesity and the Preprocedure Consultation
Both the American College of Obstetricians and Gynecologists and the Society of Obstetricians and Gynaecologists of Canada recommend a prelabor anesthesiology consultation for obese pregnant women (Table 1).7,8 Although neither society specifies the BMI at which this should occur, our department requires a prelabor consultation for all parturients with a BMI >50 kg/m2. All other obese parturients are interviewed as soon as possible after arrival on the labor and delivery unit.
In addition to a focused history and airway examination, the essential elements of the preanesthetic consultation should include an examination of the back, because poorly palpable landmarks have been associated with placement difficulty.9 The consultation will identify patients in whom neuraxial analgesia is medically indicated (e.g., anticipated difficult airway or trial of labor after cesarean) and women for whom difficult initiation of analgesia is anticipated (e.g., poor landmarks).
Tactful discussion with the patient should include both the increased risks of difficult labor analgesia initiation and potential failure, and the goals of comfort and safety. Surveys suggest that this type of discussion rarely occurs, possibly because of concerns of offending the patient. Lack of discussion may contribute to unrealistic patient expectations or incomplete informed consent.10,11
Monitoring equipment must be appropriately sized; blood pressure cuffs may not fit a conical upper arm, necessitating forearm or calf placement or invasive blood pressure monitoring. Ultrasonography may facilitate IV line placement. Labor beds and transport carts for massively obese parturients (>500 lb or 225 kg) can be difficult to maneuver, and door-frame widths may not be sufficient to allow passage of these large beds, complicating the rush to the operating room should cesarean delivery become necessary. A prearrival equipment check is therefore necessary when anticipating morbidly obese parturients. Some units have a specific nursing protocol that addresses these issues.
Advantages and Disadvantages of Neuraxial Labor Analgesia
American College of Obstetricians and Gynecologists guidelines7 do not directly recommend neuraxial labor analgesia for obese parturients, but improved maternal hemodynamic control may benefit this population, which is prone to hypertension.3,5 Tolerance for internal or tightly applied external monitoring devices can be aided by analgesia; internal devices are commonly used in obese parturients because of interference of the pannus with external ultrasound-based monitors.6 Furthermore, neuraxial blockade can provide rapid analgesia for a difficult operative vaginal delivery or an urgent cesarean delivery.5,6
Potential negative aspects of neuraxial analgesia in the obese parturient include difficulties with patient positioning for both parturients and nursing staff, and potential changes in pelvic tone and expulsive efforts in a population for whom the cause of increased labor dysfunction and operative deliveries is not well defined.12,13 Carefully avoiding extensive motor block may mitigate some of these concerns.14 Retrospective data suggest that obese parturients may have a greater incidence of both hypotension and fetal heart decelerations after initiation of neuraxial analgesia.15 Further study is needed to better define the relationship among obesity, neuraxial block characteristics, maternal hypotension, and effects on fetal heart tracings and obstetric interventions.
Induction of Labor Analgesia
Initiation of neuraxial analgesia in obese parturients is associated with increased time, needle passes, and overall “attempts” in comparison with nonobese parturients. Positioning, equipment choice, and use of ultrasonography may assist anesthesia providers with these difficulties.
Timing of Initiation of Neuraxial Analgesia
There are conflicting motivators regarding the optimal timing of neuraxial block initiation. In favor of early block placement is the potential for lengthy placement time, the desirability of a working catheter in case of urgent cesarean delivery, and evidence indicating that, at least in the general obstetric population, early neuraxial block placement does not increase the likelihood of cesarean delivery.16,17 However, the chance of failure with patient movement and relatively high catheter replacement rates (see Maintenance of Neuraxial Analgesia, below) suggest that attempts to place catheters should not be made until the need is apparent. In our opinion, the benefits of early placement greatly outweigh the risks, provided that meticulous intermittent block evaluation occurs to identify and expediently remedy problems.
Preparation of the Obese Parturient for Neuraxial Block Placement
Achieving an even, balanced sitting position in an obese parturient is time consuming, but worthwhile. In this position the adipose tissue falls laterally, easing palpation of the spinous processes.3,18 This position also affords the shortest distance to the epidural space,19 which is advantageous as this distance is greater in obese parturients.20,21 That depth, however, rarely exceeds 8 cm,20 – 22 making typical 9-cm epidural needles appropriate for most patients.22 Longer needles should be available if needed; caution with these needles is recommended because small changes in needle angle will result in larger deviations in tip position. Occasionally, adipose tissue from the buttocks may be displaced posterior and cephalad with the patient in the sitting position (forming a “shelf”), and this tissue obscures lower back landmarks. Positioning these patients laterally may actually improve the practitioner's ability to palpate landmarks. Additionally, the lateral decubitus position may be helpful if the parturient is too uncomfortable to sit. Finally, the lateral position has the advantage of fewer unintentional epidural venous punctures,23,24 more common in obese parturients,23 although the use of soft, wire-reinforced, spring-wound epidural catheters greatly decreases this complication.25,26
Landmark Location and Ultrasonography
Appropriate landmarks should be sought (Table 2). If lumbar spinous processes are not easily palpable, an imaginary line between the cervical spinous processes and gluteal cleft can help to estimate midline, and a spinal needle can be used to probe for spinous processes. Additionally, parturients themselves can verbally direct needle placement toward the midline. While patients' estimation of “center” is often overly broad, we and others find it helpful when parturients are able to assert that the needle is off midline.27
Alternatively, ultrasound visualization of neuraxial structures can locate midline, help select an optimal insertion point and specific interspace, and estimate epidural space depth. Ultrasound depth estimates have been found to be accurate in obese parturients, although less so at increasing depths.22,28 Identification of appropriate depth and direction decreases the number of needle passes required to locate the epidural space and may prevent threading an epidural catheter into a shallow, false pocket.22,29 Additionally, use of ultrasonography to identify a specific mid- or low-lumbar interspace may prevent practitioners from unintentionally choosing (and potentially puncturing the dura at) an easier-to-palpate high lumbar interspace. Identifying structures with ultrasound can be technically difficult because of excess adipose tissue, but visualization of the spinous process and ligamentum–dura unit was estimated as “good” 70% and 63% of the time, respectively,22 indicating potential utility of this tool in obese parturients. For ultrasonography to be effective in facilitating neuraxial block insertion for obese women, the skill should be mastered through regular practice in nonobese women.
While obesity does not predict a difficult neuraxial block placement per se, an obese parturient with both a poorly flexible back and difficult-to-palpate spinous processes will likely require increases in both placement time and number of needle redirections to reach the epidural space.9,30 Several authors found that “multiple attempts” (not further defined) were needed to place neuraxial catheters in obese parturients,9,30,31 and assistance from a senior obstetric anesthesiologist proved helpful in both placement and eventual block success.9,32 Chin et al. found that for practitioners experienced in ultrasound techniques, ultrasonography facilitated both spinal block placement and efficacy in nonpregnant patients with difficult spinal anatomy, including obese patients with poorly palpable spinous processes.33 Further study is required to better define placement problems and potential solutions.
Choice of Neuraxial Block: Epidural Versus Combined Spinal Epidural
While lean parturients experience fewer epidural catheter failures when analgesia is initiated with a combined spinal epidural (CSE) technique in comparison with traditional epidural technique,34 there are no data regarding CSE versus epidural analgesia for obese parturients. However, locating cerebrospinal fluid during CSE analgesia confirms the epidural needle tip location in the epidural space, i.e., not in a false pocket. Optimal dosing regimens for CSE labor analgesia in obese parturients are not well described, but limited data from cesarean deliveries suggest that standard dosing is acceptable.35
If the choice of CSE analgesia is made, a potential negative in obese parturients is that the practitioner cannot know with certainty that the epidural catheter is properly functioning until after the spinal portion of the CSE technique wanes. A possible solution is to perform the CSE technique and puncture the dura with the spinal needle without injecting medication.36 This will allow the beneficial confirmation of cerebrospinal fluid without negatively obscuring whether the catheter will function properly for a potential urgent cesarean delivery.
Unintentional Dural Puncture and Intrathecal Catheters
Reports are inconsistent as to whether the rate of unintentional dural puncture is higher in obese than in lean parturients.37,38 An option when faced with unintentional dural puncture is the placement of an intrathecal catheter. Intrathecal catheters should provide reliable, rapid-onset analgesia for emergent cesarean delivery. However, many practitioners thread an intrathecal catheter only 2 to 3 cm into the subarachnoid space, making these catheters more prone to dislodging, especially with patient movement during labor. Retrospective data suggest that when an unintentional large-bore dural puncture occurs, obese parturients are less likely to experience a postdural puncture headache than do lean parturients.37,38
MAINTENANCE OF LABOR ANALGESIA
Dosing and Neuraxial Analgesic Requirements
The results of studies assessing whether obesity influences perceived labor pain are inconsistent.38 – 40 Cervical dilation is slower,13,39,41 and the epidural local anesthetic requirements are decreased, resulting in more cephalad initial dermatomal levels for a given volume of local anesthetic.42,43 The reduced volume of the obese parturient's epidural space may contribute to this difference. We typically reduce the initial volume of the epidural bolus by approximately one third in our morbidly obese parturients, and then titrate to the desired effect.
Minimization of extensive motor block will facilitate both patient movement and expulsive efforts. Local anesthetic requirements (and their accompanying motor block) can be decreased by adding adjunctive medications such as opioids or clonidine to the epidural solution,44,45 or by administering epidural maintenance solution as a bolus rather than an infusion.46
Epidural Catheter Failure After Placement
Even after seemingly successful placement, neuraxial catheters in obese parturients remain prone to failure. Narang and Linter reported correlation of one-sided blocks with both obesity and distance to the epidural space,47 but this trend toward unilateral failure was not replicated in other studies.42 Others have proposed that correctly sited catheters fail when sliding skin and subcutaneous adipose tissue cause catheters to dislodge, or catheters are pulled into subcutaneous adipose tissue with position changes.48,49 Hamilton et al. demonstrated an average movement of 1 cm when obese parturients moved from flexed sitting to the lateral position, with a maximum of 4.3 cm.49 Several authors recommend that catheters be taped after the parturient has assumed the lateral position.18,49 Our clinicians (using wire-reinforced single-orifice catheters) prefer to thread extra catheter length (7 to 8 cm) into the epidural space to maintain sufficient catheter depth despite position change. Anecdotally, we find this technique successful; however, others have reported that increased lengths (>5 cm with polyamide catheters) left within the epidural space are associated with both one-sided blocks and increased risk of intravascular placements.26,50,51 Depth of insertion with flexible spring-wound catheters has not been specifically studied, but these catheters may be more likely to curl in the epidural space rather than project laterally or puncture a vein in comparison with stiffer polyamide catheters.
Both patients and nurses should be instructed to protect the catheter site while repositioning in bed. Catheter position and anesthetic levels should be checked regularly (at least every 2 hours) during labor to ensure adequate position and function, focusing on both the right and left sensory levels. Careful attention to optimize neuraxial analgesia may help facilitate conversion to epidural anesthesia for cesarean delivery if needed.
Dresner et al. found a trend toward increased epidural “resites” as BMI increased: 2.4% for BMI <25 kg/m2 versus 6.6% for BMI >40 kg/m2 (P < 0.01).52 Studies describing epidural catheter replacement rates have not thus far discussed the reasons for or the timing of catheter replacement in relation to original catheter placement.
Further study in obese parturients is needed to better characterize why catheters fail, circumstances and practices associated with failure, and methods to promote continued functionality in accurately placed catheters.
We suggest that early preparation, the use of appropriately sized equipment, anticipation of likely problems, and involvement of experienced nursing and anesthesia providers will improve the safety and probability of success of neuraxial labor analgesia when caring for obese parturients (Table 3). Neuraxial analgesia should be initiated in early labor, and the block should be evaluated regularly (at least every 2 hours) to ensure optimal performance and feasible use for cesarean delivery. Throughout the labor and delivery experience, both medical personnel and the parturient should engage in patient, tactful, and complete discussions to properly prepare for and cope with the labor and delivery experience.
Name: Elizabeth H. Ellinas, MD.
Role: This author wrote the manuscript.
Attestation: Elizabeth H. Ellinas approved the final manuscript.
This manuscript was handled by: Cynthia A. Wong, MD.
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