Objective
We sought to estimate the morbidity associated with regional anesthesia in morbidly obese women undergoing scheduled cesarean delivery.
Study Design
This was a retrospective cohort study of women undergoing elective scheduled cesarean delivery from September 2004 through December 2008.
Results
A total of 142 morbidly obese, 251 overweight and obese, and 185 normal-weight women met inclusion criteria. Differences between groups were identified regarding: complicated placement (5.6%, 2.8%, and 0%, respectively; P = .007), failure to establish (2%, 0%, and 0%, respectively; P = .047), and insufficient duration (4%, 0%, and 0%, respectively; P = .02) of regional anesthesia. The groups differed in the frequency of general anesthesia (6%, 0%, and 0%, respectively; P = .003), intraoperative hypotension (3%, 0%, and 0%, respectively; P = .01), and overall anesthetic complications (8.4%, 0%, and 0%, respectively; P < .0001). Prepregnancy body mass index ≥40 kg/m 2 (receiver operating characteristic area under the curve, 0.856; positive likelihood ratio, 4.0) and delivery body mass index ≥45 kg/m 2 (receiver operating characteristic area under the curve, 0.877; positive likelihood ratio, 4.1) were predictive of anesthetic complications.
Conclusion
Morbidly obese women have significant risk for anesthesia complications during cesarean delivery.
The prevalence of morbid obesity (body mass index [BMI] >40 kg/m 2 ) increased by 50% between 2000 and 2005. In the past decade, the rate of morbid obesity among reproductive-age women reached 8%. Morbidly obese women have more common complicated pregnancies, labor dystocia, and cesarean delivery than normal-weight women. A greater risk for death under general anesthesia has been noted for morbidly obese women. While 94% of cesarean deliveries in U.S. academic centers are performed under regional anesthesia, conversion to general anesthesia complicates approximately 0.8% of regional anesthesia attempts in the general population. Obesity has been documented to increase the difficulty of placing regional anesthesia in nonpregnant women. While some studies have found an increased need of conversion to general anesthesia during cesarean delivery in morbidly obese women, others have found similar rates of regional anesthesia failure between obese and nonobese women. The likelihood of regional anesthesia failure at scheduled cesarean delivery in morbidly obese women has not been well established. The aim of this study was to establish the incidence of anesthesia complications among morbidly obese women undergoing scheduled, nonemergent cesarean delivery.
Materials and Methods
In this retrospective cohort study, women undergoing scheduled nonemergent cesarean delivery between September 2004 and December 2008 at an academic tertiary care center were identified using our electronic perinatal database. Those delivering preterm (<37 weeks’ gestation by best estimate) and multiple gestations were excluded, as were those presenting with contractions or membrane rupture prior to their cesarean delivery, and those patients with contraindications to regional anesthesia.
Individual patient charts and anesthesia records were reviewed by a single investigator (L.K.V.). Only those patients who underwent an initial attempt at regional anesthesia placement (spinal, epidural, or combined spinal-epidural [CSE]) were further evaluated. The cohort was divided according to maternal pregravid BMI into 3 groups based on the World Health Organization criteria as follows: morbidly obese (BMI ≥40 kg/m 2 ), overweight and obese (BMI 25-39 kg/m 2 ), and normal weight (BMI <25 kg/m 2 ). Maternal pregravid weight and height were determined by the patient’s medical record. Pregnancy weight gain was calculated as the difference between the weight on admission for delivery and the prepregnancy weight.
Evaluated maternal clinical characteristics included: delivery BMI, race, insurance status, number of prior cesarean deliveries, concurrent medical conditions (eg, asthma, obstructive sleep apnea, diabetes, chronic hypertension, and preeclampsia), age at delivery, and American Society of Anesthesiologists (ASA) physical classification score. The ASA score is a system to assess the degree of a patient’s sickness or physical state prior to surgery, which provides standardization of terminology and allows statistical analysis of outcomes between sites.
The primary outcome measure was the composite morbidity of “anesthesia complications,” defined as the occurrence of ≥1 of the following: failure to establish regional anesthesia necessitating general anesthesia; insufficient duration of regional anesthesia, requiring supplemental intravenous analgesics or general anesthesia; profound intraoperative hypotension; cephalad spread of spinal block, resulting in insufficient respiratory effort requiring intubation; postdural puncture headache; and significant sequelae, including paralysis, cardiac arrest attributed to anesthetic toxicity, epidural abscess, aspiration, and death attributed to aspiration or failed intubation. Profound intraoperative hypotension was defined as ≥3 recorded blood pressures of <80 mm Hg systolic or 50 mm Hg diastolic necessitating intensive volume resuscitation, pressor support, and prolonged monitoring. Cephalad spread of spinal block (“high spinal”) was defined as documentation of loss of maternal respiratory drive followed by maternal oxygen desaturation requiring intubation. Complicated placement of regional anesthesia was defined as cases requiring >3 attempts at placement.
Secondary outcome measures were: number of attempts at placement of regional anesthesia and frequency of requiring supplemental intravenous analgesia. All spinal blocks were single-shot and performed in the upright sitting position. In all, 12-15 mg of bupivacaine (0.75%) plus 0.2-0.25 mg of intrathecal morphine were injected at the L3-L4 or L2-L3 interspace.
Data were analyzed using commercially available software (SPSS, version 16.0; SPSS Inc, Chicago, IL). A 2-tailed probability of P < .05 was considered to be statistically significant. The χ 2 test was utilized for binomial variables. Wilcoxon rank sum test and the Kruskal-Wallis test were utilized for discrete and continuous variables. Multivariable logistic regression analysis was performed to adjust for potential confounding factors for the maternal morbidity composite outcome and for preterm delivery. Nominal 2-sided P values are reported. P < .05 was considered statistically significant. Receiver operating characteristic analyses were performed for prediction of the composite outcome of any regional anesthesia complication. Factors included were pregravid BMI, delivery BMI, pregnancy weight gain, and ASA status.
This study was powered to detect a difference in composite morbidity in morbidly obese women, using normal-weight women as a comparative group. Assuming a 1% rate of anesthesia morbidity documented for normal-weight women, 136 women would be needed in each group to detect a 10-fold increase in the risk of the primary outcome at an alpha of 0.05 and beta of 0.20. This study was approved by the institutional review board of MetroHealth Medical Center, Cleveland, OH.
Results
A total of 578 patients met the inclusion criteria for this analysis, including 142 morbidly obese, 251 overweight and obese, and 185 normal-weight women. Baseline demographic and clinical characteristics are presented in Table 1 . The 3 groups were similar in age and number of prior cesarean deliveries. Morbidly obese women were more frequently African American, gained less weight during pregnancy, had more comorbid conditions, and had higher ASA physical classification scores than the other groups. Anesthesia and operative outcome for the 3 groups are presented in Table 2 . Complicated placement of regional anesthesia was significantly more common in morbidly obese women when differences were examined among all groups; however, the difference between morbidly obese and obese/overweight women was not significant (5.6% vs 2.8%; P = .17). Morbidly obese women also had longer anesthesia and operative times compared to obese women ( P < .0001, P < .0001).
| Characteristic | MO | Overweight and O | Nl | P value MO vs O | P value MO vs Nl |
|---|---|---|---|---|---|
| n | 142 | 251 | 185 | ||
| Age, y | 28.2 ± 5.52 | 27.5 ± 6.08) | 27.7 ± 6.35 | .1 | .3 |
| Race | |||||
| Black | 74 (51.7) | 101 (40.1) | 34 (18.6) | < .0001 | < .0001 |
| Caucasian | 55 (38.5) | 114 (45.2) | 99 (54.1) | .02 | .005 |
| Hispanic | 13 (9.1) | 35 (13.9) | 38 (20.8) | .008 | .004 |
| Others | 1 (0.7) | 2 (0.8) | 10 (5.5) | .002 | .03 |
| Insurance status | |||||
| Government | 108 (75.5) | 181 (71.8) | 103 (56.3) | .002 | .003 |
| Commercial | 20 (14) | 62 (24.6) | 58 (31.7) | .001 | < .0001 |
| None | 16 (11.2) | 8 (3.2) | 20 (10.9) | .002 | 1.0 |
| Pregravid BMI, kg/m 2 | 46.8 ± 6.87 | 31.8 ± 4.53) | 22.0 ± 1.92 | .03 | < .0001 |
| Delivery BMI, kg/m 2 | 49.4 ± 7.02 | 36.7 ± 5.42) | 27.8 ± 2.50) | .4 | < .0001 |
| Prior cesarean deliveries | 1.32 (0.91) | 1.19 (0.91) | 1.12 (0.83) | .8 | .7 |
| ASA score (U) | 2 [2–2] | 1 [1–2] | 1 [1–1] | < .0001 | .4 |
| Chronic hypertension | 41 (28.7) | 24 (9.5) | 3 (1.6) | < .0001 | < .0001 |
| Preeclampsia | 11 (7.7) | 11 (4.4) | 0 | .001 | < .0001 |
| Diabetes | 30 (21) | 37 (14) | 12 (6.6) | < .0001 | < .0001 |
| Asthma | 35 (24.5) | 42 (16.7) | 16 (8.7) | < .0001 | < .0001 |
| Obstructive sleep apnea | 9 (6.3) | 3 (1.2) | 0 | < .0001 | < .0001 |
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