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Retrospective analysis of anesthetic interventions for obese patients undergoing elective cesarean delivery
Journal of Clinical Anesthesia (2010) 22, 519–526
Original contribution
Retrospective analysis of anesthetic interventions for obese patients undergoing elective cesarean delivery☆,☆☆,★,★★ Alexander Butwick FRCA (Instructor) a,⁎, Brendan Carvalho FRCA (Assistant Professor) a , Christina Danial (Medical Student)b , Edward Riley MD (Associate Professor)a a
Department of Anesthesia, Stanford University School of Medicine, Stanford, CA 94305, USA Stanford University School of Medicine, Stanford, CA 94305, USA
b
Received 23 February 2009; revised 18 January 2010; accepted 28 January 2010
Keywords: Cesarean section; Obesity; Obstetric anesthesia
Abstract Study Objective: To examine the relationship between body mass index (BMI), perioperative times, and anesthetic interventions in patients undergoing elective cesarean delivery. Design: Retrospective chart review. Setting: University-affiliated hospital. Measurements: All patients were ranked according to BMI (kg/m2) at the time of delivery. The BMI groups were designated a priori: ≤ 29.9 kg/m2 (Group C); 30-34.9 kg/m2 (Group I); 35-39.9 kg/m2 (Group II), and ≥ 40 kg/m2 (Group III). One hundred patients (25 pts per group) underwent elective cesarean delivery. Data collected included anesthetic technique, perioperative times, anesthesia-related costs, and neonatal outcomes. Main Results: A higher percentage of Group III patients (60%) received combined spinal-epidural (CSE) anesthesia than did Group C or Group I (18% and 16%, respectively; P b 0.05). The total intraoperative period was significantly longer in Group III (101 min) compared with Groups C, I, and II (81 min, 90 min, and 92 min, respectively; P b 0.05). Total intraoperative time increased significantly with BMI (R = 0.394 kg/m2; P b 0.001). The highest anesthesia-related costs during the study were generated by patients with BMI ≥ 40 kg/m2. Conclusion: Our single-center experience showed that choice of anesthetic technique (CSE vs. spinal anesthesia) varies according to obesity class. Longer intraoperative periods must be considered in deciding upon the mode of anesthesia for patients with BMI ≥ 40 kg/m2 who undergo elective cesarean delivery. © 2010 Elsevier Inc. All rights reserved.
☆
This study was conducted at Lucile Packard Children’s Hospital and Stanford University School of Medicine, Stanford, CA. Presented in part at the 40th Annual Meeting of the Society for Obstetric Anesthesia and Perinatology (SOAP), April 2008, Chicago, IL, USA. ★ Funded internally by the Department of Anesthesia, Stanford University Medical Center. The authors involved in this study and the preparation of the manuscript received no external funding. ★★ The authors had no affiliation or relationship with any company or organization that has a potential interest in the outcome of the study. ⁎ Corresponding author. Department of Anesthesia, MC: 5640, Stanford University School of Anesthesia, 300 Pasteur Dr., Stanford, CA 94305, USA. Tel.: +1 650 736 8513; fax: +1 650 725 8544. E-mail address: [email protected] (A. Butwick). ☆☆
0952-8180/$ – see front matter © 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.jclinane.2010.01.005
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1. Introduction Maternal obesity in pregnancy has become a major public health concern in the United States. Population-based studies estimate that 29% and 8% of women of reproductive age in the U.S. have a body mass index (BMI) of at least 30 kg/m2 and 40 kg/m2, respectively [1], and that the prevalence of maternal obesity (based on a study in 9 U.S. states) has increased from 13% between 1993-1994 to 22% between 2002-2003 [2]. Obese women are at increased risk for requiring cesarean delivery [3,4]. Although regional (neuraxial) anesthetic techniques are the most commonly performed techniques for patients undergoing cesarean delivery, the anesthetic management of morbidly obese parturients requires careful planning and may often be particularly challenging. Technical difficulties may be encountered during neuraxial anesthetic placement for obese patients, and achieving adequate surgical anesthesia may vary depending on the chosen mode of neuraxial anesthesia [5]. Other perioperative complications affecting the anesthetic management of obese patients undergoing cesarean delivery include difficulty in patient positioning on the operating table, longer surgical times, and increased risk of postpartum hemorrhage [6,7]. The aim of this retrospective study was to examine the relationship between BMI and perioperative times, type and complexity of anesthetic interventions, and costs related to the provision of anesthesia in patients undergoing elective cesarean delivery. We hypothesized that maternal obesity would result in longer perioperative times, a higher rate of catheter-based neuraxial anesthetic techniques [notably combined spinal-epidural anesthesia (CSE) vs. single-shot spinal anesthesia (SSS)], and increased anesthesia-related costs.
2. Materials and methods After obtaining Lucile Packard Children's Hospital Ethics Committee approval, a retrospective chart review of all patients who underwent elective cesarean delivery over a one-year period (April 2006 to June 2007) was conducted. Lucile Packard Children's Hospital is a university tertiarycare referral center, and conducts approximately 5,000 deliveries per year with a cesarean delivery rate of approximately 30%. Study investigators accessed the hospital institutional database to obtain baseline data on all patients who underwent elective cesarean delivery during the study period. All patients were ranked according to their BMI at the time of delivery. The World Health Organization (WHO) and the National Institute of Health definitions were used to calculate BMI [weight (kg)/height (m2 )], with obesity classified as a BMI of 30 kg/m2 or greater [8]. All patients during the study period were ranked according to BMI at the time of delivery.
A. Butwick et al. The study groups were designated a priori and were subclassified (using WHO criteria) as follows: Group C (BMI ≤ 29.9 kg/m2; control group), Group 1 (BMI = 3034.9 kg/m2), Group II (BMI = 35-39.9 kg/m2), and Group III (BMI N 40 kg/m2) [8]. Following ranking of patients according to their BMI, 25 patients per group were randomly selected using a Microsoft Excel random number selection tool (Microsoft, Redmond, WA, USA). The following data were collected: maternal and obstetric demographic data, antepartum medical complications, anesthetic technique, hospital billing information related to the provision of anesthesia, and neonatal outcomes. Time periods were also recorded, including anesthesia induction time (time from start of anesthetic technique to surgical start), surgical time (from start to completion of surgery), recovery time, and hospital inpatient admission period. Professional costs for anesthesia coverage were also calculated. We used Medicare rates, which are commonly used in health services research, to estimate costs of physician services. The costs of an anesthesiologist's professional service were obtained using the Medicare reimbursement rate of ⁎$21/unit (USD; with geographical adjustment for our institution), and the ASA Relative Value system (with 7 base units startup + 4 units/hr for the perioperative period)1 [9]. The costs of equipment used for neuraxial anesthesia, based on current charges by individual manufacturers, also were calculated. The direct hospital costs based on the purchase price for a standard spinal anesthesia kit (Pencan Spinal Needle Tray; B. Braun Medical, Inc., Bethlehem, PA, USA) was $180, and for CSE anesthesia [26-gauge Gertie Marx spinal needle (IMD, Inc.; Huntsville, UT, USA) + standard epidural kit (Perifix FX Custom Epidural Anesthesia Tray; B. Braun Medical, Inc.] was $229. We did not assess other non-anesthetic or surgical equipment costs.
2.1. Statistical analysis Data are presented as means (SD), medians (interquartile ranges), and absolute values (percentages) where appropriate. Analysis was performed with SPSS Version 16 software (SPSS Institute, Inc., Chicago, IL, USA). Data were assessed for normal distribution of variance using QQ plots and Kolmogorov-Smirnov tests. One-way analysis of variance (ANOVA) and Kruskal-Wallis tests were used to compare normally distributed and non-normally distributed variables between groups, respectively. For pairwise comparison between groups, the two-sample t-test or the WilcoxonMann-Whitney test was used. Categorical data were assessed with Fisher's exact test or χ2 test, as appropriate. A P-value b 0.05 was considered statistically significant. Pearson correlation was used to examine the association between BMI and perioperative time periods and duration of hospital 1 ASA relative values guide for 2008. Park Ridge IL: American Society of Anesthesiologists; 2008.
Obese patients and cesarean delivery Table 1
521
Demographic and obstetric data BMI ≤ 29.9 kg/m2 (n = 25)
Age (yrs) 33.8 (5.7) Parity 1 [1,1] Gestational age (wks) 38 [37,38] BMI (kg/m2) 25.9 [24.7,26.7] Race Caucasian = 44% Hispanic = 20% Asian- Pacific = 28% Asian- Indian = 8%
BMI = 30-34.9 kg/m2 (n = 25)
BMI = 35-39.9 kg/m2 (n = 25)
BMI ≥ 40 kg/m2 (n = 25)
Overall P-value
34.2 (5.9) 1 [1,1] 38 [38,39] 32.2 [31.5,33.0] Caucasian = 48% Hispanic = 32% Asian- Pacific = 12% African- American = 8%
30.5 (6.1) 1 [1,2] 38 [38,39] 37.1 [36.2,38.4] Caucasian = 24% Hispanic = 56% Asian- Pacific = 4% African- American = 4% Asian- Indian = 8% Unknown = 4%
31.3 (6.1) 1 [1,2] ⁎, † 38 [37,39] 44.2 [41.7,48.6] Caucasian = 36% Hispanic = 28% Asian- Pacific = 28% African- American = 8%
0.08 0.05 0.31 0.73
Data are presented as means (SD), medians [IQR], and numbers (%). BMI = body mass index. ⁎ BMI ≤ 29.9 kg/m2 vs. BMI ≥ 40 kg/m2; P b 0.05. † BMI 30-34.9 kg/m2 vs. BMI ≥ 40 kg/m2; P b 0.05.
admission. Based upon previously published data [6], we predicted that a sample size of 25 patients per group was required to detect a 33% difference between BMI groups in the mode of anesthetic technique (CSE vs. spinal anesthesia), using ANOVA for multiple group comparisons (power = 0.8; α = 0.05).
3. Results Demographic and obstetric data are shown in Table 1. Mode of anesthesia significantly differed between groups, with more patients in Group III receiving a CSE technique than patients in Groups C, I, or II (Table 2). No patient received general anesthesia as the primary mode of anesthesia. One Group III patient who received a CSE
Table 2
technique required conversion to general anesthesia during the intraoperative period. No differences were noted in the doses for intrathecal drugs (bupivacaine, fentanyl, morphine) given between groups (12 mg, 10 μg, and 200 μg, respectively). There were no differences between study groups in the doses of intravenous (IV) vasopressor administered (phenylephrine, ephedrine) or volumes of intraoperative IV fluid given (Table 2). Intraoperative time periods [from pt entering operating room (OR) to surgical start time (OR-Sx time), surgical start time to uterine incision (Sx-UI time), and total intraoperative time] were significantly longer in Group III than Groups C, I, or II (Table 3). No differences were found between groups for uterine incision-delivery time. Linear regression analysis showed that specific intraoperative time periods (OR-Sx time, Sx-UI time, and total intraoperative time) significantly increased with patient BMI (R = 0.349,
Perioperative anesthetic data
Mode of anesthesia: Spinal CSE Patients with CSE requiring epidural supplementation Total dose phenylephrine (μg) Total dose ephedrine (mg) Total IV fluids: Crystalloid (mL) Colloid (mL)
BMI ≤ 29.9 kg/m2 (n = 25)
BMI = 30-34.9 kg/m2 (n = 25)
BMI = 35-39.9 kg/m2 (n = 25)
BMI ≥ 40 kg/m2 (n = 25)
Overall P-value
18 (72%) 7 (18%)
21 (84%) 4 (16%)
17 (68%) 8 (32%)
0.005 0.005
0
1
1
9 (36%) ⁎, †, ‡ 15 (60%) ⁎, †, ‡ [Data missing on one pt] 6 [Data missing on one pt]
0.14
450 [237, 688] 20 [20,20]
500 [500, 1,000] 15 [15,15]
450 [450, 1,000] 30 [25,35]
550 [550, 1,500] 17.5 [17.5,20]
1.0 0.18
1,454 (589) 500 [550, 850]
1,672 (522) 500 [500, 500]
1,494 (550) 500 [500, 500]
1,572 (577) 500 [500, 500]
0.54 0.11
Data are presented as means (SD), medians [IQR], or numbers (%). BMI = body mass index, CSE = combined spinal-epidural anesthesia, IV = intravenous. ⁎ BMI ≤ 29.9 kg/m2 vs. BMI ≥ 40 kg/m2; P ≤ 0.05. † BMI 30-34.9 kg/m2 vs. BMI ≥ 40 kg/m2; P = 0.001. ‡ BMI 35-39.9 kg/m2 vs. BMI ≥ 40 kg/m2; P = 0.03.
522 Table 3
A. Butwick et al. Intraoperative times, estimated blood loss, and recovery data
OR-Sx time (min) Sx-UI time (min) UI-delivery time (min) Total intraoperative time (min) EBL (mL) Preoperative HCT (%) Postoperative HCT (%) Duration of inpatient admission (days)
BMI ≤ 29.9 kg/m2 (n = 25)
BMI = 30-34.9 kg/m2 (n = 25)
BMI = 35-39.9 kg/m2 (n = 25)
BMI ≥ 40 kg/m2 (n = 25)
Overall P-value
28 [23,34] 11 [7,13] 2 [1,2] 81 [73,92] 650 [550,850] 36.1 [34.0,37.8] 30.8 [28.8,32.1] 4 [3,4]
30 [24,35] 9 [8,12] 2 [1,3] 90 [77,96] 700 [600,800] 35.6 [34.0,38.1] 30.4 [38.6,32.9] 4 [3,4]
27 [21,35] 11 [9,17] 2 [1,3] 92 [76,108] 800 [700,800] 35.5 [34.1,38.4] 30.2 [27.8,31.9] 4 [3,4]
36 [28,48] ⁎, †, ‡ 15 [12,25] ‡, #, § 2 [1,3] 101 [87,120] †, ‡, # 800 [600,1000] 35.6 [32.1,38.1] 30.5 [27.9,32.6] 4 [4,4]
0.03 b0.001 0.25 0.002 0.50 0.97 0.718 0.90
Data are presented as medians [IQRs] or numbers (%). BMI = body mass index, OR-Sx time = time from patient entering operating room to start of surgery, Sx-UI time = time from start of surgery to uterine incision, UI = uterine incision, EBL = estimated blood loss, HCT = Hematocrit. ⁎ BMI ≤ 29.9 kg/m2 vs. BMI ≥ 40 kg/m2 ; P ≤ 0.05. † BMI 30-34.9 kg/m2 vs. BMI ≥ 40 kg/m2; P ≤ 0.05. ‡ BMI 35-39.9 kg/m2 vs. BMI ≥ 40 kg/m2; P ≤ 0.05. § BMI ≤ 29.9 kg/m2 vs. BMI ≥ 40 kg/m2; P ≤ 0.001. # BMI 30-34.9 kg/m2 vs. BMI ≥ 40 kg/m2; P ≤ 0.001.
0.440, and 0.394 kg/m2; P b 0.001, respectively) (Figs. 1, 2, and 3). No differences between groups were observed for estimated blood loss (EBL) or preoperative or the earliest postoperative hematocrit (Hct) values (Table 3). No patients were given transfusion therapy (ie, red blood cells, blood products) during the study period. There were no differences between groups in duration of hospital stay following cesarean delivery (Table 3). Costs for anesthesia coverage during the perioperative period and costs for the anesthesia kit used for neuraxial block placement were significantly higher in Group III patients than the other study groups (Table 4). Neonatal
outcome data are shown in Table 5. No differences in APGAR scores, neonatal weight, or neonatal intensive care unit (NICU) admission between groups were observed.
Fig. 1 Correlation between time from patient entering operating room to surgical start time (OR-Sx time) and body mass index (BMI).
Fig. 2 Correlation between time from surgical start time to uterine incision (Sx-UI time) and body mass index (BMI).
4. Discussion Our results suggest that there is increased use of a CSE anesthetic technique in morbidly obese patients (BMI ≥ 40 kg/m2) compared with non-obese patients, as well as patients in lower obesity classes (BMI = 30-39.9 kg/m2),
Obese patients and cesarean delivery
523
Fig. 3 Correlation between total intraoperative time and body mass index (BMI).
undergoing elective cesarean delivery. The longer perioperative times observed in morbidly obese patients in our study likely partly explain the rationale for using a CSE technique in this patient subpopulation. Although previous studies have suggested that longer operative times occur in obese patients undergoing cesarean delivery, criteria for defining obesity were based on patient weight at delivery, and they varied between studies (≥ 90135 kg, ie, 200-300 lbs) [10-12]. No previous studies have specifically compared perioperative times and anesthetic interventions for elective cesarean delivery between obesity classes using WHO criteria. In addition, there is currently no consensus as to preferred approaches for neuraxial anesthesia in obese patients undergoing elective cesarean delivery. A study by Hood et al. [6] compared anesthetic and obstetric outcomes in morbidly obese (N 136.4 kg) and matchedcontrol patients. In this study, epidural anesthesia was
Table 4
performed more commonly in morbidly obese patients than in the control group (b 136.4 kg; 70.8% vs. 46.4%; P b 0.05) for cesarean delivery [6]. However, wide differences in BMI were reported between groups (BMI = 52.6 vs. 27.8 kg/m2; morbidly obese group vs. control group, respectively). In addition, data were collected for patients delivering between the years 1978 through 1989, and neuraxial anesthetic techniques have diversified since the publication of that study (with SSS anesthesia being widely used for elective cesarean delivery in non-obese patients) [13]. The lower rate of SSS anesthesia in the morbidly-obese group substantiates previously held concerns about this technique in this patient sub-population, including inadequate intraoperative anesthesia and the duration of surgery outlasting the period of spinal anesthesia [6]. The use of a CSE technique for obese patients undergoing cesarean delivery is advantageous as this technique allows neuraxial blockade to be maintained (with additional boluses of local anesthetic via the epidural catheter in-situ) after establishing adequate surgical anesthesia with a spinal technique. Based on our results, a catheter-based neuraxial approach appears to be justified for patients in Group III due to the longer intraoperative times, and the higher percentage of patients who received epidural supplementation following CSE anesthesia in Group III versus Groups I, II, and C. However, it is unclear whether epidural supplementation was given to prevent or treat intraoperative breakthrough pain; therefore, we acknowledge that the presence of an epidural catheter may be a potential confounder for increased epidural supplementation. Our results suggested a trend towards longer OR-Sx time, Sx-UI time, and total intraoperative times with increasing BMI, which was substantiated following linear regression analysis. Further work is necessary to assess the maternal and neonatal outcomes of prolonged perioperative times in patients undergoing elective as well as non-elective cesarean delivery. Our review of anesthesia records could not elucidate specific causes for the longer OR-Sx times observed in Group III compared with the other study groups. Technical
Cost data for obstetric anesthesiologist services and for anesthesia kit used for neuraxial block placement BMI ≤ 29.9 kg/m2 (n = 25)
BMI = 30-34.9 kg/m2 (n = 25)
BMI = 35-39.9 kg/m2 (n = 25)
BMI ≥ 40 kg/m2 (n = 25)
Overall P-value
Cost of anesthesiologist 250.20 (19.50) 264.41 (32.18) 262.92 (31.57) 308.88 (40.36) ⁎, †, ‡ b 0.001 services (US$) 0.006 Costs of anesthesia 180.00 [180.00-229.00] 180.00 [180.00-180.00] 180.00 [180-229.00] 229.00 [180.00-229.00] †, §, # kit (USD$) Data are presented as means (SD) or medians [IQR]. BMI = body mass index. ⁎ BMI ≤ 29.9 kg/m2 vs. BMI ≥ 40 kg/m2; P ≤ 0.001. † BMI 30-34.9 kg/m2 vs. BMI ≥ 40 kg/m2; P ≤ 0.001. ‡ BMI 35-39.9 kg/m2 vs. BMI ≥ 40 kg/m2; P ≤ 0.001. § BMI ≤ 29.9 kg/m2 vs. BMI ≥ 40 kg/m2; P ≤ 0.05. # BMI 35-39.9 kg/m2 vs. BMI ≥ 40 kg/m2; P ≤ 0.05.
524 Table 5
A. Butwick et al. Neonatal data
APGAR (one min) APGAR (5 min) Neonatal weight (kg) NICU admission
BMI ≤ 29.9 kg/m2 (n = 25)
BMI = 30-34.9 kg/m2 (n = 25)
BMI = 35-39.9 kg/m2 (n = 25)
BMI ≥ 40 kg/m2 (n = 25)
Overall P-value
8 [8, 9] 9 [9, 9] 3,340 [2,861, 3,577] 3 (12%)
8 [8, 9] 9 [9, 9] 3,538 [3,266, 4,050] 2 (8%) (n = 24)
8 [8, 9] 9 [9, 9] 3,470 [3,197, 3,776] 3 (12%)
8 [7, 9] 9 [9, 9] 3,686 [3,312, 4,059] 2 (8%)
0.20 0.63 0.10 0.94
Data are presented as medians [IQR] or numbers (%). BMI = body mass index, NICU = neonatal intensive care unit.
problems, such as difficulty in optimizing patient position and in identifying surface landmarks, prior to neuraxial block placement may have contributed to the longer OR-Sx time noted in Group III. A recent study showed a positive correlation with BMI and depth to epidural space, and included a review of earlier studies corroborating the association between BMI and depth to epidural space [14]. In our study, more Group III patients received a CSE technique than did the other study groups. We speculate that the additional time taken for CSE block placement may have contributed to longer OR-Sx times in Group III compared with other groups who received mostly spinal anesthesia. One Group III patient required conversion from a regional to a general anesthetic during the intraoperative period; no details were available (following chart review) to explain the reason for the change in anesthetic technique. A general anesthetic technique may be necessary to manage intraoperative breakthrough pain following unsuccessful neuraxial anesthesia. However, obese parturients are at increased risk of failed or difficult endotracheal intubation [15], and failed intubation and aspiration are major causes of death in obese patients undergoing general anesthesia for cesarean delivery. As a result, achieving satisfactory surgical anesthesia with a neuraxial technique has important implications for maternal outcome in obese patients requiring cesarean delivery. No previous study has assessed the cost implications associated with anesthesia coverage and equipment costs for obese patients undergoing elective cesarean delivery. Longer perioperative periods substantiate the finding of higher total cost of anesthesia coverage for patients in BMI Group III versus Group C ($308.88 vs $250.20 USD, respectively). In addition, a higher percentage of Group III patients received a CSE technique, which is associated with higher equipment costs than is SSS anesthesia. However, we did not account for other direct or indirect costs associated with increased OR time (eg, hospital costs for obstetrician, surgical assistant, OR nurses) [16]. No differences in doses of intrathecal bupivacaine, fentanyl, or morphine were observed between study groups. Although concern has been expressed about the unpredictable extent of spread of local anesthesia following spinal anesthesia [17], previous studies have suggested that BMI does not significantly affect spinal block levels in pregnant patients receiving hyperbaric spinal local anesthetic mixtures
[18-22]. No differences in total doses of vasopressors (phenylephrine, ephedrine) or IV fluid requirements were seen between groups. We did not specifically collect intraoperative hemodynamic data; thus, it is unclear whether significant differences in cardiovascular parameters occurred between obese and non-obese patients undergoing spinal anesthesia for cesarean delivery. No differences were observed between groups for EBL or preoperative or postoperative Hct values. Our results contrast with those of Perlow et al. and Johnston et al., who noted significantly higher EBL values in obese patients undergoing cesarean delivery versus nonobese patients [10,11]. However both studies included data from patients undergoing elective and nonelective cesarean delivery, and it is possible that factors associated with labor may have influenced EBL values. Variations in surgical technique also may have influenced intraoperative EBL [12]. In our study, the duration of inpatient postpartum admission was similar between groups. These results contrast with those of Hood et al. and Perlow et al., who reported longer periods of hospitalization in obese patients following cesarean delivery [6,11]. Similarly, Chu et al. reported that mean durations of hospital stay are greater in women with increased BMI, a finding that relates to higher rates of cesarean delivery and obesity-related co-morbidity [23]. However, these studies included patients undergoing elective and nonelective cesarean deliveries; thus, it is possible that higher peripartum and postpartum complication rates may have affected duration of inpatient admission postoperatively (eg, postoperative endometritis, wound infections, wound dehiscence). Our study was also underpowered to find differences in this outcome measure. Neonatal outcomes were similar between all groups (ie, APGAR scores, neonatal weight), with low rates of admission to the NICU. There are limited data assessing perinatal outcomes in obese patients undergoing elective cesarean delivery. However, a previous study assessing perinatal outcomes did not observe significant differences in the rate of NICU admission for infants born to healthy mothers with varying pre-pregnancy weights [24]. A number of factors may limit the generalizability of our findings. Individual differences in surgical practice among obstetricians are likely to have had an impact on perioperative time periods and surgical outcomes between study
Obese patients and cesarean delivery groups. A number of anesthetic factors may have influenced difficulty in block placement and OR-Sx times, including experience of the anesthesia provider performing neuraxial blockade (Resident, Fellow, Attending Physician), suboptimal patient positioning (reduced flexion), and difficulty in palpation [25]. All neuraxial blocks at our center are directly supervised by experienced obstetric anesthesia attendings, a fact that may have mitigated such incidents. Although our results show that rates of CSE were high in patients with a BMI ≥ 40 kg/m2, over a third of patients underwent SSS anesthesia for elective cesarean section. Furthermore, the rates of SSS and CSE did not differ significantly between lower BMI classes. We did not explore the basis for these variations in anesthetic technique. Physicians may individualize their choice of neuraxial technique based on specific factors, eg, individual experience with SSS versus CSE techniques, perceived surgical experience of the obstetrician, differences in patient positioning in the OR, presence of a reassuring versus nonreassuring airway. Further studies are warranted to investigate physician preferences for neuraxial techniques for different BMI classes, and to compare anesthetic outcomes between different catheter-based techniques, eg, epidural, CSE, and continuous spinal catheter in morbidly obese pregnant patients. There are potential limitations associated with a CSE technique in morbidly obese patients undergoing elective cesarean delivery. Failure to obtain cerebrospinal fluid with the spinal needle while using a CSE technique may occur (3% to 5% of CSE techniques) [26], which may require converting to epidural anesthesia or repeating neuraxial block placement. In addition, with a CSE technique the epidural catheter is not formally tested prior to surgery to assess efficacy following epidural bolus administration. If intraoperative epidural supplementation fails to provide adequate surgical anesthesia, there may be the increased risk of the patient experiencing intraoperative pain and of conversion to general anesthesia. The use of an “epidural only” technique prior to surgery would confirm the success or failure of achieving adequate surgical anesthesia following epidural bolus administration. If epidural anesthesia proved inadequate following block placement, the anesthesiologist could perform an alternative technique (eg, epidural catheter replacement) to achieve adequate surgical anesthesia. Patients receiving a CSE technique for elective cesarean delivery have lower intraoperative pain scores, shorter intraoperative times, and higher maternal satisfaction than patients receiving an “epidural only” technique [27,28]. Furthermore, catheters inserted using a CSE technique are associated with a lower failure rate compared with an epidural technique [29-32]. In conclusion, morbidly obese (BMI ≥ 40 kg/m 2 ) pregnant patients are more likely to receive CSE anesthesia for elective cesarean delivery than are patients with lower BMIs. At our academic institution, the increased use of catheter-based neuraxial techniques in morbidly obese
525 patients versus patients with lower BMIs may be justified due to longer intraoperative times and a greater requirement for intraoperative epidural supplementation. The cost of anesthesia coverage and hospital costs for anesthesia equipment were also higher in morbidly obese patients than in patients with lower BMIs.
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A. Butwick et al. spread of hyperbaric lidocaine in the postpartum patient? Reg Anesth 1994;19:330-4. Norris MC. Height, weight, and the spread of subarachnoid hyperbaric bupivacaine in the term parturient. Anesth Analg 1988;67:555-8. Norris MC. Patient variables and the subarachnoid spread of hyperbaric bupivacaine in the term parturient. Anesthesiology 1990;72:478-82. Chu SY, Bachman DJ, Callaghan WM, et al. Association between obesity during pregnancy and increased use of health care. N Engl J Med 2008;358:1444-53. Rosenberg TJ, Garbers S, Chavkin W, Chiasson MA. Prepregnancy weight and adverse perinatal outcomes in an ethnically diverse population. Obstet Gynecol 2003;102(5 Pt 1):1022-7. Ellinas EH, Eastwood DC, Patel SN, Maitra-D'Cruze AM, Ebert TJ. The effect of obesity on neuraxial technique difficulty in pregnant patients: a prospective, observational study. Anesth Analg 2009;109: 1225-31. Herbstman CH, Jaffee JB, Tuman KJ, Newman LM. An in vivo evaluation of four spinal needles used for the combined spinal-epidural technique. Anesth Analg 1998;86:520-2.
[27] Davies SJ, Paech MJ, Welch H, Evans SF, Pavy TJ. Maternal experience during epidural or combined spinal-epidural anesthesia for cesarean section: a prospective, randomized trial. Anesth Analg 1997;85:607-13. [28] Karaman S, Akercan F, Akarsu T, Firat V, Ozcan O, Karadadas N. Comparison of the maternal and neonatal effects of epidural block and of combined spinal-epidural block for Cesarean section. Eur J Obstet Gynecol Reprod Biol 2005;121:18-23. [29] Eappen S, Blinn A, Segal S. Incidence of epidural catheter replacement in parturients: a retrospective chart review. Int J Obstet Anesth 1998;7: 220-5. [30] Lee S, Lew E, Lim Y, Sia AT. Failure of augmentation of labor epidural analgesia for intrapartum cesarean delivery: a retrospective review. Anesth Analg 2009;108:252-4. [31] Norris MC. Are combined spinal-epidural catheters reliable? Int J Obstet Anesth 2000;9:3-6. [32] Pan PH, Bogard TD, Owen MD. Incidence and characteristics of failures in obstetric neuraxial analgesia and anesthesia: a retrospective analysis of 19,259 deliveries. Int J Obstet Anesth 2004;13: 227-33.
Original contribution
Retrospective analysis of anesthetic interventions for obese patients undergoing elective cesarean delivery☆,☆☆,★,★★ Alexander Butwick FRCA (Instructor) a,⁎, Brendan Carvalho FRCA (Assistant Professor) a , Christina Danial (Medical Student)b , Edward Riley MD (Associate Professor)a a
Department of Anesthesia, Stanford University School of Medicine, Stanford, CA 94305, USA Stanford University School of Medicine, Stanford, CA 94305, USA
b
Received 23 February 2009; revised 18 January 2010; accepted 28 January 2010
Keywords: Cesarean section; Obesity; Obstetric anesthesia
Abstract Study Objective: To examine the relationship between body mass index (BMI), perioperative times, and anesthetic interventions in patients undergoing elective cesarean delivery. Design: Retrospective chart review. Setting: University-affiliated hospital. Measurements: All patients were ranked according to BMI (kg/m2) at the time of delivery. The BMI groups were designated a priori: ≤ 29.9 kg/m2 (Group C); 30-34.9 kg/m2 (Group I); 35-39.9 kg/m2 (Group II), and ≥ 40 kg/m2 (Group III). One hundred patients (25 pts per group) underwent elective cesarean delivery. Data collected included anesthetic technique, perioperative times, anesthesia-related costs, and neonatal outcomes. Main Results: A higher percentage of Group III patients (60%) received combined spinal-epidural (CSE) anesthesia than did Group C or Group I (18% and 16%, respectively; P b 0.05). The total intraoperative period was significantly longer in Group III (101 min) compared with Groups C, I, and II (81 min, 90 min, and 92 min, respectively; P b 0.05). Total intraoperative time increased significantly with BMI (R = 0.394 kg/m2; P b 0.001). The highest anesthesia-related costs during the study were generated by patients with BMI ≥ 40 kg/m2. Conclusion: Our single-center experience showed that choice of anesthetic technique (CSE vs. spinal anesthesia) varies according to obesity class. Longer intraoperative periods must be considered in deciding upon the mode of anesthesia for patients with BMI ≥ 40 kg/m2 who undergo elective cesarean delivery. © 2010 Elsevier Inc. All rights reserved.
☆
This study was conducted at Lucile Packard Children’s Hospital and Stanford University School of Medicine, Stanford, CA. Presented in part at the 40th Annual Meeting of the Society for Obstetric Anesthesia and Perinatology (SOAP), April 2008, Chicago, IL, USA. ★ Funded internally by the Department of Anesthesia, Stanford University Medical Center. The authors involved in this study and the preparation of the manuscript received no external funding. ★★ The authors had no affiliation or relationship with any company or organization that has a potential interest in the outcome of the study. ⁎ Corresponding author. Department of Anesthesia, MC: 5640, Stanford University School of Anesthesia, 300 Pasteur Dr., Stanford, CA 94305, USA. Tel.: +1 650 736 8513; fax: +1 650 725 8544. E-mail address: [email protected] (A. Butwick). ☆☆
0952-8180/$ – see front matter © 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.jclinane.2010.01.005
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1. Introduction Maternal obesity in pregnancy has become a major public health concern in the United States. Population-based studies estimate that 29% and 8% of women of reproductive age in the U.S. have a body mass index (BMI) of at least 30 kg/m2 and 40 kg/m2, respectively [1], and that the prevalence of maternal obesity (based on a study in 9 U.S. states) has increased from 13% between 1993-1994 to 22% between 2002-2003 [2]. Obese women are at increased risk for requiring cesarean delivery [3,4]. Although regional (neuraxial) anesthetic techniques are the most commonly performed techniques for patients undergoing cesarean delivery, the anesthetic management of morbidly obese parturients requires careful planning and may often be particularly challenging. Technical difficulties may be encountered during neuraxial anesthetic placement for obese patients, and achieving adequate surgical anesthesia may vary depending on the chosen mode of neuraxial anesthesia [5]. Other perioperative complications affecting the anesthetic management of obese patients undergoing cesarean delivery include difficulty in patient positioning on the operating table, longer surgical times, and increased risk of postpartum hemorrhage [6,7]. The aim of this retrospective study was to examine the relationship between BMI and perioperative times, type and complexity of anesthetic interventions, and costs related to the provision of anesthesia in patients undergoing elective cesarean delivery. We hypothesized that maternal obesity would result in longer perioperative times, a higher rate of catheter-based neuraxial anesthetic techniques [notably combined spinal-epidural anesthesia (CSE) vs. single-shot spinal anesthesia (SSS)], and increased anesthesia-related costs.
2. Materials and methods After obtaining Lucile Packard Children's Hospital Ethics Committee approval, a retrospective chart review of all patients who underwent elective cesarean delivery over a one-year period (April 2006 to June 2007) was conducted. Lucile Packard Children's Hospital is a university tertiarycare referral center, and conducts approximately 5,000 deliveries per year with a cesarean delivery rate of approximately 30%. Study investigators accessed the hospital institutional database to obtain baseline data on all patients who underwent elective cesarean delivery during the study period. All patients were ranked according to their BMI at the time of delivery. The World Health Organization (WHO) and the National Institute of Health definitions were used to calculate BMI [weight (kg)/height (m2 )], with obesity classified as a BMI of 30 kg/m2 or greater [8]. All patients during the study period were ranked according to BMI at the time of delivery.
A. Butwick et al. The study groups were designated a priori and were subclassified (using WHO criteria) as follows: Group C (BMI ≤ 29.9 kg/m2; control group), Group 1 (BMI = 3034.9 kg/m2), Group II (BMI = 35-39.9 kg/m2), and Group III (BMI N 40 kg/m2) [8]. Following ranking of patients according to their BMI, 25 patients per group were randomly selected using a Microsoft Excel random number selection tool (Microsoft, Redmond, WA, USA). The following data were collected: maternal and obstetric demographic data, antepartum medical complications, anesthetic technique, hospital billing information related to the provision of anesthesia, and neonatal outcomes. Time periods were also recorded, including anesthesia induction time (time from start of anesthetic technique to surgical start), surgical time (from start to completion of surgery), recovery time, and hospital inpatient admission period. Professional costs for anesthesia coverage were also calculated. We used Medicare rates, which are commonly used in health services research, to estimate costs of physician services. The costs of an anesthesiologist's professional service were obtained using the Medicare reimbursement rate of ⁎$21/unit (USD; with geographical adjustment for our institution), and the ASA Relative Value system (with 7 base units startup + 4 units/hr for the perioperative period)1 [9]. The costs of equipment used for neuraxial anesthesia, based on current charges by individual manufacturers, also were calculated. The direct hospital costs based on the purchase price for a standard spinal anesthesia kit (Pencan Spinal Needle Tray; B. Braun Medical, Inc., Bethlehem, PA, USA) was $180, and for CSE anesthesia [26-gauge Gertie Marx spinal needle (IMD, Inc.; Huntsville, UT, USA) + standard epidural kit (Perifix FX Custom Epidural Anesthesia Tray; B. Braun Medical, Inc.] was $229. We did not assess other non-anesthetic or surgical equipment costs.
2.1. Statistical analysis Data are presented as means (SD), medians (interquartile ranges), and absolute values (percentages) where appropriate. Analysis was performed with SPSS Version 16 software (SPSS Institute, Inc., Chicago, IL, USA). Data were assessed for normal distribution of variance using QQ plots and Kolmogorov-Smirnov tests. One-way analysis of variance (ANOVA) and Kruskal-Wallis tests were used to compare normally distributed and non-normally distributed variables between groups, respectively. For pairwise comparison between groups, the two-sample t-test or the WilcoxonMann-Whitney test was used. Categorical data were assessed with Fisher's exact test or χ2 test, as appropriate. A P-value b 0.05 was considered statistically significant. Pearson correlation was used to examine the association between BMI and perioperative time periods and duration of hospital 1 ASA relative values guide for 2008. Park Ridge IL: American Society of Anesthesiologists; 2008.
Obese patients and cesarean delivery Table 1
521
Demographic and obstetric data BMI ≤ 29.9 kg/m2 (n = 25)
Age (yrs) 33.8 (5.7) Parity 1 [1,1] Gestational age (wks) 38 [37,38] BMI (kg/m2) 25.9 [24.7,26.7] Race Caucasian = 44% Hispanic = 20% Asian- Pacific = 28% Asian- Indian = 8%
BMI = 30-34.9 kg/m2 (n = 25)
BMI = 35-39.9 kg/m2 (n = 25)
BMI ≥ 40 kg/m2 (n = 25)
Overall P-value
34.2 (5.9) 1 [1,1] 38 [38,39] 32.2 [31.5,33.0] Caucasian = 48% Hispanic = 32% Asian- Pacific = 12% African- American = 8%
30.5 (6.1) 1 [1,2] 38 [38,39] 37.1 [36.2,38.4] Caucasian = 24% Hispanic = 56% Asian- Pacific = 4% African- American = 4% Asian- Indian = 8% Unknown = 4%
31.3 (6.1) 1 [1,2] ⁎, † 38 [37,39] 44.2 [41.7,48.6] Caucasian = 36% Hispanic = 28% Asian- Pacific = 28% African- American = 8%
0.08 0.05 0.31 0.73
Data are presented as means (SD), medians [IQR], and numbers (%). BMI = body mass index. ⁎ BMI ≤ 29.9 kg/m2 vs. BMI ≥ 40 kg/m2; P b 0.05. † BMI 30-34.9 kg/m2 vs. BMI ≥ 40 kg/m2; P b 0.05.
admission. Based upon previously published data [6], we predicted that a sample size of 25 patients per group was required to detect a 33% difference between BMI groups in the mode of anesthetic technique (CSE vs. spinal anesthesia), using ANOVA for multiple group comparisons (power = 0.8; α = 0.05).
3. Results Demographic and obstetric data are shown in Table 1. Mode of anesthesia significantly differed between groups, with more patients in Group III receiving a CSE technique than patients in Groups C, I, or II (Table 2). No patient received general anesthesia as the primary mode of anesthesia. One Group III patient who received a CSE
Table 2
technique required conversion to general anesthesia during the intraoperative period. No differences were noted in the doses for intrathecal drugs (bupivacaine, fentanyl, morphine) given between groups (12 mg, 10 μg, and 200 μg, respectively). There were no differences between study groups in the doses of intravenous (IV) vasopressor administered (phenylephrine, ephedrine) or volumes of intraoperative IV fluid given (Table 2). Intraoperative time periods [from pt entering operating room (OR) to surgical start time (OR-Sx time), surgical start time to uterine incision (Sx-UI time), and total intraoperative time] were significantly longer in Group III than Groups C, I, or II (Table 3). No differences were found between groups for uterine incision-delivery time. Linear regression analysis showed that specific intraoperative time periods (OR-Sx time, Sx-UI time, and total intraoperative time) significantly increased with patient BMI (R = 0.349,
Perioperative anesthetic data
Mode of anesthesia: Spinal CSE Patients with CSE requiring epidural supplementation Total dose phenylephrine (μg) Total dose ephedrine (mg) Total IV fluids: Crystalloid (mL) Colloid (mL)
BMI ≤ 29.9 kg/m2 (n = 25)
BMI = 30-34.9 kg/m2 (n = 25)
BMI = 35-39.9 kg/m2 (n = 25)
BMI ≥ 40 kg/m2 (n = 25)
Overall P-value
18 (72%) 7 (18%)
21 (84%) 4 (16%)
17 (68%) 8 (32%)
0.005 0.005
0
1
1
9 (36%) ⁎, †, ‡ 15 (60%) ⁎, †, ‡ [Data missing on one pt] 6 [Data missing on one pt]
0.14
450 [237, 688] 20 [20,20]
500 [500, 1,000] 15 [15,15]
450 [450, 1,000] 30 [25,35]
550 [550, 1,500] 17.5 [17.5,20]
1.0 0.18
1,454 (589) 500 [550, 850]
1,672 (522) 500 [500, 500]
1,494 (550) 500 [500, 500]
1,572 (577) 500 [500, 500]
0.54 0.11
Data are presented as means (SD), medians [IQR], or numbers (%). BMI = body mass index, CSE = combined spinal-epidural anesthesia, IV = intravenous. ⁎ BMI ≤ 29.9 kg/m2 vs. BMI ≥ 40 kg/m2; P ≤ 0.05. † BMI 30-34.9 kg/m2 vs. BMI ≥ 40 kg/m2; P = 0.001. ‡ BMI 35-39.9 kg/m2 vs. BMI ≥ 40 kg/m2; P = 0.03.
522 Table 3
A. Butwick et al. Intraoperative times, estimated blood loss, and recovery data
OR-Sx time (min) Sx-UI time (min) UI-delivery time (min) Total intraoperative time (min) EBL (mL) Preoperative HCT (%) Postoperative HCT (%) Duration of inpatient admission (days)
BMI ≤ 29.9 kg/m2 (n = 25)
BMI = 30-34.9 kg/m2 (n = 25)
BMI = 35-39.9 kg/m2 (n = 25)
BMI ≥ 40 kg/m2 (n = 25)
Overall P-value
28 [23,34] 11 [7,13] 2 [1,2] 81 [73,92] 650 [550,850] 36.1 [34.0,37.8] 30.8 [28.8,32.1] 4 [3,4]
30 [24,35] 9 [8,12] 2 [1,3] 90 [77,96] 700 [600,800] 35.6 [34.0,38.1] 30.4 [38.6,32.9] 4 [3,4]
27 [21,35] 11 [9,17] 2 [1,3] 92 [76,108] 800 [700,800] 35.5 [34.1,38.4] 30.2 [27.8,31.9] 4 [3,4]
36 [28,48] ⁎, †, ‡ 15 [12,25] ‡, #, § 2 [1,3] 101 [87,120] †, ‡, # 800 [600,1000] 35.6 [32.1,38.1] 30.5 [27.9,32.6] 4 [4,4]
0.03 b0.001 0.25 0.002 0.50 0.97 0.718 0.90
Data are presented as medians [IQRs] or numbers (%). BMI = body mass index, OR-Sx time = time from patient entering operating room to start of surgery, Sx-UI time = time from start of surgery to uterine incision, UI = uterine incision, EBL = estimated blood loss, HCT = Hematocrit. ⁎ BMI ≤ 29.9 kg/m2 vs. BMI ≥ 40 kg/m2 ; P ≤ 0.05. † BMI 30-34.9 kg/m2 vs. BMI ≥ 40 kg/m2; P ≤ 0.05. ‡ BMI 35-39.9 kg/m2 vs. BMI ≥ 40 kg/m2; P ≤ 0.05. § BMI ≤ 29.9 kg/m2 vs. BMI ≥ 40 kg/m2; P ≤ 0.001. # BMI 30-34.9 kg/m2 vs. BMI ≥ 40 kg/m2; P ≤ 0.001.
0.440, and 0.394 kg/m2; P b 0.001, respectively) (Figs. 1, 2, and 3). No differences between groups were observed for estimated blood loss (EBL) or preoperative or the earliest postoperative hematocrit (Hct) values (Table 3). No patients were given transfusion therapy (ie, red blood cells, blood products) during the study period. There were no differences between groups in duration of hospital stay following cesarean delivery (Table 3). Costs for anesthesia coverage during the perioperative period and costs for the anesthesia kit used for neuraxial block placement were significantly higher in Group III patients than the other study groups (Table 4). Neonatal
outcome data are shown in Table 5. No differences in APGAR scores, neonatal weight, or neonatal intensive care unit (NICU) admission between groups were observed.
Fig. 1 Correlation between time from patient entering operating room to surgical start time (OR-Sx time) and body mass index (BMI).
Fig. 2 Correlation between time from surgical start time to uterine incision (Sx-UI time) and body mass index (BMI).
4. Discussion Our results suggest that there is increased use of a CSE anesthetic technique in morbidly obese patients (BMI ≥ 40 kg/m2) compared with non-obese patients, as well as patients in lower obesity classes (BMI = 30-39.9 kg/m2),
Obese patients and cesarean delivery
523
Fig. 3 Correlation between total intraoperative time and body mass index (BMI).
undergoing elective cesarean delivery. The longer perioperative times observed in morbidly obese patients in our study likely partly explain the rationale for using a CSE technique in this patient subpopulation. Although previous studies have suggested that longer operative times occur in obese patients undergoing cesarean delivery, criteria for defining obesity were based on patient weight at delivery, and they varied between studies (≥ 90135 kg, ie, 200-300 lbs) [10-12]. No previous studies have specifically compared perioperative times and anesthetic interventions for elective cesarean delivery between obesity classes using WHO criteria. In addition, there is currently no consensus as to preferred approaches for neuraxial anesthesia in obese patients undergoing elective cesarean delivery. A study by Hood et al. [6] compared anesthetic and obstetric outcomes in morbidly obese (N 136.4 kg) and matchedcontrol patients. In this study, epidural anesthesia was
Table 4
performed more commonly in morbidly obese patients than in the control group (b 136.4 kg; 70.8% vs. 46.4%; P b 0.05) for cesarean delivery [6]. However, wide differences in BMI were reported between groups (BMI = 52.6 vs. 27.8 kg/m2; morbidly obese group vs. control group, respectively). In addition, data were collected for patients delivering between the years 1978 through 1989, and neuraxial anesthetic techniques have diversified since the publication of that study (with SSS anesthesia being widely used for elective cesarean delivery in non-obese patients) [13]. The lower rate of SSS anesthesia in the morbidly-obese group substantiates previously held concerns about this technique in this patient sub-population, including inadequate intraoperative anesthesia and the duration of surgery outlasting the period of spinal anesthesia [6]. The use of a CSE technique for obese patients undergoing cesarean delivery is advantageous as this technique allows neuraxial blockade to be maintained (with additional boluses of local anesthetic via the epidural catheter in-situ) after establishing adequate surgical anesthesia with a spinal technique. Based on our results, a catheter-based neuraxial approach appears to be justified for patients in Group III due to the longer intraoperative times, and the higher percentage of patients who received epidural supplementation following CSE anesthesia in Group III versus Groups I, II, and C. However, it is unclear whether epidural supplementation was given to prevent or treat intraoperative breakthrough pain; therefore, we acknowledge that the presence of an epidural catheter may be a potential confounder for increased epidural supplementation. Our results suggested a trend towards longer OR-Sx time, Sx-UI time, and total intraoperative times with increasing BMI, which was substantiated following linear regression analysis. Further work is necessary to assess the maternal and neonatal outcomes of prolonged perioperative times in patients undergoing elective as well as non-elective cesarean delivery. Our review of anesthesia records could not elucidate specific causes for the longer OR-Sx times observed in Group III compared with the other study groups. Technical
Cost data for obstetric anesthesiologist services and for anesthesia kit used for neuraxial block placement BMI ≤ 29.9 kg/m2 (n = 25)
BMI = 30-34.9 kg/m2 (n = 25)
BMI = 35-39.9 kg/m2 (n = 25)
BMI ≥ 40 kg/m2 (n = 25)
Overall P-value
Cost of anesthesiologist 250.20 (19.50) 264.41 (32.18) 262.92 (31.57) 308.88 (40.36) ⁎, †, ‡ b 0.001 services (US$) 0.006 Costs of anesthesia 180.00 [180.00-229.00] 180.00 [180.00-180.00] 180.00 [180-229.00] 229.00 [180.00-229.00] †, §, # kit (USD$) Data are presented as means (SD) or medians [IQR]. BMI = body mass index. ⁎ BMI ≤ 29.9 kg/m2 vs. BMI ≥ 40 kg/m2; P ≤ 0.001. † BMI 30-34.9 kg/m2 vs. BMI ≥ 40 kg/m2; P ≤ 0.001. ‡ BMI 35-39.9 kg/m2 vs. BMI ≥ 40 kg/m2; P ≤ 0.001. § BMI ≤ 29.9 kg/m2 vs. BMI ≥ 40 kg/m2; P ≤ 0.05. # BMI 35-39.9 kg/m2 vs. BMI ≥ 40 kg/m2; P ≤ 0.05.
524 Table 5
A. Butwick et al. Neonatal data
APGAR (one min) APGAR (5 min) Neonatal weight (kg) NICU admission
BMI ≤ 29.9 kg/m2 (n = 25)
BMI = 30-34.9 kg/m2 (n = 25)
BMI = 35-39.9 kg/m2 (n = 25)
BMI ≥ 40 kg/m2 (n = 25)
Overall P-value
8 [8, 9] 9 [9, 9] 3,340 [2,861, 3,577] 3 (12%)
8 [8, 9] 9 [9, 9] 3,538 [3,266, 4,050] 2 (8%) (n = 24)
8 [8, 9] 9 [9, 9] 3,470 [3,197, 3,776] 3 (12%)
8 [7, 9] 9 [9, 9] 3,686 [3,312, 4,059] 2 (8%)
0.20 0.63 0.10 0.94
Data are presented as medians [IQR] or numbers (%). BMI = body mass index, NICU = neonatal intensive care unit.
problems, such as difficulty in optimizing patient position and in identifying surface landmarks, prior to neuraxial block placement may have contributed to the longer OR-Sx time noted in Group III. A recent study showed a positive correlation with BMI and depth to epidural space, and included a review of earlier studies corroborating the association between BMI and depth to epidural space [14]. In our study, more Group III patients received a CSE technique than did the other study groups. We speculate that the additional time taken for CSE block placement may have contributed to longer OR-Sx times in Group III compared with other groups who received mostly spinal anesthesia. One Group III patient required conversion from a regional to a general anesthetic during the intraoperative period; no details were available (following chart review) to explain the reason for the change in anesthetic technique. A general anesthetic technique may be necessary to manage intraoperative breakthrough pain following unsuccessful neuraxial anesthesia. However, obese parturients are at increased risk of failed or difficult endotracheal intubation [15], and failed intubation and aspiration are major causes of death in obese patients undergoing general anesthesia for cesarean delivery. As a result, achieving satisfactory surgical anesthesia with a neuraxial technique has important implications for maternal outcome in obese patients requiring cesarean delivery. No previous study has assessed the cost implications associated with anesthesia coverage and equipment costs for obese patients undergoing elective cesarean delivery. Longer perioperative periods substantiate the finding of higher total cost of anesthesia coverage for patients in BMI Group III versus Group C ($308.88 vs $250.20 USD, respectively). In addition, a higher percentage of Group III patients received a CSE technique, which is associated with higher equipment costs than is SSS anesthesia. However, we did not account for other direct or indirect costs associated with increased OR time (eg, hospital costs for obstetrician, surgical assistant, OR nurses) [16]. No differences in doses of intrathecal bupivacaine, fentanyl, or morphine were observed between study groups. Although concern has been expressed about the unpredictable extent of spread of local anesthesia following spinal anesthesia [17], previous studies have suggested that BMI does not significantly affect spinal block levels in pregnant patients receiving hyperbaric spinal local anesthetic mixtures
[18-22]. No differences in total doses of vasopressors (phenylephrine, ephedrine) or IV fluid requirements were seen between groups. We did not specifically collect intraoperative hemodynamic data; thus, it is unclear whether significant differences in cardiovascular parameters occurred between obese and non-obese patients undergoing spinal anesthesia for cesarean delivery. No differences were observed between groups for EBL or preoperative or postoperative Hct values. Our results contrast with those of Perlow et al. and Johnston et al., who noted significantly higher EBL values in obese patients undergoing cesarean delivery versus nonobese patients [10,11]. However both studies included data from patients undergoing elective and nonelective cesarean delivery, and it is possible that factors associated with labor may have influenced EBL values. Variations in surgical technique also may have influenced intraoperative EBL [12]. In our study, the duration of inpatient postpartum admission was similar between groups. These results contrast with those of Hood et al. and Perlow et al., who reported longer periods of hospitalization in obese patients following cesarean delivery [6,11]. Similarly, Chu et al. reported that mean durations of hospital stay are greater in women with increased BMI, a finding that relates to higher rates of cesarean delivery and obesity-related co-morbidity [23]. However, these studies included patients undergoing elective and nonelective cesarean deliveries; thus, it is possible that higher peripartum and postpartum complication rates may have affected duration of inpatient admission postoperatively (eg, postoperative endometritis, wound infections, wound dehiscence). Our study was also underpowered to find differences in this outcome measure. Neonatal outcomes were similar between all groups (ie, APGAR scores, neonatal weight), with low rates of admission to the NICU. There are limited data assessing perinatal outcomes in obese patients undergoing elective cesarean delivery. However, a previous study assessing perinatal outcomes did not observe significant differences in the rate of NICU admission for infants born to healthy mothers with varying pre-pregnancy weights [24]. A number of factors may limit the generalizability of our findings. Individual differences in surgical practice among obstetricians are likely to have had an impact on perioperative time periods and surgical outcomes between study
Obese patients and cesarean delivery groups. A number of anesthetic factors may have influenced difficulty in block placement and OR-Sx times, including experience of the anesthesia provider performing neuraxial blockade (Resident, Fellow, Attending Physician), suboptimal patient positioning (reduced flexion), and difficulty in palpation [25]. All neuraxial blocks at our center are directly supervised by experienced obstetric anesthesia attendings, a fact that may have mitigated such incidents. Although our results show that rates of CSE were high in patients with a BMI ≥ 40 kg/m2, over a third of patients underwent SSS anesthesia for elective cesarean section. Furthermore, the rates of SSS and CSE did not differ significantly between lower BMI classes. We did not explore the basis for these variations in anesthetic technique. Physicians may individualize their choice of neuraxial technique based on specific factors, eg, individual experience with SSS versus CSE techniques, perceived surgical experience of the obstetrician, differences in patient positioning in the OR, presence of a reassuring versus nonreassuring airway. Further studies are warranted to investigate physician preferences for neuraxial techniques for different BMI classes, and to compare anesthetic outcomes between different catheter-based techniques, eg, epidural, CSE, and continuous spinal catheter in morbidly obese pregnant patients. There are potential limitations associated with a CSE technique in morbidly obese patients undergoing elective cesarean delivery. Failure to obtain cerebrospinal fluid with the spinal needle while using a CSE technique may occur (3% to 5% of CSE techniques) [26], which may require converting to epidural anesthesia or repeating neuraxial block placement. In addition, with a CSE technique the epidural catheter is not formally tested prior to surgery to assess efficacy following epidural bolus administration. If intraoperative epidural supplementation fails to provide adequate surgical anesthesia, there may be the increased risk of the patient experiencing intraoperative pain and of conversion to general anesthesia. The use of an “epidural only” technique prior to surgery would confirm the success or failure of achieving adequate surgical anesthesia following epidural bolus administration. If epidural anesthesia proved inadequate following block placement, the anesthesiologist could perform an alternative technique (eg, epidural catheter replacement) to achieve adequate surgical anesthesia. Patients receiving a CSE technique for elective cesarean delivery have lower intraoperative pain scores, shorter intraoperative times, and higher maternal satisfaction than patients receiving an “epidural only” technique [27,28]. Furthermore, catheters inserted using a CSE technique are associated with a lower failure rate compared with an epidural technique [29-32]. In conclusion, morbidly obese (BMI ≥ 40 kg/m 2 ) pregnant patients are more likely to receive CSE anesthesia for elective cesarean delivery than are patients with lower BMIs. At our academic institution, the increased use of catheter-based neuraxial techniques in morbidly obese
525 patients versus patients with lower BMIs may be justified due to longer intraoperative times and a greater requirement for intraoperative epidural supplementation. The cost of anesthesia coverage and hospital costs for anesthesia equipment were also higher in morbidly obese patients than in patients with lower BMIs.
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