Unintentional dural puncture is a known risk of neuraxial anesthetic techniques, occurring in approximately 1% of labor epidural catheters placed in patients with normal body habitus.1,2 The incidence of postdural puncture headache (PDPH) after unintentional dural puncture has been estimated at 50% to 60%.3,4
PDPH can be a significant cause of maternal morbidity. In addition to interfering with the mother’s ability to care for the newborn, treatment of PDPH can increase healthcare costs by prolonging the length of hospitalization and the number of emergency department visits.5 Parturients may also be at risk of developing a long-term sequel after unintentional dural puncture. In a retrospective case–control study, Webb et al.6 reported a 28% incidence of chronic headache in parturients after unintentional dural puncture with a 17-g Tuohy needle. These women were also more likely to have back pain.6
Obesity poses many challenges to healthcare providers, including increased incidence of peripartum complications.7 Hood and Dewan8 observed that the incidence of unintentional dural puncture increased to 4% in morbidly obese parturients (defined as >300 lbs). The prevalence of obesity in the United States among women aged 20 years and older has been estimated at 36%.9
Previous studies have not consistently observed a relationship between body mass index (BMI) and PDPH or need for an epidural blood patch after unintentional dural puncture. In a retrospective study of 99 subjects, Faure et al.10 reported a 45% incidence of PDPH in patients with BMI <30 kg/m2 and a 24% incidence of PDPH in patients with BMI ≥30 kg/m2 (P < 0.05). Webb et al.6 reported that parturients who developed a PDPH after an unintentional dural puncture with a 17-g Tuohy needle had higher BMI compared with those that did not develop a headache (P = 0.02).
There is also a known association between pushing during delivery and the development of PDPH after unintentional dural puncture.11 It is not known whether the effect of pushing is independent of the effect of BMI or whether an interaction between these variables exists.
Previous studies examining the relationship between BMI and PDPH have involved a relatively small number of subjects because dural puncture is an uncommon complication. Therefore, we undertook a 10-year retrospective evaluation of a large series of parturients at a single university hospital to characterize the influence of obesity on the incidence of PDPH after unintentional dural puncture. We hypothesized that parturients with greater BMI would have a lower incidence of PDPH than those with lower BMI.
The study was approved by the IRB of Northwestern University, protocol numbers STU00020926 and STU00089669. Informed consent was waived in this retrospective study. Parturients with a documented unintentional dural puncture on attempted initiation of neuraxial labor analgesia using a 17-g Tuohy needle between January 1, 2004, and December 13, 2013, were included. Subjects were identified for study inclusion by querying the obstetric anesthesia complication databases and searching the Northwestern University enterprise data warehouse for unintentional dural puncture. Study personnel reviewed the medical and anesthesia records.
Demographic information and data on anesthetic procedure and pushing during labor were obtained from the subjects who had a documented unintentional dural puncture. Abstracted data included height, weight, BMI, type of neuraxial procedure, placement of an intrathecal catheter after unintentional dural puncture, presence of PDPH, day of onset of PDPH, pain headache score (0–10 verbal numeric rating scale), active pushing during labor, conservative treatment of PDPH, epidural blood patch, date of initial epidural blood patch, and the need for repeat epidural blood patch. Subjects were considered not to have pushed if they had a cesarean delivery with an indication of arrest of dilation or nonreassuring fetal status before the second stage of labor.
Unintentional dural puncture was managed at the discretion of the attending anesthesiologist. During the study period, there was no departmental protocol for analgesia management after unintentional dural puncture. Specifically, prophylactic epidural blood patches were not administered. An intrathecal catheter was placed through the unintentional dural puncture in some patients. Others had placement of an epidural catheter at a different interspace.
Parturients reporting a PDPH were managed using a standard departmental protocol. Conservative treatment was defined as oral hydration, recommendations to increase oral caffeine intake, and administration of oral analgesics as needed. Parturients with persistent severe headache (numeric rating scale ≥6) despite conservative treatment were offered an epidural blood patch. Subject follow-up consisted of daily visits or phone calls for a minimum of 3 days and for at least an additional 2 days after an epidural blood patch was performed.
The primary outcome variable of this study was a PDPH. On the basis of data from our anesthesia complication database, we estimated an average of 60 cases of unintentional dural puncture per study year. We assumed that the incidence of PDPH after unintentional dural puncture was approximately 60% as demonstrated in a previous study from our institution.12 On the basis of institutional parturient demographics, we estimated that 25% of the subjects with unintentional dural puncture would have a BMI ≥30 kg/m2. Therefore, we anticipated that there would be 450 and 150 parturients in BMI groups of <30 kg/m2 and ≥30 kg/m2, respectively. This number provides power of 0.58, 0.78, 0.92, 0.98, and 0.99 for detecting a difference in PDPH of 10% to 20% in 2.5% increments between BMI groups at an α of 0.05. A Fisher exact test was used for sample size analysis. Calculations were performed using PASS 11 (version 11.0.10, NCSS, LLC, Kaysville, UT).
The incidence and 95% confidence interval (CI) of unintentional dural puncture were calculated from the number of neuraxial labor analgesia procedures performed during the study period. The association between BMI and PDPH was assessed using binary logistic regression. The Wilcoxon-Mann-Whitney odds and 95% CI for a random pair of BMI values from the PDPH and the non-PDPH group were determined from the area under the receiver operator characteristic curve from the binary logistic model.13,14 A recursive nonparametric classification tree analysis based on χ2 automatic interaction detection was used to determine the optimal BMI cutoff value for the risk of developing a PDPH. The difference in the proportion of parturients with PDPH and the 95% CI between low and high BMI groups, stratified at the cutoff value, was calculated using a 2-sample test for equality of proportions with continuity correction. The incidence of PDPH in women in the low and high BMI groups controlling for pushing during labor and for the placement of an intrathecal catheter after unintentional dural puncture was compared by constructing a 2 × 2 cross-tabulation table and evaluated using the Fisher exact test. Binomial CIs were calculated using the Pearson-Klopper method.
Secondary outcome analysis included the type of neuraxial procedure performed at the time of reported unintentional dural puncture, day of onset of headache, worst reported headache severity, and administration of an epidural blood patch for headache treatment. The day of onset of headache and headache severity score were compared using the Mann-Whitney U test. The frequency of an epidural blood patch for the treatment of headache was assessed with the Fisher exact test. To validate the primary and secondary findings, a sensitivity analysis was performed using a cutoff value of 30 kg/m2, which is accepted as the threshold value defining obesity by the World Health Organization (WHO). Data were also stratified according to the WHO criteria for normal (BMI <25 kg/m2), overweight (BMI ≥25 kg/m2 and <30 kg/m2), and obese (BMI ≥30 kg/m2), and the trend in the incidence of PDPH across the BMI categories was assessed using the Armitage test of trends in proportions. Missing data were excluded from the analysis on a case-wise basis. Analysis was performed using SPSS version 18.104.22.168 (IBM Corporation, Somers, NY) and RKWard version 0.6.1 and R version 3.1.2 release date October 31, 2014 (The R Foundation for Statistical Computing, Vienna, Austria). P < 0.05 was required to reject the null hypothesis.
The total number of patients with a documented unintentional dural puncture was 518.a This represents an unintentional dural puncture rate of 0.53% (95% CI, 0.48%–0.58%) of parturients receiving neuraxial labor analgesia. The characteristics of the parturients with unintentional dural puncture are shown in Table 1.
PDPH was identified in 263 parturients. The incidence of PDPH after unintentional dural puncture was 51% (95% CI, 46%–55%). Binary logistic regression identified BMI as an independent predictor of PDPH (odd ratio 0.95; 95% CI, 0.93–0.98, P = 0.001). The Wilcoxon-Mann-Whitney odds for a random pair of BMI values from a PDPH subject compared with a non-PDPH subject was 0.74 (95% CI, 0.60–0.90, P = 0.001). Nonparametric classification tree analysis identified an optimal BMI cutoff value of 31.5 kg/m2 for the prediction of a PDPH (Fig. 1). One hundred fifty-seven (30%) of the parturients had a BMI ≥31.5 kg/m2 (high group). The incidence of PDPH in parturients in the high group (39%) was lower than in parturients with a BMI <31.5 kg/m2 (56%; low group; difference −17%; 95% CI, −7% to −26%, P = 0.0004). The odds ratio for the development of a PDPH in parturients in the high BMI compared with low BMI group was 0.72 (95% CI, 0.61–0.85).
Sensitivity analysis using the WHO classification value for obesity (BMI ≥30 kg/m2) demonstrated a similar reduction in the incidence of PDPH after unintentional dural puncture (difference −14%; 95% CI, −5% to −23%, P = 0.002). The odds ratio for the development of a PDPH in parturients with a BMI ≥30 kg/m2 compared with <30 kg/m2 was 0.75 (95% CI, 0.64–0.89). The incidence of PDPH in subjects with BMI <25 kg/m2 (62% [95% CI, 50%–73%]), 25 to <30 kg/m2 (55% [95% CI, 48%–61%]), and ≥30 kg/m2 (42% [95% CI, 36%–49%]) demonstrated a decreasing trend in proportion with the increase in BMI class (P = 0.0004; Table 2).
The incidence of PDPH in parturients who pushed during labor (54%) was greater than in subjects who did not push (33%; difference 19%; 95% CI, 9%–33%, P = 0.001; Table 2). The odds ratio for developing a PDPH after unintentional dural puncture in subjects who pushed during labor compared with women who did not push was 2.4 (95% CI, 1.4–3.9). In parturients who pushed during labor, the odds ratio for a PDPH in the high BMI compared with low BMI group was 0.36 (95% CI, 0.14–0.92, P = 0.04) and 0.63 (95% CI, 0.40–0.97, P = 0.04) in parturients who did not push (Table 3). The effect was similar in parturients who pushed during labor when stratified at BMI of 30 kg/m2.
After the unintentional dural puncture, 112 (22%) parturients had an intrathecal catheter placed. The incidence of PDPH in parturients with an intrathecal catheter was 59% (95% CI, 49%–68%) compared with 48% (95% CI, 43%–54%) in women with an epidural catheter (P = 0.06; Table 2). A greater fraction of parturients in the high BMI group (32%) had placement of an intrathecal catheter compared with the low BMI group (17%; difference 15%; 95% CI, 6%–23%, P = 0.0003; Table 3). In parturients with an intrathecal catheter, the odds ratio for a PDPH in the high BMI compared with the low BMI group was 0.14 (95% CI, 0.06–0.33, P < 0.001). The effect was similar when stratified at BMI of 30 kg/m2.
The highest incidence of reported PDPH was on day 1 (Table 4). Median (interquartile range) headache severity was 8 (6 to 9) and did not differ between parturients in high compared with low BMI. There was no difference in the rate of epidural blood patch administration between the high and the low groups or rate of a second epidural blood patch. The median (interquartile range) postdelivery day for an epidural blood patch was 2 days (range 2–4 days) in the BMI <31.5 kg/m2 group and 3 days (range 2–5 days) in the BMI ≥31.5 kg/m2 group (P = 0.10). When stratified at a BMI of 30 kg/m2, the difference in incidence of a repeat epidural blood patch in the BMI <30 kg/m2 group compared with a BMI ≥30 kg/m2 was 12% (95% CI, 4%–16%, P = 0.04).
The overall rate of unintentional dural puncture (0.53%) observed in this study and the proportion of parturients with a PDPH (51%) after unintentional dural puncture are consistent with cited reports. The most important finding of this study is the significant inverse association in the proportion of parturients reporting PDPH with BMI groups after unintentional dural puncture. In our sample, we found an optimal cutoff value of 31.5 kg/m2 for the classification of subjects. However, a similar effect was observed using a WHO-recommended cutoff value of 30 kg/m2.
Our findings on the relationship of BMI with PDPH after unintentional dural puncture are consistent with the findings of Faure et al.10 but differ from the findings of Miu et al.15 who reported no difference in the incidence of PDPH after unintentional dural puncture using a cutoff BMI value of 30 kg/m2. Differences in the study by Miu et al. and the current study may explain the differences in findings. In 125 parturients, Miu et al. reported an incidence of PDPH after unintentional dural puncture of 82%, much greater than the incidence reported in the 518 parturients in the current study. Nonetheless, even at the 12% difference in the incidence of PDPH at a cutoff value of 30 kg/m2 observed in the current study, the study by Miu et al. would only have had 40% power to detect this difference if it did exist. The investigators did report that in 10 parturients ≥40 kg/m2, the incidence of PDPH was 60%, 20% lower than in women ≤40 kg/m2, but the study sample had only 29% power to detect this difference.
There are possible alterations in the epidural/intrathecal spaces in an obese parturient that may explain the lower incidence of PDPH in these patients. Evidence suggests that the increase in epidural pressure observed in obese compared with lean individuals may decrease the pressure gradient from the intrathecal to the epidural space, resulting in less cerebral spinal fluid (CSF) leak through a dural rent and a lower incidence of PDPH. Increased intraabdominal pressure may reduce non-CSF volume in the epidural space. Parturients with BMI ≥30 kg/m2 have been found to require less epidural infusate to provide equipotent analgesia compared with parturients <30 kg/m2.16 Hogan et al.17 found that magnetic resonance imaging evaluation of CSF/nerve root volume in healthy volunteers demonstrated an inverse relationship between CSF volume/nerve root volume and body weight. The volume from T11–T12 to the sacral terminus in obese volunteers was found to be significantly less than in nonobese volunteers. Hogan et al. also reported that intraabdominal pressure increases linearly with body weight. The same investigators found a decrease in CSF volume with external abdominal compression that may simulate a static increase in abdominal pressure similar to that found in pregnancy. They suggested that the mechanism involves “inward movement of soft tissue in the intervertebral foramen.” Increased abdominal pressure in the obese parturient may also enhance pregnancy-induced epidural venous engorgement, resulting in a decrease in the volume of CSF in the lumbar neuraxial canal.18
A second finding of this study was a positive association with pushing during labor and the incidence of PDPH. This result is consistent with other previous studies and presumably occurs because bearing down increases CSF loss through the dural rent.11 In our study when dichotomized at a BMI of 31.5 kg/m2, the odds of developing a PDPH was lower in high BMI parturients regardless of whether they pushed during labor.
The placement of an intrathecal catheter after an unintentional dural puncture has been reported to decrease the incidence of PDPH,19,20 although a recent meta-analysis was unable to confirm this finding.21 We did not find a difference in the incidence of PDPH in subjects who had an intrathecal catheter after unintentional dural puncture. The greater incidence of intrathecal catheters observed in the high BMI group presumably represents provider bias. Because there was no protocol for the management of unintentional dural puncture, and because of the selection bias for placement of an intrathecal catheter in high BMI patients, we are uncertain whether the increased rate of PDPH observed in low BMI patients with an intrathecal catheter placed represents a true increase in the proportion of PDPH or reflects a greater likelihood for placement of intrathecal catheters in subjects <30 kg/m2 at increased risk of PDPH.
Our findings suggest that once patients developed PDPH after unintentional dural puncture, high BMI did not confer further protection to the patient, because the pain intensity at headache presentation, the highest reported pain score from the PDPH, and administration of an epidural blood patch were similar between BMI groups. The incidence of administration of an epidural blood patch was 12% lower in the high BMI group. This difference might be clinically important if it represents a true difference.
Our results should be interpreted in the context of the study’s limitations. This study was a retrospective review of data collected for clinical care and relied on provider reporting of the occurrence of an unintentional dural puncture. Nonetheless, the rate of unintentional dural puncture was similar to a previous study from the same institution that examined the utility of a prophylactic epidural blood patch after unintentional dural puncture.12 The neuraxial procedures included in this study involved the use of a 17-g Tuohy needle, and the rate of unintentional dural puncture may vary as a function of the needle size. Bias introduced by clinical practice such as in the decision to place an intrathecal catheter may have influenced our findings. Despite the large number of subjects in this study, our sample was insufficient to examine the relationship between pushing during labor and BMI with a high level of confidence. We were unable to determine which subjects had other risk factors for PDPH such as a headache history. Although the treatment plan for the management of a PDPH is standardized in our department, we were unable to determine whether the protocol was followed in all patients. Finally, we were unable to determine whether there were any differences in the ease of labor epidural catheter placement among subjects that could have influenced the provider decision to place an intrathecal catheter or the decision to perform an epidural blood patch.
In conclusion, our findings confirm the previously reported association between high BMI and reduced likelihood of a PDPH. Our study also confirmed the association of pushing during labor and an increased likelihood of a PDPH after unintentional dural puncture. We are uncertain whether there is an interaction among pushing, BMI, and the likelihood of PDPH. Although the incidence of a PDPH was lower in subjects with high BMI, the severity and need for treatment of a PDPH were not influenced by body weight.
Name: Feyce Peralta, MD.
Contribution: This author helped design and conduct the study, collect and analyze the data, and prepare the manuscript.
Attestation: Feyce Peralta approved the final manuscript, and attests to the integrity of the original data and the analysis reported in this manuscript.
Name: Nicole Higgins, MD.
Contribution: This author helped design and conduct the study, collect and analyze the data, and prepare the manuscript.
Attestation: Nicole Higgins approved the final manuscript, and attests to the integrity of the original data and the analysis reported in this manuscript.
Name: Elizabeth Lange, MD.
Contribution: This author helped collect the data.
Attestation: Elizabeth Lange approved the final manuscript, and attests to the integrity of the original data and the analysis reported in this manuscript.
Name: Cynthia A. Wong, MD.
Contribution: This author helped collect the data.
Attestation: Cynthia A. Wong approved the final manuscript, and attests to the integrity of the original data and the analysis reported in this manuscript.
Name: Robert J. McCarthy, PharmD.
Contribution: This author helped analyze the data and prepare the manuscript.
Attestation: Robert J. McCarthy approved the final manuscript, and attests to the integrity of the original data and the analysis reported in this manuscript.
Dr. Cynthia A. Wong is the Section Editor for Obstetric Anesthesiology for the Journal. This manuscript was handled by Dr. Steven L. Shafer, Editor-in-Chief, and Dr. Wong was not involved in any way with the editorial process or decision.
a Deidentified data used in the analysis of this manuscript can be assessed as Supplemental Digital Content, http://links.lww.com/AA/B137.
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