Wall, Peter D. MD; Deucy, Erin E. MD; Glantz, J. Christopher MD, MPH; Pressman, Eva K. MD
OBJECTIVE: To examine the relationship between the type of skin incision and postoperative wound complications in an obese population.
METHODS: A hospital-based perinatal database was used to identify women with a body mass index (BMI) of greater than 35 undergoing their first cesarean delivery. Hospital and outpatient medical records were reviewed for the following variables: age, insurance status, BMI, gestational age at delivery, birth weight, smoking history, prior abdominal surgery, existing comorbidities, preoperative hematocrit, chorioamnionitis, duration of labor and membrane rupture, dilation at time of cesarean delivery, type of skin and uterine incision, estimated blood loss, operative time, antibiotic prophylaxis, use of subcutaneous drains or sutures, endometritis, and length of stay. The primary outcome variable was any wound complication requiring opening the incision. Multiple logistic regression analysis was completed to determine which of these factors contributed to the incidence of wound complications.
RESULTS: From 1994 to 2000, 239 women with a BMI greater than 35 undergoing a primary cesarean delivery were identified. The overall incidence of wound complications in this group of severely obese patients was 12.1%. Factors associated with wound complications included vertical skin incisions (odds ratio [OR] 12.4, P < .001) and endometritis (OR 3.4, P = .03). A high preoperative hematocrit was protective (OR .87, P = .03). No other factors were found to impact wound complications.
CONCLUSION: Primary cesarean delivery in the severely obese parturient has a high incidence of wound complications. Our data indicate that a vertical skin incision is associated with a higher rate of wound complications than a transverse incision.
Cesarean delivery in the severely obese parturient poses special problems. Not uncommonly, difficulty in gaining and maintaining adequate surgical exposure extends operative times and increases blood loss.1 In addition, the risk for postoperative morbidity, including wound complications, is increased several-fold, often leading to a prolonged recovery.2,3
The choice of skin incision in the obese parturient undergoing cesarean delivery is controversial. A transverse incision is thought to effect a more secure wound closure and lessen postoperative discomfort, allowing earlier mobility and increased respiratory excursion.4,5 Transverse incisions, however, sometimes lead to awkward and difficult retraction to gain adequate exposure. Postoperatively, the transverse incision likely remains within the moist skin folds of the panniculus, potentially increasing infection risk.6 In contrast, a vertical incision might allow for better visualization of the operative field with less physical exertion, thus decreasing operative time and blood loss. Postoperatively, the incision is out of moist skin folds, perhaps decreasing infection risk, and is more easily accessible for wound care.
In this study, we sought to examine the relationship between type of skin incision and postoperative wound complications in an obese population. Our hypothesis was that vertical skin incisions would be associated with a lower wound complication rate.
MATERIALS AND METHODS
We conducted a retrospective study of women delivered at Strong Memorial Hospital, University of Rochester, from 1994 to 2000. The institutional review board at the University of Rochester Medical Center exempted this study.
A hospital-based, perinatal database was used to identify women with a body mass index (BMI) of greater than 35 undergoing their first cesarean delivery. This database uses the State of New York's electronic birth certificate as a core, with additional information added regarding patient demographics, medical history, pregnancy history, and neonatal outcomes. Information is entered by data registry personnel and is used by state and local health departments. The database has been used in numerous publications and is periodically validated by record review at the state and local levels.
Once identified through the database, hospital records were reviewed for the following variables: age, insurance status, BMI, ethnicity, gestational age at delivery, existing comorbidities (eg, diabetes, hypertension, preeclampsia, etc), smoking history, prior abdominal surgery, preoperative hematocrit, chorioamnionitis, duration of labor and membrane rupture, dilatation at time of cesarean delivery, indication for cesarean delivery, type of skin and uterine incision, estimated blood loss, operative time, antibiotic prophylaxis, use of subcutaneous suture or drains, endometritis, and length of stay. Skin incisions were classified as transverse or vertical. No periumbilical transverse incisions were included. No distinction was made between supraumbilical vertical incisions and those remaining below the umbilicus. Operative time was defined as the time from skin incision until the patient left the operating room. The primary outcome variable was any wound complication, before hospital discharge, leading to opening the incision; this was further separated into infectious (eg, cellulitis or purulent wound discharge) and noninfectious etiologies (eg, seroma or hematoma).
Body mass index was calculated by prepregnant weight. Because BMI is a measure of weight relative to height, it is less subjective than when weight only is used to define obesity. A BMI greater than 29 defines obesity, though there seems to be no consensus as to how to delineate different degrees of obesity. We chose to evaluate women with a BMI greater than 35 because this has been used to characterize “severe” obesity (greater than the 95th percentile for women 20–29 years of age).7,8 Women were excluded if the medical record was incomplete or unavailable for review.
Univariate statistics for each variable were calculated. Nominal variables were assessed by χ2 or Fisher exact test. Continuous variables were assessed by the Student t test. Stepwise logistic regression model analysis was used to create a final model of risk factors for wound complications while controlling for potentially confounding variables. Significance was set at P < .05. Odds ratios with 95% confidence intervals were determined where appropriate. Based on power analysis assuming a 50% reduction in wound complications (from 30% to 15%), at α = .05 and β = .20, the study required approximately 240 subjects. StatView 5.0 (SAS Institute Inc., Cary, NC) was used for all statistical tests.
Of the 261 women with BMIs greater than 35, complete data were available for 239 (92%), and these subjects were included in the analyses. Cohort characteristics are presented in Table 1. Women having vertical incisions were significantly heavier, with an average BMI of 44.1. They were less likely to have a lower segment uterine incision and had higher preoperative hematocrits. Both groups had high rates of diabetes, hypertension, and preeclampsia. Women with vertical skin incisions were also more likely to have wound complications, despite a higher use of subcutaneous drains and sutures. When wound complications were separated into infectious and noninfectious etiologies (eg, seroma) the association with vertical skin incisions persisted.
The overall incidence of wound complications was 12.1%. On univariate analysis, women with wound complications were also noted to have an increased incidence of postoperative endometritis and a longer length of stay (Table 2). There were no significant differences for any other variables.
Factors significant (P < .05) or thought to be potential confounders on univariate analysis were entered into a final regression model. Stepwise backwards multiple logistic regression analysis confirmed an association with wound complications for vertical skin incisions and postpartum endometritis. A high preoperative hematocrit was protective (Table 3). No other factors were found to be independently statistically significant, including age, BMI, smoking, subcutaneous drains or sutures, chorioamnionitis, duration of membrane rupture, type of uterine incision, operative time, or the use of regional anesthesia.
Obesity has reached epidemic proportions in the United States, with nearly one third of reproductive-aged women considered obese.9 In pregnancy, obesity has been associated with a higher incidence of antepartum complications, such as diabetes and hypertension, and peripartum complications of macrosomia, prolonged labor, shoulder dystocia, and higher cesarean delivery rates. Postoperative wound complications also are increased in obese women and serve to lengthen hospitalization and increase cost.10–13 In addition there is considerable inconvenience, expense, and discomfort with outpatient wound care.
Cesarean delivery in the severely obese woman can be challenging even in the most experienced hands. Over the years, a variety of surgical approaches have been advocated as ways to reduce operative difficulties and decrease postoperative morbidity. Generally, these involve sub- and supraumbilical versions of a vertical or transverse skin incision.14–17 Operative considerations common to all include the necessity to balance the often competing needs for incisions that can be made relatively swiftly, allow for adequate exposure and extension if required, all while affording good wound strength and minimal postoperative complications. Although each approach has its advocates, few data are available on how each performs with respect to wound complications in an obese population.
In our study, we reviewed the outcomes in 239 severely obese woman to determine whether the type of skin incision was an independent factor in wound complication risk. The prepregnancy BMI averaged 41.5; given a “normal” pregnancy weight gain, this roughly equates to a delivery weight near 300 pounds. Our overall incidence of wound complications was 12%, a rate comparable to that noted by other investigators and several times that seen in nonobese populations.1,18
We found a significantly greater incidence of wound complications (35% compared with 9%) in women with vertical skin incisions. This association persisted when wound complications were separated into infectious and noninfectious etiologies. Unlike other investigators, we did not find that length of labor or membrane rupture, BMI, smoking, presence of chorioamnionitis, or the use of subcutaneous drains or sutures were independent predictors for wound complications.19–21 The failure to confirm these variables as risk factors might well have been due to a type II error, because our power to detect a difference was limited, given the small sample size. In addition, the use of antibiotic prophylaxis was very high in all groups, potentially diluting the influence of these other variables on the overall wound complication rate.
To date, there are no randomized trials comparing different skin incision types in an obese population undergoing cesarean delivery (literature search via MEDLINE; 1966–July 2003; all languages; search terms: “cesarean,” “obesity,” and “wound infection”). In a prospective, nonrandomized, clinical trial by Vermillion et al,18 140 women, with an average BMI of 45, undergoing cesarean delivery were studied to assess the effect of subcutaneous tissue thickness on wound infection rate. Approximately 10% of women in their study had vertical skin incisions, with a 23% wound infection rate, compared with a 6% wound infection rate in those with a transverse skin incision. Although this four-fold difference did not reach statistical significance, it compares closely to the findings in our larger cohort study.
A major limitation in our nonrandomized study is that these data were collected retrospectively from multiple providers over 7 years, thus there likely is significant variability in the surgical technique used. In addition, we were not able to precisely localize where in relation to the pannus the incision was made. This could confound our results by introducing uncontrolled variables. A prospective, randomized trial in which surgical technique and incision location are standardized would be required to precisely determine which incision leads to more complications. Wound complication ascertainment was also restricted to a review of the inpatient record. A large percentage of our patients are cared for by multiple private practitioners, and thus outpatient records were not reviewed. Given that many patients, especially those with vertical incisions, are discharged with staples in place, the overall incidence of wound complications might have been underestimated.
In conclusion, we found that the type of skin incision is an independent predictor of wound complication risk. We realize that multiple factors must be considered by the surgeon when contemplating the choice of incision; however, it seems that vertical skin incisions are associated with a higher rate of wound complications in severely obese women. This was contrary to our study hypothesis. There are several possible explanations for this finding. The subpannicular fold, though rich in microbial flora, might have a limited effect on wound breakdown in this era of almost universal antibiotic prophylaxis for cesarean delivery. In addition, our nursing staff is very attentive to keeping wounds dry and clean. There also might be as-of-yet-unknown factors inherent to vertical skin incisions, such as wound tension, that lead to a significantly greater degree of wound stress, changes in neovascularization, and subsequent alterations in healing that account for the observed disparity.
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