This study to evaluate the efficacy of NPWT in achieving early fascial closure/cutaneous cover compared to a conventional therapy in postoperative laparotomy wound dehiscence included more men than women, but the number of men in each group was not significantly different (P =1 .06). Similar studies6,7 reported that 64% of the NPWT group and 64.8% of the conventional therapy group were men; the reason for male preponderance of abdominal wound dehiscence is not clear. One possibility is that men are more likely to develop higher intra-abdominal pressure and wall tension, which can strain the tissues and wound edges causing sutures to cut through the muscles.8
In terms of age, approximately 58.6 % of the entire study population was older than 50 years. Similarly, the retrospective analysis by Ko and Jung6 reported that 58.2% in conventional therapy and 48% in the NPWT therapy group were between 50 and 70 years of age. Advanced age is associated with defective tissue repair due to the decreased functional integrity of the immune system.6 A large retrospective review conducted by Walming et al9 found that BMI >25 was a risk factor for wound dehiscence (P = .001). Considering the limited number of patients in this study, a larger sample size with a greater number of obese patients may provide valuable information on this association.
Diabetes is traditionally considered a risk factor for wound dehiscence, but a review of 27 retrospective studies by van Ramhorst et al7 showed diabetes had no significant effect on wound dehiscence occurrence. In the present study, comorbidities such as diabetes and hypertension were comparable in both the groups.
The proportion of patients with a history of emergency surgery was higher than those who had elective surgery. This is not an unexpected finding. van Ramshorst et al7 reported that patients undergoing emergency surgery had an 1.8 times greater risk of developing wound dehiscence (odds ratio = 1.8) The number of study participants who had a colostomy or ileostomy was high (21), which is also in concordance with the literature; a multivariate analysis of 265 patients by Yilmaz et al10 reported that having a colostomy or ileostomy had a statistically significant effect on the rate of wound dehiscence (P = .002).
In the current study, the most common indication for index surgeries associated with abdominal wound dehiscence was bowel perforation, most likely due to local factors such as wound infection following contamination from bowel contents. An extensive literature review on wound dehiscence by Cliby11 showed that the Centers for Disease Control and Prevention (CDC) class IV wounds—dirty surgical wounds, including bowel perforation—were associated with a greater than 30% chance of wound infection. Several previous studies1,7 have shown that malignancy and sepsis are risk factors for postoperative wound dehiscence.
The current study found that NPWT therapy facilitates granulation tissue formation, but the rate of granulation tissue formation was not evaluated as a separate factor in this study. In their cohort study among 21 patients receiving NPWT, Heller et al12 proposed that removal of exudates harboring bacteria by continuous suction helps granulation tissue formation.
In the current study, the number of days required for fascial closure consideration or complete granulation tissue cover was significantly less in the NPWT group. In a cohort study to evaluate the effect of NPWT conducted among 29 trauma patients with an open abdomen, Suliburk et al13 showed that a mean of 7 days (range 3–18 days) was required until fascial closure following NPWT therapy. This may be because only 2 patients in the current study were trauma patients or because Suliburk et al13 applied NPWT therapy over a planned laparostoma but not on wounds due to dehiscence following primary fascial closure, while the present study examined post-laparotomy wound dehiscence. In their prospective evaluation of negative pressure fascial closure in 45 patients with laparostoma following trauma, Miller et al14 reported a delayed fascial closure rate of 88%, which was significantly higher than their previous similar studies. Similar to the present study, few studies have evaluated the ability to achieve wound cover as the end point. In their cohort study involving 21 patients, Heller et al12 showed 9 achieved fascial closure and stable cutaneous cover by skin grafting, and 6 achieved healing by secondary intension.
In the current study, apart from the difference in time to fascial closure/complete granulation tissue coverage between groups, no difference was noted in the rate of reaching the final end point (ie, the number of days needed to make a decision regarding closure either by surgical method or healing by secondary intention with granulation tissue cover). After excluding the patients in whom the final outcome could not be studied due to loss to follow-up, mortality, or discontinuation of treatment due to a complication during the study period, most patients in both groups achieved surgical fascial closure or complete granulation cover of the wound. However, the time required to reach complete wound closure is critically important, in part because it affects health costs.
In this study, patients in the NPWT group were discharged from the hospital earlier than patients in the non-NPWT group. Ko and Jung6 reported a considerable (although not significant) reduction in the length of hospital stay in their NPWT group (n = 25) compared to control (n = 185) (P = .06), but the NPWT sample size could have limited the statistical power. In the current study, the difference in time to discharge was expected, because time until complete granulation coverage/fascial closure was significantly shorter in the NPWT group.
In the present study, 1 patient in the NPWT group developed an ECF (3.8 %), and 1 patient developed a VCF (3.8%) after discharge at follow-up of 4 months; no patients in the control group developed an ECF. Although an ECF has been reported as a possible complication of NPWT, the exact risk of ECF formation following NPWT therapy is not well established. In their prospective cohort study, Perez et al15 proposed that the most common risk factors for development of an ECF are underlying illness with a poor general condition rather than due to NPWT. In their multicenter observational study, Bobkiewicz et al16 established that NPWT can be used safely in the treatment of an ECF. Other factors thought to play a role are intra-abdominal sepsis, sutured enterotomy, presence of intestinal anastomosis in the wound, mechanical trauma either due to injury or excessive intraoperative bowel handling, sutures in wound area causing cut through injuries to the bowel, and presence of exposed bowel in the wound.12-16 NPWT-associated factors that can contribute are suction tubing, which may produce bowel erosions, and the use of more bowel adherent black polyurethane foam.12-17
A systematic review by Misky et al17 concluded that NPWT can be considered safe treatment for an ECF, but multiple treatment strategies were proposed to reduce the risk of ECF occurrence. Strategies related to NPWT include covering the exposed bowel with a nonadherent sheet before applying the NPWT dressing, using fewer adherent white polyvinyl foam sponges, applying continuous suction instead of intermittent suction (thereby minimizing mechanical shear and deformation of the bowel), and maintaining suction pressure at 75 mm Hg rather than at 125 mm of Hg.15-18
One (1) VCF developed in a patient in the NPWT group who had received post-pelvic radiotherapy for carcinoma of the cervix and was operated for intestinal obstruction. The patient developed a delayed VCF at the 3-month follow-up after discharge; the fistula was likely due to the prior radiotherapy and extensive surgery. The incidence of ECF following NPWT in this study is similar to other studies. In their prospective evaluation, Miller et al14 reported an incidence of 2.3% in the study population, and in their prospective observational study of 37 patients, Perez et al15 reported an incidence of 3%.
In the current study, no intra-abdominal abscess formation or ventral hernias occurred. The follow-up period in the present study was up to 6 months, which may not be sufficient to detect late complications such as an incisional hernia.16,18 Miller et al14 reported a 2.3% incidence of incisional hernia at the mean follow up period of 185 days.