A PD catheter exit site is an open wound made using a tunneler, and it is always adjacent to a catheter tube. Catheters are typically made of smooth silicone rubber, and prolonged exit-site healing sometimes leads to early CRIs. Hence, strategies that prevent delay of exit-site healing and promote exit-site stabilization are essential for PD patients.
Wound bed preparation is a systematic strategy aimed at improving wound management by identifying and removing barriers to wound healing. The prototype of the concept emerged in the 1990s, gradually gained recognition, and developed into a systematized paradigm for the strategy of chronic wound management 17,18. The concept provides clinicians with a comprehensive approach to removing barriers to healing and stimulating the healing process for maximum benefit. Schultz et al. proposed the TIME acronym, which highlights four elements that need to be resolved with regard to wound bed preparation 19. “T” stands for tissue, “I” stands for inflammation and infection, “M” refers to moisture imbalance, and “E” refers to epithelial edge advancement. According to this concept, adequate management of the postoperative exit site of a PD catheter is necessary to avoid infection, moisture imbalance, and advancement of the wound edges.
In our study, the NPWT group had lower exit-site scores on the seventh postoperative day than the non-NPWT group. The proposed effects of NPWT on postoperative PD catheter exit sites are discussed below. First, the sites are kept hygienic because they are covered with special foam dressings and sealed with clear drape on the operative field. Second, continuous negative pressure removes exudate, resulting in a properly moisturized environment. The PD catheter is blindly directed through a subcutaneous tunnel to the marked site using a tunneler. This procedure frequently causes injury to small vessels in the subcutaneous tissue. In such cases of injury, prolonged bleeding from the exit site often occurs. The system of vacuum with suction is also effective for eliminating infectious wastes at the exit site. Third, the negative pressure causes contraction of the wound edge. Twadroski et al. hypothesized that loose fit of skin around the PD catheter would increase the risk of trauma and contamination 20. NPWT can reduce the surface area of the open wound and lead to early tight fixation. We posit that these three principal mechanisms discussed above great influence the PD catheter exit site as evidenced by the significantly low exit-site scores and the early stabilization of the exit site in the NPWT group. In contrast, the non-NPWT group tended to have high exit-site scores on the seventh postoperative day as evidenced by redness, crusts, and serous drainage. This finding suggests that the exit site is susceptible to trauma due to loose fixation and moisture imbalance caused by the extra exudate, especially after the operation. These factors also paradoxically reveal the usefulness of NPWT for postoperative exit sites.
Regarding secondary outcomes, the NPWT group also had lower exit-site scores over 180 days than the non-NPWT group. However, no statistically significant differences in time to first CRI and PD-related peritonitis were noted between the two groups. These results suggest that, over the long term, exit-site score and the incidence of CRI are independent variables. Further, we hypothesized that “down-growth” and daily self-care practice have major impacts on the gap between long-term exit-site score and the actual outbreak of an infection.
As earlier noted, a PD catheter exit site is an open wound that is always adjacent to a catheter tube. Resistance to infection depends on the formation of a biological barrier formed from tissue growing along a subcutaneous cuff made of polyethylene terephthalate. The epithelium contiguous to the silicone catheter tends to invert toward the cuff, creating a sinus between the tube and the skin. The exit site on which the “down-growth” forms under experimental conditions tends not to have swelling, crust, redness, or pain unless it is infected. This is because a biological barrier composed of epithelium typically covers the catheter tube completely. However, the “down-growth” forms a dead space that promotes accumulation of metabolic products and bacterial colonization, which result in CRIs 21,22. Although PD catheter exit site “down-growth” has been reported in a few studies, only the study by Yoshino et al. reported that redundant “down-growth” and increase in dead space are associated with insufficient catheter fixation and altered metabolism 23. It is easy to anticipate that trauma and contamination in the sinus directly increase the risks of CRIs and subsequent peritonitis. It is presumed that the score of the exit site on which “down-growths” form is not necessarily reflective of the risk of infection.
For the prevention of CRI and PD catheter-related peritonitis, daily self-care practices on the exit site must be emphasized. Although our center ensured that patients underwent a three-week PD training conducted by nursing staff with the appropriate qualifications and experience during their hospitalization, daily PD catheter exit-site care tends to become more personalized as the PD duration increases. Ding et al. reported that the level of adherence to different aspects of exit-site care varies between PD patients 24. The study found that patient adherence to proper hand hygiene, mask wearing, exit-site observation, secretion examination, and effective communication with PD staff influenced CRI history and exit-site issues. Educating PD patients to recognize the importance of exit-site assessment, daily self-care, and retraining of the relevant skills must be considered useful for the prevention of CRIs.
To the best of our knowledge, this study is the first randomized controlled trial to examine the effectiveness of NPWT for postoperative PD catheter exit sites. Over the years, many strategies aimed at preventing CRI and subsequent peritonitis have been attempted. Although ISPD guidelines provide some strong recommendations, many of them are controversial or supported by limited evidence. In the study by Mori et al., it was reported that NPWT is effective for early tight fixation to the skin around the catheter 16; however, the study was observational. Our randomized prospective study shows that NPWT is associated with low exit-site scores in the early postoperative period and early stabilization of the exit site.
Our study has some limitations that should be noted. The required sample size of this study was calculated based on the estimation of statistically significant difference in exit-site scores. Although our study did not reveal statistically significant differences in time to first CRI and PD-related peritonitis between the NPWT and non-NPWT groups, larger samples and longer follow-up durations are necessary for more accurate assessments of PD patients. This is because the incidences of CRI and PD-related peritonitis have decreased considerably; for example, the incidence rate of PD-related peritonitis was reported to be 0.26 episodes/patient-year 25.
In conclusion, this study is the first randomized controlled trial to assess the effectiveness of NPWT for postoperative exit sites by comparing NPWT with conventional dressing in terms of exit-site score. The NPWT group had significantly lower exit-site scores on the seventh postoperative day and over 180 days than the non-NPWT group. Therefore, we recommend NPWT as an option for early stabilization of the exit site.