This research showed that there was no difference in the infusion volume and NPWT output volume between early anastomosis and delayed anastomosis during TAC in DCL. The presence or absence of anastomosis during TAC management does not affect NPWT output volume. In patients with delayed anastomosis who received the same infusion volume as the early anastomosis patients, anastomosis and abdominal closure were possible in all cases, and infusion restrictions were not necessary in delayed anastomosis compared with early anastomosis. However, it is necessary to exercise care when performing delayed anastomosis. When a delayed anastomosis planned for 48 hours after initial surgery is complicated, the surgeon must consider postponing anastomosis instead of performing it forcibly. Moreover, the serum albumin value 48 hours after the initial surgery is not a useful indicator of whether delayed anastomosis should be postponed or conducted.
The drainage of ascites using NPWT during TAC has been shown to be beneficial due to such effects as the reduction of intestinal edema and the lowering of inflammatory mediator levels [21–23]. However, there are also reports that suggest that NPWT output volume is correlated with infusion volume and is higher in fatal cases . When ascites are drained with NPWT, albumin is lost, which is associated with the failure of PFC after TAC . Moreover, hypoalbuminemia is a potential factor for dilutive hypoalbuminemia caused by infusion resuscitation [25, 26] and is associated with anastomotic leakage after digestive tract surgery [18–20]. Loftus et al.  found that late hypoalbuminemia is associated with failure of PFC. According to that report, no difference was observed in the serum albumin value up to 96 hours after TAC between the group with PFC and the group in which PFC could not be achieved. In this study, no difference in the serum albumin level 48 hours after surgery was observed between the no DCL group, the DCL-early group, and the DCL-delay group. Albumin loss due to NPWT output or dilution due to infusion, differenced between abdominal closure and laparotomy were not related to the albumin value. Additionally, there was no difference in the serum albumin value between the group that underwent delayed anastomosis during second-look surgery and the group in which delayed anastomosis was postponed. From these results, we cannot say that the serum albumin value after 48 hours from the initial surgery is a useful indicator of anastomosis. Considering the limited doses of albumin preparation administered and the low number of suture failures, the administration of exogenous albumin to prevent anastomotic leakage and reduce intestinal edema in cases of delayed anastomosis is not always useful.
Increased NPWT output was observed with vasopressor use. Since the NPWT output is related to prognosis, the NPWT output tended to be large in the group that received vasopressors, with the exception of the 3 patients who died within 28 days (1513.4 ± 779.7 ml vs 981.4 ± 449.3 ml; p = 0.0021). Norepinephrine is an α-adrenergic agonist that has a strong vasoconstricting action , and the possibility that it could reduce NPWT output was also considered. However, vasoconstriction leads to increase in venous reflux  and creates a special intra-abdominal environment in the only abdominal pressure is negative pressure, which could cause edema and extravasation of water and may be related to the increase in NPWT output. The selection of delayed anastomosis over early anastomosis did not increase the need for renal replacement therapy or the administration of vasoactive drugs or albumin. These findings show that the financial burden associated with delayed anastomosis is the same as that associated with early anastomosis. Interestingly, the delayed anastomosis group tended to have a shorter laparotomy duration than the early anastomosis group. The financial burden associated with TAC management is a result of delayed anastomosis. Delayed anastomosis involves considerable trauma and may be associated less with intra-abdominal contamination than with intra-abdominal sepsis and persistent inflammation resulting from intra-abdominal sepsis and intestinal edema . The laparotomy duration found in this study is considered to be a localized result in view of bias regarding the disease and that the abdomen was closed at the discretion of the surgeon.
An association between insufficient infusion and NPWT output volume has been indicated as a reason for acute kidney injury . In this study, it was observed that the NPWT output volume tended to be large in the group that received renal replacement therapy. No difference was observed in the infusion volume, but the urine volume differed. Renal damage is considered to be the reason for the suppressed urine volume and large NPWT output. However, the possibility that increased NPWT output and insufficient infusion led to the occurrence of renal damage cannot be ruled out. A bolus administration of infusion corresponding to the NPWT output volume could have prevented the need for renal replacement therapy. In NPWT management, the optimal negative pressure treatment to maximize tissue growth is approximately − 125 mmHg, and the pressure level when active bleeding due to coagulative failure is suspected is approximately − 75 mmHg [31, 32]. Loftus et al. [16, 17, 29, 33] reported that 1300–1900 ml was the median value of NPWT output up to 48 hours after TAC in 4 studies that reported NPWT output. However, this could not be confirmed except in 1 report in which the NPWT negative pressure (suction amount) was − 75 mmHg. In this study, the median value of NPWT output up to 48 hours after surgery was 1080 ml. The NPWT output was less than that in the previously mentioned report. Our suction pressure setting was − 30 cmH2O (1 mmHg = 1.36 cmH2O), and low pressure management was considered one of the factors for this comparably low output. This study showed that the presence or absence of anastomosis does not impact NPWT ejection volume; however, since the NPWT output volume is predicted to depend on the suction pressure, it is necessary to consider the difference in suction pressure.
The NPWT output was lower, and the urine volume tended to be higher, in the group that underwent anastomosis during second-look surgery than in the group with postponed anastomosis. Sustainable maintenance of urine volume is considered to have reduced NPWT output, and the suppression of intestinal edema made it possible to perform anastomosis. The group in which anastomosis was postponed had higher physiological severity and more frequently received renal replacement therapy. There was no protocol for postponing delayed anastomosis, and the decision was made at the discretion of the surgeon. In the group with postponed anastomosis, the PaO2/FiO2 ratio before the second-look surgery tended to be lower, and CRP tended to be high, and general conditions and inflammation may have been involved in the postponement of anastomosis. Regarding delayed anastomosis after 48 hours, the large NPWT output may be associated with the postponement of anastomosis reflecting persistent inflammation, intestinal edema and general conditions. Additionally, low NPWT output is not necessarily disadvantageous for delayed anastomosis. The effect of drainage due to NPWT output over 48 hours must be comprehensively evaluated in combination with other body fluid balance indicators. It is difficult to think of PFC and anastomosis as the same procedure since their purpose, time to implementation and such differ. When the ultimate goal is anastomosis, early anastomosis and delayed anastomosis can be managed with the same infusion volume. However, in terms of whether delayed anastomosis is conducted or postponed, the infusion volume is related to pathology and hence should be the subject of further study by disease with a greater number of subjects.
In this study, the delayed anastomosis group included many cases of large intestine damage due to trauma, and bias was observed. Possible reasons are as follows: In large intestine injury, there is no protocol for selecting delayed anastomosis, and the surgeon may have consciously avoided selecting patients with factors such as dislodging of the colon (mobilization) for reconstruction, etc., that may prolong the duration of surgery or cause unnecessary bleeding. In HVI and lower digestive tract perforation, controlling the leakage of intestinal contents must be considered. Even in cases in which the abdomen can be physically closed, the advantage of selecting open abdomen as a drainage effect corresponding to intra-abdominal contamination has been shown . The purpose of performing early anastomosis during the initial surgery and selecting TAC is to move the patient to intensive care with the aim of controlling rapid bleeding and contamination, shorten the surgery time to greatest the possible extent, and encourage early physiological optimization . However, it is necessary to reconsider some matters, such as the need for TAC with early anastomosis and whether patients for whom early anastomosis is possible might not have been selected for delayed anastomosis. Regarding DCL, overuse  and increased risk of abdominal complications  have also been pointed out. In addition, it is necessary to recognize that delayed anastomosis itself can have negative impacts; reports have described it as a disadvantageous treatment strategy  and have raised the possibility of ongoing peritonitis , increased anastomotic leakage if PFC is not possible during second-look surgery , and other factors.
This study has several limitations. First, our data were obtained from a single center with a limited number of diseases and cases. Second, the albumin value included in the ascites drained from NPWT was not measured, and therefore, the amount of albumin lost could not be clarified. Third, there are no clear criteria regarding the decision to perform or postpone delayed anastomosis. It is necessary to establish objective treatment selection criteria that do not depend on the subjective judgment of the surgeon. In the future, reconsideration to address multiple breaking points is required.