In this study, intraoperative GDFT based on SVV and CI obtained by FloTrac/Vigileo monitor facilitated the GI function and shorten the length of stay following major abdominal oncologic surgery.
The POGD is a primary complication following major abdominal surgery. A large prospective cohort study found that POGD (defined as intolerance of a full enteral diet) to be the most common postoperative morbid event associated with prolongation of hospital stay beyond 7 days (51% of patients).[1] The pathophysiology of POGD can be ischemic, metabolic, toxic, neurogenic, myogenic, pharmacologic, or mechanical. Perioperative fluid therapy plays a key role on POGD. Hypovolemia can cause loss of perfusion to the tip of the microvillus, triggering apoptosis and potentially necrosis, which typically requires about 3 days for recovery,[25] while excessive fluid administration may inhibit the gastrointestinal transit and result in significant interstitial edema. [26] Our previous meta-analyses and other meta-analysis found that GDFT could reduce the overall complication and facilitate recovery of GI function following major abdominal surgery.[8, 9, 24] GDFT has been suggested to apply during major abdominal surgery in high-risk patients.[27–29]. However, the role of GDFT on GI function in low-to-moderate patients remains uncertain. Some studies found that GDFT improved GI function recovery and reduced hospital stay in low-to-moderate risk patients following major abdominal surgery.[30–32] But the others suggested that the treatment benefit may be more marginal than previous believed.[13, 33–35]
The conflict of current evidence may be attributed to the following reasons. First of all, different GDFT algorithm were used in the clinical setting and there is no clear consensus as to the most effective parameter or the most appropriate method of monitoring. Our previous meta-analysis found that GDFT using CI/SVV as goals and using fluids and inotropes as interventions were associated with reduction on mortality and morbidity following major abdominal surgery.[8] Our GDFT algorithm was similar with Benes et al. study[18] and Mayer et al. study[17] which were conducted in high-risk patients. The findings of our study were in line with the previous two studies, and confirmed the beneficial effect of GDFT on recovery of GI function in low-to-moderate risk patients. Secondly, postoperative GI disorder was commonly referred to as postoperative ileus (POI). However, the heterogeneous definition of POI precludes the ability to ascertain the true incidence of the condition and study it properly within a research setting. In 2018, the American Society for Enhanced Recovery After Surgery (ERAS) and Perioperative Joint Consensus considered forgoing the traditional definition of POI for I-FEED scoring system, a more functional definition of POGD, to precisely describe the clinical manifestations of the GI disorder.[22] POGD was thus used in our study, and the I-FEED score was measured to evaluate GI function. Three categories of postoperative GI function were defined by I-FEED score system, including normal (I-FEED score 0–2), POGI (I-FEED score 3–5) and POGD (I-FEED score ≥ 6). We found GDFT significantly reduced the incidence of POGD (4% in GDFT group versus 32% in the control group) following major abdominal surgery. In addition, tolerance of an enteral diet is one of the fundamental components of postoperative hospital discharge criteria, we found that the time to first tolerate oral diet was shortened by 2 days in the GDFT group compared with the conventional fluid therapy group.
The independent effect of intraoperative volume was identified on postoperative recovery of GI function.[36–38] Adjustments in administration of fluids must be in timely manner to avoid both insufficient organ perfusion and fluid overload. In addition, the volume of crystalloid infusion during surgery was reported to have a significant effect on the structural and functional stability of the intestinal anastomosis in the early postoperative period.[36] In our study, SVV-guided GDFT significantly reduced the total amount of fluid by 29% and crystalloid administration by 27%. This suggest that the beneficial effect of GDFT on recovery of GI function can be attributed to guided and responsive fluid usage and to avoiding unnecessary and potential harmful fluid delivery when hemodynamic goals were met.
In our study, we found that GDFT guided by SVV/CI following major abdominal oncologic surgery was associated with a significant reduced postoperative hospital stay. The mean duration of hospital stay in the GDFT group was 9 days compared with 12 days in the control group. This 3 days reduction in postoperative stay is of similar magnitude to other studies.[17, 31, 32, 39] Furthermore, lower pain intensity after surgery and earlier postoperative mobilization were found in patients receiving GDFT. The potential explanation may be that GDFT could reduce the stress response and tissue edema, facilitate the recovery of patients, thus shorten length of hospital stay. However, no difference was found in the total number of patients with postoperative complications between the two groups, lack of statistical power could be a limitation to demonstrate the true association. Therefore, further prospective trials are needed to address this issue.
There were some limitations to this study that should be considered. First, this trial included a mixture of abdominal oncologic procedures which may potentially influence our results because different types of abdominal surgery led to different mechanical or manipulation forces on the gut and its mesentery. The two groups in this study were comparable with respect to surgical technique, type of procedure and operative POSSUM score. Of note, minimally invasive surgery compared with open procedure is associated with earlier recovery of GI function and shorter length of hospital stay. [4, 40, 41] Although 69% of procedures in our study were performed by laparoscopy, it was hard to draw a conclusion that GDFT may be effective in reducing POGD following laparoscopic procedures without pre-planned subgroup analysis. Further well-designed studies are thus needed to focus on this patient population. Second, although the data were collected by independent dedicated research personnel not involved in the intraoperative management of patients, we were unable to blind the anesthesiologists and investigators in operating room as to the treatment group, and hence may have introduced bias. However, intraoperative fluid administration in both groups was guided by specific fluid administration protocols, which should minimize bias. Third, the optimal cut-off value for SVV is still uncertain, results of protocols based only on variations itself should be assessed with caution. We used the 12% threshold in our study recommend by Ramsingh[32] for an SVV of over 12% indicates inadequate fluid volume.[42] A dynamic change of CI and MAP were used for decision-making to forestall potential flaws. In addition, we used a fixed tidal volume of 8 ml·kg− 1 and excluded patients with irregular heart rhythm to minimize all of potential confounders including vital volume[43] and heart rhythm[44] and assessed a sustained rise of SVV above 12% in a period of five minutes to start an intervention in order to exclude a possible bias due to surgical manipulations or other influences. Fourth, the sample size of this study was calculated based on the endpoint of length of hospital stay. The length of hospital stay is often viewed as a surrogate end-point as it may be influenced by non-medical elements, such as the type of health-care system or the patient’s desire to be discharged. However, standardized discharge criteria (Appendix 2) were used in this study [45] and mainly depends on return of GI function, and thus statistic power was sufficient to detect the difference in time to return of GI function. Finally, the GDFT strategy was only performed intraoperatively and postoperative fluid management was not standardized, so that we cannot exclude that a poor postoperative fluid management derogated the effect of an intraoperative fluid optimization.