Intravenous fluid therapy for surgical patients should be optimal. The required optimal range is however narrow and by giving too much or too little fluid can result in adverse outcome161718. An adult surgical patient without any ongoing losses or deficits should have a daily maintenance fluid requirement between 1.75 to 2.75 Liters111920. In a recent study, perioperative maintenance fluid was given 3 liters of water and 154 mmol of sodium and it was considered a ‘standard’ fluid regimen21 although it is well over the required daily maintenance. Some studies have use ‘restricted’ fluid regimen and have provided to the patients the appropriate fluid requirement2122. While others have use in true sense of restrictive fluid by giving less than the daily requirement1423. However, the exact amount that is prescribed may not necessary be the amount that is given. There can be a slight variation to actual practice.

The criteria for the inclusion for this study are based on adult population who are more than 18 years of age, who underwent elective major abdominal operation. Both open and laparoscopic abdominal surgery, exclude gynecological surgery and transplant surgery. The reviews involved looking at perioperative fluids described as ‘restrictive’, ‘liberal’ and or ‘standard’ depend on the amount of volume of fluid that is design to administer. In some studies words, like interventions, goal directed fluid and study fluid is used to denote less amount of fluid comparably to the other and therefore is carefully interpreted as restrictive.

Consideration is also given to the time in which particular fluid regime is administered and hence will define perioperative fluid. Fluid that is administered within any hospital environment on a patient a day before surgery, continue through the operation and involves 24hrs after surgery. Although one study in this analysis involves during the first 8 hours post-surgery.

The type of fluid use is considered in this study and is accepted for both colloids and crystalloids. Blood and bloods products were used by some studies within this review but were used in intention-to-treat and not included in individual study protocol. During the procedure when there is a need for blood it is overly substituted ml for ml with colloids or a higher amount of crystalloid is given depended on the protocol. Analysis of result for the study is done accordingly.

All studies of this review satisfy the criteria for inclusion if and when final outcome is assessed. Primary outcome comprises one or two endpoint and any other outcomes are measured as secondary as defined in the review.

Primary outcome measures on all studies included here is on the length of hospital stay (LOS) after the surgery. Some studies prefer to use terms like surgical readiness for discharge (RfD) as a strict guideline to ascertain their objective of study. This was done in order to avoid reasons of hospital prolong stay due to social and economic reasons about the patient. One study21although was not clear on the LOS, uses complications as major and minor as its primary and secondary endpoints respectively. All of these studies use complications and death as their secondary outcome and analysis was done accordingly.

Randomized Control Trials (RCT) compare the effects (outcome) of restrictive, standard, liberal, control, or conservative fluids and either crystalloid and colloids during peri-operative period of major abdominal surgery was searched. Multi-data base system using Embase, Medline, Scopus were searched from 1992 to March 2022. Search terms including, ‘restrictive fluid’ ‘standard fluid’ ‘liberal’, peri-operative fluids, intravenous fluid, colonic resection, major abdominal surgery and or Gastro intestinal surgery. Combination of Boolean operators AND, OR, and NOT were used. Individual articles were also search from Google scholar as few articles were difficult accessing from the main domain. Result from the primary search was then screened according to the inclusion criteria. Potential articles were hand –searched and related articles included in the reference or previously cited were sought. Articles appear to have been reported from laboratory work and on animals were excluded. Only English language was predominantly included for the analysis in this review.

The progressive characteristics of the studies were further assessed for uniformity on the data. All fluids administer should define the perioperative period. Method of randomization use in allocating patients, concealment of study patient, and type of blinding individual or investigating team and any other circumstances like protocol violation during study were assessed comprehensively to determine the quality of the methods and also bias related contamination. The quality of the study was assessed using the Scottish Intercollegial Guidelines Network (SIGN).30The included studies are carefully screen for the time (pre, intra, post operative) when fluid is administered according to peri-operative course. It demonstrates the intervention of the study and accordingly assessed the outcome. The total amount of fluid administered is recorded for analysis. Other special intervention like fasting time before operation and bowel preparation, duration of operation, type of anesthesia and post operative analgesia are listed in Table 1 to enhance our review for any heterogeneity and uniformity to the studies.

Primary analysis includes all the RCT studies as identify above with measurable end point. The consistent endpoints are the length of hospital stay (LOS) or Readiness for Discharge (RfD) and complications. Therefore, the studies which identified these outcomes should constitute the secondary analysis. Two studies as mention before were not clear on their LOS, although measuring complications would ultimately lead to variation to the LOS measurement. Goal directed fluid therapy and Doppler studies were excluded.

RevMan 5.0 software program (The Nordic Cochrane Center, The Cochrane Collaboration, Denmark) was used for the analysis of the outcome using the standard methods recommended by the Cochrane collaboration29. Pooled analysis was performed using the random-effects model with Mantel- Haenszel method. Effect sizes for dichotomous variables was calculated and is presented as risk ratio with 95 % CI and for the continuous outcome is given as weighted mean differences (WMD). Heterogeneity of the included studies was assessed by considering the I2and Chi square (X2) P value. The threshold value for I2 are 25%, 50%, and above 50%, thereby representing low, moderate and high heterogeneity respectively.

The Preferred Reporting Items for Systematic Reviews and Meta- analysis (PRISMA) statement (Figure 1) illustrates the studies identified through our initial search. Fourteen (14) studies have defined our criteria were selected in the primary analysis. Goal directed fluid therapy (GDT) or use of Doppler to monitor the amount of fluids given was not part of this review3233343536373940and therefore, five studies excluded. Only one was excluded as the study was not blinded and its concealment allocation was poor 31. The final eight (n 8) satisfied our search criteria and study quality according to the SIGN methodology assessment.

There were total of 769 patients included in the final eight 2021232425262728 randomized clinical trials. The characteristic of each study is summarized in Table 1. Five studies 2124252728were double blinded and well concealed. Two studies 2023were single blinded and one study 26 however did not specify either patient or investigator was blinded. Randomization was done by computer generating randomization in three studies 212728 by sealed envelope method 20242526 and telephone randomization in one23. All studies were done in a single center except one.21 Most of the operation done for the study were for colorectal and only two included studies 2627 were done for abdominal vascular aneurysm since it was an elective laparotomy satisfying the criteria. Bowel preparation for all studies involving the left sided colorectal procedures except for two studies 2126. Even bowel preparation was done for the abdominal vascular surgery in one study27.

Although the eight studies have assessed the outcome as either Length of hospital stay (LOS) or range of complications. When primary and secondary outcomes were analyzed, four studies 21242526use complications as their primary outcome and three studies232728 use length of hospital stay as their primary outcome. However the study by Lobo et al20 have used gastric emptying time to both solid and liquid as his primary outcome and length of hospital stay as his secondary outcome. Complication ranges from wound infection, delay organ function, organ failure and death. While, McArdle et al 23have further classify their complication in to minor and major. The major complication then becomes the primary outcome measure. In the study by Nisanevich and his colleagues, they include death as a major complication and have used to assess their primary outcome25. However, none has died from their study. Readiness for discharge (RFD) was used to denote patients who are medically fit and have been discharge by their attending surgical team but has remain in the hospital due to other social issues. Vermeulen et al 28 reported study violation due to severe complications experienced by 40 % of the patients undergoing restrictive fluid regime. Also significantly increase in the length of hospital stay in restricted group (12.3 vs 8.3 days) as compare to liberal fluid group. Three studies assessed fluid given in the post operative period only 202728. Otherwise the rest of the studies assessed fluids administration during pre, intra and post operative period.