We used the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols (PRISMA-P) 2015 statement and guidelines to inform the development of this protocol.[17, 18] See additional file 1 for the checklist.
Patient and public involvement statement
Patients were not involved in the development of this protocol.
Study design
We will incorporate the following inclusion criteria:
Cohort studies:
- Reported incident rates of POHG in surgical patients
- Published before
- Published in any language
We will exclude:
- Studies not conducted in humans
- Case-control studies, case reports, and studies that do not report the incidence of POHG will be excluded
- Meeting abstracts, review papers, and commentaries
Domain
We will include studies if they are related to POHG in surgical patients.
Population/Patients
We will include studies that report data generated from surgical patient participants, regardless of age, gender and sex.
Exposure
Early postoperative hyperglycemia will be defined as a high blood glucose within 48 hours postoperatively. The definition of “high blood glucose” will be study-specific. A vast majority of published studies define POHG as a blood glucose of 140 mg/dL and above. However, in some other studies this cutoff varies. We will carry out sensitivity analysis by using various cutoff.
Outcomes
The primary outcome will be the incidence of POHG. The second outcomes are the risk factories and postoperative outcomes associated with POHG.
Search Strategy
Geographical context
We will include studies from all over the globe. We will, however, estimate regional differences through subgroup analysis.
Database searches
The following databases will be searched: PubMed (MEDLINE), Scopus, EMBASE, Cochrane Library, OVID (HEALTH STAR), OVID (MEDLINE), Joana Briggs Institute EBF Database and Web of Science. We will use a snowballing method to include to search the citation lists of included papers. This will be accomplished by using the ‘cited by’ tool in Google Scholar. Efforts will be made to contact authors of ongoing studies and in-press literature for information regarding additional studies or missing data.
Search Terms
Our keyword search will be based on Medical Subject Headings (MeSH) and text words. The surgical care filter will contain the following MesH terms: “Postoperative Period”, OR “Perioperative Period”, OR “Surgical Procedures, Operative”. The early postoperative hyperglycemia contained MeSH terms” Hyperglycemia” OR "Blood Glucose” OR “Hypoglycemic agents” with text words “blood glucose” OR “glycemic control” OR” insulin”, This search strategy will be further adapted and tailored for use with each database, using Boolean operators (OR/ AND), truncations, proximity operators and Medical Subject Heading, as appropriate for each database. For a complete list of search terms, see online additional file 2.
Study selection and data extraction
Title and abstract screening
The citations will be downloaded into the Endnote software and will exclude duplicate articles. Two review team members (JAL, AES) will independently screen studies in two stages. In the first stage, the two reviewers (JAL, AES) will independently screen titles and abstracts. They will document, with reasons, the studies excluded from the review.
Full-text screening and data extraction
In the second stage, full-text versions of selected abstracts will be downloaded/retrieved and assessed independently by the two reviewers (JAL, AES). They will extract data from eligible papers identified during the abstract screening step. In the event of disagreement, the two authors will confer and discuss with each other and, if necessary, a third review author (PS) to reach consensus. When abstracts and subsequently included papers are not available in English, translators will be sought. Using the format of the standard data extraction form that has been validated and used somewhere,[19] we will extract the following information: first author, country in which the study was conducted, year of publication, study period, research methodology, total sample size using study level median age, year of publication, study level gender proportions, proportion of type 2 diabetes, mean body mass index, American Society of Anesthesiologists and type of surgical procedure and study limitations. Data will be extracted independently by two authors (JAL, AES). In case of missing data, one attempt will be made to contact the corresponding authors of studies by email. If the author fails to provide additional information, a decision will be made as to whether to include the study in the final review.
Assessment of methodological quality of the papers
Two authors (JAL, AES) will independently assess the quality of the papers included in the review. We are including only observational cohort studies. Therefore, assessment of methodological quality will be conducted using the Newcastle-Ottawa Quality Assessment Scale, which is a validated tool for assessing quantitative cross-sectional, case-control and cohort studies.[20] Scores between 7 and the maximum score of 9 will be defined as high quality; scores between 4 and 6 will be defined as intermediate quality and scores between 1 and 3 will be defined as low quality. Discrepancies in scoring will be resolved by discussion with a third author (PS). Studies will be included regardless of the risk of bias and quality scores, but sensitivity analysis will be conducted to ascertain the impact of their inclusion.
Data synthesis, analysis, analytic framework
We will use the metaprop function of the meta-package in R Statistical Software for analysis.[21] The primary outcome will be the incidence of POHG in surgical patients. We will use the random-effects model with a logit transformation of proportions for the pooling of studies. The confidence intervals will be calculated using the exact binomial (Clopper-Pearson) interval method.[21] We will assess the between-study heterogeneity using the I2 statistic, expressed as %, low (25%), moderate (50%), and high (75%) and Cochrane’s Q statistic (significance level < 0.05). We will perform subgroup meta-analyses to look at geographical differences in the incidence of POHG and conduct a meta-regression analysis, using study level median age, and study level gender proportions, year of study, the proportion of type 2 diabetes, mean body mass index, American Society of Anesthesiologists and type of surgical procedure. We will report absolute differences (per 1000) in the overall POHG probability. Relative risk ratios (RR) or odds ratios (OR) and 95% confidence intervals will be used to report the association of POHG with the risk factors and postoperative outcomes. The Egger’s test and funnel plots will be used to assess publication bias.
Risk of bias assessment for retained studies
We will perform sensitivity analysis by the use of subgroup meta-analyses to look at geographical differences in the incidence of POHG and conduct a meta-regression analysis,[22] using study level median age, year of publication, study level gender proportions, proportion of type 2 diabetes, mean body mass index, American Society of Anesthesiologists and type of surgical procedure. We will report absolute differences (per 1000) in the overall probability of POHG. The Egger’s test and funnel plots will be used to assess publication bias.
Presentation of results and reporting
The PRISMA guidelines will be used and the checklist will accompany the publication. Quantitative data will be summarized and presented in tables, forest plots, and maps. The incidence of POHG will be presented by continents, by study design and by surgical procedure type. Meta-regression analysis will be reported as absolute differences (per 1000) in the overall probability of POHG. We will report RR or odds ratios (OR) and the 95% CI for the association of POHG with risk factors and postoperative outcomes.
Potential amendments
The review of the protocol commenced in 2020 and the study is expected to be completed by 2021. We do not foresee amendments to this protocol. However, in case a need for amendment should arise, it will be registered and reported.
Patient and public involvement
Patients were not involved in the development of this systematic review protocol.