Literature search strategy
Our search combined both MeSH (Medical Subject Headings) terms and free-text terms to comprehensively query databases including the Chinese biomedical literature database, Vip database, CNKI, Wanfang, PubMed, Embase, Cochrane Library, and Web of Science. Searches were conducted in both English and Chinese from each database's inception to 20 December 2022. We also manually searched references and related articles from the included literature for further pertinent studies. Using PubMed as an example, the combined search strategy is articulated as follows: (("Cannula"[Mesh]) OR (((((Cannulae[Title/Abstract]) OR (Nasal Cannula[Title/Abstract])) OR (Cannula, Nasal[Title/Abstract])) OR (Nasal Cannulae[Title/Abstract])) OR (Cannulae, Nasal[Title/Abstract]))) AND (("Cardiac Surgical Procedures"[Mesh]) OR ((((((((((((Procedure, Cardiac Surgical[Title/Abstract]) OR (Procedures, Cardiac Surgical[Title/Abstract])) OR (Surgical Procedure, Cardiac[Title/Abstract])) OR (Surgical Procedures, Cardiac[Title/Abstract])) OR (Surgical Procedures, Heart[Title/Abstract]))) OR (Cardiac Surgical Procedure[Title/Abstract])) OR (Heart Surgical Procedures[Title/Abstract])) OR (Procedure, Heart Surgical[Title/Abstract])) OR (Procedures, Heart Surgical[Title/Abstract])) OR (Surgical Procedure, Heart[Title/Abstract])) OR (Heart Surgical Procedure[Title/Abstract]))). Additional search keywords included: "high-flow oxygen therapy," "high-flow nasal cannula," "nasal high-flow oxygen therapy," "HFNC," "HHFNC," "HHFN," "Congenital Heart Disease," "Heart Abnormality," "Malformation of Hearts," "infant," "child," and "pediatrics," among others.
Literature Inclusion and exclusion criteria
Literature inclusion criteria: (1) study type: randomized controlled trial (RCT) or cohort study; (2) study population: withdrawal from mechanical ventilation in children after CHS; (3) management measures: treatment with HFNC and NIV. Literature exclusion criteria: (1) duplicate publications; (2) animal trials, conference articles, academic articles; (3) literature for which the full text was not available or access to the data had failed; (4) literature for which the statistical indicators required for this study were not available after reading the complete text, or for which statistical indicators were available but data extraction was not possible, and attempts to contact the authors had failed.
Literature selection and data extraction
Two researchers independently screened the articles by reviewing the titles and abstracts based on the inclusion and exclusion criteria. Articles that did not meet the criteria were excluded. For the potentially relevant articles, a full-text review was conducted to finalize the selection. In cases of disagreement, the issues were discussed and resolved, or a decision was made by a third researcher. The extracted literature covered: (1) general information: including authors, year of publication, and sample size; (2) characteristics of study subjects: including gender and age; (3) interventions: including treatment and control measures; (4) outcome indicators: ① reintubation rate ② ICU stay duration ③ extracorporeal circulation duration ④ mechanical ventilation duration ⑤ PaO2 at 24 hour after application of oxygen therapy ⑥ PaCO2 at 24 hour after application of oxygen therapy; (5) type of study.
Risk of bias assessment in the Literature
To evaluate the methodological quality of the RCTs, we utilized the guidelines from the Cochrane Handbook for Systematic Reviews of Interventions.9 Two researchers independently assessed the RCTs for potential bias using the risk of bias assessment tool recommended by the Cochrane Handbook. For cohort studies, methodological quality was appraised using the Newcastle-Ottawa Scale (NOS), with a maximum score of 9. In cases of disagreement, the discrepancies were discussed and resolved, or adjudicated by a third researcher.
The RCT evaluation comprised seven domains: random sequence generation, allocation concealment, blinding of participants and personnel, blinding of outcome assessment, incomplete outcome data, selective reporting, and other potential sources of bias. Each domain was categorized as having a low, unclear, or high risk of bias based on the assessment criteria. These risks were designated as “L” for low risk of bias, “U” for unclear risk, and “H” for high risk. Based on these categorizations, the overall quality of the studies was ranked as “A” if they fully met the criteria, “B” if they partially met them, and “C” if they did not comply at all.
The NOS criteria for cohort studies included three main sections and eight domains, totaling a possible score of 9. Scores less than five were deemed low quality, scores between 5 and 7 were considered moderate quality, and scores between 8 and 9 were categorized as high quality.
Statistical analysis
Data processing and graphical representations (forest plots) were conducted using RevMan 5.4 software. For continuous variables, the effect measure was presented as the weighted mean difference (MD) with a 95% confidence interval (CI). For dichotomous variables, the risk ratio (RR) was utilized. Study heterogeneity was assessed using the X2 test. If P ≥ 0.05 and I2 < 50%, the studies were deemed to have low heterogeneity, and a fixed-effects model was employed for the analysis. Conversely, if P < 0.05 and I2 ≥ 50%, the studies demonstrated significant heterogeneity, prompting the use of a random-effects model. In cases of identified heterogeneity, we probed its source, conducted subgroup analyses to pinpoint the root of the heterogeneity, or executed a sensitivity analysis. Funnel plots were employed to assess potential publication bias among the studies. The significance level for the meta-analysis was set at α = 0.05, with P-values less than 0.05 indicating statistical significance.