Predictors of prolonged mechanical ventilation following tetralogy of Fallot repair: a multivariable analysis of preoperative cyanosis and intraoperative factors

Background. Tetralogy of Fallot (TOF) is the most common cyanotic congenital heart defect. Despite a dramatic reduction in early postoperative mortality, postoperative prolonged mechanical ventilation (PMV) continues to be a major determinant of morbidity, intensive-care utilization of resources, and midterm right-ventricular performance. Recognizing preoperative and intraoperative predictors of PMV may assist in the refinement of fast-track extubation pathways. The purpose was to examine whether preoperative markers of cyanosis (oxygen saturation, hematocrit) and intraoperative variables (aortic cross-clamp (ACC) time, cardiopulmonary bypass time) are associated with PMV after primary intracardiac repair of TOF. Materials and methods. In this single-center, retrospective cohort of 46 consecutive children (median age 3.0 years; range 0.1–17) who underwent primary complete TOF repair, PMV was defined a priori as postoperative invasive ventilation > 24 h. Groups were compared using the Mann-Whitney U test and Fisher exact test, and Spearman rank correlation quantified continuous associations with ventilation duration. Because of the small number of outcome events, the primary multivariable model used Firth penalized logistic regression with preoperative SpO2 and ACC time as pre-specified covariates; standard maximum-likelihood logistic regression was reported as a sensitivity analysis. Discrimination was assessed using the area under the receiver operating characteristic curve (AUROC), with 95% confidence intervals (CI) estimated from 1,000 bootstrap resamples. Results. PMV was used in 10 of 46 patients (21.7 %). Patients with PMV had lower preoperative SpO2 (median 74 vs 88 %, p = 0.020) and a longer ICU stay (median 9 vs 4 days, p < 0.001). Ventilation duration correlated inversely with preoperative SpO2 (Spearman ρ = –0.38, p = 0.009) and positively with cardiopulmonary bypass time (ρ = 0.32, p = 0.031); the correlation with ACC time was weaker and not statistically significant (ρ = 0.24, p = 0.115). In the Firth multivariable model, each 10 % absolute decrease in preoperative SpO2 was associated with an adjusted odds ratio (OR) of 1.78 (95% CI 0.97–3.26), whereas ACC time was not independently associated (per 10-min OR 1.07, 95% CI 0.79–1.44); the combined-model AUROC was 0.74 (95% CI 0.59–0.91). In the unpenalized sensitivity model, the SpO2 association reached statistical significance (per 10 % decrease OR 2.03, 95% CI 1.03–4.00). Conclusions. Lower preoperative oxygen saturation was the most consistent predictor of PMV after TOF repair, whereas intraoperative ischemic time showed a weaker, non-independent signal. Given the limited sample size and event count, these findings are hypothesis-generating and require validation in larger, prefe­rably multicenter, cohorts.