Concordance Between Anthropometric Formula Predictions and Chest Radiograph-Confirmed Endotracheal Tube Depth in Young Infants: A Retrospective Cohort Study from Saudi Arabia

Background: Accurate endotracheal tube (ETT) insertion depth is critical in infants and young children, where tracheal malposition carries significant risk. Formula-based depth estimation is widely used at the bedside, but the performance of published formulas in children under two years of age admitted to a general PICU remains poorly characterized. Methods: A retrospective, single-center study was conducted at the PICU of King Saud Medical City, Riyadh. A total of 115 patients aged 1–24 months requiring orotracheal intubation were included. ETT depth was predicted using five established formulas: height-based [(H/10)+5], weight-based [W+6], ETT size-based [ETT×3], Lee weight-based [5.5+0.5W], and Lee height-based [3+0.1H]. Agreement between predicted and radiographically confirmed insertion depth was assessed using Lin’s concordance correlation coefficient (CCC), Bland–Altman analysis, and clinical classification of predictions. Results: None of the five formulas achieved acceptable concordance (CCC < 0.75 for all). The height-based formula performed best among published formulas, with negligible bias and the highest proportion of clinically acceptable predictions. Both Lee formulas showed near-universal systematic underestimation and are not suitable for this age group. Over half of all intubations resulted in non-ideal ETT position on the first post-intubation chest X-ray. Novel cohort-derived regression equations outperformed all published formulas, with the weight-based equation (Depth = 0.385 × Weight + 9.145) emerging as the strongest predictor of insertion depth. Conclusions: No published formula achieved reliable concordance with radiographic ETT depth in children aged 1–24 months. The cohort-derived weight-based formula represents a more accurate bedside tool for this population and warrants prospective external validation. Post-intubation radiographic verification remains essential.