Material and Method: In a retrospective study of 260 cardiac patients that included those with failure to thrive, aged 2 to 7 years was done. The actual uncuffed endotracheal tube (ETT) size was compared with the predicted one, using both the ABF [ID (mm) = age (years)/4 + 4] and the HBF [ID (mm) = height (cm)/30 + 2].

Results: ABF and HBF correctly predicted 50.8% and 50.4% of ETT sizes (p = 1.0), whereas three sizes of tubes (one above and one below the predicted size) cover 95.8% and 93.5% of the patients, respectively (p = 0.24). In patients with FTT, both the ABF and HBF correctly predicted 56.6% of ETT sizes.

Conclusion: Age- and height-based formula for estimating tube size in cardio-surgical children is equivalent and independent of physical development. Age-based formula as the simple method can be recommended. The availability of three tube sizes (one smaller, one larger than estimated) should be ensured.

Keywords: Age-based formula, Anesthesia, Height-based formula, Pediatric cardiac, Tracheal tube size estimation