Purpose or Case Report: Endotracheal or nasotracheal intubation can be difficult in preterm infants in an intensive care environment, with a high rate of endobronchial tube placement. We measured tracheal length and diameter in a population of post mortem fetuses to define the relationship between gestational age or body weight and tracheal size, in order to see whether this could help future tube selection or correct placement.
Methods & Materials: Written informed consent was obtained for all patients for clinical pre-autopsy PMMR as part of our institution’s clinical post mortem assessment. T₂ weighted isotropic PMMR sequences of the head and chest were retrospectively reconstructed into 3D MPR datasets to identify the airway. We excluded only cases in which the airway was either abnormal, or image quality was inadequate to permit measurements.
We measured trachea length (defined as from mouth to carina; TL), oropharyngeal length (mouth to glottis; OL) and tracheal diameter (internal minimum luminal diameter; TD). Mid-tracheal length was calculated from TL and OL. 20 random datasets were repeated to give a measure of intra-observer and inter-observer variability. Linear regression analysis was performed in SPSS.
Results: 117 cases were analysed, with mean age 27.5 ± 8.3 weeks gestation. We found a good linear relationship between tracheal length and gestational age (TL = 0.28 GEST + 0.14; R² = 0.91), and mid-tracheal length and gestational age (MTL = 0.23 GEST + 0.29; R² = 0.94). Tracheal diameter was more difficult to measure, particularly on small fetuses, with poorer linear relationship of TD = 0.009 GEST -0.05 (R² = 0.52).
Conclusions: The linear relationship between TL, TD and gestation may help intensive care practitioners to appropriately size and more correctly place endotracheal tube in preterm infants.