Measurement of endotracheal tube secretions volume by micro computed tomography (MicroCT) scan: an experimental and clinical study

Background: Biofilm accumulates within the endotracheal tube (ETT) early after intubation. Contaminated secretions in the ETT are associated with increased risk for microbial dissemination in the distal airways and increased resistance to airflow. We evaluated the effectiveness of micro computed tomography (MicroCT) for the quantification of ETT inner volume reduction in critically ill patients. Methods: We injected a known amount of gel into unused ETT to simulate secretions. We calculated the volume of gel analyzing MicroCT scans for a length of 20 cm. We then collected eleven ETTs after extubation of critically ill patients, recording clinical and demographical data. We assessed the amount of secretions by MicroCT and obtained ETT microbiological cultures. Results: Gel volumes assessed by MicroCT strongly correlated with injected gel volumes (p < 0.001, r2 = 0.999).MicroCT revealed the accumulation of secretions on all the ETTs (median 0.154, IQR:0.02-0.837 mL), corresponding to an average cross-sectional area reduction of 1.7%. The amount of secretions inversely correlated with patients' age (p = 0.011, rho = -0.727) but not with days of intubation, SAPS2, PaO2/FiO2 assessed on admission. Accumulation of secretions was higher in the cuff region (p = 0.003). Microbial growth occurred in cultures from 9/11 ETTs, and did not correlate with secretions amount. In 7/11 cases the same microbes were identified also in tracheal aspirates. Conclusions: MicroCT appears as a feasible and precise technique to measure volume of secretions within ETTs after extubation. In patients, secretions tend to accumulate in the cuff region, with high variability among patients.