Resistance of endotracheal tubes measured after extubation in ICU patients

Methods The study was performed over patients intubated for at least 1 day in our ICU. Once the patient was extubated, tube was immediately stored in a plastic bag at room temperature and kept in a safe place until bench assessment. This was performed maximal 24 hours after extubation as follows. The endotracheal tube was attached to a filter (Hygrobac) and both were set to ASL 5000 active servo lung (IngMar medical). The lung model was set in passive condition in order to deliver two consecutive breaths at constant flow from 2 to -2 L/s. The filter was tested first then the filter and the endotracheal tube were run. The relationship of pressure (P) to flow was fitted to the following equation P=K1 flow + K2 flow 2 the where K1 and K2 are constants. P pertaining to endotracheal tube was obtained by subtracting P from filter to P from filter and endotracheal tube. Dividing P by flow led to RETT=K1+K2 flow. RETT at 1 L/s (cm H2O) was equal to K1 + K2. The relationships of K1, K2 or RETT to lenght of intubation was analysed by linear mixed model where tube brand and size were factors with random effects. Results We included 52 patients (34 male) of median (1st-3rd quartiles) age 68 (61-78) years. The median duration of intubation was 5.5 (2-9) days (min 1 max 19 days). Endotracheal tubes were from Mallinckrodt (n = 45), TaperGuard (n = 4) or Rush (n = 3) brands and internal diameter 7.0 (n = 10), 7.5 (n = 39), 8.0 (n = 3) mm. The relationships of K1, K2 or RETT to length of intubation were not significant taking into account both brand and size of endotracheal tubes (figure).