Flow resistive properties of tracheostomy tubes and impact of external work of breathing in respiratory rehabilitation after traumatic brain injury

Background: The tracheostomy is, usually, performed in order to facilitate the suctioning of bronchial secretions so preventing atelectasis, pneumonia and increased V/Q mismatching. Nevertheless, the presence of a tracheostomy tube determines an extra burden for the respiratory muscle that could be crucial in order to maintain an adequate spontaneous ventilation. Therefore, we undertook this study to measure the impact of tracheostomy tubes on resistive external work of breathing. Method: We measured, in vitro, the resistive properties of tracheostomy tubes (Shiley-Mallinkrodt Medical Italy), size 8-6 (internal diameter 7,6 mm and 6,4mm, length 81 and 78 mm, respectively), fenestrated and normally manufactured. We connected each cannula to the ‘Y’ piece of the inspiratory limb of the respiratory circuit and measured for each tube, different in size and characteristics, the drop in pressure, using the pressure transducer and pneumotacograph of the ventilator, along flow axis at different constant flow (0.5-1.0-1.2 L/s). By dividing the drop in pressure by the relative constant flow, we obtained the flow resistance (R) (cm H2O/L/s). Results: 8 normal 8 fenestrated Flow (L/s) R (cmH2O/L/s) Flow (L/s) R (cmH2O/L/s) 0.5 1.5 0.5 0.75 1.0 3.82 1.0 3.15 1.2 5.0 1.2 4.12 6 normal 6 fenestrated Flow (L/s) R (cmH2O/L/s) Flow (L/s) R (cmH2O/L/s) 0.5 2.85 0.5 2.45 1.0 9.45 1.0 8.25 1.2 11.2 1.2 10.0 Conclusion: We can conclude that at high flow (1.0-1.2) Pres (R•Flow) (resistive pressure) is substantial, particularly with tubes of small size and the pressure the respiratory muscles have to generate to overcome the flow resistance offered by the tracheostomy tubes is higher in normally manufactured tubes than in fenestrated tubes with the same internal diameter; consequently external work performed by the patient is enhanced. This conclusion is very important in pulmonary rehabilitation treatment, during acute phase when there are TBI patients with tracheotomy and placement of a tracheotomy tube.