An in vitro technique to measure resistance to compression and kinking of endotracheal tubes

Background: During intraoperative care, ventilatory parameters including peak inflating pressure (PIP) and exhaled tidal volumes are continuously monitored to assess changes in respiratory resistance and compliance. Changes in these parameters, such as an increase in PIP or a decrease in the exhaled tidal volume, may indicate various pathologic processes that may require immediate attention to prevent inadequate ventilation resulting in hypoxemia or hypercarbia. A kinked endotracheal tube (ETT) may mimic other pathologic processes including bronchospasm, mainstem intubation, or ventilator malfunction. As newer ETTs are developed, a key factor in their design should be resistance to kinking or occlusion due to patient positioning. Methods: The current project developed and describes the process for using a repeatable in vitro mechanical test to determine resistance to kinking by an ETT. Results: The mechanical testing procedure can be used to determine the compression force and distance required to kink an ETT under different conditions including temperature. The force required to induce devastating kink failure was lower during heated testing conditions. The addition of airflow through the ETTs during compression testing confirms the occurrence of airway obstruction at approximately the same time a mechanical kink is observed on the force-versus-distance curves. Conclusions: These procedures may be used to characterize and evaluate ETT designs under in vitro conditions mimicking those in the clinical practice.