The Science Journal of the American Association for Respiratory Care
Introduction: A DODS delivers oxygen only as patient flow demand triggers the device. Consequently triggering sensitivity, or trigger threshold may be important to oxygen delivery. Higher trigger threshold (greater effort required) may result in missed breaths or late oxygen delivery. To determine whether triggering sensitivity might vary between DOS models, we constructed a mechanical model and evaluated five commercially available devices.
Methods: One side of a mechanical test lung was ?driven? with a linked ventilator. The second, ?breathing? side was connected to a simulated, machined ?nose?, in which a standard nasal cannula was placed. The cannula was connected to each DODS unit. A pressure transducer coupled with a computer data acquisition system was used to monitor the pressure at the outlet of the DODS. Peak Inspiratory Flow (PIF) was controlled on the ventilator to vary the simulated inspiratory effort. Lower PIF resulted in lower pressure changes in the cannula. Starting from a setting that consistently triggered the DODS, PIF was gradually reduced to a level at which the device was not triggered. By monitoring the pressure in the cannula, the precise minimum pressure change that triggered the device (trigger threshold) was determined.
Results: The average trigger threshold observed was 0.10 cmH2O. The full range of trigger threshold was 0.025 to 0.16 cmH2O, with device D being the most sensitive, and device A the least.
Conclusions: While clinical implications cannot be directly drawn from this data, trigger sensitivity variability exists between devices. Patients with shallow breathing patterns, those who breath through their mouth, or those using a DODS while sleeping may experience reduced oxygen delivery due to missed breaths or late delivery.
(See Original for Figure)