Influence of Two Different Interfaces for Noninvasive Ventilation Compared to Invasive Ventilation on the Mechanical Properties and Performance of a Respiratory System
Noninvasive ventilation (NIV) is increasingly used ’ in the treatment of acute and chronic respiratory failure and during weaning from invasive ventilation. NIV has been applied in patients with acute hypoxemic respiratory failure, severe cardiogenic pulmonary edema, or acute exacerbation of COPD in order to decrease the need and the complications of endotracheal intubation. other
Noninvasive respiratory support can be applied either as continuous positive airway pressure (CPAP) alone or as NIV with inspiratory pressure support (NPSV) by means of a nasal or face mask. Problems with the widely used face masks result partially from air leakage,- discomfort of the patient, and pressure-related ulcerations of the nose.’ These problems may limit the duration of use and account for a large proportion of NIV failures. In an attempt to improve NIV tolerance, a helmet was developed that has been successfully used in different clinical situ-ations.”
The increased importance of NIV in intensive care medicine and the new interfaces for its application led to the development of special modes of intensive care ventilators to overcome the problems related to higher gas leakage and dead space. Only limited data are available on how the performance of a ventilatory system is affected by such a helmet or a face mask compared to standard invasive ventilation. With demand flow systems, an inspiratory effort of the patient is necessary to trigger gas flow from the respirator.
Thus, the trigger sensitivity of the whole respiratory system is of major importance for the work of breathing.’ The helmet for NIV may affect the trigger sensitivity due to its large compressible volume. Furthermore, besides the specific settings of the ventilator, individual patient characteristics like compliance and resistance of the respiratory system and respiratory rate (RR) as well as the amount of gas leakage may affect the performance of the system and could potentially result in desynchronization between ventilator and patient. Consequently, during NPSV, the patient may inspire with delayed or even without any support from the ventilator (wasted efforts). Therefore, the aim of this study was to characterize the effects of two commonly used interfaces for NIV, face mask and helmet, on the performance of an ICU ventilator in comparison to invasive ventilation, by the following means: (1) measuring delaytimes after an inspiratory effort; (2) calculating pressure time products (PTPs) for different inspiratory phases; and (3) analyzing the occurrence of wasted inspiratory efforts during varying trigger sensitivities, pressure support (PS) levels, RRs, and lung compliance values.